Method of manufacturing piezoelectric vibration reed, piezoelectric vibration reed, piezoelectric vibrator, oscillator, electronic instrument, and radio time piece

A method of manufacturing a piezoelectric vibration reed is provided. The piezoelectric vibration reed includes a pair of vibrating arm portions and a base portion. The pair of vibrating arm portions is disposed in parallel to each other. The base portion is configured to integrally support proximal end portions of the pair of vibrating arm portions in a longitudinal direction of the vibrating arm portions. The method of manufacturing the piezoelectric vibration reed forms a slit-shaped notched portion at a crotch portion located between the proximal end portions of the pair of vibrating arm portions.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2011-218238 filed on Sep. 30, 2011, the entire content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a method of manufacturing a piezoelectric vibration reed, a piezoelectric vibration reed, a piezoelectric vibrator, an oscillator, an electronic instrument, and a radio time piece.

2. Description of the Related Art

In mobile phones or portable information terminal equipment, a piezoelectric vibrator having a piezoelectric vibration reed formed of a piezoelectric material such as crystal is known as a device used for a time-of-day source, a timing source such as a control signal, or a reference signal source.

There are various types of piezoelectric vibration reeds described above are known. Known examples of such piezoelectric vibration reed include a tune-fork type piezoelectric vibration reed100having a pair of vibrating arm portions110disposed in parallel, to each other, and a base portion120which supports a proximal end portion of the vibrating arm portions110in an cantilevered manner as shown inFIG. 27. The piezoelectric vibration reed100is capable of vibrating the pair of vibrating arm portions110in the direction toward and away from each other (the direction indicated by arrows in the drawing) at a predetermined resonant frequency by applying a voltage to an excitation electrode, not shown, formed on surfaces of the pair of vibrating arm portions110.

Incidentally, the contour of the piezoelectric vibration reed100is formed generally by performing an etching process on a wafer substrate formed of crystal or the like. This point will be described in brief. An etching protection film is formed on a surface of the wafer substrate, and then the etching protection film210on a wafer substrate200is patterned into contours of the piezoelectric vibration reeds100using Photolithography technology as shown inFIG. 28. Subsequently, using the patterned etching protection film210as a mask, the piezoelectric vibration reed100shown inFIG. 27, which includes the pair of vibrating arm portions110supported by the base portion120in a cantilevered manner, is obtained by performing the etching process on the wafer substrate200by Wet Etching as shown inFIG. 29.

However, when performing the etching process by Wet Etching, the speed of etching the wafer substrate200varies depending on the directions of the crystal axes, which is a phenomenon so-called an etching anisotropy. More specifically, in the respective crystal axes of the crystal (X-axis, Y-axis, and Z-axis), the etching speed is lowered in the order of Z-axis, +X axis, −X axis, Y-axis. Therefore, by the influence of the etching anisotropy, etching residuals are likely to be generated when the contours are formed, so that the contours of the piezoelectric vibration reeds100are likely to have irregular shapes. In particular, as shown inFIG. 27andFIG. 30, etching residuals116are likely to be generated at a crotch portion115of the proximal end portions of the pair of vibrating arm portions110(the base portion).

This point will be described.

Normally, when forming the tuning-fork type piezoelectric vibration reed100, the wafer substrate200is cut out from a crystal raw stone so that the Z-axis of the crystal axis substantially matches the thickness direction (L1direction) of the piezoelectric vibration reed100, the Y-axis matches the longitudinal direction (L2direction) of the piezoelectric vibration reed100, and the X-axis matches the width direction (L3direction) of the piezoelectric vibration reed100for the purpose of obtaining desired contour by the etching process as shown inFIG. 27. However, since the etching speed varies by any means, the etching residuals116are likely to be generated at the crotch portion115between the pair of vibrating arm portions110as shown inFIG. 31.

In particular, as the etching process is proceeded and the point being processed approaches the portion of the crotch portion115, a flow of etching solution is impaired by the etching protection film210so that the reaction of etching becomes slow. Therefore, the speed of procession of the etching process in the Y-axis direction, in which the etching speed becomes the slowest, is further lowered, whereby the etching residuals116are likely to be generated.

If the etching residuals116are generated at the crotch portion115, the pair of vibrating arm portions110are resulted in unbalanced vibrations, which may result, in turn, in an increased CI value due to a change of vibration characteristics and a vibration leak.

Accordingly, by devising the shape of the etching protection film corresponding to the crotch portion while taking the difference in etching speed into account in advance, a technology to adjust the vibration balance of the pair of vibrating arm portions is known (JP-A-2005-167992).

However, even when the technology described in JP-A-2005-167992 is employed, the etching residual itself still remains significantly. Therefore, a stress tends to concentrate on coupling portions between portions of the etching residuals and the vibrating arm portions at the time of vibrations for example, and the lowering of the strength of portions where the stress is concentrated is resulted. Consequently, the corresponding portions may become a starting point of damage caused by the external impact or the like, so that the vibrating arm portions are susceptible to cracks or the like.

In addition, the etching residual may work to change the length of the pair of the vibrating arm portions, so that the change of the variation characteristic such as shifting of the resonant frequency is still likely to occur.

It is believed that the etching residuals may be reduced by performing Wet Etching for a long time. However, the time to be used for etching is increased, and hence lowering of the productivity is resulted. Furthermore, since the period to be soaked into the etching solution, which is drug solution, may increase as well, a problem that the etching protection film becomes eroded and hence a desirable etching process cannot be performed, so that the vibration characteristics may deteriorate.

SUMMARY OF THE INVENTION

In view of such circumstances, it is an object of the invention to provide a high-quality piezoelectric vibration reed having less etching residuals at a crotch portion located between a pair of vibrating arm portions, providing stable vibration characteristics, and being resistant to damage of the vibrating arm portions due to an external impact, and a method of manufacturing such a piezoelectric vibration reed.

It is another object of the invention to provide a piezoelectric vibrator having such a piezoelectric vibration reed, an oscillator, an electronic instrument, and a radio timepiece having such a piezoelectric vibrator.

In order to solve the problems as described above, one embodiment a method of manufacturing a piezoelectric vibration reed includes a contour forming step for performing an etching process on a piezoelectric wafer and forming a contour of the piezoelectric vibration reed from the piezoelectric wafer. The piezoelectric vibration reed includes a pair of vibrating arm portions disposed in parallel to each other with a center axis interposed therebetween and a base portion configured to integrally support proximal end portions of the pair of vibrating arm portions in the longitudinal direction in a cantilevered manner. The contour forming step includes a mask pattern forming step for forming etching protection films on both main surfaces of the piezoelectric wafer and forming a mask pattern corresponding to a contour of the piezoelectric vibration reed from the etching protection film by Photolithography technology. The contour forming step further includes an etching step for performing an etching process on the piezoelectric wafer by Wet Etching from both main surface sides using the mask pattern as a mask, wherein during the mask pattern forming step, a slit-shaped notched portion extending toward the base portion side along the longitudinal direction of the pair of vibrating arm portions is formed on the mask pattern at a crotch-portion-corresponding portion for forming a crotch portion located between the proximal end portions of the pair of vibrating arm portions.

In this embodiment, since etching solution comes in contact with areas of the piezoelectric wafer, which are not masked by the mask pattern, the etching process proceeds by a chemical reaction. Accordingly, the etching process can be performed on the piezoelectric wafer along the shape of the mask pattern, so that the contour of the piezoelectric vibration reed is formed.

Incidentally, by the flowing etching solution coming into contact with the piezoelectric wafer from point to point, the etching process described above is performed smoothly, and formation of the contour of the piezoelectric vibration reed is gradually in progress. However, since the pair of vibrating arm portions are arranged in parallel at a small distance, the etching solution can hardly flow between the pair of vibrating arm portions. In particular, since an area of the mask pattern surrounded from three sides by arm-portion-corresponding portions corresponding to the vibrating arm portions and the crotch-portion-corresponding portion corresponding to the crotch portion is to be etched as the progress of the etching process approaches the crotch portion, it is contemplated that the etching solution can hardly flow.

However, since the notched portions are formed on the crotch-portion-corresponding portion in the mask pattern, the etching solution can easily flow in the longitudinal direction of the pair of vibrating arm portions along the notched portions. Therefore, the speed of the progress of the etching process along the longitudinal direction in the direction toward the crotch-portion-corresponding portion can be increased. Therefore, the etching process is prevented from proceeding in accordance with the difference in etching speed depending on the direction of the crystal axis of the piezoelectric wafer, so that the etching process can be proceeded positively toward the crotch-portion-corresponding portion.

Consequently, even though the period of the etching process is the same as that of the related art, the etching residuals on the crotch portion located between the proximal end portions of the pair of vibrating arm portions are reduced in comparison with the related art. Therefore, occurrence of the stress concentration caused by the etching residuals is inhibited, and the high-quality piezoelectric vibration reed which is resistant to damage of the vibrating arm portions due to the external impact or the like is obtained. Since the problem that the lengths of the vibrating arm portions are changed by the etching residuals can hardly occur, stable vibration characteristics may be demonstrated.

Alternatively, or additionally, the notched portion has a constant notched width along the entire notched length. In this case, the etching solution can be flowed in the longitudinal direction of the pair of vibrating arm portions along the notched portion further stably and smoothly. Therefore, the etching process can be proceeded toward the crotch-portion-corresponding portion more positively, and the etching residuals on the crotch portion can further be reduced.

Alternatively, or additionally, the notched portion is formed along the center axis. In this case, since the notched portion is formed along the center axis located between the pair of vibrating arm portions (that is, the center axis in the width direction of the piezoelectric vibration reed), not only an effect that the etching residuals on the crotch portion may be reduced, but also an effect that positional deviation of the etching residuals to either one of the vibrating arm portions can be prevented easily are achieved.

In another embodiment of a method of manufacturing a piezoelectric vibration reed include forming etching protection films on both main surfaces of the piezoelectric wafer and forming a mask pattern corresponding to a contour of the piezoelectric vibration reed from the etching protection film by using Photolithography technology. The contour of the piezoelectric vibration has a pair of vibrating arm portions disposed in parallel to each other with a center axis interposed therebetween; a base portion configured to integrally support proximal end portions of the pair of vibrating arm portions in a longitudinal direction of the vibrating arm portions; and a connection portion between the proximal end portions of the pair of vibrating arm portion and the base portion. The method further includes etching the piezoelectric wafer by Wet Etching from both main surface sides using the mask pattern as a mask, the etching step comprising removing etching residuals remained on the crotch portion; and forming a notched portion by removing some of the base portion in a width direction toward a center of the piezoelectric vibration reed, the notched portion extending through the base portion, the step of forming the notched portion further comprising determining a width and a length of the notched portion based on a curvature R of the crotch portion.

Another embodiment of the present invention is a piezoelectric vibration reed manufactured by the method of manufacturing the piezoelectric vibration reed described above.

In this embodiment of the piezoelectric vibration reed, since the etching residuals on a crotch portion located between a pair of vibrating arm portions are smaller than that of the related art, a high-quality piezoelectric vibration reed providing stable vibration characteristics, and being resistant to damage of the vibrating arm portions due to an external impact is provided.

Another further embodiment is a piezoelectric vibrator which includes the piezoelectric vibration reed described in the above embodiments, and a package having a base substrate and a lid substrate coupled to each other and configured to accommodate the piezoelectric vibration reed in a cavity formed between the both substrates.

The piezoelectric vibration reed described in the above embodiments, since the high-quality piezoelectric vibration reed providing stable vibration characteristics and being resistant to damage of the vibrating arm portions due to the external impact is provided, the high-quality piezoelectric vibration reed improved in reliability in operation and durability is provided.

Another further embodiment is an oscillator which includes the above-described piezoelectric vibrator that is electrically connected to an integrated circuit as an oscillating element.

Another embodiment is an electronic instrument having the above-described piezoelectric vibrator that is electrically connected to a clocking unit.

Another embodiment is a radio timepiece where the above-described piezoelectric vibrator is electrically connected to a filter portion.

According to the oscillator, the electronic instrument, and the radio time piece in the embodiments, since the piezoelectric vibrator described above is provided, reliability in operation and durability are improved in the same manner.

According to the above-described embodiments, a high-quality piezoelectric vibration reed having less etching residuals at a crotch portion located between a pair of vibrating arm portions, providing stable vibration characteristics, and being resistant to damage of the vibrating arm portions due to an external impact is provided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, an embodiment of a piezoelectric vibration reed according to the invention will be described below.

As shown inFIG. 1, a piezoelectric vibration reed1of this embodiment is a turning-fork type vibration reed formed of a piezoelectric material such as crystal, lithium tantalate, or lithium niobate, and is configured to vibrate when a predetermined voltage is applied.

The piezoelectric vibration reed1includes a pair of vibrating arm portions10and11arranged in parallel to each other and having distal end portions10aand11aas free ends and a base portion12configured to integrally support proximal end portions10band11bside (the side of the base portions) of the pair of vibrating arm portions10and11in a cantilevered manner.

The pair of vibrating arm portions10and11are arranged so as to extend in a line symmetry with a center axis O interposed therebetween, have a constant width in the width direction, and extend along the center axis O. The base portion12is a member configured to support the proximal end portions10band11bsides of the pair of vibrating arm portions10and11in a cantilevered manner as described above, and functions as a mount member used when mounting the piezoelectric vibration reed1.

A portion located between the proximal end portions10band11bof the pair of vibrating arm portions10and11corresponds to a crotch portion15. In the illustrated example, a coupled portion between the proximal end portions10band11bof the pair of vibrating arm portions10and11and the base portion12is curved at a curvature R, and hence the crotch portion15is formed into a U-shape in plan view when viewed in the thickness direction.

Also, the pair of vibrating arm portions10and11are formed with excitation electrodes, not shown, configured to vibrate the pair of vibrating arm portions10and11on outer surfaces thereof. The base member12is formed with mount electrodes, not shown, on outer surface thereof in a state of being in conduction with the excitation electrode. Then, when a predetermined voltage is applied to the excitation electrode via the mount electrode, the pair of vibrating arm portions10and11vibrate in the direction toward and away from each other (the direction indicated by arrows inFIG. 1) at a predetermined resonant frequency due to a mutual action of the both electrodes.

Incidentally, the piezoelectric vibration reed1of this embodiment is manufactured by etching a piezoelectric wafer, described later, by Wet Etching and forming a contour thereof. However, as shown inFIG. 1andFIG. 2, there slightly remains etching residuals16at the crotch portion15described above. However, these etching residuals16are much less than the portion of the etching residuals16A of the related art indicated by a dot line and, in addition, are not formed over the entire part of the crotch portion15so as to connect the proximal end portions10band11bof the pair of vibrating arm portions10and11and are disconnected in the vicinity of the center axis O.

(Method of Manufacturing a Piezoelectric Vibration Reed)

Subsequently, a method of manufacturing the piezoelectric vibrator1described above will be described with reference to flowcharts inFIG. 3andFIG. 4. In this embodiment, a case where a crystal wafer is employed as the piezoelectric wafer will be described as an example.

The method of manufacturing the piezoelectric vibration reed1of this embodiment includes a contour forming step (S20) for forming contours of a plurality of the piezoelectric vibration reeds1from a crystal wafer20by etching the crystal wafer20by Wet Etching after a preparation (S10) of the crystal wafer20(seeFIG. 5), an electrode forming step (S30) for forming respective electrodes on each of the piezoelectric vibration reeds1after the formation of the contours, a frequency adjusting step (S40) for adjusting resonant frequencies of the respective piezoelectric vibration reeds1, and a cutting-up step (S50) for cutting off the respective piezoelectric vibration reeds1from the crystal wafer20.

The respective steps will be described in detail below.

First of all, Lambert row stone of crystal is sliced at a predetermined angle, so that the crystal wafer20having a certain thickness is obtained. In this case, the crystal wafer20is formed by performing the slicing as described above so that a Z-axis of the crystal axis substantially matches the direction of the thickness (L1direction) of the piezoelectric vibration reed1shown inFIG. 1, a Y-axis matches the length direction (L2direction) of the piezoelectric vibration reed1, and an X-axis matches the width direction (L3direction) of the piezoelectric vibration reed1.

Then, by lapping and polishing the crystal wafer20, the crystal wafer20having a predetermined thickness finished in high degree of accuracy is prepared (S10).

Subsequently, the contour forming step (S20) is performed.

The contour forming step (S20) includes a mask pattern forming step (S21) for forming the etching protecting films21(seeFIG. 5) on both main surfaces of the crystal wafer20, and forming a mask pattern22(seeFIG. 6) corresponding to the contours of the piezoelectric vibration reeds1from the etching protecting film21by Photolithography technology and an etching step (S22) for performing an etching process on the both main surfaces sides of the crystal wafer20by Wet Etching using the mask pattern22as a mask.

In the mask pattern forming step (S21), as shown inFIG. 5, the etching protecting films21are formed on the both main surfaces of the crystal wafer20(S21a) first. Examples of the etching protecting film21include a metallic film formed by laminating a base film formed of chrome, for example, and a finishing film formed of gold one one top of another, and is formed by film formation on the basis of a sputtering method or an evaporation method.

Then, the etching protecting film21is patterned to form the mask pattern22corresponding to the contours of the piezoelectric vibration reeds1(S21b).

More specifically, a photo resist film, not shown, is formed on the etching protecting film21, and then the photo resist film is patterned so as to form a contour of the piezoelectric vibration reed1, for example by a general photoresist technology. Then, the etching process is performed using the photo resist film as a mask, and portions of the etching protecting film21which is not masked are selectively removed. Then, after the etching process, the photo resist film used as the mask is removed.

Accordingly, as shown inFIG. 6andFIG. 7, the mask pattern22patterned into the contours of the above-described piezoelectric vibration reed1is formed.

Incidentally, in this embodiment, when forming the mask pattern22, notched portions23are formed at crotch-portion-corresponding portions22awhere the crotch portions15of the piezoelectric vibration reeds1are to be formed as shownFIG. 6. The notched portions23each are a slit-shaped notch extending toward the base portion12along the longitudinal direction (L2direction) of the pair of vibrating arm portions10and11, arranged so as to extend along the center axis O and having a constant notched width along the entire length of the notch.

In the illustrated example, a notched width T1of the notched portions23is on the order of ⅓ a crotch width T2.

Then, the mask pattern forming step (S21) is terminated at this time point.

Subsequently, the etching step (S22) described above is performed.

Specifically, the crystal wafer20on which the etching protecting film21is patterned is soaked into etching solution (for example, fluorine system etching solution), not shown, for a predetermined period. Then, the etching solution comes into contact with the areas of the crystal wafer20, which are not masked by the mask pattern22, and hence the etching process proceeds by the chemical reaction. Accordingly, as shown inFIG. 8, the etching process can be performed on the crystal wafer20along the shape of the mask pattern22, so that the contour of the piezoelectric vibration reed1is formed.

In particular, by the flowing etching solution coming into contact with the crystal wafer20from point to point, the etching process is performed smoothly, and formation of the contours of the piezoelectric vibration reeds1gradually proceeds. However, since the crystal wafer20is formed so that the Z-axis of the crystal axis substantially matches the thickness direction (L1direction) of the piezoelectric vibration reed1, the Y-axis thereof matches the longitudinal direction (L2direction) of the piezoelectric vibration reed1, and the X-direction thereof matches the width direction (L3direction) of the piezoelectric vibration reed1as described above, the contour of the piezoelectric vibration reed1can be formed easily with high degree of accuracy.

The contour forming step (S20) is terminated at this time point.

The plurality of piezoelectric vibration reeds1are still in a state of being coupled to the crystal wafer20via coupling portions, not shown, until the cutting-up step (S50) to be performed later.

Subsequently, the electrode forming step (S30) for forming electrodes such as the excitation electrode is performed by forming a metallic film, not shown, on the respective piezoelectric vibration reeds1whose contours are formed, and then patterning the meal film by general Photolithography technique.

During this step, a weight metallic film, not shown, for adjusting the frequency is formed on the distal end portions10aand11aof the pair of vibrating arm portions10and11simultaneously with the formation of the electrodes. The weight metallic film includes a coarse adjustment film and a fine adjustment film.

Subsequently, the frequency adjusting step (S40) for coarsely adjusting the resonant frequency is performed using the coarse film of the weight metallic film. More specifically, the frequency adjusting step (S40) is performed by irradiating the coarse adjustment film with a laser beam, evaporating part of the coarse adjustment film and changing the weight of the coarse adjustment film. The fine adjustment for adjusting the resonant frequency with higher degree of accuracy is performed in a stage of being integrated into a package as the piezoelectric vibrator.

Finally, the cutting-up step (S50) for cutting the coupling portions and separating the piezoelectric vibration reeds1from the crystal wafer20into individual pieces is performed. Accordingly, the plurality of tuning-fork type piezoelectric vibration reeds1shown inFIG. 1may be manufactured at once from a single crystal wafer20.

Incidentally, during the etching step (S22) described above, since the pair of vibrating arm portions10and11are arranged at a small distance (the crotch width) in parallel to each other, the etching solution can hardly flow between the pair of vibrating arm portions10and11. In particular, since an area of the mask pattern22surrounded from three sides by the arm-portion-corresponding portions22bcorresponding to the vibrating arm portions10and11and the crotch-portion-corresponding portion22acorresponding to the crotch portion15, is to be etched as the progress of the etching process approaches the crotch portion15as shown inFIG. 6andFIG. 9, it is contemplated that the etching solution can hardly flow.

However, since the notched portions23described above are formed on the crotch-portion-corresponding portion22ain the mask pattern22of this embodiment, the etching solution can easily flow in the longitudinal direction (L2direction) of the pair of vibrating arm portions10and11along the notched portions23.

Therefore, as shown inFIG. 9, the speed of the progress of the etching process along the longitudinal direction (L2direction) in the direction toward the crotch-portion-corresponding portion22acan be increased by an amount corresponding to the notched portions23. Therefore, the etching process is prevented from proceeding in accordance with the difference in etching speed in the direction of the crystal axis of the crystal wafer20, so that the etching process can proceed positively toward the crotch-portion-corresponding portion22a. Therefore, the etching residuals16can hardly be remained on the crotch-portion-corresponding portion22a.

Consequently, even though the period of the etching process is the same as that of the related art, the etching residuals16on the crotch portion15located between the proximal end portions10band11bof the pair of vibrating arm portions10and11are reduced in comparison with the related art as shown inFIG. 27.

Therefore, occurrence of the stress concentration caused by the etching residuals16is inhibited, and the high-quality piezoelectric vibration reed1which is resistant to damage of the vibrating arm portions10and11due to the external impact or the like is obtained. Since the problem that the lengths of the vibrating arm portions10and11are changed by the etching residuals16can hardly occur, stable vibration characteristics may be demonstrated.

As described above, according to the method of manufacturing the piezoelectric vibration reed of this embodiment, the etching residuals16on the crotch portion15located between the proximal end portions10band11bof the pair of vibrating arm portions10and11can be reduced, and hence the high-quality piezoelectric vibration reed1having stable vibration characteristics and being resistant to damage of the vibrating arm portions10and11due to the external impact or the like is obtained.

In particular, since the notched portions23have a constant notch width along the entire notch length in the embodiment described above, the etching solution easily flows along the notched portions23in the longitudinal direction (L2direction) further stably and smoothly. Therefore, the etching process can be proceeded toward the crotch-portion-corresponding portion22amore positively, and the etching residuals16on the crotch portion15may be reduced easily.

In addition, since the notched portions23are formed along the center axis O, positional deviation of the etching residuals16to either one of the vibrating arm portions10and11can easily be prevented. Therefore, the above-described advantageous effects are achieved remarkably.

In the embodiment described above, the length and the notch width of the notched portions23are not limited to those described above, and may be set freely.

These values are preferably set on the basis of the crotch width T2or a curvature R at the coupling portion between the vibrating arm portions10and11and the base portion12.

For example, as shown inFIG. 10A, if the crotch width T2is small, the etching process is subject to the difference in etching speed between the X-axis of the crystal axis which matches the width direction (L3direction) and the Y-axis of the recommended crystal axis which matches the longitudinal direction (L2direction). Therefore, even when the notched portions23are formed, the etching residuals16as of the related art can easily be generated on the crotch portion15. Therefore, in this case, by increasing the notch length of the notched portions23as shown inFIG. 10B, and making the flow of the etching solution to the Y-axis smoother, the progress of the etching process in the corresponding direction is encouraged, so that the etching residuals16can hardly be generated.

Also, as shown inFIG. 11A, for example, when the curvature R of the coupling portion between the vibrating arm portions10and11and the base portion12becomes smaller, the etching residuals16can easily be increased even when the notched portions23are formed. Therefore, in such a case, the notch width of the notched portions23is increased and the length of the notch is reduced as shown inFIG. 11B, so that the etching residuals16can be minimized.

The shape of the piezoelectric vibration reed1is not limited to the embodiment described above.

For example, as shown inFIG. 12, the base portion12may be formed with notched portion31(notch) removed respectively from both side surfaces in the width direction (L3direction) toward the center in the width direction (L3direction) in the vicinity of the connecting portion of the vibrating arm portions10and11with respect to the proximal end portions10band11b, which is so-called a notch type piezoelectric vibration reed30.

The notched portions31open respectively outward in the width direction (L3direction), and penetrate through the base portion12in the thickness direction. Therefore, in the base portion12, the portion in the vicinity of the connecting portion of the vibrating arm portions10and11with respect to the proximal end portions10band11bhas a constricted shape which is narrower in width in comparison with other portions.

With the narrow portion formed by the notches31, a route through which the vibrations excited by the vibrating arm portions10and11are transmitted to the base portion12side can be narrowed, so that the vibrations are locked on the side of the vibrating arm portions10and11and are easily inhibited from leaking toward the base portion12. Accordingly, there is provided the piezoelectric vibration reed30in which the vibration leak is effectively restrained, and a CI value is prevented from increasing, whereby the deterioration of the quality of an output signal may be inhibited.

As shown inFIG. 13, so-called a hammer-head type piezoelectric vibration reed35formed with hammer portions36having an enlarged width than other portions of the vibrating arm portions10and11on the distal end portions10aand11aof the vibrating arm portions10and11is also applicable.

In this case, with the hammer portions36, the distal end portions10aand11aof the vibrating arm portions10and11may further be increased in weight, so that the inertia moment at the time of the vibrations may be increased. Therefore, there is provided the piezoelectric vibration reed35in which the vibrations of the vibrating arm portions10and11may be facilitated, and hence the length of the vibrating arm portions10and11may be reduced correspondingly, so that further downsizing can easily be achieved.

As shown inFIG. 14, a grooved-type piezoelectric vibration reed40formed with the groove portions41on the both main surfaces of the pair of vibrating arm portions10and11is also applicable.

The groove portions41are formed at substantially centers of the vibrating arm portions10and11along the longitudinal direction (L2direction) of the vibrating arm portions10and11. Accordingly, the vibrating arm portions10and11are formed into an H-shape in cross section.

In this case, since the excitation electrodes may be opposed each other on both sides of the groove portions41, the electrical field may efficiently act in the direction in which the vibrating arm portions10and11move toward and away from each other. Therefore, the field efficiency may be enhanced even when the lateral width of the vibrating arm portions10and11is reduced, so that the piezoelectric vibration reed40suitable for downsizing is achieved.

Furthermore, as shown inFIG. 15, so-called a side-arm type piezoelectric vibration reed45in which a pair of side arms46extending along the longitudinal direction (L2direction) on the both sides in the width direction (L3direction) of the base portion12is formed integrally with the base portion12is also applicable.

More specifically, the respective side arms46extend from the base portion12toward the both sides in the width direction (L3direction) and extend from the outer side portions toward the vibrating arm portions10and11along the longitudinal direction (L2direction). In other words, the respective side arms46are positioned on the base portion12and both side of the proximal end portions10band11bof the vibrating arm portions10and11in the width direction (L3direction).

In this case, the distal end portions46aof the side arms46can be functioned as the mount portions, and mounting on the package, for example, via the mounting portion is enabled.

In this configuration, a long distance can be secured between the connecting portions of the vibrating arm portions10and11and the mount portions (the distal end portions46aof the side arms46) of the base portion12. Consequently, the vibration leak is inhibited without increasing the entire length of the piezoelectric vibration reed45, and the CI value is inhibited from increasing, whereby the deterioration of the quality of the output signal may be inhibited.

As shown inFIG. 12toFIG. 15, the shape of the piezoelectric vibration reed may be designed freely as long as it is of a tuning-fork type. A piezoelectric vibration reed in which the notch type shown inFIG. 12, the hammer-head type shown inFIG. 13, the grooved type shown inFIG. 14, and the side arm type shown inFIG. 15are arbitrarily combined is also applicable.

Subsequently, a piezoelectric vibrator having the piezoelectric vibration reed according to the embodiment described above will be described. Here, a case where the piezoelectric vibration reed in which the notch type, the hammer-head type, and the third arm type are combined is used as the piezoelectric vibration reed will be described as an example. However, the invention is not limited to the piezoelectric vibration reed in this case and other types of the piezoelectric vibration reeds may be used.

In this embodiment, the configuration common to portions described above is designated by the same reference numerals in the drawings and description will be omitted. In this embodiment, illustration of the etching residuals16on the crotch portion15is omitted.

As shown inFIG. 16toFIG. 19, a piezoelectric vibrator50of this embodiment is of a surface-mounted type including a package53in which a base substrate51and a lid substrate52are joined by, for example, anode joining or joined via a joint film or the like, not shown, and the piezoelectric vibration reed60accommodated in a cavity C formed in the interior of the package53.

The base substrate51and the lid substrate52are transparent insulative substrate formed of a glass material, for example, a soda-lime glass, and is formed into a substantially plate shape. The lid substrate52is formed with a rectangular depression52afor accommodating the piezoelectric vibration reed60on the side of a joint surface where the base substrate51is joined. The depression52adefines the cavity C for accommodating the piezoelectric vibration reed60when the base substrate51and the lid substrate52are stacked one on top of another.

The base substrate51is formed with a pair of through holes65and66configured to penetrate the base substrate51in the thickness direction. The through holes65and66are formed at positions accommodated within the cavity C. More specifically, the through holes65and66of this embodiment are such that the one through hole65is formed at a position corresponding to the base portion12of the piezoelectric vibration reed60mounted thereon and the other through hole66is formed at a position corresponding to the distal end portion11aside of the vibrating arm portion11.

Then, a pair of through electrodes67and68are formed in the pair of through holes65and66so as to be embedded therein. The through electrodes67and68are conductive core members fixed integrally with the through holes65and66, for example, and are formed so as to be flat at both ends thereof and have the substantially same thickness as the thickness of the base substrate51. Accordingly, the electric conductivity is secured on both surfaces of the base substrate51while maintaining air-tightness in the cavity C.

The through electrodes67and68are not limited to the case described above, and may be formed, for example, by inserting metal pins, not shown, in the through holes65and66and then filling glass frit between the through holes65and66and the metal pins and sintering the same. Furthermore, a conductive adhesive agent embedded in the through holes65and66is also applicable.

A pair of drawing electrodes70and71are patterned using a conductive material on an upper side (the side of a joint surface to which the lid substrate52is joined) of the base substrate51. The drawing electrode70, which is the one of the pair of drawing electrodes70and71covers the through electrode67on one end side, and extends on the other end side thereof toward the center portion of the base substrate51in the longitudinal direction (L2direction). The other drawing electrode71covers the through electrode68at one end side, and extends on the other end side thereof toward the center portion of the base substrate51in the longitudinal direction (L2direction). Therefore, the other end sides of the respective drawing electrodes70and71are arranged at the same positions of the base substrate51in the longitudinal direction (L2direction), more specifically, at positions corresponding to the distal end portions46aof the side arms46of the piezoelectric vibration reed60.

Then, bumps B formed of gold or the like respectively are formed on the other end sides of the pair of drawing electrodes70and71. The piezoelectric vibration reed60is mounted in a state in which the mount electrode of the base portion12is in contact with the bumps B. Accordingly, the piezoelectric vibration reed60is supported in a state of coming off an upper surface of the base substrate51, and is in a state of being electrically connected to the respective drawing electrodes70and71.

In this embodiment, the mount electrode is formed on the distal end portions46aof the side arms46, and the mount electrode is connected to the drawn electrodes70and71via the bumps B.

External electrodes72and73to be electrically connected respectively to the pair of through electrodes67and68are formed on the lower surface of the base substrate51.

When activating the piezoelectric vibrator50configured in this manner, a predetermined drive voltage is applied to the external electrodes72and73formed on the base substrate51. Accordingly, a current is passed through the excitation electrode of the piezoelectric vibration reed60, so that the pair of vibrating arm portions10and11may be vibrated in the direction toward and away from each other at a predetermined frequency. Then, the piezoelectric vibrator50may be used as a time-of-day source, a timing source of a control signal, or a reference signal source using the vibrations of the pair of vibrating arm portions10and11.

According to the piezoelectric vibrator50of this embodiment, since the high-quality piezoelectric vibration reed60having stable vibration characteristics and being resistant to damage of the vibrating arm portions10and11due to the external impact is provided, the high-quality piezoelectric vibration reed50improved in reliability in operation and durability is provided.

Subsequently, an embodiment of the oscillator according to the invention will be described with reference toFIG. 20.

An oscillator100of this embodiment includes the piezoelectric vibrator50configured as an oscillating element electrically connected to an integrated circuit101as shown inFIG. 20. The oscillator100includes a substrate103on which an electronic component102such as a capacitor is mounted. The substrate103includes the integrated circuit101described above for the oscillator mounted thereon, and the piezoelectric vibrator50is mounted in the vicinity of the integrated circuit101. The electronic component102, the integrated circuit101, and the piezoelectric vibrator50are electrically connected respectively by a wiring pattern, not shown. The respective components are molded by a resin, not shown.

In the oscillator100configured in this manner, when a voltage is applied to the piezoelectric vibrator50, the piezoelectric vibration reed60in the piezoelectric vibrator50vibrates. This vibration is converted into an electric signal by the piezoelectric property of the piezoelectric vibration reed60, and is input to the integrated circuit101as the electric signal. The input electric signal is subjected to various processes by the integrated circuit101and is output as a frequency signal. Accordingly, the piezoelectric vibrator50functions as an oscillating element.

In addition, by selectively setting the configuration of the integrated circuit101, that is, RTC (Real Time Clock) modules according to the request, in addition to the function of a single-function oscillator for a time piece, a function to control the date and time of operation of the single-function oscillator for a time piece or external instruments or a function to provide the time of day or a calendar may be added.

As described above, according to the oscillator100of this embodiment, since the downsized piezoelectric vibrator50described above is provided, the oscillator100improved in reliability of operation and durability is provided.

Referring now toFIG. 21, an embodiment of the electronic instrument according to the invention will be described. A portable digital assistant device (electronic instrument)110having the piezoelectric vibrator50described above as the electronic instrument will be described as an example.

The portable digital assistant device110of this embodiment is represented, for example, by a mobile phone, which is a developed and improved wrist watch of the related art. An appearance is similar to the wrist watch, including a liquid crystal display at a portion corresponding to a dial, which is configured to display current time or the like on a screen thereof. When used as a communication instrument, the same communication as the mobile phones of the related art may be performed by removing the same from the wrist and using a speaker and a microphone integrated in a portion inside a band. However, downsizing and reduction in weight are dramatically achieved in comparison with the mobile phones of the related art.

Subsequently, a configuration of the portable digital assistant device110of this embodiment will be described. The portable digital assistant device110includes the piezoelectric vibrator50and a power source unit111configured to supply power as shown inFIG. 21. The power source unit111is formed of, for example, a lithium secondary cell. The power source unit111includes a control unit112configured to perform various types of control, a clocking unit113configured to count time of day or the like, a communication unit114configured to perform communication with the outside, a display unit115configured to display various items of information, and a voltage detection unit116configured to detect the voltage of the respective functional portions are connected in parallel to each other. Then, the power is supplied to the respective functional portions by the power source unit111.

The control unit112performs sending and receiving of voice data, counting and display of the current time of day, and control of the operation of the entire system by controlling the respective functional portions. The control unit112includes an ROM in which a program is written in advance, a CPU configured to read out and execute the program written in the ROM, and an RAM used as a work area for the CPU.

The clocking unit113includes an integrated circuit having an oscillation circuit, a register circuit, a counter circuit, and an interface circuit integrated therein, and the piezoelectric vibrator50. When a voltage is applied to the piezoelectric vibrator50, the piezoelectric vibration reed60vibrates, and the vibration thereof is converted into an electric signal by the piezoelectric property of crystal, and is input to the oscillation circuit as the electric signal. The output of the oscillation circuit is binarized and is counted by the register circuit and the counter circuit. Then, sending and receiving of the signal with respect to the control unit112is performed via the interface circuit, and the current time of day, the current date, calendar information or the like are displayed on the display unit115.

The communication unit114has the same function as the mobile phones of the related art, and includes a wireless unit117, a voice processing unit118, a switch unit119, an amplifying unit120, a voice input/output unit121, a phone number input unit122, a ring tone generating unit123, and a call control memory unit124.

The wireless unit117performs sending and receiving of various types of data such as voice data with respect to a base station via an antenna125. The voice processing unit118codes and decodes the voice signal input from the wireless unit117or the amplifying unit120. The amplifying unit120amplifies the signal input from the voice processing unit118or the voice input/output unit121to a predetermined level. The voice input/output unit121is formed of a speaker, a microphone, or the like, and is configured to amplify a ring tone or a receiving voice, or collect a voice.

The ring tone generating unit123generates the ring tone according to a call from the base station. The switch unit119switches the amplifying unit120connected to the voice processing unit118to the ring tone generating unit123only at the time of incoming call, so that the ring tone generated by the ring tone generating unit123is output to the voice input/output unit121via the amplifying unit120.

The call control memory unit124stores a program relating to control of incoming and outgoing call of communication. The phone number input unit122includes, for example, numerical key from 0 to 9 and other keys, and is configured to input a telephone number of the called party by pushing these numerical key or the like.

The voltage detection unit116detects voltage drop when the voltage applied to the receptive functional portions such as the control unit112by the power source unit111is less than the predetermined value, and notifies the same to the control unit112. The predetermined voltage value at this time is a value preset as a minimum required voltage for keeping a stable operation of the communication unit114and, for example, on the order of 3V. The control unit112which receives the notification of the voltage drop from the voltage detection unit116prohibits the wireless unit117, the voice processing unit118, the switch unit119, and the ring tone generating unit123from operating. In particular, the stop of the operation of the wireless unit117which consumes a large amount of power is essential. Then, the effect that the communication unit114is disabled due to insufficient remaining battery power is displayed on the display unit115.

In other words, the operation of the communication unit114is prohibited by the voltage detection unit116and the control unit112, and that effect may be displayed on the display unit115. This display may be a literal message. However, as more intuitive display, a cross mark (x) may be shown on a phone icon displayed on an upper portion of a display surface of the display unit115.

With the provision of a power source blocking unit126which is capable of selectively blocking the electric power of a portion relating to the function of the communication unit114, the function of the communication unit114may be stopped further reliably.

As described above, according to the portable digital assistant device110of this embodiment, since the piezoelectric vibrator50described above is provided, the portable digital assistant device110improved in reliability of operation and durability is provided.

Referring now toFIG. 22, an embodiment of a radio timepiece according to the invention will be described.

A radio timepiece140of this embodiment includes the piezoelectric vibrator50electrically connected to a filter141as shown inFIG. 22, and is a timepiece having a function to receive standard radio waves including timepiece information and display an accurate time-of-day automatically corrected.

In Japan, there are two transmitting stations (transmitter stations) which transmit standard radio waves in Fukushima prefecture (40 kHz) and Saga prefecture (60 kHz), and transmit respective standard radio waves. Since long waves such as 40 kHz or 60 kHz have both a property to propagate the ground surface and a property to propagate while being reverberated between an ionization layer and the ground surface, a wide range of the propagation is achieved, so that the above-described two transmitting stations cover entire part of Japan.

Hereinafter, a functional configuration of the radio timepiece140will be described in detail.

An antenna142receives a long standard radio wave of 40 kHz or 60 kHz. The long standard radio wave is time information referred to as time code subjected to an AM modulation to a carrier wave of 40 kHz or 60 kHz. The received long standard radio wave is amplified by an amplifier143and is filtered and synchronized by the filter141having a plurality of the piezoelectric vibrators50.

The piezoelectric vibrators50of this embodiment include quartz vibrator units148and149having resonant frequencies of 40 kHz and 60 kHz which are the same as the above-described carrier frequencies, respectively.

In addition, a signal filtered and having a predetermined frequency is subjected to detection and demodulation by a detection and rectification circuit134. Subsequently, the time code is acquired via a waveform shaping circuit145, and is counted by a CPU146. The CPU146reads information such as the current year, day of year, day of the week, time of day, and the like. The read information is reflected on an RTC147, and a correct time of day information is displayed.

Since the carrier wave has 40 kHz or 60 kHz, vibrators having the above-described tuning-fork type structure are suitable for the quartz vibrator units148and149.

The above-described description is based on an example in Japan, and the frequencies of the long standard radio waves are different in foreign countries. For example, in Germany, a standard radio wave of 77.5 kHz is used. Therefore, when integrating the radio timepiece140which is compatible with foreign countries in mobile apparatuses, another piezoelectric vibrator50having a frequency different from that in Japan is required.

As described above, according to the radio timepiece140of this embodiment, since the piezoelectric vibrator50described above is provided, the radio timepiece140improved in reliability of operation and durability is provided.

Although the embodiments of the invention have been described in detail referring to the drawings, detailed configurations are not limited to these embodiments, and modifications in design without departing the scope of the invention are also included.

For example, in the embodiments described above, the piezoelectric vibration reed in the invention is employed as the surface-mounted piezoelectric vibrator50. However, the invention is not limited thereto, and the piezoelectric vibration reed of the invention may be used for the piezoelectric vibrator of a cylinder package type.

In addition, the configurations described above may be sorted out or may be changed to other configurations as needed without departing the scope of the invention.

Here, an example in which the piezoelectric vibration reed1of the above-described embodiment shown inFIG. 1and the piezoelectric vibration reed of the related art were dropped from a height of 200 cm, and how much the resonant frequency F was shifted before and after and whether or not damage occurred or not are actually confirmed will be described.

The term “damage” here means damage including cracks or breakages of the vibrating arm portions10and11due to the concentration of a stress caused by the etching residuals16.

Both of the piezoelectric vibration reed1according to the invention and the piezoelectric vibration reed of the related art are manufactured from the crystal wafer20, and the size and the shape thereof are the same. However, the piezoelectric vibration reed1according to the invention is different from the related art in that formation of the contours is achieved by performing the etching process by Wet Etching using the mask pattern22formed with the notched portions23.

The drop test described above was performed for the piezoelectric vibration reed1according to the invention and the piezoelectric vibration reed of the related art under the same conditions, and twenty-two samples each were used for the test. In this case, the drop test was repeated three times for one sample.

Consequently, as shown inFIG. 23toFIG. 26, no damage was confirmed and the breakage rate was 0% in the case of the piezoelectric vibration reed1according to the invention. In contrast, in the case of the piezoelectric vibration reed of the related art, 7 samples out of 22 samples were broken, and the breakage rate was 31.8%.

As regards a shift amount (ppm) of the resonant frequency, it was confirmed that the shift amount of the piezoelectric vibration reed of the related art was apparently larger than that of the piezoelectric vibration reed1according to the invention.

From these reasons, according to the invention, advantageous effects that the etching residuals16on the crotch portion15are smaller than that of the related art, whereby the piezoelectric vibration reed1having the advantageous effects that the stable vibration characteristics are provided, and being resist to damage of the vibrating arm portions10and11due to the external impact is obtained were actually confirmed.