Elastic wave devices, filters, and multiplexers

Abstract

To provide an acoustic wave device which can suppress spurious.SOLUTION: An acoustic wave device 100 includes: a piezoelectric body 18; a pair of comb-shaped electrodes 21 provided on the piezoelectric body 18 and including a plurality of electrode fingers 22; a reflector 25 provided on the piezoelectric body 18 so as to be arranged in line with the pair of comb-shaped electrodes 21 in an arrangement direction of the electrode fingers 22; and an additional film 50 which is provided on the piezoelectric body 18 between the pair of comb-shaped electrodes 21 and the reflector 25 so that an overlap width with the pair of comb-shaped electrodes 21 and an overlap width with the reflector 25 are equal to or less than 1 / 8 of an average pitch P of the electrode fingers 22 of the pair of comb-shaped electrodes 21 and a distance between the additional film and the pair of comb-shaped electrodes 21 and a distance between the additional film and the reflector 25 are equal to or less than 1 / 8 of the average pitch P.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an acoustic wave device, a filter, and a multiplexer.

Background Art

[0002] In high-frequency communication systems typified by mobile phones, filters are used to remove unnecessary signals outside the frequency band used for communication. For the filter, for example, an acoustic wave device including a comb-shaped electrode and a reflector is used. To reduce the size of the acoustic wave device, a configuration is known in which a first dielectric film covering the reflector is provided so as to have a side surface in the region between the comb-shaped electrode and the reflector, and a second dielectric film covering the comb-shaped electrode is provided in contact with the side surface of the first dielectric film (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0004] Spurious emissions may occur due to leakage of acoustic waves from the region between the comb-shaped electrode and the reflector.

[0005] The present invention has been made in view of the above problems, and an object thereof is to suppress spurious emissions.

Means for Solving the Problems

[0006] The present invention is an elastic wave device comprising: a piezoelectric body; a pair of comb-shaped electrodes provided on the piezoelectric body and having a plurality of electrode fingers; a reflector provided on the piezoelectric body on the pair of comb-shaped electrodes in the direction of arrangement of the plurality of electrode fingers; and an additional film provided on the piezoelectric body between the pair of comb-shaped electrodes and the reflector such that the overlap width between the pair of comb-shaped electrodes and the reflector is 1 / 8 or less of the average pitch of the plurality of electrode fingers of the pair of comb-shaped electrodes, and the distance between the pair of comb-shaped electrodes and the reflector is 1 / 8 or less of the average pitch.

[0007] In the above configuration, the additional film can be provided in a region that extends between the pair of comb-shaped electrodes and the reflector, covering more than half of the region where the intersection region where the plurality of electrode fingers of the pair of comb-shaped electrodes intersect.

[0008] In the above configuration, the value obtained by multiplying the thickness of the additional film by the density of the additional film can be set to be 0.4 times or more and 1.6 times or less the value obtained by multiplying the thickness of the plurality of electrode fingers by the duty cycle of the plurality of electrode fingers and the density of the plurality of electrode fingers.

[0009] In the above configuration, the added film can be a film mainly composed of tantalum oxide, niobium oxide, silicon oxide, or aluminum oxide.

[0010] In the above configuration, the speed of sound of transverse waves propagating in the region between the pair of comb-shaped electrodes and the reflector can be set to be 0.95 times or more and 1.05 times or less the speed of sound of transverse waves propagating in the region where the pair of comb-shaped electrodes are provided.

[0011] The present invention is an elastic wave device comprising: a piezoelectric body having a first region of a first thickness and a second region of a second thickness thinner than the first thickness; a pair of comb-shaped electrodes provided on the piezoelectric body in the first region and having a plurality of electrode fingers; and a reflector provided on the piezoelectric body in the first region, arranged in the direction of the arrangement of the plurality of electrode fingers on the pair of comb-shaped electrodes, and having the second region of the piezoelectric body between itself and the pair of comb-shaped electrodes.

[0012] In the above configuration, the thickness of the first region of the piezoelectric body can be configured to be less than or equal to twice the average pitch of the plurality of electrode fingers of the pair of comb-shaped electrodes.

[0013] The present invention is an elastic wave device comprising: a piezoelectric body; a pair of comb-shaped electrodes provided on the piezoelectric body and having a plurality of electrode fingers; and a reflector provided on the piezoelectric body on the pair of comb-shaped electrodes in the direction of the arrangement of the plurality of electrode fingers, wherein the speed of sound of transverse waves propagating in the region between the pair of comb-shaped electrodes is 0.95 times or more and 1.05 times or less than the speed of sound of transverse waves propagating in the region where the pair of comb-shaped electrodes are provided.

[0014] The present invention is a filter comprising the elastic wave device described above.

[0015] The present invention is a multiplexer equipped with the filter described above. [Effects of the Invention]

[0016] According to the present invention, spurious emissions can be suppressed. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1(a) is a plan view of the elastic wave device according to Example 1, and Figure 1(b) is a cross-sectional view AA of Figure 1(a). [Figure 2] Figures 2(a) to 2(c) are cross-sectional views showing a method for manufacturing an elastic wave device according to Example 1. [Figure 3] Figure 3(a) is a plan view of an elastic wave device relating to a comparative example, and Figure 3(b) is a cross-sectional view AA of Figure 3(a). [Figure 4] Figure 4(a) shows the speed of sound in a transverse wave in the comparative example, and Figure 4(b) shows the speed of sound in a transverse wave in Example 1. [Figure 5] Figures 5(a) and 5(b) show the results of a simulation of the relationship between the thickness of the accretionary film and the decrease in the speed of sound in transverse waves. [Figure 6] FIG. 6(a) is a plan view of a simulated model, and FIG. 6(b) is a cross-sectional view thereof. [Figure 7] FIGS. 7(a) to 7(c) show simulation results of the real part Real(Y) of admittance with respect to frequency. [Figure 8] FIG. 8(a) is a plan view of an acoustic wave device according to Modification 1 of Embodiment 1, and FIG. 8(b) is a plan view of an acoustic wave device according to Modification 2 of Embodiment 1. [Figure 9] FIG. 9(a) is a plan view of an acoustic wave device according to Modification 3 of Embodiment 1, and FIG. 9(b) is a plan view of an acoustic wave device according to Modification 4 of Embodiment 1. [Figure 10] FIG. 10 is a plan view of an acoustic wave device according to Modification 5 of Embodiment 1. [Figure 11] FIG. 11 is a cross-sectional view in a case where an additional film in Embodiment 1 is a metal film. [Figure 12] FIG. 12(a) is a plan view of an acoustic wave device according to Embodiment 2, and FIG. 12(b) is an A-A cross-sectional view of FIG. 12(a). [Figure 13] FIGS. 13(a) and 13(b) show simulation results of the real part Real(Y) of admittance with respect to the sound velocity of a transverse wave. [Figure 14] FIG. 14 is a circuit diagram of a filter according to Embodiment 3. [Figure 15] FIG. 15 is a circuit diagram of a duplexer according to Embodiment 4. [Modes for Carrying Out the Invention]

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Embodiment]

[0019] Figure 1(a) is a plan view of the elastic wave device according to Example 1, and Figure 1(b) is a cross-sectional view of AA in Figure 1(a). In Figure 1(a), hatching is applied to the comb-shaped electrode 21, reflector 25, and additional film 50 for clarity (the same applies to similar figures hereafter). The arrangement direction of the electrode fingers 22 is the X direction, the longitudinal direction of the electrode fingers 22 is the Y direction, and the thickness direction of the piezoelectric body 18 is the Z direction. The X, Y, and Z directions do not necessarily correspond to the X-axis and Y-axis directions of the crystal orientation of the piezoelectric body 18.

[0020] As shown in Figures 1(a) and 1(b), the elastic wave device 100 according to Embodiment 1 has an insulating film 12 provided on a support substrate 10. A temperature compensation film 14 is provided on the insulating film 12. A piezoelectric body 18 is provided on the temperature compensation film 14 via a bonding layer 16. An IDT (Interdigital Transducer) 20 and a reflector 25 are provided on the piezoelectric body 18. The reflector 25 is provided alongside the IDT 20 in the X direction (the direction of arrangement of electrode fingers 22). The IDT 20 and the reflector 25 are formed by a metal film 26 on the piezoelectric body 18.

[0021] The IDT20 comprises a pair of comb-shaped electrodes 21. Each comb-shaped electrode 21 includes a plurality of electrode fingers 22, a plurality of dummy electrode fingers 23, and a busbar 24 to which the plurality of electrode fingers 22 and the plurality of dummy electrode fingers 23 are connected. The tips of the electrode fingers 22 of one comb-shaped electrode 21 and the tips of the dummy electrode fingers 23 of the other comb-shaped electrode 21 face each other. The dummy electrode fingers 23 may be omitted. The region where the electrode fingers 22 of the pair of comb-shaped electrodes 21 intersect is the intersection region 40. The length of the intersection region 40 in the Y direction is the aperture length. The pair of comb-shaped electrodes 21 face each other such that the electrode fingers 22 are approximately staggered in at least a portion of the intersection region 40. The main mode elastic wave (surface acoustic wave) excited by the electrode fingers 22 in the intersection region 40 propagates mainly in the X direction. The pitch of the electrode fingers 22 of one comb-shaped electrode 21 is approximately equal to the wavelength λ of the surface acoustic wave. The pitch of the electrode fingers 22 of one comb-shaped electrode 21 is approximately twice the pitch P of the electrode fingers 22 of the pair of comb-shaped electrodes 21. The reflector 25 reflects the surface acoustic waves excited by the electrode fingers 22. As a result, the surface acoustic waves are confined within the intersection region 40.

[0022] An additional film 50 is provided on the piezoelectric body 18 between the IDT 20 and the reflector 25. The additional film 50 is provided to cover, for example, the entire region between the IDT 20 and the reflector 25. One of the two sides of the additional film 50 along the Y direction, side 51, is in contact with, for example, the side 27 of the pair of comb-shaped electrodes 21 closest to the reflector 25, and the other side 52 is in contact with, for example, the side 28 of the reflector 25 closest to the pair of comb-shaped electrodes 21. One of the two sides of the additional film 50 along the X direction, side 53, is substantially flush with, for example, the outer surface 29 of the busbar 24 of one of the pair of comb-shaped electrodes 21, and the other side 54 is substantially flush with, for example, the outer surface 30 of the busbar 24 of the other comb-shaped electrode 21.

[0023] The support substrate 10 is, for example, a sapphire substrate, spinel substrate, silicon substrate, crystal substrate, silica substrate, or alumina substrate. The insulating film 12 is a film in which the sound speed of the elastic waves propagating is faster than that of the piezoelectric body 18 and the temperature compensation film 14. For example, the sound speed of the bulk waves propagating through the insulating film 12 is faster than the sound speed of the bulk waves propagating through the piezoelectric body 18 and the temperature compensation film 14. The insulating film 12 is, for example, a polycrystalline or amorphous insulating film, such as an aluminum oxide film, a silicon film, an aluminum nitride film, a silicon nitride film, or a silicon carbide film. Multiple layers of different materials may be provided as the insulating film 12.

[0024] The temperature compensation film 14 has a temperature coefficient of elasticity with the opposite sign to that of the piezoelectric body 18. For example, the temperature coefficient of elasticity of the piezoelectric body 18 is negative, and the temperature coefficient of elasticity of the temperature compensation film 14 is positive. The temperature compensation film 14 is, for example, a silicon oxide film in which no elements other than oxygen (O) and silicon (Si) are intentionally added, or a silicon oxide film in which at least one of the following elements, such as fluorine (F), boron (B), chlorine (Cl), nitrogen (N), phosphorus (P), and sulfur (S), is intentionally added. The speed of sound of elastic waves propagating through the temperature compensation film 14 is slower than the speed of sound of elastic waves propagating through the piezoelectric body 18. For example, the speed of sound of bulk waves propagating through the temperature compensation film 14 is slower than the speed of sound of bulk waves propagating through the piezoelectric body 18. Note that the magnitude of the speed of sound (phase velocity) of surface acoustic waves is the same as the magnitude of the speed of sound of bulk waves.

[0025] The bonding layer 16 is a layer for bonding the temperature compensation film 14 and the piezoelectric body 18. For example, the bonding layer 16 is a layer in which the sound velocity of the elastic waves propagating is faster than that of the temperature compensation film 14. The bonding layer 16 is, for example, polycrystalline or amorphous, and is an aluminum oxide layer, a silicon layer, an aluminum nitride layer, a silicon nitride layer, or a silicon carbide layer. The bonding layer 16 is sufficiently thin compared to the piezoelectric body 18 and the temperature compensation film 14.

[0026] The piezoelectric element 18 is, for example, a single-crystal lithium tantalate (LiTaO3) film or a single-crystal lithium niobate (LiNbO3) film, and is, for example, a rotational Y-cut X-propagating lithium tantalate film or a rotational Y-cut X-propagating lithium niobate film.

[0027] The metal film 26 is a film mainly composed of, for example, aluminum (Al), copper (Cu), molybdenum (Mo), iridium (Ir), platinum (Pt), rhenium (Re), rhodium (Rh), ruthenium (Ru), tantalum (Ta), or tungsten (W). An adhesion film such as a titanium (Ti) film or a chromium (Cr) film may be provided between the metal film 26 and the piezoelectric element 18. An insulating film may be provided to cover the electrode finger 22 and the dummy electrode finger 23. In this case, the additional film 50 may be provided on the insulating film. The insulating film may function as a protective film.

[0028] The addition film 50 is a film mainly composed of, for example, tantalum oxide (Ta2O5), niobium oxide (Nb2O5), silicon oxide (SiO2), or aluminum oxide (Al2O3). For a film to be mainly composed of a certain element, it is permissible for the film to contain intentional or unintentional impurities other than the main component. When a certain element is the main component in a film, the concentration of that element is, for example, 50 atomic percent or more, or for example, 80 atomic percent or more. In the case of a film with two main components, such as silicon oxide, the sum of the concentrations of silicon and oxygen is, for example, 50 atomic percent or more, or for example, 80 atomic percent or more, and the concentrations of silicon and oxygen are, for example, 10 atomic percent or more each.

[0029] The surface acoustic waves excited by the electrode fingers 22 propagate within 2.0λ of the surface of the piezoelectric body 18. Therefore, in order for the temperature compensation film 14 to perform its temperature compensation function, the distance H between the upper surface of the piezoelectric body 18 and the lower surface of the temperature compensation film 14 is preferably 4.0 times (2.0λ) or less of the average pitch P of the electrode fingers 22, and more preferably 3.0 times (1.5λ) or less. The thickness of the piezoelectric body 18 is preferably 2.0 times (λ) or less of the average pitch P of the electrode fingers 22, and more preferably 1.6 times (0.8λ) or less. If the piezoelectric body 18 is too thin, the elastic waves will not be excited, so the thickness of the piezoelectric body 18 is preferably 0.2 times (0.1λ) or more of the average pitch P of the electrode fingers 22. The average pitch P of the electrode fingers 22 may be calculated by dividing the length of the IDT 20 in the X direction by the number of electrode fingers 22.

[0030] [Manufacturing method] Figures 2(a) to 2(c) are cross-sectional views showing a method for manufacturing an elastic wave device according to Example 1. As shown in Figure 2(a), a support substrate 10 with a flat top surface is prepared. The arithmetic mean roughness Ra of the top surface of the support substrate 10 is, for example, 1 nm or less. An insulating film 12 is deposited on the support substrate 10 using, for example, CVD (Chemical Vapor Deposition), sputtering, or vapor deposition. A temperature compensation film 14 is deposited on the insulating film 12 using, for example, CVD, sputtering, or vapor deposition. A piezoelectric body 18 is bonded to the temperature compensation film 14 via a bonding layer 16. The temperature compensation film 14 and the piezoelectric body 18 may be directly bonded without the bonding layer 16. For bonding, for example, a surface activation method is used. The piezoelectric body 18 here is a thicker film (substrate) than the piezoelectric body 18 in Figure 1(b).

[0031] As shown in Figure 2(b), the upper surface of the piezoelectric element 18 is polished to the desired thickness, for example by CMP (Chemical Mechanical Polishing). Then, an IDT 20 and a reflector 25 made of a metal film 26 are formed on the piezoelectric element 18, for example by photolithography and etching.

[0032] As shown in Figure 2(c), an additional film 50 is formed between the IDT 20 and the reflector 25, for example, using the lift-off method. This yields the acoustic wave device according to Example 1.

[0033] [Comparative Example] Figure 3(a) is a plan view of the elastic wave device according to the comparative example, and Figure 3(b) is a cross-sectional view AA of Figure 3(a). As shown in Figures 3(a) and 3(b), the elastic wave device 500 according to the comparative example does not have an additional film between the IDT 20 and the reflector 25. The other configurations are the same as in Example 1, so their description is omitted.

[0034] Figure 4(a) shows the speed of sound in a transverse wave in the comparative example, and Figure 4(b) shows the speed of sound in a transverse wave in Example 1. The speed of sound in a transverse wave is approximately equal to the speed of sound of the surface acoustic wave excited by the electrode fingers 22. As shown in Figure 4(a), in the comparative example, no additional film is provided between the IDT 20 and the reflector 25. Therefore, the speed of sound of transverse waves propagating in region 60 between the IDT 20 and the reflector 25 is faster than the speed of sound of transverse waves propagating in region 62 where the comb-shaped electrode 21 is provided and region 64 where the reflector 25 is provided. Since metal electrodes are present in regions 64 and 62, the speed of sound is considered to be slower than in region 60, where there are no metal electrodes and the speed of sound within the region is equivalent to that of the surface of the piezoelectric body 18.

[0035] On the other hand, as shown in Figure 4(b), in Example 1, an additional film 50 is provided between the IDT 20 and the reflector 25. The speed of sound in transverse waves can be changed by the weight of the film provided on the piezoelectric body 18. Here, when a tantalum oxide film or a niobium oxide film is used for the additional film 50, the relationship between the thickness of the additional film 50 and the amount of decrease in the speed of sound in transverse waves is simulated and shown in Figures 5(a) and 5(b). In Figures 5(a) and 5(b), the horizontal axis is the thickness of the additional film 50 (tantalum oxide film or niobium oxide film). The vertical axis is the speed of sound ratio (%) of the speed of sound of transverse waves propagating in region 60, with the case where the additional film 50 is not provided as the reference (0%). As shown in Figures 5(a) and 5(b), as the thickness of the additional film 50 increases, the speed of sound of transverse waves propagating in region 60 decreases. Therefore, in Example 1, by providing the additional film 50 between the IDT 20 and the reflector 25, the speed of sound of transverse waves propagating in region 60 is reduced, and the speed of sound of transverse waves propagating in region 60 can be made approximately the same as the speed of sound of transverse waves propagating in regions 62 and 64. In other words, the additional film 50 is provided between the IDT 20 and the reflector 25 so that the speed of sound of transverse waves propagating in region 60 is approximately the same as the speed of sound of transverse waves propagating in regions 62 and 64.

[0036] The speed of sound of a transverse wave propagating in region 60 is approximately the same as the speed of sound of a transverse wave propagating in regions 62 and 64 when the weight of the membrane in region 60 is approximately equal to the weight of the membrane in regions 62 and 64. Since an additional membrane 50 is provided in region 60, the weight of the membrane in region 60 can be defined as (H1 × ρ1), where H1 is the thickness of the additional membrane 50 and ρ1 is its density. On the other hand, the weight of the membrane in regions 62 and 64 is affected by the duty cycle of the electrode finger 22, so it can be defined as (H2 × D × ρ2), where H2 is the thickness of the electrode finger 22, D is the duty cycle, and ρ2 is its density. Therefore, when (H1 × ρ1) = (H2 × D × ρ2), the speed of sound of a transverse wave propagating in region 60 is the same as the speed of sound of a transverse wave propagating in regions 62 and 64. In Example 1, an additional film 50 of an appropriate material and thickness is provided such that the value of (H1 × ρ1) is between 0.4 and 1.6 times the value of (H2 × D × ρ2), and the speed of sound of transverse waves propagating in region 60 is approximately the same as the speed of sound of transverse waves propagating in regions 62 and 64.

[0037] For example, consider a case where electrode finger 22 is an aluminum film with a thickness of 150 nm and a duty cycle of 50%, and the additional film 50 is a tantalum oxide film or a niobium oxide film. The density of aluminum is 2700 kg / cm³. 3 The density of tantalum oxide is 8100 kg / cm³. 3 Therefore, (H1 × ρ1) = 8100 × H1, and (H2 × D × ρ2) = 150 × 0.5 × 2700 = 202500. Thus, if the added film 50 is a tantalum oxide film, setting the thickness H1 to 10.0 nm to 40.0 nm will make the sound velocity of transverse waves propagating in region 60 approximately the same as the sound velocity of transverse waves propagating in regions 62 and 64. The density of niobium oxide is 4470 kg / cm³. 3 Therefore, (H1 × ρ1) = 4470 × H1. Consequently, if the adducted film 50 is a niobium oxide film, setting the thickness H1 to 18.1 nm to 72.5 nm will make the speed of sound of transverse waves propagating in region 60 approximately the same as the speed of sound of transverse waves propagating in regions 62 and 64.

[0038] [simulation] Simulations were performed to evaluate spurious emissions for models 1, 2, and 3, in which the speed of sound of transverse waves propagating in the region 60 between the IDT20 and the reflector 25 was varied. Figure 6(a) is a plan view of the simulated models 1, 2, and 3, and Figure 6(b) is a cross-sectional view. The simulation conditions are shown below with reference to Figures 6(a) and 6(b).

[0039] Common conditions Wavelength of elastic wave λ: 2.2 μm Support substrate 10: Sapphire substrate Insulating film 12: Aluminum oxide film with a thickness of 6000 nm Temperature compensation film 14: Silicon oxide film with a thickness of 440 nm Piezoelectric material 18: Lithium tantalate film with a thickness of 660 nm IDT20, Reflector 25: A laminated film consisting of a 10nm thick titanium film and a 135nm thick aluminum film. Logarithm of IDT20: 150 pairs Logarithm of reflector 25: 20 pairs Duty cycle of electrode finger 22: 50% Length of dummy electrode finger 23 in the Y direction: 1.5λ Opening length L: 15λ Distance W between IDT20 and reflector 25: λ / 4

[0040] Conditions for Model 1 Speed ​​of sound in transverse waves in regions 62 and 64: 3750 m / s Speed ​​of sound in transverse waves in region 60: 4200 m / s Conditions for Model 2 Speed ​​of sound in transverse waves in regions 62 and 64: 3750 m / s Speed ​​of sound in transverse waves in region 60: 3570 m / s Conditions for Model 3 Speed ​​of sound in transverse waves in regions 62 and 64: 3750 m / s Speed ​​of sound in transverse waves in region 60: 2940 m / s

[0041] Figures 7(a) to 7(c) show the simulation results of the real part of admittance, Real(Y), as a function of frequency for models 1, 2, and 3. In Figures 7(a) to 7(c), the horizontal axis represents frequency [GHz], and the vertical axis represents the real part of admittance, Real(Y) [S]. As shown in Figures 7(a) to 7(c), spurious emissions 65 were observed to be large in models 1 and 3. On the other hand, spurious emissions 65 were suppressed to a smaller extent in model 2 compared to models 1 and 3. In models 1 and 3, as per the simulation conditions described above, there is a large difference between the sound velocity of transverse waves in regions 62 and 64 and the sound velocity of transverse waves in region 60. Therefore, it is thought that the discontinuity of sound velocity between regions 62, 64 and region 60 caused longitudinal mode spurious emissions, resulting in a large spurious emission 65. On the other hand, in model 2, as per the simulation conditions described above, there is a small difference between the sound velocity of transverse waves in regions 62 and 64 and the sound velocity of transverse waves in region 60. Therefore, it is thought that the spurious emission 65 was reduced because the longitudinal mode spurious emissions were suppressed. In addition, models 2 and 3 show improved Q values ​​compared to model 1.

[0042] From these simulation results, it can be seen that spurious emissions can be suppressed by reducing the difference between the sound velocity of transverse waves propagating in region 60 and the sound velocity of transverse waves propagating in regions 62 and 64. Therefore, as shown in Figure 4(a), in the comparative example, large spurious emissions occur because the difference between the sound velocity of transverse waves propagating in region 60 and the sound velocity of transverse waves propagating in regions 62 and 64 is large. On the other hand, as shown in Figure 4(b), in Example 1, spurious emissions are suppressed because the difference between the sound velocity of transverse waves propagating in region 60 and the sound velocity of transverse waves propagating in regions 62 and 64 is reduced by providing an additional film 50 between the IDT 20 and the reflector 25.

[0043] In Model 2, the speed of sound of transverse waves in region 60 is 0.952 times the speed of sound of transverse waves in regions 62 and 64. Therefore, in Example 1, in order to suppress spurious emissions 65, the speed of sound of transverse waves propagating in region 60 is set to be between 0.95 and 1.05 times the speed of sound of transverse waves propagating in regions 62 and 64. Considering that the speed of sound of transverse waves in region 60 of Model 1, 4200 m / s, is assumed to be the case when the additional film 50 is not provided, spurious emissions 65 can be suppressed by setting the value of (H1 × ρ1) to be between 0.4 and 1.6 times the value of (H2 × D × ρ2).

[0044] [Modified Example 1] Figure 8(a) is a plan view of the elastic wave device according to Modification 1 of Example 1, and Figure 8(b) is a plan view of the elastic wave device according to Modification 2 of Example 1. Figure 9(a) is a plan view of the elastic wave device according to Modification 3 of Example 1, and Figure 9(b) is a plan view of the elastic wave device according to Modification 4 of Example 1. Figures 8(a) to 9(b) illustrate a part of the elastic wave device.

[0045] As shown in Figure 8(a), in the elastic wave device 110 according to Modification 1 of Example 1, the additional film 50 is provided overlapping the comb-shaped electrode 21. The other configurations are the same as in Example 1, so their explanation is omitted. Since the comb-shaped electrode 21 is designed to obtain optimal characteristics, if the additional film 50 overlaps the comb-shaped electrode 21, the speed of sound of transverse waves may change, potentially causing spurious emissions. Therefore, from the viewpoint of suppressing spurious emissions, it is preferable that the additional film 50 does not overlap the comb-shaped electrode 21, as in Example 1. However, in the case where the additional film 50 overlaps the comb-shaped electrode 21, as in Modification 1 of Example 1, the overlap width W1 should be λ / 16 or less.

[0046] As shown in Figure 8(b), in the elastic wave device 120 according to Modification 2 of Example 1, the additional film 50 is provided overlapping the reflector 25. The other configurations are the same as in Example 1, so their explanation is omitted. The reflector 25 is also designed to obtain optimal characteristics, so if the additional film 50 overlaps the reflector 25, the speed of sound of transverse waves may change, potentially causing spurious emissions. Therefore, from the viewpoint of suppressing spurious emissions, it is preferable that the additional film 50 does not overlap the reflector 25, as in Example 1. However, if the additional film 50 overlaps the reflector 25, as in Modification 2 of Example 1, the overlap width W2 should be λ / 16 or less.

[0047] As shown in Figure 9(a), in the elastic wave device 130 according to Modification 3 of Example 1, the additional film 50 is provided away from the comb-shaped electrode 21. The other configurations are the same as in Example 1, so their explanation is omitted. If there is a region between the comb-shaped electrode 21 and the reflector 25 where the additional film 50 is not provided, the speed of sound of transverse waves in this region will increase, and spurious emissions may occur. Therefore, as in Example 1, it is preferable that the additional film 50 is not separated from the comb-shaped electrode 21, but if the additional film 50 is separated from the comb-shaped electrode 21, as in Modification 3 of Example 1, the spacing W3 should be λ / 16 or less.

[0048] As shown in Figure 9(b), in the elastic wave device 140 according to Modification 4 of Example 1, the additional film 50 is provided away from the reflector 25. The other configurations are the same as in Example 1, so their explanation is omitted. As described above, in the region between the comb-shaped electrode 21 and the reflector 25 where the additional film 50 is not provided, the speed of sound of transverse waves increases, which may cause spurious emissions. Therefore, as in Example 1, it is preferable that the additional film 50 is not far from the reflector 25, but if the additional film 50 is far from the reflector 25, as in Modification 4 of Example 1, the spacing W4 should be λ / 16 or less.

[0049] Figure 10 is a plan view of the elastic wave device according to Modification 5 of Example 1. Figure 10 shows a part of the elastic wave device. As shown in Figure 10, in the elastic wave device 150 according to Modification 5 of Example 1, the additional film 50 is provided on a part of the region 66 that extends between the comb-shaped electrode 21 and the reflector 25, with the intersection region 40. The additional film 50 is provided on more than half of the region 66, for example. The other configurations are the same as in Example 1, so their description is omitted. From the viewpoint of suppressing spurious emissions, it is preferable that the additional film 50 is provided on the entire region 66, but it is sufficient if it is provided on more than half of the region 66.

[0050] As described above, according to Example 1 and its modified form, an additional film 50 is provided on the piezoelectric body 18 between the comb-shaped electrode 21 and the reflector 25. The overlap width W1 and W2 of the additional film 50 in the X direction between the comb-shaped electrode 21 and the reflector 25 is 1 / 8 or less (λ / 16 or less) of the average pitch P of the electrode fingers 22, and the spacing W3 and W4 between the comb-shaped electrode 21 and the reflector 25 in the X direction is 1 / 8 or less (λ / 16 or less) of the average pitch P of the electrode fingers 22. By providing such an additional film 50, the influence of the additional film 50 on the comb-shaped electrode 21 and the reflector 25 is suppressed, and as shown in Figure 4(b), the sound velocity of transverse waves propagating in the region 60 between the comb-shaped electrode 21 and the reflector 25 can be brought closer to the sound velocity of transverse waves propagating in the region 62 where the comb-shaped electrode 21 is provided and the region 64 where the reflector 25 is provided. Therefore, longitudinal mode spurious emissions can be suppressed. From the viewpoint of suppressing spurious emissions, the overlap widths W1 and W2 and the spacings W3 and W4 are preferably 1 / 16 or less of the average pitch P (λ / 32) and more preferably zero. A manufacturing tolerance is acceptable for zero.

[0051] Furthermore, in Example 1 and its modified form, the additional film 50 is provided in more than half of the region 66 that extends between the comb-shaped electrode 21 and the reflector 25, with the intersection region 40 being the other half. This makes it possible to bring the sound velocity of transverse waves propagating in more than half of region 66 closer to the sound velocity of transverse waves propagating in regions 62 and 64, thereby suppressing longitudinal mode spurious emissions. From the viewpoint of suppressing spurious emissions, it is preferable that the additional film 50 is provided in more than two-thirds of region 66, more preferably in more than three-quarters of region 66, and even more preferably in the entire region.

[0052] Furthermore, in Example 1 and its modified form, the value obtained by multiplying the thickness H1 of the added film 50 by the density ρ1 of the added film 50 (H1 × ρ1) is 0.4 times or more and 1.6 times or less the value obtained by multiplying the thickness H2 of the electrode finger 22 by the duty cycle D of the electrode finger 22 and the density ρ2 of the electrode finger 22 (H2 × D × ρ2). This makes it possible to suppress longitudinal mode spurious emissions. From the viewpoint of suppressing spurious emissions, the value of (H1 × ρ1) is preferably 0.5 times or more and 1.5 times or less the value of (H2 × D × ρ2), more preferably 0.6 times or more and 1.4 times or less, and even more preferably 0.7 times or more and 1.3 times or less.

[0053] Furthermore, in Example 1 and its modified form, the speed of sound of transverse waves propagating in region 60 between the comb-shaped electrode 21 and the reflector 25 is 0.95 to 1.05 times the speed of sound of transverse waves propagating in region 62 where the comb-shaped electrode 21 is provided and the speed of sound of transverse waves propagating in region 64 where the reflector 25 is provided. This makes it possible to suppress longitudinal mode spurious emissions. From the viewpoint of suppressing spurious emissions, the speed of sound of transverse waves propagating in region 60 is preferably 0.97 to 1.03 times, and more preferably 0.98 to 1.02 times, the speed of sound of transverse waves propagating in regions 62 and 64.

[0054] Furthermore, in Example 1 and its modifications, the additional film 50 is a film mainly composed of tantalum oxide, niobium oxide, silicon oxide, or aluminum oxide. By using such an additional film 50, the speed of sound of transverse waves propagating in the region 60 between the comb-shaped electrode 21 and the reflector 25 can be easily brought closer to the speed of sound of transverse waves propagating in the region 62 where the comb-shaped electrode 21 is provided and the region 64 where the reflector 25 is provided. The additional film 50 may also be made of a metal film. Figure 11 is a cross-sectional view of the case in Example 1 where the additional film is a metal film. As shown in Figure 11, when an additional film 50a made of a metal film such as a titanium film is provided, an insulating film 35 is provided between the additional film 50a and the comb-shaped electrode 21 and the reflector 25.

[0055] In Example 1 and its modifications, the piezoelectric element 18 is shown as a piezoelectric layer provided on the support substrate 10, but it is not limited to this case. The piezoelectric element may also be a piezoelectric substrate instead of a support substrate 10. [Examples]

[0056] Figure 12(a) is a plan view of the elastic wave device according to Example 2, and Figure 12(b) is a cross-sectional view AA of Figure 12(a). As shown in Figures 12(a) and 12(b), in the elastic wave device 200 according to Example 2, no additional film is provided between the IDT 20 and the reflector 25. Instead, a recess 15 is provided in the piezoelectric body 18 between the IDT 20 and the reflector 25. The piezoelectric body 18 has a thin film region 17 in the area where the recess 15 is provided, and a thick film region 19 in the other areas which is thicker than the thin film region 17. Therefore, the IDT 20 and the reflector 25 are provided in the thick film region 19 of the piezoelectric body 18, and the piezoelectric body 18 between the IDT 20 and the reflector 25 is in the thin film region 17. That is, the IDT 20 and the reflector 25 are provided in the thick film region 19 of the piezoelectric body 18 with the thin film region 17 of the piezoelectric body 18 in between them. The other configurations are the same as in Example 1, so their description is omitted.

[0057] [simulation] Simulations were conducted to evaluate the speed of sound for models 4 and 5, which had different thicknesses of the piezoelectric element 18. Models 4 and 5 have the same structure as models 1-3 shown in Figures 6(a) and 6(b). The simulation conditions were as follows.

[0058] Common conditions Support substrate 10: Sapphire substrate Insulating film 12: Aluminum oxide film with a thickness of 6000 nm Temperature compensation film 14: Silicon oxide film with a thickness of 440 nm Piezoelectric material 18: Lithium tantalate film with a thickness of 0.1λ or 0.5λ IDT20, Reflector 25: A laminated film consisting of a 10nm thick titanium film and a 135nm thick aluminum film. Logarithm of IDT20: 150 pairs Logarithm of reflector 25: 20 pairs Duty cycle of electrode finger 22: 50% Length of dummy electrode finger 23 in the Y direction: 1.5λ Opening length L: 15λ Distance I between IDT20 and reflector 25: λ / 4 Difference in the speed of sound of transverse waves in regions 60, 62, and 64: Yes Conditions for Model 4 Wavelength of elastic wave λ: 1.5 μm Model 5 conditions Wavelength of elastic wave λ: 2.2 μm

[0059] Figures 13(a) and 13(b) show the simulation results of the real part of admittance, Real(Y), with respect to the speed of sound for transverse waves for models 4 and 5. In Figures 13(a) and 13(b), the horizontal axis represents frequency [MHz], and the vertical axis represents the real part of admittance, Real(Y) [S]. As shown in Figure 13(a), when the wavelength λ of the elastic wave is 1.5 μm, the speed of sound at the resonance point for transverse waves was 3802 m / s when the thickness of the piezoelectric material 18 was 0.1 λ, and 3966 m / s when the thickness was 0.5 λ. As shown in Figure 13(b), when the wavelength λ of the elastic wave is 2.2 μm, the speed of sound at the resonance point for transverse waves was 3777 m / s when the thickness of the piezoelectric material 18 was 0.1 λ, and 3891 m / s when the thickness was 0.5 λ. Thus, as the piezoelectric element 18 becomes thinner, the speed of sound in transverse waves decreases.

[0060] Therefore, in Example 2, the piezoelectric material 18 between the comb-shaped electrode 21 and the reflector 25 is thinned, which slows down the speed of sound of transverse waves propagating in the region between the comb-shaped electrode 21 and the reflector 25. Thus, the speed of sound of transverse waves propagating in the region between the comb-shaped electrode 21 and the reflector 25 can be brought closer to the speed of sound of transverse waves propagating in the region where the comb-shaped electrode 21 is provided and the speed of sound of transverse waves propagating in the region where the reflector is provided.

[0061] According to Example 2, the comb-shaped electrode 21 and the reflector 25 are provided in the thick film region 19 (first region) of the piezoelectric body 18, and the piezoelectric body 18 between the comb-shaped electrode 21 and the reflector 25 is a thin film region 17 (second region) that is thinner than the thick film region 19. As a result, the speed of sound of transverse waves propagating in the region between the comb-shaped electrode 21 and the reflector 25 can be brought closer to the speed of sound of transverse waves propagating in the region where the comb-shaped electrode 21 is provided and the region where the reflector 25 is provided. Therefore, longitudinal mode spurious signals can be suppressed.

[0062] Furthermore, in Example 2, it is preferable that the thickness of the thick film region 19 of the piezoelectric body 18 is twice or less (λ or less) the average pitch P of the electrode fingers 22. This makes it easier to reduce the speed of sound in transverse waves by forming a thin film region 17 on the piezoelectric body 18.

[0063] In Example 2, the recess 15 is shown as being located on the upper surface of the piezoelectric element 18, but the recess 15 may also be located on the lower surface of the piezoelectric element 18. [Examples]

[0064] Figure 14 is a circuit diagram of the filter according to Embodiment 3. As shown in Figure 14, the filter 300 according to Embodiment 3 has one or more series resonators S1 to S4 connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. At least one of the series resonators S1 to S4 and the parallel resonators P1 to P3 may be an elastic wave device from Embodiment 1, a modified example of Embodiment 1, or Embodiment 2. The number of series and parallel resonators can be set as appropriate. A ladder filter is shown as an example of the filter, but a multimode filter may also be used. [Examples]

[0065] Figure 15 is a circuit diagram of a duplexer according to Embodiment 4. As shown in Figure 15, the duplexer 400 according to Embodiment 4 has a transmit filter 70 connected between the common terminal Ant and the transmit terminal Tx. A receive filter 72 is connected between the common terminal Ant and the receive terminal Rx. The transmit filter 70 allows the transmit band signal from the high-frequency signal input from the transmit terminal Tx to pass to the common terminal Ant as the transmit signal, and suppresses signals of other frequencies. The receive filter 72 allows the receive band signal from the high-frequency signal input from the common terminal Ant to pass to the receive terminal Rx as the receive signal, and suppresses signals of other frequencies. At least one of the transmit filter 70 and the receive filter 72 can be the filter of Embodiment 3. Although a duplexer is shown as an example of a multiplexer, a triplexer or quadplexer may also be used.

[0066] Although 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 changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0067] 10...Support substrate, 12...Insulating film, 14...Temperature compensation film, 15...Recess, 16...Bonding layer, 17...Thin film region, 18...Piezoelectric material, 19...Thick film region, 20...IDT, 21...Comb-type electrode, 22...Electrode finger, 23...Dummy electrode finger, 24...Busbar, 25...Reflector, 26...Metal film, 27...Side, 28...Side, 29...Outer side, 30...Outer side, 35...Insulating film, 40...Crossing region, 50, 50a...Additional film, 51...Side, 52...Side, 53...Side, 54...Side, 60...Region, 62...Region, 64...Region, 66...Region, 70...Transmitting filter, 72...Receiving filter, 100, 110, 120, 130, 140, 150, 200, 500...Elastic wave device, 300...Filter, 400...Duplexer

Claims

1. Piezoelectric material and A pair of comb-shaped electrodes, each having multiple electrode fingers, are provided on the piezoelectric element. A reflector is provided on the piezoelectric body, arranged in the direction of the arrangement of the plurality of electrode fingers on the pair of comb-shaped electrodes, An elastic wave device comprising: an additional film provided on the piezoelectric body between the pair of comb-shaped electrodes and the reflector, wherein the overlap width between the pair of comb-shaped electrodes and the reflector is 1 / 8 or less of the average pitch of the plurality of electrode fingers of the pair of comb-shaped electrodes, and the distance between the pair of comb-shaped electrodes and the reflector is 1 / 8 or less of the average pitch.

2. The elastic wave device according to claim 1, wherein the additional film is provided in more than half of the region in which the intersection region where the plurality of electrode fingers of the pair of comb-shaped electrodes intersect is extended between the pair of comb-shaped electrodes and the reflector.

3. The elastic wave device according to claim 1 or 2, wherein the product of the thickness of the added film and the density of the added film is 0.4 times or more and 1.6 times or less the product of the thickness of the plurality of electrode fingers, the duty cycle of the plurality of electrode fingers, and the density of the plurality of electrode fingers.

4. The elastic wave device according to claim 1 or 2, wherein the added film is a film mainly composed of tantalum oxide, niobium oxide, silicon oxide, or aluminum oxide.

5. The elastic wave device according to claim 1 or 2, wherein the speed of sound of a transverse wave propagating in the region between the pair of comb-shaped electrodes and the reflector is 0.95 times or more and 1.05 times or less the speed of sound of a transverse wave propagating in the region where the pair of comb-shaped electrodes are provided.

6. A piezoelectric body having a first region of a first thickness and a second region of a second thickness that is thinner than the first thickness, A pair of comb-shaped electrodes, each having multiple electrode fingers, are provided on the piezoelectric body in the first region, An elastic wave device comprising: a reflector provided on the piezoelectric material in the first region, arranged in the direction of the arrangement of the plurality of electrode fingers on the pair of comb-shaped electrodes, and having a second region of the piezoelectric material between itself and the pair of comb-shaped electrodes.

7. The elastic wave device according to claim 6, wherein the thickness of the piezoelectric material in the first region is less than or equal to twice the average pitch of the plurality of electrode fingers of the pair of comb-shaped electrodes.

8. Piezoelectric material and A pair of comb-shaped electrodes, each having multiple electrode fingers, are provided on the piezoelectric element. An elastic wave device comprising: a reflector provided on the piezoelectric body in the direction of the arrangement of the plurality of electrode fingers on the pair of comb-shaped electrodes, wherein the speed of sound of transverse waves propagating in the region between the pair of comb-shaped electrodes is 0.95 times or more and 1.05 times or less than the speed of sound of transverse waves propagating in the region on which the pair of comb-shaped electrodes are provided.

9. A filter comprising the elastic wave device according to claim 1, 6, or 8.

10. A multiplexer comprising the filter described in claim 9.

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