WO2019082806A1

WO2019082806A1 - Acoustic wave element

Info

Publication number: WO2019082806A1
Application number: PCT/JP2018/038985
Authority: WO
Inventors: 哲也岸野; 伊藤　幹
Original assignee: 京セラ株式会社
Priority date: 2017-10-23
Filing date: 2018-10-19
Publication date: 2019-05-02
Also published as: JP7073392B2; JPWO2019082806A1

Abstract

An acoustic wave element 1 is provided with: an IDT electrode 4 that includes a plurality of electrode fingers 41; a piezoelectric layer 30 which has the IDT electrode 4 positioned on the upper surface thereof, which has a thickness less than 0.35 λ, where λ denotes a wavelength defined by two-fold of the repeating interval of the electrode fingers 41, which is made of a lithium tantalite single crystal, and which has Euler angles of 90±1, 90±2, 20 to 50; and a substrate 20 in which a transverse wave acoustic velocity V(m/s) is 5800 m/s or higher and which has a first surface joined to the lower surface of the piezoelectric layer 30.

Description

Acoustic wave element

The present invention relates to an elastic wave device.

Heretofore, elastic wave elements have been used as resonators and band filters, and in recent years, it has been required to cope with higher frequency bands. Under such circumstances, an elastic wave device using a piezoelectric thin film has been proposed. For example, WO 2012/073871 proposes an elastic wave device including a support layer provided with a recess, a piezoelectric thin film disposed so as to extend onto the recess, and an IDT electrode formed on the piezoelectric thin film. ing.

In recent years, the demand for higher frequencies of communication devices has further increased, and the provision of elastic wave elements capable of achieving higher frequencies by another method is required.

The elastic wave device of the present disclosure comprises an IDT electrode, a piezoelectric layer, and a substrate. The IDT electrode includes a plurality of electrode fingers. The piezoelectric layer is made of lithium tantalate single crystal having a thickness of less than 0.5 λ, where λ is a wavelength defined by twice the repetition interval of the plurality of electrode fingers, and the IDT electrode is located on the top surface. The Euler angles are (φ, θ, ψ) = (90 ± 0.5, 90 ± 1, 20 to 50). The substrate has a first surface which has a shear wave velocity V (m / s) of 5800 m / s or more and is bonded to the lower surface of the piezoelectric layer.

According to the above configuration, it is possible to provide an elastic wave element compatible with the increase in frequency.

It is a sectional view of an elastic wave element concerning this indication. It is a top view which shows the structure of an IDT electrode. FIGS. 3A and 3B are diagrams showing frequency characteristics of the acoustic wave device according to the present disclosure, respectively. FIGS. 4 (a) and 4 (b) are diagrams showing the frequency characteristics of the elastic wave element when the Euler angle of the piezoelectric layer is changed. FIGS. 5 (a) and 5 (b) are diagrams showing frequency characteristics of the acoustic wave device according to the reference example. FIGS. 6 (a) and 6 (b) are diagrams showing frequency characteristics of the acoustic wave device according to the reference example. It is a contour map which shows the area | region where the frequency characteristic of the elastic wave element when the Euler angle, thickness, and electrode thickness of a piezoelectric layer are changed is favorable. FIGS. 8 (a) and 8 (b) are diagrams showing frequency characteristics of the acoustic wave device, respectively. 9 (a) and 9 (b) are diagrams showing frequency characteristics of the acoustic wave device. It is sectional drawing of the modification of the elastic wave element shown in FIG. FIGS. 11 (a) to 11 (d) are diagrams showing the frequency characteristics of the modification of the acoustic wave device shown in FIG. 1, respectively. It is a diagram which shows the frequency characteristic concerning the modification of the elastic wave element shown in FIG. It is sectional drawing which shows the modification of the elastic wave element shown in FIG. It is a diagram which shows the relationship between the thickness of a piezoelectric layer, and a resonant frequency. It is a diagram showing the relation between the arrangement direction of a capacity part, and the maximum intensity of a spurious. It is a contour map which shows the relationship between the Euler angle of a support substrate, the arrangement direction of a capacity part, and the maximum intensity of a spurious. FIGS. 17 (a) to 7 (c) are exploded top views showing each configuration of a modification of the acoustic wave device shown in FIG. It is a diagram which shows the relationship between the thickness of a piezoelectric layer, and a resonant frequency. It is a diagram which shows the relationship between the thickness of a piezoelectric layer, and a resonant frequency.

Hereinafter, an example of the elastic wave element of this indication is explained in detail using a drawing.

The elastic wave device 1 (SAW device 1) according to the present embodiment includes a support substrate 10, a substrate 20, a piezoelectric layer 30, and an IDT electrode 4 as shown in FIG. The support substrate 10, the substrate 20, and the piezoelectric layer 30 are stacked in this order.

The supporting substrate 10 supports the substrate 20 and the piezoelectric layer 30 located on the upper side, and the material is not limited as long as the strength is provided. For example, a ceramic substrate, an organic substrate, a dielectric substrate such as quartz crystal or sapphire, a piezoelectric substrate, a semiconductor substrate, etc. can be exemplified, and it may be a substrate made of the same material system as the piezoelectric layer 30 described later. In this example, a single crystal silicon substrate is used.

When a silicon substrate is used as the support substrate 10, the thermal expansion coefficient is smaller than the material of the piezoelectric layer 30 described later. Therefore, when a temperature change occurs, a thermal stress is generated in the piezoelectric layer 30. At this time, the temperature dependency and the stress dependency of the elastic constant cancel each other, and the temperature change of the electrical characteristics of the SAW element 1 is reduced (temperature Special compensation).

The thickness of the support substrate 10 is not particularly limited, but may be, for example, about 100 μm to 250 μm. The thickness decreases in the order of the support substrate 10, the substrate 20, the piezoelectric layer 30, and the IDT electrode 4 described later.

The substrate 20 includes a first surface 20A and a second surface 20B opposite to the first surface 20A. Then, the second surface 20B is bonded to the upper surface of the support substrate 10, and the first surface 20A is bonded to the lower surface of the piezoelectric layer 30. In this example, the first surface 20A and the piezoelectric layer 30, and the second surface 20B and the support substrate 10 are directly bonded together, but the present invention is not limited to this. In particular, when the substrate 20 has a thickness equal to or greater than the wavelength λ defined by twice the repetition interval Pt1 of the electrode finger 41 of the IDT electrode 4 described later, a bonding layer or the like is formed between the substrate 20 and the support substrate 10. It may be joined via

The substrate 20 is made of a material having a shear wave velocity of 5800 m / s or more. As such materials, aluminum nitride (AlN), titanium nitride (TiN), silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), sapphire, alumina, boron nitride (BN), diamond, diamond like carbon ( DLC) etc. can be illustrated.

The thickness of the substrate 20 is, for example, 0.8 λ or more. More preferably, it is 1 λ or more. Although the upper limit of the thickness of the substrate 20 is not particularly limited, in the case of forming the substrate 20 by a thin film process or the like, it may be 10 λ or less in consideration of film forming property and the like.

The piezoelectric layer 30 is located on the first surface 20 </ b> A of the substrate 20. In other words, the substrate 20 and the piezoelectric layer 30 are bonded directly or indirectly. The piezoelectric layer 30 is made of lithium tantalate single crystal (LiTaO ₃ : sometimes abbreviated as LT below) having a thickness of less than 0.35λ. And, the Euler angles (φ, θ, ψ) are (90 ° ± 0.5 °, 90 ° ± 1 °, 20 ° to 50 °).

The IDT electrode 4 is located on the top surface of the piezoelectric layer 30. The IDT electrode excites a surface acoustic wave, and as shown in FIG. 2, for example, constitutes a resonator composed of a pair of comb-

like electrodes

40A and 40B. The comb-like electrode includes a plurality of electrode fingers 41. The electrode finger 41A connected to one potential and the electrode finger 41B connected to the other potential are alternately arranged so as to cross each other, and the SAW propagates along the arrangement direction of the electrode finger 41. . An interval between centers of widths of the

electrode fingers

41A and 41B is referred to as a pitch Pt1. The width of the electrode finger 41 is w1 and the thickness thereof is s.

As a material constituting such an IDT electrode 4, an Al—Cu alloy can be exemplified. The thickness is determined in consideration of the excitation efficiency of the SAW, the electromechanical coupling coefficient with the LT substrate, and the like. Further, the IDT electrode 4 may be a laminate of a plurality of electrode layers.

The protective layer 6 is located on the top surface of the IDT electrode 4 in order to reduce its oxidation. Examples of the material of the protective layer 6 include inorganic insulating materials such as silicon oxide and silicon nitride.

The results of simulating the resonance characteristics of the SAW element 1 having the above-described configuration are shown in FIG. FIG. 3 (a) shows impedance characteristics with respect to frequency, and FIG. 3 (b) shows phase characteristics. In FIG. 3A, the horizontal axis represents frequency (unit: MHz), and the vertical axis represents impedance (unit: Ω). In FIG. 3B, the horizontal axis represents frequency (unit: MHz), and the vertical axis represents impedance phase (unit: °).

The basic configuration of the simulation model 1 is as follows.

<Model 1>
Material of electrode finger 41: Thickness of Al-Cu 1% -added alloy electrode finger 41: 0.07 λ
Pitch of electrode finger 41: 1 μm (λ = 2 μm)
Number of electrode fingers 41: Cross width of 100 electrode fingers 41: 10λ
Material of piezoelectric layer 30: LiTaO ₃
Euler angles of the piezoelectric layer 30: (φ, θ, ψ) = (90 °, 90 °, 30 °) (corresponding to X cut substrate / 30 ° Y propagation)
Thickness of piezoelectric layer 30: 0.25 λ
Material of substrate 20: AlN
Thickness of substrate 20: 2λ
Material of support substrate 10: Si
Thickness of support substrate 10: 250 μm
In addition, in the piezoelectric layer, an appropriate propagation loss is assumed, and resonator characteristics in a state where there is a slight loss are shown.

The most common SAW element in the prior art uses a 42 ° rotated YX propagation LT substrate having a thickness of 1λ or more as the piezoelectric layer 30 with an Euler angle of (0, -48, 0) There is. In this case, when the pitch of the electrode fingers 41 is 1 μm, the resonance frequency is about 2 GHz. On the other hand, according to the SAW element 1, the pitch of the electrode fingers 41 is 1 μm in the model 1 as shown in FIG. 3 by changing the thickness of the conventional SAW element and the piezoelectric layer 30 and the Euler angle. It was also confirmed that the resonance frequency could be 3.05 GHz.

In Model 1, the value (sound velocity) obtained by multiplying the resonant frequency by λ is 6000 m / s. From this, it can be confirmed that the resonator functions as a resonator using an elastic wave of a mode faster than the elastic wave of the mode used in the conventional SAW element.

Furthermore, according to the waveform of FIG. 3, Δf is as large as or larger than that of the conventional SAW element, and there is no bulk wave spurious between the resonant frequency and the antiresonant frequency. It was confirmed that a SAW device 1 with low loss and excellent in characteristics could be provided.

The model 1 can provide the SAW element 1 with high frequency and less loss compared to the conventional SAW element even if the above-mentioned Euler angles are changed in the angle range of ± 1 ° and θ of ± 2 °. It was confirmed.

FIG. 4 shows changes in the impedance waveform of the resonator when the Euler angles φ and θ of the piezoelectric body are changed in the model 1. The horizontal axis is frequency (unit: MHz), and the vertical axis is impedance (unit: Ω). In FIG. 4, the horizontal axis frequency of each impedance waveform is appropriately shifted (in fact, all the resonance frequencies are almost the same) for easy viewing.

As can be seen from FIG. 4, when φ and θ deviate from the above ranges, spurious noise occurs in the vicinity of resonance and antiresonance. Specifically, from the above-mentioned Euler angle, occurrence of a small spurious is confirmed in the vicinity of the antiresonance frequency when φ is ± 1 ° and θ is ± 2 °. From this, from the above-mentioned Euler angles, when .phi. Is. +-. 1.degree. And .theta. Is. +-. 2.degree., The influence of the spurious increases. On the other hand, generation of spurious was not confirmed when the range of φ was ± 0.5 ° and θ was ± 1 ° from the above Euler angle. From the above, high frequency characteristics can be provided by setting the range of ± 0.5 ° and θ to ± 1 ° from the above-mentioned Euler angles.

Further, among the above-mentioned Euler angles, it is possible to provide the SAW element 1 having a high frequency and less loss in the range of 20 ° to 50 ° compared to the conventional SAW element, but more specifically, the thickness of the electrode There is an appropriate range in relation to the thickness of the and the piezoelectric layer. This range will be described later.

Further, according to the SAW element 1, since the substrate 20 is located on the entire lower surface of the piezoelectric layer 30, the handling is easy and the reliability can be high.

By making the substrate 20 a material having a cutoff frequency higher than the resonance frequency band of the resonator realized by the SAW element 1, leakage to the substrate 20 side is reduced, and the SAW element 1 with less loss is provided. can do. Specifically, the cutoff frequency of AlN used as the substrate 20 in this example is 3.3 GHz. For this reason, as shown in FIG. 3B, it is possible to make a resonator with less loss in the region of less than 3.3 GHz. When the thickness of AlN is reduced, part of the acoustic wave reaches the support substrate 10 and leaks. Therefore, the thickness of the substrate 20 needs to be at least 0.8 λ or more, preferably 1 λ or more. In addition, an adhesion layer or an adjustment layer for adjusting the characteristics may be inserted between the substrate 20 and the piezoelectric layer 30.

Further, the Euler angles (φ, θ, ψ) = (90 °, 90 °, 30 °) of the piezoelectric layer 30 of the model 1 means that a substrate of X-cut LT-30 ° Y propagation is used. Therefore, although the leakage in the vertical direction can be reduced by the material of the substrate 20 or the like, the leakage in the lateral direction may occur. Therefore, the IDT electrode 4 may be provided with a dummy electrode, or the speed of sound may be made different in the intersection region of the dummy electrode and the electrode finger 41. Also, the IDT may be inclined and disposed in the direction of the power flow. Further, the “apodized type” may be used in which the crossing width of the electrode finger 41 is gradually changed.

In this example, the substrate 20 is 1λ, and the supporting substrate 10 made of Si is provided on the lower surface thereof. With such a configuration, the thermal stress due to Si having a small thermal expansion coefficient is applied to the piezoelectric layer 30, so that it is possible to obtain the SAW element 1 in which the characteristic change due to the temperature change is reduced.

<Correlation between impedance characteristics and Euler angle and thickness of piezoelectric layer 30, thickness of electrode 4>
The impedance characteristics of the SAW element 1 change according to the Euler angle and thickness of the piezoelectric layer 30 and the thickness of the electrode 4. For example, with respect to the model 1, impedance characteristics when the Euler angles of the piezoelectric layer 30 are fixed (90 °, 90 °, 30 °) and the thickness of the piezoelectric layer 30 is reduced to 0.2λ are shown in FIG. FIG. 5A is a graph showing impedance characteristics with respect to frequency. The vertical axis represents impedance (unit: Ω), and the horizontal axis represents frequency (unit: MHz). FIG. 5B is a diagram showing phase characteristics with respect to frequency, in which the vertical axis is phase (unit: °) and the horizontal axis is frequency (unit: MHz). In this case, the impedance phase characteristic in the vicinity of the antiresonance rises more than -90 °. This indicates that a large loss occurs in this frequency range.

The impedance characteristics when the thickness of the piezoelectric layer 30 is increased to 0.35 λ are shown in FIG. 6 (a) and 6 (b) correspond to FIGS. 5 (a) and 5 (b). In this case, a large spurious vibration is generated on the high frequency side than the antiresonance.

Thus, the thickness of the piezoelectric layer 30 has an appropriate range, and the range is related to the Euler angle of the piezoelectric layer 30 and the thickness of the electrode 4.

FIG. 7 is a result of simulating a change in impedance characteristics with respect to the thickness of the piezoelectric layer 30 and the thickness of the electrode 4 when the Euler angle of the piezoelectric layer 30 is changed. In each graph of FIG. 7, the horizontal axis represents the thickness of the electrode 4 and the vertical axis represents the thickness of the piezoelectric layer 30, and the region (R1) with a good parameter of the impedance waveform is filled for each ridge.

Further, a region indicated as SP in FIG. 7 is a region where a large spurious vibration occurs as shown in FIG. Further, a region indicated by LS is a region where a large loss occurs in the impedance characteristic as shown in FIG. The filled area R1 excluding this area is a range in which good impedance characteristics are obtained.

In FIG. 7, a dark color portion and a light color portion exist in the region R1. Although all show good impedance characteristics, the thickness of the electrode 4, the thickness of the electrode 4 and the thickness of the piezoelectric layer 30 are adjusted so as to be the area of the dark color part of the area R1 in consideration of the manufacturing variation and the like. It is also good.

Here, FIG. 7 will be described in detail. In FIG. 7, it is confirmed that the R1 region is the same even if ψ fluctuates by ± 2 °. Further, in FIG. 7, ψ is displayed in increments of 10 °, but in the case of an intermediate angle, it is determined as follows. That is, the electrode thickness in the region R1 and the thickness of the piezoelectric layer 30 both at one angle, at the next level, and at (for example, ψ = 20 ° and ψ = 30 °) The combination is assumed to be in the R1 region in the case of any angle between the angles of the wedges of adjacent levels (for example, 20 ° ≦) ≦ 30 °). On the contrary, in the case of one angle, the combination of the electrode thickness and the thickness of the piezoelectric layer 30 which is in the region R1 but outside the range of the region R1 in the case of the next level angle is adjacent It is assumed that it is outside the region R1 between the angles of the eyebrows. As a specific example, in the case of the combination of the electrode thickness of model 1: 0.07 λ and the thickness of piezoelectric layer 30: 0.25 λ, it is located within the R1 region regardless of whether ψ is -10 ° to 60 °. . In the case of the combination of electrode thickness: 0.07 λ and piezoelectric layer thickness: 0.2 λ, the region R1 is in the case of ψ = 20 ° ± 2 °, but in the case of ψ = 30 ° ± 2 °. Since it is outside the region R1, it is estimated that it is outside the region R1 also at 23 ° ≦ ψ ≦ 27 °.

As described above, the impedance characteristics of the SAW element 1 appear spurious with a slight change with respect to the Euler angles φ and θ, but as can be seen from FIG. does not change. However, when ψ changes significantly, the resonance frequency fr and the frequency difference df (anti-resonance frequency fa−resonance frequency fr) change.

8 (a) and 8 (b), the thickness of the piezoelectric layer 30 is fixed at 0.25 λ with the parameters of the model 1, and the changes in fr and df when the thickness of the electrode 4 is changed are shown for each ridge. It shows what was plotted. In FIG. 8, the horizontal axis is frequency (unit: MHz), and the vertical axis is impedance (unit: Ω).

It can be seen from FIG. 8 that both fr and df have maximum values near ψ = 30 ° to 40 °. If ψ becomes smaller or larger than that, both fr and df become smaller. It is desirable that ψ be 20 ° to 50 °, since it is advantageous for the characteristics to be larger if both fr and df are larger. A particularly desirable range is 25 ° to 40 °. In addition, both the fr and df become larger as the thickness of the electrode 4 is made thinner, but if the thickness of the electrode 4 is made too thin, the electrical resistance becomes larger and the loss becomes larger. Therefore, the thickness of the electrode 4 is preferably 0.05λ to 0.08λ.

9 (a) and 9 (b), when the thickness of the electrode 4 is fixed to 0.07 λ by the parameter of the model 1 and the thickness of the piezoelectric layer 30 is changed, the changes between fr and df are shown in FIG. It shows what was plotted about. In FIG. 9, the horizontal axis is frequency (unit: MHz), and the vertical axis is impedance (unit: Ω).

Similar to FIG. 8, it can be seen that both fr and df have maximum values near ψ = 30 ° to 40 °. In addition, when the thickness of the piezoelectric layer 30 is reduced, fr increases while df decreases slightly. In addition, if the thickness of the piezoelectric layer 30 is too thin, the strength is reduced and the reliability is degraded, and the required processing accuracy is increased. Therefore, the thickness of the piezoelectric layer 30 is 0.225λ. It is desirable that ～ 0.3 λ.

<Modification>
In the above example, the SAW element 1 having the support substrate 10 has been described. However, since the thickness of the substrate 20 has no upper limit in electrical characteristics, the substrate 20 can be thickened to have the function as the support substrate 10 The support substrate 10 may be omitted.

For example, as shown in FIG. 10, an AlN substrate, a sapphire substrate or the like in which the substrate 20 has a thickness of about 50 μm to 250 μm may be used. In addition, an adhesion layer or an adjustment layer for adjusting the characteristics may be inserted between the substrate 20 and the piezoelectric layer 30.

<Modification 2>
Although the above example does not mention the combination example of the support substrate 10 and the substrate 20, the support substrate 10 may be made of sapphire single crystal and the substrate 20 may be made of AlN. In this case, both the support substrate 10 and the substrate 2 become an Al-based material. Therefore, when the support substrate 10 and the substrate 20 are bonded and bonded, the mismatch of the bonding interface can be reduced, so the loss of elastic waves can be reduced. Further, since strong bonding can be realized, reliability can be improved. In the case of forming the substrate 20 on the supporting substrate 10 by film forming, because of the same material system, the interface mismatch can be reduced, and the quality of the film to be formed can be enhanced, and the loss of elastic waves It can be reduced.

<Modification 3>
In the above-mentioned example, although the example which made substrate 20 AlN was explained, it is good also as substrate 20 as SiC. Since the cut-off frequency of SiC is high, it is possible to reduce the occurrence of loss on the higher frequency side than the antiresonance frequency confirmed in FIGS. Specifically, no rise in the floor level was confirmed up to around 3800 MHz with respect to the resonance of 3000 MHz.

The correlation between the impedance characteristic of the SAW element 1 when using SiC as the substrate 20, the Euler angle of the piezoelectric layer 30, and the thickness of the electrode 4 was simulated. Specifically, the piezoelectric layer 30 has two thicknesses of 0.3 λ and 0.5 λ, and an Euler angle of (86 ° to 94 °, 86 ° to 94 °, −10 ° to 70 °). The frequency characteristics were simulated by setting the thickness of V to 0.04λ to 0.08λ.

As a result, among the Euler angles of the piezoelectric layer 30, with respect to φ and θ, by setting φ = 90 ° ± 0.5 ° and θ = 90 ° ± 1 ° as in the case of FIG. Can get no waveform.

Among the Euler angles of the piezoelectric layer 30, ψ was not changed significantly in the position, intensity, etc. of the spurious even when changed. However, in the case of ψ = 20 ° or more and 30 ° or less, df was larger than other propagation angles.

Next, the thickness of the electrode 4 was changed to check the position and the magnitude of fr and spurious. As a result, the influence of the thickness of the electrode 4 was not confirmed for the magnitude of fr and spurious. However, it was confirmed that the position of the spurious shifts to the higher frequency side as the thickness of the electrode 4 is thinner. From the result, the thickness of the electrode 4 may be 0.04λ to 0.08λ. When it is 0.04 λ or more, resonance characteristics can be obtained without deterioration of the resistance as an electrode. When the wavelength is 0.08 λ or less, the position of the spurious is about 3500 MHz, and the resonance characteristics can be obtained without deterioration of the loss on the side higher than the antiresonance frequency.

Although the above simulation has been described taking the case where the single crystal substrate is used as SiC and the first surface 20A is the (0001) surface as an example, the positions of fr, df and spurious are also used when using a ceramic SiC substrate And there was no difference in strength, loss, etc. Further, in both of the single crystal SiC substrate and the ceramic SiC substrate, no change in the characteristics was observed even when rotated in the plane direction with respect to the propagation direction of the SAW (when the crucible of the SiC substrate was rotated). . That is, in the case where SiC is used as the substrate 20 in the SAW element 1, it is possible to provide the SAW element 1 having stable characteristics without being strongly affected by various parameters including the crystallinity of the substrate.

SiC is a semiconductor and generally has conductivity. As the conductivity increases, the SAW characteristics are affected, so the conductivity of the SiC substrate should be high. Specifically, the conductivity of the SiC substrate may be 1 kΩcm or more.

<Modification 4>
In the above-mentioned example, although the example which made substrate 20 AlN was explained, it is good also as substrate 20 as sapphire. The correlation between the impedance characteristic of the SAW element 1 and the Euler angle of the piezoelectric layer 30 and the thickness of the electrode 4 when sapphire was used as the substrate was simulated. Specifically, the piezoelectric layer 30 has two thicknesses of 0.3 λ and 0.5 λ, and an Euler angle of (86 ° to 94 °, 86 ° to 94 °, −10 ° to 70 °). The thickness of each was 0.04 λ to 0.08 λ, and the frequency characteristics were simulated by combining the respective conditions. As a result, as in the case of AlN and SiC, it was confirmed that the spurious and loss were reduced to obtain a resonance of 3 GHz, and it was further confirmed that the characteristic change with respect to φ and θ had the same tendency.

FIGS. 11A and 11B show frequency characteristics when the substrate 20 is made of sapphire. Further, as reference examples, frequency characteristics when the substrate 20 is made of alumina are shown in FIGS. 11 (c) and 11 (d). In FIGS. 11 (a) and 11 (c), the horizontal axis represents frequency, and the vertical axis represents impedance. In FIGS. 11B and 11D, the horizontal axis indicates the frequency and the vertical axis indicates the phase. As apparent from this figure, when the substrate 20 is made of sapphire, the cutoff frequency is higher than that of alumina, and the loss is also in the high frequency side (specifically, around 3300 MHz) than the antiresonance frequency. Was confirmed to be able to reduce the occurrence of

Thus, even in the same material system, differences in frequency characteristics occurred between sapphire and alumina. This may be due to the anisotropy of the sapphire. Therefore, the Euler angle of sapphire was changed to confirm the frequency characteristics. As a result, it has been found that when the Euler angle of sapphire is (90 °, 90 °, 140 ° to 160 °), generation of spurious can be reduced and the cutoff frequency can be positioned on a sufficiently high frequency side .

In FIG. 12, the thickness of the piezoelectric layer 30 is 0.3λ, the Euler angles (90 °, 90 °, 30 °), and the Euler angles of the substrate 20 are changed to (90 °, 90 °, 120 ° to 170 °). It shows the frequency characteristics in the case of The upper stage shows impedance characteristics, and the lower stage shows phase characteristics.

As apparent from FIG. 12, when ψ is less than 140 ° or exceeds 160 ° at the Euler angle of sapphire, the cutoff frequency shifts to the low frequency side and the loss on the high frequency side of the antiresonance frequency is aggravated. . In addition, when the angle ψ becomes 130 ° or less, there is a possibility that the spurious increases and a loss occurs. From the above, when a sapphire substrate is used as the substrate 20, (90 °, 90 °, 140 ° to 160 °) or a plane equivalent thereto (for example, (90 °, 90 °, -20 ° to -40 °) It has been found that, by setting it as in the above, it is possible to provide the SAW element 1 in which the loss is reduced even on the high frequency side of the antiresonance frequency. In sapphire, an error of ± 1 ° is allowed for ψ, θ, and ψ.

Next, frequency characteristics were simulated when the relative angle between the Euler angle of the piezoelectric layer 30 and the Euler angle of sapphire was changed. Specifically, the simulation was performed with the Euler angles of sapphire set to 140 °, 150 °, and 160 °, and the Euler angles of the piezoelectric layer 30 set to 20 °, 30 °, and 40 °. As a result, regardless of the Euler angle of the piezoelectric layer 30, it was confirmed that the Euler angles of sapphire capable of providing the SAW device 1 with small loss are (90 °, 90 °, 150 °). Among them, it was confirmed that generation of spurious can be reduced when the Euler angle of the piezoelectric layer 30 is set to 30 °.

<Modification 5>
In the above-mentioned example, although the case where piezoelectric layer 30 and substrate 20 were directly joined was explained to an example, as shown in Drawing 13, middle layer 50 may be made to intervene. The intermediate layer 50 is made of a material in which the acoustic velocity of the elastic wave propagating through the piezoelectric layer 30 is smaller than that of the piezoelectric layer 30 and the substrate 20. Such a material is, for example, SiO ₂ . Further, the thickness thereof is thinner than that of the piezoelectric layer 30, and may be, for example, 0.08λ to 0.1λ.

By providing the intermediate layer 50 having a low sound velocity, the vibration of the elastic wave propagating in the piezoelectric layer 30 is moved to the intermediate layer 50 in a large amount. As a result, the acoustic velocity of the elastic wave is reduced. Here, as the thickness of the piezoelectric layer 30 decreases, the resonance frequency shifts to the high frequency side. On the other hand, when the intermediate layer 50 is present, the elastic wave moves to the intermediate layer 50 as the thickness of the piezoelectric layer 30 becomes thinner, and as a result, the speed of sound becomes slower and the resonance frequency becomes lower. Thus, the effect of increasing the resonant frequency by thinning the piezoelectric layer 30 and the effect of decreasing the resonant frequency by thinning the piezoelectric layer 30 cancel each other. As a result, even if the film thickness of the piezoelectric layer 30 changes, the elastic wave element 1 with high robustness can be provided in which the resonance frequency does not change.

In FIG. 14, when the substrate 20 is made of AlN and the thickness of the intermediate layer 50 is 0.025λ, 0.05λ, 0.075λ, 0.1λ, 0.125λ, 0.15λ, 0.175λ, the respective piezoelectric layers 30 are formed. It shows the result of simulating the correlation between the thickness and the value of the resonant frequency (a) and the antiresonant frequency (b). The frequency is normalized to the value when the thickness of the piezoelectric layer 30 is 0.35λ (0.7 p) and the thickness of the intermediate layer 50 is 0.025 λ (0.05 p). Further, the film thickness is standardized by the pitch p (= 0.5 λ) of the IDT electrode. When the thickness of the piezoelectric layer 30 is in the range of 0.2λ to 0.35λ, setting the thickness of the intermediate layer 50 to 0.075λ to 0.125λ makes the value of fr constant even if the thickness of the piezoelectric layer 30 changes. And confirmed that it can. Further, FIG. 18 shows the same result when the substrate 20 is SiC when the substrate 20 is sapphire single crystal, but the result is almost similar to the case of AlN shown in FIG.

<Modification 6>
The SAW element 1 may include a capacitance unit 60 connected in parallel to the IDT electrode 4. Since the capacitance portion 60 can reduce df, it can be adjusted to have a desired df. When such a capacitive portion 60 is formed of an interdigital electrode similar to the IDT electrode 4, the repetitive arrangement direction D1 of the electrode fingers 43 (capacitive portion electrode fingers 43) of the capacitive portion functions as a resonator. The arrangement direction D 2 of the electrode fingers 41 of the IDT electrode 4 may be different. With such a configuration, the influence of the resonance by the capacitive section 60 can be reduced. Furthermore, when using a Si (111) plane as the support substrate 10, as shown in FIG. 15, if the arrangement direction D1 is -60 ° ± 5 °, 60 ° ± 5 °, the frequency is higher than fr. The maximum intensity of the located spurs can be lowered.

Here, the (111) plane of Si is (-45 °, -54.7 °, ψ) in Euler angles. Here, the maximum intensity of the spurious was simulated when ψ was changed. The results are shown in FIG. In FIG. 16, the horizontal axis is the arrangement direction D 1 and the vertical axis is ψ, and the maximum intensity of the spurious is indicated by contour lines. As apparent from FIG. 16, the spurious intensity can be reduced when the wedge of the support substrate 10 is set to 0 ° to 20 °, 40 ° to 140 °, and 160 ° to 180 °.

17, the arrangement direction D2 (SAW propagation direction) and the Euler angles of the piezoelectric layer 30, the substrate 20, and the support substrate 10 when the support substrate 10 and the capacitance portion 60 of the modification 6 are provided in the configuration of the modification 5 in FIG. And the arrangement direction D2 of the capacitive portion 60. FIG. FIG. 17A is a view of the piezoelectric layer 30 from the top, FIG. 17B is a view of the substrate 20 from the top, and FIG. 17C is a view of the support substrate 10 from the top. FIG. 17A also shows a schematic view showing the arrangement relationship between the IDT electrode 4 and the capacitor portion 60 disposed on the piezoelectric layer 30. As shown in FIG.

With such a relationship, the cutoff frequency of the substrate 20 is increased to reduce the loss on the high frequency side relative to the antiresonance frequency, and the intensity of the spurious generated on the high frequency side relative to the antiresonance frequency is also obtained. It can be reduced.

In addition, it is confirmed that the relationship between the arrangement direction D1 of the capacitive portions 60 and the Euler angle of the support substrate 10 is the same even when there is no substrate 20 between the piezoelectric layer 30 and the support substrate 10. doing.

1: Elastic wave element 20: Substrate 30: Piezoelectric layer 4: IDT electrode 41: Electrode finger

Claims

An IDT electrode comprising a plurality of electrode fingers,
Said IDT electrode is located on the upper surface, and it is made of lithium tantalate single crystal having a thickness of less than 0.35.lamda., Where .lambda. Is a wavelength defined by twice the repetition interval of the plurality of electrode fingers, and its Euler A piezoelectric layer having an angle of (90 ± 0.5, 90 ± 1, 20 to 50),
A substrate comprising a first surface having a shear wave velocity V (m / s) of 5800 m / s or more and directly or indirectly bonded to the lower surface of the piezoelectric layer.
The elastic wave device according to claim 1, wherein the substrate is made of any of aluminum nitride, titanium nitride, silicon nitride, silicon carbide, sapphire, diamond, boron nitride and diamond like carbon, and the thickness thereof is 1 λ or more.
The substrate includes a second surface facing the first surface,
The acoustic wave device according to claim 1, further comprising a support substrate having a thickness of more than 1 λ bonded directly or indirectly to the second surface.
The elastic wave device according to any one of claims 1 to 3, wherein the relationship between the thickness of the piezoelectric layer and the thickness of the IDT electrode is in a range R1 shown by solid lines in Fig. 7.
The elastic wave device according to claim 1 or 2, wherein the substrate is sapphire, and the Euler angles thereof are (90 ± 1, 90 ± 1, -20 to -40).
The elastic wave device according to claim 1 or 2, wherein the substrate is made of a single crystal SiC substrate and the conductivity is 1 kΩcm or more.
The elastic wave device according to any one of claims 1 to 6, wherein the thickness of the piezoelectric layer is 0.225 λ to 0.3 λ.
The elastic wave device according to any one of claims 1 to 7, wherein the thickness of the IDT electrode is 0.05 λ to 0.08 λ.
The elastic wave device according to claim 3, wherein the support substrate is silicon, and the thickness becomes thicker in the order of the piezoelectric layer, the substrate, and the support substrate.
The elastic wave device according to any one of claims 1 to 9, wherein a value obtained by multiplying the resonance frequency of the elastic wave generated by the IDT electrode by λ is 5800 m / s or more.
11. The intermediate layer according to any one of claims 1 to 10, comprising an intermediate layer made of a material having a smaller shear velocity than the piezoelectric layer and the substrate and having a thickness of not less than 0.075λ and not more than 0.125λ between the piezoelectric layer and the substrate. Acoustic wave element described in.
The elastic wave device according to claim 11, wherein the intermediate layer is a silicon dioxide film.
The substrate includes a second surface facing the first surface,
A supporting substrate which is silicon having a thickness of more than 1 λ bonded directly or indirectly to the second surface;
It includes an interdigital capacitance unit including a plurality of capacitance unit electrode fingers connected in parallel to the IDT electrode, and the arrangement direction of the capacitance unit electrode fingers is with respect to the arrangement direction of the electrode fingers of the IDT electrode The elastic wave device according to claim 1, which forms an angle of 60 ° ± 5 ° or -60 ° ± 5 °.
The Euler angle of the support substrate is (-45, -54.7, ψ), and ψ is any of 0 to 20, 40 to 140 and 160 to 180. Acoustic wave element.