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| 6898832 | Method for manufacturing a quartz crystal unit | May, 2005 | Kawashima | 29/25.35 |
| 6903618 | Quartz crystal unit, and quartz crystal oscillator having quartz crystal unit | June, 2005 | Kawashima | 331/158 |
| 6915548 | Method for manufacturing quartz crystal tuning fork resonator, quartz crystal unit having quartz crystal tuning fork resonator, and quartz crystal oscillator having quartz crystal unit | July, 2005 | Kawashima | 29/25.35 |
| 6959472 | Method for manufacturing quartz crystal oscillator | November, 2005 | Kawashima | 29/25.35 |
| 20030169118 | Quartz crystal oscillator | September, 2003 | Kawashima | 331/158 |
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. application Ser. No. 10/749,182 filed Dec. 30, 2003 now U.S. Pat. No. 7,071,794, which is a continuation-in-part of U.S. application Ser. No. 10/378,719 filed Mar. 4, 2003 and now abandoned.
1. A method for manufacturing a quartz crystal unit, comprising the steps of: forming a quartz crystal tuning fork resonator capable of vibrating in a flexural mode of an inverse phase by etching a quartz crystal wafer to form a quartz crystal tuning fork base, and first and second quartz crystal tuning fork tines connected to the quartz crystal tuning fork base, each of the first and second quartz crystal tuning fork tines having side surfaces, the quartz crystal tuning fork resonator having a piezoelectric constant e′12 to drive the quartz crystal tuning fork resonator; disposing an electrode on each of two of the side surfaces of each of the first and second quartz crystal tuning fork tines so that the electrodes disposed on the side surfaces of the first quartz crystal tuning fork tine have an electrical polarity opposite to an electrical polarity of the electrodes disposed on the side surfaces of the second quartz crystal tuning fork tine; providing a case having a mounting portion; providing a lid for covering an open end of the case; mounting the quartz crystal tuning fork resonator on the mounting portion of the case; and connecting the lid to the case to cover the open end thereof; and wherein the quartz crystal unit comprises the quartz crystal tuning fork resonator with the piezoelectric constant e′12 within a range of 0.12 C/m2 to 0.19 C/m2 in the absolute value.
2. The method according to claim 1; wherein the forming step comprises the step of forming the quartz crystal tuning fork resonator by etching the quartz crystal wafer so that the quartz crystal tuning fork resonator has an oscillation frequency in the range of 32.78 kHz to 33.85 kHz; wherein each of the first and second quartz crystal tuning fork tines has a first main surface and a second main surface opposite the first main surface; and further comprising the steps of adjusting the oscillation frequency in the quartz crystal wafer by forming a metal film on at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has the oscillation frequency lower than 32.73 kHz; adjusting the oscillation frequency in the quartz crystal wafer to a first preselected oscillation frequency by trimming the metal film formed on the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; and adjusting the oscillation frequency to a second preselected oscillation frequency after the mounting step or the connecting step.
3. The method according to claim 2; wherein the first preselected oscillation frequency is about 32.768 kHz with a frequency deviation within a range of −9000 PPM to +100 PPM; and wherein the second preselected oscillation frequency is about 32.768 kHz with a frequency deviation within a range of −100 PPM to −100 PPM.
4. The method according to claim 1; wherein each of the first and second quartz crystal tuning fork tines has a first main surface and a second main surface opposite the first main surface; wherein the side surfaces of each of the first and second quartz crystal tuning fork tines have a first side surface and a second side surface opposite the first side surface; wherein the disposing step comprises the steps of disposing a first electrode on each of the first and second main surfaces of the first and second quartz crystal tuning fork tines; and disposing a second electrode on each of the first and second side surfaces of each of the first and second quartz crystal tuning fork tines; and further comprising the steps of connecting the first electrodes disposed on the first and second main surfaces of the first quartz crystal tuning fork tine to the second electrodes disposed on the first and second side surfaces of the second quartz crystal tuning fork tine to define a first electrode terminal; and connecting the second electrodes disposed on the first and second side surfaces of the first quartz crystal tuning fork tine to the first electrodes disposed on the first and second main surfaces of the second quartz crystal tuning fork tine to define a second electrode terminal; and wherein the forming step comprises the step of forming a metal film on at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines after the connecting steps of the first and second electrodes so that the quartz crystal tuning fork resonator has an oscillation frequency lower than 32.73 kHz.
5. The method according to claim 1; wherein the quartz crystal tuning fork base has cut portions; and further comprising the step of etching the quartz crystal wafer to form the cut portions; wherein the etching steps are performed simultaneously to form the first and second quartz crystal tuning fork tines and the cut portions at the same time; wherein each of the first and second quartz crystal tuning fork tines has a first main surface and a second main surface opposite the first main surface; wherein the forming step comprises the step of forming at least one groove having a first stepped portion and a second stepped portion opposite the first stepped portion in the width direction, and a third stepped portion in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines, the first stepped portion being connected to the second stepped portion through the third stepped portion; wherein the at least one groove having the first, second and third stepped portions formed in each of the first and second main surfaces of the first quartz crystal tuning fork tine is formed after the first quartz crystal tuning fork tine is formed; wherein the at least one groove having the first, second and third stepped portions formed in each of the first and second main surfaces of the second quartz crystal tuning fork tine is formed after the second quartz crystal tuning fork tine is formed; and wherein an electrode is disposed on each of the first and second stepped portions of the at least one groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the electrodes disposed on the first and second stepped portions of the at least one groove formed in the first main surface of the first quartz crystal tuning fork tine are electrically connected to the electrodes disposed on the first and second stepped portions of the at least one groove formed in the second main surface of the first quartz crystal tuning fork tine and the electrodes disposed on the first and second stepped portions of the at least one groove formed in the first main surface of the second quartz crystal tuning fork tine are electrically connected to the electrodes disposed on the first and second stepped portions of the at least one groove formed in the second main surface of the second quartz crystal tuning fork tine, the electrodes of the first quartz crystal tuning fork tine having an electrical polarity opposite to an electrical polarity of the electrodes of the second quartz crystal tuning fork tine.
6. The method according to claim 1; wherein each of the first and second quartz crystal tuning fork tines has a first main surface and a second main surface opposite the first main surface; wherein the forming step comprises the step of forming a groove having a plurality of stepped portions including a first stepped portion and a second stepped portion opposite the first stepped portion in the width direction, and a third stepped portion in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that four grooves each having the first, second and third stepped portions are formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines, the first stepped portion being connected to the second stepped portion through the third stepped portion; wherein the side surfaces of each of the first and second quartz crystal tuning fork tines have a first side surface and a second side surface opposite the first side surface; and wherein the disposing step comprises the steps of disposing a first electrode on each of the first and second stepped portions of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; and disposing a second electrode on each of the first and second side surfaces of each of the first and second quartz crystal tuning fork tines, the first electrodes having an electrical polarity opposite to an electrical polarity of the second electrodes.
7. The method according to claim 6; wherein the quartz crystal tuning fork base has cut portions; and wherein the groove having the first second and third stepped portions is formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines after the cut portions are formed and before a metal film is formed on at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has an oscillation frequency lower than 32.73 kHz.
8. The method according to claim 7; further comprising the step of etching the quartz crystal wafer to form at least one of the cut portions; wherein the etching steps are performed simultaneously to form the first and second quartz crystal tuning fork tines and at least one of the cut portions at the same time; and further comprising the step of adjusting in the quartz crystal wafer the oscillation frequency of the quartz crystal tuning fork resonator by trimming the metal film formed on the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the oscillation frequency is about 32.768 kHz with a frequency deviation within a range of −9000 PPM to +100 PPM.
9. The method according to claim 7; wherein the forming step comprises the steps of forming the first and second quartz crystal tuning fork tines in a first etching process and forming at least one of the four grooves each having the first, second and third stepped portions formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines in a second etching process different from the first etching process; and wherein at least one of the cut portions is formed in an etching process different from the second etching process to form the at least one of the four grooves each having the first, second and third stepped portions formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines.
10. The method according to claim 7; wherein the forming step comprises the steps of forming the first and second quartz crystal tuning fork tines and the cut portions at the same time; and forming the groove having the first, second and third stepped portions in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a width W2 of the groove having the first, second and third stepped portions is within a range of 0.03 mm to 0.12 mm, at least one of the four grooves each having the first, second and third stepped portions formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines being formed after the first and second quartz crystal tuning fork tines are formed.
11. The method according to claim 6; wherein the forming step comprises the steps of forming the first and second quartz crystal tuning fork tines in a first etching process and forming the groove having the first, second and third stepped portions in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines in a second etching process different from the first etching process, the groove having the first, second and third stepped portions formed in each of the first and second main surfaces of the first quartz crystal tuning fork tine being formed after the first quartz crystal tuning fork tine is formed and the groove having the first, second and third stepped portions formed in each of the first and second main surfaces of the second quartz crystal tuning fork tine being formed after the second quartz crystal tuning fork tine is formed.
12. The method according to claim 6; wherein each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines has a central linear portion; and wherein the groove having the first, second and third stepped portions formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is formed in the central linear portion of each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a width of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is greater than a distance in the width direction of the groove measured from an outer edge of the groove to an outer edge of the corresponding one of the first and second quartz crystal tuning fork tines, at least one of the four grooves each having the first, second and third stepped portions formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines being formed after the first and second quartz crystal tuning fork tines are formed.
13. The method according to claim 6; wherein at least one of the four grooves each having the first, second and third stepped portions formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is formed before the first and second quartz crystal tuning fork tines are formed.
14. The method according to claim 6; wherein each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines has a central linear portion; wherein the groove having the first, second and third stepped portions formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is formed in the central linear portion of each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a width of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is greater than a distance in the width direction of the groove measured from an outer edge of the groove to an outer edge of the corresponding one of the first and second quartz crystal tuning fork tines and is within a range of 0.03 mm to 0.12 mm, at least one of the four grooves each having the first, second and third stepped portions formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines being formed simultaneously with the first and second quartz crystal tuning fork tines.
15. The method according to claim 6; wherein the forming step comprises the step of forming the groove in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has an oscillation frequency in the range of 32.78 kHz to 33.85 kHz in the quartz crystal wafer and a turn over temperature point thereof is in the range of 15° to 35°; and further comprising the steps of adjusting the oscillation frequency in the quartz crystal wafer by forming a metal film on at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has the oscillation frequency lower than 32.73 kHz; adjusting the oscillation frequency in the quartz crystal wafer to a first preselected oscillation frequency by trimming the metal film formed on the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; and adjusting the oscillation frequency to a second preselected oscillation frequency after the mounting step or the connecting step of the case and the lid.
16. The method according to claim 15; wherein the first preselected oscillation frequency is about 32.768 kHz with a frequency deviation within a range of −9000 PPM to +100 PPM; and wherein the second preselected oscillation frequency is about 32.768 kHz with a frequency deviation within a range of −50 PPM to +50 PPM.
17. The method according to claim 15; wherein the forming step comprises the step of forming in the quartz crystal wafer the quartz crystal tuning fork resonator having the quartz crystal tuning fork base, and the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has the oscillation frequency in the range of 34.1 kHz to 38.7 kHz before at least one of the grooves formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is formed.
18. A method for manufacturing an electronic apparatus having a display portion; and at least one quartz crystal oscillating circuit having a quartz crystal unit, comprising the steps of: forming a quartz crystal tuning fork resonator capable of vibrating in a flexural mode of an inverse phase by etching a quartz crystal wafer to form a quartz crystal tuning fork base, first and second quartz crystal tuning fork tines connected to the quartz crystal tuning fork base, each of the first and second quartz crystal tuning fork tines having side surfaces, the quartz crystal tuning fork resonator having a piezoelectric constant e′12 to drive the quartz crystal tuning fork resonator; disposing an electrode on each of two of the side surfaces of each of the first and second quartz crystal tuning fork tines so that the electrodes disposed on the side surfaces of the first quartz crystal tuning fork tine have an electrical polarity opposite to an electrical polarity of the electrodes disposed on the side surfaces of the second quartz crystal tuning fork tine; providing a case having a mounting portion; providing a lid for covering an open end of the case; mounting the quartz crystal tuning fork resonator on the mounting portion of the case; and connecting the lid to the case to cover the open end thereof; and wherein the quartz crystal unit comprises the quartz crystal tuning fork resonator with the piezoelectric constant e′12 within a range of 0.12 C/m2 to 0.19 C/m2 in the absolute value.
19. A method according to claim 18; wherein the at least one quartz crystal oscillating circuit comprises first and second quartz crystal oscillating circuits each comprised of a quartz crystal resonator, an amplifier, a plurality of capacitors, and a plurality of resistors, a mode of vibration of the quartz crystal resonator of the first quartz crystal oscillating circuit being different from that of the quartz crystal resonator of the second quartz crystal oscillating circuit; wherein the quartz crystal resonator of one of the first and second quartz crystal oscillating circuits comprises one of a length-extensional mode quartz crystal resonator, a thickness shear mode quartz crystal resonator, a width-extensional mode quartz crystal resonator, a Lame mode quartz crystal resonator, a torsional mode quartz crystal resonator and a SAW resonator; wherein the quartz crystal resonator of one of the first and second quartz crystal oscillating circuits comprises the quartz crystal tuning fork resonator; and further comprising the steps of providing an amplification circuit having a CMOS inverter, a feedback resistor, a negative resistance −RL1 for a fundamental mode of vibration of the quartz crystal tuning fork resonator, and a negative resistance −RL2 for a second overtone mode of vibration thereof; providing a feedback circuit having the quartz crystal tuning fork resonator with a series resistance of R1 of the fundamental mode of vibration and a series resistance R2 of the second overtone mode of vibration, a plurality of capacitors and a drain resistor; and electrically connecting the quartz crystal tuning fork resonator to the CMOS inverter and the feedback resistor of the amplification circuit and to the capacitors and the drain resistor of the feedback circuit having the quartz crystal tuning fork resonator; and wherein a ratio |−RL1|/R1 is greater than 2|−RL2|/R2−1, where |−RL1 |represents an absolute value of the negative resistance for the fundamental mode of vibration of quartz crystal tuning fork resonator of the amplification circuit and |−RL2|represents an absolute value of the negative resistance for the second overtone mode of vibration of the quartz crystal tuning fork resonator of the amplification circuit, an output signal of the quartz crystal oscillating circuit comprising the quartz crystal tuning fork resonator being a clock signal for use in operation of the electronic apparatus to display time information at the display portion, the clock signal having an oscillation frequency of the fundamental mode of vibration.
20. The method according to claim 19; wherein each of the first and second quartz crystal tuning fork tines has a first main surface and a second main surface opposite the first main surface; wherein the forming step comprises the step of forming in the quartz crystal wafer the quartz crystal tuning fork resonator having the quartz crystal tuning fork base, and the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has an oscillation frequency in the range of 32.78 kHz to 33.85 kHz; and further comprising the step of adjusting at least triple and in different steps the oscillation frequency of the quartz crystal tuning fork resonator; and wherein the adjusting step comprises the steps of adjusting the oscillation frequency in the quartz crystal wafer by forming a metal film on at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has the oscillation frequency lower than 32.73 kHz; adjusting the oscillation frequency thereof in the quartz crystal wafer to about 32.768 kHz with a frequency deviation within a range of −9000 PPM to +100 PPM by trimming the metal film formed on the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; and adjusting the oscillation frequency to about 32.768 kHz with a frequency deviation within a range of −50 PPM to +50 PPM after the mounting step or the connecting step of the case and the lid.
21. The method according to claim 19; wherein each of the first and second quartz crystal tuning fork tines has a first main surface and a second main surface opposite the first main surface; wherein the forming step comprises the step of forming a groove having a plurality of stepped portions including a first stepped portion and a second stepped portion opposite the first stepped portion in the width direction, and a third stepped portion in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that four grooves each having the first, second and third stepped portions are formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines, the first stepped portion being connected to the second stepped portion through the third stepped portion; wherein the side surfaces of each of the first and second quartz crystal tuning fork tines have a first side surface and a second side surface opposite the first side surface; and wherein the disposing step comprises the steps of disposing a first electrode on each of the first and second stepped portions of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; and disposing a second electrode on each of the first and second side surfaces of each of the first and second quartz crystal tuning fork tines, the first electrodes having an electrical polarity opposite to an electrical polarity of the second electrodes.
22. The method according to claim 21; wherein at least one of the four grooves each having the first, second and third stepped portions formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is formed so that the quartz crystal tuning fork resonator has a preselected oscillation frequency after the first and second quartz crystal tuning fork tines are formed.
23. The method according to claim 22; wherein the preselected oscillation frequency is in the range of 32.78 kHz to 34.4 kHz; wherein a length of at least one of the grooves formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is within a range of 30% to 80% of a length of each of the first and second quartz crystal tuning fork tines; and wherein the first electrode is disposed on each of the first and second stepped portions of the groove formed in each of the first and second main surfaces of the first and second quartz crystal tuning fork tines so that the series resistance R1 of the fundamental mode of vibration of the quartz crystal tuning fork resonator is less than the series resistance of R2 of the second overtone mode of vibration thereof, and a capacitance ratio r1 of the fundamental mode of vibration of the quartz crystal tuning fork resonator is less than a capacitance ratio r2 of the second overtone mode of vibration thereof.
24. The method according to claim 22; wherein the preselected oscillation frequency is in the range of 32.78 kHz to 34.4 kHz; wherein each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines has a central linear portion; wherein the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is formed in the central linear portion of each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a width of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is within a range of 0.03 mm to 0.12 mm and is greater than a distance in the width direction of the groove measured from an outer edge of the groove to an outer edge of the corresponding one of the first and second quartz crystal tuning fork tines.
25. The method according to claim 21; wherein the first and second quartz crystal tuning fork tines are formed after at least one of the four grooves each having the first, second and third stepped portions formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is formed.
26. The method according to claim 21; wherein the forming step comprises the sequential steps of forming in the quartz crystal wafer the quartz crystal tuning fork base, and the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has an oscillation frequency in the range of 34.1 kHz to 38.7 kHz; and forming the groove in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the oscillation frequency thereof is in the range of 32.78 kHz to 33.85 kHz; and further comprising the steps of adjusting the oscillation frequency in the quartz crystal wafer by forming a metal film on at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has the oscillation frequency lower than 32.73 kHz; adjusting the oscillation frequency in the quartz crystal wafer to about 32.768 kHz with a frequency deviation within a range of −9000 PPM to +100 PPM by trimming the metal film formed on the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; and adjusting the oscillation frequency to about 32.768 kHz with a frequency deviation within a range of −50 PPM to +50 PPM after the mounting step or the connecting step of the case and the lid.
27. The method according to claim 21; wherein the first and second quartz crystal tuning fork tines are formed simultaneously with at least one of the grooves formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a length of at least one of the grooves formed in the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is within a range of 40% to 80% of a length of each of the first and second quartz crystal tuning fork tines.
28. The method according to claim 19; further comprising the step of etching the quartz crystal wafer to form at least one groove having a plurality of stepped portions in at least one of opposite main surfaces of each of the first and second quartz crystal tuning fork tines; wherein each of the first and second quartz crystal tuning fork tines has a first side surface and a second side surface opposite the first side surface; wherein the opposite main surfaces of each of the first and second quartz crystal tuning fork tines have a first main surface and a second main surface; and further comprising the sequential steps of forming the first and second quartz crystal tuning fork tines in a first etching process; forming a groove having a plurality of stepped portions including a first stepped portion and a second stepped portion opposite the first stepped portion in the width direction, and a third stepped portion in at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines in a second etching process different from the first etching process, the first stepped portion being connected to the second stepped portion through the third stepped portion; and disposing a first electrode on each of the first and second stepped portions of the groove formed in the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines and a second electrode on each of the first and second side surfaces of each of the first and second quartz crystal tuning fork tines so that the first electrode disposed on each of the first and second stepped portions of the groove formed in the at least one of the first and second main surfaces of the first quartz crystal tuning fork tine is connected to the second electrode disposed on each of the first and second side surfaces of the second quartz crystal tuning fork tine and the first electrode disposed on each of the first and second stepped portions of the groove formed in the at least one of the first and second main surfaces of the second quartz crystal tuning fork tine is connected to the second electrode disposed on each of the first and second side surfaces of the first quartz crystal tuning fork tine.
29. The method according to claim 19; wherein at least one through-hole is formed in each of the first and second quartz crystal tuning fork tines so that a width of at least one of the through-holes formed in the first and second quartz crystal tuning fork tines is greater than a distance in the width direction of the at least one through-hole measured from an outer edge of the at least one through-hole to an outer edge of the corresponding one of the first and second quartz crystal tuning fork tines; and wherein at least one of the through-holes formed in the first and second quartz crystal tuning fork tines is formed simultaneously with the first and second quartz crystal tuning fork tines.
30. The method according to claim 19; wherein the electronic apparatus comprises a third oscillating circuit having a piezoelectric resonator, an amplifier, and a plurality of capacitors and resistors; and wherein the piezoelectric resonator is a resonator for sensing an angular velocity.
31. The method according to claim 18; wherein each of the first and second quartz crystal tuning fork tines has main surfaces; and further comprising the sequential steps of forming a groove having a plurality of stepped portions including a first stepped portion and a second stepped portion opposite the first stepped portion in the width direction, and a third stepped portion in each of two of the main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has an oscillation frequency in the range of 32.78 kHz to 33.85 kHz in the quartz crystal wafer and a turn over temperature point thereof is in the range of 15°to 35°; adjusting the oscillation frequency in the quartz crystal wafer by forming a metal film on at least one of the main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has the oscillation frequency lower than 32.73 kHz; adjusting the oscillation frequency in the quartz crystal wafer by trimming the metal film formed on the at least one of the main surfaces of each of the first and second quartz crystal tuning fork tines so that the oscillation frequency is about 32.768 kHz with a frequency deviation within a range of −9000 PPM to +100 PPM; and adjusting the oscillation frequency after the mounting step or the connecting step of the case and the lid so that the oscillation frequency is about 32.768 kHz with a frequency deviation within a range of −100 PPM to +100 PPM.
32. The method according to claim 18; wherein each of the first and second quartz crystal tuning fork tines has main surfaces; and further comprising the sequential steps of forming at least one first metal film on a surface of the quartz crystal wafer and a first resist on the at least one first metal film; forming in the quartz crystal wafer the first and second quartz crystal tuning fork tines so that an oscillation frequency of the quartz crystal tuning fork resonator is in the range of 32.78 kHz to 34.4 kHz and a turn over temperature point thereof is in the range of 15° to 35°; removing the first resist formed on the at least one first metal film and the at least one first metal film formed on the quartz crystal wafer; forming at least one second metal film on each of two of the main surfaces and each of two of the side surfaces of each of the first and second quartz crystal tuning fork tines and a second resist on the at least one second metal film; forming a first electrode on each of the two of the main surfaces of each of the first and second quartz crystal tuning fork tines and a second electrode on each of the two of the side surfaces of each of the first and second quartz crystal tuning fork tines so that the first electrodes of the first quartz crystal tuning fork tine are connected to the second electrodes of the second quartz crystal tuning fork tine to form a first electrode terminal and the first electrodes of the second quartz crystal tuning fork tine are connected to the second electrodes of the first quartz crystal tuning fork tine to form a second electrode terminal, the first electrode terminal having an electrical polarity opposite to an electrical polarity of the second electrode terminal; removing the second resist formed on the at least one second metal film; adjusting the oscillation frequency in the quartz crystal wafer by forming a metal film on at least one of the main surfaces of each of the first and second quartz crystal tuning fork tines so that the oscillation frequency of the quartz crystal tuning fork resonator is lower than 32.73 kHz; adjusting the oscillation frequency in the quartz crystal wafer by trimming the metal film formed on the at least one of the main surfaces of each of the first and second quartz crystal tuning fork tines so that the oscillation frequency is about 32.768 kHz with a frequency deviation within a range of −9000 PPM to +100 PPM; and adjusting the oscillation frequency after the mounting step or the connecting step of the case and the lid so that the oscillation frequency is about 32.768 kHz with a frequency deviation within a range of −100 PPM to +100 PPM.
33. The method according to claim 18; wherein the quartz crystal tuning fork resonator has an oscillation frequency and each of the first and second quartz crystal tuning fork tines has a first main surface and a second main surface opposite the first main surface; and further comprising the sequential steps of forming in the quartz crystal wafer the quartz crystal tuning fork base, and the first and second quartz crystal tuning fork tines by etching the quartz crystal wafer so that the quartz crystal tuning fork resonator has a first preselected oscillation frequency; forming a groove having a plurality of stepped portions including a first stepped portion and a second stepped portion opposite the first stepped portion in the width direction, and a third stepped portion in at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has a second preselected oscillation frequency, the first stepped portion being connected to the second stepped portion through the third stepped portion; disposing an electrode on each of the first and second stepped portions of the groove formed in the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; forming a metal film on at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has a third preselected oscillation frequency; trimming the metal film formed on the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has a fourth preselected oscillation frequency; and mounting the quartz crystal tuning fork resonator on the mounting portion of the case; and further comprising the step of adjusting the oscillation frequency of the quartz crystal tuning fork resonator to about 32.768 kHz with a frequency deviation within a range of −50 PPM to +50 PPM after the mounting step; wherein the at least one quartz crystal oscillating circuit comprises first and second quartz crystal oscillating circuits; wherein the first quartz crystal oscillating circuit comprises a thickness shear mode quartz crystal resonator; wherein the second quartz crystal oscillating circuit comprises the quartz crystal tuning fork resonator; wherein an output signal of the first quartz crystal oscillating circuit comprising the thickness shear mode quartz crystal resonator is a clock signal for use in operation of the electronic apparatus; and wherein an output signal of the second quartz crystal oscillating circuit comprising the quartz crystal tuning fork resonator is a clock signal for use in operation of the electronic apparatus to display time information at the display portion, the clock signal of the second quartz crystal oscillating circuit having an oscillation frequency of the fundamental mode of vibration.
34. The method according to claim 33; wherein the groove formed in the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; wherein the first preselected oscillation frequency is in the range of 34.1 kHz to 38.7 kHz; wherein the second preselected oscillation frequency is in the range of 32.78 kHz to 33.85 kHz; wherein the third preselected oscillation frequency is lower than 32.73 kHz; and wherein the fourth preselected oscillation frequency is about 32.768 kHz with a frequency deviation within a range of −9000 PPM to +100 PPM.
35. The method according to claim 18; wherein each of the first and second quartz crystal tuning fork tines has main surfaces; wherein the side surfaces have a first side surface and a second side surface opposite the first side surface; and further comprising the sequential steps of forming the first and second quartz crystal tuning fork tines in a first etching process; forming a groove having a plurality of stepped portions including a first stepped portion and a second stepped portion opposite the first stepped portion in the width direction, and a third stepped portion in each of two of the main surfaces of each of the first and second quartz crystal tuning fork tines in a second etching process different from the first etching process so that the quartz crystal tuning fork resonator has a first preselected oscillation frequency, the first stepped portion being connected to the second stepped portion through the third stepped portion; disposing a first electrode on each of the first and second stepped portions of the groove formed in each of the two of the main surfaces of each of the first and second quartz crystal tuning fork tines and a second electrode on each of the first and second side surfaces of each of the first and second quartz crystal tuning fork tines so that the first electrode disposed on each of the first and second stepped portions of the groove formed in each of the two of the main surfaces of the first quartz crystal tuning fork tine is connected to the second electrode disposed on each of the first and second side surfaces of the second quartz crystal tuning fork tine and the first electrode disposed on each of the first and second stepped portions of the groove formed in each of the two of the main surfaces of the second quartz crystal tuning fork tine is connected to the second electrode disposed on each of the first and second side surfaces of the first quartz crystal tuning fork tine; forming a metal film on at least one of the main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has a second preselected oscillation frequency; trimming the metal film formed on the at least one of the main surfaces of each of the first and second quartz crystal tuning fork tines so that the quartz crystal tuning fork resonator has a third preselected oscillation frequency; and mounting the quartz crystal tuning fork resonator on the mounting portion of the case; wherein the at least one quartz crystal oscillating circuit comprises first and second quartz crystal oscillating circuits; wherein the first quartz crystal oscillating circuit comprises a thickness shear mode quartz crystal resonator; wherein the second quartz crystal oscillating circuit comprises the quartz crystal tuning fork resonator; wherein an output signal of the first quartz crystal oscillating circuit comprising the thickness shear mode quartz crystal resonator is a clock signal for use in operation of the electronic apparatus; and wherein an output signal of the second quartz crystal oscillating circuit comprising the quartz crystal tuning fork resonator is a clock signal for use in operation of the electronic apparatus to display time information at the display portion, the clock signal of the second quartz crystal oscillating circuit having an oscillation frequency of the fundamental mode of vibration.
36. The method according to claim 35; wherein the first preselected oscillation frequency is in the range of 32.78 kHz to 33.85 kHz; wherein the second preselected oscillation frequency is lower than 32.73 kHz; and wherein the third preselected oscillation frequency is about 32.768 kHz with a frequency deviation within a range of −9000 PPM to +100 PPM.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a quartz crystal resonator, a quartz crystal unit having the quartz crystal resonator, a quartz crystal oscillator having the quartz crystal unit, an electronic apparatus comprising a display portion and the quartz crystal oscillator at least, and their manufacturing methods.
2. Background Information
There are many electronic apparatus comprising a display portion and a quartz crystal oscillator at least. For example, cellular phones, wristwatches, facsimiles and pagers comprising a quartz crystal oscillator are well known. Recently, because of high stability for frequency, miniaturization and the light weight nature of these electronic apparatus, the need for an electronic apparatus comprising a smaller quartz crystal oscillator with a high frequency stability has arisen. For example, the quartz crystal oscillator with a quartz crystal tuning fork resonator, which is capable of vibrating in a flexural mode, is widely used as a time standard in an electronic apparatus such as the cellular phones, the wristwatches, the facsimiles and the pagers. Similar to this, the same need has also arisen for an electronic apparatus comprising a length-extensional mode quartz crystal resonator with a frequency of 1 MHz to 10 MHz to decrease an electric current consumption of the electronic apparatus.
Heretofore, however, it has been impossible to obtain an electronic apparatus comprising a smaller quartz crystal oscillator with a conventional miniaturized quartz crystal tuning fork resonator, capable of vibrating in a flexural mode, and having a high frequency stability, a small series resistance and a high quality factor. When miniaturized, the conventional quartz crystal tuning fork resonator, capable of vibrating in a flexural mode, as shown in FIG. 12 (which has electrodes on the obverse faces 203 , 207 , reverse faces 204 , 208 and the four sides 205 , 206 , 209 , 210 of each tuning fork tine, as also shown in FIG. 13 —a cross-sectional view of tuning fork tines of FIG. 12), it has a smaller electromechanical transformation efficiency because the resonator shape and the electrode construction provide a small electric field (i.e. Ex becomes small), as a result of which the resonator has a low frequency stability, a large series resistance and a reduced quality factor. In FIG. 12, a conventional tuning fork resonator 200 is shown with tines 201 , 202 and a base 230 .
Moreover, for example, Japanese Patent Nos. P56-65517 and P2000-223992A and International Patent No. WO 00/44092 were published and teach grooves and electrodes constructed at tuning fork tines of a flexural mode, tuning fork, quartz crystal resonator. However, they teach nothing about a quartz crystal oscillator of the present invention having novel shape, novel electrode construction and figure of merit M for a quartz crystal tuning fork resonator, capable of vibrating in a flexural mode and about a relationship of an amplification circuit and a feedback circuit which construct a quartz crystal oscillating circuit.
Additionally, for example, there has been a big problem in the conventional oscillator with the conventional quartz crystal tuning fork resonator, such that a fundamental mode vibration of the resonator jumps to a second overtone mode vibration by shock or vibration.
Similarly, however, it has been impossible to obtain an electronic apparatus comprising a smaller quartz crystal oscillator with a conventional length-extensional mode quartz crystal resonator, capable of vibrating in a length-extensional mode, and having a frequency of 1 MHz to 10 MHz, a small series resistance and a high quality factor. As an example of a length-extensional mode quartz crystal resonator of the prior art, the length-extensional mode resonator comprising a vibrational portion, connecting portions and supporting portions, which is formed from a Z plate perpendicular to z axis, is well known, and this resonator is formed integrally by a chemical etching process. Also, electrodes are disposed opposite each other on sides of the vibrational portion formed by the chemical etching process so that the electrodes disposed opposite each other are of opposite electrical polarity.
Also, a cutting angle of the conventional length-extensional mode quartz crystal resonator is generally within a range of ZYw(0° to +5°), according to an IEEE notation. In detail, the connecting portions are connected opposite each other at both end portions of a width of the vibrational portion and at a central portion of the length direction thereof. Namely, the direction of the connecting portions constructed opposite each other corresponds to the direction of the electric field.
When an alternating current (AC) voltage is applied between the electrodes, an electric field occurs alternately in the width direction, as a result, the resonator is capable of vibrating in the length direction, but the electric field of between the electrodes becomes very small because quartz crystal is an anisotropic material and the sides of the vibrational portion have a complicated shape formed by the chemical etching process. Namely, the resonator has small electromechanical transformation efficiency because the resonator's shape and the electrode construction provide a small electric field, consequently, the resonator has a low frequency stability, a large series resistance and a reduced quality factor when it has the frequency of 1 MHz to 10 MHz.
It is, therefore, a general object of the present invention to provide embodiments of an electronic apparatus and a quartz crystal oscillator, which constructs an electronic apparatus of the present invention, comprising a quartz crystal oscillating circuit with a flexural mode, quartz crystal tuning fork resonator, capable of vibrating in a fundamental mode, and having a high frequency stability, a small series resistance and a high quality factor, or embodiments of a quartz crystal oscillator, which also constructs an electronic apparatus of the present invention, comprising a quartz crystal oscillating circuit with a length-extensional mode quartz crystal resonator having a frequency of 1 MHz to 10 MHz, a small series resistance and a high quality factor, which overcome or at least mitigate one or more of the above problems.
SUMMARY OF THE INVENTION
The present invention relates to a quartz crystal resonator, a quartz crystal unit having a quartz crystal resonator, a quartz crystal oscillator having a quartz crystal unit, and an electronic apparatus comprising a display portion and a quartz crystal oscillator at least, and their manufacturing methods. In particular, relates to the quartz crystal resonator which is a quartz crystal tuning fork resonator capable of vibrating in a flexural mode of an inverse phase, and having a groove and/or a through-hole at tuning fork tines, the quartz crystal unit having the quartz crystal tuning fork resonator, and the quartz crystal oscillator having the quartz crystal unit. In detail, the quartz crystal oscillator comprises a quartz crystal oscillating circuit having an amplification circuit and a feedback circuit, and in particular, relates to a quartz crystal oscillator having a flexural mode, quartz crystal tuning fork resonator capable of vibrating in a fundamental mode and having an output signal of a high frequency stability for the fundamental mode vibration of the resonator, and also to a quartz crystal oscillator having a suppressed second overtone mode vibration of the flexural mode, quartz crystal tuning fork resonator, in addition, relates to a quartz crystal oscillator comprising a length-extensional mode quartz crystal resonator. The quartz crystal oscillators are, therefore, available for the electronic apparatus requiring miniaturized and low priced quartz crystal oscillators with high time accuracy and shock proof.
It is an object of the present invention to provide an electronic apparatus comprising a quartz crystal oscillator with a miniature quartz crystal tuning fork resonator, capable of vibrating in a flexural mode, and having a high frequency stability, a small series resistance R 1 and a high quality factor Q 1 , whose nominal frequency for a fundamental mode vibration is within a range of 10 kHz to 200 kHz.
It is an another object of the present invention to provide an electronic apparatus comprising a quartz crystal oscillator with a flexural mode, quartz crystal tuning fork resonator, capable of vibrating in a fundamental mode, and having a high frequency stability which gives a high time accuracy.
It is a further object of the present invention to provide an electronic apparatus comprising a quartz crystal oscillator with a length-extensional mode quartz crystal resonator.
According to one aspect of the present invention, there is provided an electronic apparatus comprising a display portion and a quartz crystal oscillator at least, and said electronic apparatus having one quartz crystal oscillator, said one quartz crystal oscillator comprising: a quartz crystal oscillating circuit comprising; an amplification circuit comprising an amplifier at least and a feedback circuit comprising a quartz crystal resonator and capacitors at least, said quartz crystal resonator being a quartz crystal tuning fork resonator, capable of vibrating in a flexural mode, and said quartz crystal tuning fork resonator comprising: tuning fork tines each of which has a length, a width and a thickness and the length greater than the width and the thickness; and a tuning fork base; said tuning fork tines and said tuning fork base that are formed integrally; and electrodes disposed facing each other on sides of said tuning fork tines so that the electrodes disposed facing each other are of opposite electrical polarity and said tuning fork tines are capable of vibrating in inverse phase,
According to a second aspect of the present invention there is provided an electronic apparatus comprising a display portion and a quartz crystal oscillator at least, and said electronic apparatus comprises at least one quartz crystal oscillator comprising: an oscillating circuit comprising; an amplification circuit comprising an amplifier at least, and a feedback circuit comprising a length-extensional mode quartz crystal resonator which is one of a contour mode quartz crystal resonator.
According to a third aspect of the present invention, there is provided a method for manufacturing an electronic apparatus comprising a display portion and a quartz crystal oscillator at least, and said electronic apparatus comprising at least one quartz crystal oscillator, said at least one oscillator comprising: a quartz crystal oscillating circuit comprising; an amplification circuit comprising an amplifier at least, and a feedback circuit comprising a quartz crystal resonator and capacitors at least, said quartz crystal resonator being a quartz crystal tuning fork resonator, capable of vibrating in a flexural mode, said quartz crystal tuning fork resonator comprising the steps of: forming integrally tuning fork tines each of which has a length, a width and a thickness and the length greater than the width and the thickness and a tuning fork base; disposing electrodes facing each other on sides of said tuning fork tines so that the electrodes disposed facing each other are of opposite electrical polarity and said tuning fork tines vibrate an in inverse phase; and adjusting resonance frequency of said quartz crystal tuning fork resonator after mounting it at a mounting portion by conductive adhesives or solder so that a frequency deviation is within a range of −100 PPM to +100 PPM.
According to a fourth aspect of the present invention, there are provided a quartz crystal resonator, a quartz crystal unit and a quartz crystal oscillator, each of which has a piezoelectric constant e 12 that is within a range of 0.095 C/m 2 to 0.19 C/m 2 .
Preferably, said tuning fork resonator is constructed so that figure of merit M 1 of a fundamental mode vibration is larger than figure of merit M 2 of a second overtone mode vibration.
Preferably, the quartz crystal oscillator with said tuning fork resonator is constructed so that a ratio of an amplification rate α 1 of the fundamental mode vibration and an amplification rate α 2 of the second overtone mode vibration of said amplification circuit is larger than that of a feedback rate β 2 of the second overtone mode vibration and a feedback rate β 1 of the fundamental mode vibration of said feedback circuit, and a product of the amplification rate α 1 and the feedback rate β 1 of the fundamental mode vibration is larger than 1.
Preferably, the quartz crystal oscillator with said tuning fork resonator is constructed so that a ratio of an absolute value of negative resistance, |−RL 1 | of the fundamental mode vibration of said amplification circuit and series resistance R 1 of the fundamental mode vibration is larger than that of an absolute value of negative resistance, |−RL 2 | of the second overtone mode vibration of said amplification circuit and series resistance R 2 of the second overtone mode vibration.
Preferably, the length-extensional mode quartz crystal resonator comprises a vibrational portion, connecting portions and supporting portions, which are formed integrally by a particle method.
The present invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a block diagram of an embodiment of an electronic apparatus of the present invention, and illustrating the diagram of a facsimile apparatus;
FIG. 2 shows a diagram of an embodiment of a quartz crystal oscillating circuit constructing a quartz crystal oscillator, which constructs an electronic apparatus of the present invention;
FIG. 3 shows a diagram of the feedback circuit of FIG. 2;
FIG. 4 shows a general view of a flexural mode, quartz crystal tuning fork resonator constructing a quartz crystal oscillator, which constructs an electronic apparatus of the first embodiment of the present invention;
FIG. 5 shows a A-A′ cross-sectional view of the tuning fork base of FIG. 4, and illustrating electrode construction;
FIG. 6 shows a plan view of a quartz crystal tuning fork resonator of FIG. 4;
FIG. 7 shows a plan view of a flexural mode, quartz crystal tuning fork resonator constructing a quartz crystal oscillator, which constructs an electronic apparatus of the second embodiment of the present invention;
FIG. 8 a and FIG. 8 b show a top view and a side view of a length-extensional mode quartz crystal resonator constructing a quartz crystal oscillator, which constructs an electronic apparatus of the third embodiment of the present invention;
FIG. 9 shows a cross-sectional view of a quartz crystal unit constructing a quartz crystal oscillator, which constructs an electronic apparatus of the fourth embodiment of the present invention;
FIG. 10 shows a cross-sectional view of a quartz crystal oscillator, which constructs an electronic apparatus of the fifth embodiment of the present invention;
FIG. 11 shows a step diagram of a method for manufacturing a quartz crystal unit constructing a quartz crystal oscillator, which constructs an electronic apparatus of the present invention;
FIG. 12 is a general view of the conventional flexural mode, quartz crystal tuning fork resonator constructing a quartz crystal oscillator of the prior art, which constructs the conventional electronic apparatus;
FIG. 13 is a cross-sectional view of the tuning fork tines of FIG. 12, and illustrating electrode construction;
FIG. 14 shows a B-B′ cross-sectional view of the tuning fork tines of FIG. 4;
FIG. 15 shows a plan view of a quartz crystal unit of the present invention and omitting a lid, and constructing a quartz crystal oscillator and an electronic apparatus of the present invention;
FIG. 16 shows a plan view of a quartz crystal unit of the present invention and omitting a lid, and constructing a quartz crystal oscillator and an electronic apparatus of the present invention;
FIG. 17 shows a plan view of a quartz crystal unit of the present invention and omitting a lid, and constructing a quartz crystal oscillator and an electronic apparatus of the present invention;
FIG. 18 shows a relationship between a dimensional ratio R=W 0 /L 0 and a cut angle θ x of a length extensional mode quartz crystal resonator to give a zero temperature coefficient;
FIG. 19 shows a top view (a) and a C-C′ cross-sectional view (b) of a vibrational portion of a thickness shear mode quartz crystal resonator constructing a quartz crystal unit, and which constructs an electronic apparatus of the present invention.
FIG. 20 shows a plan view of a flexural mode, quartz crystal tuning fork resonator of the present invention, and constructing a quartz crystal unit, a quartz crystal oscillator and an electronic apparatus of the present invention;
FIG. 21 shows a D 1 -D 2 cross-sectional view of the tuning fork tines of FIG. 20;
FIG. 22 shows a D 3 -D 4 cross-sectional view of the tuning fork tines of FIG. 20;
FIG. 23 shows a plan view of a flexural mode, quartz crystal tuning fork resonator of the present invention, and constructing a quartz crystal unit, a quartz crystal oscillator and an electronic apparatus of the present invention;
FIG. 24 shows a J 1 -J 2 cross-sectional view of the tuning fork tines of FIG. 23; and
FIG. 25 shows a J 3 -J 4 cross-sectional view of the tuning fork tines of FIG. 23.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, the embodiments of the present invention will be described in more detail.
FIG. 1 shows a block diagram of an embodiment of an electronic apparatus of the present invention, and illustrating the diagram of a facsimile apparatus. As is shown in FIG. 1, the apparatus generally comprises a modem, a phonetic circuit, a timepiece circuit, a printing portion, a taking portion, an operation portion and a display portion. In this principle, perception and scanning of reflection light of light projected on manuscript in the taking portion are performed by CCD (Charge Coupled Device), in addition, light and shade of the reflection light are transformed into a digital signal, and the signal is modulated by the modem and is sent to a phone line (Communication line). Also, in a receiving side, a received signal is demodulated by the modem and is printed on a paper in the print portion by synchronizing the received signal with a signal of a sending side.
As shown in FIG. 1, a quartz crystal resonator which is one of piezoelectric resonators made of piezoelectric materials is used as a CPU clock of the control portion and the printing portion, as a clock of the phonetic circuit and the modem, and as a time standard of the timepiece. Namely, the resonator constructs a quartz crystal oscillator and an output signal of the oscillator is used. For example, it is used as a signal to display time at the display portion. In this case, a quartz crystal tuning fork resonator, capable of vibrating in a flexural mode is used, and e.g. as the CPU clock, a contour mode quartz crystal resonator such as a length-extensional mode quartz crystal resonator or a thickness shear mode quartz crystal resonator is used. In order to get the facsimile apparatus of this embodiment which operates normally, an accuracy output signal of the oscillator is required for the facsimile apparatus, which is one of the electronic apparatus of the present invention. Also, a digital display and an analogue display are included in the display of the present invention. In this embodiment, two quartz crystal resonators each of which vibrates in a different mode are used in the electronic apparatus of the present invention. But, the present invention is not limited to this, two quartz crystal resonators each of which vibrates in the same mode may be used in the electronic apparatus of the present invention. Namely, one of the two quartz crystal resonators is used as a signal for use in operation of the electronic apparatus to display time information at the display portion of the electronic apparatus. One of the two quartz crystal resonators which is used as a signal for use in operation of the electronic apparatus to display time information at the display portion has a frequency of oscillation of a fundamental mode of vibration. In more detail, a piezoelectric resonator has a fundamental mode of vibration and an overtone mode of vibration. It is needless to say that the fundamental mode of vibration and the overtone mode of vibration thereof are defined as the same mode of vibration. For example, a thickness shear mode quartz crystal resonator has a fundamental mode of vibration and a third overtone mode of vibration, the fundamental mode of vibration of the thickness shear mode quartz crystal resonator is, therefore, the same mode of vibration as the third overtone mode of vibration thereof. In stead of the quartz crystal, such a piezoelectric material may be used as LiTaO 3 , LiNbO 3 , GaPO 4 , and so on.
In this embodiment, though the facsimile apparatus is shown as an example of an electronic apparatus, the present invention is not limited to this, namely, the present invention includes all electronic apparatus, each of which comprises a quartz crystal oscillator and a display portion at least, for example, cellar phones, telephones, a TV set, cameras, a video set, video cameras, pagers, personal computers, printers, CD players, MD players, electronic musical instruments, car navigators, car electronics, timepieces, IC cards and so forth.
FIG. 2 shows a diagram of an embodiment of a quartz crystal oscillating circuit constructing a quartz crystal oscillator, which constructs an electronic apparatus of the present invention. The quartz crystal oscillating circuit 1 comprises an amplifier (CMOS Inverter) 2 , a feedback resistor 4 , a drain resistor 7 , capacitors 5 , 6 and a flexural mode, quartz crystal tuning fork resonator 3 . Namely, the oscillating circuit 1 comprises an amplification circuit 8 having the amplifier 2 and the feedback resistor 4 , and a feedback circuit 9 having the drain resistor 7 , the capacitors 5 , 6 and the quartz crystal tuning fork resonator 3 . In addition, an output signal of the oscillating circuit 1 comprising the quartz crystal tuning fork resonator 3 , capable of vibrating in a fundamental mode, is outputted through a buffer circuit (not shown in FIG. 2).
In detail, an oscillation frequency of the fundamental mode vibration is outputted through a buffer circuit as an output signal. According to the present invention, a nominal frequency of the fundamental mode vibration of the resonator is within a range of 10 kHz to 200 kHz. Especially, 32.768 kHz is an important frequency. In general, the output signal has an oscillation frequency which is within a range of −100 PPM to +100 PPM to the nominal frequency, e.g. 32.768 kHz. In more detail, the quartz crystal oscillator in this embodiment comprises a quartz crystal oscillating circuit and a buffer circuit, namely, the quartz crystal oscillating circuit comprises an amplification circuit and a feedback circuit, and the amplification circuit comprises an amplifier and a feedback resistor, and the feedback circuit comprises a flexural mode, quartz crystal tuning fork resonator, a drain resistor and capacitors. Also, flexural mode, quartz crystal tuning fork resonators which are used in a quartz crystal oscillator will be described in FIG. 4-FIG. 7 in detail. Instead of the flexural mode, quartz crystal tuning fork resonator, a contour mode resonator such as a length-extensional mode quartz crystal resonator, a width-extensional mode quartz crystal resonator and a Lame mode quartz crystal resonator or a thickness shear mode quartz crystal resonator may be used.
FIG. 3 shows a diagram of the feedback circuit of FIG. 2. Now, when angular frequency ω i of the flexural mode, quartz crystal tuning fork resonator 3 , capable of vibrating in a flexural mode, a resistance R d of the drain resistor 7 , capacitance C g , C d of the capacitors 5 , 6 , crystal impedance R ei of the quartz crystal resonator 3 , an input voltage V 1 , and an output voltage V 2 are taken, a feedback rate β i is defined by β i =|V 2 | i /|V 1 | i , where i shows vibration order, for example, when i=1 and 2, they are for a fundamental mode vibration and a second overtone mode vibration.
In addition, load capacitance C L is given by C L =C g C d /(C g +C d ), and when C g =C d =C gd and Rd>>R ei , the feedback rate β i is given by β i =1/(1+kC L 2 ), where k is expressed by a function of ω i , R d and R ei . Also, R ei is approximately equal to series resistance R i .
Thus, it is easily understood from a relationship of the feedback rate β i and load capacitance C L that the feedback rate of resonance frequency for a fundamental mode vibration and an overtone mode vibration becomes large, respectively, according to decrease of load capacitance C L . Therefore, when C L has a small value, an oscillation of the overtone mode occurs very easily, instead of that of the fundamental mode. This is the reason why a maximum amplitude of the overtone mode vibration becomes smaller than that of the fundamental mode vibration, and the oscillation of the overtone mode satisfies an amplitude condition and a phase condition simultaneously which are the continuous condition of an oscillation in an oscillating circuit.
As it is also one object of the present invention to provide a quartz crystal oscillator having a flexural mode, quartz crystal tuning fork resonator, capable of vibrating in a fundamental mode and having a high frequency stability (high time accuracy) of an output signal, and having reduced electric current consumption, in this embodiment, load capacitance C L is less than 25 pF to reduce electric current consumption. To get much reduced electric current consumption, C L is preferably less than 15 pF because electric current consumption is proportional to C L .
In addition, in order to suppress a second overtone mode vibration and to obtain a quartz crystal oscillator having an output signal of an oscillation frequency of a fundamental mode vibration, the quartz crystal oscillator in this embodiment is constructed so that it satisfies a relationship of α 1 /α 2 >β 2 /β 1 and α 1 β 1 >1, where α 1 and α 2 are, respectively, an amplification rate of the fundamental mode vibration and the second overtone mode vibration of an amplification circuit, and β 1 and β 2 are, respectively, a feedback rate of the fundamental mode vibration and the second overtone mode vibration of a feedback circuit.
In other words, the quartz crystal oscillator is constructed so that a ratio of the amplification rate α 1 of the fundamental mode vibration and the amplification rate α 2 of the second overtone mode vibration of the amplification circuit is larger than that of the feedback rate β 2 of the second overtone mode vibration and the feedback rate β 1 of the fundamental mode vibration of the feedback circuit, and also a product of the amplification rate α 1 and the feedback rate β 1 of the fundamental mode vibration is larger than 1. A description of the high frequency stability will be performed later.
Also, characteristics of the amplifier of the amplification circuit constructing the quartz crystal oscillating circuit of this embodiment can be expressed by negative resistance −RL i . For example, when i=1, negative resistance −RL 1 is for a fundamental mode vibration and when i=2, negative resistance −RL 2 is for a second overtone mode vibration. In this embodiment, the quartz crystal oscillating circuit is constructed so that a ratio of an absolute value of negative resistance, |−RL 1 | of the fundamental mode vibration of the amplification circuit and series resistance R 1 of the fundamental mode vibration is larger than that of an absolute value of negative resistance, |−RL 2 | of the second overtone mode vibration of the amplification circuit and series resistance R 2 of the second overtone mode vibration. That is to say, the oscillating circuit is constructed so that it satisfies a relationship of |−RL 1 |/R 1 >|−RL 2 |/R 2 . By constructing the oscillating circuit like this, an oscillation of the second overtone mode can be suppressed, as a result of which an output signal of a frequency of the fundamental mode vibration can be provided because an oscillation of the fundamental mode generates easily in the oscillating circuit.
FIG. 4 shows a general view of a flexural mode, quartz crystal tuning fork resonator 10 which is one of a contour mode resonator, constructing a quartz crystal oscillator, which constructs an electronic apparatus of the first embodiment of the present invention and its coordinate system o-xyz. A cut angle θ which has a typical value of 0° to 10° is rotated from a Z-plate perpendicular to the z axis about the x axis. Namely, the flexural mode, quartz crystal tuning fork resonator has the cut angel of ZYw(0° to 10°) according to an expression of the IEEE notation. The resonator 10 comprises two tuning fork tines (vibrating tines) 20 and 26 and a tuning fork base (a base) 40 . The tines 20 and 26 have grooves 21 and 27 each of which has a plurality of stepped portions including a first stepped portion and a second stepped portion opposite the first stepped portion in the width direction, and a third stepped portion connecting the first stepped portion to the second stepped portion, respectively, with the grooves 21 and 27 extending into the base 40 . Also, the base 40 has the additional grooves 32 and 36 . In addition, the tines 20 and 26 vibrate in a flexural mode of a fundamental mode and an inverse phase.
FIG. 5 shows an A-A′ cross-sectional view of the tuning fork base 40 of the quartz crystal resonator 10 in FIG. 4. In FIG. 5, the shape of the electrode construction within the base 40 for the quartz crystal resonator of FIG. 4 is described in detail. The section of the base 40 which couples to the tine 20 has the grooves 21 and 22 each of which has a plurality of stepped portions including a first stepped portion and a second stepped portion opposite the first stepped portion in the width direction, and a third stepped portion connecting the first stepped portion to the second stepped portion, cut into the obverse and reverse faces of the base 40 . Also, the section of the base 40 which couples to the tine 26 has the grooves 27 and 28 each of which has a plurality of stepped portions including a first stepped portion and a second stepped portion opposite the first stepped portion in the width direction, and a third stepped portion connecting the first stepped portion to the second stepped portion, cut into the obverse and reverse faces of the base 40 . Thus, the four grooves 21 , 22 , 27 and 28 are formed in two of main surfaces (e.g., in first and second opposite main surfaces) of each of the two tuning fork tines 20 , 26 , and an electrode is disposed on each of the first and second stepped portions of each of the four grooves 21 , 22 . 27 and 28 . In addition to these grooves, the base 40 has the grooves 32 and 36 cut between the grooves 21 and 27 , and also, the base 40 has the grooves 33 and 37 cut between the grooves 22 and 28 .
Furthermore, the grooves 21 and 22 have the first electrodes 23 and 24 both of the same electrical polarity, the grooves 32 and 33 have the second electrodes 34 and 35 both of the same electrical polarity, the grooves 36 and 37 have the third electrodes 38 and 39 both of the same electrical polarity, the grooves 27 and 28 have the fourth electrodes 29 and 30 both of same electrical polarity and the sides of the base 40 have the fifth and sixth electrodes 25 and 31 , each of opposite electrical polarity. In more detail, the fifth, fourth, and second electrodes 25 , 29 , 30 , 34 and 35 have the same electrical polarity, while the first, sixth and third electrodes 23 , 24 , 31 , 38 and 39 have the opposite electrical polarity to the others. Two electrode terminals E and E′ are constructed. That is, the electrodes disposed inside the grooves constructed opposite each other in the thickness (z axis) direction have the same electrical polarity. Also, the electrodes disposed opposite each other across adjoining grooves have opposite electrical polarity.
In addition, the resonator has a thickness t of the tines or the tines and the base, and a groove thickness t 1 . It is needless to say that the electrodes are disposed inside the grooves and on the sides of the tines. In this embodiment, the first electrodes 23 and 24 are disposed at the tine and the base, and also, the fourth electrodes 29 and 30 are disposed at the tine and the base. In addition, the electrodes are disposed on the sides of the tines opposite each other to the electrodes disposed inside the grooves. Namely, the electrodes are disposed opposite each other inside the grooves and on the sides of the tines so that the electrodes disposed opposite each other are of opposite electrical polarity. Additionally, electrodes are disposed facing each other on the sides of the tines so that the electrodes disposed facing each other are of opposite electrical polarity, and the tines are capable of vibrating in inverse phase. In more detail, a first tuning fork tine and a second tuning fork tine, and a tuning fork base are formed integrally, an electrode is disposed on both sides of the first tine and the second tine so that the electrodes disposed (facing each other) on inner sides of the first and second tines are of opposite electrical polarity. Therefore, the disposition of the electrodes disposed inside the grooves and on the sides of the tuning fork tines, described above is the same as that of the electrodes shown in FIG. 14 which shows a B-B′ cross-sectional view of the tuning fork tines 20 , 26 of the quartz crystal resonator 10 in FIG. 4, namely, the electrodes 23 , 24 are connected to the electrodes 31 , 43 to define an electrode terminal F, while the electrodes 29 , 30 are connected to the electrodes 25 , 44 to define an electrode terminal F′. It is needless to say that the electrode terminal F is electrically connected to the electrode terminal E and the electrode terminal F′ is electrically connected to the electrode terminal E′.
When a direct current voltage is applied between the electrode terminals E and E′ (E terminal: plus, E′ terminal: minus), an electric field E x occurs in the arrow direction as shown in FIG. 5. As the electric field E x occurs perpendicular to the electrodes disposed on the base, the electric field E x has a very large value and a large distortion occurs at the base, so that the quartz crystal tuning fork resonator is obtained with a small series resistance R 1 and a high quality factor Q 1 , even if it is miniaturized.
FIG. 6 shows a plan view of the resonator 10 of FIG. 4. In FIG. 6, the construction and the dimension of grooves 21 , 27 , 32 and 36 are described in detail. The groove 21 is constructed to include a portion of the central line 41 of the tine 20 , and the groove 27 is similarly constructed to include a portion of the central line 42 of the tine 26 . The width W 2 of the grooves 21 and 27 (groove width W 2 ) which include a portion of the central lines 41 and 42 respectively, is preferable because moment of inertia of the tines 20 and 26 becomes large and the tines can vibrate in a flexural mode easily. As a result, the quartz crystal tuning fork resonator capable of vibrating in a fundamental mode can be obtained with a small series resistance R 1 and a high quality factor Q 1 .
In more detail, when part widths W 1 , W 3 and a groove width W 2 are taken, the tine width W of the tines 20 and 26 has a relationship of W=W 1 +W 2 +W 3 , and the part widths W 1 , W 3 are constructed so that W 1 ≧W 3 or W 1 <W 3 . In addition, the groove width W 2 is constructed so that W 2 ≧W 1 , W 3 . In this embodiment, also, the grooves are constructed at the tines so that a ratio (W 2 /W) of the groove width W 2 and the tine width W is larger than 0.35 and less than 1, preferably larger than 0.35 and less than 0.85, and a ratio (t 1 /t) of the groove thickness t 1 and the thickness t of the tines (tine thickness t) is less than 0.79, to obtain very large moment of inertia of the tines. That is, the flexural mode, quartz crystal tuning fork resonator, capable of vibrating in the fundamental mode, and having a good frequency stability can be provided with a small series resistance R 1 , a high quality factor Q 1 and a small capacitance ratio r 1 because electromechanical transformation efficiency of the resonator becomes large markedly.
Likewise, a length l 1 of the grooves 21 , 27 provided at the tines 20 , 26 extends into the base 40 in this embodiment (which has a dimension of the length l 2 and the length l 3 of the grooves). Therefore, a groove length and a length of the tines are given by (l 1 -l 3 ) and (l-l 2 ), respectively, and a ratio of (l 1 -l 3 ) and (l-l 2 ) is within a range of 0.3 to 0.8, preferably, 0.4 to 0.8 to get a flexural mode tuning fork resonator with series resistance R 1 of a fundamental mode vibration smaller than series resistance R 2 of a second overtone mode vibration. In other words, a groove length is within a range of 30% to 80%, preferably, 40% to 80% of a length of each of the tines, so that a flexural mode tuning fork resonator with a reduced series resistance R 1 and a small motional inductance L 1 of a fundamental mode vibration and having shock proof can be obtained when the flexural mode tuning fork resonator is miniaturized. Also, a length l 2 of the base is less than 0.5 mm, preferably, within a range of 0.29 mm to 0.48 mm or within a range of 0.12 mm to 0.255 mm or within a range of 0.264 mm to 0.277 mm, so that a miniaturized flexural mode tuning fork resonator can be obtained with reduced energy losses which are caused by vibration when it is mounted on a mounting portion of a case. As be well known, the resonator can be expressed by an electrical equivalent circuit comprising motional capacitance C 1 , motional inductance L 1 , series resistance R 1 connected in series, and shunt capacitance C 0 connected to C 1 , L 1 and R 1 in parallel.
Furthermore, the total length l is determined by the frequency requirement and the size of the housing case. Simultaneously, to get a flexural mode, quartz crystal tuning fork resonator, capable of vibrating in a fundamental mode with suppression of the second overtone mode vibration which is an unwanted mode vibration, there is a close relationship between the groove length l 1 and the total length l. Namely, a ratio (l 1 /l) of the groove length l 1 and the total length l is within a range of 0.2 to 0.78 because the quantity of charges which generate within the grooves and on the sides of the tines or the tines and the base can be controlled by the ratio, as a result, the second overtone mode vibration which is an unwanted mode vibration, can be suppressed, and simultaneously, a frequency stability of the fundamental mode vibration gets high. Therefore, the flexural mode, quartz crystal tuning fork resonator, capable of vibrating easily in a fundamental mode and having high frequency stability can be provided. Also, the total length l is less than 2.18 mm, preferably, within a range of 1.2 mm to 2 mm, more preferably, 0.8 mm to 1.2 mm, and groove length l 1 is less than 1.29 mm, preferably, within a range of 0.32 mm to 1.1 mm, more preferably, within a range of 0.32 mm to 0.85 mm, to get a smaller-sized tuning fork resonator with about 32.768 kHz and a small motional inductance L 1 which vibrates in a flexural mode and a fundamental mode.
In more detail, series resistance R 1 of the fundamental mode vibration becomes smaller than series resistance R 2 of the second overtone mode vibration. Namely, R 1 <R 2 , preferably, R1<0.86R 2 , therefore, a quartz crystal oscillator comprising an amplifier (CMOS inverter), capacitors, resistors and a quartz crystal unit with the quartz crystal tuning fork resonator of this embodiment can be obtained, which is capable of vibrating in the fundamental mode easily. In addition, in this embodiment the grooves 21 and 27 of the tines 20 and 26 extend into the base 40 in series, but embodiment of the present invention includes a plurality of grooves divided in the length direction of the tines. Namely, the plurality of grooves are formed in each of the two of the main surfaces (e.g., in each of the first and second opposite main surfaces) of each of the tuning fork tines 20 , 26 . In addition, the grooves may be constructed only at the tines (l 3 =0). From l 3 =0, the four grooves 21 , 22 . 27 and 28 each of which has a fourth stepped portion opposite the third stepped portion in the length direction are formed in the two of the main surfaces (e.g., in the first and second opposite main surfaces) of each of the tuning fork tines 20 , 26 , and the first stepped portion is connected to the second stepped portion through the third and fourth stepped portions.
In this embodiment, the groove length l 1 corresponds to electrode length disposed inside the grooves, though the electrode is not shown in FIG. 6, but, when the electrode length is less than the groove length, the length l 1 is of the electrode length. Namely, the ratio (l 1 /l) in this case is expressed by a ratio of electrode length l 1 of the grooves and the total length l. In order to achieve the above-mentioned object, it may be satisfied with at least one groove with the ratio constructed at the obverse and reverse faces of each tine. As a result, the flexural mode, quartz crystal tuning fork resonator, capable of vibrating very easily in the fundamental mode and having the high frequency stability can be realized. Also, a fork portion of this embodiment has a rectangular shape, but this invention is not limited to this, for example, the fork portion may have a U shape.
In addition, a space of between the tines is given by W 4 , and in this embodiment, the space W 4 and the groove width W 2 are constructed so that W 4 ≧W 2 , and more, the space W 4 is within a range of 0.05 mm to 0.35 mm and the groove width W 2 is within a range of 0.03 mm to 0.12 mm because it is easy to form a tuning fork shape and grooves of the tuning fork tines separately by a photo-lithographic process and an etching process, consequently, a frequency stability for a fundamental mode vibration gets higher than that for a second overtone mode vibration. In this embodiment, a quartz wafer with the thickness t of 0.05 mm to 0.15 mm is used. In order to get a smaller-sized quartz crystal tuning fork resonator, capable of vibrating in a flexural mode, and a small motional inductance L 1 , it is necessary that groove width W 2 is less than 0.07 mm, preferably, larger than 0.015 mm and less than 0.04 mm and tine width W is less than 0.18 mm, and preferably, the W is larger than 0.05 mm and less than 0.1 mm, more preferably, larger than 0.03 mm and less than 0.075 mm. Also, a groove thickness t 1 is within a range of 0.01 mm to 0.085 mm approximately, and part widths W 1 , W 3 are less than 0.021 mm, preferably, less than 0.015 mm. In more detail, a dimension of the part widths W 1 , W 3 is very dependent on a manufacturing technology. Therefore, when the technology is taken into account, W 1 and W 3 have a value of larger than 0.008 mm and less than 0.015 mm, preferably, larger than 0.01 mm and less than 0.014 mm to get a small motional inductance L 1 . In addition, the groove provided on at least one of the obverse face and the reverse face of the tuning fork tines of the present invention may be a through hole, namely, the groove thickness t 1 =0. Moreover, another example of the tuning fork tines having t 1 =0 is shown in FIG. 20 and which shows a plan view of a flexural mode, quartz crystal tuning fork resonator 600 . In detail, the resonator 600 comprises tuning fork tines 601 , 602 and tuning fork base 603 , the base 603 has cut portions 604 , 605 , and the tines 601 , 602 have central linear portions 616 , 617 , respectively. The tine 601 has through holes 606 , 608 , 610 and grooves 607 , 609 and the tine 602 has through holes 611 , 613 , 615 and grooves 612 , 614 . Each of the tines 601 , 602 has a width W, and the through holes and the grooves have a width W 2 larger than or equal to part widths W 1 , W 3 , where W is given by W=W 1 +W 2 +W 3 . Namely, the tuning fork tines have a first tuning fork tine 601 and a second tuning fork tine 602 , and three through holes are formed at each of the first and second tuning fork tines so that a width W 2 of the through holes is greater than the part widths W 1 and/or W 3 . For example, the width W 2 of the through holes has a value lager than 0.02 mm and less than 0.04 mm and the part widths W 1 and W 3 have a value larger than 0.008 mm and less than 0.014 mm. In this embodiment, the through holes are dived into the length direction of the first and second tuning fork tines. When the first tuning fork tine 601 has three through holes comprising first, second and third through holes 610 , 608 , 606 divided in the length direction, the groove 609 is formed between the first through 610 and second through hole 608 and the groove 606 is formed between the second through hole 608 and the third through hole 606 . Similar to this, when the second tuning fork tine 602 has three through holes comprising first, second and third through holes 615 , 613 , 611 divided in the length direction, the groove 614 is formed between the first through 615 and second through hole 613 and the groove 612 is formed between the second through hole 613 and the third through hole 611 . In other words, each of the first and second tuning fork tines has three through holes divided in the length direction and a groove is formed in at least one or each of the obverse and reverse faces between two through holes. In this embodiment, though a groove is formed between two through holes, but this invention is not limited to this, the groove may be not formed between the two through holes. Namely, a frame portion is formed between the two through holes. In addition, FIG. 21 shows a D 1 -D 2 cross-sectional view of the tuning fork tines 601 , 602 . The tine 601 has electrodes 618 , 621 disposed on side surfaces and electrodes 619 , 620 disposed in grooves 609 , 626 , while the tine 602 has electrodes 622 , 625 disposed on side surfaces and electrodes 623 , 624 disposed in grooves 614 , 627 . The electrodes 618 , 621 , 623 , 624 are connected electrically to form an electrode terminal G 1 , while the electrodes 619 , 620 , 622 , 625 are connected electrically to form an electrode terminal G 2 . Moreover, FIG. 22 shows a D 3 -D 4 cross-sectional view of the tuning fork tines 601 , 602 . The tine 601 has electrodes 618 , 621 disposed on side surfaces and electrodes 628 , 629 disposed in a through hole 610 , while the tine 602 has electrodes 622 , 625 disposed on side surfaces and electrodes 630 , 631 disposed in a through hole 615 . The electrodes 618 , 621 , 630 , 631 are connected electrically to form an electrode terminal G 3 , while the electrodes 628 , 629 , 622 , 625 are connected electrically to form an electrode terminal G 4 . The electrode terminals G 1 and G 3 have the same electrical polarity, while the electrode terminals G 2 and G 4 have the same electrical polarity different from the electrical polarity of the electrode terminals G 1 and G 3 . When an alternating current voltage is applied to the electrode terminals G 1 , G 3 and the electrode terminals G 2 , G 4 , the tuning fork resonator vibrates in a flexural mode of an inverse phase. In this embodiment, frame portions are not shown at the tuning fork base 603 , but the tuning fork base may have frame portions protruding from the tuning fork base. Moreover, when a length of the grooves and a length of the through holes are defined by l m and l a , respectively, there are two relationships so that l m ≧l a or l m <l a . In more detail, a length l a of the through holes in this embodiment is within a range of 0.03 mm to 0.45 mm, preferably, 0.05 mm to 0.3 mm and a length l m of the grooves is within a range of 0.01 mm to 0.5 mm, preferably, 0.025 mm to 0.35 mm. One of the two relationships is selected so that the tuning fork resonator has a small motional inductance L 1 . It is needless to say that a relationship of the length l a and the length l m can be applied to a tuning fork resonator in FIG. 23. In addition, a further example of the tuning fork tines having t 1 =0 is shown in FIG. 23 and which shows a plan view of a flexural mode, quartz crystal tuning fork resonator 650 . In detail, the resonator 650 comprises tuning fork tines 651 , 652 and tuning fork base 653 , the base 653 has cut portions 654 , 655 , and the tines 651 , 652 have central linear portions 666 , 667 , respectively. The tine 651 has through holes 656 , 657 , 658 , 659 and a groove 660 and the tine 652 has through holes 661 , 662 , 663 , 664 and a groove 665 . Each of the tines 601 , 602 has a width W, and the grooves have a width W 2 larger than or equal to part widths W 1 , W 3 , where W is given by W=W 1 +W 2 +W 3 . Namely, when each of the first and second tuning fork tines has a first side surface and a second side surface opposite the first side surface, and obverse and reverse faces each of which has a central linear portion, a through hole is formed between the first side surface and the central linear portion and/or a through hole is formed between the second side surface and the central linear portion so that the central linear portion is not included in the through hole. Namely, a width of the through hole is less than a half of the tine width W. In this embodiment, the through holes are divided into the width and length directions of the corresponding one of the first and second tuning fork tines. The groove 660 is formed between the through holes 656 , 657 , between the through holes 658 , 659 , between 656 , 658 and between the through holes 657 , 659 , while the groove 665 is formed between the through holes 661 , 662 , between the through holes 663 , 664 , between 661 , 663 and between the through holes 662 , 664 . Namely, the through holes 656 , 657 , 658 , 659 are formed in the groove 660 and the through holes 661 , 662 , 663 , 664 are formed in the groove 665 . In this embodiment, though a groove is formed between the through holes, this invention is not limited to this, but the groove may be not formed between the through holes. In addition, two through holes at each of left and right sides of the central linear portion are formed in the length direction in this embodiment, but the through holes more than two may be formed in the length direction. In addition, two through holes are formed symmetrically in the width direction to the central linear portion in this embodiment, but the two through holes may be formed asymmetrically in the width direction to the central linear portion. Moreover, FIG. 24 shows a J 1 -J 2 cross-sectional view of the tuning fork tines 651 , 652 . The tine 651 has electrodes 668 , 672 disposed on side surfaces and electrodes 669 , 670 , 671 disposed in through holes 656 , 657 , while the tine 652 has electrodes 673 , 678 disposed on side surfaces and electrodes 674 , 675 , 676 disposed in through hole 661 , 662 . The electrodes 668 , 672 , 674 , 675 , 676 are connected electrically to form an electrode terminal N 1 , while the electrodes 669 , 670 , 671 , 673 , 678 are connected electrically to form an electrode terminal N 2 . In addition, FIG. 25 shows a J 3 -J 4 cross-sectional view of the tuning fork tines 651 , 652 . The tine 651 has electrodes 668 , 672 disposed on side surfaces and electrodes 679 , 680 disposed in grooves 660 , 683 , while the tine 652 has electrodes 673 , 678 disposed on side surfaces and electrodes 681 , 682 disposed in grooves 665 , 684 . The electrodes 668 , 672 , 681 , 682 are connected electrically to form an electrode terminal N 3 , while the electrodes 679 , 680 , 673 , 678 are connected electrically to form an electrode terminal N 4 . The electrode terminals N 1 and N 3 have the same electrical polarity, while the electrode terminals N 2 and N 4 have the same electrical polarity different from the electrical polarity of the electrode terminals N 1 and N 3 . When an alternating current voltage is applied to the electrode terminals N 1 , N 3 and the electrode terminals N 2 , N 4 , the tuning fork resonator vibrates in a flexural mode of an inverse phase. In this embodiment, frame portions are not shown at the tuning fork base 653 , but the tuning fork base may have frame portions protruding from the tuning fork base. Moreover, the through holes are formed at each of first and second tuning fork tines by etching simultaneously with the first and second tuning fork tines. But, at least one through hole may be formed at each of first and second tuning fork tines by etching in a step different from the step of forming the first and second tuning fork tines. In addition, each of the first and second tuning fork tines has a plurality of through holes in the length direction, an overall length of the through holes is within a range of 20% to 80%, preferably, 30% to 70%, of a length of each of the tuning fork tines. Moreover, when a width of the groove formed in the width direction between two through holes and a width of the through holes are defined by w m and w a , respectively, the groove and the through holes are formed so that w m ≧w a or w m <w a . Namely, they are formed so that the tuning fork resonator has a small motional inductance L 1 . Also, a width of the through holes in this embodiment is within a range of 0.008 mm to 0.03 mm, preferably, 0.01 mm to 0.02 mm. As a result, the tuning fork resonator can be obtained with a small motional inductance L 1 , so that an oscillating circuit with the tuning fork resonator can be provided with short rise-time of an output signal when an alternating current voltage is applied to the oscillating circuit.
In more detail, to obtain a flexural mode, quartz crystal tuning fork resonator with a high frequency stability which gives high time accuracy, it is necessary to obtain the resonator whose resonance frequency is not influenced by shunt capacitance because quartz crystal is a piezoelectric material and the frequency stability is very dependent on the shunt capacitance. In order to decrease the influence on the resonance frequency by the shunt capacitance, figure of merit M i (hereafter a merit value M i ) plays an important role. Namely, the merit value M i that expresses inductive characteristics, electromechanical transformation efficiency and a quality factor of a flexural mode, quartz crystal tuning fork resonator, is defined by a ratio (Q i /r i ) of a quality factor Q i and capacitance ratio r i , namely, M i is given by M i =Q i /r i , where i shows vibration order of the resonator, and for example, when i=1 and 2, the merit values M 1 and M 2 are a value for a fundamental mode vibration and a second overtone mode vibration of the flexural mode, quartz crystal tuning fork resonator, respectively.
Also, a frequency difference Δf of resonance frequency f s of mechanical series independent on the shunt capacitance and resonance frequency f r dependent on the shunt capacitance is inversely proportional to the merit value M i . The larger the value M i becomes, the smaller the difference Δf becomes. Namely, the influence on the resonance frequency f r by the shunt capacitance decreases because it is close to the resonance frequency f s . Accordingly, the larger the M i becomes, the higher the frequency stability of the flexural mode, quartz crystal tuning fork resonator becomes because the resonance frequency f r of the resonator is almost never dependent on the shunt capacitance. Namely, the quartz crystal tuning fork resonator can be provided with a high time accuracy.
In detail, the flexural mode, quartz crystal tuning fork resonator can be obtained with the merit value M 1 of the fundamental mode vibration larger than the merit value M 2 of the second overtone mode vibration by the above-described tuning fork shape, grooves and dimensions. That is to say, a relationship of M 1 >M 2 is obtained. As an example, when resonance frequency of a flexural mode, quartz crystal tuning fork resonator is about 32.768 kHz for a fundamental mode vibration and the resonator has a value of W 2 /W=0.5, t 1 /t=0.34 and l 1 /l=0.48, though there is a distribution in production, the resonator has a value of M 1 >65 and M 2 <30, respectively.
Namely, the flexural mode, quartz crystal tuning fork resonator which vibrates in the fundamental mode can be provided with high inductive characteristics, good electromechanical transformation efficiency (small capacitance ratio r 1 and small series resistance R 1 ) and a high quality factor. As a result, a frequency stability of the fundamental mode vibration becomes higher than that of the second overtone mode vibration, and simultaneously, the second overtone mode vibration can be suppressed because capacitance ratio r 2 and series resistance R 2 of the second overtone mode vibration become larger than capacitance ratio r 1 and series resistance R 1 of the fundamental mode vibration, respectively. In particular, r 2 has a value larger than 1500 in this embodiment.
Therefore, the resonator capable of vibrating in the fundamental mode vibration can be provided with a high time accuracy because it has the high frequency stability. Consequently, a quartz crystal oscillator comprising the flexural mode, quartz crystal tuning fork resonator of this embodiment outputs an oscillation frequency of the fundamental mode vibration as an output signal, and the frequency of the output signal has a very high stability, namely, excellent time accuracy. In other words, the quartz crystal oscillator of this embodiment has a remarkable effect such that a frequency change by ageing becomes extremely small. Also, an oscillation frequency of the resonator of this embodiment is adjusted so that a frequency deviation is within a range of −100 PPM to +100 PPM to a nominal frequency, e.g. 32.768 kHz, after mounting it at a mounting portion of a case or a lid by conductive adhesives or solder.
In addition, the groove thickness t 1 of the present invention is the thinnest thickness of the grooves because quartz crystal is an anisotropic material and the groove thickness t 1 has a distribution when it is formed by a chemical etching method. In deta