JP7312562B2 - Acoustic wave resonator and its manufacturing method, filter and multiplexer - Google Patents

Description

The present invention relates to an acoustic wave resonator, its manufacturing method, filter and multiplexer, and more particularly to an acoustic wave resonator having a pair of comb-shaped electrodes, its manufacturing method, filter and multiplexer.

A surface acoustic wave resonator is known as an acoustic wave resonator used in communication devices such as smartphones. It is known to bond a piezoelectric substrate forming a surface acoustic wave resonator to a support substrate. It is known to provide a silicon oxide film between a piezoelectric substrate and a support substrate (eg Patent Documents 1 and 2).

JP 2015-115870 A WO2017/043427

In Patent Documents 1 and 2, the silicon oxide film provided between the piezoelectric substrate and the supporting substrate is a film formed on the supporting substrate by CVD (Chemical Vapor Deposition), sputtering or vacuum deposition. Such a silicon oxide film has an unstable crystal structure, and is not sufficiently effective in improving the temperature characteristics of the acoustic wave resonator. Moreover, it is required to increase the strength of the support substrate.

The present invention has been made in view of the above problems, and an object of the present invention is to improve temperature characteristics and strength.

The present invention comprises: a support substrate that is a single crystal or polycrystal having a Young's modulus larger than that of quartz; an amorphous quartz substrate provided on the support substrate; a piezoelectric substrate that is provided on the quartz substrate and is a single crystal containing lithium tantalate or lithium niobate as a main component; a second amorphous layer mainly composed of a constituent element of the piezoelectric substrate; a pair of comb-shaped electrodes provided on the piezoelectric substrate;an aluminum oxide layer provided between the quartz substrate and the second amorphous layer, in contact with the quartz substrate, and thinner than the quartz substrate;An elastic wave resonator comprising

In the above structure, the support substrate may be a sapphire substrate, an alumina substrate, a silicon substrate, or a silicon carbide substrate.

In the above structure, the quartz substrate may be thicker than the piezoelectric substrate, and the support substrate may be thicker than the quartz substrate.

In the above structure, the aluminum oxide layer may have a thickness of 100 nm or less.

In the above structure, a third amorphous layer is provided between the aluminum oxide layer and the second amorphous layer, is in contact with the aluminum oxide layer and the second amorphous layer, and contains aluminum and oxygen as main components.

In the above structure, the thickness of the first amorphous layer and the thickness of the second amorphous layer may be 10 nm or less.

The present invention comprises the steps of: bonding an amorphous quartz substrate to a monocrystalline or polycrystalline support substrate having a Young's modulus greater than that of quartz; forming an aluminum oxide layer thinner than the quartz substrate on a surface of the quartz substrate opposite to the support substrate; bonding a single crystal piezoelectric substrate containing lithium tantalate or lithium niobate as a main component to the surface of the aluminum oxide layer opposite to the support substrate; forming a pair of comb-shaped electrodes on a surface of the piezoelectric substrate opposite to the quartz substrate; A method of manufacturing an acoustic wave resonator including

In the above configuration, the step of bonding the piezoelectric substrate to the surface of the aluminum oxide layer opposite to the quartz substrate may include a step of activating the surfaces of the aluminum oxide layer and the piezoelectric substrate and bonding the activated surfaces of the aluminum oxide layer and the piezoelectric substrate at room temperature.

The present invention is a filter including the elastic wave resonator.

The present invention is a multiplexer including the above filters.

According to the present invention, temperature characteristics and strength can be improved.

FIG. 1(a) is a plan view of the elastic wave resonator in Example 1, and FIG. 1(b) is a cross-sectional view taken along the line AA of FIG. 1(a). FIGS. 2A to 2C are cross-sectional views (part 1) showing the method of manufacturing the elastic wave resonator according to the first embodiment. 3A to 3C are cross-sectional views (part 2) showing the method of manufacturing the elastic wave resonator according to the first embodiment. FIGS. 4A to 4D are schematic diagrams showing a bonding method of substrates in Example 1. FIG. FIG. 5 is a cross-sectional view of an acoustic wave resonator according to Example 1. FIG. 6A to 6C are cross-sectional views showing a method of manufacturing an acoustic wave resonator according to Example 2. FIG. FIG. 7 is a cross-sectional view of an acoustic wave resonator according to Example 2. FIG. FIG. 8 is a diagram showing the bonding strength with respect to the thickness T3 of the aluminum oxide layer. 9A is a circuit diagram of a filter according to Example 3, and FIG. 9B is a circuit diagram of a duplexer according to Modification 1 of Example 3. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1(a) is a plan view of the elastic wave resonator in Example 1, and FIG. 1(b) is a cross-sectional view taken along the line AA of FIG. 1(a). The arrangement direction of the electrode fingers is the X direction, the extending direction of the electrode fingers is the Y direction, and the stacking direction of the supporting substrate and the piezoelectric substrate is the Z direction. The X-direction, Y-direction and Z-direction do not necessarily correspond to the X-axis direction and Y-axis direction of the crystal orientation of the piezoelectric substrate. When the piezoelectric substrate is a rotated Y-cut X-propagation substrate, the X-direction is the X-axis direction of the crystal orientation.

As shown in FIGS. 1A and 1B, a quartz substrate 11 is provided under the piezoelectric substrate 12 . A support substrate 10 is provided under the quartz substrate 11 . The thicknesses of the support substrate 10, the quartz substrate 11 and the piezoelectric substrate 12 are assumed to be T0, T1 and T2, respectively.

An elastic wave resonator 20 is provided on the piezoelectric substrate 12 . Acoustic wave resonator 20 has IDT 22 and reflector 24 . The reflectors 24 are provided on both sides of the IDT (Inter Digital Transducer) 22 in the X direction. IDT 22 and reflector 24 are formed by metal film 14 on piezoelectric substrate 12 .

The IDT 22 includes a pair of comb electrodes 18 facing each other. The comb-shaped electrode 18 includes a plurality of electrode fingers 15 and a busbar 16 to which the plurality of electrode fingers 15 are connected. A crossing region 25 is a region where the electrode fingers 15 of the pair of comb-shaped electrodes 18 intersect. The length of the intersection region 25 is the aperture length. A pair of comb-shaped electrodes 18 are provided facing each other such that the electrode fingers 15 are substantially alternated in at least a portion of the intersection region 25 . Elastic waves excited by the plurality of electrode fingers 15 in the intersecting region 25 mainly propagate in the X direction. The pitch of the electrode fingers 15 of one comb-shaped electrode of the pair of comb-shaped electrodes 18 is approximately the wavelength λ of the elastic wave. The wavelength λ of the elastic wave is approximately the pitch of two electrode fingers 15 . The reflector 24 reflects the elastic waves (surface acoustic waves) excited by the electrode fingers 15 of the IDT 22 . This confines the acoustic wave within the intersection region 25 of the IDT 22 .

The piezoelectric substrate 12 is a single-crystal lithium tantalate (LiTaO ₃ ) substrate or a single-crystal lithium niobate (LiNbO ₃ ) substrate, such as a rotated Y-cut X-propagating lithium tantalate substrate or a rotated Y-cut X-propagating lithium niobate substrate. The quartz substrate 11 is an amorphous silicon oxide substrate whose main component is silicon oxide (SiO ₂ ).

The support substrate 10 is a substrate having a Young's modulus and thermal conductivity greater than those of the quartz substrate 11, such as a sapphire substrate, an alumina substrate, a silicon substrate, and a silicon carbide substrate. The sapphire substrate is a single crystal aluminum oxide ( _Al2O3 ) _substrate . The alumina substrate is _a polycrystalline aluminum oxide ( _Al2O3 ) substrate. The silicon substrate is a monocrystalline or polycrystalline silicon (Si) substrate. The silicon carbide substrate is a monocrystalline or polycrystalline silicon carbide (SiC) substrate.

The metal film 14 is a film containing, for example, Al (aluminum), Cu (copper), or Mo (molybdenum) as a main component, such as an Al film, a Cu film, or a Mo film. An adhesion film such as a Ti (titanium) film or a Cr (chromium) film may be provided between the electrode fingers 15 and the piezoelectric substrate 12 . The adhesion film is thinner than the electrode finger 15 . An insulating film may be provided to cover the electrode fingers 15 . The insulating film functions as a protective film or temperature compensating layer.

The thickness T0 is, for example, 50 μm to 500 μm. The thickness T1 is, for example, 1 μm to 100 μm. The thickness T2 is, for example, 0.5 μm to 20 μm, and is, for example, equal to or less than the wavelength λ of elastic waves. The wavelength λ of elastic waves is, for example, 1 μm to 6 μm. The number of pairs of two electrode fingers 15 is, for example, 20 to 300 pairs. The duty ratio of the IDT 22 is the thickness of the electrode fingers 15/the pitch of the electrode fingers 15, and is, for example, 30% to 80%. The aperture length of the IDT 22 is, for example, 10λ to 50λ.

[Manufacturing method of Example 1]
2(a) to 3(c) are cross-sectional views showing the method of manufacturing the elastic wave resonator according to the first embodiment. As shown in FIG. 2A, the upper surface of the support substrate 10 and the lower surface of the quartz substrate 11 are irradiated with ions 54 . Thereby, the upper surface of the support substrate 10 and the lower surface of the quartz substrate 11 are activated.

As shown in FIG. 2B, the upper surface of the support substrate 10 and the lower surface of the quartz substrate 11 are bonded at room temperature. As shown in FIG. 2C, the upper surface of the quartz substrate 11 is flattened by, for example, CMP (Chemical Mechanical Polishing). As a result, the thickness of the quartz substrate 11 becomes T1.

As shown in FIG. 3A, the upper surface of the quartz substrate 11 and the lower surface of the piezoelectric substrate 12 are irradiated with ions 54 . Thereby, the upper surface of the quartz substrate 11 and the lower surface of the piezoelectric substrate 12 are activated.

As shown in FIG. 3B, the upper surface of the quartz substrate 11 and the lower surface of the piezoelectric substrate 12 are bonded at room temperature. As shown in FIG. 3C, the upper surface of the piezoelectric substrate 12 is flattened by, for example, CMP. As a result, the thickness of the piezoelectric substrate 12 becomes T2. After that, by forming a metal film 14 on the piezoelectric substrate 12, the elastic wave resonator shown in FIGS. 1(a) and 1(b) can be manufactured. The upper surface of the quartz substrate 11 and the lower surface of the piezoelectric substrate 12 may be bonded at room temperature, the quartz substrate 11 may be thinned, and then the upper surface of the support substrate 10 and the lower surface of the quartz substrate 11 may be bonded at room temperature.

2(a) and 2(b) and FIGS. 3(a) and 3(b), the case where the piezoelectric substrate 12 is bonded onto the quartz substrate 11 will be described as an example. FIGS. 4A to 4D are schematic diagrams showing a bonding method of substrates in Example 1. FIG.

As shown in FIG. 4(a), the quartz substrate 11 is amorphous and has atoms 50a. A natural oxide film 11 c is formed on the upper surface of the quartz substrate 11 . Natural oxide film 11c is composed of atoms 50a and oxygen.

As shown in FIG. 4B, the piezoelectric substrate 12 is a single crystal substrate, and atoms 52a of the elements forming the piezoelectric substrate 12 are regularly arranged. A natural oxide film 12 c is formed on the lower surface of the piezoelectric substrate 12 . The natural oxide film 12c is composed of atoms 52a and oxygen.

As shown in FIGS. 4A and 4B, the upper surface of the quartz substrate 11 and the lower surface of the piezoelectric substrate 12 are irradiated with ions 54 or the like in vacuum. The ions 54 are ions of an inert element (for example, rare gas element) such as Ar (argon) ions. Ions 54 or the like are irradiated as an ion beam, a neutralized beam or plasma. Thereby, the upper surface of the quartz substrate 11 and the lower surface of the piezoelectric substrate 12 are activated. When using Ar ions, for example, the Ar ion current is set to 25 mA to 200 mA, and the Ar ion irradiation time is set to about 30 seconds to 120 seconds.

An amorphous layer 11b is formed on the upper surface of the quartz substrate 11, as shown in FIG. 4(c). Amorphous layer 11 b contains atoms 50 a and ions 54 of constituent elements of quartz substrate 11 . An amorphous layer 12 a is formed on the lower surface of the piezoelectric substrate 12 . The amorphous layer 12 a contains atoms 52 a and ions 54 of the constituent elements of the piezoelectric substrate 12 . Unbonded bonds are formed (that is, activated) on the surfaces of the amorphous layers 11b and 12a.

As shown in FIG. 4(d), when the amorphous layers 11b and 12a are laminated while maintaining a vacuum, the dangling bonds are bonded to form a strong bond. Thereby, the quartz substrate 11 and the piezoelectric substrate 12 are bonded. Since such bonding is performed at room temperature (for example, 100° C. or lower and −20° C. or higher, preferably 80° C. or lower and 0° C. or higher), thermal stress can be suppressed. Whether or not the bonding is performed at normal temperature can be confirmed by the temperature dependence of the residual stress. In other words, the residual stress is the lowest at the temperature at which it is joined.

When the quartz substrate 11 and the piezoelectric substrate 12 are joined together, an amorphous layer 32 composed of the amorphous layers 11b and 12a is formed between the quartz substrate 11 and the piezoelectric substrate 12. FIG.

FIG. 5 is a cross-sectional view of an acoustic wave resonator according to Example 1. FIG. FIG. 5 illustrates an amorphous layer formed in room temperature bonding. As shown in FIG. 5, an amorphous layer 30 is provided between the support substrate 10 and the quartz substrate 11 . The amorphous layer 30 includes an amorphous layer 10 a in contact with the support substrate 10 and an amorphous layer 11 a in contact with the quartz substrate 11 . The amorphous layers 10a and 11a are in contact. An amorphous layer 32 is provided between the quartz substrate 11 and the piezoelectric substrate 12 . The amorphous layer 32 includes an amorphous layer 11 b in contact with the quartz substrate 11 and an amorphous layer 12 a in contact with the piezoelectric substrate 12 . Amorphous layers 11b and 12a are in contact with each other.

In the amorphous layer 30, the amorphous layer 10a contains constituent elements of the support substrate 10 as main components and an element (for example, Ar) for surface activation. When the supporting substrate 10 is a sapphire substrate, the amorphous layer 10a is mainly composed of Al (aluminum) and O (oxygen) and contains elements for surface activation. The amorphous layer 11a is mainly composed of Si and O and contains elements for surface activation. The amorphous layer 10 a contains almost no elements other than the constituent elements of the quartz substrate 11 among the constituent elements of the support substrate 10 . For example, the amorphous layer 10a hardly contains Si. The amorphous layer 11 a contains almost no elements other than the constituent elements of the quartz substrate 11 among the constituent elements of the support substrate 10 . For example, the amorphous layer 11a hardly contains Al.

In the amorphous layer 32, the amorphous layer 11b is mainly composed of Si and O and contains elements for surface activation. The amorphous layer 12a is mainly composed of the constituent elements of the piezoelectric substrate 12 and contains an element for surface activation. When the piezoelectric substrate 12 is a lithium tantalate substrate, the amorphous layer 12a is mainly composed of Ta (tantalum), Li (lithium) and oxygen, and contains elements for surface activation. The amorphous layer 11 b contains almost no elements other than the constituent elements of the piezoelectric substrate 12 among the constituent elements of the quartz substrate 11 . For example, the amorphous layer 11b hardly contains Ta and Li. The amorphous layer 12 a contains almost no constituent elements of the piezoelectric substrate 12 other than the constituent elements of the quartz substrate 11 . For example, the amorphous layer 12a hardly contains Si.

The thickness of the amorphous layers 10a, 11a, 11b and 12a is preferably greater than 0 nm, more preferably 0.5 nm or more. Thereby, the bondability between the support substrate 10 and the quartz substrate 11 and the bondability between the quartz substrate 11 and the piezoelectric substrate 12 can be improved. The thickness of the amorphous layers 10a, 11a, 11b and 12a is preferably 10 nm or less, more preferably 5 nm or less, and even more preferably 3 nm or less. Thereby, deterioration of the characteristics of the elastic wave resonator can be suppressed.

Support substrate 10, quartz substrate 11, piezoelectric substrate 12, amorphous layers 10a, 11a, 11b and 12a can be observed using a TEM (Transmission Electron Microscope) method. Since the amorphous layers 11a and 11b have the same constituent elements as the quartz substrate 11 and are amorphous, they may be difficult to observe with a TEM.

If the piezoelectric substrate 12 is a single crystal substrate containing lithium tantalate or lithium niobate as a main component, the coefficient of linear expansion is large. As a result, the pitch of the electrode fingers 15 changes with temperature, and the temperature coefficient of the resonance frequency and the like increases. Therefore, the piezoelectric substrate 12 is bonded to a substrate having a small coefficient of linear expansion.

Table 1 is a table showing linear expansion coefficients, thermal conductivities and Young's moduli of lithium tantalate substrates and various substrates.

As shown in Table 1, the linear expansion coefficient in the X-axis direction of the lithium tantalate substrate is 16.1 ppm/°C. The coefficient of linear expansion of the substrate to which the lithium tantalate substrate is bonded should be close to zero. From this point of view, a quartz substrate is preferable. However, quartz substrates have low thermal conductivity and Young's modulus. For this reason, the heat dissipation deteriorates. In addition, it has low strength and may be deformed or cracked due to thermal stress or the like. On the other hand, a sapphire substrate, an alumina substrate, a silicon substrate, and a silicon carbide substrate have high thermal conductivity and Young's modulus, and high heat dissipation and strength. However, the coefficient of linear expansion is larger than that of the quartz substrate, and the temperature coefficient of the resonance frequency is large.

Therefore, the piezoelectric substrate 12 is bonded onto the quartz substrate 11, and the quartz substrate 11 is bonded to the support substrate 10 having a large Young's modulus.

The quartz substrate 11 is formed by melting quartz or crystal and then solidifying it. Such a quartz glass substrate is amorphous and has a small coefficient of linear expansion as shown in Table 1. On the other hand, a silicon oxide film formed on the upper surface of the support substrate 10 or the lower surface of the piezoelectric substrate 12 using the CVD method, the sputtering method, or the vacuum deposition method does not become ideal quartz as shown in Table 1. For example, a silicon oxide film formed in this way may be a film containing amorphous and polycrystalline. Also, the composition ratio of oxygen and silicon may deviate from 2:1. Furthermore, unintended elements may be included. Furthermore, it is difficult to form the silicon oxide film thick enough to compensate for the linear expansion coefficient of the piezoelectric substrate 12 .

According to the first embodiment, as shown in FIG. 2B, an amorphous quartz substrate 11 is bonded onto a support substrate 10 of single crystal or polycrystal having a Young's modulus larger than that of quartz. As shown in FIG. 3B, a single-crystal piezoelectric substrate 12 mainly composed of lithium tantalate or lithium niobate is bonded to the surface of the quartz substrate 11 opposite to the support substrate 10 . As shown in FIG. 1B, a pair of comb-shaped electrodes 18 are formed on the surface of the piezoelectric substrate 12 opposite to the quartz substrate 11 . This makes it possible to reduce the frequency temperature coefficient of the acoustic wave resonator and increase the strength of the substrate.

By making the thermal conductivity of the support substrate 10 higher than that of quartz, heat dissipation can be improved. When a sapphire substrate, an alumina substrate, a silicon substrate, or a silicon carbide substrate is used as the support substrate 10, the strength and heat dissipation of the substrate can be improved.

When the surfaces of the support substrate 10 and the quartz substrate 11 are activated and bonded at room temperature, an amorphous layer 30 in contact with the support substrate 10 and the quartz substrate 11 is formed between the support substrate 10 and the quartz substrate 11 as shown in FIG. The amorphous layer 30 includes an amorphous layer 10a (first amorphous layer) which is in contact with the support substrate 10 and contains the constituent elements of the support substrate 10 as main components. When the surfaces of the quartz substrate 11 and the piezoelectric substrate 12 are activated and bonded at room temperature, an amorphous layer 32 in contact with the piezoelectric substrate 12 is formed between the quartz substrate 11 and the piezoelectric substrate 12 . The amorphous layer 32 includes an amorphous layer 12a (second amorphous layer) that is in contact with the piezoelectric substrate 12 and is mainly composed of the constituent elements of the piezoelectric substrate 12 .

Note that "mainly composed" means that the content is contained to the extent that the effects of Examples 1 and 2 are exhibited, and that it contains intentionally or unintentionally added impurities, for example, 50 atomic % or 80 atomic % or more of the constituent elements.

In order to compensate for the linear expansion coefficient of the piezoelectric substrate 12, the thickness T1 of the quartz substrate 11 is preferably thicker than the thickness T2 of the piezoelectric substrate 12, more preferably twice or more than T2. Moreover, the thickness T1 is preferably 1 μm or more, more preferably 10 μm or more. As the quartz substrate 11 becomes thicker, its strength and heat dissipation deteriorate. Therefore, the thickness T1 of the quartz substrate 11 is preferably 10 times or less the thickness T2 of the piezoelectric substrate 12, and more preferably 5 times or less. The thickness T1 is preferably 100 μm or less, more preferably 50 μm or less.

The thickness T0 of the support substrate 10 is preferably thicker than the thickness T1 of the quartz substrate 11, more preferably twice or more than T1, from the viewpoint of improving the strength and heat dissipation of the substrate. Also, the thickness T0 is preferably 50 μm or more, more preferably 100 μm or more. In order to suppress spurious and loss, the thickness T2 of the piezoelectric substrate 12 is preferably 10 times or less the wavelength λ of the elastic wave, and preferably λ or less.

6A to 6C are cross-sectional views showing a method of manufacturing an acoustic wave resonator according to Example 2. FIG. As shown in FIG. 6(a), an aluminum oxide layer 13 is formed on the upper surface of the quartz substrate 11 after FIG. 2(c) of the first embodiment. The aluminum oxide layer 13 is formed using, for example, a sputtering method, a vacuum deposition method, or a CVD method. The aluminum oxide layer 13 thus formed is polycrystalline and/or amorphous. As shown in FIG. 6B, the upper surface of the aluminum oxide layer 13 and the lower surface of the piezoelectric substrate 12 are irradiated with ions 54 . This activates the upper surface of the aluminum oxide layer 13 and the lower surface of the piezoelectric substrate 12 .

As shown in FIG. 6C, the upper surface of the aluminum oxide layer 13 and the lower surface of the piezoelectric substrate 12 are bonded at room temperature. The upper surface of the piezoelectric substrate 12 is flattened using, for example, the CMP method. An IDT 22 made of a metal film 14 and a reflector 24 are formed on the piezoelectric substrate 12 . The thickness of the aluminum oxide layer 13 is T3. Other manufacturing methods are the same as those in Example 1, and descriptions thereof are omitted.

FIG. 7 is a cross-sectional view of an acoustic wave resonator according to Example 2. FIG. FIG. 7 illustrates an amorphous layer formed in room temperature bonding. As shown in FIG. 7, an amorphous layer 34 is provided between the aluminum oxide layer 13 and the piezoelectric substrate 12 . The amorphous layer 34 includes an amorphous layer 13 a contacting the aluminum oxide layer 13 and an amorphous layer 12 a contacting the piezoelectric substrate 12 . Amorphous layers 13a and 12a are in contact with each other.

In the amorphous layer 34, the amorphous layer 13a is mainly composed of Al and O and contains elements for surface activation. The amorphous layer 12a is mainly composed of the constituent elements of the piezoelectric substrate 12 and contains Ar. When the piezoelectric substrate 12 is a lithium tantalate substrate, the amorphous layer 12a is mainly composed of Ta, Li and oxygen, and contains elements for surface activation. The amorphous layer 13 a contains almost no elements other than the constituent elements of the piezoelectric substrate 12 among the constituent elements of the aluminum oxide layer 13 . For example, the amorphous layer 13a contains little Ta and Li. The amorphous layer 12 a contains almost no elements other than the constituent elements of the aluminum oxide layer 13 among the constituent elements of the piezoelectric substrate 12 . For example, the amorphous layer 12a hardly contains Al. The configuration of the amorphous layer 30 is the same as in the first embodiment.

The thickness of the amorphous layers 10a, 11a, 13a and 12a is preferably greater than 0 nm, more preferably 0.5 nm or more. Thereby, the bondability between the support substrate 10 and the quartz substrate 11 and the bondability between the aluminum oxide layer 13 and the piezoelectric substrate 12 can be improved. The thickness of the amorphous layers 10a, 11a, 13a and 12a is preferably 10 nm or less, more preferably 5 nm or less, and even more preferably 3 nm or less. Thereby, deterioration of the characteristics of the elastic wave resonator can be suppressed.

A piezoelectric substrate 12 (42° rotated Y-cut X-propagation lithium tantalate substrate) was bonded to the quartz substrate 11, and the bonding strength between the quartz substrate 11 and the piezoelectric substrate 12 was measured. As in Example 1, a sample in which the piezoelectric substrate 12 was directly bonded to the quartz substrate 11 and a sample in which the aluminum oxide layer 13 was formed on the quartz substrate 11 using a sputtering method and the aluminum oxide layer 13 and the piezoelectric substrate 12 were bonded were prepared. The bonding method is the method described in FIGS. 4(a) to 4(d).

FIG. 8 is a diagram showing the bonding strength with respect to the thickness T3 of the aluminum oxide layer. As shown in FIG. 8, when the quartz substrate 11 and the piezoelectric substrate 12 are bonded at room temperature without providing the aluminum oxide layer 13, the bonding strength is about 0.5 J/m ² . After forming the aluminum oxide layer 13 on the quartz substrate 11, when the aluminum oxide layer 13 and the piezoelectric substrate 12 are bonded together at room temperature, the bonding strength becomes 1 J/m ² or more. As the thickness T3 of the aluminum oxide layer 13 increases, the bonding strength decreases. This is probably because the flatness of the upper surface of the aluminum oxide layer 13 deteriorates as the thickness of the aluminum oxide layer 13 increases.

According to the second embodiment, the aluminum oxide layer 13 thinner than the quartz substrate 11 is formed on the surface of the quartz substrate 11 opposite to the supporting substrate 10 . A piezoelectric substrate 12 is bonded to the surface of the aluminum oxide layer 13 opposite to the quartz substrate 11 . Thereby, joint strength can be improved. The step of bonding the aluminum oxide layer 13 and the piezoelectric substrate 12 includes a step of activating the surfaces of the aluminum oxide layer 13 and the piezoelectric substrate 12 and bonding the activated surfaces of the aluminum oxide layer 13 and the piezoelectric substrate 12 at room temperature. Thereby, joint strength can be improved.

When the aluminum oxide layer 13 and the piezoelectric substrate 12 are bonded at room temperature, the amorphous layer 34 includes an amorphous layer 13a (third amorphous layer) containing aluminum and oxygen as main components. Amorphous layer 13a is provided between aluminum oxide layer 13 and amorphous layer 12a and is in contact with aluminum oxide layer 13 and amorphous layer 12a.

The thickness T3 of the aluminum oxide layer 13 is preferably 100 nm or less, more preferably 50 nm or less. The thickness T3 of the aluminum oxide layer 13 is preferably 1 nm or more, more preferably 5 nm or more. Thereby, joint strength can be improved.

FIG. 9A is a circuit diagram of a filter according to Example 3. FIG. As shown in FIG. 9A, one or more series resonators S1 to S3 are connected in series between an input terminal Tin and an output terminal Tout. One or more parallel resonators P1 and P2 are connected in parallel between the input terminal Tin and the output terminal Tout. At least one of the one or more series resonators S1 to S3 and the one or more parallel resonators P1 and P2 can use the acoustic wave resonator of the first or second embodiment. The number of resonators of the ladder-type filter and the like can be set as appropriate. The filter may be a multimode filter.

[Modification 1 of Embodiment 3]
FIG. 9B is a circuit diagram of a duplexer according to modification 1 of embodiment 3. FIG. As shown in FIG. 9B, a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 allows a signal in the transmission band among high-frequency signals input from the transmission terminal Tx to pass through the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 42 allows signals in the reception band among the high-frequency signals input from the common terminal Ant to pass through the reception terminal Rx as reception signals, and suppresses signals of other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the third embodiment.

A duplexer has been described as an example of a multiplexer, but a triplexer or a quadplexer may be used.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

REFERENCE SIGNS LIST 10 support substrate 10a, 11a, 11b, 12a, 13a amorphous layer 11 quartz substrate 12 piezoelectric substrate 13 aluminum oxide layer 15 electrode finger 18 comb-shaped electrode 20 elastic wave resonator 22 IDT

Claims (10)

a support substrate that is a single crystal or polycrystal having a Young's modulus greater than that of quartz;
an amorphous quartz substrate provided on the support substrate;
a single-crystal piezoelectric substrate mainly composed of lithium tantalate or lithium niobate provided on the quartz substrate;
a first amorphous layer provided between the supporting substrate and the quartz substrate, being in contact with the supporting substrate and containing a constituent element of the supporting substrate as a main component;
a second amorphous layer which is provided between the quartz substrate and the piezoelectric substrate, is in contact with the piezoelectric substrate, and contains a constituent element of the piezoelectric substrate as a main component;
a pair of comb-shaped electrodes provided on the piezoelectric substrate;
an aluminum oxide layer provided between the quartz substrate and the second amorphous layer, in contact with the quartz substrate, and thinner than the quartz substrate;
An elastic wave resonator comprising: 2. The acoustic wave resonator according to claim 1, wherein said supporting substrate is a sapphire substrate, an alumina substrate, a silicon substrate, or a silicon carbide substrate. 3. The acoustic wave resonator according to claim 1, wherein said quartz substrate is thicker than said piezoelectric substrate, and said support substrate is thicker than said quartz substrate. 4. The elastic wave resonator according to claim 1, wherein the aluminum oxide layer has a thickness of 100 nm or less . The elastic wave resonator according to any one of claims 1 to 4, further comprising a third amorphous layer provided between the aluminum oxide layer and the second amorphous layer, in contact with the aluminum oxide layer and the second amorphous layer, and containing aluminum and oxygen as main components. 6. The acoustic wave resonator according to claim 1, wherein the thickness of said first amorphous layer and the thickness of said second amorphous layer are 10 nm or less. a step of bonding an amorphous quartz substrate onto a single-crystal or polycrystalline support substrate having a Young's modulus greater than that of quartz;
forming an aluminum oxide layer thinner than the quartz substrate on the surface of the quartz substrate opposite to the supporting substrate;
bonding a single-crystal piezoelectric substrate containing lithium tantalate or lithium niobate as a main component to the surface of the aluminum oxide layer opposite to the support substrate;
forming a pair of comb-shaped electrodes on a surface of the piezoelectric substrate opposite to the quartz substrate;
A method of manufacturing an acoustic wave resonator comprising: 8. The method for manufacturing an acoustic wave resonator according to claim 7 , wherein the step of bonding the piezoelectric substrate to the surface of the aluminum oxide layer opposite to the quartz substrate includes the step of activating surfaces of the aluminum oxide layer and the piezoelectric substrate, and bonding the activated surfaces of the aluminum oxide layer and the piezoelectric substrate at room temperature. A filter comprising the acoustic wave resonator according to any one of claims 1 to 6 . A multiplexer including the filter of claim 9.

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