Acoustic wave device

Abstract

An acoustic wave device includes a support substrate including a top surface and a bottom surface and a cavity or air gap, a piezoelectric layer on the support substrate and including a top surface and a bottom surface, and an electrode on the top surface of the piezoelectric layer and including a top surface and a bottom surface. At least a portion of the electrode is over the cavity or air gap and satisfies the equation 0.002Tg ≤ 0.5(Lb - Ls) < Te, where Ls is a maximum length of the top surface of the electrode, Lb is a maximum length of the bottom surface of the electrode, Tg is a distance between the top surface of the piezoelectric layer and the top surface of the support substrate, and Te is a thickness of the electrode.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 121,343, filed December 4, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to acoustic devices, each comprising a piezoelectric layer of lithium niobate or lithium tantalate. Background Technology

[0004] In known acoustic devices, adjusting the frequency and suppressing stray noise are both difficult.

[0005] It is known that the frequency of an acoustic device can be adjusted by changing the thickness of a protective film covering the electrodes (e.g., interdigital transducer electrodes) of that device. However, when the protective film covers both the series and parallel arm resonators of a trapezoidal filter, the change in the film thickness affects both the series and parallel arm resonators, leading to an increase in fractional bandwidth and consequently, more spurious emissions. Summary of the Invention

[0006] In a preferred embodiment of the invention, the acoustic device includes at least one electrode located on the piezoelectric layer and at least partially above the cavity or air gap, such that when the temperature of the acoustic device or the ambient temperature of the acoustic device changes, the stress on the piezoelectric layer side of the electrode can be dispersed, which can reduce or suppress polarization reversal in the piezoelectric layer. The equation 0.002Tg ≤ 0.5(Lb-Ls) < Te can be satisfied, where Ls is the maximum length of the top surface of the electrode, Lb is the maximum length of the bottom surface of the electrode, and Tg is the distance between the top surface of the piezoelectric layer and the cavity or air gap.

[0007] According to a preferred embodiment of the present invention, an acoustic wave device includes: a support substrate; a piezoelectric layer including a first main surface and a second main surface, the second main surface being on opposite sides of the piezoelectric layer on the first main surface and in a first direction relative to the first main surface; at least one pair of functional electrodes facing each other in a second direction intersecting the first direction and disposed adjacent to each other on the first main surface; and a space defining a cavity in the support substrate or an air gap between the support substrate and the piezoelectric layer. In a plan view along the first direction, the space overlaps with at least a portion of the at least one pair of functional electrodes. Half of the difference between the maximum length of the bottom surface of one of the at least one pair of functional electrodes in the second direction and the maximum length of the top surface of one of the at least one pair of functional electrodes in the second direction is equal to or greater than about 0.2% of the thickness of the piezoelectric layer from the first main surface to the space, and equal to or less than the thickness of one of the at least one pair of functional electrodes in the first direction.

[0008] Half of the difference between the maximum length of the bottom surface of one of the at least one pair of functional electrodes in the second direction and the maximum length of the top surface of one of the at least one pair of functional electrodes in the second direction may be equal to or greater than about 0.9% of the thickness of the piezoelectric layer from the first main surface to the space.

[0009] Half of the difference between the maximum length of the bottom surface of one of the at least one pair of functional electrodes in the second direction and the maximum length of the top surface of one of the at least one pair of functional electrodes in the second direction may be equal to or greater than about 2% of the thickness of the piezoelectric layer from the first main surface to the space.

[0010] In a cross section including a first direction and a second direction, one of the functional electrodes in at least a pair of functional electrodes may include a first side and a second side, and the first side and / or the second side may include a curved portion.

[0011] The thickness of the piezoelectric layer can be equal to or greater than about 0.05 μm and equal to or less than about 1 μm. An electrically insulating layer can be disposed between the piezoelectric layer and the supporting substrate.

[0012] One of the at least one pair of functional electrodes may include a plurality of first electrodes, a first bus electrode connected to the plurality of first electrodes, a plurality of second electrodes, and a second bus electrode connected to the plurality of second electrodes. The thickness of the piezoelectric layer may be equal to or greater than 2p, where p is the center-to-center distance between adjacent first and second electrodes.

[0013] The piezoelectric layer may include lithium niobate or lithium tantalate. A first-order thickness shear mode bulk wave may be used as the dominant wave. One of the at least one pair of functional electrodes may include at least one pair of electrodes facing each other, and the ratio d / p may be equal to or less than about 0.5, where d is the thickness of the piezoelectric layer and p is the center-to-center distance between the at least one pair of adjacent and facing electrodes.

[0014] The functional electrode can be an IDT electrode, and the plate wave can be used as the main wave.

[0015] According to a preferred embodiment of the present invention, an acoustic wave device includes: a support substrate, including a top surface and a bottom surface, and a cavity or air gap; a piezoelectric layer on the top surface of the support substrate, including a top surface and a bottom surface; and an electrode on the top surface of the piezoelectric layer, including a top surface and a bottom surface. At least a portion of the electrode is above the cavity or air gap. The equation 0.002Tg ≤ 0.5(Lb-Ls) < Te is satisfied, where Ls is the maximum length of the top surface of the electrode, Lb is the maximum length of the bottom surface of the electrode, Tg is the distance between the top surface of the piezoelectric layer and the top surface of the support substrate, and Te is the thickness of the electrode.

[0016] It can satisfy the equation 0.009Tg≤0.5(Lb-Ls), or it can satisfy the equation 0.02Tg≤0.5(Lb-Ls).

[0017] The first and / or second side of the electrode may include a bent portion. The electrode may include a first electrode, a first bus electrode connected to the first electrode, a second electrode, and a second bus electrode connected to the second electrode. The piezoelectric layer may include lithium niobate or lithium tantalate. A first-order thickness shear mode volume wave may be used as the dominant wave. The electrode may be an IDT electrode, and a plate wave may be used as the dominant wave.

[0018] The above and other elements, features, steps, characteristics, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings. Attached Figure Description

[0019] Figure 1A This is a schematic perspective view showing an acoustic device according to a first preferred embodiment of the present invention.

[0020] Figure 1B This is a plan view showing the electrode structure on the piezoelectric layer.

[0021] Figure 2 It is along Figure 1A The cross-sectional view taken from line AA in the diagram.

[0022] Figure 3A This is a schematic elevation cross-sectional view showing a Lamb wave propagating in a piezoelectric film of an acoustic device.

[0023] Figure 3B This is a cross-sectional view showing a bulk wave propagating in a piezoelectric film of an acoustic device.

[0024] Figure 4 The diagram schematically illustrates the body waves that occur when a voltage is applied across the electrodes of an acoustic device.

[0025] Figure 5 This is a graph showing the resonant characteristics of an acoustic wave device according to a first preferred embodiment of the present invention.

[0026] Figure 6 This is a graph showing the relationship between the ratio d / p and the fractional bandwidth of the acoustic device as a resonator.

[0027] Figure 7 This is a plan view of an acoustic device according to a second preferred embodiment of the present invention.

[0028] Figure 8 This is a partial cross-sectional perspective view of an acoustic device according to a third preferred embodiment of the present invention.

[0029] Figure 9 This is a close-up cross-sectional view of the electrodes of the acoustic device according to the fourth preferred embodiment of the present invention.

[0030] Figure 10 and Figure 11 It is a graph showing the relationship between von Mises stress and the equation 0.5(Lb-Ls) / Tg.

[0031] Figure 12 and Figure 13 This is a close-up cross-sectional view of the first and second modification electrodes of the acoustic device according to a fourth preferred embodiment of the present invention.

[0032] Figure 14 This is a diagram showing the stress intensity of an acoustic device with a second modification electrode.

[0033] Figure 15 This is a diagram showing the stress intensity of the first modified electrode of the acoustic device with comparative examples.

[0034] Figure 16 This is a diagram showing the stress intensity of a comparative acoustic device. Detailed Implementation

[0035] A preferred embodiment of the present invention includes a piezoelectric layer 2 made of lithium niobate or lithium tantalate, and a first electrode 3 and a second electrode 4 facing each other in a direction intersecting the thickness direction of the piezoelectric layer 2.

[0036] A bulk wave in the first thickness shear mode is used. Furthermore, the first electrode 3 and the second electrode 4 can be adjacent electrodes, and when the thickness of the piezoelectric layer 2 is d, and the center-to-center distance between the centers of the first electrode 3 and the second electrode 4 is p, the ratio d / p can, for example, be less than or equal to about 0.5. With this configuration, the size of the acoustic device can be reduced, and the Q value can be increased. A Lamb wave as a plate wave can be used, and resonance characteristics due to the Lamb wave can be obtained.

[0037] The acoustic device 1 includes a piezoelectric layer 2 made of LiNbO3. The piezoelectric layer 2 can also be made of LiTaO3. The cutting angle of the LiNbO3 or LiTaO3 can be Z-cut, or it can be rotationally Y-cut or X-cut. For example, a propagation direction of approximately ±30° for Y or X propagation can be used. The thickness of the piezoelectric layer 2 is not limited and can be greater than or equal to approximately 50 nm and less than or equal to approximately 1000 nm, for example, to effectively excite a first thickness shear mode. The piezoelectric layer 2 has opposing first main surfaces 2a and second main surfaces 2b (or top and bottom surfaces). Electrodes 3 and 4 are disposed on the first main surface 2a. Electrode 3 is an example of a "first electrode," and electrode 4 is an example of a "second electrode." Figure 1A and Figure 1B In this structure, multiple electrodes 3 are connected to a first busbar 5, and multiple electrodes 4 are connected to a second busbar 6. Electrodes 3 and 4 may intersect each other. Electrodes 3 and 4 may each have a rectangular or substantially rectangular shape and may have a length direction. In a direction perpendicular to the length direction, each electrode 3 is opposite to its adjacent electrode in the electrode 4. Both the length direction of electrodes 3 and 4 and the direction perpendicular to their length directions are directions that intersect the thickness direction of the piezoelectric layer 2. For this reason, it can be considered that each electrode 3 is opposite to its adjacent electrode in the electrode 4 in the direction intersecting the thickness direction of the piezoelectric layer 2. Alternatively, the length directions of electrodes 3 and 4 may be interchanged with the directions perpendicular to their length directions, such as... Figure 1A and Figure 1B As shown. In other words, in Figure 1A and Figure 1B In this configuration, electrodes 3 and 4 can extend in the directions in which the first busbar 5 and the second busbar 6 extend. In this case, in... Figure 1A and Figure 1B In this configuration, the first busbar 5 and the second busbar 6 extend in the direction in which the electrodes 3 and 4 extend. Adjacent electrode pairs, one connected to a first potential and the other to a second potential, are arranged in a direction perpendicular to the length direction of the electrodes 3 and 4. The adjacent state of the electrodes 3 and 4 does not mean that they are in direct contact, but rather that they are separated by a gap. When the electrodes 3 and 4 are adjacent, no electrodes connected to the hot electrode or ground electrode, including other electrodes 3 and 4, are placed between them.

[0038] The number of electrode pairs 3 and 4 is not necessarily an integer and can be 1.5 pairs, 2.5 pairs, etc. For example, 1.5 electrode pairs means there are 3 electrodes 3 and 4, where two electrodes are in an electrode pair and one is not in a pair. For example, the center-to-center distance between the centers of electrodes 3 and 4 (i.e., the spacing between electrodes 3 and 4) can fall within the range of greater than or equal to about 1 μm and less than or equal to about 10 μm. The center-to-center distance between the centers of electrodes 3 and 4 can be the distance between the centers of the width dimensions of electrodes 3 and 4 in a direction perpendicular to the length direction of electrodes 3 and 4. In addition, when there is more than one electrode 3 and 4 (e.g., when the number of electrodes 3 and 4 is two such that electrodes 3 and 4 define an electrode pair, or when the number of electrodes 3 and 4 is three or more such that electrodes 3 and 4 define 1.5 or more electrode pairs), the center-to-center distance between the centers of electrodes 3 and 4 represents the average of the distances between any adjacent electrodes 3 and 4 in 1.5 or more electrode pairs. For example, the width of each of electrodes 3 and 4 (i.e., the dimension of each of electrodes 3 and 4 in the direction perpendicular to the length direction) can fall within the range of approximately 150 nm greater than or equal to and approximately 1000 nm less than or equal to. The center-to-center distance between the centers of electrodes 3 and 4 can be the distance between the center of the dimension (width dimension) of electrode 3 in the direction perpendicular to the length direction of electrode 3 and the center of the dimension (width dimension) of electrode 4 in the direction perpendicular to the length direction of electrode 4.

[0039] Since a Z-cut piezoelectric layer 2 can be used, the direction perpendicular to the length direction of electrodes 3 and 4 is also perpendicular to the polarization direction of piezoelectric layer 2. This does not apply when a piezoelectric material with a different cut angle is used as piezoelectric layer 2. The term "perpendicular" is not limited to the case of strict perpendicularity, but can be substantially perpendicular (the angle formed between the direction perpendicular to the length direction of electrodes 3 and 4 and the polarization direction can be, for example, about 90° ± 10°).

[0040] The support substrate 8 can be laminated to the second main surface 2b of the piezoelectric layer 2 via an electrically insulating layer or a dielectric film 7. For example... Figure 2 As shown, the electrically insulating layer 7 can be frame-shaped and may include an opening 7a, and the support substrate 8 can be frame-shaped and may include an opening 8a. This configuration allows for the formation of a space including, for example, a cavity 9 or an air gap. The cavity 9 can be configured not to impede the vibration of the excitation region C of the piezoelectric layer 2. Therefore, the support substrate 8 can be laminated to the second main surface 2b via the electrically insulating layer 7 at a location that does not overlap with the portion where at least one electrode pair is disposed. The electrically insulating layer 7 is not required. Therefore, the support substrate 8 can be laminated directly or indirectly onto the second main surface 2b of the piezoelectric layer 2.

[0041] The electrically insulating layer 7 can be made of silicon dioxide. In addition to silicon dioxide, suitable electrically insulating materials such as silicon oxynitride or aluminum oxide can also be used. The support substrate 8 can be made of Si or other suitable materials. The planar orientation of Si can be (100), (110), or (111). High-resistivity Si with a resistivity greater than or equal to about 4 kΩ can be used, for example. The support substrate 8 can also be made of suitable electrically insulating materials or suitable semiconductor materials. Examples of materials for the support substrate 8 include: piezoelectrics such as aluminum oxide, lithium tantalate, lithium niobate, and quartz crystals; various ceramics such as aluminum oxide, magnesium oxide, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, talc, and forsterite; dielectrics such as diamond and glass; and semiconductors such as gallium nitride.

[0042] The first electrode 3 and the second electrode 4, as well as the first busbar 5 and the second busbar 6, can be made of a suitable metal or alloy (such as an Al or AlCu alloy). The first electrode 3 and the second electrode 4, as well as the first busbar 5 and the second busbar 6, can include a structure such as an Al film, which can be laminated onto a Ti film. Adhesive layers other than the Ti film can be used.

[0043] To drive the acoustic wave device 1, an alternating current (AC) voltage is applied between the first electrode 3 and the second electrode 4. An AC voltage is also applied between the first busbar 5 and the second busbar 6 to achieve resonant characteristics using a bulk wave in a first-order thickness shear mode within the piezoelectric layer 2. In the acoustic wave device 1, when the thickness of the piezoelectric layer 2 is d, and the distance between the centers of adjacent first electrodes 3 and second electrodes 4 in the electrode pair is p, the ratio d / p can, for example, be less than or equal to about 0.5. For this reason, a bulk wave in a first-order thickness shear mode can be effectively excited, resulting in good resonant characteristics. The ratio d / p can be less than or equal to about 0.24, and in this case, even better resonant characteristics can be obtained. When there is more than one electrode, the center-to-center distance p between the centers of adjacent electrodes 3 and 4 is the average distance between the centers of any two adjacent electrodes 3 and 4.

[0044] With the above configuration, even if the number of electrode pairs is reduced to minimize size, the Q value of the acoustic device 1 is unlikely to decrease. The Q value is unlikely to decrease with a reduced number of electrode pairs because the acoustic device 1 is a resonator that does not require reflectors on both sides, and therefore has low propagation loss. Since a bulk wave in a first-order thickness shear mode is used, reflectors are not required.

[0045] Reference Figure 3A and Figure 3B The differences between Lamb waves used in known acoustic devices and volume waves in the first-order thickness shear mode of a preferred embodiment of the present invention are described.

[0046] Figure 3A It is a schematic elevation cross-sectional view used to illustrate a Lamb wave propagating in a piezoelectric film of an acoustic device described in Japanese Unexamined Patent Application Publication No. 2012-257019.

[0047] like Figure 3A As indicated by the arrow, the wave propagates in the piezoelectric film 201. In the piezoelectric film 201, the first main surface 201a and the second main surface 201b are opposite to each other, and the thickness direction connecting the first main surface 201a and the second main surface 201b is the Z-direction. The X-direction is the direction in which the electrode fingers of the interdigital transducer electrodes are arranged. Figure 3A As shown, the Lamb wave propagates along the X direction. The Lamb wave is a plate wave, therefore the piezoelectric film 201 vibrates as a whole, but the wave propagates along the X direction. Therefore, resonant characteristics are obtained by arranging reflectors on both sides. For this reason, wave propagation loss occurs, and the Q value decreases as the size decreases (i.e., as the number of electrode pairs decreases).

[0048] On the contrary, such as Figure 3B As shown, in the acoustic wave device 1, a vibrational displacement is induced in the thickness shear direction, so the wave propagates and resonates essentially along the direction (i.e., the Z direction) connecting the first main surface 2a and the second main surface 2b of the piezoelectric layer 2. In other words, the X-direction component of the wave is significantly smaller than the Z-direction component. Since the resonance characteristic is obtained from the propagation of the wave along the Z-direction, a reflector is not required. Therefore, no propagation loss is caused when the wave propagates to the reflector. Therefore, even if the number of electrode pairs is reduced to decrease the size, the Q value is unlikely to decrease.

[0049] like Figure 4 As shown, the amplitude direction of the bulk wave in the first-order thickness shear mode is opposite between the first region 451 and the second region 452 included in the excitation region C of the piezoelectric layer 2, wherein the excitation region C is as follows: Figure 1B As shown. Figure 4 The diagram schematically illustrates the body wave when a higher voltage is applied to electrode 4 than to electrode 3. The first region 451 is the region in excitation region C between the first main surface 2a and a virtual plane VP1 perpendicular to the thickness direction of the piezoelectric layer 2 and dividing it in two. The second region 452 is the region in excitation region C between the virtual plane VP1 and the second main surface 2b.

[0050] As described above, the acoustic device 1 includes at least one electrode pair. However, since waves do not propagate in the X direction, the number of electrode pairs 4 does not necessarily need to be two or more. In other words, only one electrode pair may be provided.

[0051] For example, the first electrode 3 is an electrode connected to a thermal potential, and the second electrode 4 is an electrode connected to a ground potential. Of course, the first electrode 3 can be connected to a ground potential, and the second electrode 4 can be connected to a thermal potential. As described above, each of the first electrode 3 or the second electrode 4 is connected to a thermal potential or to a ground potential, and no floating electrode is provided.

[0052] Figure 5 The graph shows the resonant characteristics of the acoustic wave device 1. The design parameters for the acoustic wave device 1 with resonant characteristics can be as follows. For example, the piezoelectric layer 2 is made of LiNbO3 with Euler angles of (0°, 0°, 90°) and a thickness of approximately 400 nm. However, as mentioned above, the piezoelectric layer 2 can be LiTaO3, and other suitable Euler angles and thicknesses can be used.

[0053] For example, when viewed in a direction perpendicular to the length direction of the first electrode 3 and the second electrode 4, the length of the overlapping region of the first electrode 3 and the second electrode 4 (i.e., the excitation region C) can be about 40 μm, the number of electrode pairs of electrodes 3 and 4 can be 21, the distance between the centers of the first electrode 3 and the second electrode 4 can be about 3 μm, the width of each electrode in the first electrode 3 and the second electrode 4 can be about 500 nm, and the ratio d / p can be about 0.133.

[0054] For example, the electrical insulating layer 7 can be made of a silicon dioxide film with a thickness of about 1 μm.

[0055] The support substrate 8 can be made of Si.

[0056] The length of the excitation region C can be along the length direction of the first electrode 3 and the second electrode 4.

[0057] Within the manufacturing and measurement tolerances between all electrode pairs, the distance between any adjacent electrodes in an electrode pair may be equal or substantially equal. In other words, the first electrode 3 and the second electrode 4 may be arranged with equal or substantially equal spacing.

[0058] from Figure 5 It is evident that, despite the absence of a reflector, a good resonant characteristic with a fractional bandwidth of approximately 12.5% ​​can be obtained.

[0059] When the thickness of the piezoelectric layer 2 is d, and the center-to-center distance between the centers of the electrode pairs is p, the ratio d / p can, for example, be less than or equal to about 0.5, or less than or equal to about 0.24. (Refer to the following...) Figure 6 Further discussion on the ratio d / p.

[0060] With Figure 5Similar to the case of acoustic devices with resonant characteristics shown, acoustic devices can be set with different ratios d / 2p. Figure 6 It is a graph showing the relationship between the ratio d / 2p and the fractional bandwidth when the acoustic device 1 is used as a resonator.

[0061] from Figure 6 The non-limiting example shown readily demonstrates that when the ratio d / 2p > 0.25 (i.e., when the ratio d / p > 0.5), the fractional bandwidth is less than about 5%. Conversely, for example, when the ratio d / 2p ≤ 0.25 (i.e., the ratio d / p ≤ 0.5), if the ratio d / p is varied within the range of 0 to 0.5, the fractional bandwidth can be set to about 5% or higher, i.e., a resonator with a high coupling coefficient can be configured. For example, when the ratio d / 2p < 0.12 (i.e., the ratio d / p is less than or equal to about 0.24), the fractional bandwidth can be increased to about 7% or higher. Furthermore, if the ratio d / p is adjusted within this range, a resonator with a much wider fractional bandwidth can be obtained, and thus a resonator with a much higher coupling coefficient can be realized. Therefore, it has been found and confirmed that when the ratio d / p is set to about 0.5 or less, for example, a resonator using a first-order thickness shear mode with a high coupling coefficient can be configured.

[0062] As described above, at least one electrode pair can be a pair, and in the case of one electrode pair, p is defined as the center-to-center distance between the centers of adjacent first electrode 3 and second electrode 4. In the case of 1.5 or more electrode pairs, p can be defined as the average center-to-center distance s between the centers of any adjacent electrodes 3, 4.

[0063] For the thickness d of the piezoelectric layer 2, when the piezoelectric layer 2 has a thickness variation, the average thickness can be used.

[0064] Figure 7 This is a plan view of an acoustic wave device 31 according to a second preferred embodiment of the present invention. In the acoustic wave device 31, an electrode pair including a first electrode 3 and a second electrode 4 is disposed on the first main surface 2a of the piezoelectric layer 2. Figure 7 In this context, K represents the overlap width. As mentioned above, in the acoustic device 31, the number of electrode pairs can be one. Similarly, in this case, when the ratio d / p is less than or equal to about 0.5, for example, a first-order thickness shear mode of bulk wave can be effectively excited.

[0065] Figure 8 This is a partial cross-sectional perspective view of an acoustic device according to a third preferred embodiment of the present invention.

[0066] The acoustic wave device 81 includes a support substrate 82. The support substrate 82 has a groove opening to its top surface. A piezoelectric layer 83 is laminated onto the support substrate 82, which defines a cavity 9. An IDT electrode 84 is disposed on the piezoelectric layer 83 above the cavity 9. Reflectors 85 and 86 are disposed on both sides of the IDT electrode 84 in the direction of acoustic wave propagation. Figure 8 In the diagram, the outer periphery of cavity 9 is shown by a dashed line. IDT electrode 84 includes a first busbar 84a, a second busbar 84b, an electrode 84c defining a plurality of first electrode fingers, and an electrode 84d defining a plurality of second electrode fingers. Electrode 84c is connected to the first busbar 84a, and electrode 84d is connected to the second busbar 84b. Electrodes 84c and 84d intersect each other.

[0067] In the acoustic wave device 81, an alternating field can be applied to the IDT electrode 84 located above the cavity 9, thereby exciting a Lamb wave as a plate wave. Furthermore, reflectors 85 and 86 are disposed on both sides of the IDT electrode 84, thereby obtaining Lamb wave-based resonant characteristics. Therefore, the acoustic wave device 81 can use a plate wave.

[0068] When the temperature of the acoustic device or the ambient temperature of the acoustic device changes, stress can concentrate at the end of the electrode (first electrode or second electrode) adjacent to the piezoelectric layer, such as... Figure 16 As shown, this can cause polarization reversal in the piezoelectric layer. The effect of stress can increase as the thickness of the piezoelectric layer decreases. Even if the temperature of the acoustic device or the ambient temperature of the acoustic device changes, the preferred embodiment of the present invention can suppress polarization reversal in the piezoelectric layer.

[0069] Figure 9 , Figure 12 and Figure 13 An acoustic wave device 1 is shown, each of which includes a support substrate 8 and an optional electrically insulating layer 7 on the support substrate 8 (only when...). Figure 9 As shown in the diagram, a piezoelectric layer 2, comprising a first main surface 2a and a second main surface 2b, is mounted on a support substrate 8. A functional electrode 10, which may be a first electrode 3 or a second electrode 4, is located on the first main surface 2a of the piezoelectric layer 2. The support substrate 8, an optional electrically insulating layer 7, and the piezoelectric layer 2 may define a cavity 9. The functional electrode 10 may be included in an IDT electrode. The functional electrode 10 may be covered by a protective layer (not shown) made of SiO2 or the like. Although Figure 9 , Figure 12 and Figure 13 A single functional electrode 10 is shown, but the shape of the functional electrode 10 can be applied to some or all of the first electrode 3 and / or the second electrode 4. For example, Figure 9 , Figure 12 and Figure 13The shape of the functional electrode 10 shown can be applied to one or more pairs of first electrodes 3 and second electrodes 4.

[0070] Equation 0.5(Lb-Ls) (which is half the difference between the length Lb of the bottom surface of the functional electrode 10 and the length Ls of the top surface of the functional electrode 10) can be equal to or greater than 0.002Tg and less than Te, where Tg is the height from the first main surface 2a of the piezoelectric layer 2 to the cavity 9 (or the top surface of the supporting substrate 8), and Te is the thickness of the functional electrode 10, i.e., 0.002Tg ≤ 0.5(Lb-Ls) < Te. If the lengths of the top and bottom surfaces of the functional electrode 10 vary, then the lengths Lb and Ls can be the maximum lengths of the top and bottom surfaces of the functional electrode 10. In this way, even if the temperature of the acoustic device 1 or the ambient temperature around the acoustic device 1 changes, the stress acting on the end of the functional electrode 10 on the piezoelectric layer side can be reduced.

[0071] exist Figure 9 In this configuration, the electrically insulating layer 7 is laminated onto the second main surface 2b of the piezoelectric layer 2 on the side facing the support substrate 8. Therefore, Tg represents the sum of the thickness of the piezoelectric layer 2 and the thickness of the electrically insulating layer 7. The lamination of the electrically insulating layer 7 can be omitted. A space or cavity 9 is provided in a portion of the support substrate 8, but it can also be an air gap provided between the support substrate 8 and the piezoelectric layer 2.

[0072] Figure 10 and Figure 11 The graph shows the relationship between the equation 0.5(Lb-Ls) / Tg and the stress intensity. Figure 10 The relationship between equation 0.5(Lb-Ls) / Tg and stress intensity is shown when the thickness Tg is 500 μm. Figure 11 The relationship between the equation 0.5(Lb-Ls) / Tg and the stress intensity is shown when the thickness Tg is 1 μm. This is achieved through comparison. Figure 10 and Figure 11 It can be seen that when the thickness Tg decreases from 500 μm to 1 μm, the stress decreases, and the equation 0.5(Lb-Ls) / Tg is equal to or greater than 0.002. It can also be seen that when the thickness Tg decreases from 500 μm to 1 μm, the stress decreases further, and the equation 0.5(Lb-Ls) / Tg is equal to or greater than 0.009. Furthermore, it can be seen that when the thickness Tg decreases from 500 μm to 1 μm, the stress stabilizes at a low level, and the equation 0.5(Lb-Ls) / Tg is equal to or greater than 0.02. If the equation 0.5(Lb-Ls) exceeds the thickness Te, manufacturing may become difficult; therefore, the equation 0.5(Lb-Ls) / Tg can be set to be less than Te to make manufacturing easier.

[0073] Figure 12 A first modification to the functional electrode 10 is shown. The functional electrode 10 may have, for example... Figure 12 The shape shown includes a first side 11 having a first surface 11a and a second surface 11b, and a second side 12 having a first surface 12a and a second surface 12b. The first surface 11a may include a first angle θ1, which is the angle between the first surface 11a and the first main surface 2a, and the second surface 11b may include a second angle θ2, which is the angle between the second surface 11b and the first main surface 2a and is smaller than the first angle θ1 (i.e., θ2 < θ1). The first surface 12a and the second surface 12b of the second side 12 may include the same or different angles as the first side. If the angles of the first side 11 and the second side 12 are the same, the functional electrode 10 is symmetrical about a vertical axis passing through the middle of the functional electrode 10. Then, the stress at the piezoelectric layer side of the functional electrode 10 can be dispersed, and the polarization reversal of the piezoelectric layer 2 can be reduced or suppressed.

[0074] The functional electrode 10 may include at least a first layer 13 and a second layer 14 laminated on the first layer 13. The first layer 13 may be made of any one of Cu, Ti, Mo, W, Pt, Ni, and Cr as the main component, and the second layer 14 may be made of Al. This configuration allows for the achievement of a desired resistance in the functional electrode 10, or improves the reliability and adhesion of the functional electrode 10. The functional electrode 10 may be covered by a protective layer (not shown) made of SiO2 or the like.

[0075] Figure 13 A second modification to the functional electrode 10 is shown. The functional electrode 10 may have, for example... Figure 13 The shape shown. The first side 11 and / or the second side 12 may include a bent portion. The first side 11 and the second side 12 may have the same shape or different shapes. By the bent portion, the stress at the end of the functional electrode 10 on the piezoelectric layer side of the functional electrode 10 can be dispersed, and the polarization reversal of the piezoelectric layer 2 can be reduced or suppressed. The functional electrode 10 may be covered by a protective layer (not shown) made of SiO2 or the like.

[0076] Figures 14-16 The stress intensity on the acoustic device according to the comparative example is shown respectively. Figure 16 ), the first modification of functional electrode 10 ( Figure 15 ) and the second modification of functional electrode 10 ( Figure 14 ).and Figure 16 Compared to the stress in acoustic equipment, Figure 14 and Figure 15 The stress in the acoustic equipment is lower. (Compared to) Figure 15 Compared to the stress in acoustic equipment, Figure 14The stress applied to the piezoelectric layer in the acoustic device is even smaller.

[0077] It should be noted that each preferred embodiment described herein is exemplary, and partial substitutions or combinations of configurations are possible in different preferred embodiments. While preferred embodiments of the invention have been described above, it should be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Therefore, the scope of the invention is defined only by the appended claims.

Claims

1. An acoustic device, comprising: Support substrate; The piezoelectric layer includes a first main surface and a second main surface, the second main surface being on the opposite side of the piezoelectric layer of the first main surface and in a first direction relative to the first main surface; At least one pair of functional electrodes are disposed facing each other in a second direction intersecting the first direction and adjacent to each other on the first main surface; as well as The space defines a cavity in the supporting substrate or an air gap between the supporting substrate and the piezoelectric layer, wherein, In a plan view along the first direction, the space overlaps with at least a portion of the at least one pair of functional electrodes, and Half of the difference between the maximum length of the bottom surface of one of the at least one pair of functional electrodes in the second direction and the maximum length of the top surface of the one of the at least one pair of functional electrodes in the second direction is equal to or greater than 0.2% of the thickness of the piezoelectric layer from the first main surface to the space, and equal to or less than the thickness of the one of the at least one pair of functional electrodes in the first direction.

2. The acoustic device according to claim 1, wherein, Half of the difference between the maximum length of the bottom surface of one of the at least one pair of functional electrodes in the second direction and the maximum length of the top surface of the one of the at least one pair of functional electrodes in the second direction is equal to or greater than 0.9% of the thickness of the piezoelectric layer from the first main surface to the space.

3. The acoustic device according to claim 1, wherein, Half of the difference between the maximum length of the bottom surface of one of the at least one pair of functional electrodes in the second direction and the maximum length of the top surface of the one of the at least one pair of functional electrodes in the second direction is equal to or greater than 2% of the thickness of the piezoelectric layer from the first main surface to the space.

4. The acoustic device according to claim 1, wherein, In a cross-section including the first direction and the second direction, one of the at least one pair of functional electrodes includes a first side and a second side, and The first side and / or the second side includes a curved portion.

5. The acoustic device according to claim 1, wherein, The thickness of the piezoelectric layer is equal to or greater than 0.05 μm and equal to or less than 1 μm.

6. The acoustic device according to claim 1, wherein, An electrically insulating layer is disposed between the piezoelectric layer and the supporting substrate.

7. The acoustic device according to claim 1, wherein, One of the at least one pair of functional electrodes includes a plurality of first electrodes, a first bus electrode connected to the plurality of first electrodes, a plurality of second electrodes, and a second bus electrode connected to the plurality of second electrodes.

8. The acoustic device according to claim 7, wherein, The thickness of the piezoelectric layer is equal to or greater than 2p, where p is the center-to-center distance between adjacent first and second electrodes.

9. The acoustic device according to claim 1, wherein, The piezoelectric layer includes lithium niobate or lithium tantalate.

10. The acoustic device according to claim 9, wherein, The first-order thickness shear mode volume wave was used as the main wave.

11. The acoustic device according to claim 10, wherein, One of the at least one pair of functional electrodes comprises at least one pair of electrodes facing each other, and The ratio d / p is equal to or less than 0.5, where d is the thickness of the piezoelectric layer and p is the center-to-center distance between at least one pair of electrodes adjacent to and facing each other.

12. The acoustic device according to claim 1, wherein, The functional electrode is an IDT electrode, and plate waves are used as the main waves.

13. An acoustic wave device, comprising: A support substrate, including a top surface, a bottom surface, and a cavity or an air gap; A piezoelectric layer on the top surface of the support substrate and including a top surface and a bottom surface; And An electrode on the top surface of the piezoelectric layer and including a top surface and a bottom surface, wherein At least a part of the electrode is above the cavity or the air gap, and The equation 0.002Tg ≤ 0.5(Lb - Ls) < Te is satisfied, where Ls is the maximum length of the top surface of the electrode, Lb is the maximum length of the bottom surface of the electrode, Tg is the distance between the top surface of the piezoelectric layer and the top surface of the support substrate, and Te is the thickness of the electrode.

14. The acoustic device according to claim 13, wherein, The equation 0.009Tg ≤ 0.5(Lb - Ls) is satisfied.

15. The acoustic device according to claim 13, wherein, The equation 0.02Tg ≤ 0.5(Lb - Ls) is satisfied.

16. The acoustic device according to claim 13, wherein, The first side and / or the second side of the electrode includes a curved portion.

17. The acoustic device according to claim 13, wherein, The electrode includes a first electrode, a first bus electrode connected to the first electrode, a second electrode, and a second bus electrode connected to the second electrode.

18. The acoustic device according to claim 13, wherein, The piezoelectric layer includes lithium niobate or lithium tantalate.

19. The acoustic device according to claim 18, wherein, The first-order thickness shear mode bulk wave is used as the main wave.

20. The acoustic device according to claim 13, wherein, The electrode is an IDT electrode, and plate waves are used as the main waves.

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