JP2009111623A - Piezoelectric vibrating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric vibrating device which has superior temperature characteristics, has both the high-frequency accuracy and excitation efficiency, and low cost. <P>SOLUTION: The piezoelectric vibration device 1 is provided with a substrate 10, a piezoelectric thin film 23, an upper electrode 24, a lower electrode 25, insulating films 26 and 27 for temperature compensation, and a support part 30. The insulating films 26 and 27 for temperature compensation form a piezoelectric vibrating part 20, with the piezoelectric thin film 23, the upper electrode 24 and the lower electrode 25. The piezoelectric vibrating part 20 is supported by the support part 30, while floating with respect to the substrate 10 across a gap. The piezoelectric vibration device 1 uses a contour vibration mode of the piezoelectric vibrating part 20. The piezoelectric vibrating part 20 includes a piezoelectric driving part 21 and a piezoelectric part 22 to be driven with no piezoelectric thin film 23 formed. The piezoelectric part 22 to be driven is formed at a portion of the piezoelectric vibrating part 20, which includes the center part of vibration in the contour vibration mode. The areas of the insulating films 26 and 27 for temperature compensation are set larger than the area of the piezoelectric thin film 23. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  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. For this reason, conventionally, for example, in Patent Document 1, various piezoelectric vibration devices using a contour vibration mode as bulk waves have been proposed.

  FIG. 11 is a schematic plan view of the piezoelectric vibration device 100 described in Patent Document 1. FIG. 12 is a cross-sectional view taken along the line DD in FIG. FIG. 13 is a cross-sectional view taken along line EE in FIG.

  As shown in FIG. 12, the piezoelectric vibration device 100 includes a film-like piezoelectric body 101. The piezoelectric body 101 includes a first main surface 101a and a second main surface 101b that face each other. A first electrode 102 is formed on the first main surface 101 a of the piezoelectric body 101. On the other hand, a second electrode 103 is formed on the second main surface 101 b of the piezoelectric body 101. The first electrode 102 and the second electrode 103 are disposed so as to overlap with each other with the piezoelectric body 101 interposed therebetween. A first additional film 107 is formed below the first electrode 102, while a second additional film 108 is formed on the second electrode 103.

A part of the laminated body 106 including the piezoelectric body 101, the first electrode 102 and the second electrode 103, and the first additional film 107 and the second additional film 108 is supported while being floated from the base body 105. Has been. In the piezoelectric vibration device 100, the portion of the laminated body 106 that is supported while being floated from the base body 105 constitutes the piezoelectric vibration portion 104.
WO2007 / 086696 A1 pamphlet

  By the way, the resonance frequency of the piezoelectric body 101 changes with the temperature of the piezoelectric body 101. For this reason, if the temperature of the piezoelectric body 101 changes, the frequency characteristics of the piezoelectric vibration device 100 also change. In view of the temperature dependence of the frequency characteristics of the piezoelectric vibration device 100, Patent Document 1 discloses that the first additional film 107 and the second additional film 108 have a temperature coefficient opposite to the temperature coefficient of the sound velocity of the piezoelectric body 101. It is described that the temperature characteristics of the piezoelectric body 101 are compensated by providing the above.

  However, when the first additional film 107 and the second additional film 108 are provided in order to compensate for the temperature characteristics of the piezoelectric body 101, the cost for forming the first additional film 107 and the second additional film 108. There was a problem that it took. In addition, since the end portion of the piezoelectric vibrating portion 104 is thick, the processing accuracy of the outer dimensions of the piezoelectric vibrating portion 104 tends to be lowered. Since the outer dimension of the piezoelectric vibrating portion 104 is a factor that greatly affects the frequency characteristics, there is a problem that the frequency accuracy of the piezoelectric vibrating device 100 decreases when the processing accuracy of the outer dimension of the piezoelectric vibrating portion 104 decreases.

  An object of the present invention is to provide a piezoelectric vibration device that eliminates the above-mentioned drawbacks of the prior art, has good temperature characteristics, has high frequency accuracy and excitation efficiency, and is low in cost.

  According to the present invention, a base, a piezoelectric thin film having first and second main surfaces disposed above and facing the base, and a first electrode formed on the first main surface of the piezoelectric thin film, A second electrode formed on the second main surface of the piezoelectric thin film so that at least a part of the first electrode overlaps with the first electrode through the piezoelectric thin film; a first main surface side of the piezoelectric thin film; The piezoelectric thin film is laminated on at least one side of the surface side so as to at least partially overlap with the first electrode or the second electrode, and the piezoelectric thin film, the first electrode, and the second electrode are piezoelectric. A temperature compensation film constituting the vibration part and a support part that is fixed to the base and supports the piezoelectric vibration part in a state of being floated with a gap from the base, using the contour vibration mode of the piezoelectric vibration part In the piezoelectric vibration part, the first and second electrodes and the piezoelectric thin film are formed. The piezoelectric driven part and the piezoelectric driven part in which the piezoelectric thin film is not formed are formed on a part of the piezoelectric vibrating part including the antinodes of vibration in the contour vibration mode, and temperature compensation is performed. A piezoelectric vibration device is provided in which the area of the film is larger than the area of the piezoelectric thin film.

  Here, the “piezoelectric vibration portion” is a portion that is supported in a floating state with respect to the base and vibrates when an AC voltage is applied between the first electrode and the second electrode. . The piezoelectric vibration part has a piezoelectric drive part and a piezoelectric driven part.

  The “piezoelectric drive unit” is a portion of the piezoelectric vibration unit in which the first electrode, the piezoelectric thin film, and the second electrode overlap when viewed in plan, and the first electrode and the second electrode A portion that is actually excited when an alternating current is applied between the two.

  The “piezoelectric driven portion” is a portion of the piezoelectric vibrating portion where the piezoelectric thin film is not formed, and the portion is obtained by applying an alternating current between the first electrode and the second electrode. Although it is not excited itself, it refers to a portion that vibrates with the piezoelectric drive unit when the piezoelectric drive unit is excited.

  In the piezoelectric vibration device according to the present invention, the temperature compensation film is preferably formed on the entire surface of the piezoelectric vibration portion.

  In the piezoelectric vibration device according to the present invention, it is preferable that the piezoelectric driven portion is formed on at least a part of a portion of the piezoelectric vibration portion having an electric flux density equal to or lower than an average value of the electric flux density of the piezoelectric vibration portion.

  Moreover, when viewed in plan, the area of the piezoelectric driven part is preferably 1/5 or more and 1/3 or less of the area of the piezoelectric vibrating part.

  In a specific aspect of the piezoelectric vibration device according to the present invention, the piezoelectric driven portion includes an end portion in a main vibration direction of the piezoelectric vibration portion.

  In the piezoelectric vibration device according to the present invention, it is preferable that the interface between the piezoelectric drive unit and the piezoelectric driven unit is linear when viewed in plan.

  In another specific aspect of the piezoelectric vibration device according to the present invention, the temperature compensation film is substantially made of silicon oxide.

  According to the present invention, the piezoelectric driven portion in which the temperature compensation film is formed but the piezoelectric thin film is not formed is provided, and the area where the temperature compensation film is formed is larger than the area where the piezoelectric thin film is formed. Thus, the thickness of the temperature compensation film can be reduced without degrading the temperature characteristics of the piezoelectric vibration device.

  In addition, by reducing the thickness of the temperature compensation film, it is possible to reduce the thickness of the end portion of the piezoelectric vibrating portion. Therefore, since the processing accuracy of the outer dimensions of the piezoelectric vibration part that greatly affects the frequency characteristics of the piezoelectric vibration device can be increased, the frequency accuracy of the piezoelectric vibration device can be increased.

  Furthermore, since the cost required for forming the temperature compensation film can be reduced by reducing the thickness of the temperature compensation film, the manufacturing cost of the piezoelectric vibration device can be reduced.

  Further, by forming the piezoelectric driven part so as to include the vibration abdominal part in the contour vibration mode, it is possible to suppress a decrease in excitation efficiency of the piezoelectric vibration device caused by providing the piezoelectric driven part not forming the piezoelectric thin film. And high excitation efficiency can be realized.

  That is, by forming the piezoelectric driven part so as to include the vibration abdomen in the contour vibration mode, and making the area where the temperature compensation film is formed larger than the area where the piezoelectric thin film is formed, the temperature characteristics are good, It is possible to realize a piezoelectric vibration device that has both high frequency accuracy and excitation efficiency and is low in cost.

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

  FIG. 1 is a schematic plan view of a piezoelectric vibration device 1 according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view taken along the line AA in FIG. FIG. 3 is a schematic cross-sectional view taken along the line BB in FIG. 4 is a schematic cross-sectional view taken along the line CC in FIG.

  In the present embodiment, the piezoelectric vibration device 1 uses a contour vibration mode, specifically, a spread vibration mode. More specifically, the piezoelectric vibration device 1 uses a spread vibration mode mainly including vibration in the width direction.

  As shown in FIG. 2 and the like, the piezoelectric vibration device 1 includes a substrate 10 as a base, a first temperature compensation insulating film 26, a first conductive layer 28, and a piezoelectric thin film disposed above the substrate 10. 23, a second conductive layer 29, and a second temperature compensation insulating film 27.

  The substrate 10 can be formed of a semiconductor such as a Si-based semiconductor or an insulator such as glass.

  As shown in FIGS. 2 and 5, a first temperature compensation insulating film 26 is formed on the substrate 10. As shown in FIG. 2, at least a part of the first temperature compensation insulating film 26 overlaps the piezoelectric thin film 23 via the lower electrode 25. As shown in FIG. 1, the area of the first temperature compensation insulating film 26 is larger than the area of the piezoelectric thin film 23 described later.

  As shown in FIG. 5, the first temperature compensation insulating film 26 has a central portion that is located at the center and has a substantially rectangular shape in plan view. The central portion of the first temperature compensation insulating film 26 is formed in a rectangular shape having one corresponding long side and short side. In the first temperature compensation insulating film 26, an end portion is connected to each short side of the central portion of the first temperature compensation insulating film 26.

  As shown in FIG. 2, the central portion of the first temperature compensation insulating film 26 is held in a state of being floated from the substrate 10 with a gap D therebetween. Each end portion of the first temperature compensation insulating film 26 includes a portion fixed to the substrate 10 and an inclined portion connecting the fixed portion and the central portion. In the present embodiment, the central portion of the first temperature compensation insulating film 26 is formed on the entire surface of the piezoelectric vibrating portion 20.

  In the present embodiment, the first temperature compensating insulating film 26 and a second temperature compensating insulating film 27 described later are insulating films for compensating the temperature characteristics of the piezoelectric vibrating portion 20. Here, “compensating for temperature characteristics” specifically means reducing the temperature dependence of the frequency characteristics of the piezoelectric drive unit. Further, the “temperature compensation insulating film” refers to an insulating film that reduces the temperature dependence of the frequency characteristics of the piezoelectric drive unit. Specifically, the “temperature compensation insulating film” is an insulating film that makes the absolute value of the temperature coefficient of sound velocity of the piezoelectric drive unit smaller than the absolute value of the temperature coefficient of sound speed of the piezoelectric thin film. The “temperature compensation insulating film” is usually a temperature coefficient having the opposite sign to the temperature coefficient of the sound velocity of the piezoelectric thin film, or a temperature coefficient having the same sign as the temperature coefficient of the sound speed of the piezoelectric thin film, It has a temperature coefficient with an absolute value smaller than the absolute value.

  That is, the “temperature-compensating insulating film” is laminated directly on the piezoelectric thin film or via another layer, and has a temperature coefficient opposite in sign to the temperature coefficient of sound velocity of the piezoelectric thin film, or directly on the piezoelectric thin film. Alternatively, the insulating film is not particularly limited as long as the insulating film has a temperature coefficient of the same sign as that of the sound velocity of the piezoelectric thin film and a small absolute value. For example, the “temperature compensation insulating film” has at least one of a function as a protective film for protecting the inside, a function as a reinforcing film, and a function for adjusting a resonance frequency by adding mass together with a temperature compensation function. It may be.

  In the present embodiment, an example in which both the first temperature compensation insulating film 26 and the second temperature compensation insulating film 27 are formed will be described. However, the first temperature compensation insulating film 26 and the second temperature compensation insulating film 26 Only one of the two temperature compensation insulating films 27 may be formed.

  The material for forming the first and second temperature compensating insulating films 26 and 27 can be appropriately selected according to the material for forming the piezoelectric thin film 23. Specifically, the material forming the first and second temperature compensating insulating films 26 and 27 is a material having a temperature coefficient opposite in sign to the temperature coefficient of the sound speed of the material forming the piezoelectric thin film 23, or the piezoelectric thin film 23. Can be appropriately selected from materials having a temperature coefficient having an absolute value smaller than the absolute value of the temperature coefficient of the sound velocity of the material forming the. The material for forming the first and second temperature compensation insulating films 26 and 27 is not strictly limited to an insulating material, and may be hindered by the relationship with the piezoelectric thin film 23, the upper electrode 24, and the lower electrode 25. It may have a conductivity that does not cause damage.

Specific examples of the material for forming the first and second temperature compensation insulating films 26 and 27 include dielectric materials such as silicon oxide and SiN represented by SiO ₂ , piezoelectric materials such as ZnO and AlN, A semiconductor material such as Si can be given.

  The first and second temperature compensation insulating films 26 and 27 may be formed by stacking a conductive film and an insulating film. In that case, the conductive film can be formed of, for example, Al, Cu, Elinvar, or Invar.

  The first temperature compensation insulating film 26 and the second temperature compensation insulating film 27 may be formed of different materials or may be formed of the same material.

  As shown in FIGS. 2 and 6, the first conductive layer 28 is formed on the first temperature compensation insulating film 26. The first conductive layer 28 includes a lower electrode 25 having a substantially rectangular shape in plan view that constitutes the piezoelectric vibrating portion 20, and a first terminal electrode 31 connected to the lower electrode 25.

  The lower electrode 25 is formed only at a part of the substantially rectangular central portion of the first temperature compensation insulating film 26. Specifically, the lower electrode 25 is not formed at both ends on the long side of the central portion of the first temperature compensation insulating film 26. That is, the lower electrode 25 is formed only at the center of the center portion of the first temperature compensation insulating film 26 in the width direction.

  The materials of the first conductive layer 28 and the second conductive layer 29 described later are not particularly limited. An appropriate conductive material can be used for forming the first conductive layer 28 and the second conductive layer 29. Examples of the conductive material include Al, Cu, Au, Pt, Ni, Mo, Ru, Ir, W, and alloys thereof. Specific examples of the conductive alloy include enliver and invar.

  As shown in FIGS. 2 and 7, the piezoelectric thin film 23 is formed on the first conductive layer 28. The piezoelectric thin film 23 includes a central portion constituting the piezoelectric vibrating portion 20 and both end portions connected to the central portion. The planar shape of the central portion of the piezoelectric thin film 23 is substantially equal to the planar shape of the lower electrode 25. The piezoelectric thin film 23 is polarized in the thickness direction. The piezoelectric thin film 23 has a first main surface 23a and a second main surface 23b facing each other. The first main surface 23 a is in contact with the second conductive layer 29. On the other hand, the second main surface 23 b is in contact with the first conductive layer 28.

The piezoelectric thin film 23 can be formed of an appropriate piezoelectric material. Examples of the piezoelectric material include piezoelectric ceramics and piezoelectric single crystals. Specific examples of piezoelectric ceramics include zinc oxide (ZnO), aluminum nitride (AlN), lead zirconate titanate ceramics (PZT piezoelectric ceramics), and the like. Specific examples of the piezoelectric single crystal include lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), and quartz.

  As shown in FIGS. 2 and 8, the second conductive layer 29 is formed on the piezoelectric thin film 23 and the end portion of the first temperature compensation insulating film 26. The second conductive layer 29 includes an upper electrode 24 having a substantially rectangular shape in plan view that constitutes the piezoelectric vibrating portion 20, and a second terminal electrode 32 connected to the upper electrode 24. The upper electrode 24 is at least partially overlapped with the lower electrode 25 via the piezoelectric thin film 23. In the present embodiment, the planar shape of the upper electrode 24 is substantially equal to the planar shape of the central portion of the piezoelectric thin film 23. For this reason, the entire upper electrode 24 and the entire lower electrode 25 are overlapped via the piezoelectric thin film 23.

  The upper electrode 24, together with the lower electrode 25, applies an AC voltage to the piezoelectric thin film 23 to excite the piezoelectric driving unit 21 of the piezoelectric vibrating unit 20.

  In the present embodiment, the case where the planar shape of the upper electrode 24 and the planar shape of the lower electrode 25 are equal will be described. However, the planar shape of the upper electrode 24 and the planar shape of the lower electrode 25 may be different. For example, as long as the upper electrode 24 and the lower electrode 25 are not in contact with each other, one of the upper electrode 24 and the lower electrode 25 may be formed larger than the other electrode.

  Here, the “piezoelectric vibration part 20” refers to a part that is supported in a floating state with respect to the substrate 10 and vibrates when an AC voltage is applied between the upper electrode 24 and the lower electrode 25. The first and second temperature compensating insulating films 26 and 27, the upper electrode 24, the piezoelectric thin film 23, and the lower electrode 25 are included.

  The “piezoelectric drive unit 21” is a portion of the piezoelectric vibration unit 20 where the upper electrode 24, the piezoelectric thin film 23, and the lower electrode 25 overlap when viewed in plan. The portion that is actually excited when an alternating current is applied between the two.

  The “piezoelectric driven portion 22” is a portion of the piezoelectric vibrating portion 20 where the piezoelectric thin film 23 is not formed. When an alternating current is applied between the upper electrode 24 and the lower electrode 25, Although the portion itself is not excited, it refers to a portion that vibrates together with the piezoelectric drive unit 21 when the piezoelectric drive unit 21 is excited.

  As shown in FIGS. 1 and 2, a second temperature compensation insulating film 27 is formed on the ends of the second conductive layer 29 and the piezoelectric thin film 23. At least a part of the second temperature compensation insulating film 27 overlaps the piezoelectric thin film 23 via the upper electrode 24. The area of the second temperature compensation insulating film 27 is larger than the area of the piezoelectric thin film 23 described above. The second temperature compensation insulating film 27 has a central portion that is located at the center and has a substantially rectangular shape in plan view. The central portion of the second temperature compensation insulating film 27 is formed in a rectangular shape having one corresponding long side and short side. In the second temperature compensation insulating film 27, an end is connected to each short side of the central portion of the second temperature compensation insulating film 27. In the present embodiment, the central portion of the second temperature compensation insulating film 27 is formed on the entire surface of the piezoelectric vibrating portion 20.

  The piezoelectric vibrating portion 20 is formed in a rectangular shape having first and second sides 20a and 20b facing each other and third and fourth sides 20c and 20d facing each other when viewed in plan. Yes. In the present embodiment, the first and second sides 20a and 20b are short sides, and the third and fourth sides 20c and 20d are long sides. The ratio of the first and second sides 20a, 20b to the third and fourth sides 20c, 20d is about 1: 1.5.

  The piezoelectric vibration device 1 uses a spreading vibration mode mainly including vibrations in the extending direction of the first and second sides 20 a and 20 b, that is, the width direction of the piezoelectric vibrating portion 20. Specifically, in the piezoelectric vibrating portion 20, the third and fourth sides 20c and 20d are greatly displaced along the width direction from the initial state, while the first and second sides 20a and 20b are long. There is not much displacement along the direction. In particular, the central portions of the first and second sides 20a and 20b are hardly displaced, and the central portions of the first and second sides 20a and 20b are substantially nodes. In the piezoelectric vibrating portion 20 in which such a spread vibration mode is excited, the end portions in the width direction in contact with the third and fourth sides 20c and 20d, which are the end portions in the main vibration direction, are the antinodes of vibration. For this reason, the piezoelectric driven part 22 includes an abdominal part of vibration in the contour vibration mode.

  As shown in FIGS. 1 and 2, the piezoelectric vibrating portion 20 is supported at a position separated from the substrate 10 by a gap D by a support portion 30 fixed to the substrate 10. The support portion 30 includes both end portions of the first temperature compensation insulating film 26, the first terminal electrode 31, both end portions of the piezoelectric thin film 23, the second terminal electrode 32, and the second temperature compensation insulation. It is comprised by the both ends of the film | membrane 27. FIG. That is, in the present embodiment, the piezoelectric vibrating portion 20 and the support portion 30 are configured by the same thin film member.

  Note that it is not always necessary to provide both end portions of the piezoelectric thin film 23. However, when both end portions of the piezoelectric thin film 23 are not provided, it is necessary to form the first and second temperature compensating insulating films 26 and 27 with sufficient strength to support the piezoelectric vibrating portion 20.

  The support unit 30 supports the piezoelectric vibrating unit 20 at the approximate center of the first and second sides 20 a and 20 b, that is, at the approximate center of the longitudinal end of the piezoelectric vibrating unit 20. As described above, in the present embodiment in which the spread vibration mode in which the vibration in the width direction is the main is used, the substantially center of the end portion in the length direction of the piezoelectric vibration unit 20 is a node that hardly displaces. Accordingly, the support unit 30 supports the piezoelectric vibration unit 20 at the node.

  Next, with reference to FIG. 1 to FIG. 3 and FIG. 9, the positional relationship among the piezoelectric vibration unit 20, the piezoelectric driving unit 21, the piezoelectric driven unit 22, and the first and second temperature compensation insulating films 26 and 27. This will be described in detail.

  As described above, the piezoelectric thin film 23 is formed only on a part of the piezoelectric vibrating portion 20. Specifically, the piezoelectric thin film 23 is formed in a hatched portion in FIG. For this reason, as shown also in FIG. 2, only the central portion in the width direction in which the piezoelectric thin film 23 is formed of the piezoelectric vibrating portion 20 becomes the piezoelectric driving portion 21. Both ends of the piezoelectric vibration unit 20 in the width direction become the piezoelectric driven units 22.

  Here, as described above, in the present embodiment, both end portions in the width direction of the piezoelectric vibrating portion 20 are antinodes of vibration in the contour vibration mode, and a central portion in the width direction of the piezoelectric vibrating portion 20 is a node of vibration. Therefore, the piezoelectric driven part 22 is formed in a part of the piezoelectric vibration part 20 including the antinode of vibration in the contour vibration mode.

  In addition, the vibration abdominal portion in the contour vibration mode is a portion where the electric flux density is lower than the other portions. Therefore, the piezoelectric driven portion 22 of the piezoelectric vibrating portion 20 is in the relationship with the electric flux density. It is formed in a portion where the bundle density is low. The relationship between the formation position of the piezoelectric driven portion 22 and the electric flux density will be described in more detail with reference to FIG. FIG. 9 is a conceptual diagram showing the electric flux density of the piezoelectric vibrating portion 20 using contour lines. A region surrounded by the first contour line 35a shown in FIG. 9 represents a region having the highest electric flux density. A region surrounded by the first contour line 35a and the second contour line 35b is a region having the next highest electric flux density. A region having the next highest electric flux density is a region surrounded by the second contour line 35b and the third contour line 35c. The region located outside the third contour line 35c is the region having the lowest electric flux density.

  Here, the second contour line 35 b indicates a portion that is an average value of the electric flux density of the piezoelectric vibrating portion 20, and a region surrounded by the second contour line 35 b is an average of the electric flux density of the piezoelectric vibrating portion 20. The region has an electric flux density higher than the value. On the other hand, the region other than the region surrounded by the second contour line 35 b is a region having an electric flux density equal to or lower than the average value of the electric flux density of the piezoelectric vibrating portion 20.

  In the present embodiment, as shown in FIG. 1, the piezoelectric driven unit 22 is a region other than the region surrounded by the second contour line 35 b having an electric flux density equal to or lower than the average value of the electric flux density of the piezoelectric vibrating unit 20. Is formed at least in part. Specifically, the piezoelectric driven unit 22 is formed in the entire region other than the region surrounded by the second contour line 35 b having an electric flux density equal to or lower than the average value of the electric flux density of the piezoelectric vibrating unit 20. . In the present embodiment, the area of the piezoelectric driven unit 22 when viewed in plan is set to 1/5 or more and 1/3 or less of the area of the piezoelectric vibrating unit 20.

  On the other hand, the areas of the first and second temperature compensation insulating films 26 and 27 are larger than the area of the piezoelectric thin film 23. That is, the areas of the first and second temperature compensation insulating films 26 and 27 are made larger than the area of the piezoelectric drive unit 21. Specifically, in this embodiment, as shown in FIGS. 2 and 3, the piezoelectric vibration unit 20 is formed entirely. Therefore, in the present embodiment, the areas of the first and second temperature compensation insulating films 26 and 27 are set to be not less than 3 times and not more than 5 times the area of the piezoelectric driven portion 22.

  By the way, the temperature coefficient of sound velocity of the piezoelectric vibrating section 20 is the same as that of the piezoelectric thin film 23 and the temperature coefficients of the first and second temperature compensating insulating films 26 and 27. The weighted average value is obtained by the volume ratio with the temperature compensation insulating films 26 and 27. Therefore, as one method for reducing the temperature coefficient of the sound velocity of the piezoelectric vibrating portion 20 and improving the temperature characteristics of the piezoelectric vibrating portion 20, the volume of the first and second temperature compensating insulating films 26 and 27 with respect to the piezoelectric thin film 23 is reduced. A method of increasing the ratio is mentioned.

  The upper electrode 24 and the lower electrode 25 are very thin and have a small volume compared to the piezoelectric thin film 23 and the first and second temperature compensation insulating films 26 and 27. Accordingly, the influence of the temperature coefficient and volume of the sound velocity of the upper electrode 24 and the lower electrode 25 on the temperature coefficient of the sound velocity of the piezoelectric vibrating portion 20 is in a negligible range. The temperature coefficient and volume of 25 sound speeds are not considered.

  In the present embodiment, the areas of the first and second temperature compensation insulating films 26 and 27 are larger than the area of the piezoelectric thin film 23. Therefore, when the thicknesses of the first and second temperature compensating insulating films 26 and 27 and the piezoelectric thin film 23 are constant, the conventional first and second temperature compensating insulating films 26 and 27 and the piezoelectric thin film 23 The volume ratio of the first and second temperature compensation insulating films 26 and 27 with respect to the piezoelectric thin film 23 can be increased as compared with the configuration having the same area. Accordingly, the temperature coefficient of the sound velocity of the piezoelectric vibrating portion 20 can be further reduced, and thus the temperature characteristics of the piezoelectric vibrating portion 20 can be further improved.

  If equivalent temperature characteristics are obtained, the first and second temperature compensations are compared with the conventional first and second temperature compensation insulating films 26 and 27 and the piezoelectric thin film 23 having the same area. The thickness of the insulating films 26 and 27 can be reduced.

  By reducing the thicknesses of the first and second temperature compensation insulating films 26 and 27, the thickness of the end portion of the piezoelectric vibrating portion 20 can be reduced. Therefore, since the processing accuracy of the outer dimensions of the piezoelectric vibrating portion 20 that greatly affects the frequency characteristics of the piezoelectric vibrating portion 20 can be increased, the frequency accuracy of the piezoelectric vibrating device 1 can be increased. In particular, when the piezoelectric vibrating portion 20 is processed by etching, the processing accuracy of the outer dimensions of the piezoelectric vibrating portion 20 is likely to decrease as the thickness of the first and second temperature compensating insulating films 26 and 27 increases. For this reason, in the piezoelectric vibration device in which the piezoelectric vibration unit 20 is formed by etching, the frequency accuracy of the piezoelectric vibration device can be further improved.

By reducing the thickness of the first and second temperature compensating insulating films 26 and 27, the cost required for forming the first and second temperature compensating insulating films 26 and 27 can be reduced. The manufacturing cost of the vibration device 1 can be reduced. Specifically, for example, when the piezoelectric thin film 23 is a SiO ₂ thin film, the area of the piezoelectric driven part 22 is set to about 1/5 or more and 1/3 or less of the area of the piezoelectric vibrating part 20 as in the present embodiment. By setting, it is expected that the manufacturing cost of the piezoelectric vibration device 1 is reduced by about 1.5 to 3.0% as compared with the case where the piezoelectric thin film 23 is formed on the entire piezoelectric vibration unit 20.

  From the viewpoint of reducing the temperature coefficient of sound velocity of the piezoelectric vibrating portion 20, the formation position of the piezoelectric driven portion 22 is not particularly limited. For example, the piezoelectric driven portion 22 may be formed at the center of the piezoelectric vibrating portion 20. That is, the piezoelectric driven portion 22 may be formed at the vibration node in the contour vibration mode where the electric flux density is high. However, when the piezoelectric driven portion 22 is formed at the vibration node in the contour vibration mode, the excitation efficiency of the piezoelectric vibration device 1 may be greatly reduced. However, even in that case, the temperature coefficient of the sound velocity of the piezoelectric vibrating portion 20 can be reduced.

  Incidentally, even when the piezoelectric thin film 23 is formed on the entire surface of the piezoelectric vibrating portion 20, the entire piezoelectric thin film 23 does not contribute equally to vibration. In the piezoelectric thin film 23, a portion having a high electric flux density contributes greatly to vibration, while a portion having a low electric flux density does not contribute much to vibration. That is, even when the piezoelectric thin film 23 is formed on the entire surface of the piezoelectric vibrating portion 20, only the portion of the piezoelectric thin film 23 having a high electric flux density substantially contributes to the vibration. In view of this, in the present embodiment, the piezoelectric thin film 23 has an electric flux density lower than the average value of the electric flux density of the piezoelectric vibrating portion 20, and at least part of the portion including the vibration abdominal portion in the contour vibration mode. A configuration is adopted in which the piezoelectric driven portion 22 is used as the piezoelectric driven portion 22. According to this configuration, even if the portion including the vibration abdominal portion in the contour vibration mode with a low electric flux density is used as the piezoelectric driven portion 22, as described above, the portion does not contribute much to the vibration. The volume of the piezoelectric thin film 23 can be reduced without significantly reducing the efficiency.

  In particular, in the present embodiment, the piezoelectric drive unit 21 on which the piezoelectric thin film 23 is formed is formed in a shape substantially along the contour line 35b shown in FIG. As a result, the portion having a high electric flux density can be used as the piezoelectric driving portion 21 and the piezoelectric driven portion 22 can be formed only in the portion having a low electric flux density. Accordingly, particularly high excitation efficiency can be realized. As described above, from the viewpoint of obtaining high excitation efficiency, it is preferable to form the piezoelectric driving unit 21 and the piezoelectric driven unit 22 in a shape substantially along the contour line 35, but the present invention is limited to this configuration. It is not something. For example, the shape of the piezoelectric drive unit 21 and the piezoelectric driven unit 22 may be determined in consideration of the workability of the piezoelectric vibration unit 20.

  Further, from the viewpoint of further reducing the temperature coefficient of sound velocity of the piezoelectric vibrating section 20, it is preferable that the volume ratio of the first and second temperature compensating insulating films 26 and 27 to the piezoelectric thin film 23 is larger. Therefore, it is preferable that the first and second temperature compensating insulating films 26 and 27 have a larger area, and the first and second temperature compensating insulating films 26 and 27 are formed on the entire surface of the piezoelectric vibrating portion 20. Is particularly preferred.

  Similarly, the area of the piezoelectric thin film 23 is preferably as small as possible from the viewpoint of further reducing the temperature coefficient of sound velocity of the piezoelectric vibration unit 20 and further reducing the manufacturing cost of the piezoelectric vibration device 1. In other words, it is preferable that the area ratio of the piezoelectric driven portion 22 to the piezoelectric vibrating portion 20 is larger. From the viewpoint of further reducing the temperature coefficient of sound velocity of the piezoelectric vibrating portion 20 and reducing the manufacturing cost of the piezoelectric vibrating device 1, the area ratio of the piezoelectric driven portion 22 to the piezoelectric vibrating portion 20 is 1/5 or more. Is preferred. By doing so, the temperature coefficient of the sound velocity of the piezoelectric vibration unit 20 can be further reduced, and the manufacturing cost of the piezoelectric vibration device 1 can be further reduced.

  However, when the area of the piezoelectric thin film 23 is reduced, the area of the piezoelectric drive unit 21 is also reduced. For this reason, when the area of the piezoelectric thin film 23 is reduced, the excitation characteristics of the piezoelectric vibration device 1 tend to deteriorate. Therefore, from the viewpoint of obtaining good excitation characteristics, it is preferable to reduce the area of the piezoelectric driven portion 22 where the piezoelectric thin film 23 is not formed. Specifically, considering that the area of the region where the electric flux density is lower than the average value of the electric flux density of the piezoelectric vibrating unit 20 is usually about 1/3, the piezoelectric driven unit 22 with respect to the piezoelectric vibrating unit 20 It is preferable to set the area ratio to 1/3 or less.

  That is, by setting the area ratio of the piezoelectric driven portion 22 to the piezoelectric vibrating portion 20 to be 1/5 or more and 1/3 or less, the temperature coefficient of sound velocity of the piezoelectric vibrating portion 20 can be further reduced, and the piezoelectric vibrating device 1 The manufacturing cost can be further reduced.

  As described above, in this embodiment, the case of using the spread vibration mode mainly including the vibration in the width direction of the contour vibration has been described. However, the piezoelectric vibration device according to the present invention mainly uses the vibration in the length direction. The spread vibration mode, the spread vibration mode that vibrates greatly in both the width direction and the length direction, the length vibration mode, or the width vibration mode may be used. Even in the case of using the spread vibration mode that mainly vibrates in the length direction, the spread vibration mode that vibrates in both the width direction and the length direction, the length vibration mode, or the width vibration mode, the same as in this embodiment In addition, it is preferable to form the piezoelectric driven portion 22 in a part of the piezoelectric vibrating portion 20 including the antinode of vibration in the contour vibration mode.

  Specifically, when the spread vibration mode or the width vibration mode mainly including the vibration in the width direction of the contour vibration is used as in the present embodiment, the piezoelectric driven is applied to the end in the width direction of the piezoelectric vibration unit 20. It is preferable to form the portion 22. On the other hand, when using the spread vibration mode or the length vibration mode mainly including the vibration in the length direction of the contour vibration, the piezoelectric driven portion 22 is formed at the end portion in the length direction of the piezoelectric vibration portion 20. Is preferred. When using the spread vibration mode that vibrates greatly in both the width direction and the length direction, it is preferable to form the piezoelectric driven part 22 so as to surround the piezoelectric driving part 21 on the entire peripheral part of the piezoelectric vibrating part 20. .

(Method for Manufacturing Piezoelectric Vibration Device 1)
Next, a method for manufacturing the piezoelectric vibration device 1 will be described. First, a sacrificial layer for forming a gap D shown in FIG. 2 is formed on the substrate 10. The sacrificial layer can be formed by, for example, a sputtering method or a photo etching method. The material of the sacrificial layer is preferably one that can withstand high temperatures during the formation of the piezoelectric thin film 23 and can be easily removed chemically. Specific examples of the sacrificial layer material include metals such as Ge, Sb, Ti, Al, and Cu, inorganic materials such as zinc oxide and phosphate silicate glass, and organic polymers such as polytetrafluoroethylene.

  The thickness of the sacrificial layer is preferably set to such an extent that a gap D can be formed so that the piezoelectric vibrating portion 20 does not contact the substrate 10 when the piezoelectric vibrating portion 20 vibrates. The thickness of the sacrificial film can be, for example, about 0.5 μm to several μm.

  Next, the sacrificial layer is planarized by plasma processing such as plasma etching or ion etching. Thereby, for example, the surface roughness (Ra) of the sacrificial film is set to 5 μm or less. Next, a first temperature compensation piezoelectric film 26, a first conductive layer 28, a piezoelectric thin film 23, a second conductive layer 29, and a second temperature compensation piezoelectric film 27 are sequentially formed on the sacrificial film. These films and layers can be produced by, for example, forming by sputtering, chemical vapor deposition (CVD), electron beam evaporation or the like and then patterning. Examples of the patterning method include a laser trimming method, an ion beam method, a photo etching method, and a lift-off method. Next, the sacrificial layer is removed by reactive ion etching, wet etching, or the like, and finally the mask used for etching is removed, whereby the piezoelectric vibration device 1 can be completed.

(Modification)
In the above embodiment, the example in which the piezoelectric driving unit 21 is formed in a shape along the contour line 35 of the electric flux density shown in FIG. 9 has been described. However, the interface between the piezoelectric driving unit 21 and the piezoelectric driven unit 22 is planar. The piezoelectric drive unit 21 may be formed so as to be linear when viewed. Specifically, like the piezoelectric vibration device 1a shown in FIG. 10, the piezoelectric drive unit 21 may be formed so that the planar shape is substantially rectangular. In this case, the degree of freedom of the processing method of the piezoelectric drive unit 21 is expanded, and the processing of the piezoelectric drive unit 21 is facilitated. For example, the piezoelectric drive unit 21 can be easily processed by a method such as laser trimming or ion beam etching.

FIG. 1 is a schematic plan view of a piezoelectric vibration device according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view taken along the line AA in FIG. FIG. 3 is a schematic cross-sectional view taken along the line BB in FIG. 4 is a schematic cross-sectional view taken along the line CC in FIG. FIG. 5 is a schematic plan view for explaining the planar shape of the first temperature compensation insulating film. FIG. 6 is a schematic plan view for explaining the planar shape of the first conductive layer. FIG. 7 is a schematic plan view for explaining the planar shape of the piezoelectric thin film. FIG. 8 is a schematic plan view for explaining the planar shape of the second conductive layer. FIG. 9 is a conceptual diagram showing the electric flux density of the piezoelectric vibrating portion 20 using contour lines. FIG. 10 is a plan view of a piezoelectric vibration device according to a modification of the present invention. FIG. 11 is a schematic plan view of the piezoelectric vibration device described in Patent Document 1. FIG. 12 is a cross-sectional view taken along the line DD in FIG. FIG. 13 is a cross-sectional view taken along line EE in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric vibration apparatus 10 ... Board | substrate (base | substrate)
DESCRIPTION OF SYMBOLS 20 ... Piezoelectric vibration part 21 ... Piezoelectric drive part 22 ... Piezoelectric driven part 23 ... Piezoelectric thin film 23a ... 1st main surface 23b ... 2nd main surface 24 ... Upper electrode (1st electrode)
25 ... Lower electrode (second electrode)
26. First temperature compensation insulating film (temperature compensation film)
27. Second insulating film for temperature compensation (temperature compensating film)
30 ... support part D ... gap

Claims (7)

A substrate;
A piezoelectric thin film having a first main surface and a second main surface, which are arranged above the base and face each other;
A first electrode formed on a first main surface of the piezoelectric thin film;
A second electrode formed on the second main surface of the piezoelectric thin film so that at least a portion thereof overlaps the first electrode via the piezoelectric thin film;
At least a part of the piezoelectric thin film overlaps at least one of the first main surface side and the second main surface side of the piezoelectric thin film via the first electrode or the second electrode. A temperature compensation film that is laminated with the piezoelectric thin film, the first electrode, and the second electrode to form a piezoelectric vibration unit;
A support part that is fixed to the base body and supports the piezoelectric vibration part in a state of being floated with a gap with respect to the base body;
Utilizing the contour vibration mode of the piezoelectric vibration part,
The piezoelectric vibration unit includes a piezoelectric driving unit in which the first and second electrodes and the piezoelectric thin film are formed, and a piezoelectric driven unit in which the piezoelectric thin film is not formed,
The piezoelectric driven part is formed in a part of the piezoelectric vibration part including a vibration abdomen in a contour vibration mode,
The piezoelectric vibration device, wherein an area of the temperature compensation film is larger than an area of the piezoelectric thin film.   The piezoelectric vibration device according to claim 1, wherein the temperature compensation film is formed on the entire surface of the piezoelectric vibration portion.   3. The piezoelectric device according to claim 1, wherein the piezoelectric driven portion is formed on at least a part of a portion of the piezoelectric vibrating portion having an electric flux density equal to or lower than an average value of an electric flux density of the piezoelectric vibrating portion. Vibration device.   4. The piezoelectric vibration according to claim 1, wherein, when viewed in a plan view, an area of the piezoelectric driven portion is 1/5 or more and 1/3 or less of an area of the piezoelectric vibrating portion. apparatus.   The piezoelectric vibration device according to claim 1, wherein the piezoelectric driven portion includes an end portion in a main vibration direction of the piezoelectric vibration portion.   6. The piezoelectric vibration device according to claim 1, wherein an interface between the piezoelectric driving unit and the piezoelectric driven unit is linear when viewed in a plan view.   The piezoelectric vibration device according to claim 1, wherein the temperature compensation film is substantially made of silicon oxide.

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