Elastic wave device, high-frequency front-end circuit, and communication device

Abstract

This invention reduces stray emissions. The elastic wave device (1) includes a support substrate (4), a piezoelectric layer (6), and an IDT electrode (7). The support substrate (4) comprises quartz. The piezoelectric layer (6) is formed on the support substrate (4) and comprises LiTaO3. The IDT electrode (7) is formed on the piezoelectric layer (6) and has a plurality of electrode fingers (72). The IDT electrode (7) is formed on the negative side of the piezoelectric layer (6). The cut angle of the piezoelectric layer (6) is 39°Y or more and 48°Y or less.

Description

Technical Field

[0001] This invention relates broadly to elastic wave devices, high-frequency front-end circuits, and communication devices, and more specifically to elastic wave devices having a support substrate and a piezoelectric layer, high-frequency front-end circuits having elastic wave devices, and communication devices having high-frequency front-end circuits. Background Technology

[0002] Previously, elastic wave devices having a support substrate and a piezoelectric layer were known (for example, see Patent Document 1).

[0003] The elastic wave device described in Patent Document 1 includes: a support substrate comprising quartz; a piezoelectric layer comprising LiTaO3 (lithium tantalate) stacked on the support substrate; and an IDT electrode formed on the piezoelectric layer.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: U.S. Patent Application Publication No. 2018 / 0109241 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, in the conventional elastic wave device described in Patent Document 1, depending on the polarization direction or cut angle of the piezoelectric layer, stray light caused by the Rayleigh mode may be generated around 0.7 times the passband of the elastic wave device itself, which may cause the characteristics of the elastic wave device to deteriorate.

[0009] The present invention was made in view of the above-mentioned aspects, and the object of the present invention is to provide an elastic wave device, a high-frequency front-end circuit, and a communication device that can reduce spurious emissions.

[0010] Technical solutions for solving the problem

[0011] One aspect of the present invention relates to an elastic wave device comprising a support substrate, a piezoelectric layer, and an IDT electrode. The support substrate comprises quartz. The piezoelectric layer, formed on the support substrate, comprises LiTaO3. The IDT electrode, having a plurality of electrode fingers, is formed on the piezoelectric layer. The IDT electrode is formed on the negative side of the piezoelectric layer. The cut angle of the piezoelectric layer is 39°Y or greater and 48°Y or less.

[0012] One aspect of the present invention relates to a high-frequency front-end circuit comprising a filter and an amplifier circuit. The filter includes the elastic wave device, allowing high-frequency signals of a given frequency band to pass through. The amplifier circuit is connected to the filter and amplifies the amplitude of the high-frequency signal.

[0013] One aspect of the present invention relates to a communication device comprising the aforementioned high-frequency front-end circuit and signal processing circuit. The signal processing circuit processes the high-frequency signal.

[0014] Invention Effects

[0015] The elastic wave device, high-frequency front-end circuit, and communication device according to the above-described manner of the present invention can reduce spurious emissions. Attached Figure Description

[0016] Figure 1 This is a circuit diagram of the elastic wave device involved in the implementation method.

[0017] Figure 2 This is a structural diagram of a communication device equipped with the same elastic wave device.

[0018] Figure 3 This is a cross-sectional view of the same elastic wave device.

[0019] Figure 4A This is a top view of the main parts of the same elastic wave device. Figure 4B yes Figure 4A Sectional view along line X1-X1.

[0020] Figure 5 It is a graph showing the relationship between the cut angle of the piezoelectric layer and the phase characteristics of the Rayleigh mode.

[0021] Figure 6 It is a graph showing the relationship between the cutting angle of the piezoelectric layer and TCF.

[0022] Figure 7 This is a cross-sectional view of an elastic wave device according to a variation of the implementation. Detailed Implementation

[0023] Hereinafter, the elastic wave device, high-frequency front-end circuit, and communication device according to the embodiments will be described with reference to the accompanying drawings. The embodiments and the like referred to below... Figure 3 , Figure 4A , Figure 4B as well as Figure 7 This is a schematic diagram, and the size and thickness ratios of the components shown may not reflect the actual size ratios.

[0024] (Implementation Method)

[0025] (1) Structure of elastic wave device, multiplexer, high-frequency front-end circuit and communication device

[0026] The structures of the elastic wave device, multiplexer, high-frequency front-end circuit, and communication device involved in the embodiments will be described with reference to the accompanying drawings.

[0027] (1.1) Elastic wave device

[0028] like Figure 1 As shown, the elastic wave device 1 according to the embodiment is disposed between a first terminal 101 and a second terminal 102 different from the first terminal 101. The first terminal 101 is electrically connected to an external antenna 200 of the elastic wave device 1. The elastic wave device 1 is a trapezoidal filter and includes a plurality of (e.g., nine) elastic wave resonators 31 to 39. The plurality of elastic wave resonators 31 to 39 include a plurality of (e.g., five) series arm resonators (elastic wave resonators 31, 33, 35, 37, 39) disposed on a first path r1 connecting the first terminal 101 and the second terminal 102, and a plurality of (e.g., four) parallel arm resonators (elastic wave resonators 32, 34, 36, 38) disposed on a plurality of (four) second paths r21, r22, r23, r24 that connect a plurality of (four) nodes N1, N2, N3, N4 on the first path r1 to ground. Furthermore, in the elastic wave device 1, elements that function as inductors or capacitors may be arranged on the first path r1, other than as series arm resonators. Additionally, in the elastic wave device 1, elements that function as inductors or capacitors may be arranged on each of the second paths r21, r22, r23, and r24, other than as parallel arm resonators.

[0029] (1.2) Multiplexer

[0030] like Figure 2 As shown, the multiplexer 100 according to the embodiment includes a first terminal 101, a second terminal 102, a third terminal 103, a first filter 21 composed of an elastic wave device 1, and a second filter 22.

[0031] The first terminal 101 is an antenna terminal that can be electrically connected to an external antenna 200 of the multiplexer 100.

[0032] The first filter 21 is a first receiving filter that includes the elastic wave device 1 and is disposed between the first terminal 101 and the second terminal 102. The first filter 21 allows high-frequency signals in a given first frequency band to pass through and attenuates signals outside the first frequency band.

[0033] The second filter 22 is a second receiving filter disposed between the first terminal 101 and the third terminal 103. The second filter 22 allows high-frequency signals in a given second frequency band to pass through and attenuates signals outside the second frequency band.

[0034] The first filter 21 and the second filter 22 have different passbands. In the multiplexer 100, the passband of the first filter 21 is a lower frequency band compared to the passband of the second filter 22. Therefore, in the multiplexer 100, the passband of the second filter 22 is located on the higher frequency side than the passband of the first filter 21. In the multiplexer 100, for example, the maximum frequency of the passband of the first filter 21 is lower than the minimum frequency of the passband of the second filter 22.

[0035] In the multiplexer 100, the first filter 21 and the second filter 22 are connected to a common first terminal 101.

[0036] In addition, the multiplexer 100 also includes a fourth terminal 104, a fifth terminal 105, a third filter 23, and a fourth filter 24. However, in the multiplexer 100, the fourth terminal 104, the fifth terminal 105, the third filter 23, and the fourth filter 24 are not essential components.

[0037] The third filter 23 is a first transmitting filter disposed between the first terminal 101 and the fourth terminal 104. The third filter 23 allows high-frequency signals of a given third frequency band to pass through and attenuates signals outside the third frequency band.

[0038] The fourth filter 24 is a second transmitting filter disposed between the first terminal 101 and the fifth terminal 105. The fourth filter 24 allows high-frequency signals of a given fourth frequency band to pass through and attenuates signals outside the fourth frequency band.

[0039] (1.3) High-frequency front-end circuit

[0040] like Figure 2 As shown, the high-frequency front-end circuit 300 includes a multiplexer 100, a first amplifier circuit 303, and a first switching circuit 301. Furthermore, the high-frequency front-end circuit 300 also includes a second amplifier circuit 304 and a second switching circuit 302. However, in the high-frequency front-end circuit 300, the second amplifier circuit 304 and the second switching circuit 302 are not essential components.

[0041] The first amplifier circuit 303 is electrically connected to the first filter 21 and the second filter 22 of the multiplexer 100. More specifically, the first amplifier circuit 303 is connected to the first filter 21 and the second filter 22 via the first switching circuit 301. The first amplifier circuit 303 amplifies and outputs the high-frequency signal (received signal) that has passed through the antenna 200, the multiplexer 100, and the first switching circuit 301. The first amplifier circuit 303 is a low-noise amplifier circuit.

[0042] The first switching circuit 301 has two selected terminals that are independently connected to the second terminal 102 and the third terminal 103 of the multiplexer 100, and a common terminal connected to the first amplifier circuit 303. That is, the first switching circuit 301 is connected to the first filter 21 via the second terminal 102 and to the second filter 22 via the third terminal 103.

[0043] The first switching circuit 301 is, for example, constructed from an SPDT (Single Pole Double Throw) type switch. The first switching circuit 301 is controlled by a control circuit (not shown). The first switching circuit 301 connects the common terminal and the selected terminal according to the control signal from the control circuit. The first switching circuit 301 can also be constructed from a switching IC (Integrated Circuit). Furthermore, in the first switching circuit 301, the selected terminal connected to the common terminal is not limited to one, but can be multiple. That is, the high-frequency front-end circuit 300 can also be configured to handle carrier aggregation.

[0044] The second amplifier circuit 304 amplifies the high-frequency signal (transmit signal) output from an external source (e.g., the RF signal processing circuit 402 described later) of the high-frequency front-end circuit 300, and outputs it to the antenna 200 via the second switching circuit 302 and the multiplexer 100. The second amplifier circuit 304 is a power amplifier circuit.

[0045] The second switching circuit 302 is, for example, constructed from an SPDT (Single Pole Double Throw) type switch. The second switching circuit 302 is controlled by the aforementioned control circuit. The second switching circuit 302 connects the common terminal and the selected terminal according to the control signal from the aforementioned control circuit. The second switching circuit 302 can also be constructed from a switching IC (Integrated Circuit). Furthermore, in the second switching circuit 302, the selected terminal connected to the common terminal is not limited to one, but can be multiple.

[0046] (1.4) Communication device

[0047] like Figure 2 As shown, the communication device 400 includes a high-frequency front-end circuit 300 and a signal processing circuit 401. The signal processing circuit 401 processes high-frequency signals. The signal processing circuit 401 includes an RF signal processing circuit 402 and a baseband signal processing circuit 403. However, the baseband signal processing circuit 403 is not an essential component.

[0048] The RF signal processing circuit 402 processes the high-frequency signals received by the antenna 200. The high-frequency front-end circuit 300 transmits high-frequency signals (received signals and transmitted signals) between the antenna 200 and the RF signal processing circuit 402.

[0049] The RF signal processing circuit 402, for example, is an RFIC (Radio Frequency Integrated Circuit) that performs signal processing on the high-frequency signal (received signal). For instance, the RF signal processing circuit 402 performs down-conversion and other signal processing on the high-frequency signal (received signal) input from the antenna 200 via the high-frequency front-end circuit 300, and outputs the received signal generated by this signal processing to the baseband signal processing circuit 403. The baseband signal processing circuit 403, for example, is a BBIC (Baseband Integrated Circuit). The received signal processed in the baseband signal processing circuit 403 is used, for example, as an image signal for image display or as an audio signal for communication.

[0050] Furthermore, the RF signal processing circuit 402 performs signal processing such as up-conversion on the high-frequency signal (transmit signal) output from the baseband signal processing circuit 403, and outputs the processed high-frequency signal to the second amplifier circuit 304. The baseband signal processing circuit 403 performs, for example, given signal processing for a transmitted signal from outside the communication device 400.

[0051] (2) Components of an elastic wave device

[0052] Hereinafter, the constituent elements of the elastic wave device 1 according to the embodiment will be described with reference to the accompanying drawings. Here, the elastic wave device 1 will be described with reference to an elastic wave resonator.

[0053] like Figure 3 , Figure 4A as well as Figure 4B As shown, the elastic wave device 1 includes a support substrate 4, a piezoelectric layer 6, and an IDT (Interdigital Transducer) electrode 7.

[0054] (2.1) Support base plate

[0055] The support substrate 4 is a substrate containing quartz. More specifically, the support substrate 4 supports the piezoelectric layer 6 and the IDT electrode 7. In the support substrate 4, the sound speed of the propagating bulk wave is higher than the sound speed of the elastic wave propagating in the piezoelectric layer 6. In the support substrate 4, the sound speed of the lowest volume wave among the multiple propagating bulk waves is higher than the sound speed of the elastic wave propagating in the piezoelectric layer 6. Each of the multiple elastic wave resonators 3 is a single-port type elastic wave resonator with reflectors (e.g., short-circuit grids) on both sides of the elastic wave propagation direction of the IDT electrode 7. However, reflectors are not necessary. In addition, each elastic wave resonator 3 is not limited to a single-port type elastic wave resonator; for example, it can also be a longitudinally coupled type elastic wave resonator containing multiple IDT electrodes.

[0056] (2.2) Piezoelectric layer

[0057] In this embodiment, the piezoelectric layer 6 is directly stacked on the support substrate 4. The piezoelectric layer 6 has a first main surface 61 on the side of the IDT electrode 7 and a second main surface 62 on the side of the support substrate 4. The piezoelectric layer 6 is formed on the support substrate 4 such that the second main surface 62 is on the support substrate 4 side.

[0058] A piezoelectric layer 6 is formed on the support substrate 4 and contains LiTaO3 (lithium tantalate). More specifically, the piezoelectric layer 6 is, for example, a Γ°Y-cut X-propagating LiTaO3 piezoelectric single crystal. When the three crystal axes of the LiTaO3 piezoelectric single crystal are defined as the X-axis, Y-axis, and Z-axis, the Γ°Y-cut X-propagating LiTaO3 piezoelectric single crystal is a LiTaO3 single crystal cut at a plane with an axis rotated Γ° from the Y-axis to the Z-axis as its normal, and it is a single crystal in which surface acoustic waves propagate in the X-axis direction. Γ° is, for example, 39° or more and 48° or less. If the cutting angle is set to Γ (°), and the Euler angle of the piezoelectric layer 6 is set to... The cutting angle of piezoelectric layer 6 is Γ = θ + 90°. Piezoelectric layer 6 is not limited to Γ°Y cutting X propagating LiTaO3 piezoelectric single crystal; for example, it can also be Γ°Y cutting X propagating LiTaO3 piezoelectric ceramic.

[0059] In the elastic wave resonator 3 of the elastic wave device 1 according to the embodiment, as the mode of the elastic wave propagating in the piezoelectric layer 6, there exist longitudinal waves, SH waves, or SV waves, or a combination of these. In the elastic wave resonator 3, the mode with SH wave as the main component is used as the dominant mode. The so-called higher-order mode refers to the stray mode generated at a higher frequency side compared with the dominant mode of the elastic wave propagating in the piezoelectric layer 6. Whether the mode of the elastic wave propagating in the piezoelectric layer 6 is "the dominant mode with SH wave as the main component" can be confirmed, for example, by analyzing the displacement distribution using the finite element method using the parameters of the piezoelectric layer 6 (material, Euler angle, and thickness, etc.) and the parameters of the IDT electrode 7 (material, thickness, and electrode finger period, etc.), and analyzing the deformation. The Euler angle of the piezoelectric layer 6 can be obtained through analysis.

[0060] Furthermore, the single crystal material and cutting angle of the piezoelectric layer 6 can be appropriately determined based on the required specifications of the filter (filter characteristics such as pass characteristics, attenuation characteristics, temperature characteristics, and bandwidth).

[0061] When the wavelength of the elastic wave, determined by the electrode finger period of the IDT electrode 7, is set to λ, the thickness of the piezoelectric layer 6 is 3.5λ or less. The electrode finger period refers to the period of the multiple electrode fingers 72 of the IDT electrode 7. This improves the Q value.

[0062] Preferably, the thickness of the piezoelectric layer 6 is 2.5λ or less. This improves the TCF (Temperature Coefficients of Frequency). More preferably, the thickness of the piezoelectric layer 6 is 1.5λ or less. This allows for adjustment of the electromechanical coupling coefficient over a wide range. Even more preferably, the thickness of the piezoelectric layer 6 is 0.05λ or more and 0.5λ or less. This allows for adjustment of the electromechanical coupling coefficient over an even wider range.

[0063] (2.3) IDT electrode

[0064] The IDT electrode 7 is formed on the piezoelectric layer 6. The term "formed on the piezoelectric layer 6" includes both cases where it is formed directly on the piezoelectric layer 6 and cases where it is formed indirectly on the piezoelectric layer 6. The IDT electrode 7 is located on the opposite side of the support substrate 4, separated from the piezoelectric layer 6.

[0065] The IDT electrode 7 can be formed from suitable metallic materials such as Al, Cu, Pt, Au, Ag, Ti, Ni, Cr, Mo, W, or alloys primarily composed of any of these metals. Furthermore, the IDT electrode 7 can also have a structure in which multiple metal films comprising these metals or alloys are stacked. For example, the IDT electrode 7 is an Al film, but it is not limited to this; for example, it can also be a stacked film consisting of a close-fitting film of Ti film formed on the piezoelectric layer 6 and a main electrode film of Al film formed on the close-fitting film. The thickness of the close-fitting film is, for example, about 10 nm. Furthermore, the thickness of the main electrode film is, for example, about 130 nm.

[0066] like Figure 4A as well as Figure 4B As shown, the IDT electrode 7 has multiple busbars 71 and multiple electrode fingers 72. The multiple busbars 71 include a first busbar 711 and a second busbar 712. The multiple electrode fingers 72 include multiple first electrode fingers 721 and multiple second electrode fingers 722. Additionally, in... Figure 4B The diagram of the support substrate 4 is omitted.

[0067] The first busbar 711 and the second busbar 712 are elongated strips with a second direction D2 (X-axis direction) orthogonal to the first direction D1 (Γ°Y direction) along the thickness direction of the support substrate 4 as their long side direction. In the IDT electrode 7, the first busbar 711 and the second busbar 712 are opposed to each other in a third direction D3 orthogonal to both the first direction D1 and the second direction D2.

[0068] A plurality of first electrode fingers 721 are connected to a first busbar 711 and extend toward a second busbar 712. Here, the plurality of first electrode fingers 721 extend from the first busbar 711 along a third direction D3. The tips of the plurality of first electrode fingers 721 are separated from the second busbar 712. For example, the plurality of first electrode fingers 721 have the same length and width as each other.

[0069] A plurality of second electrode fingers 722 are connected to a second busbar 712 and extend toward a first busbar 711. Here, the plurality of second electrode fingers 722 extend from the second busbar 712 along a third direction D3. The leading edge of each of the plurality of second electrode fingers 722 is separate from the first busbar 711. For example, the plurality of second electrode fingers 722 have the same length and width as each other. Figure 4A In the example, the length and width of the plurality of second electrode fingers 722 are the same as the length and width of the plurality of first electrode fingers 721.

[0070] In the IDT electrode 7, a plurality of first electrode fingers 721 and a plurality of second electrode fingers 722 are arranged alternately and spaced apart from each other in the second direction D2. Therefore, adjacent first electrode fingers 721 and second electrode fingers 722 are separated along the long side of the first busbar 711. The electrode finger period of the IDT electrode 7 is the distance between the corresponding sides of adjacent first electrode fingers 721 and second electrode fingers 722. When the width of the first electrode finger 721 or second electrode finger 722 is set to W1 and the spacing width between adjacent first electrode fingers 721 and second electrode fingers 722 is set to S1, the electrode finger period of the IDT electrode 7 is defined as (W1+S1). In the IDT electrode 7, the duty cycle, which is the value obtained by dividing the width W1 of the electrode finger by the electrode finger period, is defined as W1 / (W1+S1). The duty cycle is, for example, 0.5. When the wavelength of the elastic wave, determined by the period of the electrode fingers of the IDT electrode 7, is set as λ, λ is defined by the repetition period P1 of the plurality of first electrode fingers 721 and the plurality of second electrode fingers 722.

[0071] Regarding a group of electrode fingers (multiple electrode fingers 72) comprising multiple first electrode fingers 721 and multiple second electrode fingers 722, any structure in which the multiple first electrode fingers 721 and multiple second electrode fingers 722 are arranged alternately in the second direction D2 is acceptable, but it is not necessary for the multiple first electrode fingers 721 and multiple second electrode fingers 722 to be arranged alternately. For example, it is also possible to have a mixed region in which the first electrode fingers 721 and the second electrode fingers 722 are arranged one by one alternately and a region in which two of the first electrode fingers 721 or the second electrode fingers 722 are arranged in the second direction D2. The number of each of the multiple first electrode fingers 721 and multiple second electrode fingers 722 in the IDT electrode 7 is not particularly limited.

[0072] (2.4) IDT electrode configuration and piezoelectric layer cutting angle

[0073] like Figure 3 As shown, the IDT electrode 7 is formed on the negative side of the piezoelectric layer 6. More specifically, in the piezoelectric layer 6, the first main surface 61 is the negative surface, and the second main surface 62 is the positive surface. In other words, the piezoelectric layer 6 is formed on the support substrate 4 such that the first main surface 61 is the negative surface, and the second main surface 62 is the positive surface. Moreover, the IDT electrode 7 is formed on the first main surface 61 of the piezoelectric layer 6, i.e., the negative surface.

[0074] The cutting angle of piezoelectric layer 6 is greater than 39°Y and less than 48°Y. For example... Figure 5As shown, when the cut angle of the piezoelectric layer 6 is above 39°Y and below 48°Y, the phase characteristics are superior compared to the cases where the cut angle of the piezoelectric layer 6 is less than 39°Y and the cases where the cut angle of the piezoelectric layer 6 is greater than 48°Y.

[0075] Preferably, the cutting angle of the piezoelectric layer 6 is 42°Y or greater. For example... Figure 6 As shown, it can reduce TCF. For example, it can reduce the absolute value of TCF to below 5 ppm / ℃.

[0076] More preferably, the cutting angle of the piezoelectric layer 6 is 44°Y or higher. This allows for further reduction of the TCF. For example, the absolute value of the TCF can be reduced to 2 ppm / ℃ or less.

[0077] (2.5) Sound velocity of the supporting substrate

[0078] The sound velocity of the slow transverse wave propagating on the support substrate 4 is 3950 m / s or higher. More specifically, the sound velocity of the aforementioned slow transverse wave propagating on the support substrate 4 is greater than the resonant sound velocity of 3800 m / s, and the anti-resonant sound velocity is 3950 m / s or higher. As a result, good resonant and anti-resonant characteristics can be obtained.

[0079] More preferably, the sound velocity of the slow transverse wave propagating on the support substrate 4 is 4100 m / s or higher. More specifically, the sound velocity of the slow transverse wave propagating on the support substrate 4 is 4100 m / s or higher, which is the sum of the difference (150 m / s) between the anti-resonance sound velocity (3950 m / s) and the resonance sound velocity (3800 m / s) and the anti-resonance sound velocity (3950 m / s). This improves the characteristics of the trapezoidal filter.

[0080] (2.6) Relationship between the support substrate and the IDT electrode

[0081] The angle formed by the Z-axis of the supporting substrate 4 and the X-axis (second direction D2) of LiTaO3 is ±20° or less. Figure 3 In the example, the angle formed by the Z-axis of the support substrate 4 and the direction in which the multiple electrode fingers 72 of the IDT electrode 7 are arranged (second direction D2) is ±20° or less. As a result, the sound speed of the slow transverse wave propagating on the support substrate 4 can be 4100 m / s or more.

[0082] More preferably, the angle formed by the Z-axis of the supporting substrate 4 and the X-axis (second direction D2) of LiTaO3 is parallel. Figure 3 In the example, the Z-axis of the support substrate 4 is parallel to the direction in which the multiple electrode fingers 72 of the IDT electrode 7 are arranged (second direction D2). Therefore, Z-propagation can be configured, thus enabling high-speed sounding in the support substrate 4.

[0083] (3) Effect

[0084] In the elastic wave device 1 according to the embodiment, the IDT electrode 7 is formed on the negative side of the piezoelectric layer 6, and the cut angle of the piezoelectric layer 6 is 39°Y or more and 48°Y or less. As a result, stray emissions can be reduced.

[0085] In the elastic wave device 1 according to the embodiment, the sound velocity of the support substrate 4 is 3950 m / s. This results in good resonance and anti-resonance characteristics. Consequently, the characteristics of the trapezoidal filter can be improved.

[0086] In the elastic wave device 1 according to the embodiment, the angle formed by the Z-axis of the support substrate 4 and the X-axis (second direction D2) of LiTaO3 is ±20° or less. As a result, the sound velocity of the slow transverse wave can be 4100 m / s or more.

[0087] In the elastic wave device 1 according to the embodiment, the Z-axis of the support substrate 4 is parallel to the X-axis (second direction D2) of LiTaO3. Therefore, it can be set to propagate in the Z direction, thus enabling high-speed sounding in the support substrate 4.

[0088] In the elastic wave device 1 according to the embodiment, the cut angle of the piezoelectric layer 6 is 42°Y or more. This reduces the TCF (transient charge filtration efficiency). For example, the absolute value of the TCF can be reduced to 5 ppm / °C or less.

[0089] In the elastic wave device 1 according to the embodiment, the cut angle of the piezoelectric layer 6 is 44°Y or more. This allows for further reduction of the TCF (transient charge filtration efficiency). For example, the absolute value of the TCF can be reduced to 2 ppm / °C or less.

[0090] In the elastic wave device 1 according to the embodiment, the piezoelectric layer 6 is directly stacked on the support substrate 4. As a result, stray emissions can be further reduced, and thus characteristic degradation can be suppressed.

[0091] In the elastic wave device 1 according to the embodiment, the thickness of the piezoelectric layer 6 is 3.5λ or less. As a result, the Q value can be improved.

[0092] In the elastic wave device 1 according to the embodiment, the thickness of the piezoelectric layer 6 is 2.5λ or less. As a result, the TCF can be improved.

[0093] In the elastic wave device 1 according to the embodiment, the thickness of the piezoelectric layer 6 is 1.5λ or less. As a result, the electromechanical coupling coefficient can be adjusted over a wide range.

[0094] In the elastic wave device 1 according to the embodiment, the thickness of the piezoelectric layer 6 is 0.05λ or more and 0.5λ or less. This allows for adjustment of the electromechanical coupling coefficient over a wider range.

[0095] (4) Variations

[0096] Hereinafter, variations of the implementation method will be described.

[0097] As a variation of the implementation, the piezoelectric layer 6 is not limited to being directly laminated on the support substrate 4, but can also be formed indirectly on the support substrate 4. In other words, it can also be as follows: Figure 7 As shown, other layers exist between the piezoelectric layer 6 and the supporting substrate 4. Figure 7 In another example, a low-velocity film 5 may be formed on the support substrate 4, and a piezoelectric layer 6 may be formed on the low-velocity film 5.

[0098] like Figure 7 As shown, the modified example of the elastic wave device 1a includes a support substrate 4, a low-velocity film 5, a piezoelectric layer 6, and an IDT electrode 7.

[0099] The low-velocity sound membrane 5 is a membrane in which the velocity of sound of the bulk wave propagating in the low-velocity sound membrane 5 is lower than the velocity of sound of the bulk wave propagating in the piezoelectric layer 6. The low-velocity sound membrane 5 is disposed between the support substrate 4 and the piezoelectric layer 6. By disposing the low-velocity sound membrane 5 between the support substrate 4 and the piezoelectric layer 6, the velocity of sound of the elastic wave is reduced. The energy of the elastic wave is essentially concentrated in the low-velocity medium. Therefore, the energy containment effect of the elastic wave into the piezoelectric layer 6 and into the IDT electrode 7 that excites the elastic wave can be improved. As a result, compared to the case where the low-velocity sound membrane 5 is not disposed, losses can be reduced and the Q value can be improved.

[0100] The material of the low-velocity membrane 5 is, for example, silicon oxide. However, the material of the low-velocity membrane 5 is not limited to silicon oxide, and may also be glass, silicon oxynitride, tantalum oxide, silicon oxide with added fluorine, carbon, or boron, or a material with the above-mentioned materials as the main components.

[0101] When the material of the low-velocity acoustic membrane 5 is silicon oxide, the temperature characteristics can be improved. LiTaO3, the material of the piezoelectric layer 6, has a negative temperature constant, while silicon oxide has a positive temperature constant. Therefore, in the elastic wave device 1a, the absolute value of the TCF can be reduced. Furthermore, the inherent acoustic impedance of silicon oxide is lower than that of LiTaO3, the material of the piezoelectric layer 6. Therefore, it is possible to achieve both an increase in the electromechanical coupling coefficient, i.e., an expansion of the relative bandwidth and an improvement in the frequency-temperature characteristics.

[0102] The thickness of the low-velocity film 5 is preferably 2.0λ or less. By setting the thickness of the low-velocity film 5 to 2.0λ or less, the film stress can be reduced, which in turn makes it possible to reduce wafer warpage, improve yield, and stabilize characteristics. Furthermore, if the thickness of the low-velocity film 5 is in the range of 0.1λ or more and 0.5λ or less, the electromechanical coupling coefficient remains essentially unchanged.

[0103] In addition, there may be multiple layers between the support substrate 4 and the piezoelectric layer 6, not limited to a single layer (low-velocity film 5) as described above.

[0104] In the above-described modified example of the elastic wave device 1a, it also achieves the same effect as the elastic wave device 1 according to the embodiment.

[0105] The embodiments and modifications described above are merely a part of the various embodiments and modifications of the present invention. Furthermore, the embodiments and modifications can be modified in various ways, such as by design, to achieve the objectives of the present invention.

[0106] (Way)

[0107] The following methods are disclosed in this specification.

[0108] The elastic wave device (1; 1a) according to the first embodiment includes a support substrate (4), a piezoelectric layer (6), and an IDT electrode (7). The support substrate (4) comprises quartz. The piezoelectric layer (6) is formed on the support substrate (4) and comprises LiTaO3. The IDT electrode (7) is formed on the piezoelectric layer (6) and has a plurality of electrode fingers (72). The IDT electrode (7) is formed on the negative side of the piezoelectric layer (6). The cut angle of the piezoelectric layer (6) is 39°Y or more and 48°Y or less. According to the elastic wave device (1; 1a) according to the first embodiment, stray emissions can be reduced.

[0109] In the elastic wave device (1; 1a) according to the second embodiment, in the first embodiment, the sound velocity of the slow transverse wave propagating on the support substrate (4) is 3950 m / s or higher. According to the elastic wave device (1; 1a) according to the second embodiment, good resonance characteristics and anti-resonance characteristics can be obtained.

[0110] In the elastic wave device (1; 1a) according to the third embodiment, in the second embodiment, the sound velocity of the slow transverse wave propagating on the support substrate (4) is 4100 m / s or higher. According to the elastic wave device (1; 1a) according to the third embodiment, the characteristics of the trapezoidal filter can be improved.

[0111] In the elastic wave device (1; 1a) according to the fourth embodiment, in any of the first to third embodiments, the angle formed by the Z-axis of the support substrate (4) and the X-axis (second direction D2) of LiTaO3 is ±20° or less. According to the elastic wave device (1; 1a) according to the fourth embodiment, the sound velocity of the slow transverse wave can be 4100 m / s or more.

[0112] In the elastic wave device (1; 1a) according to the fifth embodiment, in the fourth embodiment, the Z-axis of the support substrate (4) is parallel to the X-axis (second direction D2) of LiTaO3. According to the elastic wave device (1; 1a) according to the fifth embodiment, it can be set to propagate in the Z direction, thus enabling high-speed sounding in the support substrate (4).

[0113] In the elastic wave device (1; 1a) according to the sixth embodiment, in any of the first to fifth embodiments, the cut angle of the piezoelectric layer (6) is 42°Y or more. According to the elastic wave device (1; 1a) according to the sixth embodiment, the TCF can be reduced. For example, the absolute value of the TCF can be reduced to 5 ppm / ℃ or less.

[0114] In the elastic wave device (1; 1a) according to the seventh embodiment, in the sixth embodiment, the cut angle of the piezoelectric layer (6) is 44°Y or higher. According to the elastic wave device (1; 1a) according to the seventh embodiment, the TCF can be further reduced. For example, the absolute value of the TCF can be made to be 2 ppm / ℃ or less.

[0115] In the elastic wave device (1) according to the eighth embodiment, in any of the first to seventh embodiments, the piezoelectric layer (6) is directly stacked on the support substrate (4). According to the elastic wave device (1) according to the eighth embodiment, stray emissions can be further reduced, thereby suppressing characteristic degradation.

[0116] The high-frequency front-end circuit (300) according to the ninth embodiment includes filters (first filter 21; second filter 22; third filter 23; fourth filter 24) and amplifier circuits (first amplifier circuit 303; second amplifier circuit 304). The filters include elastic wave devices (1; 1a) of any of the first to eighth embodiments, allowing high-frequency signals of a given frequency band to pass through. The amplifier circuits are connected to the filters to amplify the amplitude of the high-frequency signals. According to the high-frequency front-end circuit (300) according to the ninth embodiment, spurious emissions can be reduced in the elastic wave devices (1; 1a).

[0117] The communication device (400) according to the tenth embodiment includes the high-frequency front-end circuit (300) and signal processing circuit (401) of the ninth embodiment. The signal processing circuit (401) processes the high-frequency signal. According to the communication device (400) according to the tenth embodiment, spurious emissions can be reduced in the elastic wave device (1; 1a).

[0118] Description of Reference Numerals

[0119] 1, 1a: Elastic wave device;

[0120] 21: First filter (filter);

[0121] 22: Second filter (filter);

[0122] 23: Third filter (filter);

[0123] 24: Filter No. 4;

[0124] 4: Support base plate;

[0125] 6: Piezoelectric layer;

[0126] 7: IDT electrode;

[0127] 72: Electrode finger;

[0128] 300: High-frequency front-end circuit;

[0129] 303: First amplifier circuit (amplifier circuit);

[0130] 304: Second amplifier circuit (amplifier circuit);

[0131] 400: Communication device;

[0132] 401: Signal processing circuit;

[0133] D2: Second direction.

Claims

1. An elastic wave device, comprising: Support substrate, comprising quartz; A piezoelectric layer, formed on the support substrate, comprises LiTaO3; and An IDT electrode is formed on the piezoelectric layer and has multiple electrode fingers. The IDT electrode is formed on the negative side of the piezoelectric layer. The cutting angle of the piezoelectric layer is greater than 39°Y and less than 48°Y. The thickness of the piezoelectric layer is greater than 0.05λ and less than 0.5λ. The sound speed of the slow transverse wave propagating on the support substrate is greater than the sound speed of resonance.

2. The elastic wave device according to claim 1, wherein, The sound velocity of the slow transverse wave propagating on the support substrate is above 3950 m / s.

3. The elastic wave device according to claim 2, wherein, The sound velocity of the slow transverse wave propagating on the support substrate is above 4100 m / s.

4. The elastic wave device according to any one of claims 1 to 3, wherein, The angle formed by the Z-axis of the supporting substrate and the X-axis of the LiTaO3 is less than ±20°.

5. The elastic wave device according to claim 4, wherein, The Z-axis of the support substrate is parallel to the X-axis of the LiTaO3.

6. The elastic wave device according to any one of claims 1 to 3, wherein, The cutting angle of the piezoelectric layer is 42°Y or higher.

7. The elastic wave device according to claim 6, wherein, The cutting angle of the piezoelectric layer is 44°Y or higher.

8. The elastic wave device according to any one of claims 1 to 3, wherein, The piezoelectric layer is directly stacked on the supporting substrate.

9. A high-frequency front-end circuit, comprising: A filter comprising the elastic wave device according to any one of claims 1 to 8, allowing high-frequency signals of a given frequency band to pass through; and An amplifier circuit, connected to the filter, amplifies the amplitude of the high-frequency signal.

10. A communication device comprising: The high-frequency front-end circuit as described in claim 9; and The signal processing circuit processes the high-frequency signal.

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