JP4265499B2 - Piezoelectric vibrating piece and piezoelectric device - Google Patents

Description

  The present invention relates to an improvement of a piezoelectric vibrating piece and a piezoelectric device in which the piezoelectric vibrating piece is accommodated in a package or case.

Piezoelectric vibrators and piezoelectrics in small information devices such as HDDs (hard disk drives), mobile computers, IC cards, mobile communication devices such as mobile phones, car phones, and paging systems, and piezoelectric gyro sensors Piezoelectric devices such as oscillators are widely used.
12 is a schematic plan view showing an example of a piezoelectric vibrating piece conventionally used in a piezoelectric device, and FIG. 13 is an end view taken along line AA in FIG.
In the figure, a piezoelectric vibrating reed 1 is formed by etching a piezoelectric material such as quartz to form the outer shape shown in the figure. A rectangular base 2 attached to a package (not shown) or the like, A pair of vibrating arms 3 and 4 extended rightward is provided, and long grooves 3a and 4a are formed on the main surfaces (front and back surfaces) of these vibrating arms, and necessary driving electrodes are formed. (See Patent Document 1).
In such a piezoelectric vibrating piece 1, when a driving voltage is applied via a driving electrode, the piezoelectric vibrating piece 1 is flexibly oscillated so that the distal ends of the vibrating arms 3 and 4 approach and separate from each other. The signal of the frequency of is extracted.

By the way, such a piezoelectric vibrating piece 1 is required to be formed in a small size in accordance with the downsizing of the above-described various products to which the piezoelectric device using the piezoelectric vibrating piece 1 is attached. It must be formed as small as possible. In particular, it is required to reduce the overall length AL1. Since downsizing of products is constantly progressing, the piezoelectric vibrating reed 1 has a structure that can be made smaller.
Here, the frequency f of the piezoelectric vibrating reed 1 which is a tuning fork type piezoelectric vibrating reed as shown is proportional to w / l ² where l is the length of the vibrating arms 3 and 4 and w is the arm width.

JP 2002-261575 A

By the way, such a piezoelectric vibrating piece 1 has a plurality of vibration modes. When the vibration mode by the fundamental wave is used, if the miniaturization is advanced as described above, the CI (crystal impedance) in the vibration by the fundamental wave will be described. ) There is a property of increasing the value.
In order to prevent this, when the length Pl of the long grooves 3a and 4a is increased to increase the electric field efficiency, the CI value of the second harmonic becomes small.
If the CI value of the second harmonic / CI value of the fundamental wave is 1 or more, that is, unless the CI value of the second harmonic is larger than the CI value of the fundamental wave, There is a problem in that oscillation tends to occur at a second-order harmonic rather than a wave, and the vibration characteristics of the piezoelectric vibrating piece 1 deteriorate.

  The present invention has been made to solve the above problems, and provides a piezoelectric vibrating piece that can be reduced in size without deteriorating vibration characteristics and a piezoelectric device using such a piezoelectric vibrating piece. Objective.

According to the first aspect of the present invention, the first aspect includes a base portion formed of a piezoelectric material, and a plurality of vibrating arms formed integrally with the base portion and extending in parallel with each other. The piezoelectric is gradually reduced in width as it goes to the tip side, and has a change point of the arm width where the continuous reduction width ends before the tip part, and the tip side is further widened from this change point of the arm width This is achieved by the vibrating piece.
According to the configuration of the first aspect of the present invention, the vibration arm is provided at a position where the width is the narrowest as a change point of the arm width at a position slightly closer to the base than the distal end of the vibration arm. From the arm width change point, the arm width is made wider.
Thereby, the frequency of the secondary harmonic of the piezoelectric vibrating piece is lowered, and the CI value of the secondary harmonic is increased. For this reason, the piezoelectric vibrating piece is less likely to vibrate at the second harmonic, and the vibration characteristics can be maintained well.

According to a second aspect of the invention, according to the configuration of the first aspect of the invention, each of the vibrating arms has a bottomed long groove extending in the length direction, and an electrode is formed in the long groove. Features.
According to the configuration of the second invention, the electric field efficiency of the vibrating arm portion of the piezoelectric vibrating piece can be improved, and the CI value of the fundamental wave can be lowered. In this case, simply by providing the long groove, the CI value of the second-order harmonic is also reduced at the same time, but the accompanying reduction in the CI value of the second-order harmonic is suppressed by the configuration of the first invention. Therefore, it is easy to vibrate in the fundamental wave, and it can be made difficult to vibrate in the second harmonic.

According to a third invention, in the configuration of the first or second invention, the length of the vibrating arm with respect to the base is defined as L, and the length from the base to the change point of the arm width is defined as CL. In some cases, CL / L is approximately greater than 0.75 and less than 0.93.
According to the configuration of the third invention, when CL / L is smaller than about 0.75 or larger than 0.93, the value of the second harmonic / fundamental wave becomes large, and the harmonic Since the CI value of the wave cannot be sufficiently high, the adverse effects due to the vibration mode of the second harmonic cannot be effectively suppressed.

In a fourth aspect of the invention, in the configuration of the third aspect, when the length of the vibrating arm with respect to the base is L and the length from the base to the change point of the arm width is CL, CL / L is approximately greater than 0.78 and less than 0.91.
According to the configuration of the fourth invention, when the CL / L is substantially larger than 0.78 and smaller than 0.91, the CI value of the second harmonic / CI value of the fundamental wave is It is possible to almost certainly set “1” or less, and it is possible to almost certainly suppress the adverse effect caused by the vibration mode of the second harmonic.

According to a fifth invention, in any one of the first to fourth inventions, the length of the vibrating arm with respect to the base is L, and the length from the base to the change point of the arm width is PL is smaller than CL, where CL is PL and the length based on the base of the long groove is PL.
According to the fifth aspect of the invention, since the PL is smaller than the CL, the weight from the change point of the arm width of the vibrating arm becomes heavier, and it is difficult to oscillate at the second harmonic. be able to.

  According to a sixth aspect of the present invention, there is provided a piezoelectric device in which a piezoelectric vibrating piece is accommodated in a package or case, wherein the piezoelectric vibrating piece is formed of a piezoelectric material and the base portion. And a plurality of resonating arms extending in parallel with each other, and the resonating arms are gradually reduced in width toward the front end side, and a continuous reduced width is provided in front of the front end portion. This is achieved by a piezoelectric device that has an arm width change point that ends and the tip side is further widened than the arm width change point.

According to a seventh invention, in the configurations of the second to fifth inventions, at least one long groove on the front and back surfaces of each vibrating arm is extended to the distal end side, and the other surface having a non-extended long groove is formed on the long groove. Further, a metal coating part for frequency adjustment is provided on the tip side.
According to the configuration of the seventh invention, in addition to the operational effects based on the configurations of the second to fifth inventions, the tuning fork type vibrating piece having the vibrating arms extending in parallel with each other from the base portion is provided on the vibrating arm. Since the long groove is extended to the front end side on at least one of the front surface and the back surface, the electric field efficiency is improved, so that the CI value is lowered accordingly.
In addition, since there is a relatively large room on the front side of the long groove of the vibrating arm on the surface having the long groove that is not extended on the front surface or the back surface, an electrode for frequency adjustment can be easily provided here.

An eighth invention is characterized in that, in the configuration of the seventh invention, the extended long groove is formed so as to reach the tip of the vibrating arm.
According to the configuration of the eighth invention, in the case of extending the long groove, the electric field efficiency is most improved and the CI value is reduced by extending until reaching the tip of the vibrating arm provided with the extended long groove. Can be measured.

1 to 4 show a first embodiment of a piezoelectric device according to the present invention. FIG. 1 is a schematic plan view thereof, FIG. 2 is a schematic sectional view taken along line BB of FIG. 1, and FIG. 4 is a schematic plan view of a piezoelectric vibrating piece used in the piezoelectric device of FIG. 4, and FIG. 4 is a cross-sectional end view taken along the line CC of FIG.
In these drawings, the piezoelectric device 30 shows an example in which a piezoelectric vibrator is configured, and the piezoelectric device 30 houses a piezoelectric vibrating piece 32 in a package 37 as shown in FIGS. 1 and 2. . As shown in FIG. 2, the package 37 is formed by laminating a first substrate 55 and a second substrate 56. For example, an aluminum oxide ceramic green sheet is formed as an insulating material. After forming the shape, it is formed by sintering.

  As shown in FIG. 2, the package 37 forms a space of the internal space S by removing the material inside the second substrate 56. This internal space S is a housing space for housing the piezoelectric vibrating piece 32. Then, on the electrode portions 31 and 31 formed on the first substrate 55, the positions of the extraction electrodes 33 a and 34 a provided at the base portion of the piezoelectric vibrating piece 32 are placed using the conductive adhesives 43 and 43. Are joined. The electrode portions 31 and 31 are connected to mounting terminals 41 and 42 on the back surface of the package through conductive through holes. The package 37 is hermetically sealed by housing the piezoelectric vibrating piece 32 and then bonding a transparent glass lid 40 using a sealing material 38. Thus, after the lid 40 is sealed, the frequency can be adjusted by trimming the electrode (not shown) of the piezoelectric vibrating piece 32 by irradiating the laser beam LB from the outside.

The piezoelectric vibrating piece 32 is formed of, for example, quartz, and a piezoelectric material such as lithium tantalate or lithium niobate can be used in addition to quartz. As shown in FIG. 3, the piezoelectric vibrating piece 32 includes a base 51 fixed to the package 37 side, and a pair of vibrations extending in parallel with the base 51 as a base end and splitting into two forks upward in the figure. Arms 35 and 36 are provided.
The main surfaces of the vibrating arms 35 and 36 are preferably formed with long grooves 33 and 34 extending in the length direction, respectively, and as shown in FIG. 4, excitation electrodes as drive electrodes are provided in the long grooves. (References omitted).

The excitation electrode is formed in the long groove and on the side surface of each vibrating arm, and for each vibrating arm, the electrode in the long groove and the electrode provided on the side surface are paired. Each electrode is described in FIG. The drawn electrodes 33a and 34a are respectively routed around. Thereby, when the piezoelectric device 30 is mounted on a mounting substrate or the like, an external driving voltage is applied from the mounting terminals 41 and 42 to the lead electrodes 33a and 34a of the piezoelectric vibrating piece 32 via the electrode portions 31 and 31, respectively. And is transmitted to each of the excitation electrodes described above.
Thereby, by applying a driving voltage to the excitation electrodes in the long grooves 33 and 34, the electric field efficiency inside the region where the long grooves of the respective vibrating arms are formed can be increased during driving. As the long grooves 33 and 34 are longer, the electric field efficiency of the material forming the vibrating arms 35 and 36 is improved, and the length PL from the base 51 of the long grooves 33 and 34 with respect to the entire length L of the vibrating arms is at least PL / It is known that the CI value of the piezoelectric vibrating piece 32 decreases as the length increases up to about L = 0.7.

  Further, in the piezoelectric vibrating piece 32, the vibrating arms 35 and 36 are formed in the shape shown in FIG. Since each resonating arm has the same shape, the resonating arm 35 will be described. At the base end T extending from the base 51, the resonating arm width W1 is the largest, and this arm width is reduced to the position of U on the front end side. Further, as it goes from the position U to the distal end side of the vibrating arm 35, the width gradually decreases continuously to the position P, that is, with respect to the vibrating arm over the distance CL. A portion P is a change point of the arm width, and the arm width is further enlarged on the distal end side than the change point P of the arm width.

The present embodiment is configured as described above. Next, the operation of this embodiment will be described with reference to FIGS. 5 and 6.
The piezoelectric vibrating piece 32 has a plurality of vibration modes, and the fundamental wave that is normally used is, for example, 32.768 kHz. On the other hand, the second harmonic of the piezoelectric vibrating piece 32 is in the vicinity of 250 kHz.
5A shows the piezoelectric vibrator 32 of the present embodiment, B shows the conventional piezoelectric vibrating piece 1 described in FIG. 12, the left end of each straight line of A and B indicates the frequency of the fundamental wave, and the right end. Indicates the frequency of the second harmonic. In the piezoelectric vibrator 32 of the present embodiment, by adopting the shape described in FIG. 3, the frequency of the second harmonic can be lowered as shown in FIG.

FIG. 6 shows the position of the arm width change point P and the secondary bending vibration eigenvalue (secondary frequency) / fundamental bending vibration eigenvalue (fundamental wave frequency) of the piezoelectric vibrating piece 32 of the present embodiment. It is a graph which shows a relationship. The horizontal axis in FIG. 6 indicates the distance from the base 51 to the arm width change point P when the total length L of the vibrating arm in FIG.
In the piezoelectric vibrating piece 32, when the drive level is changed by changing the drive voltage when attempting to excite with the fundamental wave, the second harmonic wave is changed to a state in which the fundamental wave vibrates normally. May cause abnormal oscillation called parametric excitation, resulting in an unstable excitation state.

In such a state, when the CI value of the second harmonic / the CI value of the fundamental wave is 1 or more, that is, when the CI value of the second harmonic is larger than the CI value of the fundamental wave, It becomes easier to oscillate at the second harmonic than the wave, and this adversely affects the drive level.
In FIG. 6, when the value on the vertical axis, that is, the secondary bending vibration eigenvalue (secondary frequency) / fundamental bending vibration eigenvalue (fundamental wave frequency) increases, the CI value of the second harmonic decreases. In order to avoid the deterioration of the drive level as described above, the value of the vertical axis in FIG. 6 needs to be lowered in order to sufficiently increase the CI value of the second harmonic.

When the position of the arm width change point P of the piezoelectric vibrating piece 32 is in the range of 0.75 to G (0.93) in FIG. 6, the CI value of the second harmonic of the piezoelectric vibrating piece 32 / CI of the fundamental wave The value can be effectively lowered, and therefore, the influence of the second harmonic can be considerably suppressed when the piezoelectric vibrating piece 32 is driven.
Further, when the position of the arm width change point P of the piezoelectric vibrating piece 32 is in the range of E (0.78) to F (0.91) in FIG. 6, the CI value of the second harmonic / CI of the fundamental wave The value can be made almost surely “1” or less, and the adverse effect of the vibration mode of the second harmonic can be almost certainly suppressed.
Furthermore, in FIG. 3, it is preferable that the length PL of the long groove be smaller than the length CL from the base 51 to the arm width change point P. As a result, the weight of the vibrating arm from the arm width change point P becomes heavier, and it is possible to make oscillation less likely at the second harmonic.

7 and 8 show a second embodiment of the piezoelectric vibrating piece.
In these drawings, the portions denoted by the same reference numerals as those of the piezoelectric vibrating reed described in FIGS. 1 to 4 have a common configuration, and therefore, the overlapping description is omitted as much as possible, and the following description will focus on the differences.

  As shown in FIG. 7, the piezoelectric vibrating piece 32-1 includes a base portion 51 fixed to the package 37 side, and a pair extending in parallel with the base portion 51 as a base end, divided upward and downward in the figure. The vibrating arms 35 and 36 are provided. These resonating arms 35 and 36 are gradually reduced in width from the base end portion to the position P, where P is an arm width change point, and from the arm width change point P Further, the structure in which the arm width is enlarged on the tip side is the same as the piezoelectric vibrating piece 32 described above.

  7A shows the surface side of the piezoelectric vibrating piece 32-1, that is, the surface facing the lid body 40 in FIG. 2, and FIG. 7B shows the back side of the piezoelectric vibrating piece 32-1. That is, the surface facing the mounting surface (bottom surface inside the package) of the piezoelectric vibrating piece 32 in FIG. 2 is shown.

Long grooves 33, 33-1, 34, and 34-1 extending in the length direction are formed on the main surfaces of the vibrating arms 35 and 36, respectively, and driving electrodes are provided in the long grooves as shown in FIG. Some excitation electrodes 61 and 62 are provided.
Specifically, as shown in FIG. 7A, long grooves 33 and 34 having the same length as the conventional one are formed on the surface side of the vibrating arms 35 and 36, respectively. Further, as shown in FIG. 7B, long grooves 33-1 and 34-1 are formed on the back side of the vibrating arms 35 and 36, which are extended to the tip side by a length of l1 as compared with the conventional case. Yes. These long grooves can be formed by half-etching simultaneously with an etching operation for forming the outer shape of the piezoelectric vibrating piece 32 or in another process.

The excitation electrodes 61 and 62 are formed in the long groove and on the side surfaces of the vibrating arms 35 and 36, and the electrodes in the long groove and the electrodes provided on the side surfaces are paired for each vibrating arm. Excitation electrodes 61 and 62 are respectively routed to extraction electrodes 33a and 34a shown in FIG. Thereby, when the piezoelectric device 30 is mounted on a mounting substrate or the like, an external driving voltage is applied from the mounting terminals 41 and 42 to the lead electrodes 33a and 34a of the piezoelectric vibrating piece 32 via the electrode portions 31 and 31, respectively. And is transmitted to each of the excitation electrodes described above.
Thereby, by applying a driving voltage to the excitation electrodes in the long grooves 33 and 34, the electric field efficiency inside the region where the long grooves of the respective vibrating arms are formed can be increased during driving.

Here, as the long grooves are longer, the electric field efficiency of the material forming the vibrating arms 35 and 36 is improved, and the CI value can be reduced. In order to obtain such an effect as much as possible, it is preferable to make the long grooves on the front and back sides of the vibrating arms 35 and 36 longer. In this embodiment, as shown in FIG. The long grooves 33 and 34 on the side have the same length as the conventional ones, and on the tip side from this, the excitation electrodes 61 and 62 use the region where the electrodes on the left and right side edges of the vibrating arm are integrally connected to each other. The metal cover parts 63 and 63 for adjustment are formed.
The metal covering portions 63 and 63 are portions used for frequency adjustment by a mass reduction method by being trimmed through the lid 40 by the laser beam LB or the like described in FIG. Therefore, the metal covering portions 63 and 63 may be formed integrally with the excitation electrodes 61 and 62 or may be formed by attaching another metal. The excitation electrodes 61 and 62 are formed by depositing chromium (Cr) as an underlayer on the quartz crystal, for example, about 900 angstroms, and depositing gold (Au) on the layer 500 to 600 angstroms thereon, by sputtering or the like. In contrast, the metal cover portions 63 and 63 can be formed by forming a film with a thickness of about 10,000 angstroms using the same metal, for example.

Thus, in the present embodiment, the electric field efficiency is improved by the length of the long grooves 33-1 and 34-1 on the back surface side of the vibrating arms 35 and 36 to the tip side, so that the CI value is lowered accordingly. Can do. Moreover, as shown in FIG. 7A, the metal covering portions 63 and 63 are formed on the surface side of the vibrating arms 35 and 36, so that the frequency adjustment is performed after the lid 40 is joined as in the conventional case. can do.
That is, according to the piezoelectric vibrating piece 32-1 of the second embodiment, the weight from the arm width change point P to the vibrating arm is increased based on the configuration common to the piezoelectric vibrating piece 32 of the first embodiment. It becomes heavier and more difficult to oscillate at the second harmonic. In addition, the CI value in the fundamental wave can be made extremely low.

FIG. 9 is a graph showing the length of the long groove and the CI value ratio in the present embodiment, and the horizontal axis represents the length of the long groove formed in the tuning fork type vibrating piece when the total length of the vibrating arm is 1.4 mm. Shows the length. The CI value is reduced as the long groove is longer.
Thus, according to the present embodiment, it is possible to provide a piezoelectric vibrating piece that can be reduced in size while suppressing an increase in CI value, and a piezoelectric device using such a piezoelectric vibrating piece.

FIG. 10 is a view showing a third embodiment of the piezoelectric vibrating piece, showing only the back side thereof, and the excitation electrodes are substantially the same as those in FIG.
FIG. 11 is a schematic perspective view showing the tip of one vibrating arm 35.
In these drawings, since the piezoelectric vibrating piece 32-2 of the third embodiment is the same as that of the second embodiment except for the configuration shown in the drawing, only the differences will be described.

As shown in FIG. 10, in this piezoelectric vibrating piece 32-2, the long grooves 33-2 and 34-2 on the back surfaces of the vibrating arms 35 and 36 are further extended and formed over the entire length of each vibrating arm. Yes.
In this case, as shown in FIG. 11, the electrodes connecting the electrodes on the side surfaces of the respective vibrating arms are connected so as to wrap around the tip end surface 35a of the vibrating arms, for example.
Thus, in the third embodiment, the electric field efficiency is further improved and the CI value can be further reduced by the length of the long groove. Other functions and effects are the same as those of the second embodiment.

The present invention is not limited to the above-described embodiment. Each configuration of each embodiment can be appropriately combined or omitted, and can be combined with other configurations not shown.
The present invention is not limited to the case where the piezoelectric vibrating piece is accommodated in the box-shaped package, the case where the piezoelectric vibrating piece is accommodated in the cylindrical container, the piezoelectric vibrating piece functioning as a gyro sensor, Can be applied to any piezoelectric device using a piezoelectric vibrating piece regardless of the name of a piezoelectric vibrator, a piezoelectric oscillator, or the like.

The schematic plan view which shows embodiment of the piezoelectric device of this invention. BB schematic sectional drawing of FIG. FIG. 2 is a schematic plan view of a piezoelectric vibrating piece used in the piezoelectric device of FIG. 1. The CC sectional view taken on the line of FIG. Explanatory drawing about the piezoelectric material used for the piezoelectric device of FIG. The graph which shows the relationship between the position which provides the change point of an arm width, and the secondary bending vibration eigenvalue (secondary frequency) / fundamental bending vibration eigenvalue (fundamental frequency) about the piezoelectric vibrating piece of FIG. FIG. 6 is a schematic front view and back view of a piezoelectric vibrating piece according to a second embodiment used in the piezoelectric device of FIG. 1. The DD line cutting | disconnection end elevation of FIG. FIG. 8 is a graph showing the CI value ratio corresponding to the length of the long groove when the total length of the vibrating arm is 1.4 mm for the piezoelectric vibrating piece used in the piezoelectric device of FIG. 7. The schematic back view of 3rd Embodiment of a piezoelectric vibrating piece. FIG. 11 is a schematic perspective view illustrating a distal end portion of a vibrating arm of the piezoelectric vibrating piece in FIG. 10. FIG. 6 is a schematic plan view showing an example of a conventional piezoelectric vibrating piece. FIG. 13 is an end view taken along line AA in FIG. 12.

Explanation of symbols

  30 ... Piezoelectric device, 32, 32-1, 32-2 ... Piezoelectric vibrating piece, 33, 34 ... Long groove, 35, 36 ... Vibrating arm, P, P ... Changing arm width point.

Claims (2)

A base formed of piezoelectric material;
A plurality of vibrating arms formed integrally with the base and extending parallel to each other;
With
The vibrating arm is continuously reduced in width as it goes to the distal end side, and has a change point of the arm width where the continuous reduction width ends before the tip, and the tip further than the change point of the arm width The side is widened,
The vibrating arm has a bottomed long groove extending in the length direction, and an electrode is formed in the long groove,
One long groove on each of the front and back surfaces of each vibrating arm is extended, and the other surface having a non-extended long groove is provided with a metal coating portion for frequency adjustment on the tip side of the long groove. Piezoelectric vibrating piece. 2. The piezoelectric vibrating piece according to claim 1 , wherein the extended long groove is formed to reach a distal end portion of a vibrating arm.

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