Piezoelectric resonator

Abstract

A piezoelectric resonator (10) is provided with: a polarization-inverted piezoelectric laminated body (11) in which 10 or more piezoelectric layers (111, 112) made of piezoelectric material and having substantially equal fundamental resonance frequencies, which are values obtained by dividing an acoustic velocity by twice the thickness, are laminated so that the directions of components of polarization in a direction parallel to or perpendicular to the in-plane direction of the layers are alternately reversed; a pair of electrodes (121, 122) provided so as to sandwich the polarization-inverted piezoelectric laminated body (11) from both sides in the lamination direction; and a support body (13) for supporting one (122) of the pair of electrodes (121, 122).

Description

Piezoelectric resonator

[0001] The present invention relates to a piezoelectric resonator that is a component of a frequency filter used in communication devices such as smartphones.

[0002] Communication devices such as smartphones use frequency filters that extract specific frequency bands from signal currents converted from electromagnetic waves across a wide frequency band received by an antenna. Piezoelectric resonators are known as elements used in such frequency filters. Piezoelectric resonators include surface acoustic wave (SAW) types and bulk acoustic wave (BAW) types (see, for example, Patent Document 1).

[0003] A SAW piezoelectric resonator has an IDT (Inter-Digital Transducer) consisting of two interdigital electrodes interdigitated with each other on the surface of a piezoelectric film (piezoelectric film), and two grating reflectors sandwiching the IDT. A BAW piezoelectric resonator has a piezoelectric film sandwiched between two plate electrodes. In both types, when an AC signal with various superimposed frequencies is applied between the two electrodes, the piezoelectric film resonates at a resonant frequency determined by the gap between the interdigital electrodes (in the case of a SAW piezoelectric resonator) and the thickness of the piezoelectric film (in the case of a BAW piezoelectric resonator). While the interdigital electrodes of a SAW piezoelectric resonator are separated only by a narrow gap, a BAW piezoelectric resonator has a piezoelectric film between the electrodes. Therefore, BAW piezoelectric resonators generally have higher voltage resistance than SAW piezoelectric resonators.

[0004] There are three main types of BAW piezoelectric resonators: HBAR (High-overtone Bulk Acoustic Resonator), FBAR (Film Bulk Acoustic Resonator), and SMR (Solidly Mounted Resonator). These three types of BAW piezoelectric resonators have a piezoelectric film sandwiched between two plate electrodes, which is supported on the flat surface of a substrate in the HBAR, on the surface of a substrate around the gap in the FBAR, and on an acoustic Bragg reflector in the SMR. The acoustic Bragg reflectors have different acoustic impedances and are connected to each other by a sound velocity v B The thickness d B The value v divided by 2 B / 2d B (Half the wavelength is the thickness d B It is made by alternately laminating two types of films with approximately the same frequency (corresponding to the frequency of sound waves equal to ).

[0005] International Publication No. WO2016 / 013659

[0006] In an HBAR, part of the vibration energy generated in the piezoelectric film leaks to the substrate through one of the electrodes, causing a composite resonance between the piezoelectric film and the substrate, resulting in vibrations at a frequency different from the original resonant frequency, with the same intensity as the resonant frequency.

[0007] In FBARs and SMRs, the presence of air (cavity) or an acoustic Bragg reflector under one of the electrodes prevents the vibrations generated in the piezoelectric film from leaking to the outside through that electrode. However, since the air or acoustic Bragg reflector alone cannot completely prevent the vibrations from leaking, vibrations occur at different frequencies, although they are weaker than the original resonant frequency.

[0008] The problem to be solved by the present invention is to provide a BAW type piezoelectric resonator that can suppress the transmission of vibrations generated in the piezoelectric film to the substrate and the acoustic Bragg reflector.

[0009] The piezoelectric resonator according to the present invention, which has been made to solve the above problems, is characterized by comprising: a) a polarization-inverted piezoelectric laminate formed by stacking 10 or more piezoelectric layers, each made of a piezoelectric material and having approximately the same fundamental resonance frequency, which is the sound velocity divided by twice the thickness, such that the directions of polarization components parallel and perpendicular to the in-plane direction of the layers are alternately inverted; b) a pair of electrodes disposed on both sides of the polarization-inverted piezoelectric laminate in the stacking direction; and c) a support for supporting one of the pair of electrodes.

[0010] In the case of an HBAR, a substrate with a flat surface is used as the support; in the case of an FBAR, a substrate with a gap on the surface is used, with one of the electrodes supported on the substrate surface around the gap; and in the case of an SMR, an acoustic Bragg reflector can be used.

[0011] In the case of an HBAR (where a substrate having a flat surface is used as the support), the polarization inverted piezoelectric laminate is preferably formed by laminating 30 or more piezoelectric layers.

[0012] The piezoelectric resonator according to the present invention uses a polarization-inverted piezoelectric laminate consisting of ten or more piezoelectric layers (hereinafter referred to as n layers (n≧10)) with substantially equal fundamental resonant frequency v / 2d, which is calculated by dividing the sound velocity v by twice the thickness d. The layers are stacked so that the polarization components parallel to and perpendicular to the in-plane direction of the layers alternate. When an AC signal (AC voltage) having the same frequency as the fundamental resonant frequency v / 2d is applied between a pair of electrodes in the thickness direction of the polarization-inverted piezoelectric laminate, n / 2 wavelengths of vibrations are generated within the polarization-inverted piezoelectric laminate, with the thickness d of one piezoelectric layer being half the wavelength. The greater the number of resonant waves generated within the polarization-inverted piezoelectric laminate (the number of waves in the entire polarization-inverted piezoelectric laminate; different from the "wave number," which is the number of waves per unit length), i.e., the greater the number of piezoelectric layers n, the more stable the resonance and the less likely it is that vibration energy will leak outside the polarization-inverted piezoelectric laminate. By setting n to 10 or greater, vibrations at frequencies different from the fundamental resonant frequency can be suppressed to the same degree in the HBAR as in a conventional FBAR or SMR (having only one piezoelectric layer), and can be almost completely suppressed in the FBAR or SMR. Furthermore, by setting n to 30 or greater, vibrations at frequencies different from the fundamental resonant frequency can be almost completely suppressed in the HBAR as well.

[0013] In the piezoelectric resonator according to the present invention, the polarization-inverted piezoelectric stack can be preferably formed by stacking piezoelectric layers so that the polarization is tilted from directions perpendicular and parallel to the in-plane direction of the layers, with the direction of the polarization component parallel to the piezoelectric layers alternately inverted. Such a polarization-inverted piezoelectric stack generates a transverse wave resonance in which the thickness d of each piezoelectric layer is half the wavelength and the in-plane vibration propagates in the stacking direction. This polarization-inverted piezoelectric stack can be fabricated by magnetron sputtering, in which sputtered particles made of a piezoelectric material such as ScAlN are incident on the substrate surface in a direction tilted relative to the normal, and then the substrate is rotated 180° about the normal, followed by similar sputtered particles.

[0014] According to the present invention, a BAW type piezoelectric resonator can be obtained that can suppress the transmission of vibrations generated in the piezoelectric film to the substrate and the acoustic Bragg reflector.

[0015] 1 is a schematic longitudinal sectional view showing an HBAR according to a first embodiment of the piezoelectric resonator of the present invention; 2 is a schematic longitudinal sectional view showing an example of a preferred configuration of the piezoelectric resonator of the first embodiment; 3 is a schematic view showing a magnetron sputtering apparatus used in manufacturing the piezoelectric resonators of the first and second embodiments; 4 is a graph showing the results of calculation of the impedance frequency characteristics of an HBAR of a comparative example having one piezoelectric layer; 5 is a graph showing the results of calculation of the impedance frequency characteristics of the piezoelectric resonator of the first embodiment having 10 layers; 6 is a graph showing the results of calculation of the impedance frequency characteristics of the piezoelectric resonator of the first embodiment having 30 layers; 7 is a graph showing the results of calculation of the impedance frequency characteristics of the piezoelectric resonator of the first embodiment having 100 layers; 8 is a scanning electron microscope (SEM) photograph of the longitudinal cross section of a fabricated example of the piezoelectric resonator of the first embodiment having 10 layers; 9 is a SEM photograph of the longitudinal cross section of a fabricated example of the piezoelectric resonator of the first embodiment having 30 layers. 1 is a graph showing the results of X-ray diffraction measurement of a fabricated example of a piezoelectric resonator according to the first embodiment having 10 layers. 2 is a graph showing the results of X-ray diffraction measurement of a fabricated example of a piezoelectric resonator according to the first embodiment having 30 layers. 3 is a graph showing the measurement results of the frequency characteristics of impedance of fabricated examples of piezoelectric resonators according to the first embodiment having 10 and 30 layers. 4 is a schematic vertical cross-sectional view of an SMR according to a second embodiment of the piezoelectric resonator according to the present invention. 5 is a schematic vertical cross-sectional view of another example of a piezoelectric resonator according to the second embodiment. 6 is a graph showing the calculation results of the frequency characteristics of impedance of an SMR of a comparative example having one piezoelectric layer. 7 is a graph showing the calculation results of the frequency characteristics of impedance of a piezoelectric resonator according to the second embodiment having 10 layers. 8 is a graph showing the calculation results of the frequency characteristics of impedance of a piezoelectric resonator according to the second embodiment having 30 layers. 9 is an SEM photograph of a vertical cross-section of a fabricated example of a piezoelectric resonator according to the second embodiment having 10 layers. 10 is a graph showing the measurement results of the frequency characteristics of impedance for a fabricated example of a piezoelectric resonator according to a second embodiment, in which the number of layers is 10. FIG. 11 is a schematic vertical cross-sectional view showing an FBAR, which is a modified example of a piezoelectric resonator according to the present invention.

[0016] 1 to 13, an embodiment of a piezoelectric resonator according to the present invention will be described.

[0017] (1) Piezoelectric Resonator of the First Embodiment (1-1) Configuration of the Piezoelectric Resonator of the First Embodiment The piezoelectric resonator 10 of the first embodiment is an HBAR. As shown in FIGS. 1 and 2, this piezoelectric resonator 10 includes a polarization-inverted piezoelectric laminate 11, a pair of electrodes composed of a first electrode 121 and a second electrode 122, and a substrate 13.

[0018] In the polarization-inverted piezoelectric laminate 11 in this embodiment, the first piezoelectric layer 111 and the second piezoelectric layer 112 made of a piezoelectric material are alternately laminated, together with 10 layers or more (FIG. 1), preferably 30 layers or more (FIG. 2). The first piezoelectric layer 111 and the second piezoelectric layer 112 are both such that the polarization P is inclined from the directions perpendicular (in the vertical direction in the figure) and parallel (in the horizontal direction in the figure) to the in-plane direction (the horizontal direction in the figure). The components of the polarization P in the direction parallel to the in-plane direction are opposite to each other (the former is in the right direction in the figure, and the latter is in the left direction in the figure) between the first piezoelectric layer 111 and the second piezoelectric layer 112. The first piezoelectric layer 111 and the second piezoelectric layer 112 are made of the same material, and sound waves propagate at the same sound velocity v. In this embodiment, since transverse wave resonance occurs in the polarization-inverted piezoelectric laminate 11 as described later, the sound velocity v mentioned here is the sound velocity of the transverse wave (the sound velocity of the transverse wave is 1 / 2 of the sound velocity of the longitudinal wave). Also, the first piezoelectric layer 111 and the second piezoelectric layer 112 have the same thickness d.

[0019] The first electrode 121 and the second electrode 122 are provided so as to sandwich the polarization-inverted piezoelectric laminate 11 from both sides in the stacking direction of the first piezoelectric layer 111 and the second piezoelectric layer 112 (the vertical direction in FIGS. 1 and 2).

[0020] The substrate 13 is a flat plate material, and its surface (upper surface) supports the second electrode 122. The substrate 13 corresponds to the above-mentioned support.

[0021] In this embodiment, for the piezoelectric material of the polarization-inverted piezoelectric laminate 11 (the first piezoelectric layer 111 and the second piezoelectric layer 112), Sc x Al 1-x N (scandium aluminum nitride, 0 < x < 1) can be preferably used. Sc x Al 1-x N has a wurtzite-type crystal structure that is hexagonal. Sc x Al 1-xOther than N: AlN (aluminum nitride), ZnO (zinc oxide), Mg 1-x Zn x Alternatively, a piezoelectric material such as magnesium zinc oxide (O) may be used. Metals such as gold (Au) and aluminum (Al) may be used as the material for the first electrode 121 and the second electrode 122. Silica glass, silicon, or the like may be used as the material for the substrate 13.

[0022] (1-2) Method for Manufacturing the Piezoelectric Resonator of the First Embodiment The method for manufacturing the piezoelectric resonator 10 of the first embodiment is the same as that for manufacturing the piezoelectric resonator 10 of the first embodiment. x Al 1-x An example of a case consisting of N will be explained.

[0023] First, a substrate S is prepared by vapor-depositing a metal that will become the second electrode 122 on the surface of the substrate 13. Next, the substrate S is placed on the substrate holder 52 of the magnetron sputtering apparatus 50 shown in FIG. 3 with the second electrode 122 facing up. A target T made of an ScAl alloy is placed on the cathode electrode 51 of the magnetron sputtering apparatus 50. In this state, magnetron sputtering is performed in a nitrogen-containing gas atmosphere to generate sputtered particles SP. The generated sputtered particles SP are incident at an oblique angle on the surface of the substrate S fixed to the substrate holder 52, thereby producing a second piezoelectric layer 112 whose polarization P is inclined relative to the in-plane direction of the layer. Next, the substrate S is rotated 180° around an axis perpendicular to the substrate S, and the sputtered particles SP are incident at an oblique angle on the surface of the substrate S using the same method as described above. This produces one first piezoelectric layer 111 whose polarization P is inclined relative to the in-plane direction of the layer and whose component parallel to the in-plane direction of the polarization P is 180° different from that of the second piezoelectric layer 112. By repeating the same procedure, a total of 10 or more second piezoelectric layers 112 and first piezoelectric layers 111 are produced, alternately. Finally, a first electrode 121 is produced by evaporating metal on the surface of the uppermost first piezoelectric layer 111, thereby obtaining the piezoelectric resonator 10 of this embodiment.

[0024] (1-3) Operation of the Piezoelectric Resonator of the First Embodiment The operation of the piezoelectric resonator 10 of the first embodiment will be described. An AC signal (AC voltage) having the same frequency as the fundamental resonant frequency v / 2d is applied between the first electrode 121 and the second electrode 122. As a result, as shown by the wavy lines in FIGS. 1 and 2 , transverse waves are generated, with the thickness d of the first piezoelectric layer 111 and the second piezoelectric layer 112 being a half wavelength, vibrating in the in-plane direction and traveling in the stacking direction. A resonant state due to the transverse wave vibration is formed throughout the polarization-inverted piezoelectric stack 11. The greater the number of piezoelectric layers (hereinafter simply referred to as the "number of layers"), including the first piezoelectric layer 111 and the second piezoelectric layer 112, the more stable the resonance and the less likely it is that vibration energy will leak to the substrate 13.

[0025] In the piezoelectric resonator 10 of the first embodiment, by setting the number of layers to 10 or more, it is possible to suppress, to the same extent as in FBARs and SMRs, the composite resonance of the polarization inverted piezoelectric laminate 11 and the substrate 13 at frequencies different from the fundamental resonance frequency. Furthermore, by setting the number of layers to 30 or more, it is possible to almost completely suppress the resonance at frequencies different from the fundamental resonance frequency.

[0026] In order to confirm the effect of increasing the number of layers in this way, the frequency characteristics of impedance were calculated theoretically for several examples with different numbers of layers. x Al 1-x The calculation was performed assuming that N (x=0.6) and the polarization P is inclined at an angle of 45° with respect to the lamination direction.

[0027] The calculation results are shown in Figures 4A to 4D. Figure 4A shows the case where the number of layers is one (comparative example), Figure 4B shows the case where the number of layers is ten (this embodiment), Figure 4C shows the case where the number of layers is thirty (a preferred configuration within this embodiment), and Figure 4D shows the case where the number of layers is 100 (same as above). The frequency at which the impedance reaches a minimum corresponds to the resonant frequency. When the number of layers is one (comparative example), there are many frequencies at which the impedance reaches a minimum, and vibrations occur at many frequencies different from the fundamental resonant frequency. In contrast, when the number of layers is ten, the number of frequencies at which the impedance reaches a minimum is reduced compared to when the number of layers is one, and is comparable to that of the comparative SMR with one layer (Figure 10A) shown below. When the number of layers is 30 and 100, there is only one frequency at which the impedance reaches a minimum, and resonance is achieved only at the fundamental resonant frequency.

[0028] (1-4) Example of Manufacturing the Piezoelectric Resonator of the First Embodiment Next, an example of manufacturing the piezoelectric resonator 10 of the first embodiment will be described. In this example, Sc 0.43 Al 0.57 Using alloys, we fabricated two types with 10 layers and 30 layers.

[0029] Scanning electron microscope (SEM) photographs of the longitudinal cross section of the fabricated piezoelectric resonator 10 are shown in FIG. 5A for the one with 10 layers and in FIG. 5B for the one with 30 layers. x Al 1-x A zigzag pattern is seen, which indicates that the first piezoelectric layers 111 and the second piezoelectric layers 112, whose c-axes of N are oriented in different directions, are alternately stacked in the vertical direction of the figure. x Al 1-x The direction of polarization P of N is parallel to the direction of the c-axis.

[0030] X-ray diffraction measurements were performed on the fabricated piezoelectric resonator 10 by irradiating it with X-rays from a direction tilted by an inclination angle χ from the stacking direction of the polarization-inverted piezoelectric laminate 11 while varying the inclination angle χ. The measurement results are shown in FIG. 6A for the 10-layer piezoelectric resonator and in FIG. 6B for the 30-layer piezoelectric resonator. These results indicate that the average inclination angle of the c-axis from the stacking direction was +45.1° for one of the first piezoelectric layer 111 and the second piezoelectric layer 112 and -44.7° for the other piezoelectric layer in the 10-layer piezoelectric resonator (positive or negative indicates that the in-plane c-axes are oriented 180° apart from each other). In the 30-layer piezoelectric resonator, the average inclination angle of the c-axis from the stacking direction was +38.0° for one piezoelectric layer and -40.2° for the other piezoelectric layer.

[0031] Next, the impedance frequency characteristics of the fabricated piezoelectric resonators 10 were measured. The results are shown in Figure 7. In both cases, a minimum value due to resonance at the fundamental resonance frequency was observed near 1.2 GHz. The width around the minimum value was narrower when the number of layers was 30 than when the number of layers was 10, indicating a greater effect of trapping vibrations.

[0032] (2) Piezoelectric Resonator of the Second Embodiment (2-1) Configuration of the Piezoelectric Resonator of the Second Embodiment The piezoelectric resonator 20 of the second embodiment is an SMR. As shown in Figures 8 and 9, the piezoelectric resonator 20 includes a polarization-inverted piezoelectric laminate 21, a pair of electrodes consisting of a first electrode 221 and a second electrode 222, and an acoustic Bragg reflector 23. The polarization-inverted piezoelectric laminate 21, the first electrode 221, and the second electrode 222 may be similar to the polarization-inverted piezoelectric laminate 11, the first electrode 121, and the second electrode 122 of the first embodiment. The polarization-inverted piezoelectric laminate 21 may have a total of 10 or more first piezoelectric layers 211 and second piezoelectric layers 212.

[0033] The acoustic Bragg reflector 23 corresponds to the support body described above, and is formed by alternately laminating first acoustic impedance layers 231 and second acoustic impedance layers 232. The first acoustic impedance layer 231 and the second acoustic impedance layer 232 may be provided in multiple layers as shown in Fig. 8, or may be provided in only one layer as shown in Fig. 9. The first acoustic impedance layer 231 and the second acoustic impedance layer 232 have different acoustic impedances and are separated by a sound velocity v B The thickness d B The value v divided by 2 B / 2d B are approximately equal. This value v B / 2d B By matching the fundamental resonant frequency v / 2d of the poled piezoelectric laminate 21, vibrations of the fundamental resonant frequency are reflected by the acoustic Bragg reflector 23, preventing leakage to the outside. The materials for the first acoustic impedance layer 231 and the second acoustic impedance layer 232 can be, for example, SiO2 (silicon dioxide) for one and W (tungsten) or Mo (molybdenum) for the other. W and Mo are materials with higher acoustic impedance than SiO2. As shown in FIG. 9, a substrate 24 may be further provided below the acoustic Bragg reflector 23. The substrate 24 may also be provided below the acoustic Bragg reflector 23 shown in FIG. 8.

[0034] (2-2) Manufacturing Method of Piezoelectric Resonator of Second Embodiment The piezoelectric resonator 20 of the second embodiment can be manufactured by placing a substrate S, on which the second electrodes 222 are vapor-deposited on the surfaces of the acoustic Bragg reflectors 23, in place of the substrate 13 of the first embodiment, on a substrate holder 52 of a magnetron sputtering device 50. The acoustic Bragg reflector 23 can be manufactured by alternately forming first acoustic impedance layers 231 and second acoustic impedance layers 232 using a vapor deposition method, magnetron sputtering method, or the like.

[0035] (2-3) Operation of the Piezoelectric Resonator of the Second Embodiment The operation of the piezoelectric resonator 20 of the second embodiment will now be described. As in the first embodiment, an AC signal (AC voltage) having the same frequency as the fundamental resonant frequency v / 2d is applied between the first electrode 221 and the second electrode 222. As a result, as shown by the dashed lines in FIGS. 8 and 9 , transverse waves are generated, with the thickness d of the first piezoelectric layer 211 and the second piezoelectric layer 212 being a half wavelength, the vibration direction being the in-plane direction, and the propagation direction being the stacking direction. A resonant state due to the transverse wave vibration is formed throughout the poled piezoelectric stack 21. Because this vibration has the same frequency as the fundamental resonant frequency v / 2d, it is reflected by the acoustic Bragg reflector 23, preventing leakage to the outside. Furthermore, the greater the number of piezoelectric layers, including the first piezoelectric layer 211 and the second piezoelectric layer 212, the more stable the resonance becomes, and the more easily the vibration is confined within the poled piezoelectric stack 21. As a result, by setting the number of layers to 10 or more, it is possible to almost completely prevent the polarization-inverted piezoelectric laminate 21 and the acoustic Bragg reflector 23 from resonating together at a frequency different from the fundamental resonance frequency.

[0036] In order to confirm this effect, the frequency characteristics of impedance were theoretically calculated for several examples with different numbers of layers. x Al 1-x The calculation was performed assuming that N (x=0.6) and the polarization P is inclined at an angle of 45° with respect to the lamination direction.

[0037] The calculation results are shown in Figures 10A to 10C. Figure 10A shows the case where the number of layers is one (comparative example), Figure 10B shows the case where the number of layers is ten (this embodiment), and Figure 10C shows the case where the number of layers is thirty (same as above). When the number of layers is one (comparative example), there are multiple frequencies at which the impedance becomes a minimum, and vibrations occur at multiple frequencies different from the fundamental resonant frequency. (Note that compared to the HBAR with only one piezoelectric layer shown in Figure 4A, the number of frequencies at which vibrations different from the fundamental resonant frequency occur are fewer. This is because in the SMR, vibrations having the fundamental resonant frequency are reflected by acoustic Bragg reflector 23.) In contrast, when the number of layers is ten or thirty, there is only one frequency at which the impedance becomes a minimum, and resonance is obtained only at the fundamental resonant frequency.

[0038] (2-4) Example of Manufacturing the Piezoelectric Resonator of the Second Embodiment Next, an example of manufacturing the piezoelectric resonator 20 of the second embodiment will be described. In this example, Sc 0.43 Al 0.57 An alloy was used, and the number of layers was 10. The acoustic Bragg reflector 23 used had one first acoustic impedance layer 231 and one second acoustic impedance layer 232.

[0039] A scanning electron microscope (SEM) photograph of the vertical cross section of the fabricated piezoelectric resonator 20 is shown in FIG. x Al 1-x A zigzag pattern is seen, which indicates that the first piezoelectric layers 211 and the second piezoelectric layers 212, whose c-axes of N are oriented in different directions, are alternately stacked in the vertical direction of the figure. x Al 1-x The direction of polarization P of N is parallel to the direction of the c-axis.

[0040] The impedance frequency characteristics of the fabricated piezoelectric resonator 20 were measured. The results are shown in Figure 12. A minimum value due to resonance at the fundamental resonance frequency is observed near 1.0 GHz. No minimum values ​​due to resonance at other frequencies are observed near this frequency, indicating that resonance is achieved only at the fundamental resonance frequency.

[0041] (3) Modifications The present invention is not limited to the above-described embodiment, and various modifications are possible.

[0042] For example, in the above embodiment, the first piezoelectric layer 111 (211) and the second piezoelectric layer 112 (212) are made of the same piezoelectric material and have the same thickness, but the two piezoelectric layers may be made of different piezoelectric materials. In that case, since the sound speed v is generally different in the first piezoelectric layer 111 (211) and the second piezoelectric layer 112 (212), the thickness d of both layers is set so that the fundamental resonant frequency v / 2d between the two layers is approximately the same value.

[0043] In the above embodiment, a polarization inverted piezoelectric laminate 11 (21) in which the polarization is inclined from directions perpendicular and parallel to the in-plane direction is used, but a polarization inverted piezoelectric laminate in which piezoelectric layers are stacked so that the polarization is perpendicular to the in-plane direction and alternately inverts, or a polarization inverted piezoelectric laminate in which piezoelectric layers are stacked so that the polarization is parallel to the in-plane direction and alternately inverts, may also be used.

[0044] While the above embodiments have shown examples of the piezoelectric resonator 10 which is an HBAR and the piezoelectric resonator 20 which is an SMR, the present invention also encompasses an FBAR piezoelectric resonator 30 shown in Fig. 13. This piezoelectric resonator 30 has a polarization-inverted piezoelectric laminate 31 having a configuration similar to that of the above-described polarization-inverted piezoelectric laminate 11 (21), a first electrode 321 and a second electrode 322 disposed on either side of the polarization-inverted piezoelectric laminate 31 in the lamination direction, and a substrate (support) 33 having a void 331 on its surface. The second electrode 322 is supported by the surface of the substrate 33 around the void 331.

[0045] DESCRIPTION OF SYMBOLS 10... Piezoelectric resonator (HBAR) 11, 21, 31... Polarization-inverted piezoelectric laminate 111, 211... First piezoelectric layer 112, 212... Second piezoelectric layer 121, 221, 321... First electrode 122, 222, 322... Second electrode 13, 33... Substrate (support) 20... Piezoelectric resonator (SMR) 23... Acoustic Bragg reflector (support) 231... First acoustic impedance layer 232... Second acoustic impedance layer 24... Substrate 30... Piezoelectric resonator (FBAR) 331... Air gap 50... Magnetron sputtering apparatus 51... Cathode electrode 52... Substrate holder P... Polarization S... Substrate to be processed SP... Sputtered particles T... Target

Claims

1. A piezoelectric resonator comprising: a) a polarization inverted piezoelectric laminate formed by laminating 10 or more piezoelectric layers, each made of a piezoelectric material and having approximately the same fundamental resonance frequency, which is the sound velocity divided by twice the thickness, such that the directions of the polarization components parallel and perpendicular to the in-plane direction of the layers are alternately inverted; b) a pair of electrodes arranged to sandwich the polarization inverted piezoelectric laminate from both sides in the lamination direction; and c) a support for supporting one of the pair of electrodes.

2. A piezoelectric resonator according to claim 1, wherein said support is an acoustic Bragg reflector.

3. A piezoelectric resonator according to claim 1, wherein said support is a substrate having a gap on its surface, said one electrode being supported on said surface around the periphery of said gap.

4. A piezoelectric resonator according to claim 1, wherein said support is a substrate having a flat surface.

5. The piezoelectric resonator according to claim 4, wherein said polarization inversion piezoelectric laminate is formed by laminating 30 or more piezoelectric layers.

6. A piezoelectric resonator as described in any one of claims 1 to 5, characterized in that the polarization inversion piezoelectric laminate is formed by laminating each piezoelectric layer such that the polarization is inclined from directions perpendicular and parallel to the piezoelectric layer, and the direction of the component parallel to the piezoelectric layer is alternately inverted.

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