Elastic wave device

Abstract

To suppress spurious.SOLUTION: An elastic wave device 100 includes: a piezoelectric substrate 12; and a pair of comb-shaped electrodes 21 which is provided on the piezoelectric substrate 12, each includes a plurality of electrode fingers 22 and a plurality of dummy electrode fingers 23 (metal sections) which are provided between the electrode fingers 22 adjacent to each other in a short-side direction (X direction) of the plurality of electrodes 22 among the plurality of electrode fingers 22 and have lengths in a long-side direction (Y direction) shorter than the plurality of electrode fingers 22 and in which the plurality of electrode fingers 22 are alternately arranged in at least a part and acoustic velocity of elastic waves propagating in a dummy region 34 where the plurality of dummy electrode fingers 23 are positioned is faster than acoustic velocity of elastic waves propagating in a central region 31 of an intersection region 30 where the plurality of electrode fingers 22 intersect each other and being equal to or less than 1.10 times.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an elastic wave device.

Background Art

[0002] In a high-frequency communication system typified by a mobile phone, an elastic wave device is used. As an elastic wave device, an elastic wave device including a pair of comb-shaped electrodes including a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected is known (for example, Patent Documents 1 to 3). Further, as a method for reducing spurious without degrading the Q value, an elastic wave device using a piston mode is known (for example, Patent Documents 4 and 5).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0004] Spurious can be suppressed by using the piston mode. However, there is still room for improvement in terms of suppressing spurious.

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

Means for Solving the Problems

[0006] The present invention includes a piezoelectric substrate, a plurality of electrode fingers provided on the piezoelectric substrate, and a plurality of metal portions provided between adjacent electrode fingers in the short direction of the plurality of electrode fingers and having a length in the longitudinal direction shorter than that of the plurality of electrode fingers. The plurality of electrode fingers are alternately arranged at least partially, and the sound velocity of an elastic wave propagating in a region where the plurality of metal portions are located is faster than and not more than 1.10 times the sound velocity of an elastic wave propagating in a central region of an intersection region where the plurality of electrode fingers intersect each other. The elastic wave device includes a pair of comb-shaped electrodes.

[0007] In the above configuration, the sound velocity of the elastic wave propagating in the region where the plurality of metal portions are located can be set to be 1.03 times or more the sound velocity of the elastic wave propagating in the central region.

[0008] In the above configuration, the plurality of metal portions of one of the pair of comb-shaped electrodes face the plurality of electrode fingers of the other comb-shaped electrode, and the width in the short direction can be configured such that the plurality of metal portions are smaller than the plurality of electrode fingers.

[0009] In the above configuration, a first insulating film provided on the piezoelectric substrate covering the plurality of electrode fingers in the central region, and a second insulating film provided on the piezoelectric substrate covering the plurality of metal portions in the region where the plurality of metal portions are located and mainly composed of a material having a faster sound velocity of elastic waves than the first insulating film can be provided.

[0010] In the above configuration, an additional film provided at an end portion in the longitudinal direction of the plurality of electrode fingers can be provided.

[0011] The present invention relates to an elastic wave device including a piezoelectric substrate, a plurality of electrode fingers provided on the piezoelectric substrate, and a plurality of metal parts provided between adjacent electrode fingers among the plurality of electrode fingers in the short side direction of the plurality of electrode fingers, the width of the plurality of metal parts in the short side direction being smaller than that of the plurality of electrode fingers, and a pair of comb-shaped electrodes in which the plurality of electrode fingers are alternately arranged at least partially.

[0012] In the above configuration, two of the plurality of metal parts may be provided between the adjacent electrode fingers, and the width of the plurality of metal parts in the short side direction may be 0.56 times or more and 0.64 times or less the width of the plurality of electrode fingers in the short side direction.

[0013] In the above configuration, three of the plurality of metal parts may be provided between the adjacent electrode fingers, and the width of the plurality of metal parts in the short side direction may be 0.39 times or more and 0.45 times or less the width of the plurality of electrode fingers in the short side direction.

[0014] In the above configuration, the width of the plurality of electrode fingers in the short side direction may be equal from one end connected to the bus bar to the other end on the opposite side, and the widths of the plurality of metal parts in the short side direction may be equal to each other.

[0015] The present invention relates to an elastic wave device including a piezoelectric substrate, a plurality of electrode fingers provided on the piezoelectric substrate, and a plurality of metal parts provided between adjacent electrode fingers among the plurality of electrode fingers in the short side direction of the plurality of electrode fingers, the plurality of metal parts being mainly composed of a material having a higher sound velocity of elastic waves than that of the plurality of electrode fingers, and a pair of comb-shaped electrodes in which the plurality of electrode fingers are alternately arranged at least partially.

Advantages of the Invention

[0016] According to the present invention, spurious can be suppressed.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Embodiments for Carrying Out the Invention

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

Examples

[0019] Fig. 1(a) is a plan view of the surface acoustic wave device 100 according to Example 1, and Fig. 1(b) is a cross-sectional view taken along line A-A of Fig. 1(a). The short side direction of the electrode finger 22 is defined as the X direction, the long side direction of the electrode finger 22 is defined as the Y direction, and the thickness direction of the piezoelectric substrate 12 is defined as the Z direction. The short side direction of the electrode finger 22 is also the arrangement direction of the plurality of electrode fingers 22. The X direction, Y direction, and Z direction do not necessarily correspond to the X-axis direction and Y-axis direction of the crystal orientation of the piezoelectric substrate 12. When the piezoelectric substrate 12 is a piezoelectric substrate of rotation Y-cut X-propagation, the X direction is the X-axis direction of the crystal orientation.

[0020] As shown in Figs. 1(a) and 1(b), the piezoelectric substrate 12 is bonded onto the support substrate 10. The support substrate 10 is, for example, a sapphire substrate, an alumina substrate, a spinel substrate, a quartz substrate, a crystal substrate, a silicon carbide substrate, or a silicon substrate. The piezoelectric substrate 12 is, for example, a single crystal lithium tantalate substrate or a single crystal lithium niobate substrate, and is, for example, a rotation Y-cut X-propagation lithium tantalate substrate or a rotation Y-cut X-propagation lithium niobate substrate. The piezoelectric substrate 12 may be, for example, a 30° to 50° Y-cut X-propagation lithium tantalate substrate. An insulating layer such as silicon oxide, aluminum oxide, and / or aluminum nitride may be provided between the support substrate 10 and the piezoelectric substrate 12. In this way, the piezoelectric substrate 12 is bonded to the support substrate 10 directly or indirectly.

[0021] An IDT (Interdigital Transducer) 20 and a reflector 25 are provided on a piezoelectric substrate 12. The IDT 20 includes a pair of comb-shaped electrodes 21. The comb-shaped electrodes 21 include a plurality of electrode fingers 22, a plurality of dummy electrode fingers 23 provided in two or more between each of the adjacent electrode fingers 22 in the X direction, and a bus bar 24 to which the plurality of electrode fingers 22 and the plurality of dummy electrode fingers 23 are connected. Here, a case where two dummy electrode fingers 23 are provided between each of the adjacent electrode fingers 22 in the X direction is shown as an example. The widths of the electrode fingers 22 and the dummy electrode fingers 23 in the X direction are constant from one end connected to the bus bar 24 to the other end on the opposite side. The width of the dummy electrode fingers 23 in the X direction is smaller than the width of the electrode fingers 22 in the X direction. The thickness of the electrode fingers 22 and the thickness of the dummy electrode fingers 23 are the same. The same thickness allows a difference of the order of manufacturing error, for example, allowing a range from 0.95 times to 1.05 times. The dummy electrode fingers 23 are an example of the metal part in the claims.

[0022] The IDT 20 and the reflector 25 are formed by a metal film 26 on the piezoelectric substrate 12. The metal film 26 is a film mainly composed of, for example, aluminum, copper, molybdenum, iridium, platinum, rhenium, rhodium, ruthenium, tantalum, or tungsten. An adhesion film such as titanium or chromium may be provided between the electrode fingers 22, the dummy electrode fingers 23, and the bus bar 24, and the piezoelectric substrate 12. The adhesion film is thinner than the electrode fingers 22, the dummy electrode fingers 23, and the bus bar 24.

[0023] The region where the electrode fingers 22 of the pair of comb-shaped electrodes 21 intersect is the intersection region 30. The length in the Y direction of the intersection region 30 is the aperture length. The pair of comb-shaped electrodes 21 face each other such that the electrode fingers 22 are alternately arranged in the X direction in at least a part of the intersection region 30. The elastic wave (surface elastic wave) of the main mode excited by the electrode fingers 22 in the intersection region 30 mainly propagates in the X direction. The pitch of the electrode fingers 22 of one of the comb-shaped electrodes 21 is approximately the wavelength λ of the surface elastic wave. Approximately twice the pitch D of the plurality of electrode fingers 22 is the wavelength λ. The reflector 25 reflects the surface elastic wave excited by the electrode fingers 22 of the IDT 20. Thereby, the surface elastic wave is confined within the intersection region 30 of the IDT 20.

[0024] The intersection region 30 has an edge region 32 which is a region located at the edge in the Y direction and a central region 31 which is a region located inside the edge region 32 in the Y direction. The edge region 32 can also be said to be the region where the tip of the electrode finger 22 of the intersection region 30 is located. The region located between the tip of the electrode finger 22 of one comb-shaped electrode 21 and the tip of the dummy electrode finger 23 of the other comb-shaped electrode 21 is the gap region 33. The region where the dummy electrode finger 23 is located is the dummy region 34. The region where the bus bar 24 is located is the bus bar region 35. The dummy region 34 is an example of the region where a plurality of metal parts in the claims are located.

[0025] An additional film 40 is provided on the piezoelectric substrate 12 in the edge region 32. The additional film 40 covers the electrode finger 22 located in the edge region 32. The additional film 40 is also provided in the portion where the electrode finger 22 is not provided in the edge region 32. The additional film 40 is not provided in the central region 31, the gap region 33, the dummy region 34, and the bus bar region 35.

[0026] The additional film 40 is an insulating film mainly composed of, for example, silicon oxide, tantalum oxide, or niobium oxide. However, as long as it is possible to adjust the sound velocity of the elastic wave propagating in the edge region 32, a film mainly composed of other materials may also be used.

[0027] Here, for a certain film to be mainly composed of a certain element, it is allowed that the film contains intentional or unintentional impurities other than the main component. When a certain element is the main component in a certain film, the concentration of the certain element is, for example, 50 atomic% or more, and for example, 80 atomic% or more. In the case of two elements being the main components such as silicon oxide, the total of the concentration of silicon and the concentration of oxygen is, for example, 50 atomic% or more, and for example, 80 atomic% or more, and the concentration of silicon and the concentration of oxygen are each, for example, 10 atomic% or more.

[0028] [Manufacturing method] A method for manufacturing the elastic wave device 100 according to Embodiment 1 will be described. First, the piezoelectric substrate 12 is bonded onto the support substrate 10 using, for example, the surface activation method. Thereafter, the piezoelectric substrate 12 is polished using, for example, the CMP (Chemical Mechanical Polishing) method to obtain a desired thickness. Next, after forming a metal film 26 on the piezoelectric substrate 12, it is patterned into a desired shape. As a result, an IDT 20 including a pair of comb-shaped electrodes 21 each including a plurality of electrode fingers 22, a plurality of dummy electrode fingers 23, and a bus bar 24, and a reflector 25 are formed on the piezoelectric substrate 12. The metal film 26 is formed using, for example, a sputtering method, a vacuum evaporation method, or a CVD (Chemical Vapor Deposition) method, etc. The patterning of the metal film 26 uses, for example, a photolithography method and an etching method.

[0029] Next, an additional film 40 is formed so as to cover the electrode fingers 22 in the edge region 32. The additional film 40 is formed, for example, by forming a mask layer having an opening in the edge region 32 on the piezoelectric substrate 12, then forming the additional film 40 using the mask layer as a mask, and thereafter removing the mask layer. The mask layer uses, for example, a photoresist. The additional film 40 is formed using, for example, a sputtering method, a vacuum evaporation method, or a CVD method. As a result, the elastic wave device 100 according to Embodiment 1 is formed.

[0030] [Comparative Example] FIG. 2(a) is a plan view of the elastic wave device 500 according to the comparative example, and FIG. 2(b) is a cross-sectional view taken along line A-A of FIG. 2(a). As shown in FIGS. 2(a) and 2(b), in the comparative example, one of the comb-shaped electrodes 21 has one dummy electrode finger 23 facing the tip of the electrode finger 22 of the other comb-shaped electrode 21 between adjacent electrode fingers 22 in the X direction. The width of the dummy electrode finger 23 in the X direction is the same as the width of the electrode finger 22 in the X direction. Since the other configurations are the same as those in Embodiment 1, the description thereof is omitted.

[0031] [Sound Velocity of Elastic Wave] FIG. 3(a) is a diagram showing the sound velocity of elastic waves in the comparative example, and FIG. 3(b) is a diagram showing the sound velocity of elastic waves in Example 1. As shown in FIG. 3(a), in the elastic wave device 500 according to the comparative example, the dummy electrode fingers 23 have the same width and the same thickness as the electrode fingers 22. For this reason, the sound velocity of the elastic waves propagating through the dummy region 34 is the same as the sound velocity of the elastic waves propagating through the central region 31. Since the additional film 40 is provided in the edge region 32, the sound velocity of the elastic waves propagating through the edge region 32 is slower than the sound velocity of the elastic waves propagating through the central region 31. The piston mode can be realized because the sound velocity of the elastic waves propagating through the edge region 32 is slower than the sound velocity of the elastic waves propagating through the central region 31. The sound velocity of the elastic waves propagating through the gap region 33 is faster than the sound velocity of the elastic waves propagating through the central region 31 and the dummy region 34. Note that the sound velocity of the elastic waves is the sound velocity of surface elastic waves (e.g., SH waves) propagating on the surface of the piezoelectric substrate 12.

[0032] As shown in FIG. 3(b), in the elastic wave device 100 according to Example 1, two dummy electrode fingers 23 having a width smaller than that of the electrode fingers 22 are provided between the adjacent electrode fingers 22 in the X direction in one of the comb-shaped electrodes 21. By providing such dummy electrode fingers 23, the sound velocity of the elastic waves propagating through the dummy region 34 becomes faster than the sound velocity of the elastic waves propagating through the central region 31. The sound velocity of the elastic waves propagating through the dummy region 34 is, for example, 1.10 times or less the sound velocity of the elastic waves propagating through the central region 31. Since the other aspects are the same as those in FIG. 3(a), the description thereof is omitted.

[0033] The sound velocity of the elastic waves can be obtained, for example, by Equation (1). In Equation (1), V is the sound velocity, ρ is the density, E is the Young's modulus, and ν is the Poisson's ratio.

Equation

[0034] To realize the piston mode, it is preferable that the length of the central region 31 in the Y direction and the length of the edge region 32 in the Y direction satisfy a certain relationship. For example, the length of the central region 31 in the Y direction is preferably longer than the total length of the edge region 32 in the Y direction. The length of each edge region 32 in the Y direction is preferably 1λ or less (for example, 1 / 20 or less of the aperture length), and more preferably 0.5λ or less (for example, 1 / 40 or less of the aperture length). The length of each edge region 32 in the Y direction is preferably 0.05λ or more (for example, 1 / 400 or more of the aperture length), and more preferably 0.1λ or more (for example, 1 / 200 or more of the aperture length). The edge region 32 may be provided only on one side of the central region 31. The length of the gap region 33 in the Y direction is preferably 2λ or less (for example, 1 / 10 or less of the aperture length), and more preferably 1λ or less (for example, 1 / 20 or less of the aperture length). The length of each gap region 33 in the Y direction is preferably 0.1λ or more (for example, 1 / 200 or more of the aperture length), and more preferably 0.2λ or more (for example, 1 / 100 or more of the aperture length).

[0035] [Simulation 1] Simulation 1 regarding the increase in the sound velocity of the elastic wave propagating through the dummy region 34 in Example 1 will be described. Fig. 4(a) is a plan view of models A and B for which Simulation 1 was performed, and Fig. 4(b) is a cross-sectional view taken along line A-A of Fig. 4(a). Fig. 4(c) is a plan view of model C for which Simulation 1 was performed, and Fig. 4(d) is a cross-sectional view taken along line A-A of Fig. 4(c). Although reflectors 25 sandwiching the IDT 20 are provided, they are not shown in Figs. 4(a) and 4(c) for the sake of clarity of the figure. As shown in Figs. 4(b) and 4(d), in all of models A, B, and C, the piezoelectric substrate 12 is bonded onto the support substrate 10 with the insulating layer 13 and the insulating layer 14 interposed therebetween. Also, as shown in Figs. 4(a) and 4(c), in all of models A, B, and C, an additional film 40 is provided in the edge region 32.

[0036] As shown in FIG. 4(a), in Model A and Model B, one dummy electrode finger 23 is provided between each of the electrode fingers 22 adjacent in the X direction in one of the comb-shaped electrodes 21. In Model A, the width of the dummy electrode finger 23 is the same as the width of the electrode finger 22. In Model B, the width of the dummy electrode finger 23 is smaller than the width of the electrode finger 22. As shown in FIG. 4(c), in Model C, two dummy electrode fingers 23 having a width smaller than that of the electrode finger 22 are provided between each of the electrode fingers 22 adjacent in the X direction in one of the comb-shaped electrodes 21.

[0037] The simulation conditions are as follows. Common conditions for Models A, B, and C Wavelength λ of surface acoustic wave: 2.2 μm Support substrate 10: Sapphire substrate Insulating layer 13: Aluminum oxide layer with a thickness of 2.72λ Insulating layer 14: Silicon oxide layer with a thickness of 0.2λ Piezoelectric substrate 12: 42° Y-cut X-propagating lithium tantalate substrate with a thickness of 0.3λ Electrode finger 22, dummy electrode finger 23, and bus bar 24: Aluminum film with a thickness of 0.07λ Additional film 40: Niobium oxide film with a thickness of 0.01λ Width W1 of electrode finger 22: 0.55 μm Pitch D of electrode finger 22: 1.1 μm Conditions for Model A Width W2 of dummy electrode finger 23: 0.55 μm Distance L1 between electrode finger 22 and dummy electrode finger 23: 0.55 μm Conditions for Model B Width W2 of dummy electrode finger 23: 0.33 μm Distance L1 between electrode finger 22 and dummy electrode finger 23: 0.66 μm Conditions for Model C Width W2 of dummy electrode finger 23: 0.33 μm Distance L2 between electrode finger 22 and dummy electrode finger 23 and distance L3 between dummy electrode fingers 23: 0.33 μm

[0038] FIG. 5 is a diagram showing the absolute value |Y| of admittance with respect to frequency in Simulation 1. In the absolute value |Y| of admittance, peaks of the resonance frequency fr and the anti-resonance frequency fa are observed. As shown in FIG. 5, in Model B, the resonance frequency fr is shifted to the higher frequency side compared to Model A. In Model C, the resonance frequency fr is shifted to the higher frequency side compared to Model B. The speed of sound propagating through the dummy region 34 increases when the width W2 of the dummy electrode finger 23 is made narrower as in Model B, compared to the case where the width W2 of the dummy electrode finger 23 is the same as the width W1 of the electrode finger 22 as in Model A. In such a case, the resonance frequency fr of Model B is shifted to the higher frequency side compared to Model A. Since the resonance frequency fr of Model C is shifted to the higher frequency side compared to Model B, it can be seen that the speed of sound propagating through the dummy region 34 in Model C is higher than that in Model B. Therefore, in Example 1, as shown in FIG. 3(b), the speed of sound of the elastic wave propagating through the dummy region 34 increases.

[0039] [Simulation 2] Simulation 2 regarding the speed of sound and spurious in the dummy region 34 was performed. Simulation 2 was performed using models D, E, F, G, and H having the structures shown in FIGS. 4(a) and 4(b). The simulation conditions are as follows. Common conditions for models D, E, F, G, and H Wavelength λ of the surface acoustic wave: 5.0 μm Support substrate 10: Sapphire substrate Insulating layer 13: Aluminum oxide layer with a thickness of 2.72λ Insulating layer 14: Silicon oxide layer with a thickness of 0.2λ Piezoelectric substrate 12: 42° Y-cut X-propagation lithium tantalate substrate with a thickness of 0.3λ Electrode finger 22, dummy electrode finger 23, and bus bar 24: Aluminum film with a thickness of 0.1λ Additional film 40: Niobium oxide film with a thickness of 0.01λ Width W1 of the electrode finger 22: 1.25 μm Pitch D of the electrode finger 22: 2.5 μm Speed of sound in the central region 31: 3750 m / s Sound velocity in the edge region 32: 3675 m / s Sound velocity in the gap region 33: 4200 m / s Conditions of Model D Sound velocity in the dummy region 34: the same as the sound velocity in the central region 31 (3750 m / s) Conditions of Model E Sound velocity in the dummy region 34: 1.03 times the sound velocity in the central region 31 (3862.5 m / s) Conditions of Model F Sound velocity in the dummy region 34: 1.05 times the sound velocity in the central region 31 (3937.5 m / s) Conditions of Model G Sound velocity in the dummy region 34: 1.08 times the sound velocity in the central region 31 (4050 m / s) Conditions of Model H Sound velocity in the dummy region 34: 1.10 times the sound velocity in the central region 31 (4125 m / s)

[0040] Figures 6(a) to 7(b) are diagrams showing the real part Real(Y) of the admittance with respect to the frequency in Simulation 2. In the real part Real(Y) of the admittance, a spurious response is observed to be larger compared to the absolute value |Y|. As shown in Figure 6(a), Model E has a reduced spurious compared to Model D. As shown in Figure 6(b), Model F has a reduced spurious compared to Model E. As shown in Figures 7(a) and 7(b), Models G and H have an increased spurious around 780 MHz compared to Model F, but the spurious is reduced compared to Model D.

[0041] From the results of Simulation 2, it can be seen that, like Models E to H, by making the sound velocity of the elastic wave in the dummy region 34 faster than the sound velocity of the elastic wave in the central region 31, the spurious can be reduced. Also, since Models G and H have a larger spurious than Model F, it can be seen that there is an upper limit to the sound velocity of the elastic wave in the dummy region 34. From the perspective of reducing the spurious, the sound velocity of the elastic wave in the dummy region 34 is preferably 1.10 times or less, more preferably 1.08 times or less, and even more preferably 1.06 times or less the sound velocity of the elastic wave in the central region 31.

[0042] In the IDT20, when the displacements of the standing waves generated in the Y direction are completely canceled out with positive and negative signs, no spurious signals are generated. However, the portion that cannot be canceled out appears as spurious signals. When the sound velocity of the elastic waves in the dummy region 34 becomes faster than the sound velocity of the elastic waves in the central region 31, the shape of the standing wave changes due to the improvement of the confinement effect. Due to the change in the shape of the standing wave, the portion where the displacements of the standing wave cannot be canceled out with positive and negative signs is reduced. As a result, it is considered that the spurious signals are reduced in Models E to H.

[0043] [Modified Example 1] FIG. 8(a) is a plan view of the elastic wave device 110 according to Modified Example 1 of Example 1, and FIG. 8(b) is a cross-sectional view taken along line A-A of FIG. 8(a). As shown in FIGS. 8(a) and 8(b), in Modified Example 1 of Example 1, one dummy electrode finger 23 is provided between each of the adjacent electrode fingers 22 in the X direction in one comb-shaped electrode 21. The tip of the dummy electrode finger 23 of one comb-shaped electrode 21 faces the tip of the electrode finger 22 of the other comb-shaped electrode 21. The width of the dummy electrode finger 23 in the X direction is smaller than the width of the electrode finger 22 in the X direction. Since the other configurations are the same as those in Example 1, the description thereof is omitted. Also in Modified Example 1 of Example 1, the sound velocity of the elastic waves in the dummy region 34 becomes faster than the sound velocity of the elastic waves in the central region 31. The sound velocity of the elastic waves propagating through the dummy region 34 is, for example, 1.10 times or less the sound velocity of the elastic waves propagating through the central region 31.

[0044] [Experiment] An experiment was conducted to fabricate the elastic wave devices according to Example 1 and Modified Example 1 of Example 1 and evaluate the spurious signals. The experimental conditions are as follows. Common Conditions Wavelength λ of the surface elastic wave: 3 μm Support substrate 10: Sapphire substrate Piezoelectric substrate 12: 42°Y-cut X-propagating lithium tantalate substrate with a thickness of 0.15λ Electrode finger 22, dummy electrode finger 23, and bus bar 24: Aluminum film with a thickness of 0.03λ Additional film 40: Niobium oxide film with a thickness of 0.007λ Width of the electrode finger 22: 0.76 μm Duty ratio of the electrode finger 22: 50% Conditions of Example 1 Width of dummy electrode finger 23: 0.5 μm Duty ratio of dummy electrode finger 23: 50% Sound velocity in dummy region 34: 1.05 times the sound velocity in central region 31 Conditions of Modification 1 of Example 1 Width of dummy electrode finger 23: 0.5 μm Duty ratio of dummy electrode finger 23: 30% Sound velocity in dummy region 34: 1.03 times the sound velocity in central region 31

[0045] Fig. 9 shows the experimental results of the real part Real(Y) of admittance with respect to frequency in Example 1 and Modification 1 of Example 1. As shown in Fig. 9, also in the experimental results of Example 1 with a sound velocity difference of 1.05 times between the dummy region 34 and the central region 31 and Modification 1 of Example 1 with a sound velocity difference of 1.03 times, results similar to the simulation results of Model F with a sound velocity difference of 1.05 times and Model E with a sound velocity difference of 1.03 times shown in Fig. 6(b) were obtained.

[0046] Figs. 10(a) and 10(b) show the experimental results of the real part Real(Y) of admittance with respect to frequency when the laminated structure of the substrate is changed in Example 1 and Modification 1 of Example 1. Fig. 10(b) shows the experimental results when, in addition to the structure of Fig. 10(a), a high sound velocity film with a thickness of 0.25λ is provided between the support substrate 10 and the piezoelectric substrate 12. As shown in Figs. 10(a) and 10(b), even when the laminated structure of the substrate is different, results similar to those in Fig. 9 were obtained. From this, it can be said that the influence of the laminated structure of the substrate is small.

[0047] [Modifications 2 and 3] FIG. 11(a) is a plan view of the elastic wave device 120 according to Modification 2 of Example 1, and FIG. 11(b) is a cross-sectional view taken along line A-A of FIG. 11(a). As shown in FIGS. 11(a) and 11(b), in Modification 2 of Example 1, one dummy electrode finger 23 having the same width as the electrode finger 22 is provided between each of the electrode fingers 22 adjacent in the X direction in one of the comb-shaped electrodes 21. The dummy electrode finger 23 faces the tip of the electrode finger 22 and is formed mainly of a material having a higher sound velocity than the electrode finger 22. For example, when the electrode finger 22 is formed mainly of aluminum, the dummy electrode finger 23 is formed mainly of beryllium or sodium. When the electrode finger 22 is formed mainly of gold, molybdenum, or tungsten, the dummy electrode finger 23 is formed mainly of aluminum. The comparison of the sound velocities here may be made by comparing the sound velocities obtained from the above Equation (1). Since the other configurations are the same as those in Example 1, the description thereof is omitted. Also in Modification 2 of Example 1, the sound velocity of the elastic wave in the dummy region 34 is higher than the sound velocity of the elastic wave in the central region 31. The sound velocity of the elastic wave propagating through the dummy region 34 is, for example, 1.10 times or less the sound velocity of the elastic wave propagating through the central region 31.

[0048] FIG. 12(a) is a plan view of the elastic wave device 130 according to Modification 3 of Example 1, and FIG. 12(b) is a cross-sectional view taken along line A-A of FIG. 12(a). As shown in FIGS. 12(a) and 12(b), in Modification 3 of Example 1, one dummy electrode finger 23 having the same width as the electrode finger 22 is provided between each pair of adjacent electrode fingers 22 in the X direction in one of the comb-shaped electrodes 21. The dummy electrode finger 23 faces the tip of the electrode finger 22 and is formed mainly of the same material as the electrode finger 22. A protective film 42 is provided on the piezoelectric substrate 12 in the crossing region 30, the gap region 33, and the bus bar region 35 to cover the electrode finger 22 and the bus bar 24. A protective film 44 mainly composed of a material having a higher sound velocity than that of the protective film 42 is provided on the piezoelectric substrate 12 in the dummy region 34 to cover the dummy electrode finger 23. For example, when the protective film 42 is formed mainly of silicon oxide, the protective film 44 is formed mainly of silicon nitride. The thicknesses of the protective film 42 and the protective film 44 are the same. The comparison of the sound velocities here may be made by comparing the sound velocities obtained from the above Equation (1). Since the other configurations are the same as those in Example 1, the description thereof is omitted. Also in Modification 3 of Example 1, the sound velocity of the elastic wave in the dummy region 34 is higher than the sound velocity of the elastic wave in the central region 31. The sound velocity of the elastic wave propagating through the dummy region 34 is, for example, 1.10 times or less the sound velocity of the elastic wave propagating through the central region 31.

[0049] As described above, according to Example 1 and its modifications, the sound velocity of the elastic wave propagating through the dummy region 34 is higher than and 1.10 times or less the sound velocity of the elastic wave propagating through the central region 31. Thereby, spurious can be suppressed as shown in FIGS. 6(a) to 7(b). From the viewpoint of suppressing spurious, the sound velocity of the elastic wave propagating through the dummy region 34 is preferably 1.09 times or less, more preferably 1.08 times or less, and still more preferably 1.07 times or less the sound velocity of the elastic wave propagating through the central region 31.

[0050] In addition, in Example 1 and its modified examples, the sound velocity of the elastic wave propagating through the dummy region 34 is 1.03 times or more the sound velocity of the elastic wave propagating through the central region 31. Thereby, spurious can be suppressed as shown in FIGS. 6(a) to 7(a). From the viewpoint of suppressing spurious, the sound velocity of the elastic wave propagating through the dummy region 34 is preferably 1.04 times or more, and more preferably 1.05 times or more the sound velocity of the elastic wave propagating through the central region 31.

[0051] In addition, in Example 1, as shown in FIG. 1(a), in one of the comb-shaped electrodes 21, two dummy electrode fingers 23 are provided between the electrode fingers 22 adjacent in the X direction among the plurality of electrode fingers 22. The width of the dummy electrode finger 23 in the X direction is smaller than the width of the electrode finger 22 in the X direction. By providing such dummy electrode fingers 23, the sound velocity of the elastic wave propagating through the dummy region 34 becomes faster than the sound velocity of the elastic wave propagating through the central region 31. Therefore, spurious can be suppressed.

[0052] When two dummy electrode fingers 23 are provided between each of the electrode fingers 22 adjacent in the X direction, the width of the dummy electrode finger 23 in the short side direction (X direction) may be 0.56 times or more and 0.64 times or less the width of the electrode finger 22 in the short side direction (X direction). In this case, the duty ratios of the electrode finger 22 and the dummy electrode finger 23 can be within the range of 30% to 70%, improving the ease of manufacture. Also, the sound velocity of the elastic wave in the dummy region 34 becomes 1.03 times or more and 1.10 times or less the sound velocity of the elastic wave in the central region 31. The widths of the dummy electrode fingers 23 in the short side direction are preferably equal to each other. Equal widths allow for a difference of the order of manufacturing error, for example, allowing 0.95 times or more and 1.05 times or less.

[0053] FIG. 13(a) is a plan view of the case where three dummy electrode fingers 23 are provided between adjacent electrode fingers 22 in Example 1, and FIG. 13(b) is a cross-sectional view taken along line A-A of FIG. 13(a). As shown in FIGS. 13(a) and 13(b), three dummy electrode fingers 23 may be provided between each of the adjacent electrode fingers 22 in the X direction. In this case, the width of the dummy electrode finger 23 in the short side direction (X direction) may be 0.39 times or more and 0.45 times or less the width of the electrode finger 22 in the short side direction (X direction). In this case, the duty ratios of the electrode finger 22 and the dummy electrode finger 23 can be within the range of 30% to 70%, and the manufacturability is improved. Also, the sound velocity of the elastic wave in the dummy region 34 is 1.03 times or more and 1.10 times or less the sound velocity of the elastic wave in the central region 31. The widths of the dummy electrode fingers 23 in the short side direction are preferably equal to each other.

[0054] Note that the number of dummy electrode fingers 23 provided between each of the adjacent electrode fingers 22 in the X direction is not limited to two or three, and may be two or more.

[0055] Also, in Modification 1 of Example 1, as shown in FIG. 8(a), the dummy electrode fingers 23 of one comb-shaped electrode 21 face the electrode fingers 22 of the other comb-shaped electrode 21, and the width of the dummy electrode fingers 23 in the short side direction (X direction) is smaller than the width of the electrode fingers 22 in the short side direction (X direction). Thereby, the sound velocity of the elastic wave propagating through the dummy region 34 becomes faster than the sound velocity of the elastic wave propagating through the central region 31. Therefore, spurious can be suppressed.

[0056] Also, in Modification 2 of Example 1, as shown in FIGS. 11(a) and 11(b), the dummy electrode fingers 23 are mainly composed of a material having a faster sound velocity of elastic waves than the electrode fingers 22. Thereby, the sound velocity of the elastic wave propagating through the dummy region 34 becomes faster than the sound velocity of the elastic wave propagating through the central region 31. Therefore, spurious can be suppressed.

[0057] Also, in Modification Example 3 of Example 1, as shown in FIG. 12(b), a protective film 42 (first insulating film) is provided on the piezoelectric substrate 12 so as to cover the electrode fingers 22 in the central region 31. In the dummy region 34, a protective film 44 (second insulating film) mainly composed of a material having a higher acoustic velocity of elastic waves than that of the protective film 42 is provided on the piezoelectric substrate 12 so as to cover the dummy electrode fingers 23. As a result, the acoustic velocity of the elastic waves propagating through the dummy region 34 becomes higher than the acoustic velocity of the elastic waves propagating through the central region 31. Therefore, spurious can be suppressed.

[0058] In addition, as a method of making the acoustic velocity of the elastic waves propagating through the dummy region 34 higher than the acoustic velocity of the elastic waves propagating through the central region 31, methods other than the above-described method may be used. For example, the thickness of the dummy electrode fingers 23 may be made thinner than that of the electrode fingers 22. For example, the thickness of the piezoelectric substrate 12 in the dummy region 34 may be made thinner than that of the piezoelectric substrate 12 in the central region 31. For example, a material having a higher acoustic velocity of elastic waves than that of the piezoelectric substrate 12 may be provided in the dummy region 34.

Example

[0059] In Example 1, the case where the elastic wave device is an elastic wave resonator was shown. In Example 2 and Modification Examples of Example 2, the case where the elastic wave device is a filter and a duplexer will be described. FIG. 14(a) is a circuit diagram of a filter 200 according to Example 2. As shown in FIG. 14(a), one or more series resonators S1 to S4 are connected in series between an input terminal Tin and an 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. The elastic wave resonators of Example 1 and its modification examples may be used for at least one of the series resonators S1 to S4 and the parallel resonators P1 to P3. The number of series resonators and parallel resonators, etc. can be set as appropriate. Although a ladder-type filter is shown as an example of the filter, the filter may be a multi-mode filter.

[0060] FIG. 14(b) is a circuit diagram of the duplexer 210 according to a modified example of Example 2. As shown in FIG. 14(b), a transmission filter 70 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 72 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 70 passes, as a transmission signal, a signal in the transmission band among the high-frequency signals input from the transmission terminal Tx to the common terminal Ant, and suppresses signals of other frequencies. The reception filter 72 passes, as a reception signal, a signal in the reception band among the high-frequency signals input from the common terminal Ant to the reception terminal Rx, and suppresses signals of other frequencies. At least one of the transmission filter 70 and the reception filter 72 can be the filter of Example 2. Although the duplexer is shown as an example of the multiplexer, a triplexer or a quadruplexer may also be used.

[0061] As described above in detail with respect to the embodiments of the present invention, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Description of Reference Numerals

[0062] 10... support substrate, 12... piezoelectric substrate, 20... IDT, 21... comb-shaped electrode, 22... electrode finger, 23... dummy electrode finger, 24... bus bar, 25... reflector, 26... metal film, 30... intersection region, 31... central region, 32... edge region, 33... gap region, 34... dummy region, 35... bus bar region, 40... additional film, 42... protective film, 44... protective film, 70... transmission filter, 72... reception filter, 100, 110, 120, 130, 500... surface acoustic wave device, 200... filter, 210... duplexer

Claims

1. A piezoelectric substrate, a plurality of electrode fingers provided on the piezoelectric substrate, and a plurality of metal parts provided between the electrode fingers adjacent to each other in the short direction of the plurality of electrode fingers and having a length in the longitudinal direction shorter than that of the plurality of electrode fingers, each including a pair of comb-shaped electrodes in which the plurality of electrode fingers are alternately arranged at least partially, and the sound velocity of the elastic wave propagating in the region where the plurality of metal parts are located is faster than the sound velocity of the elastic wave propagating in the central region of the intersection region where the plurality of electrode fingers intersect and is 1.10 times or less. An elastic wave device comprising:

2. The elastic wave device according to claim 1, wherein the sound velocity of the elastic wave propagating in the region where the plurality of metal parts are located is 1.03 times or more of the sound velocity of the elastic wave propagating in the central region.

3. The plurality of metal parts of one of the pair of comb-shaped electrodes face the plurality of electrode fingers of the other comb-shaped electrode, The elastic wave device according to claim 1 or 2, wherein the width in the short direction is smaller for the plurality of metal parts than for the plurality of electrode fingers.

4. A first insulating film provided on the piezoelectric substrate covering the plurality of electrode fingers in the central region, A second insulating film provided on the piezoelectric substrate covering the plurality of metal parts in the region where the plurality of metal parts are located and mainly composed of a material having a faster sound velocity of elastic waves than the first insulating film, the elastic wave device according to claim 1 or 2.

5. The elastic wave device according to claim 1 or 2, further comprising an additional film provided at an end in the longitudinal direction of the plurality of electrode fingers.

6. A piezoelectric substrate, a plurality of electrode fingers provided on the piezoelectric substrate, and a plurality of metal parts provided between the electrode fingers adjacent to each other in the short direction of the plurality of electrode fingers and having a width in the short direction smaller than that of the plurality of electrode fingers, each including a pair of comb-shaped electrodes in which the plurality of electrode fingers are alternately arranged at least partially. An elastic wave device comprising:

7. Two of the plurality of metal parts are provided between the adjacent electrode fingers, The elastic wave device according to claim 6, wherein the width of the plurality of metal parts in the short direction is 0.56 times or more and 0.64 times or less of the width of the plurality of electrode fingers in the short direction.

8. Three of the plurality of metal parts are provided between the adjacent electrode fingers, The width of the plurality of metal parts in the short-side direction is 0.39 times or more and 0.45 times or less the width of the plurality of electrode fingers in the short-side direction. The surface acoustic wave device according to claim 6.

9. The widths of the plurality of electrode fingers in the short-side direction are equal from one end connected to the bus bar to the other end on the opposite side. The widths of the plurality of metal parts in the short-side direction are equal to each other. The surface acoustic wave device according to claim 7 or 8.

10. A piezoelectric substrate, A surface acoustic wave device provided on the piezoelectric substrate, including a plurality of electrode fingers, and a plurality of metal parts provided between adjacent electrode fingers among the plurality of electrode fingers in the short-side direction of the plurality of electrode fingers and mainly composed of a material having a higher acoustic velocity of surface acoustic waves than the plurality of electrode fingers, and including a pair of comb-shaped electrodes in which the plurality of electrode fingers are alternately arranged at least partially.

Images