WO2020189115A1

WO2020189115A1 - Composite substrate, electronic device, method for manufacturing composite substrate, and method for manufacturing electronic device

Info

Publication number: WO2020189115A1
Application number: PCT/JP2020/005744
Authority: WO
Inventors: 小林　正宏; 清行奥長; 益田　紀彰
Original assignee: 日本電気硝子株式会社
Priority date: 2019-03-15
Filing date: 2020-02-14
Publication date: 2020-09-24
Also published as: JPWO2020189115A1

Abstract

Provided is a composite substrate that can enhance stability of filter characteristics against temperature change.　A composite substrate 1 is a composite substrate that is used for an electronic device. The composite substrate 1 is characterized by being provided with a support substrate 2, and a piezoelectric substrate 3 that is provided on the support substrate 2, wherein the support substrate 2 is formed of crystallized glass obtained by depositing a β-quartz solid solution and/or a β-eucryptite solid solution.

Description

Composite substrate, electronic device, manufacturing method of composite substrate and manufacturing method of electronic device

The present invention relates to a composite substrate, an electronic device using the composite substrate, and a composite substrate and a method for manufacturing the electronic device.

Surface acoustic wave elements (so-called SAW filters) are used, for example, as bandpass filters in communication devices such as mobile phones. Since the piezoelectric substrate for forming a surface acoustic wave element is required to have a high electromechanical coupling coefficient at a high sound velocity, lithium niobate (LiNbO ₃ : hereinafter LN) capable of satisfying these required characteristics and the like. Lithium tantalate (LiTaO ₃ : hereinafter LT) is mainly used. However, LN and LT have a large coefficient of thermal expansion, and the amount of thermal expansion and contraction due to a temperature change is large. The thermal expansion / contraction behavior due to this temperature change affects the pass frequency band or cutoff frequency band of the bandpass filter. Specifically, the center frequency of the bandpass filter fluctuates, for example, the signal of the frequency that should originally pass through the bandpass filter is attenuated, and the filter characteristic, that is, the separation characteristic of a specific frequency signal deteriorates. Therefore, it is necessary to suppress the thermal expansion / contraction behavior of the surface acoustic wave element due to temperature changes.

In order to suppress the thermal expansion / contraction behavior of the surface acoustic wave element due to temperature change, Patent Document 1 proposes a composite substrate using a Sialon sintered body having a relatively small coefficient of thermal expansion as a support substrate.

International Publication No. 2018/05621

Even with a composite substrate using a Sialon sintered body, there is still room for improvement in suppressing the performance deterioration of the surface acoustic wave element due to the operating environment temperature. In the composite substrate described in Patent Document 1, by using a Sialon sintered body having a relatively small coefficient of thermal expansion as the support substrate, the thermal expansion / contraction behavior due to temperature change can be suppressed to some extent, but the support is still supported. Since thermal expansion / contraction occurs in the Sialon sintered body used for the substrate, the thermal expansion / contraction behavior of the composite substrate cannot be completely suppressed.

Further, in recent years, electronic devices using surface acoustic wave elements have been miniaturized and highly integrated, and heat is more likely to be accumulated in the electronic devices than ever before. Therefore, further suppression of temperature influence is desired. Furthermore, in the future, congestion (competition) in the frequency band of the output signal is predicted, and stricter frequency output control will be required. Therefore, as described above, it is desired to further suppress the thermal expansion / contraction behavior of the electronic device due to the temperature change and further stabilize the filter characteristics.

An object of the present invention is a composite substrate, an electronic device using the composite substrate, a method for manufacturing the composite substrate, and the electronic device, which can enhance the stability of filter characteristics against temperature changes when used in an electronic device. Is to provide a manufacturing method for.

The composite substrate of the present invention is a composite substrate used for an electronic device, and includes a support substrate and a piezoelectric substrate provided on the support substrate, and the support substrate is a β-quartz solid solution and / or β-U. It is characterized in that it is composed of crystallized glass formed by precipitating a cryptotite solid solution.

It is preferable that the average coefficient of thermal expansion of the support substrate in the range of 30 ° C. or higher and 380 ° C. or lower is -1 × 10 ^-7 / ° C. or higher and 1 × 10 ^-7 / ° C. or lower.

Support substrate is in mass%, SiO ₂ 55% to 75%, Al ₂ O ₃ 15% to 30%, Li ₂ O 2% to 5%, Na ₂ O 0% to 3%, K ₂ O 0% to 3%, MgO 0% ~ 5 %, ZnO 0% ~ 3%, BaO 0% ~ 5%, TiO 2 0% ~ 5%, ZrO 2 0% ~ 4%, P 2 O 5 0% ~ 5%, It is preferably composed of crystallized glass having a composition containing ₂₀ % to 2.5% of SnO.

The amount of β-quartz solid solution and / or β-eucryptite solid solution precipitated on the support substrate is preferably 50% by mass or more.

A bonding layer is further provided between the support substrate and the piezoelectric substrate, and the bonding layer may contain metal and its thickness may be 15 nm or less. Further, the support substrate and the piezoelectric substrate may be directly bonded.

It is preferable that the piezoelectric substrate is a lithium niobate crystal substrate or a lithium tantalate crystal substrate, and the thickness of the piezoelectric substrate is 20 μm or less.

It is preferable that the arithmetic average roughness Ra of the surface of the support substrate bonded to the piezoelectric substrate and the surface bonded to the piezoelectric substrate of the piezoelectric substrate is 0.5 nm or less, respectively.

The electronic device of the present invention includes the composite substrate and a comb-shaped electrode provided on the piezoelectric substrate, and is characterized in that it is configured to be capable of generating surface acoustic waves on the piezoelectric substrate.

The method for manufacturing a composite substrate of the present invention is the above-mentioned method for manufacturing a composite substrate, which includes a step of preparing a support substrate and a step of joining a piezoelectric substrate to the support substrate, and comprises a β-quartz solid solution and / or β-. It is characterized in that crystallized glass formed by precipitating a eucryptite solid solution is used as a support substrate.

In the process of joining the piezoelectric substrate to the support substrate, it is preferable to join the support substrate and the piezoelectric substrate by atomic diffusion bonding. Further, in the step of joining the piezoelectric substrate to the support substrate, it is preferable to join the support substrate and the piezoelectric substrate by surface activation bonding.

After the step of joining the piezoelectric substrate to the support substrate, it is preferable that a step of polishing only the piezoelectric substrate side to make the composite substrate thinner is further provided.

The method for manufacturing an electronic device of the present invention is characterized by including a step of providing a comb-shaped electrode on the piezoelectric substrate of the composite substrate.

According to the present invention, a composite substrate, an electronic device using the composite substrate, a method for manufacturing the composite substrate, and the electronic device, which can enhance the stability of filter characteristics against temperature changes when used in an electronic device. Manufacturing method can be provided.

FIG. 1 is a front sectional view of the composite substrate according to the first embodiment of the present invention. FIG. 2 is a front sectional view of a composite substrate according to a modified example of the first embodiment of the present invention. FIG. 3 is a schematic perspective view of the electronic device according to the second embodiment of the present invention.

(Composite board)
FIG. 1 is a front sectional view of the composite substrate according to the first embodiment of the present invention. The composite substrate 1 of the present embodiment shown in FIG. 1 is used for an electronic device such as a surface acoustic wave element. The composite substrate 1 includes a support substrate 2 and a piezoelectric substrate 3 provided on the support substrate 2. The support substrate 2 has a first main surface 2a and a second main surface 2b facing each other. The piezoelectric substrate 3 has a third main surface 3a and a fourth main surface 3b that face each other. The first main surface 2a of the support substrate 2 is a surface bonded to the piezoelectric substrate 3. The third main surface 3a of the piezoelectric substrate 3 is a surface bonded to the support substrate 2.

The first main surface 2a of the support substrate 2 and the third main surface 3a of the piezoelectric substrate 3 are directly joined. In the present specification, the direct coupling refers to a bonding made of resin or the like without an adhesive layer. The case where a bonding layer such as a metal layer is formed between the bonding surfaces at the time of bonding is also included in the direct bonding. However, the direct bonding includes the case where the bonding surfaces are directly bonded to each other without going through the bonding layer. As shown in FIG. 1, the composite substrate 1 of the present embodiment does not have a bonding layer between the support substrate 2 and the piezoelectric substrate 3. The first main surface 2a of the support substrate 2 and the third main surface 3a of the piezoelectric substrate 3 are directly joined.

The piezoelectric substrate 3 is not particularly limited, but is, for example, a lithium niobate crystal substrate or a lithium tantalate crystal substrate.

The support substrate 2 is composed of crystallized glass obtained by precipitating a β-quartz solid solution and / or a β-eucryptite solid solution. The average coefficient of thermal expansion of the support substrate 2 of the present embodiment at 30 ° C. or higher and 380 ° C. or lower is -1 × 10 ^-7 / ° C. or higher and 1 × 10 ^-7 / ° C. or lower. The coefficient of thermal expansion of the support substrate 2 itself is -1 × 10 ^-7 / ° C. or higher and 1 × 10 ^-7 / ° C. or lower at 30 ° C. or higher and 380 ° C. or lower. As described above, the coefficient of thermal expansion of the support substrate 2 is substantially 0.

The amount of β-quartz solid solution and / or β-eucryptite solid solution precipitated on the support substrate 2 is preferably 50% by mass or more, more preferably 70% by mass or more. If the amount of β-quartz solid solution and / or β-eucryptite solid solution deposited is too small, it is difficult to obtain the effect of reducing the coefficient of thermal expansion. On the other hand, the upper limit of the precipitation amount of the β-quartz solid solution and / or the β-eucryptite solid solution is not particularly limited, but is practically 99% by mass or less. When both β-quartz solid solution and β-eucryptite are contained, it is preferable that the total amount satisfies the above range.

The support substrate 2 is not particularly limited as long as it can precipitate a β-quartz solid solution and / or a β-eucryptite solid solution. For example, the support substrate 2 has a mass% of SiO ₂ 55% to 75%, Al ₂ O ₃ 15% to 30%, Li ₂ O 2% to 5%, Na ₂ O 0% to 3%, and K ₂ O. 0% ~ 3%, MgO 0 % ~ 5%, ZnO 0% ~ 3%, BaO 0% ~ 5%, TiO 2 0% ~ 5%, ZrO 2 0% ~ 4%, P 2 O 5 0% ~ It is preferably composed of crystallized glass having a composition containing 5% and ₂₀ % to 2.5% of SnO. The reason why the above glass composition range is preferable will be described below.

SiO ₂ forms a glass skeleton and also serves as a constituent component of the main crystal. The content of SiO ₂ is preferably 55% to 75%, more preferably 60% to 75%. If the content of SiO ₂ is too small, the coefficient of thermal expansion tends to be high and the chemical durability tends to be low. On the other hand, if the content of SiO ₂ is too large, the meltability tends to decrease. Further, the viscosity of the glass melt increases, which tends to make it difficult to clarify or mold.

Al ₂ O ₃ forms a glass skeleton and also serves as a constituent of the main crystal. The content of Al ₂ O ₃ is preferably 15% to 30%, more preferably 17% to 27%. If the content of Al ₂ O ₃ is too small, the coefficient of thermal expansion tends to be high and the chemical durability tends to be lowered. On the other hand, if the content of Al ₂ O ₃ is too large, the meltability tends to decrease. In addition, the viscosity tends to increase, making it difficult to clarify or molding. In addition, it becomes easy to devitrify.

Li ₂ O is a constituent component of the main crystal, which has a great influence on crystallinity and is a component that improves meltability and moldability by lowering the viscosity. The content of Li ₂ O is preferably 2% to 5%, more preferably 2% to 4.8%. If the content of Li ₂ O is too small, the main crystals are difficult to precipitate and the meltability is lowered. Further, the viscosity tends to increase, making it difficult to clarify or molding. On the other hand, if the content of Li ₂ O is too large, devitrification is likely to occur.

Na ₂ O is a component for lowering the viscosity and improving the meltability and moldability. The content of Na ₂ O is preferably 0% to 3%, more preferably 0.1% to 1%. If the content of Na ₂ O is too large, devitrification tends to occur and the coefficient of thermal expansion tends to increase.

K ₂ O is a component for lowering the viscosity and improving the meltability and moldability. The K ₂ O content is preferably 0% to 3%, more preferably from 0.1% to 1%. If the content of K ₂ O is too large, devitrification tends to occur and the coefficient of thermal expansion tends to increase.

MgO is a component for adjusting the coefficient of thermal expansion. The content of MgO is preferably 0% to 5%, more preferably 0.1% to 3%, and even more preferably 0.3% to 2%. If the content of MgO is too large, devitrification tends to occur and the coefficient of thermal expansion tends to increase.

ZnO is a component for adjusting the coefficient of thermal expansion. The ZnO content is preferably 0% to 3%, more preferably 0.1% to 1%. If the ZnO content is too high, devitrification is likely to occur.

BaO is a component for improving meltability and moldability by lowering the viscosity. The content of BaO is preferably 0% to 5%, more preferably 0.1% to 3%. If the BaO content is too high, devitrification is likely to occur.

TiO ₂ and ZrO ₂ are components that act as nucleating agents for precipitating crystals in the crystallization step. The content of TiO ₂ is preferably 0% to 5%, more preferably 1% to 4%. The content of ZrO ₂ is preferably 0% to 4%, more preferably 0.1% to 3%. If the content of TiO ₂ or ZrO ₂ is too high, devitrification is likely to occur.

P ₂ O ₅ is a component that promotes phase separation and assists in the formation of crystal nuclei. The content of P ₂ O ₅ is preferably 0% to 5%, more preferably 0.1% to 4%. If the content of P ₂ O ₅ is too large, it becomes easy to separate the phases in the melting step, and it becomes difficult to obtain a glass having a desired composition.

SnO ₂ is a component that acts as a fining agent. The content of SnO ₂ is preferably 0% to 2.5%, more preferably 0.1% to 2%. If the content of SnO ₂ is too large, the color tone becomes too dark and the light is easily devitrified.

In addition to the above components, B ₂ O ₃ , SrO, CaO and the like can be appropriately contained as long as the effects of the present invention are not impaired.

The feature of this embodiment is that the support substrate 2 in the composite substrate 1 is composed of crystallized glass obtained by precipitating a β-quartz solid solution and / or a β-eucryptite solid solution. As a result, the coefficient of thermal expansion of the support substrate 2 can be made substantially zero. Therefore, the support substrate 2 hardly undergoes thermal expansion or contraction due to a temperature change. Further, since the piezoelectric substrate 3 bonded to the support substrate 2 is restrained by the support substrate 2, thermal expansion / contraction of the piezoelectric substrate 3 is suppressed. As a result, the composite substrate 1 is unlikely to thermally expand or contract due to temperature changes. Therefore, by using the composite substrate 1 of the present embodiment for an electronic device that utilizes a surface acoustic wave or the like, the stability of the filter characteristics with respect to a temperature change can be improved.

The average coefficient of thermal expansion of the support substrate 2 is preferably -1 × 10 ^-7 / ° C. or higher and 1 × 10 ^-7 / ° C. or lower at 30 ° C. or higher and 380 ° C. or lower as in the present embodiment. When the coefficient of thermal expansion of the support substrate 2 is within the above range, the stability of the filter characteristics of the electronic device with respect to temperature changes can be more reliably enhanced.

It is preferable that the support substrate 2 and the piezoelectric substrate 3 are directly bonded. Thereby, the binding force of the piezoelectric substrate 3 by the support substrate 2 can be effectively increased. Therefore, the stability of the filter characteristics of the electronic device with respect to the temperature change can be further enhanced.

The dimensions of the composite substrate 1 in a plan view are preferably φ50 mm or more and φ400 mm or less, more preferably φ100 mm or more and φ400 mm or less, and further preferably φ100 mm or more and φ300 mm or less. When the composite substrate 1 and the electronic device using the composite substrate 1 are small, heat tends to be accumulated in the electronic device, so that the temperature change tends to be large. The composite substrate 1 of the present embodiment is particularly suitable when used in a small electronic device because it can enhance the stability of the filter characteristics against a temperature change. Alternatively, since heat is likely to be accumulated in the electronic device even in the integrated electronic device, the composite substrate 1 is suitable as the substrate used for such an electronic device.

The thickness of the piezoelectric substrate 3 is preferably 20 μm or less, more preferably 5 μm or less, and even more preferably 2 μm or less. As a result, good device characteristics can be exhibited in the electronic device using the composite substrate 1. The thickness of the piezoelectric substrate 3 is preferably 0.3 μm or more, and more preferably 1 μm or more. In this case, the piezoelectric substrate 3 is not easily damaged.

(Modification example)
FIG. 2 is a front sectional view of the composite substrate according to the modified example of the first embodiment. As shown in FIG. 2, the composite substrate 11 includes a bonding layer 14 provided between the support substrate 2 and the piezoelectric substrate 3. The bonding layer 14 is not particularly limited, but is, for example, a layer containing a metal such as a Ti layer or a layer containing a semiconductor such as a Si layer. The bonding layer 14 may be a layer in which the components of the metal and the support substrate 2 and / or the piezoelectric substrate 3 are mixed. Further, the bonding layer 14 may be composed of a single metal or an alloy. The thickness of the bonding layer 14 is preferably 15 nm or less, more preferably 10 nm or less, and further preferably 8 nm or less. In this case, the bonding layer 14 is unlikely to affect the amount of residual strain between the support substrate 2 and the piezoelectric substrate 3. Therefore, as in the first embodiment, the stability of the filter characteristics with respect to temperature changes can be enhanced. The thickness of the bonding layer 14 is preferably 1 nm or more, more preferably 2 nm or more.

(Electronic device)
FIG. 3 is a schematic perspective view of the electronic device according to the second embodiment of the present invention. The electronic device 20 includes the composite substrate 1 of the first embodiment, and the first comb-shaped electrode 25A and the second comb-shaped electrode 25B provided on the composite substrate 1. An input terminal 26A is connected to the first comb-shaped electrode 25A. An output terminal 26B is connected to the second comb-shaped electrode 25B.

The electronic device 20 is an elastic wave device. The electronic device 20 is configured to be capable of generating elastic waves, specifically, elastic surface waves, on the piezoelectric substrate 3. In the electronic device 20, the elastic wave is excited by applying the signal input from the input terminal 26A to the first comb-shaped electrode 25A. The elastic wave propagates through the piezoelectric substrate 3, is converted into a signal by the second comb-shaped electrode 25B, and the signal is taken out from the output terminal 26B. As a result, the signal input from the input terminal 26A is filtered. However, the circuit configuration of the electronic device 20 is not limited to the above. The electronic device 20 may have at least one comb-shaped electrode.

Since the electronic device 20 has the composite substrate 1 of the first embodiment, it is possible to improve the stability of the filter characteristics against temperature changes.

An example of a method for manufacturing a composite substrate according to the present invention will be described below with reference to FIG.

(Manufacturing method of composite substrate)
The support substrate 2 shown in FIG. 1 is produced by melting a raw material batch prepared by blending a glass raw material at a predetermined ratio, molding the raw material into a predetermined shape, and crystallizing the glass raw material under a predetermined temperature condition.

The melting temperature of the glass batch is preferably about 1600 ° C to 1800 ° C from the viewpoint of productivity and homogeneity. The crystallization conditions include heat treatment at 600 ° C. to 800 ° C. for 1 hour to 5 hours to generate crystal nuclei (crystal nucleation stage), and then at 800 ° C. to 950 ° C. for 0.5 hours to 3 hours. It is preferable to perform heat treatment to precipitate the main crystal (crystal growth stage).

On the other hand, prepare the piezoelectric substrate 3. Next, the first main surface 2a of the support substrate 2 and the third main surface 3a of the piezoelectric substrate 3 are flattened and smoothed. Specifically, each of the above surfaces is preferably an arithmetic average roughness Ra (hereinafter Ra): 0.5 nm or less, more preferably 0.3 nm or less, and 0.2 nm or less by polishing or the like. Is even more preferable. Ra in this specification is based on JIS B 0601: 2013. The total surface of each surface is preferably set to 1.5 μm or less, and more preferably 1.0 μm or less by polishing or the like. Thereby, in a later step, the support substrate 2 and the piezoelectric substrate 3 can be suitably bonded by direct bonding, and the bonding strength can be increased more reliably. The lower limit of Ra on each of the above surfaces is, for example, 0.05 nm or more. The lower limit of TTV on each of the above surfaces is, for example, 0.5 μm or more. In these cases, the support substrate 2 and the piezoelectric substrate 3 can be suitably joined without causing an excessive increase in polishing time or the like in the flattening and smoothing steps. The method for manufacturing the composite substrate 1 does not necessarily have to include a step of flattening and smoothing the first main surface 2a of the support substrate 2 and the third main surface 3a of the piezoelectric substrate 3.

Next, the first main surface 2a of the support substrate 2 and the third main surface 3a of the piezoelectric substrate 3 are activated. This activation is performed, for example, by irradiating the surface with a neutral atom beam of an inert gas (argon or the like), or by irradiating a plasma or an ion beam. These irradiations can be performed using, for example, an ion gun, a FAB (Fast Atom Beam) gun, or the like. The FAB gun has a higher energy per particle than the ion gun, and has a high ability to remove the oxide film and the adsorption layer on the substrate surface that hinder the normal temperature bonding. Therefore, it is easy to set the state of the molecule on each surface to which the support substrate 2 and the piezoelectric substrate 3 are bonded to be a state in which a bonding hand that is not bound to another substance is arranged. Therefore, it is preferable to use a FAB gun for activating the surface. By performing the above activation, the piezoelectric substrate 3 and the support substrate 2 can be suitably bonded by direct bonding at room temperature in a later step, and the bonding strength can be increased more reliably. The method for manufacturing the composite substrate 1 does not necessarily have to include a step of activating the respective surfaces of the piezoelectric substrate 3 and the support substrate 2. In the present invention, the normal temperature refers to, for example, a temperature range of 5 to 50 ° C.

Next, the first main surface 2a of the support substrate 2 and the third main surface 3a of the piezoelectric substrate 3 are joined by direct bonding. Specifically, both substrates are pressed with the first main surface 2a of the support substrate 2 and the third main surface 3a of the piezoelectric substrate 3 facing each other. As the bonding method to be used, ADB: atomic diffusion bonding or SAB: surface-activated bonding, which can be bonded at room temperature, is preferable. Alternatively, optical contacts may be used.

The ratio of the actually bonded area to the bonding interface between the support substrate 2 and the piezoelectric substrate 3 is preferably 80% or more, and more preferably 90% or more. When the bonding area ratio is large as described above, a good composite substrate in which the support substrate 2 and the piezoelectric substrate 3 are firmly bonded is obtained.

After joining the support substrate 2 and the piezoelectric substrate 3, it is preferable to thin the piezoelectric substrate 3 by grinding and polishing only the piezoelectric substrate 3 side. Specifically, the thickness of the piezoelectric substrate 3 is preferably 20 μm or less, more preferably 5 μm or less, and even more preferably 2 μm or less by grinding and polishing. As a result, good device characteristics can be exhibited in the electronic device using the composite substrate 1. By joining by the above method, the joining strength can be increased more reliably, so that the piezoelectric substrate 3 is unlikely to be peeled off from the support substrate 2 even by vibration during grinding and polishing.

In the composite substrate 1 produced in this manner, since the first main surface 2a of the support substrate 2 and the third main surface 3a of the piezoelectric substrate 3 are directly bonded, they are bonded via an adhesive layer. The binding force of the piezoelectric substrate 3 by the support substrate 2 is stronger than that of the case where the support substrate 2 is used. As a result, the thermal expansion / contraction behavior of the composite substrate 1 due to an external temperature change can be effectively suppressed. This can contribute to device design with excellent frequency / temperature characteristics. Therefore, it is possible to provide an electronic device having stable filter characteristics. However, at the time of bonding, the bonding layer 14 shown in FIG. 2 may be formed between the support substrate 2 and the piezoelectric substrate 3. For example, when ADB or SAB is used for bonding, the bonding layer 14 is formed between the support substrate 2 and the piezoelectric substrate 3.

When the bonding layer 14 is provided between the support substrate 2 and the piezoelectric substrate 3, the bonding layer 14 is bonded after the above-mentioned flattening and smoothing steps and before the above-mentioned activation step or room temperature bonding step. A metal thin film is formed on the surface. Specifically, a step of forming a metal thin film made of, for example, Ti or the like is provided on at least one of the support substrate 2 and the piezoelectric substrate 3. The metal thin film layer may be formed on the joint surface of both the support substrate 2 and the piezoelectric substrate 3, or may be formed on one of the joint surfaces of the support substrate 2 or the piezoelectric substrate 3.

(Example)
Hereinafter, the present invention will be described based on examples, but the present invention is not limited to these examples. An example in which ADB is used as the joining method of the support substrate and the piezoelectric substrate is shown in Example 1. An example in which SAB is used as the joining method is shown in Example 2.

(Example 1)
(1) In Preparation mass% of the supporting _{_{_{_{substrate, SiO 2 66%, Al 2}}}} O 3 23%, Li 2 O 4%, Na 2 O 0.5%, MgO 1%, BaO 1.5%, TiO 2 2 %, so that the glass having a composition of ZrO 2 _2%, the raw material powder were blended, and homogeneously mixed. The obtained raw material batch was melted at 1600 ° C. or higher and 1800 ° C. or lower until it became homogeneous to obtain molten glass. Next, the molten glass was formed into a plate shape. Next, the molten glass formed into a plate shape was cooled to room temperature using a slow cooling furnace to obtain a plate-shaped crystalline glass.

Next, the plate-like crystalline glass was heated at a rate of 300 ° C./hour from room temperature to a temperature within the range of 760 ° C. or higher and 780 ° C. or lower, and held for 3 hours for nucleation. Next, the temperature was raised to a temperature within the range of 870 ° C. or higher and 890 ° C. or lower at a rate of 120 ° C./hour, and the temperature was maintained for 1 hour for crystallization. Then, the temperature was lowered to room temperature at 300 ° C./hour to obtain a plate-shaped crystallized glass. When the precipitated crystals were analyzed, it was confirmed that a β-quartz solid solution was precipitated as the main crystal. As a result of measuring the coefficient of thermal expansion of the obtained plate-shaped crystallized glass using a dilatometer, the average coefficient of thermal expansion in the temperature range of 30 ° C. to 380 ° C. was 0 / ° C.

Next, the plate-shaped crystallized glass was cut into a disk shape having a diameter of 100 mm, and the surface of the plate-shaped crystallized glass was polished to a mirror surface shape. The thickness of the plate-shaped crystallized glass was 0.2 mm. The mirrored surface of the plate-shaped crystallized glass was measured with an atomic force microscope (AFM). As a result, Ra: 0.2 nm and TTV: 0.9 μm. From the above, a support substrate was obtained.

(2) Fabrication and Evaluation of Composite Substrate A composite is formed by directly bonding a lithium niobate crystal substrate (LN substrate) having a diameter of 100 mm and a thickness of 0.2 mm as a piezoelectric substrate to the support substrate prepared in (1) by ADB. Obtained a substrate. Specifically, a composite substrate was obtained by forming a microcrystalline metal thin film on each of the bonding surfaces of the support substrate and the piezoelectric substrate by a sputtering method and then directly bonding them under vacuum. Almost no bubbles were observed at the bonding interface between the support substrate and the LN substrate, and the bonding was good. Furthermore, the cross section of the composite substrate was observed with a scanning electron microscope (SEM). As a result, it was confirmed that there was no gap at the bonding interface and the support substrate and the LN substrate were firmly bonded.

(Example 2)
A lithium tantalate crystal substrate (LT substrate) as a piezoelectric substrate having a diameter of 100 mm and a thickness of 0.35 mm is bonded to the support substrate produced in the same manner as in (1) of Example 1 by SAB. A microcrystalline metal thin film was formed on the surface by a sputtering method. Next, a composite substrate was obtained by activating the surfaces of each microcrystalline metal thin film to be bonded to each other using a FAB gun and then directly bonding them under vacuum. A Si film (thickness 10 nm) was used as the microcrystalline metal thin film. Almost no bubbles were observed at the bonding interface between the support substrate and the LT substrate, and the bonding was good. In addition, the cross section of the composite substrate was observed with a scanning electron microscope (SEM). As a result, it was confirmed that there was no gap at the bonding interface and the support substrate and the LT substrate were firmly bonded.

Furthermore, the bonding strength of the produced composite substrate was evaluated by the blade crack method. Specifically, "Bounding of silicon wafer for silicon-on-insulator" W. P. Maszara, et. Based on the method described in al Journal of Applied Physics 64, 4943 (1988), a certain amount of blades (thickness: 76 μm) are inserted into the composite interface from four locations at 90 ° intervals from the end face of the composite substrate, and the peeling length thereof. The surface energy value: Δγ (J / m ² ) was calculated from this. The Δγ value was calculated by the formula shown below.

L: Crack length (mm)
y: 1/2 thickness (μm) of the blade
t1, t2: Thickness of each substrate (μm)
E1, E2: Young's modulus (GPa) of each substrate

The surface energy value of the produced composite substrate was 1.2 (J / m ² ) on average measured at four points. As described above, the surface energy value of the composite substrate exceeds 0.7 (J / m ² ) required for the grinding and polishing processes, and it is confirmed that the composite substrate has sufficient bonding strength. did it.

Next, the piezoelectric substrate side of the composite substrate produced by the above SAB was ground and polished to make it thinner. First, a high-rigidity grinding machine (manufactured by Tokyo Seimitsu Co., Ltd.) was used to perform grinding so that the thickness of the piezoelectric substrate was about 2 μm. Since it has sufficient joint strength, it can be processed without causing problems such as breakage during descent. The average thickness of the processed piezoelectric substrate was 1.98 μm, and the in-plane thickness variation of the piezoelectric substrate was 0.52 μm.

Next, by polishing the above-ground composite substrate, further thinning and flattening were performed. Polishing was performed using a CMP apparatus (manufactured by Tokyo Seimitsu Co., Ltd.) so that the thickness of the piezoelectric substrate was about 1 μm and Ra was 0.5 nm or less. Since it has sufficient joint strength as in the case of grinding, it was possible to process without causing problems such as breakage during processing. The average thickness of the processed piezoelectric substrate was 0.96 μm, the in-plane thickness variation of the piezoelectric substrate was 0.39 μm, and Ra was 0.10 nm.

Next, after forming a comb-shaped electrode having an L / S of 1.6 μm on the composite substrate produced as described above, the composite substrate was cut into a size of 1 mm × 1.5 mm. As a result, a chip-shaped SAW filter was obtained. 100 samples of such a SAW filter were prepared, and the filter characteristics in the 1.05 GHz band as a frequency band were evaluated.

As a result of the evaluation, it was confirmed that the average impedance ratio was 65 dB and the bandwidth was 3.5%, and that the SAW filter had a sufficient function. The frequency temperature characteristic (TCF) was −15 ppm / ° C. in the anti-resonant frequency region and −5 ppm / ° C. in the resonance frequency region in the temperature range of −40 ° C. to 100 ° C. The TCF of the SAW filter using the Sialon support substrate, which is a conventional technique, is generally about ± 20 ppm / ° C., and the SAW filter provided with the composite substrate according to the present invention is superior to the conventional product in TCF. It could be confirmed.

Unlike the conventional Sialon support substrate, a support substrate made of crystallized glass having a coefficient of thermal expansion of substantially 0 is used, and the piezoelectric substrate is restrained by the support substrate to prevent thermal expansion and contraction of the piezoelectric substrate. It can be made less likely to occur. Therefore, by using the composite substrates of Examples 1 and 2 for the electronic device, the frequency temperature characteristic (TCF) can be significantly improved. Therefore, the filter characteristics of the electronic device can be stabilized.

1 ... Composite substrate 2 ... Support substrate 2a ... First main surface 2b ... Second main surface 3 ... Piezoelectric substrate 3a ... Third main surface 3b ... Fourth main surface 11 ... Composite substrate 14 ... Bonding layer 20 ... Electronic device 25A ... First comb-shaped electrode 25B ... Second comb-shaped electrode 26A ... Input terminal 26B ... Output terminal

Claims

A composite substrate used for electronic devices
Support board and
The piezoelectric substrate provided on the support substrate and
With
A composite substrate, characterized in that the support substrate is made of crystallized glass formed by precipitating a β-quartz solid solution and / or a β-eucryptite solid solution.
The composite substrate according to claim 1, wherein the average thermal expansion coefficient of the support substrate in the range of 30 ° C. or higher and 380 ° C. or lower is -1 × 10-7 / ° C. or higher and 1 × 10-7 / ° C. or lower.
In terms of mass%, the supporting substrate is SiO 2 55% to 75%, Al 2 O 3 15% to 30%, Li 2 O 2% to 5%, Na 2 O 0% to 3%, K 2 O 0%. ~ 3%, MgO 0% ~ 5%, ZnO 0% ~ 3%, BaO 0% ~ 5%, TiO 2 0% ~ 5%, ZrO 2 0% ~ 4%, P 2 O 5 0% ~ 5% The composite substrate according to claim 1 or 2, which is composed of crystallized glass having a composition containing 20 % to 2.5% of SnO.
The composite substrate according to any one of claims 1 to 3, wherein the amount of β-quartz solid solution and / or β-eucryptite solid solution precipitated in the support substrate is 50% by mass or more.
A bonding layer is further provided between the support substrate and the piezoelectric substrate.
The composite substrate according to any one of claims 1 to 4, wherein the bonding layer contains a metal and has a thickness of 15 nm or less.
The composite substrate according to any one of claims 1 to 4, wherein the support substrate and the piezoelectric substrate are directly bonded to each other.
The piezoelectric substrate is a lithium niobate crystal substrate or a lithium tantalate crystal substrate.
The composite substrate according to any one of claims 1 to 6, wherein the thickness of the piezoelectric substrate is 20 μm or less.
Any of claims 1 to 7, wherein the arithmetic mean roughness Ra of the surface of the support substrate bonded to the piezoelectric substrate and the surface of the piezoelectric substrate bonded to the support substrate is 0.5 nm or less, respectively. The composite substrate according to one item.
The composite substrate according to any one of claims 1 to 8 and
The comb-shaped electrode provided on the piezoelectric substrate and
With
An electronic device configured to be capable of generating surface acoustic waves on the piezoelectric substrate.
The method for manufacturing a composite substrate according to any one of claims 1 to 8.
The process of preparing the support substrate and
The step of joining the piezoelectric substrate to the support substrate and
With
A method for producing a composite substrate, which comprises using a crystallized glass obtained by precipitating a β-quartz solid solution and / or a β-eucryptite solid solution as the support substrate.
The method for manufacturing a composite substrate according to claim 10, wherein in the step of joining the piezoelectric substrate to the support substrate, the support substrate and the piezoelectric substrate are joined by atomic diffusion bonding.
The method for manufacturing a composite substrate according to claim 10, wherein in the step of joining the piezoelectric substrate to the support substrate, the support substrate and the piezoelectric substrate are joined by surface activation bonding.
The composite substrate according to any one of claims 10 to 12, further comprising a step of polishing only the piezoelectric substrate side and thinning the composite substrate after the step of joining the piezoelectric substrate to the support substrate. Manufacturing method.
A method for manufacturing an electronic device, comprising a step of providing a comb-shaped electrode on the piezoelectric substrate of the composite substrate according to any one of claims 1 to 8.