Elastic wave device, splitter, and communication device

Abstract

To solve the problem in which: there is a demand for an elastic wave device using plate waves or bulk waves and having stable frequency characteristics in high temperature or in low temperature.SOLUTION: An elastic device comprises: an LT layer including a rotation Y-cut X-propagation LT single crystal; and an IDT electrode adjacent to the LT layer, having a plurality of electrode fingers, and configured to excite elastic waves. The cut angle θ of the rotation Y-cut X-propagation LT single crystal satisfies 10°≤θ≤90°. The elastic wave is a plate wave or a bulk wave.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to an elastic wave device which is an electronic component using elastic waves, a demultiplexer including the elastic wave device, and a communication device.

Background Art

[0002] Elastic wave devices using elastic waves are known. The elastic wave device is, for example, a SAW (Surface Acoustic Wave) device. The elastic wave device has, for example, a piezoelectric substrate and exciting electrodes for applying a voltage to the upper surface or the lower surface of the substrate to excite elastic waves.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an elastic wave device using plate waves or bulk waves, those with stable frequency characteristics at high temperatures or low temperatures are required.

Means for Solving the Problems

[0005] An elastic wave device including an LT layer containing a rotation Y-cut X-propagation LT single crystal, an IDT electrode adjacent to the LT layer and having a plurality of electrode fingers and configured to excite elastic waves, wherein a cut angle θ of the rotation Y-cut X-propagation LT single crystal satisfies 10° ≤ θ ≤ 90°, and the elastic wave is a plate wave or a bulk wave.

[0006] An elastic wave device comprising an LT layer including a rotation Y-cut X-propagation LT single crystal, an IDT electrode adjacent to the LT layer, having a plurality of electrode fingers, and configured to excite an elastic wave, wherein a cut angle θ of the rotation Y-cut X-propagation LT single crystal satisfies 10° ≦ θ ≦ 90°, and a resonance frequency fr [GHz] of the elastic wave and a pitch p [μm] of the IDT electrode satisfy fr·p > 3 [GHz·μm].

Effect of the Invention

[0007] According to one aspect of the present disclosure, the temperature stability of the elastic wave device can be improved.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments and comparative examples according to the present disclosure will be described with reference to the drawings. Note that the drawings used in the following description are schematic, and the dimensional ratios on the drawings do not necessarily match the actual ones. Also, the dimensional ratios do not match between the drawings.

[0010] The surface acoustic wave device according to the present disclosure may have any direction as upward or downward. Hereinafter, for convenience, a rectangular coordinate system represented by the D1 axis, D2 axis, and D3 axis is attached to the drawing, and terms such as the upper surface or the lower surface may be used with the positive side of the D3 axis as upward. Also, in the case of a plan view or a planar perspective view, unless otherwise specified, it means looking in the D3 direction. Note that the D1 axis is defined to be parallel to the arrangement direction of electrode fingers described later. The D2 axis is defined to be parallel to the extending direction of electrode fingers described later.

[0011] Embodiments in the present disclosure are shown below. Also, the configurations described in the following multiple embodiments may be freely combined with other embodiments and comparative examples respectively.

[0012] 〔First Embodiment〕 A first embodiment of the surface acoustic wave device according to the present disclosure will be described. FIGS. 1 and 2 are schematic views showing a partial cross-sectional structure of the surface acoustic wave device 1. The surface acoustic wave device 1 has a support substrate 2, an LT (LiTaO3) layer 3, and an IDT electrode 5, and the surface acoustic wave device 1 is configured by laminating the support substrate 2, the multilayer film 4, the LT layer 3, and the IDT electrode 5 upward in this order.

[0013] (Support Substrate) The support substrate 2 is a substrate that supports the LT layer 3, the multilayer film 4, and the IDT electrode 5, and the support substrate 2 and the multilayer film 4 are located below the LT layer 3. The material of the support substrate 2 is not particularly limited as long as it has a certain strength. For example, when the support substrate 2 is made of a material with a smaller linear expansion coefficient compared to the LT layer 3, the change in electrical characteristics due to temperature change can be reduced by reducing the deformation of the LT layer 3 due to temperature change. Also, the material of the support substrate 2 may be a material with a higher transverse wave velocity of the elastic wave propagating through it compared to the transverse wave velocity of the elastic wave propagating through the LT layer 3. When a material with a higher transverse wave velocity of the elastic wave propagating through it compared to the transverse wave velocity of the elastic wave propagating through the LT layer 3 is selected for the material of the support substrate 2, the leakage of the elastic wave to the support substrate 2 side can be reduced, and an elastic wave device 1 with excellent frequency characteristics can be provided. Further, the support substrate 2 may be a material with high thermal conductivity. For example, when a material with higher thermal conductivity than the LT layer 3 is selected, an elastic wave device 1 with excellent heat dissipation can be provided.

[0014] Examples of the material of the support substrate 2 include single crystals such as sapphire (Al2O3) and silicon (Si). In this embodiment, the case where Si is used as the support substrate 2 will be described as an example.

[0015] (LT layer) The LT layer 3 is composed of a rotated Y-cut X-propagating single crystal of LiTaO3 (lithium tantalate).

[0016] The LT layer 3 is formed relatively thin compared to a general surface acoustic wave device or the like. The thickness of the LT layer 3 may be appropriately set to be thinner than the pitch p (described later) of the IDT electrode 5. A configuration in which the thickness of the LT layer 3 is thinner than the pitch p of the IDT electrode 5 contributes to the excitation of elastic waves propagating in the stacking direction excited in the IDT electrode 5. In the embodiments of the present disclosure, plate waves and A1 mode Lamb waves are excited as elastic waves, but for example, elastic waves such as bulk waves in which the entire LT layer 3 vibrates over the entire thickness may also be used. The thickness of the LT layer 3 may be 1 μm or less. It may be 0.3 μm, 0.35λ μm, 0.4 μm, or other desired thicknesses. The cut angle (described later) of the LT layer 3 may be set as appropriate.

[0017] (Multilayer film) The multilayer film 4 reflects elastic waves propagating in the stacking direction, such as bulk waves or plate waves excited by the IDT electrode 5, in the D3 direction. Thereby, leakage of the excited elastic waves can be reduced.

[0018] The multilayer film 4 is an acoustic reflection film configured by alternately stacking a low acoustic impedance layer 41 including a portion having a lower acoustic impedance compared to the layer in contact above and a high acoustic impedance layer 42 including a portion having a higher acoustic impedance compared to the layer in contact above. The multilayer film 4 reflects waves in the stacking direction propagating from above at the interface between the low acoustic impedance layer 41 and the high acoustic impedance layer 42.

[0019] The multilayer film 4 is a Bragg mirror that utilizes Bragg reflection and can selectively reflect only elastic waves having a specific frequency band in the D3 direction. For example, when the wavelength of the elastic wave to be reflected is λ, the thickness of at least one layer of the multilayer film 4 may be λ / 4. By setting the thickness of at least one layer of the multilayer film 4 to λ / 4, elastic waves with a wavelength of λ can be reflected. The multilayer film 4 contributes to reducing spurious due to unwanted waves and also contributes to reducing the loss of the elastic wave device 1.

[0020] In the multilayer film 4, the layer closest to the LT layer 3 when counted from the D3 direction may be a low acoustic impedance layer 41. When the acoustic impedance of the LT layer 3 is greater than that of the low acoustic impedance layer 41, the interface between the LT layer 3 and the low acoustic impedance layer 41 becomes a free end, and fundamental modes such as the A1 mode and the SH1 mode are excited in the LT layer 3. When the first layer is a high acoustic impedance layer 42, higher-order modes such as the S1 mode and the SH2 mode are excited, but there is a demerit that the electromechanical coupling coefficient becomes small.

[0021] The number of stacked layers of the multilayer film 4 may be set as appropriate. For example, the total number of stacked layers of the multilayer film 4 may be 3 or more and 12 or less. The thickness of each layer of the multilayer film 4 may be set as appropriate and may be uniform or different. By appropriately setting the number of stacked layers and the thickness of each layer of the multilayer film 4, the elastic wave propagating in the stacking direction excited by the IDT electrode 5 can be effectively reflected upward in the stacking direction. In addition, spurious vibrations generated by multiple reflections of elastic waves in the multilayer film 4 can also be reduced.

[0022] The material of the low acoustic impedance layer 41 is, for example, silicon dioxide (SiO2). As the material of the high acoustic impedance layer 42, for example, hafnium oxide (HfO2), tantalum oxide (Ta2O5), zirconium oxide (ZrO2), tungsten (W), molybdenum (Mo), etc. can be used. The material of the multilayer film 4 is not limited to these as long as it satisfies the magnitude relationship of the acoustic impedance with the layer in contact above, and various materials may be used.

[0023] As shown in FIG. 2, at least one layer of the multilayer film 4 may be a temperature compensation layer 47 containing a temperature compensation material. The temperature compensation material generally refers to all materials whose Young's modulus increases with an increase in temperature. LiTaO3 used for the LT layer 3 is a material whose Young's modulus decreases with an increase in temperature. Therefore, when used at high temperatures, compared with when used at normal temperatures, within the substance The velocity of the propagating elastic wave decreases. Since the Young's modulus of the temperature compensation material increases with the increase in temperature, when used at high temperatures, the velocity of the elastic wave propagating in the substance increases compared to when used at normal temperature. The decrease in the velocity of the elastic wave due to the temperature change of the LT layer 3 and the increase in the velocity of the elastic wave due to the temperature change of the temperature compensation layer 47 can be offset to a certain extent. Therefore, the change in frequency becomes small. As a result, the TCFr (described later) and / or TCFa (described later) of the elastic wave device 1 are reduced. Also, due to the change in Young's modulus accompanying the decrease in temperature, the TCFr (described later) and / or TCFa (described later) are reduced even at low temperatures. By including the temperature compensation layer 47 in the multilayer film 4, the temperature stability is improved. For example, the probability that the performance of the elastic wave device 1 can be exhibited at a level equivalent to that at room temperature even when used at high or low temperatures increases. The temperature compensation layer 47 may be included in the first layer when viewed from above in the stacking direction of the multilayer film 4, or may be included in an appropriate layer.

[0024] The temperature compensation layer 47 may be included in any one of the three layers counted from above in the stacking direction of the multilayer film 4. When the distance between the temperature compensation layer 47 and the LT layer 3 is close, the offset by the temperature compensation material works strongly, and the TCFr and / or TCFa are further improved.

[0025] Silicon dioxide (SiO2) is mainly used as the temperature compensation material included in the temperature compensation layer 47, but various other materials may also be used.

[0026] (IDT electrode) As shown in FIG. 1 or 2, the IDT electrode 5 is formed adjacent to the LT layer 3. The term "adjacent" as used here includes the case where there is an intervening layer such as an adhesive layer between the LT layer 3 and the IDT electrode 5. The IDT electrode 5 may be formed above the LT layer 3 as shown in FIG. 1 or 2, may be formed below the LT layer 3, or may be formed such that at least a part thereof is embedded in the LT layer 3. The IDT electrode 5 is composed of a pair of comb electrodes facing each other. The pair of comb electrodes facing each other are configured to be connected to different potentials. The pair of comb electrodes have a plurality of electrode fingers 52.

[0027] The lengths of the plurality of electrode fingers 52 are, for example, equal to each other. Note that in the IDT electrode 5, the lengths of the plurality of electrode fingers 52 change according to the position in the propagation direction. So-called apodization may be applied. By applying apodization, the propagation of the elastic wave to be utilized can be dominated, and the propagation of other elastic waves can be reduced. Also, the thickness of the electrode finger 52 may be appropriately set according to required electrical characteristics and the like.

[0028] The IDT electrode 5 may have dummy electrode fingers protruding from the bus bar. Also, it may have a floating electrode between the plurality of electrode fingers 52. The IDT electrode 5 may have a varying width between a pair of opposing comb electrodes or may be inclined with respect to the D1 direction.

[0029] The IDT electrode 5 is made of a material having conductivity. For the material of the IDT electrode 5, for example, various conductive materials such as Al (aluminum), Cu (copper), Pt (platinum), Mo (molybdenum), Au (gold), or alloys thereof can be adopted, and further, these plurality of layers may be laminated to form it. Also, although not shown, when the IDT electrode 5 is composed of a laminate of multiple layers, an underlayer may be interposed at the lamination interface. For example, the IDT electrode 5 may be Al and the underlayer may be Ti.

[0030] The number of electrode fingers 52 may be appropriately set according to the electrical characteristics required for the elastic wave device 1. In FIGS. 1 to 3, the number of electrode fingers 52 is shown as small as a schematic diagram. Actually, more electrode fingers 52 than those shown may be arranged.

[0031] As shown in FIGS. 1 to 3, the repetition interval for each one in the D1 direction of the plurality of electrode fingers 52 is called a pitch p. The pitch p refers to the center-to-center distance of the electrode fingers 52 in the D1 direction. Pitch By adjusting p, the wavelength and frequency of the elastic wave resonating with the signal excited by the IDT electrode 5 can be controlled.

[0032] The pitch of the IDT electrode 5 is basically constant in the IDT electrode 5. Note that the pitch of the IDT electrode 5 does not have to be constant, or the IDT electrode 5 may have a special portion with respect to most (for example, 80% or more) of the pitches. Examples of the special portion include a portion where the pitch becomes narrower or wider than most, or a thinning portion where a small number of electrode fingers 52 are substantially thinned. The most part may be, for example, a portion that excites a main wave, and the pitch of the portion that excites the main wave does not have to be constant. When the pitch of the IDT electrode 5 is not constant, for example, the degree of freedom in design with respect to the capacitance and / or frequency characteristics of the elastic wave device 1 is improved. When the pitch of the IDT electrode 5 has a special portion, for example, the energy loss of the elastic wave excited in most parts is reduced.

[0033] In the present disclosure, the pitch p refers to the pitch of the IDT electrode 5 when the pitch of the IDT electrode 5 is constant, refers to the average value of the pitch of the IDT electrode 5 when the pitch of the IDT electrode 5 is not constant, and refers to the pitch of most of the IDT when most of the pitches of the IDT electrode 5 are constant but there is a special portion. When the pitch of the portion that excites the main wave of the IDT electrode 5 is not constant, the average value of the pitch of the portion that excites the main wave of the IDT electrode 5 may be used as the pitch p.

[0034] The pitch p may be 2 μm or less. By setting the pitch p of the IDT electrode 5 to 2 μm or less, it contributes to the utilization of the elastic wave propagating in the D1 direction excited in the IDT electrode 5. The excited elastic wave may be, for example, a plate wave or an A1 mode Lamb wave. The pitch p of the plurality of electrode fingers 52 may be 0.5 μm, 1.0 μm, or 1.5 μm, or other desired lengths. The pitch p may be 2 μm or more. By setting the pitch p of the IDT electrode 5 to 2 μ m or more, it contributes to the utilization of the elastic wave propagating in the stacking direction excited in the IDT electrode 5. The excited elastic wave may be, for example, a bulk wave. The pitch p of the plurality of electrode fingers 52 may be 3 μm, 3.5 μm, or 4 μm, or other desired lengths.

[0035] In the elastic wave device 1, when the product of the resonance frequency fr [GHz] and the pitch p [μm] of the IDT electrode 5 is 3 [GHz·μm] or more, a vibration mode in which the entire LT layer 3 vibrates over the entire thickness is excited. Examples of the vibration mode in which the entire LT layer 3 vibrates over the entire thickness include plate waves or bulk waves. The vibration mode in which the entire LT layer 3 vibrates over the entire thickness can excite elastic waves in a high frequency band of 4 GHz or more.

[0036] (Cut angle) The cut angle indicates the plane orientation as viewed from the crystal axis of the LT single crystal constituting the LT layer 3. As a method for indicating the LT single crystal by the cut angle, it is defined in Japanese Industrial Standard (JIS) C6760 "Single crystal wafer for surface acoustic wave devices - Specifications and measurement methods". Also in the present disclosure, using this indication method, it is expressed as "θ-rotated Y-cut X-propagating LT single crystal (θ: cut angle)".

[0037] In the first embodiment, the cut angle θ of the LT layer 3 may affect the resonance frequency temperature coefficient (which may be represented as TCFr in the following description) and the anti-resonance frequency temperature coefficient (which may be represented as TCFa in the following description) of the elastic wave device 1. Here, TCFr and TCFa are indices of the frequency shift amount due to temperature, and the unit is expressed in ppm / K. The closer the absolute values of TCFr and TCFa are to 0 ppm / K, the smaller the change amount of the frequency due to temperature becomes, which contributes to the temperature stability of the elastic wave device 1. The absolute values of TCFr and TCFa are If it is 30 ppm /

[0038] K or less, it is easy to use as a general SAW filter. The absolute values of TCFr and TCFa may be 20 ppm / K or less. The absolute values of TCFr and TCFa may be 10 ppm / K or less.

[0039] In the first embodiment, the cut angle θ of the LT layer 3 exhibits excellent TCFr and TCFa when 10° ≤ θ ≤ 90°.

[0040] 〔Second Embodiment〕 The second embodiment according to the present disclosure will be described. The configurations of the elastic wave device 1, the support substrate 2, the LT layer 3, and the IDT electrode 5 are common to those of the first embodiment. Hereinafter, the description of the common parts will be omitted, and only the different parts will be described.

[0041] (Hollow portion) As shown in FIG. 3, the elastic wave device 1 may have a cavity portion 6. The cavity portion 6 may be formed surrounded by the support substrate 2 and the LT layer 3, or may penetrate the support substrate 2 downward.

[0042] The elastic wave device 1 can reflect the elastic wave propagating in the stacking direction excited by the IDT electrode 5 upward in the D3 direction by the cavity portion 6.

[0043] 〔Comparative Example〕 The comparative example in the present disclosure will be described. The configurations of the elastic wave device 1, the LT layer 3, and the IDT electrode 5 are common to those of the first embodiment. Hereinafter, the description of the common parts will be omitted, and only the different parts will be described.

[0044] (Leaky elastic surface wave) The elastic wave device 1 of the comparative example is a leaky SAW that uses a leaky elastic surface wave (which may be referred to as LSAW in the following description). The leaky elastic surface wave radiates bulk waves into the LT layer 3 while propagating near the surface of the LT layer 3. Since the comparative example does not use the elastic wave propagating in the stacking direction, it does not have a reflection structure such as the multilayer film 4 or the cavity portion 6.

[0045] 〔Simulation〕 The following shows the simulation results for the comparative example, the first embodiment, and the second embodiment.

[0046] Verification was performed on TCFr, TCFa, and df when controlling the cut angle θ of LT layer 3 by simulation. Also, verification was performed on the impedance frequency characteristics at room temperature (25 °C) and high temperature (95 °C).

[0047] (Regarding the comparative example) In the comparative example, simulation was performed under the following conditions. LT layer 3 Cut angle θ: Changed from 10° to 145°. IDT electrode 5 Material: Al Thickness: 0.16 μm Pitch p: 1.25 μm Duty: 0.56 Resonant frequency fr: Approximately 1600 MHz With the above conditions, the following results as shown in Fig. 4 were obtained for the surface acoustic wave device 1. Also, Fig. 5 shows the impedance frequency characteristics of the surface acoustic wave device 1 at 25 °C and 95 °C when the cut angle θ of the surface acoustic wave device 1 according to the comparative example is 70° under the above conditions.

[0048] (Regarding the first embodiment) In the first embodiment, simulation was performed under the following conditions. Support substrate 2 Material: Si LT layer 3 Thickness: 0.37 μm Cut angle θ: Changed from 10° to 145°. Multilayer film 4 Number of layers: 8 layers Low acoustic impedance layer 41 Material: SiO2 Thickness: 0.2 μm High acoustic impedance layer 42: HfO2 Material: HfO2 Thickness: 0.16 μm IDT electrode 5 Material: Al Thickness: 0.11 μm Pitch p: 1.25 μm Duty: 0.56 Resonant frequency fr: approximately 5300 MHz Under the above conditions, results as shown in FIG. 6 were obtained. From the results of FIG. 6, the range of the cut angle θ where TCFr, TCFa, and / or df exhibit constant values was specified. FIG. 6 according to the first embodiment shows different behavior from FIG. 4 according to the comparative example.

[0049] (Regarding TCFr) In the range where the cut angle θ is 10° ≤ θ ≤ 90°, the absolute value of TCFr of the elastic wave device 1 shows 30 ppm / K or less. Compared with the entire range shown in FIG. 4 according to the comparative example, it shows good TCFr. The elastic wave device 1 with the absolute value of TCFr of 30 ppm / K or less can be used, for example, in a filter for communication.

[0050] In the range where the cut angle θ is 80° ≤ θ ≤ 105°, the TCFr of the elastic wave device 1 transitions from around -50 ppm / K to around -10 ppm / K. Compared with the TCFr of the elastic wave device 1 when the cut angle θ is 105° ≤ θ ≤ 150°, the TCFr of the elastic wave device 1 when the cut angle θ is 10° ≤ θ ≤ 80° is significantly improved.

[0051] Particularly in the range where the cut angle θ is 25° ≤ θ ≤ 75°, the absolute value of TCFr of the elastic wave device 1 shows 5 ppm / K or less. The elastic wave device 1 with the absolute value of TCFr of 5 ppm / K or more contributes extremely greatly to the improvement of temperature stability when used in a communication filter. For example, the probability of maintaining frequency characteristics equivalent to those at room temperature (about 25°C) even at a high temperature (about 95°C) increases.

[0052] (Regarding TCFa) In the range where the cut angle θ is 10° ≤ θ ≤ 90°, the absolute value of TCFa of the elastic wave device 1 shows 40 ppm / K or less. Compared with the entire range shown in FIG. 4 according to the comparative example, it shows good TCFa.

[0053] In the range where the cut angle θ satisfies 75° ≤ θ ≤ 105°, the TCFa of the surface acoustic wave device 1 transitions from around -60 ppm / K to around -10 ppm / K. Compared with the TCFa of the surface acoustic wave device 1 when the cut angle θ satisfies 105° ≤ θ ≤ 150°, the TCFa of the surface acoustic wave device 1 when the cut angle θ satisfies 10° ≤ θ ≤ 75° is significantly improved.

[0054] Also, in the range where the cut angle θ satisfies 10° ≤ θ ≤ 85°, the absolute value of the TCFa of the surface acoustic wave device 1 is 30 ppm / K or less, showing good TCFa compared with the entire range shown in FIG. 4 related to the comparative example. The surface acoustic wave device 1 with the absolute value of the TCFa of 30 ppm / K or less can be used, for example, for communication filters.

[0055] In the range where the cut angle θ satisfies 25° ≤ θ ≤ 80°, the absolute value of the TCFa of the surface acoustic wave device 1 is 20 ppm / K or less. The surface acoustic wave device 1 with the absolute value of the TCFa of 20 ppm / K or more contributes to the improvement of temperature stability when used for communication filters.

[0056] (Regarding the compatibility between TCF and df) In the range where the cut angle θ satisfies 60° ≤ θ ≤ 150°, the fractional bandwidth df of the surface acoustic wave device 1 is 1% or more. For the surface acoustic wave device 1 in the range where the cut angle θ satisfies 60° ≤ θ ≤ 90°, df is 1% or more and the absolute value of the TCFr is 30 ppm / K or less. The surface acoustic wave device 1 with df of 1% or more and the absolute value of the TCFr of 30 ppm / K or less contributes to the compatibility between filter characteristics and temperature stability in communication filters.

[0057] In the range where the cut angle θ satisfies 75° ≤ θ ≤ 150°, the fractional bandwidth df of the surface acoustic wave device 1 is 2% or more. For the surface acoustic wave device 1 in the range where the cut angle θ satisfies 75° ≤ θ ≤ 90°, df is 2% or more and the absolute value of the TCFr is 20 ppm / K or less. The surface acoustic wave device 1 with df of 2% or more and the absolute value of the TCFr of 20 ppm / K or less contributes to the compatibility between filter characteristics and temperature stability in communication filters. For example, when used in wireless communication terminals such as mobile phones, a communication filter with high temperature stability can be provided. For example, it can be used in base stations of mobile phones and the like.

[0058] When the cut angle θ is in the range of 90° ≤ θ ≤ 150°, the specific bandwidth df of the surface acoustic wave device 1 is 3% or more. When the cut angle θ is in the range of 90° ≤ θ ≤ 105°, for the surface acoustic wave device 1, df is 3% or more and the absolute value of TCFr is 40 ppm / K or less. The surface acoustic wave device 1 with df of 3% or more and the absolute value of TCFr of 40 ppm / K or less contributes to the compatibility of filter characteristics and temperature stability in a communication filter. For example, it can be used in a wireless communication terminal such as a mobile phone. For example, it can be applied to a wideband due to a high specific bandwidth df.

[0059] Fig. 8 shows the impedance frequency characteristics at 25°C and 95°C when the cut angle θ of the surface acoustic wave device 1 according to the first embodiment is 70° under the above conditions. Fig. 9 shows the impedance frequency characteristics at 25°C and 95°C when the cut angle θ of the surface acoustic wave device 1 according to the first embodiment is 115° under the above conditions. Comparing Fig. 8 and Fig. 9, the amount of movement of the impedance frequency characteristics at θ = 70° is small and hardly changes compared with that at θ = 115°.

[0060] Comparing with the surface acoustic wave device 1 according to the comparative example shown in Fig. 5, even when using the LT layer 3 with the same cut angle θ the amount of movement of the impedance frequency characteristics of the surface acoustic wave device 1 according to the first embodiment is smaller than that of the surface acoustic wave device 1 according to the comparative example.

[0061] From Fig. 8, the surface acoustic wave device 1 having the LT layer 3 with θ = 70° shows excellent temperature stability. Also, from Fig. 6, in the range of 60° ≤ θ < 70°, better TCFr and TCFa are shown compared with θ = 70°. The surface acoustic wave device 1 having the LT layer 3 with 60° ≤ θ ≤ 70° can reduce the influence of temperature on the frequency characteristics during use from room temperature to 95°. When the cut angle θ is in the range of 60° ≤ θ ≤ 70°, the surface acoustic wave device 1 shows df of 1% or more and the absolute value of TCFr of 5 ppm / K or less. The surface acoustic wave device with df of 1% or more and the absolute value of TCFr of 5 ppm / K or less The surface acoustic wave device 1 contributes, for example, to achieving both filter characteristics and extremely high temperature stability in a communication filter.

[0062] (Regarding the second embodiment) In the second embodiment, simulations were performed under the following conditions. Support substrate 2 Material: Si LT layer 3 Thickness: 0.37 μm The cut angle θ was changed from 10° to 145°. IDT electrode 5 Material: Al Thickness: 0.11 μm Pitch p: 1.25 μm Duty: 0.56 Resonance frequency fr: approximately 5300 MHz The results as shown in FIG. 7 were obtained under the above conditions. From the results of FIG. 7, the range of the cut angle θ in which TCFr, TCFa, and / or df show constant values was specified.

[0063] (Regarding TCFr) In the range where the cut angle θ is 10° ≤ θ ≤ 90°, the absolute value of TCFr of the surface acoustic wave device 1 shows 50 ppm / K or less. The surface acoustic wave device 1 with the absolute value of TCFr of 50 ppm / K or less can be used, for example, in a filter for communication.

[0064] In the range where the cut angle θ is 70° ≤ θ ≤ 100°, TCFr of the surface acoustic wave device 1 transitions from around -70 ppm / K to around -20 ppm / K. Comparing with TCFr of the surface acoustic wave device 1 when the cut angle θ is 100° ≤ θ ≤ 145°, TCFr of the surface acoustic wave device 1 when the cut angle θ is 10° ≤ θ ≤ 70° is significantly improved.

[0065] Particularly in the range where the cut angle θ is 25° ≤ θ ≤ 70°, the absolute value of TCFr of the surface acoustic wave device 1 shows 20 ppm / K or less. Comparing with the entire range shown in FIG. 4 according to the comparative example, it shows good TCFr. The surface acoustic wave device 1 with the absolute value of TCFr of 20 ppm / K or less contributes to improving temperature stability, for example, when used in a communication filter.

[0066] Particularly in the range where the cut angle θ satisfies 25° ≤ θ ≤ 60°, the absolute value of TCFr of the elastic wave device 1 is 10 ppm / K or less. The elastic wave device 1 with the absolute value of TCFr of 10 ppm / K or less of the elastic wave device 1 greatly contributes to the improvement of temperature stability when used in a communication filter. For example, the probability of maintaining frequency characteristics equivalent to those at room temperature (about 25°C) even at a high temperature (about 95°C) increases.

[0067] (Regarding TCFa) In the range where the cut angle θ satisfies 70° ≤ θ ≤ 100°, the TCFa of the elastic wave device 1 transitions from around -70 ppm / K to around -30 ppm / K. Compared with the TCFa of the elastic wave device 1 when the cut angle θ satisfies 85° ≤ θ ≤ 145°, the TCFa of the elastic wave device 1 when the cut angle θ satisfies 10° ≤ θ ≤ 70° is significantly improved.

[0068] Particularly in the range where the cut angle θ satisfies 25° ≤ θ ≤ 60°, the absolute value of TCFa of the elastic wave device 1 is 20 ppm / K or less. It shows good TCFa compared with the entire range shown in FIG. 4 according to the comparative example. The elastic wave device 1 with the absolute value of TCFa of 20 ppm / K or less of the elastic wave device 1 contributes to the improvement of temperature stability when used in a communication filter, for example.

[0069] Also, in the range where the cut angle θ satisfies 15° ≤ θ ≤ 60°, the absolute value of TCFa of the elastic wave device 1 is 20 ppm / K or less. It shows good TCFa compared with the entire range shown in FIG. 4 according to the comparative example. The elastic wave device 1 with the absolute value of TCFa of 20 ppm / K or less contributes to the improvement of temperature stability when used in a communication filter, for example.

[0070] When the cut angle θ is in the range of 25° ≤ θ ≤ 40°, the absolute value of TCFa of the elastic wave device 1 is 10 ppm / K or less. The elastic wave device 1 with the absolute value of TCFa of 10 ppm / K or less greatly contributes to the improvement of temperature stability when used in, for example, a filter for communication. For example, the probability of maintaining frequency characteristics equivalent to those at room temperature (about 25°C) even at a high temperature (about 95°C) increases. Since df is 1% or less, it can be used as a transmitter, for example. It can be used as a reference signal, for example.

[0071] (Regarding the compatibility between TCF and df) When the cut angle θ is in the range of 55° ≤ θ ≤ 150°, the fractional bandwidth df of the elastic wave device 1 is 1% or more. For the elastic wave device 1 when the cut angle θ is in the range of 55° ≤ θ ≤ 80°, df is 1% or more and the absolute value of TCFr is 40 ppm / K or less. The elastic wave device 1 with df of 1% or more and the absolute value of TCFr of 40 ppm / K or less contributes to the compatibility between filter characteristics and temperature stability in a communication filter.

[0072] When the cut angle θ is in the range of 55° ≤ θ ≤ 75°, for the elastic wave device 1, df is 1% or more and the absolute value of TCFr is 30 ppm / K or less. The elastic wave device 1 with df of 1% or more and the absolute value of TCFr of 30 ppm / K or less contributes to the compatibility between filter characteristics and temperature stability in a communication filter.

[0073] When the cut angle θ is in the range of 65° ≤ θ ≤ 75°, for the elastic wave device 1, df is 2% or more and the absolute value of TCFr is 30 ppm / K or less. The elastic wave device 1 with df of 2% or more and the absolute value of TCFr of 30 ppm / K or less contributes to the compatibility between filter characteristics and temperature stability in a communication filter. It can be used in a wireless communication terminal such as a mobile phone, for example. It can be used in a base station of a mobile phone, for example.

[0074] When the cut angle θ is θ = 55°, for the surface acoustic wave device 1, df is 1% or more and the absolute value of TCFr is 10 ppm / K or less. The surface acoustic wave device 1 with df being 1% or more and the absolute value of TCFr being 10 ppm / K or less contributes extremely greatly to achieving both filter characteristics and temperature stability in a communication filter. For example, when used in a wireless communication terminal such as a mobile phone, a communication filter with high temperature stability can be provided.

[0075] When the cut angle θ is θ = 70°, for the surface acoustic wave device 1, df is 2.5% or more and the absolute value of TCFr is 20 ppm / K or less. The surface acoustic wave device 1 with df being 2.5% or more and the absolute value of TCFr being 20 ppm / K or less contributes to achieving both filter characteristics and temperature stability in a communication filter. For example, when used in a wireless communication terminal such as a mobile phone, a communication filter with high temperature stability can be provided. For example, it can be used in a base station of a mobile phone or the like.

[0076] (Comparative Example, Comparison of the First and Second Embodiments) FIGS. 6 and 7 according to the first and second embodiments show different behaviors from FIG. 4 according to the comparative example.

[0077] While in FIG. 4 according to the comparative example, TCFr, TCFa, and df of the surface acoustic wave device 1 show a gentle change depending on the cut angle θ, in FIGS. 6 and 7 according to the first and second embodiments, TCFr, TCFa, and df of the surface acoustic wave device 1 change significantly near θ = 90°, showing characteristics different from those of the comparative example.

[0078] In the first and second embodiments, the thickness of the LT layer 3 is set such that a vibration mode in which the entire LT layer 3 vibrates over the entire thickness is excited. This vibration mode has an influence on the fractional bandwidth df when the cut angle θ is changed and on the sound velocity when the temperature changes, which is different from that of the LSAW in the comparative example. When using this vibration mode, selecting the cut angle θ shown by the above simulation results contributes to realizing a surface acoustic wave device 1 with high temperature stability or / and a surface acoustic wave device 1 with excellent fractional bandwidth df.

[0079] In addition, when the product of the resonance frequency fr [GHz] and the pitch p [μm] of the IDT electrode 5 is 3 [GHz· μm] or more, unlike the LSAW, a vibration mode in which the entire LT layer 3 vibrates over the entire thickness is excited. Therefore, the selection of the cut angle θ shown in the first and second embodiments contributes to the realization of the elastic wave device 1 with high temperature stability or / and the elastic wave device 1 with excellent specific bandwidth df. In a high frequency band due to a vibration mode in which the entire LT layer 3 vibrates over the entire thickness, the influence on the frequency due to temperature change is larger than that of the LSAW. By using the first and second embodiments for the elastic wave device 1 used in a high frequency band, it contributes to the realization of the elastic wave device 1 with excellent temperature stability in the high frequency band. The elastic wave device 1 used in a high frequency band refers to, for example, one using a resonance frequency of 4 GHz or more as shown in FIGS. 8 and 9.

[0080] In a high frequency band due to a vibration mode in which the entire LT layer 3 vibrates over the entire thickness, the influence on the frequency due to temperature change is larger than that of the LSAW. By using the first and second embodiments for the elastic wave device 1 used in a high frequency band, it contributes to the realization of the elastic wave device 1 with excellent temperature stability in the high frequency band. The elastic wave device 1 used in a high frequency band refers to, for example, one using a resonance frequency of 4 GHz or more as shown in FIGS. 8 and 9.

[0081] 〔First usage example: Demultiplexer〕 FIG. 10 is a circuit diagram schematically showing the configuration of a demultiplexer 200 as a usage example of the elastic wave device 1.

[0082] The demultiplexer 200 has, for example, a transmission filter 203 that filters a transmission signal from a transmission terminal 201 and outputs it to an antenna terminal 202, and a reception filter 205 that filters a reception signal from the antenna terminal 202 and outputs it to a pair of reception terminals 204.

[0083] The transmission filter 203 is configured by, for example, a plurality of elastic wave devices 1 in a ladder type filter. That is, the transmission filter 203 has a plurality (one or more) of elastic wave devices 1 connected in series between the transmission terminal 201 and the antenna terminal 202, and a plurality (one or more) of elastic wave devices 1 (parallel arms) that connect the series line (series arm) and the reference potential.

[0084] The receiving filter 205 includes, for example, an acoustic wave device 1 and a multi-mode filter (including a double-mode filter) 207. The multi-mode filter 207 has a plurality (three in the illustrated example) of IDT electrodes 4 arranged in the array direction of a plurality of electrode fingers 52.

[0085] Although the case where the demultiplexer 200 includes a transmitting filter 203 and a receiving filter 205 has been described, it is not limited thereto. The demultiplexer 200 may be, for example, a diplexer or a multiplexer including three or more filters.

[0086] 〔Second usage example: Communication device〕 FIG. 11 is a block diagram showing a main part of a communication device 300 as a usage example of the demultiplexer 200. The communication device 300 performs wireless communication using radio waves and includes the demultiplexer 200.

[0087] In the communication device 300, a transmission information signal TIS including information to be transmitted is modulated and its frequency is raised (converted into a high-frequency signal of a carrier frequency) by an RF-IC (Radio Frequency Integrated Circuit) 301 to obtain a transmission signal TS. The transmission signal TS has unnecessary components outside the transmission passband removed by a band-pass filter 302a, is amplified by an amplifier 303a, and is input to the demultiplexer 200 (transmission terminal 201). Then, the demultiplexer 200 (transmission filter 203) removes unnecessary components outside the transmission passband from the input transmission signal TS and outputs the transmission signal TS after the removal to the antenna terminal 202 or the antenna 305. The antenna 305 converts the input electrical signal (transmission signal TS) into a wireless signal (radio wave) and transmits it.

[0088] In the communication device 300, the radio signal (radio wave) received by the antenna 305 is converted into an electrical signal (received signal RS) by the antenna 305 and input to the diplexer 200 (antenna terminal 202). The diplexer 200 (reception filter 205) removes unnecessary components other than the passband for reception from the input received signal RS, and the signal is amplified by the amplifier 303b from the reception terminal 204, and unnecessary components other than the passband for reception are removed by the bandpass filter 302b. Then, the received signal RS is subjected to frequency down-conversion and demodulation by the RF-IC 301 to obtain a received information signal RIS.

[0089] Note that the transmission information signal TIS and the received information signal RIS may be low-frequency signals (baseband signals) containing appropriate information, for example, analog voice signals or digitized voice signals. A passband of the radio signal (e.g., 5 GHz or higher) is also possible. The modulation method may be any of phase modulation, amplitude modulation, frequency modulation, or a combination of any two or more of these. In FIG. 11, the direct conversion method is illustrated as the circuit method, but other appropriate methods may be used, for example, the double superheterodyne method. Also, FIG. 11 schematically shows only the main part, and a low-pass filter, an isolator, etc. may be added at appropriate positions, and the positions of amplifiers, etc. may be changed.

[0090] 〔Summary〕 (1) The surface acoustic wave device according to the first aspect of the present disclosure includes an LT layer including a rotation Y-cut X-propagation LT single crystal, and an IDT electrode adjacent to the LT layer and having a plurality of electrode fingers and configured to excite a surface acoustic wave. The cut angle θ of the rotation Y-cut X-propagation LT single crystal satisfies 10° ≤ θ ≤ 90°, and the surface acoustic wave is a plate wave or a bulk wave.

[0091] (2) The elastic wave device according to the second aspect of the present disclosure includes an LT layer containing a rotation Y-cut X-propagation LT single crystal, and an IDT electrode that is adjacent to the LT layer, has a plurality of electrode fingers, and is configured to excite elastic waves. The cut angle θ of the rotation Y-cut X-propagation LT single crystal satisfies 10° ≤ θ ≤ 90°, and the resonance frequency fr [GHz] of the elastic wave and the pitch p [μm] of the IDT electrode satisfy fr·p > 3 [GHz·μm].

[0092] (3) The elastic wave device according to the third aspect of the present disclosure is in any one of the above first or second aspects and includes a multilayer film located below the LT layer. The multilayer film includes at least one low acoustic impedance layer including a portion having a lower acoustic impedance compared to the upper contacting layer, and at least one high acoustic impedance layer including a portion having a higher acoustic impedance compared to the upper contacting layer, and θ satisfies 10° ≤ θ ≤ 75°.

[0093] (4) The elastic wave device according to the fourth aspect of the present disclosure is in the third aspect above, and θ satisfies 60° ≤ θ ≤ 70°.

[0094] (5) The elastic wave device according to the fifth aspect of the present disclosure is in any one of the above first or second aspects, and includes a multilayer film located below the LT layer. The multilayer film includes at least one low acoustic impedance layer including a portion having a lower acoustic impedance compared to the upper contacting layer, and at least one high acoustic impedance layer including a portion having a higher acoustic impedance compared to the upper contacting layer, and θ satisfies 60° ≤ θ ≤ 90°.

[0095] (6) The elastic wave device according to the sixth aspect of the present disclosure is in any one of the above third to fifth aspects, and the temperature compensation layer included in the multilayer film includes a material whose Young's modulus increases as the temperature rises.

[0096] (7) The elastic wave device according to the seventh aspect of the present disclosure is the elastic wave device according to the sixth aspect, wherein the temperature compensation layer is located in a range of three layers or less from the upper side in the stacking direction among the multilayer films.

[0097] (8) The elastic wave device according to the eighth aspect of the present disclosure is the elastic wave device according to any one of the sixth or seventh aspects, wherein the temperature compensation layer contains silicon dioxide.

[0098] (9) The elastic wave device according to the ninth aspect of the present disclosure is the elastic wave device according to any one of the first or second aspects, and includes a cavity portion located below the LT layer, and θ satisfies 10° ≤ θ ≤ 70°.

[0099] (10) The elastic wave device according to the tenth aspect of the present disclosure is the elastic wave device according to the ninth aspect, wherein θ satisfies 25° ≤ θ ≤ 60°.

[0100] (11) The elastic wave device according to the eleventh aspect of the present disclosure is the elastic wave device according to any one of the first or second aspects, and includes a cavity portion located below the LT layer, and θ satisfies 55° ≤ θ ≤ 80°.

[0101] (12) The elastic wave device according to the twelfth aspect of the present disclosure is the elastic wave device according to any one of the first to eleventh aspects, wherein the thickness of the LT layer is small compared to the pitch p of the plurality of electrode fingers.

[0102] (13) The elastic wave device according to the thirteenth aspect of the present disclosure is the elastic wave device according to any one of the first to twelfth aspects. When the temperature characteristic of the resonance frequency fr is TCFr, the absolute value of TCFr is less than 30 ppm / K.

[0103] (14) The elastic wave device according to the fourteenth aspect of the present disclosure is the elastic wave device according to any one of the first to thirteenth aspects. When the temperature characteristic of the anti-resonance frequency fa is TCFa, the absolute value of TCFa is less than 40 ppm / K.

[0104] (15) The elastic wave device according to the fifteenth aspect of the present disclosure is the elastic wave device according to any one of the first to fourteenth aspects, wherein the elastic wave is a plate wave.

[0105] (16) The elastic wave device according to the 16th aspect of the present disclosure is, in any of the 1st to 15th aspects, wherein the plate wave is an A1 mode drum wave.

[0106] (17) The elastic wave device according to the 17th aspect of the present disclosure is, in any of the 1st to 14th aspects, wherein the elastic wave is a bulk wave.

[0107] (18) The demultiplexer according to the 18th aspect of the present disclosure includes an antenna terminal, a transmission filter that filters a signal output to the antenna terminal, and a reception filter that filters a signal input from the antenna terminal, and includes the elastic wave device according to any of the 1st to 17th aspects.

[0108] (19) The communication device according to the 19th aspect of the present disclosure includes an antenna, the demultiplexer according to the 18th aspect in which the antenna terminal is connected to the antenna, and an IC connected to a terminal opposite to the antenna terminal with respect to the signal path with respect to the transmission filter and the reception filter.

[0109] 1: Elastic wave device 2: Support substrate 3: LT layer 4: Multilayer film 41: Low acoustic impedance layer 42: High acoustic impedance layer 47: Temperature compensation layer 5: IDT electrode 52: Electrode finger 6: Cavity 200: Demultiplexer 201: Transmission terminal 202: Antenna terminal 203: Transmission filter 204: Reception terminal 205: Reception filter 207: Multimode type filter 300: Communication terminal 301: RF-IC 302: Bandpass filter 303: Amplifier 305: Antenna

Claims

1. An LT layer including a rotation Y-cut X-propagation LT single crystal, an IDT electrode adjacent to the LT layer, having a plurality of electrode fingers, and configured to excite an elastic wave, and comprising, wherein a cut angle θ of the rotation Y-cut X-propagation LT single crystal satisfies 10° ≤ θ ≤ 90° and the elastic wave is a plate wave or a bulk wave Elastic wave device.

2. An LT layer including a rotation Y-cut X-propagation LT single crystal, an IDT electrode adjacent to the LT layer, having a plurality of electrode fingers, and configured to excite an elastic wave, and comprising, wherein a cut angle θ of the rotation Y-cut X-propagation LT single crystal satisfies 10° ≤ θ ≤ 90° and a resonance frequency fr [GHz] of the elastic wave and a pitch p [μm] of the IDT electrode satisfy fr·p > 3 [GHz·μm] and Elastic wave device.

3. Comprising a multilayer film located below the LT layer, wherein the multilayer film includes at least one low acoustic impedance layer including a portion having a lower acoustic impedance compared to an upper contact layer, and at least one high acoustic impedance layer including a portion having a higher acoustic impedance compared to an upper contact layer, and θ satisfies 10° ≤ θ ≤ 75° The elastic wave device according to any one of Claims 1 or 2.

4. θ satisfies 60° ≤ θ ≤ 70° The elastic wave device according to Claim 3.

5. Comprising a multilayer film located below the LT layer, wherein the multilayer film includes at least one low acoustic impedance layer including a portion having a lower acoustic impedance compared to an upper contact layer, and at least one high acoustic impedance layer including a portion having a higher acoustic impedance compared to an upper contact layer, and θ satisfies 60° ≤ θ ≤ 90° The elastic wave device according to any one of Claims 1 or 2.

6. The temperature compensation layer included in the multilayer film includes a material whose Young's modulus increases with an increase in temperature The elastic wave device according to Claim 3.

7. The temperature compensation layer is located in a range of three layers or less from the top in the stacking direction of the multilayer film The elastic wave device according to Claim 6.

8. The temperature compensation layer includes silicon dioxide The elastic wave device according to Claim 6.

9. Comprising a cavity portion located below the LT layer, where θ satisfies 10° ≤ θ ≤ 70° The elastic wave device according to any one of Claims 1 or 2.

10. θ satisfies 25° ≤ θ ≤ 60° The elastic wave device according to Claim 9.

11. A cavity portion is provided below the LT layer, wherein θ satisfies 55° ≤ θ ≤ 80°. The elastic wave device according to any one of claims 1 or 2.

12. The thickness of the LT layer is smaller compared to the pitch p of the plurality of electrode fingers. The elastic wave device according to any one of claims 1 or 2.

13. When the temperature characteristic of the resonance frequency fr is TCF r, the absolute value of the TCF r is smaller than 30 ppm / K. The elastic wave device according to any one of claims 1 or 2.

14. When the temperature characteristic of the anti-resonance frequency fa is TCF a, the absolute value of the TCF a is smaller than 40 ppm / K. The elastic wave device according to any one of claims 1 or 2.

15. The elastic wave is a plate wave. The elastic wave device according to any one of claims 1 or 2.

16. The plate wave is an A1 mode drum wave. The elastic wave device according to claim 15.

17. The elastic wave is a bulk wave. The elastic wave device according to any one of claims 1 or 2.

18. An antenna terminal, A transmission filter for filtering a signal output to the antenna terminal, A reception filter for filtering a signal input from the antenna terminal, and having A demultiplexer including the elastic wave device according to any one of claims 1 or 2.

19. An antenna, The demultiplexer according to claim 18, wherein the antenna terminal is connected to the antenna, An IC connected to a terminal opposite to the antenna terminal as viewed from the signal path with respect to the transmission filter and the reception filter, and having a communication device.

Images