JP7438674B2 - Piezoelectric thin film resonators, filters and multiplexers - Google Patents

Description

The present invention relates to piezoelectric thin film resonators, filters and multiplexers.

Piezoelectric thin film resonators are used, for example, as filters and multiplexers in wireless devices such as mobile phones. A piezoelectric thin film resonator has a structure in which a lower electrode and an upper electrode face each other with a piezoelectric film in between. The region where the lower electrode and the upper electrode face each other with the piezoelectric film in between is the resonance region.

It is known to provide an additional film within the resonance region (for example, Patent Document 1). It is known to provide a slit or an adjustment hole in the lower electrode or the upper electrode (for example, Patent Documents 2 and 3). It is known to vary the thickness of the piezoelectric film (Patent Document 4).

Japanese Patent Application Publication No. 2006-319796 Japanese Patent Application Publication No. 2006-180290 JP2009-27554A US Patent No. 9991871

In Patent Documents 1 to 4, spurious components can be suppressed. However, the resonance characteristics deteriorate. Or spurious suppression is not sufficient.

The present invention has been made in view of the above problems, and an object thereof is to suppress deterioration of resonance characteristics and/or suppress spurious.

The present invention includes a substrate, a lower electrode provided on the substrate, a piezoelectric film provided on the lower electrode, and the lower electrode to form a resonance region in which at least a part of the piezoelectric film is sandwiched, defined between an upper electrode provided on the piezoelectric film and a first surface and a second surface that reflect elastic waves within the resonance region, and including the lower electrode, the piezoelectric film, and the upper electrode; a laminated film, at least one of which has a plurality of convex portions and a plurality of concave portions, and the lower electrode, the piezoelectric film, and the upper electrode constituting the convex portion and the concave portion have the same material and the same thickness ; The piezoelectric thin film resonator is provided with a step difference between the convex portion and the concave portion that is 0.1 times or more the thickness of the laminated film.

The present invention includes a substrate, a lower electrode provided on the substrate, a piezoelectric film provided on the lower electrode, and the lower electrode to form a resonance region in which at least a part of the piezoelectric film is sandwiched, defined between an upper electrode provided on the piezoelectric film and a first surface and a second surface that reflect elastic waves within the resonance region, and including the lower electrode, the piezoelectric film, and the upper electrode; a laminated film, at least one of which has a plurality of convex portions and a plurality of concave portions, and the lower electrode, the piezoelectric film, and the upper electrode constituting the convex portion and the concave portion have the same material and the same thickness ; At least one of the plurality of convex portions and the plurality of concave portions is a piezoelectric thin film resonator provided at a period greater than 1/2 and less than 3/2 of the thickness of the laminated film.

In the above configuration, at least one of the plurality of convex portions and the plurality of concave portions may be provided at regular intervals .

In the above configuration, the planar shape of the resonance region is rectangular , and the angle between the direction of the period and the direction in which the short side of the rectangle extends is within 20 degrees.

In the above configuration, at least one of the plurality of convex portions and the plurality of concave portions may be provided without periodicity.

In the above configuration, the planar shape of at least one of the plurality of convex portions and the plurality of concave portions may be a polygon having at least one set of non-parallel opposing sides.

In the above configuration, at least one of the plurality of convex portions and the plurality of concave portions may be provided at or near the center of gravity of the resonance region.

In the above structure, the step difference between the convex portion and the concave portion may be 0.1 times or more the thickness of the laminated film.

In the above configuration, the lower electrode is in contact with a first gap, the upper electrode is in contact with a second gap, the first surface is an interface between the lower electrode and the first gap, and the second surface is in contact with the upper The structure may be an interface between the electrode and the second gap.

The present invention is a filter including the piezoelectric thin film resonator described above.

The present invention is a multiplexer including the above filter.

According to the present invention, it is possible to suppress deterioration of resonance characteristics and/or suppress spurious.

FIG. 1 is a plan view of an acoustic wave device according to Example 1. 2(a) and 2(b) are sectional views taken along the line AA in FIG. 1. 3(a) is a cross-sectional view of the laminated film in Comparative Example 1, and FIG. 3(b) and FIG. 3(c) are cross-sectional views of the laminated film in Example 1. FIGS. 4(a) to 4(d) are cross-sectional views showing simulated samples A to D. FIGS. 5(a) and 5(b) are diagrams showing simulation results showing the magnitude of impedance with respect to frequency. FIGS. 6A and 6B are plan views of a piezoelectric thin film resonator according to Modification 1 of Example 1. FIG. FIGS. 7A and 7B are plan views of piezoelectric thin film resonators according to Modifications 2 and 3 of Example 1. FIGS. FIGS. 8A and 8B are plan views of piezoelectric thin film resonators according to Modifications 4 and 5 of Example 1. FIGS. 9(a) is a plan view of the acoustic wave device according to Example 2, and FIG. 9(b) is a sectional view taken along line AA in FIG. 9(a). 10(a) is a cross-sectional view of a laminated film in Comparative Example 1, and FIG. 10(b) and FIG. 10(c) are cross-sectional views of a laminated film in Example 2. 11(a) is a circuit diagram of a filter according to a third embodiment, and FIG. 11(b) is a circuit diagram of a duplexer according to a first modification of the third embodiment.

Examples will be described below with reference to the drawings.

FIG. 1 is a plan view of an acoustic wave device according to Example 1, and FIGS. 2(a) and 2(b) are sectional views taken along line AA in FIG. FIG. 1 mainly illustrates a substrate 10, a lower electrode 12, a piezoelectric film 14, and an upper electrode 16.

As shown in FIGS. 1 to 2(b), a recess is provided on the upper surface of the substrate 10, and the recess forms a void 30. A lower electrode 12 is provided above the gap 30. A piezoelectric film 14 is provided on the lower electrode 12. An upper electrode 16 is provided on the piezoelectric film 14 . Laminated film 18 includes lower electrode 12, piezoelectric film 14, and upper electrode 16. The lower and upper surfaces of the laminated film 18 are reflective surfaces 54 and 55. The reflective surface 54 is the interface between the laminated film 18 and the void 30, and the reflective surface 55 is the interface between the laminated film 18 and the void (air). Additional films other than the lower electrode 12, piezoelectric film 14, and upper electrode 16 may be provided within the laminated film 18.

A region where the lower electrode 12 and the upper electrode 16 face each other with at least a portion of the piezoelectric film 14 in between is a resonant region 50 . Within the resonant region 50, elastic waves are reflected by reflective surfaces 54 and 55. As a result, the thickness longitudinal vibration resonates in the laminated film 18 within the resonance region 50. The wavelength of the thickness longitudinal vibration is approximately twice the thickness of the laminated film 18. The planar shape of the resonance region 50 is approximately rectangular, and the short side is L1 and the long side is L2. In plan view, the air gap 30 is larger than the resonance area 50, and the outer periphery of the air gap 30 is located outside the outer periphery of the resonance area 50. Between the outer periphery of the resonance region 50 and the outer periphery of the air gap 30 is an outer periphery region 56 . A region outside the outer periphery of the void 30 and provided with the piezoelectric film 14 is a support region 58 .

A plurality of recesses 52 or a plurality of protrusions 51 are provided within the resonance region 50. In FIG. 2(a), a plurality of recesses 52 are provided in an island shape. In FIG. 2(b), a plurality of convex portions 51 are provided in an island shape. The period P of the convex portions 51 and the concave portions 52 is approximately 1/2 of the wavelength λ of the transverse mode elastic wave 60 propagating in the lateral direction (that is, in the plane direction of the piezoelectric film 14). The wavelength λ of the elastic wave 60 propagating in the lateral direction is about 1 time or 1 to several tens of times the wavelength of the elastic wave in the thickness longitudinal vibration mode (twice the thickness of the laminated film 18). The width W of the convex portion 51 and the concave portion 52 is approximately 1/2 of the period P. Note that in FIG. 2A, the elastic wave 60 is visualized as the amplitude of the wave, and the actual elastic wave 60 is not illustrated.

A hole 35 is provided in the lower electrode 12 . The hole 35 communicates with the cavity 30 via an introduction path 34 under the lower electrode 12. The hole 35 and the introduction path 34 are for introducing an etching solution into the sacrificial layer when etching the sacrificial layer used to form the void 30.

As the substrate 10, an insulating substrate or a semiconductor substrate such as a silicon substrate, a sapphire substrate, a spinel substrate, an alumina substrate, a quartz substrate, a glass substrate, a ceramic substrate, or a GaAs substrate can be used. Examples of the lower electrode 12 and the upper electrode 16 include ruthenium (Ru), chromium (Cr), aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), and tantalum (Ta). , platinum (Pt), rhodium (Rh), or iridium (Ir), or a laminated film of these materials.

For the piezoelectric film 14, other than aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lead titanate (PbTiO ₃ ), etc. can be used. Further, for example, the piezoelectric film 14 mainly contains aluminum nitride and may contain other elements to improve resonance characteristics or piezoelectricity. For example, the piezoelectricity of the piezoelectric film 14 is improved by using scandium (Sc), two elements, a group 2 element and a group 4 element, or two elements, a group 2 element and a group 5 element, as additive elements. do. Therefore, the effective electromechanical coupling coefficient of the piezoelectric thin film resonator can be improved. Group 2 elements are, for example, calcium (Ca), magnesium (Mg), strontium (Sr) or zinc (Zn). Group 4 elements are, for example, titanium, zirconium (Zr) or hafnium (Hf). Group 5 elements are, for example, tantalum, niobium (Nb) or vanadium (V). Furthermore, the piezoelectric film 14 mainly contains aluminum nitride and may also contain boron (B).

3(a) is a cross-sectional view of the laminated film in Comparative Example 1, and FIG. 3(b) and FIG. 3(c) are cross-sectional views of the laminated film in Example 1. As shown in FIG. 3A, the laminated film 18 of Comparative Example 1 was not provided with any convex portions or concave portions. A transverse mode acoustic wave 60 propagates within the laminated film 18 . The elastic wave 60 is a visualized amplitude. When the transverse mode elastic wave 60 propagates, transverse mode spurious is generated. As shown in FIG. 1, when the resonant region 50 is substantially rectangular, the transverse mode elastic waves 60 reflected from opposite sides of the resonant region 50 become standing waves and spurious waves are likely to be generated.

As shown in FIG. 3(b), in Example 1, a convex portion 51 and a concave portion 52 are provided in the laminated film 18. The height of the step between the convex portion 51 and the concave portion 52 is d, and the period P of the concave portion 52 is λ/2. Since the geometrical shape is discontinuous at the boundary between the convex portion 51 and the concave portion 52, the transverse mode elastic wave 60 is reflected. Therefore, the boundary between the convex portion 51 and the concave portion 52 becomes a node 62 of the transverse mode elastic wave 60. The boundaries between the convex portions 51 and the concave portions 52 are arranged at intervals of 1/4 of the wavelength λ of the elastic wave 60. Therefore, the elastic wave 60 cannot exist, and the transverse mode elastic wave 60 cannot propagate. Thereby, spurious caused by the transverse mode elastic wave 60 can be suppressed.

As shown in FIG. 3C, in Example 1, the layer structure of the laminated film 18 in the convex portion 51 and the concave portion 52 is substantially the same. That is, the material and thickness of the lower electrode 12 are approximately the same in the convex portion 51 and the concave portion 52, the material and thickness of the piezoelectric film 14 are approximately the same in the convex portion 51 and the concave portion 52, and The material and thickness of the convex portion 51 and the concave portion 52 are substantially the same. Further, when an additional film is provided in the laminated film 18, the material and thickness of the additional film are substantially the same for the convex portions 51 and the concave portions 52. As a result, the propagation characteristics of the longitudinal vibration mode elastic wave 64 in the convex portion 51 and the concave portion 52 are substantially the same. Therefore, for example, the resonant frequencies of the convex portion 51 and the concave portion 52 are the same, and deterioration of resonance characteristics can be suppressed.

[simulation]
Transverse mode spurious in Comparative Example 1 and Example 1 was simulated. The simulation conditions are as follows.
Lower electrode 12: Ruthenium film with a thickness of 198 nm Piezoelectric film 14: Aluminum nitride film with a thickness of 981 nm Upper electrode 16: Ruthenium film with a thickness of 217 nm Length of short side L1 of resonance region 50: 80 μm
Length of long side L2 of resonance region 50: 327 μm
The resonance region 50 has a size such that the impedance is approximately 50Ω at 2.5GHz.

FIGS. 4(a) to 4(d) are cross-sectional views showing simulated samples A to D. 4(a) to FIG. 4(d) illustrate one period of the laminated film 18 of the convex portions 51 and the concave portions 52.

As shown in FIG. 4(a), sample A is Comparative Example 1, and the convex portion 51 and the concave portion 52 are not provided. In this structure, the wavelength λ of the transverse mode acoustic wave 60 is approximately 18.2 μm.

As shown in FIG. 4(b), in sample B, the period P of the convex portions 51 and the concave portions 52 was set to λ/2=9.1 μm. The distance between the center of the convex portion 51 and the center of the concave portion 52 is λ/4. The height d of the step between the convex portion 51 and the concave portion 52 was set to 0.15 times the thickness t of the laminated film 18.

As shown in FIG. 4(c), in sample C, the period P of the convex portions 51 and the concave portions 52 is set to λ/2 = 9.1 μm, and the height d of the step between the convex portions 51 and the concave portions 52 is set to the laminated film 18. The thickness was set to 0.25 times the thickness t.

As shown in FIG. 4(d), in sample D, the period P of the convex portions 51 and the concave portions 52 was 6.05 μm. This corresponds to approximately 2/3×λ/2. The height d of the step between the convex portion 51 and the concave portion 52 was set to 0.15 times the thickness t of the laminated film 18.

FIGS. 5(a) and 5(b) are diagrams showing simulation results showing the magnitude of impedance with respect to frequency. The vertical axis is in arbitrary units. FIG. 5(b) is an enlarged view of the range 65 in FIG. 5(a). As shown in FIG. 5(a), the resonant frequency fr and the anti-resonant frequency fa do not change from samples A to D. The magnitude of the impedance at the resonant frequency fr and the anti-resonant frequency fa is also the same for samples A to D. In this way, the resonance characteristics of samples A to D are almost unchanged. This is because the layer structure of the laminated film 18 in the convex portion 51 and the concave portion 52 is substantially the same.

As shown in FIG. 5(b), four spurious signals 66a to 66d are generated in a frequency range lower than the resonance frequency fr. A dotted line 67 in a frequency range lower than the resonant frequency fr indicates an ideal impedance with no spurious generated. Compared to sample A, samples B to D have impedances closer to the dotted line 67, and spurious waves are suppressed. In this way, since the laminated film 18 has the periodic convex portions 51 and concave portions 52, spurious waves are suppressed.

Looking at each of the spurious signals 66a to 66d, in the spurious signal 66a, the magnitudes of the peaks of samples B to D are approximately the same, and are smaller than the peak of sample A. In samples B to D, the spurious 66a can be suppressed to the same extent.

In the spurious 66b, the peak of sample B is comparable to the peak of sample A. The peak of sample C is smaller than the peak of sample B, and the peak of sample D is smaller than the peak of sample C.

For spurious 66c, the peaks of samples B and D are comparable and smaller than the peak of sample A. The peak of sample C is smaller than the peaks of samples B and D.

For spurious 66d, the peaks of samples B and D are comparable and smaller than the peak of sample A. The peak of sample C is smaller than the peaks of samples B and D.

As described above, samples B to D have smaller peaks of spurious waves 66a to 66d than sample A, and can suppress spurious waves 66a to 66d.

Comparing sample C with sample B, the peaks of samples C and B are comparable for spurious 66a, but the peak of sample C is lower than sample B for spurious 66b to 66d. In this way, sample C, which has a large step height d, can suppress spurious noise more than sample B.

Comparing sample D with B, for spurious 66a, 66c, and 66d, the peaks of samples D and B are comparable, but for spurious 66b, the peak of sample D is smaller than the peak of sample B, and the peak of sample D is smaller than that of sample D. small. In this way, in the sample C in which the periods P of the convex portions 51 and the concave portions 52 are different, it is possible to suppress specific spurious waves 66b.

As described above, the height d of the step between the convex portions 51 and the concave portions 52 is preferably 0.1 times or more, more preferably 0.15 times or more, and still more preferably 0.25 times or more the thickness t of the laminated film 18. preferable. If the height d is too large, the piezoelectric film 14 will break between the convex portions 51 and the concave portions 52. Therefore, the height d is preferably 0.9 times or less than the thickness t, more preferably 0.7 times or less, and even more preferably 0.5 times or less.

The period P of the convex portions 51 and the concave portions 52 is preferably about 1/2 of the wavelength λ of the transverse mode elastic wave 60. Depending on the spurious to be suppressed, the period P can be appropriately set, for example, in a range greater than λ/4λ and smaller than 3λ/4.

[Modification 1 of Example 1]
FIGS. 6A and 6B are plan views of a piezoelectric thin film resonator according to Modification 1 of Example 1. FIG. As shown in FIG. 6(a), the length of the short side L1 of the resonance region 50 is equal to or less than 1/2 of the length of the long side L2. As shown in FIG. 6(b), the length of the short side L1 of the resonance region 50 is ⅓ or less of the length of the long side L2.

When a high-power high-frequency signal is applied between the lower electrode 12 and the upper electrode 16, the laminated film 18 in the resonance region 50 generates heat. At the periphery of the resonance region 50, heat is conducted through the laminated film 18 and is easily radiated to the substrate 10. Since the distance to the outer periphery of the resonance region 50 is long in the center of the resonance region 50, heat is not easily radiated. As a result, when the temperature of the laminated film 18 at the center of the resonance region 50 rises, the laminated film 18 will be destroyed. For this reason, the power durability decreases.

Therefore, as in the first modification of the first embodiment, the short side L1 is set to be 1/2 or less or 1/3 or less of the long side L2. As a result, the distance between the central portion of the resonant region 50 and the outer periphery of the resonant region 50 is shortened, and heat dissipation from the central portion of the resonant region 50 is improved. Therefore, power durability is improved.

However, when the short side L1 of the resonance region 50 becomes short, a standing wave having a large amplitude of the transverse mode elastic wave 60 tends to exist between the long side L2. This makes spurious signals more likely to be generated. Therefore, the laminated film 18 has a convex portion 51 and a concave portion 52 having a period P in the direction in which the short side L1 extends. Thereby, spurious components can be suppressed.

[Modification 2 of Example 1]
FIG. 7A is a plan view of a piezoelectric thin film resonator according to a second modification of the first embodiment. As shown in FIG. 7A, the convex portions 51 or concave portions 52 of the resonance region 50 are provided irregularly. This makes it difficult for standing waves with large amplitudes to exist in the resonance region 50 for the plurality of transverse mode elastic waves. Therefore, spurious signals can be suppressed.

[Modification 3 of Example 1]
FIG. 7(b) is a plan view of the piezoelectric thin film resonator according to the third modification of the first embodiment. As shown in FIG. 7B, the planar shape of the convex portion 51 or the concave portion 52 of the resonance region 50 is a polygonal shape that does not have at least one set of parallel opposing sides. As a result, the transverse mode elastic waves reflected at the boundary between the convex portions 51 and the concave portions 52 are repeatedly reflected within the convex portions 51 or the concave portions 52, making it difficult for standing waves with large amplitudes to exist. Therefore, spurious signals can be suppressed.

[Modification 4 of Example 1]
FIG. 8A is a plan view of a piezoelectric thin film resonator according to Modification Example 4 of Example 1. As shown in FIG. 8A, the planar shape of the resonance region 50 is approximately rectangular, and the length of the short side L1 is less than or equal to 1/2 of the length of the long side L2. In this way, when the short side L1 is much shorter than the long side L2, it is difficult for a transverse mode standing wave to exist in the extending direction of the long side L2, and a transverse mode standing wave exists in the extending direction of the short side L1. It's easy to do. Therefore, the convex portion 51 and the concave portion 52 may have a rectangular shape extending in the direction in which the long side L2 extends.

[Modification 5 of Example 1]
FIG. 8(b) is a plan view of a piezoelectric thin film resonator according to a fifth modification of the first embodiment. As shown in FIG. 8(b), the planar shape of the resonance region 50 is a substantially elliptical shape having a short axis L3 and a long axis L4. The convex portion 51 or the concave portion 52 is provided near the center 69 of the resonance region 50 of the long axis L4 (the point where the short axis L3 and the long axis L4 intersect). The planar shape of the convex portion 51 or the concave portion 52 is a crescent.

When the planar shape of the resonance region 50 is approximately elliptical, the transverse mode standing waves are concentrated near the focal point. Therefore, the laminated film 18 tends to generate heat at the focal point near the center 69 of the resonance region 50. Therefore, by providing the convex portion 51 or the concave portion 52 at or near the center 69 of the resonance region 50, it becomes difficult for standing waves to concentrate near the center 69. Therefore, heat generation in the laminated film 18 near the center 69 of the resonance region 50 can be suppressed. Therefore, power durability can be improved. Similarly to the first embodiment, spurious noise can also be suppressed.

According to the first embodiment and its modifications, at least one of the resonance regions 50 has a plurality of convex portions 51 and a plurality of concave portions 52, and the layer configurations of the laminated film 18 in the convex portions 51 and the concave portions 52 are approximately the same. be. The laminated film 18 is defined between a reflective surface 54 (first surface) and a reflective surface 55 (second surface) that reflect acoustic waves, and includes a lower electrode 12, a piezoelectric film 14, and an upper electrode 16.

As a result, as shown in FIG. 5(a), the resonance characteristics of the convex portion 51 and the concave portion 52 are approximately the same. Therefore, deterioration of resonance characteristics such as Q value can be suppressed. Note that the layer structure of the laminated film 18 in the convex portions 51 and the concave portions 52 is substantially the same, which means that the material of each of the plurality of layers constituting the laminated film 18 is approximately the same in the convex portions 51 and the concave portions 52. The thickness of the convex portion 51 and the concave portion 52 are substantially the same. The fact that the materials and thicknesses are substantially the same allows for errors that occur when the laminated film 18 is formed on the convex portions 51 and the concave portions 52 at the same time, and errors equivalent to manufacturing errors.

When the lower surface of the lower electrode 12 is in contact with the air gap 30 (first air gap) and the upper surface of the upper electrode 16 is in contact with the air (second air gap), the reflective surface 54 corresponds to the interface between the lower electrode 12 and the air gap 30. However, the reflective surface 55 corresponds to the interface between the upper electrode 16 and air.

As in Example 1 and Modifications 1 and 4 thereof, at least one of the plurality of convex portions 51 and concave portions 52 is provided at a substantially constant period P. Thereby, spurious can be suppressed as shown in FIG. 5(b). Note that the substantially constant period P allows an error of approximately ±1/16 of the wavelength λ of the elastic wave propagating in the lateral direction.

The period P is larger than 1/4 and smaller than 3/4 of the wavelength λ of the elastic wave 60 propagating in the lateral direction. Thereby, the presence of standing waves of the transverse mode elastic waves 60 can be suppressed, and spurious waves can be suppressed. Preferably, the substantially constant period P is larger than 3/8 and smaller than 5/8 of the wavelength λ of the elastic wave 60 propagating in the lateral direction. Assuming that the wavelength of the elastic wave 60 propagating in the horizontal direction is comparable to the wavelength of the elastic wave of longitudinal vibration, the period P is preferably larger than 1/2 and smaller than 3/2 of the thickness of the laminated film 18, More preferably, it is larger than 3/4 and smaller than 5/4.

The planar shape of the resonance region 50 is approximately rectangular, and the direction of the approximately constant period P is approximately parallel to the short side L1 of the approximately rectangle. Thereby, spurious on the short side L1 where spurious is likely to be generated can be suppressed. Note that "substantially parallel" allows an error to the extent that spurious noise can be suppressed. The angle between the direction of the period P and the stretching direction of the short side L1 is, for example, in the range of ±20°.

As in the second modification of the first embodiment, at least one of the plurality of convex portions 51 and concave portions 52 may be provided irregularly (that is, without periodicity). This makes it possible to suppress spurious signals in a plurality of transverse modes.

In Embodiment 1 and Modifications 1, 2, and 4, examples of the planar shape of the convex portion 51 or the recessed portion 52 are approximately square and approximately rectangular, but the planar shape of the recessed portion 52 is approximately circular, approximately elliptical, It may be approximately elliptical.

As in the third modification of the first embodiment, the planar shape of at least one of the plurality of convex portions 51 and concave portions 52 may be a polygonal shape having at least one set of non-parallel opposing sides. This makes it possible to suppress spurious signals in a plurality of transverse modes.

As in the fifth modification of the first embodiment, at least one of the plurality of convex portions 51 and concave portions 52 may be provided at or near the center 69 (for example, the center of gravity) of the resonance region 50. Standing waves tend to gather at the center 69 of the resonance region 50. Therefore, by providing the convex portion 51 or the concave portion 52 at the center 69 of the resonant region 50, heat generation of the laminated film 18 near the center 69 of the resonant region 50 can be suppressed.

When the planar shape of the resonance region 50 is approximately elliptical, standing waves tend to gather at the focal point of the ellipse of the resonance region 50. Therefore, it is preferable to provide the convex portion 51 or the concave portion 52 at the focal point near the center 69 of the resonance region 50.

9(a) is a plan view of the acoustic wave device according to Example 2, and FIG. 9(b) is a sectional view taken along line AA in FIG. 9(a). As shown in FIGS. 9A and 9B, an additional film 20 is provided on the laminated film 18 between the reflective surfaces 54 and 55. The piezoelectric film 14 is not provided with any convex portions or concave portions. The period P of the additional film 20 is approximately 1/2 of the wavelength λ of the transverse mode acoustic wave 60. The width W of the additional film 20 is approximately 1/2 of the period P. The other configurations are the same as those in Example 1, and their explanation will be omitted.

10(a) is a cross-sectional view of a laminated film in Comparative Example 1, and FIG. 10(b) and FIG. 10(c) are cross-sectional views of a laminated film in Example 2. As shown in FIG. 10(a), as explained in FIG. 3(a), in Comparative Example 1, the transverse mode elastic wave 60 becomes a standing wave and spurious waves are likely to be generated.

As shown in FIG. 10(b), in Example 2, additional films 20 are provided on the upper electrode 16 at a period P. The period P is λ/2. The acoustic impedance is different between the region 53a where the additional film 20 is provided and the region 53b where it is not provided. Therefore, the geometrical shape becomes discontinuous at the boundary between the regions 53a and 53b, and the transverse mode elastic wave 60 is reflected. Therefore, similarly to FIG. 3(b) of Example 1, the elastic wave 60 cannot exist, and the transverse mode elastic wave 60 cannot propagate. Thereby, spurious caused by the transverse mode elastic wave 60 can be suppressed.

As shown in FIG. 10(c), in Example 2, the thickness of the laminated film 18 is different between regions 53a and 53b. Therefore, the propagation characteristics of the elastic wave 64a of longitudinal vibration in the region 53a and the propagation characteristic of the elastic wave 64b of longitudinal vibration in the region 53b are different. For example, the resonant frequencies of regions 53a and 53b are different. As a result, resonance characteristics such as the Q value are lowered compared to the first embodiment.

According to the second embodiment, the plurality of additional films 20 are provided in the laminated film 18 at a period larger than 1/4 and smaller than 3/4 of the wavelength λ of the elastic wave propagating in the lateral direction. Thereby, spurious caused by the transverse mode elastic wave 60 can be suppressed. It is preferable that the period P is larger than 3/8 and smaller than 5/8 of the wavelength λ of the elastic wave 60 propagating in the lateral direction. Assuming that the wavelength of the elastic wave 60 propagating in the horizontal direction is comparable to the wavelength of the elastic wave of longitudinal vibration, the period P is preferably larger than 1/2 and smaller than 3/2 of the thickness of the laminated film 18, More preferably, it is larger than 3/4 and smaller than 5/4.

The plurality of additional films 20 are provided at a substantially constant period P. Thereby, spurious components can be further suppressed. Note that, as in the first embodiment, the substantially constant period P allows an error of about ±1/16 of the wavelength λ of the elastic wave propagating in the lateral direction.

The planar shape of the resonance region 50 is substantially rectangular, and the direction of the substantially constant period P is substantially parallel to the direction in which the short side L1 of the substantially rectangular shape extends. Thereby, spurious on the short side L1 where spurious is likely to be generated can be suppressed. Note that "substantially parallel" allows an error to the extent that spurious noise can be suppressed. The angle between the direction of the period P and the stretching direction of the short side L1 is, for example, in the range of ±20°.

In Embodiments 1 and 2 and their modifications, the case where a concave portion serving as a void 30 is provided on the top surface of the substrate 10 has been described as an example, but the top surface of the substrate 10 is flat and the void has a dome-shaped bulge. may have.

Furthermore, in Examples 1 and 2 and their modifications, an example has been described in which the reflecting surface 54 is an interface between the laminated film 18 and the void 30, but the reflecting surface 54 is an interface between the laminated film 18 and an acoustic reflective film that reflects elastic waves. It can also be an interface. In the acoustic reflection film, films with high acoustic impedance and films with low acoustic impedance are alternately provided. The film thicknesses of the film with high acoustic impedance and the film with low acoustic impedance are, for example, approximately 1/4 of the wavelength of the longitudinally vibrating elastic wave.

Although an example has been described in which the planar shape of the resonance region 50 is substantially rectangular or substantially elliptical, the planar shape of the resonance region 50 may be a substantially polygonal shape such as a substantially pentagonal shape. It may be a substantially polygonal shape in which at least one pair of opposing sides are not parallel.

Example 3 is an example of a filter and a duplexer using the piezoelectric thin film resonators of Examples 1 and 2 and their modifications. FIG. 11(a) is a circuit diagram of a filter according to the third embodiment. As shown in FIG. 11(a), one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P4 are connected in parallel between the input terminal Tin and the output terminal Tout. The piezoelectric thin film resonator of Example 1 and its modifications can be used for at least one of the one or more series resonators S1 to S4 and the one or more parallel resonators P1 to P4. The number of resonators of the ladder filter can be set as appropriate.

FIG. 11(b) is a circuit diagram of a duplexer according to a first modification of the third embodiment. As shown in FIG. 11(b), a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 passes signals in the transmission band among the signals input from the transmission terminal Tx to the common terminal Ant as transmission signals, and suppresses signals at other frequencies. The reception filter 42 passes signals in the reception band among the signals input from the common terminal Ant to the reception terminal Rx as reception signals, and suppresses signals at other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the third embodiment. A high-power high-frequency signal is applied to the transmission filter 40 . Therefore, it is preferable to use the filter of the third embodiment as the transmission filter 40.

Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also be used.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention as described in the claims. Changes are possible.

10 Substrate 12 Lower electrode 14 Piezoelectric film 16 Upper electrode 18 Laminated film 20 Additional film 30 Gap 50 Resonance region 51 Projection 52 Recess 53a, 53b Region 54, 55 Reflection surface

Claims (11)

A substrate and
a lower electrode provided on the substrate;
a piezoelectric film provided on the lower electrode;
an upper electrode provided on the piezoelectric film and forming a resonance region sandwiching at least a portion of the piezoelectric film with the lower electrode;
The resonant region is defined between a first surface and a second surface that reflect elastic waves, includes the lower electrode, the piezoelectric film, and the upper electrode, and at least one has a plurality of convex portions and a plurality of concave portions. and a laminated film in which the lower electrode, the piezoelectric film, and the upper electrode constituting the convex portion and the concave portion have the same material and thickness , respectively;
Equipped with
A piezoelectric thin film resonator, wherein the step between the convex portion and the concave portion is 0.1 times or more the thickness of the laminated film. A substrate and
a lower electrode provided on the substrate;
a piezoelectric film provided on the lower electrode;
an upper electrode provided on the piezoelectric film and forming a resonance region sandwiching at least a portion of the piezoelectric film with the lower electrode;
The resonant region is defined between a first surface and a second surface that reflect elastic waves, includes the lower electrode, the piezoelectric film, and the upper electrode, and at least one has a plurality of convex portions and a plurality of concave portions. and a laminated film in which the lower electrode, the piezoelectric film, and the upper electrode constituting the convex portion and the concave portion have the same material and thickness , respectively;
Equipped with
In the piezoelectric thin film resonator, at least one of the plurality of convex portions and the plurality of concave portions are provided at a period larger than 1/2 and smaller than 3/2 of the thickness of the laminated film. 3. The piezoelectric thin film resonator according to claim 1, wherein at least one of the plurality of convex portions and the plurality of concave portions are provided at a constant period. 4. The piezoelectric thin film resonator according to claim 2, wherein the resonance region has a rectangular planar shape, and the angle between the direction of the period and the direction in which the short side of the rectangle extends is within 20 degrees. The piezoelectric thin film resonator according to claim 1, wherein at least one of the plurality of convex portions and the plurality of concave portions are provided without periodicity. 2. The piezoelectric thin film resonator according to claim 1, wherein the planar shape of at least one of the plurality of convex portions and the plurality of concave portions is a polygonal shape having at least one set of non-parallel opposing sides. The piezoelectric thin film resonator according to any one of claims 1 to 6, wherein at least one of the plurality of convex portions and the plurality of concave portions is provided at or near the center of gravity of the resonance region. 3. The piezoelectric thin film resonator according to claim 2, wherein the step difference between the convex portion and the concave portion is 0.1 times or more the thickness of the laminated film. The lower electrode is in contact with a first gap, the upper electrode is in contact with a second gap, the first surface is an interface between the lower electrode and the first gap, and the second surface is an interface between the upper electrode and the first gap. 9. The piezoelectric thin film resonator according to claim 1, wherein the piezoelectric thin film resonator is an interface with two voids. A filter comprising a piezoelectric thin film resonator according to any one of claims 1 to 9 . A multiplexer comprising a filter according to claim 10 .

Images