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

Abstract

The present invention reduces stray noise. An elastic wave device (1) includes a supporting substrate (4), a piezoelectric layer (6), and an IDT electrode (7). The supporting substrate (4) includes quartz. The piezoelectric layer (6) is formed on the supporting substrate (4) and includes 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 front side of the piezoelectric layer (6). The cutting angle of the piezoelectric layer (6) is less than 49°Y.

Description

Technical Field

[0001] The present invention broadly relates to an elastic wave device, a high-frequency front-end circuit, and a communication device, and more specifically, to an elastic wave device having a supporting substrate and a piezoelectric layer, a high-frequency front-end circuit having the elastic wave device, and a communication device having the high-frequency front-end circuit. Background Art

[0002] Conventionally, an elastic wave device including a supporting substrate and a piezoelectric layer is known (for example, see Patent Document 1).

[0003] The elastic wave device described in Patent Document 1 includes: a supporting substrate made of quartz; a piezoelectric layer made of LiTaO 3 (lithium tantalate) stacked on the supporting 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] Problems to be solved by the invention

[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, spurious emission from a high-order mode may occur at approximately three times the passband of the elastic wave device itself, causing degradation in the characteristics of the elastic wave device.

[0009] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an elastic wave device, a high-frequency front-end circuit, and a communication device capable of reducing spurious emission.

[0010] Technical solutions to problems

[0011] An elastic wave device according to one embodiment of the present invention includes a supporting substrate, a piezoelectric layer, and an IDT electrode. The supporting substrate comprises quartz. The piezoelectric layer is formed on the supporting substrate and comprises LiTaO3. The IDT electrode is formed on the piezoelectric layer and has a plurality of electrode fingers. The IDT electrode is formed on the front side of the piezoelectric layer. The piezoelectric layer has a cut angle of 49° or less.

[0012] A high-frequency front-end circuit according to one embodiment of the present invention includes a filter and an amplifier circuit. The filter includes the elastic wave device and passes a high-frequency signal in a predetermined frequency band. The amplifier circuit is connected to the filter and amplifies the amplitude of the high-frequency signal.

[0013] A communication device according to one embodiment of the present invention includes the high-frequency front-end circuit and a signal processing circuit. The signal processing circuit processes the high-frequency signal.

[0014] Effects of the Invention

[0015] According to the elastic wave device, high-frequency front-end circuit, and communication device according to the above-described aspects of the present invention, spurious emission can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a circuit diagram of an elastic wave device according to an embodiment.

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

[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 elastic wave device shown above. Figure 4B yes Figure 4A X1-X1 line cross-sectional view.

[0020] Figure 5 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 cut angle of the piezoelectric layer and TCF.

[0022] Figure 7 It is a cross-sectional view of an elastic wave device according to a modified example of the embodiment. DETAILED DESCRIPTION

[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. Figure 3 、 Figure 4A 、 Figure 4B as well as Figure 7 These are schematic drawings, and the sizes and thickness ratios of the components in the drawings do not necessarily reflect actual dimensional ratios.

[0024] (Implementation Method)

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

[0026] The configurations of an elastic wave device, a multiplexer, a high-frequency front-end circuit, and a communication device according to the embodiments will be described with reference to the drawings.

[0027] (1.1) Elastic wave device

[0028] like Figure 1 As shown, the elastic wave device 1 according to the embodiment is provided between a first terminal 101 and a second terminal 102, which is different from first terminal 101. First terminal 101 is electrically connected to an antenna 200 external to elastic wave device 1. Elastic wave device 1 is a ladder-type filter including a plurality (e.g., nine) of elastic wave resonators 31 to 39. These plurality of elastic wave resonators 31 to 39 include a plurality (e.g., five) of series-arm resonators (elastic wave resonators 31, 33, 35, 37, and 39) provided on a first path r1 connecting first terminal 101 and second terminal 102, and a plurality (e.g., four) of parallel-arm resonators (elastic wave resonators 32, 34, 36, and 38) provided on a plurality (e.g., four) of second paths r21, r22, r23, and r24 connecting a plurality (e.g., four) of nodes N1, N2, N3, and N4 on first path r1 to ground, respectively. Furthermore, in the elastic wave device 1, an element functioning as an inductor or capacitor may be disposed on the first path r1 as an element other than the series arm resonator. Furthermore, in the elastic wave device 1, an element functioning as an inductor or capacitor may be disposed on each of the second paths r21, r22, r23, and r24 as an element other than the parallel arm resonator.

[0029] (1.2) Multiplexer

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

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

[0032] First filter 21 is a first reception filter that includes elastic wave device 1 and is provided between first terminal 101 and second terminal 102. First filter 21 passes high-frequency signals in a predetermined first frequency band and attenuates signals outside the first frequency band.

[0033] The second filter 22 is a second reception filter provided between the first terminal 101 and the third terminal 103. The second filter 22 passes high-frequency signals in a predetermined second frequency band 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 than the passband of the second filter 22. Therefore, in the multiplexer 100, the passband of the second filter 22 is located at a 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] The multiplexer 100 also includes a fourth terminal 104, a fifth terminal 105, a third filter 23, and a fourth filter 24. However, the fourth terminal 104, the fifth terminal 105, the third filter 23, and the fourth filter 24 are not essential components of the multiplexer 100.

[0037] The third filter 23 is a first transmission filter provided between the first terminal 101 and the fourth terminal 104. The third filter 23 passes high-frequency signals in a predetermined third frequency band and attenuates signals outside the third frequency band.

[0038] The fourth filter 24 is a second transmission filter provided between the first terminal 101 and the fifth terminal 105. The fourth filter 24 passes high-frequency signals in a predetermined fourth frequency band 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 the multiplexer 100, a first amplifier circuit 303, and a first switch circuit 301. Furthermore, the high-frequency front-end circuit 300 includes a second amplifier circuit 304 and a second switch circuit 302. However, the second amplifier circuit 304 and the second switch circuit 302 are not essential components of the high-frequency front-end circuit 300.

[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 switch circuit 301. The first amplifier circuit 303 amplifies and outputs a high-frequency signal (received signal) that has passed through the antenna 200, the multiplexer 100, and the first switch circuit 301. The first amplifier circuit 303 is a low-noise amplifier circuit.

[0042] The first switch circuit 301 has two selected terminals 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. In other words, the first switch 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 switch circuit 301 is composed of, for example, a SPDT (Single Pole Double Throw) type switch. The first switch circuit 301 is controlled by a control circuit (not shown). The first switch circuit 301 connects the common terminal and the selected terminal according to a control signal from the above-mentioned control circuit. The first switch circuit 301 can also be composed of a switch IC (Integrated Circuit). In addition, in the first switch circuit 301, the selected terminal connected to the common terminal is not limited to one, and can also be multiple. That is, the high-frequency front-end circuit 300 can also be configured to cope with carrier aggregation.

[0044] The second amplifier circuit 304 amplifies a high-frequency signal (transmission signal) output from outside the high-frequency front-end circuit 300 (e.g., the RF signal processing circuit 402 described later), and outputs the amplified signal to the antenna 200 via the second switch circuit 302 and the multiplexer 100. The second amplifier circuit 304 is a power amplifier circuit.

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

[0046] (1.4) Communication device

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

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

[0049] The RF signal processing circuit 402 is, for example, a Radio Frequency Integrated Circuit (RFIC), and performs signal processing on high-frequency signals (received signals). For example, the RF signal processing circuit 402 performs signal processing such as down-conversion 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 is, for example, a Baseband Integrated Circuit (BBIC). The received signal processed by the baseband signal processing circuit 403 is used, for example, as an image signal for image display or as an audio signal for telephone calls.

[0050] Furthermore, the RF signal processing circuit 402 performs signal processing such as up-conversion on the high-frequency signal (transmission 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 predetermined signal processing on, for example, a transmission signal from outside the communication device 400.

[0051] (2) Components of the Elastic Wave Device

[0052] Hereinafter, components of an elastic wave device 1 according to an embodiment will be described with reference to the drawings. Here, the elastic wave device 1 will be described focusing on a single elastic wave resonator.

[0053] like Figure 3 As shown, elastic wave device 1 includes a supporting substrate 4 , a piezoelectric layer 6 , and IDT (Interdigital Transducer) electrodes 7 .

[0054] (2.1) Support base plate

[0055] The supporting substrate 4 is a substrate made of quartz. More specifically, the supporting substrate 4 supports the piezoelectric layer 6 and the IDT electrode 7. The acoustic velocity of the bulk wave propagating in the supporting substrate 4 is higher than the acoustic velocity of the elastic wave propagating in the piezoelectric layer 6. The acoustic velocity of the bulk wave with the lowest acoustic velocity among the multiple bulk waves propagating in the supporting substrate 4 is higher than the acoustic velocity of the elastic wave propagating in the piezoelectric layer 6. Each of the multiple elastic wave resonators 3 is a single-port elastic wave resonator having a reflector (e.g., a short-circuit grid) on both sides of the IDT electrode 7 in the direction of elastic wave propagation. However, the reflector is not required. In addition, each elastic wave resonator 3 is not limited to a single-port elastic wave resonator, and for example, it can also be a longitudinally coupled elastic wave resonator including multiple IDT electrodes.

[0056] (2.2) Piezoelectric layer

[0057] In this embodiment, the piezoelectric layer 6 is directly laminated on the support substrate 4. More specifically, the piezoelectric layer 6 has a first principal surface 61 on the IDT electrode 7 side and a second principal surface 62 on the support substrate 4 side. The piezoelectric layer 6 is formed on the support substrate 4 so that the second principal surface 62 is on the support substrate 4 side.

[0058] The piezoelectric layer 6 is formed on the supporting substrate 4 and contains LiTaO3 (lithium tantalate). In more detail, the piezoelectric layer 6 is, for example, a Γ°Y-cut X-propagation LiTaO3 piezoelectric single crystal. When the three crystal axes of the LiTaO3 piezoelectric single crystal are set as the X-axis, the Y-axis, and the Z-axis, the Γ°Y-cut X-propagation LiTaO3 piezoelectric single crystal is a LiTaO3 single crystal cut at a plane whose normal line is an axis rotated Γ° from the Y-axis to the Z-axis with the X-axis as the center axis, and is a single crystal in which surface acoustic waves propagate in the X-axis direction. Γ° is, for example, greater than 38° and less than 48°. If the cutting angle is set to Γ(°), and the Euler angle of the piezoelectric layer 6 is set to ( θ, ψ), the cut angle of the piezoelectric layer 6 is Γ = θ + 90°. The piezoelectric layer 6 is not limited to a Γ°Y-cut X-propagation LiTaO3 piezoelectric single crystal. For example, it may be a Γ°Y-cut X-propagation LiTaO3 piezoelectric ceramic.

[0059] In the elastic wave resonator 3 of the elastic wave device 1 according to the embodiment, the modes of the elastic waves propagating through the piezoelectric layer 6 include longitudinal waves, SH waves, SV waves, or a combination of these. In the elastic wave resonator 3, a mode with the SH wave as the primary component is used as the primary mode. A high-order mode refers to a spurious mode generated at a higher frequency than the primary mode of the elastic waves propagating through the piezoelectric layer 6. Whether the mode of the elastic waves propagating through the piezoelectric layer 6 is a "primary mode with the SH wave as the primary component" can be confirmed, for example, by analyzing the displacement distribution and deformation using the finite element method using parameters of the piezoelectric layer 6 (material, Euler angles, thickness, etc.) and parameters of the IDT electrode 7 (material, thickness, electrode finger period, etc.). The Euler angles of the piezoelectric layer 6 can be determined through analysis.

[0060] The single crystal material and cut angle of the piezoelectric layer 6 may be appropriately determined according to, for example, the required specifications of the filter (filter characteristics such as passband 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 λ, the thickness of the piezoelectric layer 6 is 3.5λ or less. The electrode finger period is the period of the plurality of electrode fingers 72 of the IDT electrode 7. This can improve the Q value.

[0062] The thickness of the piezoelectric layer 6 is preferably 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. Further 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 phrase "formed on the piezoelectric layer 6" includes directly forming on the piezoelectric layer 6 and indirectly forming on the piezoelectric layer 6. The IDT electrode 7 is located on the opposite side of the support substrate 4 with the piezoelectric layer 6 interposed therebetween.

[0065] The IDT electrode 7 can be formed of an appropriate metal material such as Al, Cu, Pt, Au, Ag, Ti, Ni, Cr, Mo, W, or an alloy based on any of these metals. Furthermore, the IDT electrode 7 may also have a structure in which a plurality of metal films comprising these metals or alloys are stacked. For example, the IDT electrode 7 is an Al film, but this is not limited to this. For example, the IDT electrode 7 may also be a stacked film comprising a bonding film composed of a Ti film formed on the piezoelectric layer 6 and a main electrode film composed of an Al film formed on the bonding film. The thickness of the bonding film is, for example, approximately 10 nm. Furthermore, the thickness of the main electrode film is, for example, approximately 130 nm.

[0066] like Figure 4A as well as Figure 4B As shown, the IDT electrode 7 includes a plurality of bus bars 71 and a plurality of electrode fingers 72. The plurality of bus bars 71 include a first bus bar 711 and a second bus bar 712. The plurality of electrode fingers 72 include a plurality of first electrode fingers 721 and a plurality of second electrode fingers 722. Figure 4B In the figure, the support substrate 4 is omitted.

[0067] The first bus bar 711 and the second bus bar 712 are long strips with their longitudinal sides oriented in a second direction D2 (X-axis direction) perpendicular to a first direction D1 (Γ°Y direction) along the thickness of the support substrate 4. In the IDT electrode 7, the first bus bar 711 and the second bus bar 712 face each other in a third direction D3 perpendicular to both the first direction D1 and the second direction D2.

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

[0069] The plurality of second electrode fingers 722 are connected to the second bus bar 712 and extend toward the first bus bar 711. Here, the plurality of second electrode fingers 722 extend from the second bus bar 712 along the third direction D3. The front ends of the plurality of second electrode fingers 722 are separated from the first bus bar 711. For example, the plurality of second electrode fingers 722 have the same length and width. Figure 4A In the example, the length and width of the plurality of second electrode fingers 722 are respectively 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, the first electrode fingers 721 and the second electrode fingers 722 that are adjacent in the longitudinal direction of the first bus bar 711 are separated. The electrode finger period of the IDT electrode 7 is the distance between the corresponding sides of the adjacent first electrode fingers 721 and second electrode fingers 722. When the width of the first electrode finger 721 or the second electrode finger 722 is set to W1 and the spacing width between the 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 by (W1+S1). In the IDT electrode 7, the duty cycle, which is the value obtained by dividing the electrode finger width W1 by the electrode finger period, is defined by W1 / (W1+S1). The duty cycle is, for example, 0.5. When the wavelength of the elastic wave determined by the electrode finger period of the IDT electrode 7 is denoted 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 set of electrode fingers (plurality of electrode fingers 72) including a plurality of first electrode fingers 721 and a plurality of second electrode fingers 722, any structure in which the plurality of first electrode fingers 721 and the plurality of second electrode fingers 722 are spaced apart in the second direction D2 may be sufficient. A structure in which the plurality of first electrode fingers 721 and the plurality of second electrode fingers 722 are alternately spaced apart from each other may be sufficient. For example, a mixture of regions in which the first electrode fingers 721 and the second electrode fingers 722 are spaced apart from each other and regions in which two first electrode fingers 721 or two second electrode fingers 722 are spaced apart in the second direction D2 may exist. The number of the plurality of first electrode fingers 721 and the number of the plurality of second electrode fingers 722 in the IDT electrode 7 is not particularly limited.

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

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

[0074] The cutting angle of the piezoelectric layer 6 is less than 49°Y. Figure 5 As shown, when the piezoelectric layer 6 is within the range of 49°Y or less, the phase characteristic is better when the IDT electrode 7 is formed on the front side of the piezoelectric layer 6 than when the IDT electrode 7 is formed on the back side of the piezoelectric layer 6 .

[0075] Preferably, the cutting angle of the piezoelectric layer 6 is 38°Y or more. Figure 6 As shown, TCF can be reduced. For example, the absolute value of TCF can be reduced to 10 ppm / °C or less.

[0076] More preferably, the cutting angle of the piezoelectric layer 6 is 42°Y or more. Figure 6 As shown, TCF can be reduced. For example, the absolute value of TCF can be reduced to 5 ppm / °C or less.

[0077] More preferably, the cut angle of the piezoelectric layer 6 is 44°Y or greater. This can further reduce the TCF. For example, the absolute value of the TCF can be reduced to 2 ppm / °C or less.

[0078] Furthermore, the cut angle of the piezoelectric layer 6 is preferably not more than 48°Y. This can further reduce the TCF. For example, the absolute value of the TCF can be made not more than 2 ppm / °C.

[0079] (2.5) Sound velocity of the supporting substrate

[0080] The acoustic velocity of the slow shear wave propagating through the support substrate 4 is greater than 3950 m / s. More specifically, the acoustic velocity of the slow shear wave propagating through the support substrate 4 is greater than the acoustic velocity of 3800 m / s for resonance and greater than the acoustic velocity of 3950 m / s for antiresonance. This enables excellent resonant and antiresonant characteristics to be achieved.

[0081] More preferably, the acoustic velocity of the slow shear wave propagating through the support substrate 4 is greater than or equal to 4100 m / s. More specifically, the acoustic velocity of the slow shear wave propagating through the support substrate 4 is greater than or equal to the sum of the difference (150 m / s) between the antiresonant acoustic velocity of 3950 m / s and the resonant acoustic velocity of 3800 m / s, and the antiresonant acoustic velocity of 3950 m / s. This improves the characteristics of the ladder filter.

[0082] (2.6) Relationship between the supporting substrate and the IDT electrode

[0083] The angle formed by the Z axis of the support substrate 4 and the X axis (second direction D2) of the LiTaO 3 is less than ±20°. Figure 3 In the example, the angle formed by the Z-axis of the support substrate 4 and the direction in which the plurality of electrode fingers 72 of the IDT electrode 7 are arranged (the second direction D2) is ±20° or less. This allows the acoustic velocity of the slow transverse wave propagating through the support substrate 4 to be set to 4100 m / s or more.

[0084] More preferably, the angle formed by the Z axis of the support substrate 4 and the X axis (the second direction D2) of the LiTaO 3 is parallel. Figure 3In the example, the Z axis of the support substrate 4 is parallel to the direction (second direction D2) in which the plurality of electrode fingers 72 of the IDT electrode 7 are arranged. This enables Z propagation, thereby increasing the acoustic velocity in the support substrate 4.

[0085] (3) Effect

[0086] In the elastic wave device 1 according to the embodiment, IDT electrode 7 is formed on the front surface side of piezoelectric layer 6 , and the cut angle of piezoelectric layer 6 is not more than 49° Y. This can reduce spurious emission.

[0087] In the elastic wave device 1 according to the embodiment, the acoustic velocity of the supporting substrate 4 is 3950 m / s. This allows for good resonance and anti-resonance characteristics, thereby improving the characteristics of the ladder filter.

[0088] 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 the LiTaO 3 is ±20° or less. This allows the acoustic velocity of the slow shear wave to be 4100 m / s or more.

[0089] 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 the LiTaO 3 . This enables Z propagation, thereby increasing the acoustic velocity in the support substrate 4 .

[0090] In the elastic wave device 1 according to the embodiment, the cut angle of the piezoelectric layer 6 is 38°Y or greater. This can reduce the TCF. For example, the absolute value of the TCF can be reduced to 10 ppm / °C or less.

[0091] In the elastic wave device 1 according to the embodiment, the cut angle of the piezoelectric layer 6 is 42°Y or greater. This further reduces the TCF. For example, the absolute value of the TCF can be reduced to 5 ppm / °C or less.

[0092] In the elastic wave device 1 according to the embodiment, the cut angle of the piezoelectric layer 6 is 44°Y or greater. This further reduces the TCF. For example, the absolute value of the TCF can be reduced to 2 ppm / °C or less.

[0093] In the elastic wave device 1 according to the embodiment, the cut angle of the piezoelectric layer 6 is 48°Y or less. This further reduces the TCF. For example, the absolute value of the TCF can be reduced to 2 ppm / °C or less.

[0094] In the elastic wave device 1 according to the embodiment, the piezoelectric layer 6 is directly laminated on the supporting substrate 4. This further reduces spurious emission and thus suppresses degradation of characteristics.

[0095] In the elastic wave device 1 according to the embodiment, the thickness of the piezoelectric layer 6 is 3.5λ or less. This can increase the Q value.

[0096] In the elastic wave device 1 according to the embodiment, the thickness of the piezoelectric layer 6 is 2.5λ or less. This can improve the TCF.

[0097] In elastic wave device 1 according to the embodiment, the thickness of piezoelectric layer 6 is 1.5λ or less. This allows the electromechanical coupling coefficient to be adjusted over a wide range.

[0098] In elastic wave device 1 according to the embodiment, the thickness of piezoelectric layer 6 is not less than 0.05λ and not more than 0.5λ. This allows the electromechanical coupling coefficient to be adjusted in a wider range.

[0099] (4) Modification

[0100] Modifications of the embodiment will be described below.

[0101] As a modification of the embodiment, the piezoelectric layer 6 is not limited to being directly laminated on the support substrate 4, but may also be indirectly formed on the support substrate 4. In other words, Figure 7 As shown in FIG, there are other layers between the piezoelectric layer 6 and the supporting substrate 4. Figure 7 In the example, the low-acoustic-velocity film 5 may be formed on the supporting substrate 4 , and the piezoelectric layer 6 may be formed on the low-acoustic-velocity film 5 .

[0102] like Figure 7 As shown, an elastic wave device 1 a according to a modified example includes a supporting substrate 4 , a low-acoustic-velocity film 5 , a piezoelectric layer 6 , and an IDT electrode 7 .

[0103] The low-acoustic-velocity film 5 is a film that reduces the acoustic velocity of bulk waves propagating through the low-acoustic-velocity film 5 compared to the acoustic velocity of bulk waves propagating through the piezoelectric layer 6. The low-acoustic-velocity film 5 is disposed between the support substrate 4 and the piezoelectric layer 6. By disposing the low-acoustic-velocity film 5 between the support substrate 4 and the piezoelectric layer 6, the acoustic velocity of elastic waves is reduced. The energy of the elastic waves is essentially concentrated in the medium with a low acoustic velocity. Therefore, the energy confinement of the elastic waves within the piezoelectric layer 6 and within the IDT electrode 7 that excites the elastic waves can be enhanced. As a result, losses can be reduced and the Q value can be improved compared to a case where the low-acoustic-velocity film 5 is not disposed.

[0104] The material of the low acoustic velocity film 5 is, for example, silicon oxide. Furthermore, the material of the low acoustic velocity film 5 is not limited to silicon oxide, and may be glass, silicon oxynitride, tantalum oxide, a compound of silicon oxide with fluorine, carbon, or boron added, or a material containing these materials as main components.

[0105] When the low-acoustic-velocity film 5 is made of silicon oxide, the temperature characteristics can be improved. The elastic constant of LiTaO3, the material of the piezoelectric layer 6, has a negative temperature characteristic, while the temperature characteristics of silicon oxide have a positive temperature characteristic. Therefore, the absolute value of the TCF in the elastic wave device 1a can be reduced. Furthermore, the intrinsic acoustic impedance of silicon oxide is lower than that of LiTaO3, the material of the piezoelectric layer 6. This allows for an increase in the electromechanical coupling coefficient, i.e., an expansion of the relative bandwidth, and an improvement in the frequency-temperature characteristics.

[0106] The thickness of the low-acoustic-velocity film 5 is preferably 2.0λ or less. By setting the thickness of the low-acoustic-velocity film 5 to 2.0λ or less, film stress can be reduced, resulting in reduced wafer warpage, improved yield, and stabilized characteristics. Furthermore, if the thickness of the low-acoustic-velocity film 5 is within the range of 0.1λ to 0.5λ, the electromechanical coupling coefficient remains essentially unchanged.

[0107] Furthermore, the presence of a single layer (low acoustic velocity film 5 ) between the support substrate 4 and the piezoelectric layer 6 is not limited to the above-described one, and a plurality of layers may be stacked.

[0108] The elastic wave device 1 a according to the above-described modification also produces the same effects as those of the elastic wave device 1 according to the embodiment.

[0109] The embodiment and modified examples described above are only a part of various embodiments and modified examples of the present invention. In addition, as long as the purpose of the present invention can be achieved, the embodiment and modified examples can be variously changed according to design and the like.

[0110] (Way)

[0111] The following aspects are disclosed in this specification.

[0112] The elastic wave device (1; 1a) according to the first embodiment comprises a supporting substrate (4), a piezoelectric layer (6), and an IDT electrode (7). The supporting substrate (4) comprises quartz. The piezoelectric layer (6) is formed on the supporting 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 front side of the piezoelectric layer (6). The cutting angle of the piezoelectric layer (6) is less than 49°Y. According to the elastic wave device (1; 1a) according to the first embodiment, it is possible to reduce stray noise.

[0113] In the elastic wave device (1; 1a) according to the second embodiment, the acoustic velocity of the slow transverse wave propagating through the supporting substrate (4) in the first embodiment is 3950 m / s or greater. According to the elastic wave device (1; 1a) according to the second embodiment, good resonance characteristics and anti-resonance characteristics can be obtained.

[0114] In the elastic wave device (1; 1a) according to the third embodiment, in the second embodiment, the acoustic velocity of the slow transverse wave propagating through the support substrate (4) is 4100 m / s or greater. According to the elastic wave device (1; 1a) according to the third embodiment, the characteristics of the ladder filter can be improved.

[0115] In the elastic wave device (1; 1a) according to a fourth embodiment, in any one 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 the LiTaO3 is less than or equal to ±20°. According to the elastic wave device (1; 1a) according to the fourth embodiment, the speed of sound of the slow transverse wave can be made greater than or equal to 4100 m / s.

[0116] In the elastic wave device (1; 1a) according to the fifth embodiment, the Z axis of the support substrate (4) and the X axis (second direction D2) of the LiTaO3 are parallel in the fourth embodiment. According to the elastic wave device (1; 1a) according to the fifth embodiment, Z propagation can be achieved, thereby achieving a high acoustic velocity in the support substrate (4).

[0117] In the elastic wave device (1; 1a) according to a sixth embodiment, in any one of the first to fifth embodiments, the cut angle of the piezoelectric layer (6) is 38°Y or greater. 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 10 ppm / °C or less.

[0118] In the elastic wave device (1; 1a) according to the seventh embodiment, the piezoelectric layer (6) has a cut angle of 42°Y or greater as in the sixth embodiment. According to the elastic wave device (1; 1a) according to the seventh embodiment, the TCF can be reduced. For example, the absolute value of the TCF can be reduced to 5 ppm / °C or less.

[0119] In the elastic wave device (1; 1a) according to the eighth embodiment, the piezoelectric layer (6) has a cut angle of 44°Y or greater in the seventh embodiment. According to the elastic wave device (1; 1a) according to the eighth embodiment, the TCF can be further reduced. For example, the absolute value of the TCF can be reduced to 2 ppm / °C or less.

[0120] In the elastic wave device (1; 1a) according to the ninth aspect, in any one of the first to eighth aspects, the cut angle of the piezoelectric layer (6) is 48°Y or less. According to the elastic wave device (1; 1a) according to the ninth aspect, the TCF can be further reduced. For example, the absolute value of the TCF can be reduced to 2 ppm / °C or less.

[0121] In the elastic wave device (1) according to the tenth embodiment, in any one of the first to ninth embodiments, the piezoelectric layer (6) is directly laminated on the supporting substrate (4). According to the elastic wave device (1) according to the tenth embodiment, spurious emission can be further reduced, thereby suppressing degradation of characteristics.

[0122] The high-frequency front-end circuit (300) according to the eleventh 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 filter includes an elastic wave device (1; 1a) according to any one of the first to tenth embodiments, and allows a high-frequency signal in a given frequency band to pass through. The amplifier circuit is connected to the filter and amplifies the amplitude of the high-frequency signal. According to the high-frequency front-end circuit (300) according to the eleventh embodiment, spurious signals can be reduced in the elastic wave device (1; 1a).

[0123] The communication device (400) according to the 12th embodiment includes the high-frequency front-end circuit (300) according to the 11th embodiment and a signal processing circuit (401). The signal processing circuit (401) processes a high-frequency signal. According to the communication device (400) according to the 12th embodiment, spurious emission can be reduced in the elastic wave device (1; 1a).

[0124] Description of Reference Numerals

[0125] 1, 1a: elastic wave device;

[0126] 21: 1st filter (filter);

[0127] 22: 2nd filter (filter);

[0128] 23: 3rd filter (filter);

[0129] 24: 4th filter (filter);

[0130] 4: Support base plate;

[0131] 6: piezoelectric layer;

[0132] 7: IDT electrode;

[0133] 72: electrode finger;

[0134] 300: high frequency front-end circuit;

[0135] 303: first amplifier circuit (amplifier circuit);

[0136] 304: second amplifier circuit (amplifier circuit);

[0137] 400: Communication device;

[0138] 401: signal processing circuit;

[0139] D2: Second direction.

Claims

1. An elastic wave device comprising: a support substrate comprising quartz; a piezoelectric layer formed on the supporting substrate and containing LiTaO 3 ; and The IDT electrode is formed on the piezoelectric layer and has a plurality of electrode fingers. The IDT electrode is formed on the front side of the piezoelectric layer. The cutting angle of the piezoelectric layer is less than 49°Y, The thickness of the piezoelectric layer is not less than 0.05λ and not more than 0.5λ, The sound velocity of the slow transverse wave propagating in the support substrate is greater than the sound velocity of the resonance.

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

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

4. The elastic wave device according to any one of claims 1 to 3, wherein The angle formed by the Z-axis of the support substrate and the X-axis of the LiTaO 3 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 LiTaO 3 .

6. The elastic wave device according to any one of claims 1 to 3, wherein The cut angle of the piezoelectric layer is greater than or equal to 38°Y.

7. The elastic wave device according to claim 6, wherein The cut angle of the piezoelectric layer is greater than or equal to 42°Y.

8. The elastic wave device according to claim 7, wherein The cut angle of the piezoelectric layer is greater than or equal to 44°Y.

9. The elastic wave device according to any one of claims 1 to 3, wherein: The cut angle of the piezoelectric layer is less than or equal to 48°Y.

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

11. A high-frequency front-end circuit comprising: A filter comprising the elastic wave device according to any one of claims 1 to 10, which passes high-frequency signals in a predetermined frequency band; and The amplifier circuit is connected to the filter and amplifies the amplitude of the high-frequency signal.

12. A communication device comprising: The high-frequency front-end circuit according to claim 11; and The signal processing circuit processes the high-frequency signal.

Images