Surface acoustic wave device

Abstract

This invention provides a surface acoustic wave (SAW) element with reduced sound loss and a higher Q value. The SAW element includes: a piezoelectric substrate (11); and a pair of IDT electrodes, having a pair of busbars (2a, 2b) formed on the upper surface of the piezoelectric substrate (11), and a plurality of electrode fingers (3a, 3b) extending from these busbars (2a, 2b) in a comb-like manner, wherein the thickness of the electrode fingers (3a, 3b) in the non-crossing region (RB) where the electrode fingers (3a, 3b) do not cross is smaller than the thickness of the electrode fingers (3a, 3b) in the crossing region (ZAB).

Description

Technical Field

[0001] This invention relates to a surface acoustic wave device that converts frequency signals into surface acoustic waves. Background Technology

[0002] For wireless communication applications, resonators are being developed to construct filters or duplexers with steep migration characteristics over a wide bandwidth. For example, it is known that temperature-compensated surface acoustic wave (TC-SAW) elements using LiNbO3 as a piezoelectric substrate, with a temperature-compensated film including silicon oxide deposited on the surface of the piezoelectric substrate, exhibit small variations in characteristics with temperature changes and thus achieve a relatively high Q value.

[0003] On the other hand, to cope with the ever-increasing communication traffic, duplexers or filters require steep migration characteristics and low loss characteristics over a wider frequency band. To meet this requirement, the Q value of the SAW that constitutes the resonator is one of the important indicators, and various studies have been conducted to improve this indicator.

[0004] Patent Document 1 describes an electroacoustic transducer that, regarding the area between two opposing busbars, five regions are provided along the direction of extension of the busbars: a central excitation region with interlaced electrode fingers, inner edge regions on both sides, and outer edge regions on both sides. The electroacoustic transducer is structured such that it operates in a piston mode with high Q value and low spuriousness by increasing or decreasing the width of the electrode fingers located in the inner edge regions, etc.

[0005] In addition, reference 2 describes the following elastic wave device: the intersection area of ​​the first electrode finger and the second electrode finger, which serve as IDT electrodes, is divided into a central part and low-velocity parts on both sides, and the electrode finger in the central part is thicker than that in the low-velocity parts.

[0006] However, neither Patent Document 1 nor Patent Document 2 describes any technology related to the features of these electrode fingers outside the area where the electrode fingers connected to the busbar intersect.

[0007] [Existing technical documents]

[0008] [Patent Literature]

[0009] [Patent Document 1] Japanese Patent No. 5503020

[0010] [Patent Document 2] International Patent Publication No. 2018 / 088188 Summary of the Invention

[0011] [The problem the invention aims to solve]

[0012] The present invention was made under these circumstances, providing a surface acoustic wave element with reduced sound loss and a higher Q value.

[0013] [Technical means to solve the problem]

[0014] This surface acoustic wave element includes: a piezoelectric substrate; and

[0015] A pair of interdigital transducer electrodes (IDT electrodes) includes a pair of busbars formed on the piezoelectric substrate and a plurality of electrode fingers extending from each of these busbars toward opposing busbars in a comb-like pattern, and forming an intersection region. The intersection region is the area where, when viewed along the arrangement direction of the plurality of electrode fingers, an electrode finger connected to one busbar intersects with an electrode finger connected to another busbar.

[0016] The thickness of the electrode fingers in the non-crossing region outside the crossing region is smaller than the thickness of the electrode fingers in the crossing region.

[0017] The surface acoustic wave element may also include the following structure.

[0018] (a) When viewed along the arrangement direction of the plurality of electrode fingers, the cross region includes two end regions, which are regions containing the ends of these electrode fingers, and these end regions become low-sound-speed regions where the propagation speed of surface acoustic waves is slower than that of the cross region to the inside.

[0019] (b) According to (a), wherein the electrode finger is formed by connecting a first electrode finger film disposed in the non-intersecting region and a second electrode finger film disposed in the intersecting region and having a thickness greater than that of the first electrode finger film; and in the end region, the end of the first electrode finger film opposite to the end connected to the busbar, i.e., the front end, and the end of the second electrode finger film on the first electrode finger film side, i.e., the base end, are stacked together, and the end of the second electrode finger film opposite to the base end included in the end region, i.e., the front end, and a propagation speed adjustment film for increasing the thickness of the electrode finger to make the propagation speed of the surface acoustic wave low are stacked, thereby forming the low sound speed region.

[0020] (c) According to (b), wherein the first electrode finger film is formed on a support film, the support film is formed on the piezoelectric substrate in a region other than the formation region of the second electrode finger film and contains a dielectric, and the front end portion of the first electrode finger film is stacked on the upper surface side of the base end portion of the second electrode finger film; and the propagation speed regulating film is stacked on the upper surface side of the front end portion of the second electrode finger film. Furthermore, the propagation speed regulating film includes an extension extending toward the support film toward the non-intersecting region side.

[0021] (d) According to (b) and (c), wherein, in the non-crossing region, for each of the pair of busbars, a plurality of dummy electrode fingers extending from the other busbar are formed between the ends of the plurality of electrode fingers connected to one of the busbars and the other busbar. Furthermore, the thickness of the dummy electrode fingers is smaller than the thickness of the electrode fingers in the crossing region.

[0022] (e) According to (b) to (d), wherein the density of the first electrode finger membrane and the propagation speed regulating membrane is smaller than that of the second electrode finger membrane.

[0023] (f) A dielectric film is formed in at least a portion of the upper surface of the surface acoustic wave element on which the interdigitated transducer electrodes are formed. In this case, the piezoelectric substrate is LiNbO3, and the dielectric film is composed of a material selected from the group of dielectric materials, which consists of silicon oxide, silicon oxynitride, or fluorine-doped silicon oxide having a frequency temperature characteristic that varies in the opposite direction to the frequency temperature characteristic of the piezoelectric substrate.

[0024] (g) The piezoelectric substrate is LiNbO3, and the tangent angles in the Euler angle (φ, θ, ψ) expression are φ, ψ = 0°±10°, and θ = 38°±10°.

[0025] [The effects of the invention]

[0026] According to this surface acoustic wave element, in a pair of IDT electrodes disposed on a piezoelectric substrate, the thickness of the electrode finger in the non-crossing region outside the crossing region is configured to be smaller than the thickness of the electrode finger in the crossing region, thereby reducing the loss associated with the scattering of surface acoustic waves and thus enabling a higher Q value. Attached Figure Description

[0027] Figure 1 (a)~ Figure 1 (d) is a structural diagram of the SAW element in the first embodiment.

[0028] Figure 2 of (a), Figure 2 (b) is a structural diagram of a SAW element in a comparative form.

[0029] Figure 3 This is a frequency-admittance characteristic diagram of the SAW element in the first embodiment and comparative form.

[0030] Figure 4 This is a frequency-Bode Q-value characteristic diagram of the SAW element in the first embodiment and comparative form.

[0031] Figure 5 of (a), Figure 5 (b) is a structural diagram of a SAW element with virtual electrode fingers.

[0032] Figure 6 of (a), Figure 6 (b) is a structural diagram of the SAW element in the second embodiment.

[0033] Figure 7 These are frequency-admittance characteristic diagrams of the SAW element in the first and second embodiments.

[0034] Figure 8 These are frequency-Bode Q-value characteristic diagrams of the SAW element in the first and second embodiments.

[0035] Figure 9 of (a), Figure 9 (b) is a structural diagram of the SAW element in the third embodiment.

[0036] Figure 10 This is the frequency-admittance characteristic diagram of the SAW element in the third embodiment.

[0037] Figure 11 This is a frequency-Bode Q-value characteristic diagram of the SAW element in the third embodiment.

[0038] [Explanation of Symbols]

[0039] ZAB: Intersection area

[0040] EB: End region

[0041] RB: Non-intersecting region

[0042] 11: Piezoelectric substrate

[0043] 2a, 2b: Busbars

[0044] 3a, 3b: Electrode pointers

[0045] 31: First electrode membrane

[0046] 32: Second electrode membrane

[0047] 33: Propagation speed regulating membrane

[0048] 331: Extension

[0049] 5: Dielectric film

[0050] 6: Support membrane Detailed Implementation

[0051] Figure 1 (a)~ Figure 1 (d) represents the basic structure of the surface acoustic wave (SAW) device according to the first embodiment. Figure 1 In this example, a TC (Temperature Compensate)-SAW element with temperature compensation function is configured, and as an example of a closed mode, a structural example of a SAW element operating in piston mode is shown.

[0052] Figure 1 (a) is an enlarged plan view schematically showing a portion of the IDT electrode disposed on the SAW element. Figure 1 (b) is Figure 1 A longitudinal side view of the SAW element at the location indicated by the dashed line IB-IB in (a). Furthermore, Figure 1 (c) is along Figure 1 The distribution of SAW propagation velocity observed along the Y-axis is shown in (a). Figure 1 (d) is a distribution of the amplitude of the SAW observed along the Y-axis.

[0053] The SAW element in this example includes an IDT electrode formed on a rectangular piezoelectric substrate 11 for SAW excitation. In the following description, the direction along the long side of the rectangular piezoelectric substrate 11 (however, the description of its planar shape is omitted) will also be referred to as the longitudinal direction. Figure 1 The X direction in (a) is also called the lateral direction along the shorter side (as described). Figure 1 Y direction in ).

[0054] For example, the IDT electrodes are arranged in a longitudinal direction along each long side of the piezoelectric substrate 11, including: two busbars 2a and 2b, respectively connected to signal ports 12a and 12b; and a plurality of electrode fingers 3a and 3b, formed in a lateral direction extending from each busbar 2a and 2b.

[0055] As the piezoelectric material constituting the piezoelectric substrate 11, examples include lithium niobate (LiNbO3) or lithium tantalate (LiTaO3), aluminum nitride (AlN), scandium-doped aluminum nitride, etc.

[0056] Furthermore, the piezoelectric substrate 11 of this embodiment includes: (i) a piezoelectric substrate on which a piezoelectric thin film is formed on the surface of a substrate containing a non-piezoelectric material, or (ii) a laminated substrate formed by stacking a non-piezoelectric material and a piezoelectric material. As (i), an example is the formation of an aluminum nitride piezoelectric thin film on the surface of a sapphire substrate, which is a non-piezoelectric material. As (ii), an example is a laminated substrate formed by stacking a silicon substrate, which is a non-piezoelectric material, and a LiTaO3 substrate, which is a piezoelectric material.

[0057] When using LiNbO3 as a piezoelectric material, examples can be given of piezoelectric materials with the following Euler angles (φ, θ, ψ) and the cut angles of LiNbO3 being φ, ψ = 0°±10°, θ = 38°±10°; or piezoelectric materials with φ, ψ = 0°±10°, θ = -85°±15°; or piezoelectric materials with φ, ψ = 0°±10°, θ = 131°±15° or φ = 0°±10°, θ = -90°±10°, ψ = -90°±10°.

[0058] When using LiTaO3 as a piezoelectric material, examples can be given of piezoelectric materials with cut angles of φ, ψ = 0°±10° and θ = 132°±15° in the Euler angle (φ, θ, ψ) representation; or piezoelectric materials with φ, ψ = 0°±10° and θ = -90°±15°.

[0059] like Figure 1 As shown in (a), the electrode finger 3a connected to one of the busbars 2a is arranged to extend toward the busbar 2b located in the opposite position. Furthermore, the electrode finger 3b connected to the other busbar 2b is arranged to extend toward one of the busbars 2a. Moreover, when viewed along the arrangement direction of the electrode fingers 3a and 3b, the electrode fingers 3a connected to one of the busbars 2a and the electrode fingers 3b connected to the other busbar 2b are arranged in an alternating pattern.

[0060] As described above, the area where electrode fingers 3a and 3b are arranged in an intersecting manner corresponds to the intersection region of the IDT electrodes. Furthermore, when viewed from the intersection region, on each busbar 2a and 2b side, the leading edge of the electrode finger 3a or 3b connected to one busbar 2a or 2b does not reach the other busbar 2b or 2a, thus forming two regions where electrode fingers 3a and 3b do not intersect. These regions correspond to the non-intersecting region (sometimes also called the "gap region") RB.

[0061] Furthermore, the aforementioned cross region includes two end regions EB, which are regions containing the ends of these electrode fingers 3a and 3b. Figure 1 (a)~ Figure 1 (d) Figure 2 of (a), Figure 2 In (b), the areas in the intersection region other than these end regions EB are marked with the symbol "ZAB" (described later). Figure 5 of (a), Figure 5 (b) Figure 6 of (a), Figure 6 (b) Figure 9 of (a), Figure 9 (The same applies to (b)).

[0062] In addition, two regions will be formed, each containing a busbar 2a and a busbar 2b, also known as busbar region SB.

[0063] In the SAW element of the first embodiment including the structure described above, each electrode finger 3a and electrode finger 3b is configured such that the thickness of the electrode finger 3a and electrode finger 3b in the non-crossing region RB is smaller than the thickness of the electrode finger 3a and electrode finger 3b in the crossing region ZAB.

[0064] As a method to differentiate the thicknesses of electrode finger 3a and electrode finger 3b based on the formed regions (intersecting region ZAB, non-intersecting region RB), for example, Figure 1 (a)~ Figure 1 The SAW element shown in (d) has the following structure: a first electrode finger film 31 and a second electrode finger film 32 with different thicknesses are connected to form electrode fingers 3a and 3b.

[0065] At this time, by making the thickness of the second electrode finger film 32 disposed in the intersection region ZAB larger than that of the first electrode finger film 31 disposed in the non-intersection region RB (making the thickness of the first electrode finger film 31 smaller than that of the second electrode finger film 32), a configuration can be formed. Figure 1 (a)~ Figure 1 Electrode fingers 3a and 3b are shown in (d). The reason for the different thicknesses of the first electrode finger film 31 and the second electrode finger film 32 will be explained later.

[0066] Furthermore, in Figure 1 (a)~ Figure 1 In the IDT electrode shown in (d), in order to operate the SAW element in closed mode, i.e., piston mode, a low-sound velocity region is set in the two end regions EB, where the propagation speed of the SAW is slower than that in the inner cross region ZAB.

[0067] As a specific method for setting the end region EB as a low-sound-velocity region, the first electrode finger membrane 31 and the second electrode finger membrane 32, as described above, are connected in a stacked manner. In addition, at the front end of the second electrode finger membrane 32, which is located on the opposite side from the connection position of these electrode finger membranes 31 and 32, a propagation speed adjustment membrane 33 is provided for increasing the thickness of the electrode fingers 3a and 3b.

[0068] Furthermore, when running SAW elements in closed mode, utilizing piston mode is not a necessary requirement.

[0069] In the following description, the end of the first electrode finger membrane 31 that is connected to the busbar 2a and the busbar 2b is referred to as the base end, and the end opposite to the base end is referred to as the front end. Similarly, the end of the second electrode finger membrane 32 that is connected to the first electrode finger membrane 31 is referred to as the base end, and the end opposite to the base end is referred to as the front end.

[0070] at this time, Figure 1 of (a), Figure 1 In the SAW element shown in (b), the front end of the first electrode finger film 31 and the base end of the second electrode finger film 32 are stacked and connected vertically, and the stacked portion is disposed in the previously described end region EB. Furthermore, the front end of the second electrode finger film 32 is stacked on a propagation speed adjustment film 33, which increases the thickness of the front ends of the electrode fingers 3a and 3b to reduce the propagation speed of the SAW, and the portion of the second electrode finger film 32 stacked thereon is disposed in the end region EB.

[0071] Thus, in the end regions EB located on both sides of the intersection region ZAB, a laminated structure is formed by the front end of the first electrode finger film 31 and the base end of the second electrode finger film 32, or the front end of the second electrode finger film 32 and the propagation speed regulating film 33, creating a region where the thickness of the electrode fingers 3a and 3b is greater than that of the intersection region ZAB. As a result, the propagation speed of the SAW in the end region EB is lower than that of the SAW in the intersection region ZAB. On the other hand, the thickness of the first electrode finger film 31 located in the non-intersection region RB is smaller than the thickness of the second electrode finger film 32 in the intersection region ZAB and the laminated portion of the end region EB, therefore, the propagation speed is faster than in these regions ZAB and EB.

[0072] Through the aforementioned structure, it is possible to form Figure 1 The distribution of SAW propagation velocity shown in (c) results in the ability to excite SAWs with… Figure 1 The amplitude distribution of the piston pattern SAW is shown in (d).

[0073] In addition, Figure 1 (a)~ Figure 1In the SAW element with the structure shown in (d), the materials of these metal films can also be selected such that the density of the first electrode finger film 31 and the propagation speed regulating film 33 is smaller than that of the second electrode finger film 32.

[0074] For example, when aluminum (Al) is selected as the metal constituting the first electrode finger film 31 and the propagation speed regulating film 33, platinum (Pt), copper (Cu), gold (Au), silver (Ag), tungsten (W), molybdenum (Mo), cobalt (Co), iron (Fe), nickel (Ni), chromium (Cr), and tantalum (Ta) can be selected as the metal constituting the second electrode finger film 32.

[0075] Furthermore, when the metal constituting the first electrode finger film 31 and the propagation speed regulating film 33 is an alloy or laminate structure containing two or more metals, including a metal (second metal) with a density smaller than that of the metal constituting the second electrode finger film 32 (first metal), the effective density of the first electrode finger film can be reduced by using the second metal as the main constituent material containing more than 50% by volume.

[0076] Furthermore, when the SAW element forms a dielectric film 5 as described later, by using materials whose densities of the first electrode finger film 31 and the propagation speed adjustment film 33 are close to the density of the dielectric film 5, the effect of reducing the reflection of the SAW on the first electrode finger film 31 can also be obtained. As an example of such a material, when the dielectric film 5 is made of silicon dioxide (SiO2), the case where the first electrode finger film 31 and the propagation speed adjustment film 33 are made of aluminum (Al) can be illustrated.

[0077] In addition, Figure 1 The description is omitted in (a), but a base film containing titanium (Ti) or chromium (Cr) may be provided between the piezoelectric substrate 11 and the IDT electrodes (busbar 2a, busbar 2b or electrode finger 3a, electrode finger 3b, etc.) to improve the adhesion of these IDT electrodes.

[0078] In addition to the structure described above, the SAW element in this example can also be as follows: Figure 1 As shown in (a), it is configured as a TC-SAW element having a temperature compensation function to compensate for the influence of the frequency temperature characteristics of the piezoelectric material constituting the piezoelectric substrate 11.

[0079] In the TC-SAW device, a dielectric film 5 is formed (also referred to as "loaded") on the upper surface of the piezoelectric substrate 11 on which IDT electrodes (busbar 2a, busbar 2b, electrode finger 3a, electrode finger 3b) are formed. Furthermore, to avoid complicating the illustrations, in... Figure 1 In the plan view (a), the description of the dielectric film 5 is omitted (the state of the lower surface side of the dielectric film 5 is shown).

[0080] The dielectric film 5 mounted on the TC-SAW element can be a dielectric film having a frequency-temperature characteristic opposite to that of the piezoelectric material of the piezoelectric substrate 11. For example, if the piezoelectric material of the piezoelectric substrate 11 has a negative frequency-temperature characteristic where the frequency excited decreases with increasing temperature, a dielectric film 5 having a positive frequency-temperature characteristic where the frequency increases with increasing temperature can be mounted. Conversely, for a piezoelectric substrate 11 containing a piezoelectric material with a positive frequency-temperature characteristic, a dielectric film 5 having a negative frequency-temperature characteristic can be mounted. In this way, by mounting a dielectric film 5 having a frequency-temperature characteristic opposite to that of the piezoelectric substrate 11, the influence of temperature changes around the SAW element can be reduced.

[0081] For example, LiNbO3, as described above, has a negative frequency temperature characteristic. Therefore, it can be exemplified that a piezoelectric substrate 11 made of LiNbO3 is loaded with a dielectric film 5 containing silicon dioxide, silicon oxynitride (the stoichiometric ratio is not particularly limited, it can be SiNO, or nitrogen-doped silicon oxynitride in SiO2), or fluorine-doped silicon dioxide, which has a positive frequency temperature characteristic. The dielectric film 5 containing these materials can be loaded by methods such as chemical vapor deposition (CVD) or sputtering.

[0082] Furthermore, temperature compensation is not a necessary requirement for the SAW element. In this case, a protective film can be used to cover the surface of the piezoelectric substrate 11 with a non-piezoelectric silicon nitride or the like.

[0083] Electrode fingers 3a and 3b are formed by the first electrode finger film 31 and the second electrode finger film 32 with different thicknesses as described above. A SAW element is manufactured in the end region EB, in which the first electrode finger film 31 and the second electrode finger film 32 are stacked, and the second electrode finger film 32 and the propagation speed regulating film 33 are stacked. As a specific example, the case where they are formed into films separately can be illustrated.

[0084] For example, after forming a metal film of a predetermined thickness containing aluminum on the upper surface of the piezoelectric substrate 11, busbar 2a, busbar 2b, first electrode finger film 31, and propagation speed adjustment film 33 are patterned by etching or the like. Then, using a lift-off method or the like, a copper metal film with a thickness greater than the aluminum metal film is formed into a second electrode finger film 32 and patterned, so that the stacked portion in the end region EB remains on the upper surface of the piezoelectric substrate 11 patterned with the first electrode finger film 31 or the propagation speed adjustment film 33.

[0085] Therefore, the first electrode finger membrane 31 can be connected to the second electrode finger membrane 32, which has a greater thickness, to form electrode fingers 3a and 3b. In addition, by providing a stacked portion of the first electrode finger membrane 31, the second electrode finger membrane 32, and the propagation speed regulating membrane 33 in the end region EB, a low sound speed region can be formed.

[0086] If the approximate design variables of other SAW elements are shown, the distance d between the center lines of electrode fingers 3a and 3b is set to λ / 2 relative to the wavelength λ corresponding to the design frequency of the SAW element. Furthermore, from the viewpoint of fully enclosing acoustic energy, the width of the non-crossing region RB is preferably set to 1.6d to 6d (0.8λ to 3λ), and appropriately to about 2d to 4d (1λ to 2λ).

[0087] However, in order to form a high-velocity region of enclosed acoustic energy, for example, busbars 2a and 2b are formed using the same metal film as the first electrode finger film 31, thereby removing the aforementioned limitation, and thus enabling the width dimension of the non-intersecting region RB to be about 0.1d to 1d.

[0088] In the SAW element with the structure described above, it is configured such that by connecting the first electrode finger film 31 and the second electrode finger film 32, the thickness of the electrode fingers 3a and 3b in the non-crossing region RB is smaller than the thickness of the electrode fingers 3a and 3b in the crossing region ZAB. The reason for this configuration will be explained below.

[0089] Figure 1 The SAW element operating in piston mode, as shown in (c), enables the waveguide width to be substantially uniform. Therefore, compared to the apodization method used in existing SAW elements, which involves gradually varying the length of the electrode fingers, it has the advantages of minimal degradation of the effective electromechanical coupling coefficient and suppression of spurious emissions.

[0090] On the other hand, the non-crossing region RB serves to enclose the SAW within the IDT, but there are few studies on optimizing the structure of the non-crossing region RB. Therefore, the inventors of this application have studied the structure of the non-crossing region RB suitable for SAW elements operating in a closed mode including a piston mode.

[0091] When the piezoelectric material of the piezoelectric substrate 11 has a typical convex slowness curve, the SAW excited in the cross region ZAB of the IDT and conducted on the piezoelectric substrate 11 is reflected when it enters the region with high sound velocity, i.e., the non-cross region RB, due to the difference in sound velocity. As a result, the SAW can be confined within the cross region ZAB of the IDT.

[0092] However, it is generally known that when a wave is reflected at a structurally discontinuous point, scattering occurs simultaneously with the reflection. In the aforementioned SAW element, the scattering that occurs when the SAW wave is reflected in the non-crossing region RB also leads to an increase in the acoustic loss of the SAW element.

[0093] Therefore, the inventors focused on the thickness of the electrode fingers 3a and 3b in the non-intersecting region RB. By reducing the thickness of the electrode fingers 3a and 3b in the region, the structural difference between the region in the non-intersecting region RB where the electrode fingers 3a and 3b are provided and the region where these electrode fingers 3a and 3b are not provided can be reduced.

[0094] As a result, the structural symmetry of the non-crossing region RB becomes higher. Therefore, it is believed that the scattering of SAW when it enters the non-crossing region RB can be suppressed through the structure, thereby forming a low-loss SAW element.

[0095] To verify the appropriateness of the design concept described above, a device was created that uses... Figure 1 of (a), Figure 1 (b) describes the model of the SAW element structure and performs characteristic analysis using the finite element method (FEM).

[0096] If we list the design variables, the spacing of the IDTs is 4 μm, the width of the cross region ZAB is 51.4 μm, the width of the end region EB is 2.6 μm, the width of the non-cross region RB is 13 μm, the electrode material of the first electrode finger film 31 and the second electrode finger film 32 is copper (Cu), the thickness of the first electrode finger film 31 and the propagation speed adjustment film 33 is 88 nm, the thickness of the second electrode finger film 32 is 260 nm, and silicon dioxide (SiO2) with a thickness of 1.4 μm is loaded as the dielectric film 5. In addition, the piezoelectric material of the piezoelectric substrate 11 is LiNbO3 with a 126.5XY sectional area (expressed in Euler angles (φ, θ, ψ) = (0°, 36.5°, 0°)).

[0097] As a contrasting example, a model was created in Figure 2 of (a), Figure 2 (b) shows a model of a SAW element with uniformly thick electrode fingers 30a and 30b, and the same FEM analysis was performed. The design variables other than the fact that the thickness of electrode fingers 30a and 30b is fixed at 260 nm, and that a copper propagation velocity modulation film 33 with a thickness of 88 nm is placed on its upper surface to set the end region EB as a low-velocity region, are... Figure 1 of (a), Figure 1 The SAW element shown in (b) is the same as that in the first embodiment.

[0098] The results of FEM analysis of the SAW element in the first embodiment and the comparative embodiment are shown below. Figure 3 , Figure 4 .

[0099] Figure 3 The change in admittance relative to the frequency variation of SAW is shown. Figure 4 The variation of Bode Q as a Q value relative to the frequency variation of SAW is shown.

[0100] Bode Q is calculated based on the following equation (1).

[0101] Bode Q=(ω|S11|group_delay(S11))

[0102] / (1-|S11| 2 (1)

[0103] Here, ω|S11| is the angular frequency of the reflection coefficient S11 of the SAW element, group_delay(S11) is the group delay of the reflection coefficient S11, and |S11| is the amplitude of the reflection coefficient S11.

[0104] according to Figure 3 The results show that the SAW element of the first embodiment exhibits admittance characteristics that are substantially equivalent to those of the SAW element of the comparative form as a conventional structure, and obtains good characteristics of spurious suppression.

[0105] On the other hand, regarding Figure 4 The Bode Q value is approximately 2400 in the comparative SAW element and approximately 2500 in the SAW element of the first embodiment. Thus, compared with the SAW element of the existing structure, the SAW element of the first embodiment shows an improvement of about 100 in Bode Q, and can be considered a low-loss SAW element.

[0106] According to the SAW element of this embodiment, the following effects exist. In a pair of IDT electrodes disposed on the piezoelectric substrate 11, the thickness of electrode fingers 3a and 3b in the non-crossing region RB outside the cross region ZAB is configured to be smaller than the thickness of electrode fingers 3a and 3b in the cross region ZAB. Therefore, the loss associated with SAW scattering is reduced, thereby enabling a higher Q value.

[0107] Here, as Figure 5 of (a), Figure 5As shown in (b), in the non-crossing region RB of the SAW element in this example, for each of the busbars 2a and 2b, a plurality of dummy electrode fingers 34 extending from the other busbar 2b or busbar 2a can also be formed between the ends of the plurality of electrode fingers 3a and 3b connected to one of the busbars 2a and 2b and the other busbar 2b or busbar 2a, away from these ends (described later). Figure 6 of (a), Figure 6 (b) Figure 9 of (a), Figure 9 (The same as the SAW element shown in (b)).

[0108] At this time, the thickness of the dummy electrode finger 34 located in the non-crossing region RB is preferably greater than the thickness of the electrode fingers 3a and 3b in the crossing region ZAB (in Figure 5 of (a), Figure 5 In the example shown in (b), the thickness of the second electrode (referring to the membrane 32) is small. Therefore, a high-velocity region can be formed for the intersection region ZAB, and the periodicity of the structure can also be made equal to that of the intersection region ZAB.

[0109] Furthermore, when the thickness of the dummy electrode finger 34 is greater than that of the electrode fingers 3a and 3b in the cross region ZAB, reflection will also occur when the elastic wave invades the region with different sound speeds. Therefore, the elastic wave can be more effectively confined within the cross region ZAB.

[0110] Subsequently, on Figure 6 of (a), Figure 6 The structure of the SAW element of the second embodiment shown in (b) will be described. In the SAW element of the second embodiment, the front end of the first electrode finger film 31 is stacked on the upper surface side of the base end of the second electrode finger film 32, and the propagation speed regulating film 33 is stacked on the upper surface side of the front end of the second electrode finger film 32. In this respect, it differs from the SAW element of the first embodiment where the front end of the first electrode finger film 31 and the propagation speed regulating film 33 are stacked on the lower surface side of the second electrode finger film 32.

[0111] More specifically, in the region outside the formation area of ​​the second electrode finger film 32 on the piezoelectric substrate 11, a support film 6, such as a silicon dioxide (SiO2) dielectric, is formed as a temperature compensation film. The first electrode finger film 31 is formed on the upper surface side of the support film 6, and forms a bridge-like connection between the busbars 2a and 2b and the second electrode finger film 32. At this time, the leading end of the first electrode finger film 31 is stacked on the upper surface side of the base end of the second electrode finger film 32.

[0112] Furthermore, the propagation speed regulating film 33 is directly laminated on the upper surface of the front end of the second electrode finger film 32. Alternatively, a protective film containing silicon nitride or the like may be provided on the upper surface of the first electrode finger film 31 and the propagation speed regulating film 33.

[0113] For example, when the first electrode finger film 31 is directly disposed in the non-crossing region RB on the piezoelectric substrate 11, there is a risk of loss due to the weak excitation accompanying the contact between the base end of the first electrode finger film 31 and the base end of the second electrode finger film 32.

[0114] In contrast, such as Figure 6 of (a), Figure 6 As shown in the second embodiment (b), by providing the first electrode finger film 31 on the support film 6 containing a non-piezoelectric dielectric, it is possible to suppress the weak excitation, thereby achieving further reduction in losses.

[0115] Figure 7 , Figure 8 The figure shows a model of the SAW element of the second embodiment, which was subjected to FEM analysis and its characteristics were compared with those of the SAW element of the first embodiment.

[0116] remove Figure 6 of (a), Figure 6 Apart from the structural differences shown in (b), all design variables are the same as those in the simulation model of the first embodiment.

[0117] according to Figure 7 The results show that the SAW element of the second embodiment exhibits admittance characteristics that are substantially equivalent to those of the SAW element of the first embodiment, and achieves good characteristics of spurious suppression.

[0118] In addition, regarding Figure 8 The Bode Q value, in FEM analysis, is approximately 2500 in both the first and second embodiments of the SAW element. Thus, the SAW element of the second embodiment has characteristics equivalent to those of the SAW element of the first embodiment, and is compatible with... Figure 2 (a)~ Figure 4 The described structure of the SAW element has low loss characteristics compared to existing structures.

[0119] Then, Figure 9 of (a), Figure 9 The SAW element of the third embodiment shown in (b) has the following structure: relative to the use of Figure 6 of (a), Figure 6The SAW element of the second embodiment described in (b) is provided with an extension 331 for improving the electromechanical coupling coefficient of the IDT electrode.

[0120] That is, in the SAW element, the propagation speed regulating film 33a includes an extension 331 extending onto the support film 6 toward the non-crossing region RB side.

[0121] If the extension 331 is provided, the electrodes 331, which have different potentials from the first electrode finger film 31 provided in the non-crossing region RB, are arranged alternately, thus forming an electrostatic capacitor. On the other hand, the extension 331 is formed on the support film 6 containing a non-piezoelectric dielectric, therefore, it does not excite the SAW.

[0122] Therefore, by increasing the electrostatic capacitance of the SAW resonator, the capacitance ratio can be increased compared to the case without the extension 331, thereby reducing the effective electromechanical coupling coefficient.

[0123] Furthermore, when the extension 331 is formed on the piezoelectric substrate 11, a stray response is generated due to the excitation of the SAW generated in the extension 331. Therefore, it may become a SAW element that is not suitable for use as a filter or duplexer resonator.

[0124] Figure 10 , Figure 11 The model of the SAW element in the third embodiment is fabricated, FEM analysis is performed, and it is compared with... Figure 2 of (a), Figure 2 The characteristics of the SAW elements in the comparative form shown in (b) are compared.

[0125] The length of the extension 331 is varied to 6.4 μm (short) and 12.8 μm (long). Apart from this, all design variables are the same as those in the simulation model of the third embodiment.

[0126] according to Figure 10 The results show that, compared to the comparative SAW element, the SAW element of the third embodiment with extension 331 exhibits a steep migration characteristic as the anti-resonance point moves towards the resonance point, and also achieves good stray suppression. Furthermore, when the extension 331 is extended, a further tendency for the anti-resonance point to move towards the resonance point is observed.

[0127] Furthermore, regarding the Bode Q value, regardless of the length of the extension, the SAW element in the third embodiment has approximately 2700. Compared with the SAW element of the existing structure, an improvement of about 300 Bode Q can be observed, resulting in a low-loss SAW element.

[0128] The above is in use Figure 1 (a)~ Figure 1 (d) Figure 5 of (a), Figure 5 (b) Figure 6 of (a), Figure 6 (b) Figure 9 of (a), Figure 9 In the SAW elements described in (b), to suppress the effects of expansion and contraction due to temperature changes, a support substrate with a low coefficient of thermal expansion can be attached to the bottom surface of the piezoelectric substrate 11. Examples of support substrates include silicon (Si), crystal (SiO2), glass, diamond (C), and sapphire (Al2O3). A dielectric layer (e.g., silicon dioxide) or a metal layer may also be formed between the support substrate and the piezoelectric substrate 11.

[0129] Furthermore, the method of making the thicknesses of electrode fingers 3a and 3b different between the non-crossing region RB and the crossing region ZAB is not limited to the method of connecting the first electrode finger film 31 and the second electrode finger film 32 with different thicknesses.

[0130] For example, after forming a metal film of uniform thickness and patterning the electrode fingers 3a and 3b, the thickness of the electrode fingers 3a and 3b in the non-crossing region RB can be reduced by etching away a portion of the electrode fingers 3a and 3b in the non-crossing region RB.

[0131] The SAW components described above can be used in... Figure 1 (a)~ Figure 1 (d) Figure 5 of (a), Figure 5 (b) Figure 6 of (a), Figure 6 (b) Figure 9 of (a), Figure 9 The single SAW element shown in (b) is used as an electronic component. Alternatively, the piezoelectric substrate 11 can be unfolded in the longitudinal direction, and grating reflectors can be provided in front of and behind the IDT electrode.

[0132] Furthermore, the SAW element can also be applied to acoustic resonators or acoustic filters with multiple IDT electrodes disposed on a common piezoelectric substrate 11.

[0133] Furthermore, the SAW component in this example can be used in filters, duplexers, quadplexers, and other devices with filtering functions. Additionally, the device can be incorporated into power amplifier modules (PAMiD), power amplifiers (PAiD), power amplifier duplexers (PAD), and other power amplifier duplexer modules, as well as diversity front-end modules (DiFEM).

Claims

1. A surface acoustic wave element, characterized in that, include: Piezoelectric substrate; as well as A pair of interdigital transducer electrodes, including: A pair of busbars are formed on the piezoelectric substrate; and Multiple electrode fingers extend from each of these busbars in a comb-like pattern towards the opposing busbars. The pair of interdigital transducer electrodes form an intersecting region. The intersection region is the area where, when viewed along the arrangement direction of these multiple electrode fingers, an electrode finger connected to one busbar intersects with an electrode finger connected to another busbar. The thickness of the electrode fingers in the non-crossing region outside the cross region is smaller than the thickness of the electrode fingers in the cross region. in, When viewed along the arrangement direction of the plurality of electrode fingers, the intersection region includes two end regions. The two end regions are the regions that contain the ends of these electrode fingers. These end regions become low-sound-speed regions where surface acoustic waves propagate slower than in the inner intersection regions. The electrode finger is formed by connecting a first electrode finger film disposed in the non-intersecting region and a second electrode finger film disposed in the intersecting region and having a thickness greater than that of the first electrode finger film. In the end region, the end of the first electrode finger membrane opposite to the end connected to the busbar (i.e., the front end) and the end of the second electrode finger membrane on the first electrode finger membrane side (i.e., the base end) are stacked together, and the end of the second electrode finger membrane opposite to the base end (i.e., the front end) and a propagation speed regulating film for increasing the thickness of the electrode fingers to make the propagation speed of the surface acoustic wave low are stacked together, thereby forming the low sound speed region.

2. The surface acoustic wave element according to claim 1, characterized in that, The first electrode finger film is formed on the support film, the support film is formed in a region on the piezoelectric substrate other than the formation region of the second electrode finger film and contains a dielectric, and the front end of the first electrode finger film is stacked on the upper surface side of the base end of the second electrode finger film; The propagation speed regulating film is stacked on the upper surface side of the front end of the second electrode finger film.

3. The surface acoustic wave element according to claim 2, characterized in that, The propagation speed regulating membrane includes an extension extending onto the support membrane toward the non-intersection region side.

4. The surface acoustic wave element according to any one of claims 1 to 3, characterized in that, In the non-intersecting region, for each of the pair of busbars, between the ends of the plurality of electrode fingers connected to one of the busbars and the other busbar, a plurality of dummy electrode fingers are formed extending from the other busbar away from these ends.

5. The surface acoustic wave element according to claim 4, characterized in that, The thickness of the dummy electrode finger is smaller than the thickness of the electrode finger in the intersection region.

6. The surface acoustic wave element according to any one of claims 1 to 3, characterized in that, The density of the first electrode membrane and the propagation speed regulating membrane is smaller than that of the second electrode membrane.

7. The surface acoustic wave element according to any one of claims 1 to 3, characterized in that, A dielectric film is formed in at least a portion of the upper surface side of the surface acoustic wave element on which the interdigital transducer electrodes are formed.

8. The surface acoustic wave element according to claim 7, characterized in that, The piezoelectric substrate is LiNbO3. The dielectric film is composed of materials selected from a group of dielectric materials, which consists of silicon oxide, silicon oxynitride, or fluorine-doped silicon oxide having frequency-temperature characteristics that vary in the opposite direction to the frequency-temperature characteristics of the piezoelectric substrate.

9. The surface acoustic wave element according to any one of claims 1 to 3, characterized in that, The piezoelectric substrate is LiNbO3, and the tangent angles in the Euler angle (φ, θ, ψ) expression are φ, ψ = 0°±10°, and θ = 38°±10°.

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