JP4930381B2 - Piezoelectric vibration device - Google Patents

Description

  The present invention relates to a piezoelectric vibration device using a bulk wave, and more particularly to a piezoelectric vibration device using a contour vibration mode such as a spread vibration mode, a length vibration mode, or a width vibration mode in a bulk wave.

  Piezoelectric vibration devices using bulk waves have the advantages of higher Q and higher power durability than surface acoustic wave devices using surface acoustic waves. Conventionally, a piezoelectric resonator using a thickness longitudinal vibration mode as a bulk wave has been proposed. However, when the thickness longitudinal vibration mode is used, it is easy to provide a resonator having a relatively high resonance frequency, but it is difficult to provide a resonator having a low resonance frequency.

  The following Patent Document 1 discloses a piezoelectric resonator using a spread vibration mode as a resonator that can be used in a lower frequency range. FIG. 22 is a schematic perspective view for explaining the piezoelectric resonator described in Patent Document 1. FIG.

  In the piezoelectric vibrator 101, a frame body 102 made of a silicon-based material is used. In the opening of the frame body 102, the vibrating portion 104 is supported by the support beams 103 and 103. The vibration part 104 has a relatively thick diaphragm 105 made of a silicon material. On this diaphragm 105, a lower electrode 106, a piezoelectric thin film 107, and an upper electrode 108 are laminated to constitute a piezoelectric vibrating portion.

By applying an alternating electric field between the upper electrode 108 and the lower electrode 106, the piezoelectric vibration part is excited and vibrates together with the diaphragm 105. Here, it is described that a piezoelectric vibrator having a resonance frequency of 1 to 10 MHz can be provided by utilizing the response of the spread vibration mode.
JP-A-8-186467

  In general, in a piezoelectric vibrator using a spreading vibration mode, the resonance frequency is determined by the size of the planar shape of the piezoelectric vibration part and is considered not to depend on the thickness of the piezoelectric vibration part. However, for example, in the piezoelectric vibrator 101, the diaphragm 105 is laminated on the piezoelectric vibrating portion, and the vibrating portion has a certain thickness. Therefore, even when the above-described spread vibration mode is used, it has been found that the vibration mode depending on the thickness direction is coupled to the spread vibration mode, and the resonance frequency has thickness dependence.

  On the other hand, the thickness of the diaphragm 105 may vary due to processing variations. In such a case, since the resonance frequency has thickness dependency, the resonance frequency has to be varied. Therefore, the yield tends to decrease.

  An object of the present invention is a piezoelectric vibration device using a bulk wave that eliminates the above-mentioned drawbacks of the prior art, has a high Q, and is excellent in electric power durability. It is an object of the present invention to provide a piezoelectric vibration device that uses contour vibration that does not easily depend on the thickness of the vibration portion and that is less susceptible to variations in characteristics due to variations in thickness of the vibration portion.

According to the present invention, a film-like piezoelectric body having first and second main surfaces facing each other, a first electrode formed on the first main surface of the piezoelectric body, and a first electrode of the piezoelectric body. The first electrode and the second electrode arranged so as to overlap with each other via the piezoelectric body, and the first and second electrodes overlap with each other via the piezoelectric body. And the piezoelectric vibration part further comprises a support member that supports the piezoelectric vibration part, and the piezoelectric vibration part overlaps the first and second electrodes via the piezoelectric body. The portion is supported by the support member so as to be in a floated state, and uses the contour vibration mode of the piezoelectric vibration portion , and the piezoelectric vibration portion is the first and second electrodes. An additional film laminated on the surface opposite to the surface in contact with the piezoelectric body. Provided on at least one of the additional film, characterized in that a second region of different thicknesses and said first region including a node of vibration of the piezoelectric vibrating unit, a first region, the piezoelectric A vibration device is provided.

  In a specific aspect of the piezoelectric vibration device according to the present invention, the film-like piezoelectric body has a piezoelectric body extension that extends to the outside of the piezoelectric vibration section where the first and second electrodes overlap, The body extension is fixed to the support member. In this case, since the thin piezoelectric vibrating portion is formed by laminating the first and second electrodes on the first and second main surfaces of the film-like piezoelectric body, the piezoelectric vibrating portion can be reduced in size. The height can be reduced.

  In the case of a structure in which the support member is a substrate, and the piezoelectric extension portion is fixed to the upper surface of the substrate in a state where the piezoelectric vibration portion is floated on the substrate with a gap, complicated processing is required. The flat board | substrate which does not carry out can be used, and cost can be reduced. In addition, since the piezoelectric vibration part having a relatively thin thickness is floated across the gap, it is possible to further reduce the height.

In still another specific aspect of the present invention, in the outer peripheral edge portion of the piezoelectric body excluding the portion where the piezoelectric body extension portion is provided, the piezoelectric body has a shape that does not reach the outside of the piezoelectric vibrating portion. ing. In this case, since the piezoelectric body does not reach the outside of the piezoelectric vibrating portion except the piezoelectric extension portion, the size of the planar shape of the piezoelectric body can be reduced, and the miniaturization can be promoted.
In still another specific aspect of the piezoelectric vibration device according to the present invention, the thickness of the piezoelectric vibration part is 1/40 or less of the wavelength of the contour vibration mode. In this case, it is possible to provide a piezoelectric vibration device with extremely small variation in frequency characteristics, and it is possible to increase the yield of the piezoelectric vibration device.

  In the piezoelectric vibration device according to the present invention, the piezoelectric vibration part may be configured to have various planar shapes.

  In a specific aspect of the present invention, the piezoelectric vibration part has a rectangular planar shape having a short side and a long side, the contour vibration mode is a spread vibration mode, and the thickness of the piezoelectric vibration part is In addition, it is set to 1/20 or less of the short side dimension of the piezoelectric vibration part. In this case, a piezoelectric vibration device using the spread vibration mode as the contour vibration mode can be provided, and the thickness of the piezoelectric vibration part is set to 1/20 or less of the short side dimension of the piezoelectric vibration part. Can be made extremely small.

  Further, in another specific aspect of the present invention, the piezoelectric vibration part has a rectangular planar shape having a short side and a long side, the contour vibration mode is a length vibration mode, and the piezoelectric vibration part In this case, the length vibration mode is used as the contour vibration mode, and the frequency characteristic variation is very small. A vibration device can be provided.

In this onset bright, the piezoelectric vibrating unit further comprises a first additional layer that is laminated on the opposite side to the side on which the piezoelectric in contact in at least one of the second electrode. As with pressurized film, a protective film or a temperature compensating dielectric film, or by laminating a metal film, to enhance the environmental resistance, or reduced frequency dependence due to the temperature, or it can enhance the mechanical strength .

  In the piezoelectric vibration device according to the present invention, preferably, in the additional film, a first region including a portion where a piezoelectric vibration node of the piezoelectric vibration unit is located, and a second region having a thickness different from the first region. And an area. In this case, the resonance frequency of the piezoelectric vibration device can be adjusted by making the thickness of the additional film in the first region including the vibration node different from the thickness of the additional film in the second region. For example, the frequency is adjusted in the direction of lowering the resonance frequency by making the thickness of the additional film in the first region smaller than that of the additional film in the second region. can do. In this case, the thickness of the additional film may be zero in the first region.

  Conversely, by relatively increasing the thickness of the additional film in the first region, the frequency can be adjusted in the direction of increasing the resonance frequency. In this case, the thickness of the additional film in the second region is zero. May be.

The piezoelectric vibration device according to the present invention can be used for various resonators and filters. However, in a specific aspect of the present invention, a piezoelectric resonator having a frequency in the range of 1 to 100 MHz is provided. That is, although the contour vibration mode is used, a piezoelectric vibration device that can be used in a relatively low frequency range can be provided.
(The invention's effect)

  In the piezoelectric vibration device according to the present invention, the first electrode is formed on the first main surface and the second electrode is formed on the second main surface of the film-like piezoelectric body, and the first and second electrodes are formed. Are in a state in which the piezoelectric vibrating portion overlapping with the piezoelectric body is floated. Therefore, it is a relatively thick member such as the diaphragm described in Patent Document 1 and does not require a portion that vibrates in response to the vibration of the piezoelectric vibrating portion. Therefore, variations in resonance frequency due to variations in processing of other members hardly occur.

  In addition, since the contour vibration mode is used, the frequency characteristic is hardly dependent on the thickness of the piezoelectric vibration part. In addition, since it is a relatively thick member such as the diaphragm described in Patent Document 1 and does not require a portion that vibrates in response to the vibration of the piezoelectric vibration portion, the frequency characteristic also exhibits piezoelectric vibration. It is hard to depend on the thickness of the part. Therefore, it is possible to further reduce variation in frequency characteristics such as the resonance frequency.

  In addition, since it is not necessary to provide a portion that is laminated on a piezoelectric vibrating portion such as the diaphragm described in Patent Document 1 and vibrates in response to piezoelectric vibration, the thickness of the vibrating portion can be reduced and the size can be reduced. In particular, the height can be lowered.

  Further, since the contour vibration mode is used instead of the thickness longitudinal vibration mode, it is possible to provide a resonator and a filter that can be used in a low frequency range as compared with the case where the thickness longitudinal vibration mode is used. Furthermore, since the contour vibration mode in the bulk wave is used, a piezoelectric vibration device having a high Q and excellent power durability can be provided.

  Therefore, according to the present invention, a piezoelectric vibration device using a bulk wave having a high Q and excellent power durability, which can be used in a low frequency range, and also causes variations in frequency characteristics such as resonance characteristics. It is difficult to provide a piezoelectric vibration device using a piezoelectric vibration mode.

  In particular, when the thickness of the piezoelectric vibration part is set to 1/40 or less of the wavelength of the contour vibration mode, the frequency variation can be further reduced as will be apparent from an experimental example described later.

1A and 1B are a schematic plan view of a piezoelectric vibration device according to a first embodiment of the present invention and a cross-sectional view taken along line AA in FIG. 2 (a) and 2 (b) are cross-sectional views taken along lines BB and CC in FIG. 1 (a). FIG. 3 is a schematic plan view for explaining a change in the vibration state in the spread vibration mode. 4 (a) and 4 (b) show the results of analyzing the displacement state of each part by the finite element method when the piezoelectric vibrating part of the first embodiment is thin and relatively thick. It is each typical sectional drawing. FIG. 5 is a schematic cross-section along the thickness direction showing the result of analyzing the displacement state of each part in the piezoelectric vibration part when the thickness of the piezoelectric vibration part in the piezoelectric vibration device of the first embodiment is increased by the finite element method. FIG. FIG. 6 is a diagram illustrating a relationship between the normalized thickness of the vibrator and the resonance frequency fluctuation amount in the piezoelectric vibration device according to the first embodiment. FIG. 7 is a schematic plan view for explaining the piezoelectric vibration device according to the second embodiment. FIG. 8 is a schematic plan view for explaining the change in the vibration mode in the length vibration mode used in the second embodiment. FIG. 9 is a schematic plan view for explaining the piezoelectric vibration device of the third embodiment. FIG. 10 is a schematic plan view for explaining the change in the vibration mode in the width direction vibration mode used in the second embodiment. FIGS. 11A and 11B are a schematic plan view of a piezoelectric vibration device according to a fourth embodiment of the present invention and a cross-sectional view taken along the line EE in FIG. 12A and 12B are cross-sectional views taken along lines FF and GG in FIG. FIGS. 13A and 13B are a schematic plan view of a piezoelectric vibration device according to a fifth embodiment of the present invention and a cross-sectional view taken along the line II in FIG. 14A and 14B are cross-sectional views taken along lines JJ and KK in FIG. FIG. 15 is a cross-sectional view for explaining a modification of the piezoelectric vibration device according to the present invention. FIG. 16 is a schematic perspective view for explaining the relationship between a recess and a node position when a recess is provided in a region including a node on one side in a vibrator using the width vibration mode or the spread vibration mode. FIG. 17 is a diagram illustrating the resonance characteristics of the piezoelectric vibration device in which the additional films on both sides are formed to have a uniform film thickness. FIG. 18 is a diagram illustrating resonance characteristics of the piezoelectric vibration device according to the modified example illustrated in FIG. 15. FIG. 19 is a cross-sectional view for explaining another modification of the piezoelectric vibration device of the present invention. 20 is a diagram illustrating resonance characteristics of the piezoelectric vibration device illustrated in FIG. FIG. 21 is a schematic cross-sectional view for explaining the width-direction dimension of a portion where a part of the additional film is removed in the modification shown in FIG. FIG. 22 is a diagram showing a change in the resonance frequency when the removal width for removing a part of the additional film is changed in the modification shown in FIG. FIG. 23 is a schematic perspective view for explaining an example of a conventional piezoelectric vibration device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric vibration apparatus 2 ... Board | substrate 3 ... Piezoelectric vibration part 4 ... Piezoelectric thin film 4a, 4b ... Piezoelectric extension part 5 ... 1st electrode 6 ... 2nd electrode 7 ... Additional film 8 ... Additional film 9, 10 ... Terminal Electrode 11 ... Piezoelectric vibration device 21 ... Piezoelectric vibration device 23 ... Piezoelectric vibration portion 23a ... Short side 23b ... Long side 31 ... Piezoelectric vibration device 33 ... Piezoelectric vibration portion 33a ... Short side 33b ... Long side 41 ... Piezoelectric vibration device 42 ... Substrate DESCRIPTION OF SYMBOLS 43 ... Piezoelectric vibration part 51 ... Piezoelectric vibration apparatus 52 ... Gap formation material layer 62, 63 ... Additional film 64 ... Additional film 65 ... Piezoelectric vibration apparatus 71 ... Piezoelectric vibrator 71a ... Recessed part D ... Gap H ... Gap L ... Gap N ... Node Q ... removal width

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  1A and 1B are a plan view of a piezoelectric vibration device according to a first embodiment of the present invention and a cross-sectional view taken along line AA in FIG. 2 (a) and 2 (b) are cross-sectional views taken along lines BB and CC in FIG. 1 (a).

  The piezoelectric vibration device 1 is a piezoelectric resonator using a spread vibration mode among contour vibrations as a bulk wave.

  In the present embodiment, the substrate 2 made of a semiconductor or an insulator is used as the support member. The semiconductor and the insulator constituting the substrate 2 are not particularly limited, and for example, an insulator such as a Si-based semiconductor or glass is used.

  On the substrate 2, a piezoelectric vibrating portion 3 having a rectangular planar shape is configured. Here, the piezoelectric vibrating portion 3 is a film-like piezoelectric body, that is, the piezoelectric thin film 4, the electrode 5 formed on the lower surface as the first main surface of the piezoelectric thin film 4, and the second main surface of the piezoelectric thin film 4. And a second electrode 6 formed on the upper surface of the substrate. The piezoelectric thin film 4 has a polarization axis direction as a thickness direction. The first electrode 5 and the second electrode 6 are overlapped in the thickness direction via the piezoelectric thin film 4, and the overlapped portion is a piezoelectric vibrating portion 3 having a rectangular planar shape shown in FIG. It is.

The piezoelectric thin film 4 is made of an appropriate piezoelectric material. Examples of such piezoelectric materials include zinc oxide (ZnO), aluminum nitride (AlN), lead zirconate titanate ceramics (PZT piezoelectric ceramics), lithium niobate (LiNbO ₃ ), and lithium tantalate (LiTaO _3). ) And crystal. That is, the piezoelectric thin film may be formed of either a piezoelectric single crystal or a piezoelectric ceramic.

  The first electrode 5 and the second electrode 6 are provided to apply an alternating voltage to the piezoelectric thin film 4 and excite the piezoelectric thin film 4. The material constituting the first and second electrodes 5 and 6 is not particularly limited, and an appropriate conductive material can be used. Examples of such a conductive material include Al, Cu, Au, Pt, Ni, or an alloy thereof, such as Elinvar and Invar.

  In the present embodiment, in the piezoelectric vibrating portion 3, the additional film 7 is laminated on the first main surface side of the piezoelectric thin film 4 so as to cover the first electrode 5. The additional film 8 is also laminated on the upper surface side as the second main surface of the piezoelectric thin film 4.

  The additional films 7 and 8 may function as a protective film for protecting the inside, may have a function as a reinforcing film, or may be a film for compensating temperature characteristics. Good. Further, an additional film 7 and / or an additional film 8 may be provided in order to adjust the resonance frequency by mass addition.

  The additional film may be formed on the first main surface side and / or the second main surface side of the piezoelectric body, or in the present invention, the piezoelectric vibrating portion may not have the additional film. .

Since the additional films 7 and 8 are used so as to perform at least one of these functions, the material constituting the additional films 7 and 8 may be a material corresponding to these functions. . For example, in order to perform temperature compensation or protect the piezoelectric vibrating portion, the additional films 7 and 8 may be formed of a dielectric thin film such as SiO ₂ or SiN. Further, the additional films 7 and 8 may be formed of a conductive material such as Al, Cu, Elinvar, or Invar. However, when the additional films 7 and 8 are made of a conductive material, it is desirable to form the additional films 7 and 8 so as not to impair the functions of the electrodes 5 and 6.

  Further, the additional films 7 and 8 may be a piezoelectric material such as ZnO or AlN, or may be a semiconductor material such as Si.

  In the present embodiment, in the piezoelectric vibration part 3, the piezoelectric thin film 4, the first and second electrodes 5, 6 and the additional films 7 and 8 are formed and laminated by a thin film forming method. Although it does not specifically limit as such a thin film formation method, PVD method, CVD method, etc. can be used. In the piezoelectric vibration part 3 formed by laminating each member by the thin film forming method, the thickness can be reduced and the height can be reduced.

  In the piezoelectric vibration device 1 of the present embodiment, the piezoelectric vibration unit is arranged in a state of being floated from the substrate 2 via the gap D. Moreover, since the piezoelectric vibration part 3 is floating from the board | substrate 2, it is not restrained and can vibrate smoothly.

  In addition, the formation method of the said gap D is not specifically limited. For example, a solvent-removable material layer that is removed by a solvent that does not dissolve the piezoelectric thin film 4, the first and second electrodes 5, 6 and the additional films 7, 8 is formed on the substrate 2, and then the piezoelectric thin film 4. A laminate composed of the first and second electrodes 5 and 6 and the additional films 7 and 8 is formed by a thin film forming method. Then, the solvent-removable material layer may be removed with the solvent, whereby the gap D can be formed.

  The piezoelectric vibrating portion 3 is supported in the following manner on the substrate 2 as a support member. The piezoelectric thin film 4 extends beyond the piezoelectric vibrating portion 3 to the outside in the long side direction of the piezoelectric vibrating portion 3. The piezoelectric thin film portions extended to the outside of the piezoelectric vibrating portion 3 are referred to as piezoelectric body extending portions 4a and 4b. As is clear from FIG. 1A, the piezoelectric extension portions 4 a and 4 b extend from the piezoelectric vibrating portion 3 to the outside in the long side direction of the piezoelectric vibrating portion 3.

  The piezoelectric thin film 4 is fixed to the substrate 2 at the piezoelectric extension portions 4a and 4b. In the present embodiment, the additional film 7 provided below is fixed to the upper surface of the substrate 2, that is, the additional film 7 is formed so as to have a gap D. On the additional film 7, the first electrode 5, the piezoelectric thin film 4, and the second electrode 6 are sequentially formed, and the second additional film 8 is further formed.

  On the other hand, in the portion where the additional film 7 is fixed to the substrate 2, that is, outside the gap D, there are piezoelectric extension portions 4a and 4b. Therefore, the piezoelectric thin film 4 has the piezoelectric extension portions 4a and 4b. In the portion to be fixed, it is fixed to the substrate 2 through the additional film 7. In the present embodiment, since the additional film 7 is provided, the piezoelectric extension portions 4a and 4b are fixed to the substrate 2 via the additional film 7. However, in the case where the additional film 7 is not provided. The piezoelectric extension portions 4 a and 4 b may be directly fixed to the upper surface of the substrate 2. Further, in the structure in which the additional film 7 is provided, the piezoelectric extension portions 4a and 4b do not necessarily have to be provided. In that case, the piezoelectric extension portion 4a and 4b have sufficient strength to fix the piezoelectric vibrating portion to the substrate 2. It is necessary to form the additional film 7 so as to have it.

  The first electrode 5 is connected to a first terminal electrode 9 provided along the first edge of the substrate 2 via the lower surface of the piezoelectric extension 4a (FIG. 1 ( a)).

  On the other hand, the second electrode 6 is connected to the second terminal electrode 10 provided on the second edge of the substrate via the upper surface of the piezoelectric extension 4b.

  Accordingly, when an AC voltage is applied from the terminal electrodes 9 and 10, the piezoelectric vibrating portion 3 is excited by the piezoelectric effect. In the present embodiment, the piezoelectric vibrating portion 3 has a rectangular planar shape having a long side and a short side. The piezoelectric thin film 4 has a thickness direction in the polarization axis direction. Therefore, although the vibration mode is excited, in this embodiment, the spread vibration mode belonging to the contour vibration mode is strongly excited among the excited vibrations, and the resonance characteristic by the spread vibration mode is used.

  Therefore, since the spread vibration mode belonging to the contour vibration mode in the bulk wave is used, the Q is high and the power durability is excellent. In addition, in the present embodiment, the piezoelectric vibrating portion 3 is arranged so as to float from the substrate 2 with a gap D therebetween. Therefore, the piezoelectric vibration part 3 vibrates freely without being restrained by the substrate 2 due to the piezoelectric effect. Therefore, good resonance characteristics can be obtained. Moreover, the piezoelectric thin film 4 does not reach the outer peripheral edge of the piezoelectric vibrating portion 3 except for the portions where the piezoelectric extension portions 4a and 4b reaching the portion fixed to the substrate 2 as the support member are provided. . Accordingly, the piezoelectric vibrating portion 3 can be freely displaced and vibrated without being constrained by the substrate 2.

  FIG. 3 is a schematic plan view showing the vibration mode in the spread vibration mode. In the spread vibration mode, the piezoelectric vibration part 3A having a square planar shape is displaced as in the vibration state indicated by the broken line in the figure. Then, each part is displaced from the vibration state shown by the broken line in the figure as shown by the arrows in the figure, and the reverse vibration state is obtained. The displacement is repeated between the vibration mode indicated by the broken line and the reverse vibration mode. Therefore, the displacement in the expansion vibration mode is vibration in the plane, that is, in the in-plane direction of the piezoelectric vibration portion 3A having a rectangular planar shape, and is basically hardly affected by the vibration mode in the thickness direction.

  However, as described above, in fact, even in the piezoelectric vibration part using the contour vibration mode such as the spread vibration mode, the thickness is limited, so the influence of the vibration mode in the thickness direction cannot be avoided. In the piezoelectric vibration device described in Document 1, the resonance characteristics tend to vary due to the influence thereof.

  That is, in the piezoelectric vibration device described in Patent Document 1 described above, since the relatively thin diaphragm 105 made of a silicon material is laminated on the piezoelectric thin film, the resonance characteristics vary due to variations in the thickness of the diaphragm 105. There was a problem. On the other hand, in the piezoelectric vibration device of the present embodiment, it is not necessary to stack such a relatively thick plate-shaped diaphragm in the piezoelectric vibration unit 3. That is, the portion that vibrates as the piezoelectric vibration portion is only the laminated film portion in which the piezoelectric thin film 4, the electrodes 5 and 6, and the additional films 7 and 8 are laminated. It can be formed with high accuracy by the method. Therefore, since the thickness variation of the vibrating portion hardly occurs, the resonance characteristic does not easily vary. Therefore, characteristics can be stabilized and yield can be improved.

  In the piezoelectric vibration device 1 according to the present embodiment, preferably, the thickness of the piezoelectric vibration unit 3 is set to 1/40 or less of the resonance frequency of the resonance characteristic by the spread vibration mode, thereby causing resonance due to thickness variation of the piezoelectric thin film 4. The frequency variation can be made extremely small. This will be described with reference to FIGS.

  The results shown in FIGS. 4 to 6 are results obtained by simulation using the finite element method.

  In the above simulation, the assumed specifications of the piezoelectric vibration device are as follows.

  The additional film 7, the first electrode 5, the piezoelectric thin film 4, the second electrode 6, and the additional film 8 are formed on the Si-based substrate so as to have the following materials and thicknesses, and the piezoelectric vibrating portion has a short side. It is assumed that the piezoelectric vibration device 1 having a rectangular planar shape with a length of 190 μm × long side length of 300 μm and a wavelength of 190 μm × 2 = 380 μm is manufactured.

Additional film 7: SiO ₂ , thickness 1.3 μm / first electrode 5: Pt, thickness 0.1 μm / piezoelectric thin film 4: AlN film, thickness 1.6 μm / second electrode 6: Pt, thickness 0.1 μm / Additional film 8: SiO ₂ , thickness 1.3 μm. Thickness of the entire piezoelectric vibrating portion 3 including the additional films 7 and 8 = 4.4 μm.

  According to such a structure, the resonance frequency of the piezoelectric vibration device 1 is about 18 MHz. Similar to the piezoelectric vibration device 1 except that the ratio of the film thickness of the first and second electrodes 5 and 6 made of Al to the film thickness of the piezoelectric thin film 4 is fixed at 1:16, and The dimension in the short side direction of the rectangle constituting the piezoelectric vibrating portion was 113 μm, and the thickness of the piezoelectric thin film 4 and the thickness of the electrodes 6 and 7 were changed. For such a plurality of piezoelectric vibration devices, the relationship between the frequency fluctuation amount and the normalized vibrator thickness obtained by normalizing the thickness of the vibration part, that is, the thickness of the piezoelectric vibration part 3 including the additional films 7 and 8 with the wavelength, is finite. It was obtained by simulation by the element method. Results are shown.

  The horizontal axis of FIG. 6 indicates the ratio of the normalized vibrator thickness, that is, the thickness of the vibrating portion to the wavelength, and the vertical axis indicates the resonance frequency fluctuation amount (ppm). The resonance frequency fluctuation amount is a fluctuation amount from the design resonance frequency.

  4 (a) and 4 (b) show the results of obtaining the displacement state of the vibration part by the finite element method when the normalized vibrator thickness is 0.01 and 0.08, and FIG. It is a figure which shows typically the change of the vibration mode calculated | required with the finite element method in case the said normalization vibrator thickness is 0.40.

  As apparent from FIGS. 4A, 4B and 5, when the standardized thickness of the vibrator in the piezoelectric vibrating portion 3 is increased, a relatively large number of portions are displaced in the thickness direction. It can be seen that the influence of the vibration mode appears.

  On the other hand, as is clear from FIG. 6, according to the simulation, if the normalized vibrator thickness is 0.025 or less, that is, if the vibrator thickness is 1/40 of the wavelength or less. It can be seen that the fluctuation amount of the resonance frequency when the thickness varies by 1% is extremely small as 1 ppm or less. On the other hand, the wavelength is determined by the short side dimension of the rectangular vibrating portion. Therefore, if the thickness of the piezoelectric vibration part is set to 1/20 or less of the length of the short side of the rectangular planar piezoelectric vibration part 3, the amount of fluctuation of the resonance frequency can be remarkably reduced.

  FIG. 7 is a schematic plan view of a piezoelectric vibration device according to another embodiment of the present invention, and FIG. 8 is a plan view schematically showing the vibration state of the piezoelectric vibration portion.

  In the piezoelectric vibration device 21 shown in FIG. 7, the piezoelectric vibration unit 23 uses the length vibration mode in the contour vibration mode. Accordingly, the piezoelectric vibration portion 23 has a rectangular planar shape having a short side 23a and a long side 23b as schematically shown in FIG. 7, and in the long side direction as shown in FIG. It expands and contracts. That is, from the initial state of the piezoelectric vibrating portion 23A shown in FIG. 8, the state of extension in the long side direction as shown by the broken line and the vibration state of the state of contraction in the length direction from the original state are repeated. It is displaced to. As described above, even when the length vibration mode is used, the displacement is mostly in the in-plane directions of the first and second main surfaces of the piezoelectric vibration portion 23. Therefore, the displacement is the same as in the first embodiment. Similarly, good resonance characteristics that do not depend much on the thickness can be realized.

  FIG. 9 is a schematic plan view of a piezoelectric vibration device according to a third embodiment of the present invention, and FIG. 10 is a schematic plan view for explaining a change in the vibration state of the piezoelectric vibration unit. .

  In the piezoelectric vibration device 31 according to the third embodiment, the piezoelectric vibration unit 33 uses the width vibration mode in the contour vibration mode. The other points are the same as in the second embodiment. The piezoelectric vibration part 33 using the width vibration mode has a rectangular planar shape and has a short side 33a and a long side 33b. When excited, the long side 33b is displaced along the short side direction from the initial state indicated by the solid line, as shown in FIG. That is, as indicated by the broken line, the displacement is repeated between the state in which the width direction dimension, that is, the dimension along the short side direction is increased, and the contracted state in which the dimension in the short side direction is decreased. become. Since this width direction vibration mode is also in-plane vibration, good resonance characteristics that do not depend on the thickness of the vibration part can be obtained.

  As described above, in the present invention, the contour vibration mode is used in the bulk wave, and this contour vibration mode is not limited to the spread vibration mode shown in the first embodiment, but the length vibration mode and the width described above. A vibration mode may be used.

  FIGS. 11A and 11B are a schematic plan view of a piezoelectric vibration device according to a fourth embodiment of the present invention and a cross-sectional view taken along line EE in FIG. 11A. (A) And (b) is each sectional drawing which follows the FF line | wire and GG line | wire of Fig.11 (a).

  The piezoelectric vibration device 41 of this embodiment has a substrate 42 as a support member. A recess is formed on the upper surface of the substrate 42, and a gap H is provided by the recess. That is, in the first embodiment, the gap D is provided between the upper surface of the substrate 2 and the piezoelectric vibrating portion 3 that is floated from the upper surface of the substrate 2, but in this embodiment, the gap D is formed on the upper surface of the substrate 42. A gap H is formed by forming the recess. Therefore, the piezoelectric vibrating portion 43 provided on the gap H is in a floating state.

  Regarding other structures, the piezoelectric vibration device 41 of the present embodiment is configured in the same manner as the piezoelectric vibration device 1 of the first embodiment. Accordingly, the same portions are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, on the gap H, the piezoelectric thin film 4, the first and second electrodes 5, 6 and the additional films 7 and 8 are formed by a thin film forming method. However, in manufacturing, a concave portion is formed in advance on the upper surface of the substrate 42 made of Si or the like by processing such as etching. Then, the solvent-removable material layer used in the first embodiment is formed in the recess so as to fill the recess. Thereafter, a laminated portion including the piezoelectric thin film 4, the first and second electrodes 5 and 6, and the additional films 7 and 8 is formed by a thin film forming method. That is, the additional film 7, the first electrode 5, the piezoelectric thin film 4, the second electrode 6, and the additional film 8 are sequentially formed by a thin film forming method. Then, the gap H is formed by removing the solvent-removable material layer with a solvent.

  As described above, the gap for bringing the piezoelectric vibrating portion formed using the piezoelectric thin film 4 into a floating state may be provided by forming a concave portion on the upper surface of the substrate 42.

  FIG. 13A is a plan view for explaining a piezoelectric vibration device according to a fifth embodiment of the present invention, and FIG. 13B is a cross-sectional view taken along the line II of FIG. It is. FIGS. 14A and 14B are cross-sectional views taken along lines JJ and KK in FIG.

  The piezoelectric vibration device 51 according to the fifth embodiment is the same as the piezoelectric vibration device 1 according to the first embodiment except that the structure for providing a gap for making the piezoelectric vibration portion affected is different. is there. Accordingly, the same parts are denoted by the same reference numerals, and detailed description thereof is omitted.

  The piezoelectric vibration device 51 of the present embodiment has a substrate 2 as a support member. Then, as in the case of the first embodiment, the additional film 7, the first electrode 5, the piezoelectric thin film 4, the second electrode 6, and the second additional film 8 are sequentially formed on the substrate 2 in the same manner as in the first embodiment. The laminated portion formed by the above is configured, and the piezoelectric vibrating portion 3 is provided. However, in the present embodiment, the gap L for bringing the piezoelectric vibrating portion 3 into a floating state below the first additional film 7 is provided by providing an opening in the gap forming material layer 52 by the side etching method. Is formed.

  That is, an opening is provided in a part of the gap forming material layer 52, and the piezoelectric vibrating portion 3 is formed above the opening. Therefore, the opening forms the gap L.

  In order to form the gap L, in this embodiment, first, a gap forming material layer 52 is formed on the substrate 2. The gap forming material layer 52 is formed of, for example, a solvent-removable material that is removed by a solvent that does not dissolve the piezoelectric thin film 4, the first and second electrodes 5 and 6, and the additional films 7 and 8. For this formation method, an appropriate thin film formation method such as vapor deposition can be used.

  Thereafter, after forming the gap forming material layer 52 on the upper surface of the substrate 2, the additional film 7, the first electrode 5, the piezoelectric thin film 4, and the second electrode 6 described above are formed on the gap forming material layer 52. And the 2nd additional film | membrane 8 is formed in order by a thin film formation method. Next, in the gap forming material layer 52, isotropic side etching may be performed from the side to the portion where the opening as the gap L shown in FIG. The etching can be performed using a solvent that dissolves the solvent-removable material layer and does not dissolve the laminated portion including the piezoelectric thin film 4. Thus, the gap L may be formed by side etching from the side.

  As described above, in the piezoelectric vibration device of the present invention, as shown in the fourth and fifth embodiments, the gap for bringing the piezoelectric vibration part into a floating state can be formed by various methods. .

  In the piezoelectric vibration device according to the present invention, the thickness of the additional film is not necessarily uniform. Such a modification will be described with reference to FIGS.

  FIG. 15 corresponds to a modification of the piezoelectric vibration device according to the fourth embodiment, and is a cross-sectional view of the piezoelectric vibration device of this modification corresponding to the cross-sectional view shown in FIG.

  In the piezoelectric vibration device 61 of this modification example, as in the fourth embodiment, the piezoelectric vibration unit 3 is configured on the substrate 2, and the piezoelectric vibration unit 3 includes the piezoelectric thin film 4, the first and second films. Electrodes 5 and 6 and additional films 62 and 63 are provided. The difference from the fourth embodiment is that the additional films 62 and 63 are provided in place of the additional films 7 and 8 of the fourth embodiment, and the width mode or the spread mode is used as the vibration mode to be used. Is used. That is, the piezoelectric vibrating portion has a rectangular planar shape having a length direction and a width direction, and FIG. 15 shows a cross section in a direction orthogonal to the length direction.

  Therefore, in the piezoelectric vibration device 61 of the modified example, the vibration in the width mode or the expansion mode is excited, and the node of the vibration appears at the position indicated by the arrow M in FIG. That is, the vibration node M exists at the center in the width direction of the piezoelectric vibration portion.

  On the other hand, in this modified example, the additional film 62 is formed to have a uniform thickness on the lower surface of the piezoelectric vibrating portion, like the additional film 7.

  On the other hand, the additional film 63 is removed in the first region including the vibration node M, and is provided in the second region. In other words, the additional film 63 is removed in the first region, and has a concave shape in the cross section.

  In this modification, in at least one of the additional films 63, the additional film is removed in the first region, and the thickness of the additional film in the second region is relatively increased with respect to the first region. As described above, since the additional film 63 is removed in the first region including the vibration node, in the present modification, compared to a corresponding structure in which a flat additional film is provided on the upper surface of the piezoelectric vibrating portion 3. The resonance frequency can be lowered.

  That is, after forming the piezoelectric vibration device of the fourth embodiment having the resonance characteristics shown in FIG. 17, the thickness of the additional film 63 in the first region is set to 0 as in the modification shown in FIG. In this case, the resonance characteristics shown in FIG. 18 can be obtained.

  This is due to the following reason.

  As shown in a schematic perspective view in FIG. 16, a piezoelectric vibrator 71 using a rectangular plate-like width mode or spreading mode is assumed. In this piezoelectric vibrator 71, it is assumed that a recess 71a is formed at the center of the upper surface so as to extend in the length direction. In this case, when the piezoelectric vibrator 71 vibrates in the width mode or the spread mode, the vibration node N is located in the recess as shown in FIG. That is, the modification shown in FIG. 15 corresponds to such a model. In this case, the mass addition in the vibration node and the mass addition in the second region other than the vibration node are different as described above. Further, it is considered that the resonance frequency is lowered.

  In FIG. 15, the additional film 63 is removed and the thickness is 0 in the first region, but an additional film may be formed in the first region. It is only necessary that the thickness of the additional film in the first region is made thinner than the thickness of the additional film in the second region, as indicated by a one-dot chain line at O. Then, by setting the thickness of the additional film in the first region to be smaller than the thickness of the additional film in the second region or 0, the resonance frequency can be lowered as described above.

  Therefore, in the present invention, the resonance frequency is adjusted by adjusting the thickness of the additional film provided on at least one surface of the piezoelectric vibrating portion so that the thickness of the additional film in the first region is 0 or thin. Can be adjusted.

  In FIG. 19, contrary to the modification shown in FIG. 15, in the additional film 64, the thickness of the additional film in the first region is relatively thick, and the additional film 64 is removed in the second region. It is sectional drawing which shows another modification. Regarding other structures, the piezoelectric vibration device 65 of the present modification is the same as the piezoelectric vibrator 61.

  Here, as in the case of the piezoelectric vibration device 61, the width mode or the expansion mode is used, and therefore the vibration node M is located in the first region. Since the additional film 64 is removed in the second region, the mass addition effect is different between the first region and the second region. FIG. 20 shows the resonance characteristics of the piezoelectric vibration device 65 of this modification. As shown in FIG. 20, the resonance frequency is increased as compared with the resonance frequency of the piezoelectric vibration device shown in FIG.

  Thus, in the additional film provided on at least one surface, the resonant frequency can be increased by removing the additional film in the first region. In this case, as indicated by the alternate long and short dash line P in FIG. 19, the resonance frequency can be increased as long as the additional film in the second region is not set to 0 and is thinner than the additional film in the first region. That is, since the resonance frequency changes in the direction of increasing due to the difference in mass addition effect, it is not always necessary to remove the additional film in the second region.

  In the modification shown in FIG. 15, in the additional film 63, the resonance frequency can be adjusted by adjusting the width direction dimension Q of the first region.

  This will be described with reference to FIG. 21 and FIG.

As shown in a schematic cross-sectional view in FIG. 21, in the modification shown in FIG. 15, the additional film 63 made of SiO ₂ is removed in the first region. In this case, the width of the first region, that is, the removal width Q of the additional film was changed, and the change in the resonance frequency was obtained. The results are shown in FIG.

In the experiment, the structure of the piezoelectric vibration part is a laminated structure of SiO ₂ / Al / AlN / Al / SiO ₂ from above, and the thickness is 2.6 μm, 0.1 μm / 1.6 μm / 0 from above. .1 μm / 2.6 μm. And the length direction dimension of the piezoelectric vibration part was 179.2 micrometers, and the width direction dimension was 112 micrometers. The horizontal axis of FIG. 22 was ratio: (lateral width Q with the SiO ₂ film removed from the additional film) / (size in the piezoelectric vibration part width direction). As can be seen from FIG. 22, when this ratio is in the vicinity of 0.4 to 0.6, the resonance frequency is the lowest. Therefore, even when the piezoelectric vibrating portion has the same shape, when the additional film 63 is removed in the first region, the resonance frequency can be lowered by about 1 to 2 MHz by adjusting the removal width Q. Thus, it can be seen that the piezoelectric vibration device can be downsized.

  The additional film can be removed or partially thinned using various methods such as reactive ion etching (RIE), ion milling, laser processing, or wet etching. Alternatively, the first region and the second region are previously formed by a lift-off method, masking, or the like when forming the additional film, rather than a method of partially removing the thin film after forming the additional film or performing a process of reducing the thickness. Additional films with different thicknesses may be formed.

Claims (12)

A film-like piezoelectric body having first and second main surfaces facing each other;
A first electrode formed on a first main surface of the piezoelectric body;
The second electrode is formed on the second main surface of the piezoelectric body, and includes a first electrode and a second electrode arranged so as to overlap via the piezoelectric body,
The portion where the first and second electrodes overlap via the piezoelectric body constitutes a piezoelectric vibrating portion,
A support member supporting the piezoelectric vibration unit;
The piezoelectric vibration part is supported by the support member so as to be in a floating state in a portion where the first and second electrodes overlap with each other through the piezoelectric body, and the contour vibration mode of the piezoelectric vibration part And use
The piezoelectric vibration unit further includes an additional film laminated on a surface of the first and second electrodes opposite to the surface in contact with the piezoelectric body, and at least one of the additional films is the A piezoelectric vibration device comprising: a first region including a vibration node of the piezoelectric vibration unit; and a second region having a thickness different from the first region.   2. The piezoelectric vibration device according to claim 1, wherein in the first region, the thickness of the additional film is made thinner than the thickness in the second region.   3. The piezoelectric vibration device according to claim 2, wherein in the first region, the thickness of the thin portion is 0, and the additional film is provided only in the second region.   2. The piezoelectric vibration device according to claim 1, wherein in the first region, the thickness of the additional film is larger than the thickness in the second region.   The piezoelectric vibration device according to claim 4, wherein the thickness of the additional film is set to 0 in the second region, and the additional film is provided only in the first region. The film-like piezoelectric body has a piezoelectric extension extending to the outside of the piezoelectric vibration section in which the first and second electrodes overlap with each other via the piezoelectric body;
The piezoelectric vibration device according to claim 1, wherein the piezoelectric body is fixed to the support member in the piezoelectric extension portion.   The piezoelectric vibration according to claim 6, wherein the support member is a substrate, and the piezoelectric extension is fixed to an upper surface of the substrate in a state where the piezoelectric vibration unit is floated on the substrate with a gap. apparatus.   8. The piezoelectric body according to claim 6 or 7, wherein the piezoelectric body has a shape that does not reach the outside of the piezoelectric vibration portion in an outer peripheral edge portion of the piezoelectric body excluding a portion where the piezoelectric extension portion is provided. The piezoelectric vibration device as described.   The piezoelectric vibration device according to any one of claims 1 to 8, wherein a thickness of the piezoelectric vibration part is set to 1/40 or less of a wavelength of the contour vibration mode.   The piezoelectric vibration part has a rectangular planar shape having a short side and a long side, the contour vibration mode is a spread vibration mode, and the thickness of the piezoelectric vibration part is a short side dimension of the piezoelectric vibration part. The piezoelectric vibration device according to any one of claims 1 to 9, wherein the piezoelectric vibration device is 1/20 or less. The piezoelectric vibration part has a rectangular planar shape having a short side and a long side, the contour vibration mode is a length vibration mode, and the thickness of the piezoelectric vibration part is equal to that of the long side of the piezoelectric vibration part. The piezoelectric vibration device according to any one of claims 1 to 9 , wherein the size is 1/20 or less of the size.   The piezoelectric vibration device according to claim 1, which is a piezoelectric resonator having a frequency in a range of 1 to 100 MHz.

Images