JPWO2021002046A1 - Bonds and seismic elements - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bonded body capable of improving the Q value of an elastic wave element. A bonded body 9A includes a support substrate 6, a piezoelectric material substrate 1A, and a multilayer film 2 between the support substrate and the piezoelectric material substrate. The multilayer film 2 has a structure in which a first layer 2a having a composition of SiOx and a second layer 2b made of a metal oxide are alternately laminated, and x in SiOx has a value larger than 2. .. [Selection diagram] Fig. 3

Description

The present invention relates to a bonded body of a piezoelectric material substrate and a supporting substrate and an elastic wave element.

Surface acoustic wave devices that can function as filter elements and oscillators used in mobile phones, etc., and surface acoustic wave devices such as Lamb wave elements and thin film resonators (FBAR) that use piezoelectric thin films. Are known. As such an elastic wave device, a support substrate and a piezoelectric substrate that propagates an elastic surface wave are bonded to each other, and a comb-shaped electrode capable of exciting an elastic surface wave is provided on the surface of the piezoelectric substrate. By attaching a support substrate having a thermal expansion coefficient smaller than that of the piezoelectric substrate to the piezoelectric substrate in this way, it is possible to suppress a change in the size of the piezoelectric substrate when the temperature changes, and to obtain frequency characteristics as a surface acoustic wave device. It suppresses change.

It is known that when joining a piezoelectric substrate and a silicon substrate, a silicon oxide film is formed on the surface of the piezoelectric substrate, and the piezoelectric substrate and the silicon substrate are directly bonded via the silicon oxide film (Patent Document 1). .. At the time of this bonding, the surface of the silicon oxide film and the surface of the silicon substrate are irradiated with a plasma beam to activate the surfaces, and direct bonding is performed (plasma activation method).

Further, a so-called FAB (Fast Atom Beam) method of direct bonding is known (Patent Document 2). In this method, each bonding surface is activated by irradiating each bonding surface with a neutralized atomic beam at room temperature, and the bonding is performed directly.

_{Further, an intermediate layer made of Ta 2} O ₅ or the like is provided between the piezoelectric single crystal substrate and the support substrate, and the surface is activated by irradiating the intermediate layer and the support substrate with a neutralizing beam, respectively, to directly bond them. It has been proposed to do so (Patent Document 3).

Patent Document 4 proposes a structure in which a multilayer film in which a plurality of _{SiO 2} layers and Ta ₂ O ₅ layers are laminated is provided between a support substrate and a piezoelectric material substrate.

U.S. Pat. No. 7213314B2 Japanese Patent Application Laid-Open No. 2014-086400 WO 2017/163722 A1 WO 2018/154950 A1

In the elastic wave element of Patent Document 3, characteristics such as Q value were improved for medium frequencies (for 4G of 0.7 to 3.5 GHz, etc.). However, it was found that there was little improvement in the Q value for high frequencies (for 5G at 3.5 to 6 GHz, etc.).

_{Further, as described in Patent Document 4, in an elastic wave element in which a multilayer film of SiO 2} / Ta ₂ O ₅ is inserted between a support substrate and a piezoelectric material substrate, the elastic wave element moves from the piezoelectric material substrate to the support substrate. The elastic wave that leaks is reflected by the multilayer film to reduce loss. However, for high frequencies (for 5G of 3.5 to 6 GHz, etc.), it has become clear that the improvement of the Q value is not always sufficient even with such an elastic wave element.

An object of the present invention is to provide a bonded body capable of improving the Q value of an elastic wave element.

The present invention is a support substrate,
It comprises a piezoelectric material substrate and a multilayer film between the support substrate and the piezoelectric material substrate.
The multilayer film has _{a structure in which a first layer having a composition of SiO x} and a second layer made of a metal oxide are alternately laminated, and _x in SiO x has a value larger than 2. It is characterized by that.

The present invention relates to an elastic wave device, which comprises the joint and electrodes provided on the piezoelectric material substrate.

As described in Patent Document 4, the present inventor _{has inserted a multilayer film of SiO 2} / Ta ₂ O ₅ between a support substrate and a piezoelectric material substrate for high frequencies (3.5 to 6 GHz). For 5G, etc.), we examined the reason why the Q value improvement is not always sufficient. As a result, it is difficult to obtain a desired Q value in the high frequency region because the quality of the multilayer film suitable for medium frequency (4G, etc.) and the quality of the multilayer film suitable for higher frequency (5G, etc.) are different. I guessed it was.

Based on these speculations, the present inventor has come up with the idea of changing the silicon oxide constituting the first layer constituting the multilayer film to an oxygen-rich composition, and actually implements such a bonded body and an elastic wave element using the same. I tried to make a prototype. As a result, it was found that the Q value was further improved. In particular, we have found that a high Q value can be obtained even in the high frequency band (5G band), and have reached the present invention.

(A) shows a state in which the multilayer film 2 is provided on the piezoelectric material substrate 1, (b) shows a state in which the bonding layer 4 is provided on the multilayer film 2, and (c) shows a state in which the bonding layer 4 is provided. Shows the activated state of the surface of. (A) shows a state in which the surface of the support substrate 6 is activated, and (b) shows a joint 9 of the support substrate and the piezoelectric material substrate. (A) shows a state in which the piezoelectric material substrate 1A of the bonded body 9A is thinned by processing, and (b) shows a state in which an electrode is provided on the bonded body 9A. (A) shows a bonded body 9B obtained by directly bonding the bonded layer 4 provided on the multilayer film and the bonded layer 14 provided on the support substrate 6, and (b) is the piezoelectric of the bonded body 9B. The elastic wave element 10B obtained by providing the electrode 11 on the material substrate 1A is shown. (A) shows a bonded body 9C obtained by directly bonding the multilayer film 2 and the support substrate 6, and (b) shows a state in which an electrode is provided on the piezoelectric material substrate 1A of the bonded body 9C. ..

Hereinafter, the present invention will be described in detail with reference to the drawings as appropriate.
As shown in FIG. 1A, the piezoelectric material substrate 1 has a pair of surfaces 1a and 1b. A multilayer film 2 is formed on one of the surfaces 1a. In this example, the multilayer film 2 is obtained by alternately providing the first layer 2a and the second layer 2b on the piezoelectric material substrate 1.

As shown in FIG. 1 (b), the bonding layer 4 can be further provided on the surface 3 of the multilayer film 2. In this case, as shown in FIG. 1 (c), the surface of the bonding layer 4 is irradiated with a neutralizing beam as shown by an arrow A to activate the surface of the bonding layer 4 with the activated surface 5. can do.

On the other hand, as shown in FIG. 2A, the surface of the support substrate 6 is irradiated with a neutralizing beam as shown by an arrow B to activate the surface of the support substrate 6 to form an activated surface 6a. Next, as shown in FIG. 2 (b), the activated surface 5 of the first bonding layer 4 and the activated surface 6a of the support substrate 6 are brought into direct contact with each other and pressure is applied to obtain FIG. 2 (b). A conjugate 9 is obtained as shown. Arrow C is the junction boundary.

In a preferred embodiment, the surface 1b of the piezoelectric material substrate 1 of the bonded body 9 is further polished to reduce the thickness of the piezoelectric material substrate 1A as shown in FIG. 3A to reduce the thickness of the piezoelectric material substrate 1A. obtain. 1c is a polished surface. In FIG. 3B, the elastic wave element 10A is manufactured by forming a predetermined electrode 11 on the polished surface 1c of the piezoelectric material substrate 1A.

In a preferred embodiment, the bonding layer 14 is also provided on the support substrate 6, and the activated surface 12 thereof is directly bonded to the bonding layer 14 on the multilayer film. As a result, the bonded body 9B as shown in FIG. 4A is obtained. The junction boundary is indicated by the arrow C. As shown in FIG. 4B, the elastic wave element 10B can be obtained by providing the electrode 11 on the piezoelectric material substrate 1A of this bonded body.

Further, in a preferred embodiment, the support substrate and the multilayer film are directly bonded to each other. As a result, the bonded body 9C as shown in FIG. 5 (a) is obtained. The junction boundary is indicated by the arrow C. As shown in FIG. 5B, the elastic wave element 10C can be obtained by providing the electrode 11 on the piezoelectric material substrate 1A of this bonded body.

In the present invention, the multilayer film provided between the support substrate and the piezoelectric material substrate _{alternates between a first layer having a composition of SiO x} (x is larger than 2) and a second layer made of a metal oxide. It has a structure laminated on.

That is, it has an oxygen-rich composition in which x is larger than 2 in _{SiO x} constituting the first layer. By making x larger than 2, the Q value becomes high when applied to an elastic wave element. From this point of view, x is preferably 2.03 or more, more preferably 2.05 or more, and even more preferably 2.10 or more. Further, when x exceeds 2.50, the Q value decreases, so it is preferably 2.50 or less, preferably 2.45 or less, and even more preferably 2.40 or less.

The metal oxide constituting the second layer is not particularly limited, but an oxide of one or more metals selected from the group consisting of tantalum, hafnium, zirconium, titanium and magnesium is preferable, and tantalum oxide, hafnium oxide, and the like. Zirconium oxide is particularly preferred. The composition of these metal oxides is not particularly limited, but Ta ₂ O _y (4.5 ≦ y ≦ 5), HfO _z and ZrO _z (1.8 ≦ z ≦ 2) are particularly preferable.

The composition of each layer constituting the multilayer film is measured as follows.
Under the conditions for performing multi-layer film formation, single-layer film formation is performed on a Si substrate with a thickness of 150 nm and the film formation conditions are changed. After that, the RBS spectrum was acquired by the Pelletron 3SDH manufactured by National Electrostatics Corporation by the RBS (Rutherford Backscattering Spectrometry) method, and the spectrum was calculated from the spectrum obtained by theoretical calculation. In the case of SiOx, it is carried out under the following measurement conditions.
Incident ion: ⁴ He ⁺⁺
Incident energy: 2300keV
Incident angle: 0deg
Scattering angles: 160 and 120deg
Sample current: 7nA
Beam diameter: 2mmΦ
In-plane rotation: No irradiation amount: 60 μC

The method for forming each layer of the multilayer film is not limited, and examples thereof include a sputtering method, a chemical vapor deposition method (CVD), and thin film deposition. Here, particularly preferably, the oxygen ratio of each layer can be controlled by adjusting the amount of oxygen gas flowing into the chamber during reactive sputtering in which the sputtering targets are Si, Ta, Hf, and Zr. be.

The specific manufacturing conditions of each layer constituting the multilayer film are appropriately selected because they depend on the chamber specifications, but in a preferable example, the total pressure is 0.28 to 0.34 Pa and the oxygen partial pressure is 1.2 × ^10-3 to 1.2 × 10-3. The film thickness is 5.7 × ^10-2 Pa, and the film formation temperature is between room temperature and 200 ° C.

In the present invention, a multilayer film formed by alternately laminating the first layer and the second layer is provided between the piezoelectric material substrate and the support substrate. Further, it is preferable that the number of layers of the first layer and the number of layers of the second layer are two or more, respectively. However, even if the number of layers of the first layer and the second layer is too large, the action and effect do not change significantly. Therefore, from this viewpoint, the total number of the first layer and the second layer is preferably 10 or less, respectively.

In a preferred embodiment, one or more bonding layers can be provided between the piezoelectric material substrate and the support substrate. Examples of the material of such a bonding layer include the following.
Si _(1-v) O _v, Ta ₂ O ₅ , Al ₂ O _3, Nb ₂ O ₅ , TiO ₂ .

In more preferred embodiments, the bonding layer provided between the supporting substrate and the piezoelectric material substrate _has a composition of _{Si (1-v) O v} (0.008 ≦ v ≦ 0.408).

This composition has a _{considerably lower oxygen ratio than SiO 2} (corresponding to v = 0.667). Such silicon oxide Si _(1-v) of the composition O _v be to further interposed bonding layer made of, it is possible to further enhance the insulating properties of the bonding layer.

In the composition of the _{Si (1-v) O} v constituting each bonding layer, when v is less than 0.008, the electrical resistance is lowered in the bonding layer. Therefore, v is preferably 0.008 or more, more preferably 0.010 or more, particularly preferably 0.020 or more, and particularly preferably 0.024 or more. Further, since the bonding strength is further improved by setting v to 0.408 or less, it is preferable to set v to 0.408 or less, and further preferably 0.225 or less.

The thickness of each bonding layer is not particularly limited, but is preferably 0.01 to 10 μm, more preferably 0.01 to 0.5 μm from the viewpoint of manufacturing cost.

The film forming method of each bonding layer is not limited, and examples thereof include a sputtering method, a chemical vapor deposition method (CVD), and thin film deposition. Here, particularly preferably, the oxygen ratio (v) of each bonding layer can be controlled by adjusting the amount of oxygen gas flowing into the chamber during reactive sputtering using Si as the sputtering target. ..

The specific manufacturing conditions of each bonding layer depend on the chamber specifications and are appropriately selected. In a preferred example, the total pressure is 0.28 to 0.34 Pa and the oxygen partial pressure is 1.2 × ^{10-3 to} 5.7. Set to × ^10-2 Pa and set the film formation temperature to room temperature. Further, as the Si target, B-doped Si can be exemplified.
The oxygen concentration in the junction layer is measured by EDS under the following conditions.
measuring device:
Elemental analysis is performed using an elemental analyzer (JEOL JEM-ARM200F).
Measurement condition:
The sample sliced by the FIB (focused ion beam) method is observed at an acceleration voltage of 200 kV.

In the present invention, the support substrate may be composed of a single crystal or a polycrystal. The material of the support substrate is preferably selected from the group consisting of silicon, sialon, sapphire, cordierite, mullite and alumina. Alumina is preferably translucent alumina.

The silicon may be single crystal silicon, polycrystalline silicon, or high resistance silicon.

Sialon is a ceramic obtained by sintering a mixture of silicon nitride and alumina, and has the following composition.
Si _6-w Al _w O _w N _8-w
That is, Sialon has a composition in which alumina is mixed in silicon nitride, and w indicates the mixing ratio of alumina. w is more preferably 0.5 or more. Further, w is more preferably 4.0 or less.

Sapphire is a single crystal having a composition of _{Al 2} O ₃ , and alumina is a polycrystal having a composition of _{Al 2} O _3. Cordierite is a ceramic having a composition of _{2MgO · 2Al 2 O 3 · 5SiO} 2. Mullite is a ceramic having a composition in the range of _{3Al 2 O 3 · 2SiO 2 ~2Al} 2 O 3 · SiO 2.

Piezoelectric material The material of the substrate is not limited as long as it has the required piezoelectricity, but a single crystal having a composition of _{LiAO 3 is preferable.} Here, A is one or more elements selected from the group consisting of niobium and tantalum. Therefore, LiAO ₃ may be lithium niobate, lithium tantalate, or a lithium niobate-lithium tantalate solid solution.

Hereinafter, each component of the present invention will be further described.
The application of the bonded body of the present invention is not particularly limited, and for example, it can be suitably applied to elastic wave elements and optical elements.
As the surface acoustic wave element, an elastic surface wave device, a Lamb wave element, a thin film resonator (FBAR) and the like are known. For example, a surface acoustic wave device has an IDT (Interdigital Transducer) electrode (also called a comb-shaped electrode or a surface acoustic wave) on the input side that excites a surface acoustic wave and an output side that receives a surface acoustic wave on the surface of a piezoelectric material substrate. The IDT electrode of the above is provided. When a high-frequency signal is applied to the IDT electrode on the input side, an electric field is generated between the electrodes, and surface acoustic waves are excited and propagate on the piezoelectric material substrate. Then, the propagated surface acoustic wave can be taken out as an electric signal from the IDT electrode on the output side provided in the propagation direction.

A metal film may be provided on the bottom surface of the piezoelectric material substrate. The metal film plays a role of increasing the electromechanical coupling coefficient near the back surface of the piezoelectric material substrate when a Lamb wave element is manufactured as an elastic wave device. In this case, the Lamb wave element has a structure in which comb-tooth electrodes are formed on the surface of the piezoelectric material substrate and the metal film of the piezoelectric material substrate is exposed by the cavity provided in the support substrate. Examples of the material of such a metal film include aluminum, aluminum alloy, copper, and gold. When manufacturing a Lamb wave element, a composite substrate having a piezoelectric material layer having no metal film on the bottom surface may be used.

Further, a metal film and an insulating film may be provided on the bottom surface of the piezoelectric material substrate. The metal film acts as an electrode when a thin film resonator is manufactured as an elastic wave device. In this case, the thin film resonator has a structure in which electrodes are formed on the front and back surfaces of the piezoelectric material substrate and the metal film of the piezoelectric material substrate is exposed by making the insulating film a cavity. Examples of the material of such a metal film include molybdenum, ruthenium, tungsten, chromium, and aluminum. Examples of the material of the insulating film include silicon dioxide, phosphorus silica glass, and boron phosphorus silica glass.

Further, examples of the optical element include an optical switching element, a wavelength conversion element, and an optical modulation element. Further, a periodic polarization inversion structure can be formed in the piezoelectric material substrate.

When the object of the present invention is an elastic wave element and the material of the piezoelectric material substrate is lithium tantalate, 123 to 133 from the Y axis to the Z axis centering on the X axis which is the propagation direction of the elastic surface wave. It is preferable to use the one rotated by ° (for example, 128 °) because the propagation loss is small.
When the piezoelectric material substrate is made of lithium niobate, the one rotated by 86 to 94 ° (for example, 90 °) from the Y axis to the Z axis around the X axis, which is the propagation direction of surface acoustic waves. It is preferable to use it because the propagation loss is small. Further, the size of the piezoelectric material substrate is not particularly limited, but is, for example, 50 to 150 mm in diameter and 0.2 to 60 μm in thickness.

In order to obtain the conjugate of the present invention, the following method is preferable.
First, the surfaces to be bonded (the surface of the multilayer film, the surface of the bonding layer, the surface of the piezoelectric material substrate, the surface of the supporting substrate) are flattened to obtain a flat surface. Here, methods for flattening each surface include lap polishing and chemical mechanical polishing (CMP). The flat surface preferably has Ra ≦ 1 nm, and more preferably 0.3 nm or less.

Next, each surface of each bonding layer is washed to remove the residue of the abrasive and the processing alteration layer. Methods for cleaning the surface include wet cleaning, dry cleaning, scrub cleaning, and the like, but scrub cleaning is preferable in order to obtain a clean surface easily and efficiently. In this case, it is particularly preferable to use Sunwash LH540 as a cleaning solution and then wash with a scrub washing machine using a mixed solution of acetone and IPA.

Next, each joint surface is activated by irradiating each joint surface with a neutralizing beam.
When the surface is activated by the neutralized beam, it is preferable to generate and irradiate the neutralized beam by using an apparatus as described in Patent Document 2. That is, a saddle field type high-speed atomic beam source is used as the beam source. Then, an inert gas is introduced into the chamber, and a high voltage is applied to the electrodes from a DC power source. As a result, the electron e moves due to the saddle field type electric field generated between the electrode (positive electrode) and the housing (negative electrode), and a beam of atoms and ions due to the inert gas is generated. Of the beams that reach the grid, the ion beam is neutralized by the grid, so that the beam of neutral atoms is emitted from the high-speed atomic beam source. The atomic species constituting the beam is preferably an inert gas (argon, nitrogen, etc.).
The voltage at the time of activation by beam irradiation is preferably 0.5 to 2.0 kV, and the current is preferably 50 to 200 mA.

Then, in a vacuum atmosphere, the activated joint surfaces are brought into contact with each other and joined. The temperature at this time is room temperature, but specifically, it is preferably 40 ° C. or lower, and more preferably 30 ° C. or lower. Further, the temperature at the time of joining is particularly preferably 20 ° C. or higher and 25 ° C. or lower. The pressure at the time of joining is preferably 100 to 20000 N.

(Experiment A)
A surface acoustic wave element was prototyped by the method described with reference to FIGS. 1 to 3.
Specifically, a lithium tantalate substrate (LT substrate) having an OF portion, a diameter of 4 inches, and a thickness of 250 μm was used as the piezoelectric material substrate 1. In the LT substrate, the propagation direction of surface acoustic waves (SAW) is X, and the cut-out angle is 128 ° Y-cut X propagation L, which is a rotating Y-cut plate.
A T substrate was used. The surface 1a of the piezoelectric material substrate 1 was mirror-polished so that the arithmetic average roughness Ra was 0.3 nm. However, Ra is measured with an atomic force microscope (AFM) in a field of view of 10 μm × 10 μm.

Next, the first layer 2a and the second layer 2b were alternately formed on the piezoelectric material substrate 1 in pairs (4 layers in total) by a sputtering method to obtain a multilayer film 2. However, the composition of SiOx constituting the first layer was changed as shown in Table 1. The composition of the second layer was hafnium oxide HfO ₂ . The thickness of the first layer and the thickness of the second layer were set to 150 nm, respectively. The film forming methods for the first layer and the second layer are as described above. In addition, each composition was adjusted by changing the oxygen ratio in the atmosphere.

Next, Si (1-x) Ox (x = 0.10) (50 nm) was formed as the bonding layer 4 on the multilayer film 2. Specifically, the DC sputtering method was used, and boron-doped Si was used as the target. In addition, oxygen gas was introduced as an oxygen source. At this time, the total pressure of the atmosphere in the chamber and the partial pressure of oxygen were adjusted by adjusting the amount of oxygen gas introduced. The arithmetic mean roughness Ra of the surface of the bonding layer 4 was 0.2 to 0.6 nm. Next, the bonding layer 4 was subjected to chemical mechanical polishing (CMP) to adjust the film thickness to 80 to 190 nm and Ra to 0.08 to 0.4 nm.

On the other hand, as the support substrate 6, a support substrate 6 having an orientation flat (OF) portion and made of silicon having a diameter of 4 inches and a thickness of 500 μm was prepared. The surface of the support substrate 6 is finished by chemical mechanical polishing (CMP), and the arithmetic average roughness Ra is 0.2 nm.

Next, the surface of the bonding layer 4 and the surface of the Si substrate which is the support substrate 6 were irradiated with a neutralizing beam to activate the surfaces and directly bonded.
Specifically, the surface of the bonding layer 4 and the surface of the support substrate 6 were washed to remove stains, and then introduced into a vacuum chamber. ^{After vacuuming to 10-6} Pa, each surface was irradiated with a high-speed atomic beam (acceleration voltage 1 kV, Ar flow rate 27 sccm) for 120 seconds. Then, the beam irradiation surface (activated surface) of the bonding layer 4 and the activated surface of the support substrate 6 were brought into contact with each other, and then pressurized at 10000 N for 2 minutes for bonding. Then, the obtained conjugates of each example were heated at 100 ° C. for 20 hours.

Next, the surface of the piezoelectric material substrate 1 was ground and polished so that the thickness was 1 μm from the initial 250 μm. Next, an electrode pattern for measurement was formed to obtain a surface acoustic wave element. Then, the Q values at a frequency of 5.5 GHz are measured and shown in Table 1.

However, the Q value was measured as follows.
A surface acoustic wave resonator was created on the wafer, and the frequency characteristics were measured using a network analyzer. Thus obtained frequency characteristics from the resonance frequency f _r, and calculates the half width Delta] f _r, to obtain a Q value by obtaining f _r / _{Δf r.}

As shown in Table 1, in Comparative Examples 1 and 2, x = 1.88 and 1.97, but all had the same Q value.
On the other hand, in Examples 1, 2, 3, 4, and 5, x = 2.01, 2.05, 2.13, 2.21, 2.45, but the Q value is larger than that of Comparative Example 1. Improved.
In Comparative Example 3, x = 2.52, but the Q value was deteriorated as compared with Comparative Example 1. In this case, it is probable that the film density had decreased.

(Experiment B)
In Experiment A, the material of the second layer was changed _{from hafnium oxide to tantalum oxide Ta 2} O _5. The composition of SiOx, which is the material of the first layer, was the same as in Experiment A. Then, when the Q value of the obtained element was measured, the same result as in Experiment A was obtained.

(Experiment C)
In Experiment A, the material of the second layer was changed _{from hafnium oxide to zirconium oxide (ZrO 2).} The composition of SiOx, which is the material of the first layer, was the same as in Experiment A. Then, when the Q value of the obtained element was measured, the same result as in Experiment A was obtained.

The present invention is a support substrate,
It comprises a piezoelectric material substrate and a multilayer film between the support substrate and the piezoelectric material substrate.
The multilayer film has _{a structure in which a first layer having a composition of SiO x} and a second layer made of a metal oxide are alternately laminated, and _x in SiO x is 2.01 or more and 2.50 or less. It is characterized by being.

In the present invention, the multilayer film provided between the support substrate and the piezoelectric material substrate is _{composed of a first layer having a SiO x} composition (x is 2.01 or more and 2.50 or less ) and a metal oxide. It has a structure in which the second layer is alternately laminated.

That is, it has an oxygen-rich composition in which x is 2.01 or more _{in SiO x} constituting the first layer. By making x larger than 2, the Q value becomes high when applied to an elastic wave element. From this point of view, x is preferably 2.03 or more, more preferably 2.05 or more, and even more preferably 2.10 or more. Further, when x exceeds 2.50, the Q value decreases, so the value is 2.50 or less, preferably 2.45 or less, and more preferably 2.40 or less.

The present invention is a support substrate,
It comprises a piezoelectric material substrate having a thickness of 0.2 to 60 μm, which is made of lithium niobate, lithium tantalate or a solid solution of lithium niobate-lithium tantalate , and a multilayer film between the support substrate and the piezoelectric material substrate. and the assembly that,
With the electrode provided on the piezoelectric material substrate
The present invention relates to a surface acoustic wave element for surface acoustic waves having a frequency of 3.5 to 6 GHz.

Here, the multilayer film is SiO _x It has a structure in which a first layer having the above composition and a second layer made of a metal oxide are alternately laminated, and SiO _x X is 2.01 or more and 2.50 or less, and the metal oxide is selected from the group consisting of tantalum oxide, hafnium oxide and zirconium oxide.

As the metal oxide constituting the second layer, tantalum oxide, hafnium oxide, and zirconium oxide are particularly preferable. The composition of these metal oxides is not particularly limited, but Ta ₂ O _y (4.5 ≦ y ≦ 5), HfO _z and ZrO _z (1.8 ≦ z ≦ 2) are particularly preferable.

The material of the piezoelectric material substrate is preferably a single crystal having a composition of _{LiAO 3.} Here, A is one or more elements selected from the group consisting of niobium and tantalum. Therefore, LiAO ₃ may be lithium niobate, lithium tantalate, or a lithium niobate-lithium tantalate solid solution.

Hereinafter, each component of the present invention will be further described.
The application of the joined body of the present invention is a surface acoustic wave device. Surface acoustic wave devices include input-side IDT (Interdigital Transducer) electrodes (also called comb-shaped electrodes or surface acoustic waves) that excite surface acoustic waves and output-side IDTs that receive surface acoustic waves on the surface of a surface acoustic wave. It is provided with an electrode. When a high-frequency signal is applied to the IDT electrode on the input side, an electric field is generated between the electrodes, and surface acoustic waves are excited and propagate on the piezoelectric material substrate. Then, the propagated surface acoustic wave can be taken out as an electric signal from the IDT electrode on the output side provided in the propagation direction.

Piezoelectric material When the substrate material is lithium tantalate, it is rotated 123 to 133 ° (for example, 128 °) from the Y axis to the Z axis around the X axis, which is the propagation direction of surface acoustic waves. Is preferable because the propagation loss is small.
When the piezoelectric material substrate is made of lithium niobate, the one rotated by 86 to 94 ° (for example, 90 °) from the Y axis to the Z axis around the X axis, which is the propagation direction of surface acoustic waves. It is preferable to use it because the propagation loss is small. Further, the size of the piezoelectric material substrate is not particularly limited, but is, for example, 50 to 150 mm in diameter and 0.2 to 60 μm in thickness.

Claims (8)

Support board,
It comprises a piezoelectric material substrate and a multilayer film between the support substrate and the piezoelectric material substrate.
The multilayer film has _{a structure in which a first layer having a composition of SiO x} and a second layer made of a metal oxide are alternately laminated, and _x in SiO x has a value larger than 2. A joint characterized by that. The bonded body according to claim 1, wherein x satisfies 2.03 ≦ x ≦ 2.50 in the first layer. The conjugate according to claim 1 or 2, wherein the metal oxide is selected from the group consisting of tantalum oxide, hafnium oxide and zirconium oxide. The bonded body according to any one of claims 1 to 3, wherein the thickness of the first layer and the thickness of the second layer are 20 nm or more and 500 nm or less, respectively. The bonded body according to any one of claims 1 to 4, wherein the multilayer film has two or more layers of the first layer and the second layer, respectively. Between the supporting substrate and the piezoelectric material _substrate, characterized in that it comprises a bonding layer having a composition of _{Si (1-v) O v} (0.008 ≦ v ≦ 0.408), wherein The bonded body according to any one of items 1 to 5. An elastic wave element comprising the bonded body according to any one of claims 1 to 6 and an electrode provided on the piezoelectric material substrate. The elastic wave element according to claim 7, wherein the elastic wave element has a frequency of 3.5 to 6 GHz.

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