JPH08162893A - Piezoelectric component and manufacture of piezoelectric component - Google Patents

Abstract

PURPOSE: To obtain a structure of a piezoelectric component with small size and high stability and its manufacture by applying direct bonding to a stress buffer plate having a Young's modulus smaller than that of a vibration piezoelectric plate or a base which has a smaller thermal expansion rate, the vibration piezoelectric plate and a base so as to fix them. CONSTITUTION: A stress buffer plate 3 has a Young's modulus smaller than that of a vibration piezoelectric plate 1 or a base 2 which has a smaller thermal expansion rate. Furthermore, part of the vibration piezoelectric plate 1 in the vicinity of its surrounding is fixed to the stress buffer plate 3 by direct bonding and part of the stress buffer plate 3 is fixed to the base 2 by direct bonding. Since the vibration piezoelectric plate 1 uses no adhesives but is fixed by direct bonding in this way, a stress due to contraction/expansion of the adhesives is not exerted to the piezoelectric plate 1 and no gas is generated from the adhesives. Furthermore, it is not required to take a difference between the thermal expansion rate of the adhesives and the piezoelectric plate 1 and heat resistance of the adhesives into account, then heat processing at a high temperature is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-sized and highly stable piezoelectric component structure and a method for manufacturing the same.

[0002]

2. Description of the Related Art Various piezoelectric components are used in various filters, vibrators, etc. because of their high stability and high functions and characteristics that cannot be realized by electric circuits. In particular, it is used as an important device in the field of information equipment, and with the recent development of satellite communication, mobile phones, etc., miniaturization and high performance of elements have been one of the major goals.

For example, in the case of a crystal oscillator, strict frequency stability is required. Since the frequency of the crystal unit changes when stress is applied to the vibrating crystal plate, various measures have been taken to reduce the stress applied to the vibrating crystal plate.
As a conventional crystal unit, a unit in which an AT-cut crystal plate is supported by a metal support frame is known. FIG. 4 shows an example of these conventional crystal oscillators. In FIG. 4, 1
Is an AT-cut quartz plate, 4 is an electrode deposited on both sides of the quartz plate 1, 11 is a holding portion for holding the quartz plate 1, and 12 is a conductive adhesive for bonding the holding portion 11 and the quartz plate 1. .
The electrodes 4 are electrically connected to different holding portions 11 via a conductive adhesive 12.

[0004]

In the conventional crystal unit, a metal holder 11 and a conductive adhesive 12 are usually used to hold the crystal plate 1. However, when the metal holding unit 11 is used, the coefficient of thermal expansion is different from the coefficient of thermal expansion of the crystal, so that when the temperature of the crystal resonator changes, thermal stress is generated between the holding unit 11 and the crystal plate 1. . Crystal plate 1
Since the oscillation frequency of depends largely on the stress in the crystal,
Such a holding method has a problem that the crystal resonator becomes unstable with respect to temperature change. In order to solve this problem, a structure is adopted in which a large gap is provided between the electrode portion 4 and the holding portion 11 so that the vibrating portion of the crystal plate 1 is not stressed. However, since the conductive adhesive 12 is used, stress due to expansion and contraction of the adhesive at the time of bonding is applied to the crystal plate 1. Further, thermal stress is generated due to the difference in thermal expansion coefficient between the adhesive 12 and the crystal plate 1. Further, the adhesive strength is not sufficient and a large adhesive area is required. Conductive adhesive 12
Since there is a problem in the heat resistance of, the soldering can be performed only at a low temperature. There are problems such as release of gas accompanying curing of the conductive adhesive 12, insufficient stability against mechanical vibration, and deterioration of the adhesive. Therefore, there is a problem that the stability of the crystal unit deteriorates.
There is a method of using various other adhesives instead of the conductive adhesive, but this problem is basically not solved as long as the adhesive is used.

Further, in an example of the manufacturing process of the crystal unit shown in FIG. 5, the crystal plate is cut first, and thereafter,
Polishing the individually separated quartz plates. for that reason,
If the quartz plate is cut into small pieces to make a small quartz oscillator, a very small quartz plate must be handled in the polishing process. In order to polish such a minute quartz plate, it is necessary to use an advanced polishing device, and it is difficult to use this manufacturing method to accurately manufacture a smaller quartz oscillator. Was.

Next, an electrode is vapor-deposited on the cut vibration part,
It is necessary to handle the cut quartz plates individually when connecting with the holding portion 11, and a certain size or more is required to apply the conductive adhesive. After that, the frequency is adjusted and it is hermetically sealed in a metal package.
Due to the reasons for cutting and polishing, the reason for conductive adhesive, etc.
Unless the crystal plate has a width of 2 mm or more and a length of 5 mm or more, it is difficult to produce a highly stable crystal resonator. In addition, if the crystal plate itself is large, it must be mounted in a separate container for hermetic sealing, and a considerable size is required for the entire crystal resonator.

On the other hand, in order to solve the problem of the thermal stress of the holding portion, for example, Japanese Patent Laid-Open No. 02-261210 discloses a structure in which a vibrating crystal plate is held by a crystal plate having substantially the same thermal expansion. . This example is shown in FIG. In FIG. 6, 1
3 is a vibrating crystal piece, 14 is an exciting electrode deposited on both sides of the vibrating crystal piece 13, 15 is a holding crystal piece for holding the vibrating crystal piece 13, 16 is a base, 17 is a vibrating crystal piece 13 and holding water. Conductive adhesive for fixing crystal piece 15, 18
Is an adhesive for bonding the holding crystal piece 15 and the base 16.

The fixing direction (XX direction) of the vibrating crystal piece 13 and the holding crystal piece 15, the holding crystal piece 15 and the base 16
The fixing direction (Z-Z) of is orthogonal to. With such a configuration, the holding crystal blank 15 has a free end in the longitudinal direction, can be expanded and contracted with respect to heat, and does not generate stress. Further, the vibrating crystal piece 13 has its longitudinal direction in the crystal piece 1
Both end sides are fixed so as to coincide with the longitudinal direction of 5. Therefore, the expansion and contraction of the vibrating crystal piece 13 in the longitudinal direction is affected by the holding crystal piece 15, but they are made of the same material and have the same coefficient of thermal expansion, so that thermal stress does not occur. With such a configuration, it is possible to prevent a frequency change due to thermal expansion and obtain good temperature characteristics.

However, since the vibrating crystal piece 13 and the holding crystal piece 15 are fixed by using the conductive adhesive, various problems caused by the conductive adhesive, such as adhesion at the time of bonding, are caused. The problem that the stress is applied to the crystal due to the expansion and contraction of the agent, the problem that thermal stress occurs due to the difference in the coefficient of thermal expansion between the adhesive and the crystal, that the adhesive strength is insufficient and a large adhesive area is required, and the conductive adhesive Since it has a problem with heat resistance of solder, it can only be processed at low temperature during soldering, gas is released due to hardening of the conductive adhesive, it is not sufficiently stable against mechanical vibration, and further deterioration of the adhesive Problems etc. are not solved. Therefore, the present quartz crystal resonator also has a problem that it cannot have sufficient stability in terms of temperature characteristics and deterioration.

Further, in order to solve the problems such as the generation of stress and gas due to the conductive adhesive, for example, JP-A-6-
As disclosed in Japanese Patent Publication No. 021745, there has been considered a method of joining a piezoelectric element such as a crystal oscillator to a holding member such as silicon via a glass plate by using a direct joining technique. FIG. 7 shows this example. In FIG. 7, 1 is a vibrating crystal plate, 2 is a silicon substrate, 22 is a glass plate, 4 is an excitation electrode, 5 is an electrode lead portion, and 6 is a terminal. It is necessary to heat in order to perform direct bonding, and in the bonding of quartz and silicon, which have different thermal expansion coefficients, one of them may be destroyed by thermal stress. Therefore, there is a problem that heat treatment can be performed only at a low temperature, and it is difficult to obtain sufficient bonding strength. In addition, JP-A-6-021
In Japanese Patent Publication No. 745, a glass plate having a coefficient of thermal expansion substantially equal to that of quartz is sandwiched between the quartz and silicon to reduce the influence on the quartz. However, with respect to the direct bonding of glass and silicon, there is a problem that glass has a coefficient of thermal expansion almost equal to that of quartz, so that there is a risk of breaking during heat treatment.

Further, products such as crystal oscillators, temperature-compensated crystal oscillators (TCXO), and voltage-controlled crystal oscillators (VCXO) have been made as applied products of crystal oscillators, but these products are also downsized. It is an important development goal. FIG. 8 shows an external view of a generally obtained TCXO. Here, for ease of understanding, a state in which a part of the case is removed is shown. In FIG. 8, 19
Is a crystal oscillator, 20 is a control circuit unit including an oscillation circuit, a voltage control circuit, a temperature sensor, and the like, and 21 is a case. The crystal oscillator 19 and the control circuit unit 20 are separately made, and then combined and housed in a case 21. Therefore, there is a problem that it is very difficult to reduce the size as a whole. Further, these problems are not limited to crystal oscillators, and various piezoelectric components (piezoelectric filters and SAW filters) are strongly affected by stress as long as mechanical vibration is used, and therefore similar problems occur.

As described above, in the conventional piezoelectric component, the stress due to the expansion and contraction of the adhesive at the time of bonding due to the conductive adhesive used for bonding the piezoelectric element such as the crystal resonator and the holding portion There are problems with piezoelectric components, deterioration of adhesive strength against vibration, etc., reliability problems with heating during soldering, problems of gas release, and problems of adhesive deterioration. The characteristics were unstable. Further, in miniaturization of piezoelectric components and products to which they are applied, there is a basic problem due to their structure. Further, in the piezoelectric component to which direct bonding is applied, the members are easily broken by thermal stress, and it is difficult to heat-treat at high temperature, and it is difficult to obtain sufficient bonding strength.

The present invention has been made in order to solve the problems of the conventional piezoelectric component as described above, and an object thereof is to provide a small-sized and highly stable piezoelectric component and a manufacturing method thereof.

[0014]

In order to achieve the above object, a piezoelectric component of the present invention comprises a vibrating piezoelectric plate, a substrate, and one or more stress buffer plates, one of the stress buffer plates. The Young's modulus of at least one layer has a smaller value than the Young's modulus of the one having the smaller thermal expansion coefficient among the vibration piezoelectric plate and the substrate, and the vibration piezoelectric plate, the substrate, and the stress buffer plate are It is fixed by direct bonding.

Further, another piezoelectric component of the present invention comprises a vibrating piezoelectric plate, a substrate, and one or more stress buffer plates, and at least one Young's modulus of the stress buffer plate is the vibration. A piezoelectric plate for vibration and a substrate having a smaller value than the Young's modulus of the larger thermal expansion coefficient, and the piezoelectric plate for vibration,
The substrate and the stress buffer plate are fixed by anodic bonding.

Still another piezoelectric component of the present invention comprises a vibrating piezoelectric plate, a substrate, and one or more stress buffer plates, wherein at least one of the stress buffer plates has a Young's modulus as described above. The vibration piezoelectric plate and the substrate each have a smaller value than the Young's modulus, and the one of the vibration piezoelectric plate and the substrate having a smaller thermal expansion coefficient and the stress buffer plate are fixed by direct bonding, and the vibration One of the piezoelectric plate and the substrate having a larger coefficient of thermal expansion and the stress buffer plate are fixed by anodic bonding.

In the above structure, the substrate is preferably either a silicon substrate or a glass substrate.
Further, in the above structure, the stress buffer plate is preferably a lithium niobate substrate. In the above structure, the vibrating piezoelectric plate is a crystal having at least a pair of excitation electrodes, and is preferably used as a crystal oscillator. Further, in the above structure, the vibrating piezoelectric plate is a crystal having at least two pairs of excitation electrodes, and is preferably used as a crystal filter.

On the other hand, the method for manufacturing a piezoelectric component of the present invention comprises a vibrating piezoelectric plate, a substrate, and one or more stress buffer plates, and at least one Young's modulus of the stress buffer plates is A method for manufacturing a piezoelectric component having a smaller value than a Young's modulus of a vibrating piezoelectric plate and the substrate having a smaller thermal expansion coefficient, wherein the vibrating piezoelectric plate, the stress buffer plate, and the surface of the substrate are Hydrophilic treatment is performed to bring them into contact, and in that state, the piezoelectric plate is heat-treated within a temperature range in which the piezoelectric plate shows piezoelectricity even after the heat treatment, and the vibration piezoelectric plate, the stress buffer plate, and the substrate are directly bonded. Let

Another method of manufacturing a piezoelectric component of the present invention comprises a vibrating piezoelectric plate, a substrate, and one or more stress buffer plates, and at least one of the stress buffer plates has a Young's modulus A method of manufacturing a piezoelectric component having a smaller value than the Young's modulus of a larger thermal expansion coefficient of the vibration piezoelectric plate and the substrate, wherein the vibration piezoelectric plate, the stress buffer plate, and the substrate A temperature range in which the piezoelectric plates exhibit piezoelectricity even after heat treatment, with their surfaces being in contact with each other and applying voltages between the vibration piezoelectric plate and the stress buffer plate and between the stress buffer plate and the substrate, respectively. Heat treatment is performed in the inside to anodic bond the vibration piezoelectric plate, the stress buffer plate, and the substrate.

Still another method of manufacturing a piezoelectric component according to the present invention comprises a vibrating piezoelectric plate, a substrate, and one or more stress buffer plates, and at least one of the stress buffer plates has a Young's modulus. Is a method of manufacturing a piezoelectric component having a smaller value than the Young's modulus of the larger one of the vibrating piezoelectric plate and the substrate, the vibrating piezoelectric plate and the substrate having a larger thermal expansion coefficient. While applying a voltage between the one and the stress buffer plate, in that state, heat treatment is performed within a temperature range in which the piezoelectric plate shows piezoelectricity even after heat treatment,
One of the piezoelectric plate for vibration and the substrate having a larger thermal expansion coefficient and the stress buffer plate are anodically bonded, and the piezoelectric plate for vibration and the one having a smaller thermal expansion coefficient and the surface of the stress buffer plate. Are subjected to a hydrophilic treatment and brought into contact with each other, and in that state, they are heat-treated within a temperature range in which the piezoelectric plate shows piezoelectricity even after heat treatment, and one of the vibrating piezoelectric plate and the substrate having a smaller coefficient of thermal expansion is Directly joined to the stress buffer plate.

[0021]

According to the piezoelectric component and the method for manufacturing the same of the present invention configured as described above, since the vibrating piezoelectric plate is fixed by direct bonding without using an adhesive, the stress due to the expansion and contraction of the adhesive causes the piezoelectric element to move. It does not add to the plate and does not generate gas from the adhesive. Further, since it is not necessary to consider the heat resistance of the adhesive in the difference in coefficient of thermal expansion between the adhesive and the piezoelectric plate, heat treatment can be performed at a high temperature. As a result, the bonding strength becomes strong,
Stability against vibration is improved and vibration characteristics are not deteriorated. Further, it is stable against heat during soldering and the like, and does not deteriorate due to high heat. Further, the vibrating piezoelectric plate is fixed to the substrate at an accurate position together with the stress buffer plate, so that the space for sealing can be reduced and the piezoelectric component as a whole can be easily downsized. Further, the vibration piezoelectric plate and the stress buffer plate are fixed to the substrate, and by using silicon as the substrate, a control circuit and the like can be incorporated and integrated. Furthermore, by using a crystal as the piezoelectric plate, it is possible to fabricate a crystal oscillator, a temperature-compensated crystal oscillator, a voltage-controlled crystal oscillator, etc. that are extremely highly stable and integrated into a single chip. Can be miniaturized.

[0022]

Embodiments of the piezoelectric component and the method for manufacturing the same according to the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a perspective view of a piezoelectric vibrator according to a first embodiment of the piezoelectric component of the present invention. In FIG. 1, the piezoelectric vibrator includes a piezoelectric plate for vibration 1, a substrate 2, a stress buffer plate 3,
The excitation electrode 4, the electrode lead-out portion 5, and the terminal 6 are provided. The stress buffer plate 3 has a Young's modulus smaller than that of the vibrating piezoelectric plate 1 or the substrate 2 having the smaller thermal expansion coefficient. In addition, a part of the vibrating piezoelectric plate 1 in the vicinity of the periphery is a stress buffer plate 3.
Is directly fixed to the substrate 2, and a part of the stress buffer plate 3 is fixed to the substrate 2 by direct bonding. Vibration piezoelectric plate 1
An AT-cut crystal oscillator was used as the substrate, a silicon substrate was used as the substrate 2, and a lithium niobate substrate was used as the stress buffer plate 3, and a crystal oscillator was formed on the silicon substrate.

Here, the direct joining will be described. The direct bonding is a crystal surface on the adhered surface of the substrates without interposing an adhesive between silicon substrates, a single crystal such as a silicon plate and a glass plate, a glass plate and a crystal plate, or an oxide or a nitride. This is a technique in which a direct bond is established by using a covalent bond between a constituent atom and a constituent atom on the crystal surface of the other substrate. Firm adhesion can be obtained by bringing a silicon substrate, a glass plate, a crystal plate, etc., which have been subjected to polishing, washing, and hydrophilic group formation treatment into contact with each other in a clean atmosphere, and performing heat treatment. The adhesion strength shows a value of about several tens of kgw / cm ² even in the initial stage of just contacting after the hydrophilic group forming treatment, and further, by applying heat treatment, the value is several hundred kgw / cm ^2.
It rises to cm ² or more.

Specifically, such a bond is formed as follows. After the hydrophilic group formation treatment, in the initial stage of merely bringing them into contact with each other, the substrates to be bonded are bonded to each other through a hydrogen bond between a hydrophilic group formed on the surface and water molecules existing between the surfaces to be bonded. There is. By performing heat treatment in this state, the water molecules existing at the interface are removed from the interface, and the bond via the water molecule gradually changes to a strong covalent bond between the crystal constituent atoms. Therefore, in the fixing using direct bonding, the fixing strength is high, and since no adhesive is used at all, it is resistant to heat treatment, vibration, etc., and unnecessary gas is not emitted.

However, since the direct bonding requires heat treatment, the direct bonding of materials having different thermal expansion coefficients may cause a phenomenon of destruction due to thermal stress. The thermal expansion coefficient of the AT-cut quartz plate is approximately 9 × 10 ⁻⁶ in the largest direction, whereas the thermal expansion coefficient of the silicon substrate is approximately 6 × 10 ⁻⁶ . Therefore, when heat treatment is performed at a high temperature, a large tension is applied to the silicon substrate, and the silicon substrate is continuously broken by the tension and destroyed. As a result, depending on the thicknesses of the silicon substrate and the crystal plate, the heat treatment temperature for providing sufficient bonding strength may not be achieved. There is also a method of directly joining a quartz plate and a silicon substrate with a buffer plate having a coefficient of thermal expansion intermediate between them, but in this case as well, the thickness between these members and the coefficient of thermal expansion are In some cases, sufficient heat treatment cannot be achieved due to the above reasons.

Generally, a large tension is applied near the joint surface of the member having a small coefficient of thermal expansion. In the case of the present embodiment, a large amount of tension is applied to the silicon side in the direct bonding of quartz and silicon. Here, when directly bonded through a material having a small Young's modulus (stress buffer plate), the stress buffer plate is greatly distorted by a small stress, so the strain due to the difference in thermal expansion coefficient between the two substrates is concentrated on the stress buffer plate, Only small stress is generated. For this reason,
By sandwiching a member having a Young's modulus smaller than the member to which tension is applied as a stress buffer plate near the joint surface,
It becomes possible to withstand greater tension. This means that heat treatment at a higher temperature is possible and the strength of direct bonding can be increased. The Young's moduli of the AT-cut quartz, silicon, and lithium niobate crystals used in this example are 7.8 × 10 ¹⁰ and 20 × 1, respectively.
0 ¹⁰ and 17 × 10 ¹⁰ . Further, the AT-cut quartz and the coefficient of thermal expansion of silicon are 13.71 × 10 ⁻⁶ and
It is 3.35 × 10 ⁻⁶ , which satisfies the above condition.

After the crystal unit is formed, it is necessary to reflow at 200 ° C. or more for soldering on the substrate. However, when a conductive adhesive is used as in the conventional example, the reliability against solder reflow is poor, and the resonance frequency is generally 2 to 3 p before and after solder reflow.
pm fluctuates. On the other hand, in the crystal unit having the structure of this embodiment, since the conductive adhesive is not used, the characteristics of the crystal unit are greatly improved. As a specific example, an AT-cut crystal plate having a size of 1 mm × 3 mm as a vibration piezoelectric plate, a lithium niobate substrate having a size of 1 mm × 1 mm as a stress buffer plate, and a P-type having a size of 3 mm × 4.5 mm as a substrate Using a silicon single crystal plate, a plurality of crystal resonators having the structure of the above-described first embodiment of the present invention were manufactured. For comparison, a plurality of comparative crystal oscillators having a structure in which a vibrating crystal plate having a size of 1 mm × 3 mm is adhered to a conventional metal holding portion by a conductive adhesive is also prepared and compared with the crystal oscillator of the present invention. The solder reflow characteristics of the frequency of the quartz crystal unit were measured. As a result, the number of resonance frequency fluctuations of 2 ppm or more due to the solder reflow was less than half that of the comparative crystal oscillator.

Furthermore, since a circuit for driving and controlling the vibrating crystal plate can be incorporated in the silicon substrate, it is possible to manufacture a crystal oscillator, a temperature-compensated crystal oscillator, and a voltage-controlled crystal oscillator that are integrated into one chip. Become. In Figure 2,
The perspective view of the temperature-compensated crystal oscillator integrated into one chip is shown. In FIG. 2, the temperature-compensated crystal oscillator includes a vibrating crystal plate 1, a silicon substrate 2, a stress buffer plate 3, an excitation electrode 4, an electrode lead-out portion 5, and a control circuit 7.

Although direct bonding is used in this embodiment, anodic bonding may be used for bonding the piezoelectric vibration plate 1 and the stress buffer plate 3 and the substrate 2 and the stress buffer plate 3. Here, the anodic bonding will be described. The anodic bonding is a bonding method that does not use an adhesive like the direct bonding, and the bonding is performed by heating while applying a voltage between the two substrates. In order to apply a voltage to both substrates, it is necessary to deposit electrodes in advance. For example, in the case of a silicon substrate and a glass substrate, electrodes are vapor-deposited on the glass substrate and a voltage is applied between the electrodes vapor-deposited on the silicon substrate and the glass substrate. In addition, before heating, it is not preferable that an electric current flows between the substrates, so an insulator such as silicon oxide may be vapor-deposited in advance. As an example, there is a case where silicon substrates are anodically bonded to each other. In this case, silicon oxide is deposited on at least one of the silicon substrates to insulate the silicon substrates from each other. Before heating, both substrates are in close contact with each other due to the voltage applied between the substrates, but are in a non-bonded state. When heating is performed from this state, a current flows between both substrates when the temperature exceeds a certain temperature. At this time, the insulation between the two substrates is destroyed and the substrates are joined together. This is because the insulation between the substrates is easily broken by the temperature rise, and at the moment when the insulation is broken, the atoms of both substrates move at the bonding surface, the voids are filled, and the recombination between the atoms occurs. It is considered. Since the anodic bonding is performed at a high temperature, the stress increases as the temperature decreases. For this reason,
Unlike direct bonding, tension is applied to the one with the higher coefficient of thermal expansion. Therefore, by using a material having a Young's modulus smaller than that of the piezoelectric vibrating plate 1 and the substrate 2 having a larger thermal expansion coefficient as the stress buffer plate 3, anodic bonding can be performed at a high temperature. In this case, it is needless to say that since a conductive adhesive is not used to fix the piezoelectric plate, a very highly stable vibrator can be produced.

(Second Embodiment) A second embodiment of the piezoelectric component and the manufacturing method thereof according to the present invention will be described in detail below with reference to FIG. In FIG. 3, (a), (b),
(C), (d), (e) and (f) show respective steps of the method for manufacturing the piezoelectric component (piezoelectric vibrator) according to the second embodiment. Further, the piezoelectric vibrator according to the second example includes a vibrating crystal plate 1, a silicon substrate 2, a stress buffer plate 3, an excitation electrode 4, and an electrode lead portion 5. Further, in FIG. 3, 8 is a crystal blank, 9 is a lithium niobate substrate, and 10 is a silicon blank. The stress buffer plate 3 has a Young's modulus smaller than the Young's modulus of the vibrating quartz plate 1 and the silicon substrate 2, that is, the Young's modulus of the silicon substrate 2, and is formed of, for example, lithium niobate. Has been done. The crystal blank 8 has a thickness of 350 μm and a size of 3 inches, an AT-cut crystal blank, the lithium niobate substrate 9 has a thickness of 350 μm, a size of 3 inches, a lithium niobate substrate, and the silicon substrate 10 has a plane orientation ( 100), a P-type single crystal silicon substrate having a thickness of 450 μm and a size of 3 inches was used.

As shown in FIG. 3A, the quartz crystal plate 8 was previously etched to a depth of 80 μm so that a predetermined number and a predetermined pattern of the vibrating crystal plate 1 were left. In addition, a recess having a depth of 50 μm was formed on the lithium niobate substrate 9 so that a predetermined number and a predetermined pattern of the stress buffer plate 3 were left. The crystal blank 8
All the portions of the vibrating crystal plate 1 remaining on the top and all the portions of the stress buffer plate 3 remaining on the lithium niobate substrate 9 are in contact with each other at predetermined positions. It was determined. Next, the surfaces of the crystal blank 8 and the lithium niobate substrate 9 were mirror-polished, and the surfaces were hydrophilized with a mixed solution of ammonia water, hydrogen peroxide solution and water, and washed with water. After that, it was carefully washed so that dust was not present at the portion where the vibrating crystal plate 1 and the stress buffer plate 3 were in contact with each other. Next, the crystal blank 8 and the lithium niobate substrate 9 were brought into contact with each other while keeping their surfaces clean.
Although it has a considerable adhesive strength as it is, it was subjected to a heat treatment so as to have a strength not lower than the strength at which polishing can be performed later. Since the crystal transition temperature of the crystal is 870 ° C., if the crystal is heated above this temperature, it will not exhibit piezoelectricity when returned to room temperature. Therefore, the heat treatment temperature cannot be 870 ° C. or higher. In this example, the heat treatment temperature was set to 500 ° C, for example.

Next, as shown in FIG. 3 (b), in order to separate the stress buffer plates 3 one by one, they were directly bonded to the crystal blank 8 while holding the crystal blank 8 side. The lithium niobate substrate 9 was polished. Next, in order to directly bond the silicon substrate 10 and the stress buffer plate 3 formed on the quartz crystal plate 8, the surfaces thereof are mirror-polished, and further, a mixed solution of ammonia water, hydrogen peroxide solution and water is added. The surface was hydrophilized with and washed with water. Then, it was washed carefully so that dust was not present on the surfaces of the stress buffer plate 3 and the silicon substrate 10 formed on the quartz crystal plate 8. Next, FIG.
As shown in (c), the silicon substrate 10 and the stress buffer plate 3 formed on the quartz crystal plate 8 were brought into contact with each other while keeping their surfaces clean. Although it has a considerable adhesive strength as it is, it was subjected to a heat treatment so as to have a strength not lower than the strength at which polishing can be performed later. For the same reason as above,
Although the heat treatment temperature cannot be raised to 870 ° C. or higher, since the Young's modulus of lithium niobate is smaller than that of silicon, it can be heated to a relatively high temperature. In this example, the heat treatment temperature was set to 500 ° C., for example.

Next, as shown in FIG. 3D, while holding the crystal element plate 8 side, the silicon substrate 10 fixed by the stress buffer plate 3 directly bonded to the crystal element plate 8 is polished. Further, etching was performed from the side of the silicon substrate 10 where the stress buffer plate 3 was not directly joined to form an opening. After that, while holding the silicon substrate 10 side, the crystal element plate 8 fixed by the stress buffer plate 3 directly bonded to the silicon substrate 10 was polished to separate the vibrating crystal plate 1 individually. The state is shown in FIG.

Next, as shown in FIG. 3 (f), the quartz crystal plate 8 is arranged so as to face the vibrating quartz crystal plate 1 at approximately the center thereof.
A pair of excitation electrodes 4 was formed. At this time, the electrode lead-out portion 5 was also formed at the same time. In the case of this example, these were formed by vacuum-depositing chromium to a thickness of 20 nm (200 Å) and gold to a thickness of 50 nm (500 Å). Finally, the silicon substrates 10 were separated one by one to obtain crystal oscillators.

Since the vibration crystal plate 1, the stress buffer plate 3 and the silicon substrate 2 are processed with very precise dimensions by applying semiconductor processing techniques such as photolithography and etching, A very small, highly accurate, and high-performance crystal unit can be obtained. Further, in the present embodiment, a silicon substrate was used as the substrate and a lithium niobate plate was used as the stress buffer plate, but any material may be used as long as it satisfies the above-mentioned conditions, and is particularly limited to these materials. Not done. Further, it is needless to say that by using at least one layer of the stress buffering plate, it is possible to join them in the same manner and the same effect can be obtained.

Further, in the above embodiment, an example in which the heat treatment temperature in the direct bonding is 500 ° C. has been described, but the present invention is not limited to this, and 100 ° C. to 3 ° C.
50 ° C, 350 ° C to 500 ° C, 500 ° C to 570 ° C, 5
When the adhesive strength of the sample heat-treated in the range of 70 ° C. to 860 ° C. was examined, it was confirmed that the higher the temperature, the higher the adhesive strength. Therefore, it is only necessary to select a heat treatment temperature that is easy to carry out within a temperature range in which the piezoelectric component exhibits piezoelectricity even after the heat treatment and the properties of the piezoelectric component do not significantly change.

Further, in the above embodiment, the example in which the stress buffer plate is one layer has been described, but the present invention is not limited to this, and the case where the stress buffer plate is two layers, three layers, or more layers is used. However, it goes without saying that it becomes possible to perform direct bonding by selecting a material having an appropriate Young's modulus. Furthermore, in the above-mentioned examples, the lithium niobate plate was used as the stress buffer plate and the crystal oscillator was used as the piezoelectric oscillator. However, the material is not limited to these materials, and may satisfy the conditions described above. Needless to say, the same effect can be obtained by using one or more layers of stress buffering plates for the same adhesion.

Further, although direct bonding is used in the above embodiment, even when anodic bonding is used, there is an advantage that an adhesive is not used, and a stress buffer plate having a small Young's modulus is sandwiched in the bonding surface. As a result, it is possible to prevent damage due to stress during heat treatment, heat treatment at a higher temperature is possible, and it is possible to increase the bonding strength. As a result, highly stable piezoelectric components can be manufactured.

[0039]

As described above, according to the piezoelectric component and the method of manufacturing the same of the present invention, the vibrating piezoelectric plate does not use an adhesive,
Since it is fixed by direct bonding, stress due to expansion and contraction of the adhesive is not applied to the piezoelectric plate, and gas is not generated from the adhesive. Further, since it is not necessary to consider the heat resistance of the adhesive in the difference in coefficient of thermal expansion between the adhesive and the piezoelectric plate, heat treatment can be performed at a high temperature. On the other hand, in order to bond substrates having greatly different coefficients of thermal expansion, by sandwiching stress buffer plates with a small Young's modulus, it becomes possible to perform heat treatment at a higher temperature, and as a result, the bonding strength becomes stronger, Stability against vibration is improved and vibration characteristics are not deteriorated. Also,
It is stable against heat during soldering and does not deteriorate even when exposed to high heat. Further, the vibrating piezoelectric plate is fixed to the substrate at an accurate position together with the stress buffer plate, so that the space for sealing can be reduced and the piezoelectric component as a whole can be easily miniaturized. Further, the vibration piezoelectric plate and the stress buffer plate are fixed to the substrate, and by using silicon as the substrate, a control circuit and the like can be incorporated and integrated.
Furthermore, by using a crystal as the piezoelectric plate, it is possible to fabricate a crystal oscillator, a temperature-compensated crystal oscillator, a voltage-controlled crystal oscillator, etc. that are extremely highly stable and integrated into a single chip. Can be miniaturized. Further, by using a silicon substrate, a crystal plate, a glass plate or the like for the vibration piezoelectric plate, the stress buffer plate, the lid portion and the substrate portion, it becomes possible to apply the semiconductor processing technology, and the dimensions can be precisely processed. Therefore, a very small, highly accurate, and high-performance piezoelectric vibrator can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a crystal resonator according to a first embodiment of a piezoelectric component of the present invention.

FIG. 2 is a perspective view showing a configuration of a temperature-compensated crystal oscillator (TCXO) which is made into one chip in the first embodiment.

3 (a) to 3 (f) are cross-sectional views showing the respective steps of the second embodiment of the piezoelectric component and the manufacturing method thereof according to the present invention.

FIG. 4 is a perspective view showing a configuration of a conventional crystal unit.

FIG. 5 is a process diagram showing a conventional method for manufacturing a crystal unit.

FIG. 6 is a perspective view showing the configuration of another conventional crystal resonator.

FIG. 7 is a perspective view showing the configuration of still another conventional crystal resonator.

FIG. 8 is a perspective view showing the appearance of a conventional temperature-compensated crystal oscillator.

[Explanation of symbols]

 1: Quartz plate for vibration 2: Silicon substrate 3: Stress buffer plate 4: Excitation electrode 5: Electrode extraction part 6: Terminal 7: Control circuit 8: Crystal blank plate 9: Lithium niobate substrate 10: Silicon blank plate 11: Hold Part 12: Conductive adhesive 13: Vibration crystal piece 14: Excitation electrode 15: Holding crystal piece 16: Base 17: Conductive adhesive 18: Adhesive 19: Crystal oscillator 20: Control circuit 21: Case 22: Buffer Board

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Eda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (10)

[Claims] 1. A vibrating piezoelectric plate, a substrate, and one or more stress buffer plates, wherein at least one of the stress buffer plates has a Young's modulus which is higher than that of the vibrating piezoelectric plate and the substrate. A piezoelectric component having a smaller expansion coefficient than that of Young's modulus and in which the vibration piezoelectric plate, the substrate, and the stress buffer plate are fixed by direct bonding. 2. A vibrating piezoelectric plate, a substrate, and one or more stress buffer plates, wherein at least one of the stress buffer plates has a Young's modulus which is higher than that of the vibrating piezoelectric plate and the substrate. A piezoelectric component having a smaller expansion coefficient than the Young's modulus, and in which the vibration piezoelectric plate, the substrate, and the stress buffer plate are fixed by anodic bonding. 3. A vibrating piezoelectric plate, a substrate, and one or more stress buffer plates, wherein at least one of the stress buffer plates has a Young's modulus greater than that of each of the vibration piezoelectric plate and the substrate. The vibrating piezoelectric plate and the substrate having a smaller thermal expansion coefficient and the stress buffer plate having a smaller value than the Young's modulus are fixed by direct bonding, and the vibrating piezoelectric plate and the substrate have a thermal expansion coefficient. A piezoelectric component in which the one having a higher rate and the stress buffer plate are fixed by anodic bonding. 4. The piezoelectric component according to claim 1, wherein the substrate is one of a silicon substrate and a glass substrate. 5. The piezoelectric component according to claim 1, wherein the stress buffer plate is a lithium oxide niobate substrate. 6. The piezoelectric component according to claim 1, wherein the vibrating piezoelectric plate is a crystal having at least a pair of excitation electrodes and is used as a crystal resonator. 7. The piezoelectric component according to claim 1, wherein the vibrating piezoelectric plate is a crystal having at least two pairs of excitation electrodes and is used as a crystal filter. 8. A vibrating piezoelectric plate, a substrate, and one or more stress buffer plates, wherein at least one Young's modulus of the stress buffer plate is equal to that of the vibration piezoelectric plate and the substrate. A method for manufacturing a piezoelectric component having a smaller expansion coefficient than the Young's modulus, which comprises the vibration piezoelectric plate,
The stress buffer plate and the surface of the substrate are brought into contact with each other by hydrophilic treatment, and in that state, heat treatment is performed within a temperature range in which the piezoelectric plate exhibits piezoelectricity even after heat treatment, the vibration piezoelectric plate, and A method for manufacturing a piezoelectric component, in which a stress buffer plate and the substrate are directly bonded. 9. A vibrating piezoelectric plate, a substrate, and one or more stress buffer plates, wherein at least one Young's modulus of the stress buffer plate is equal to that of the vibration piezoelectric plate and the substrate. A method of manufacturing a piezoelectric component having a smaller expansion coefficient than the Young's modulus, the vibration piezoelectric plate comprising:
The stress buffer plate and the surface of the substrate are brought into contact with each other, and a voltage is applied between the vibration piezoelectric plate and the stress buffer plate and between the stress buffer plate and the substrate, and in that state, even after the heat treatment. A method of manufacturing a piezoelectric component, wherein a heat treatment is performed within a temperature range in which a piezoelectric plate exhibits piezoelectricity, and the vibration piezoelectric plate, the stress buffer plate, and the substrate are anodically bonded. 10. A vibrating piezoelectric plate, a substrate, and one or more stress buffer plates, wherein at least one of the stress buffer plates has a Young's modulus which is higher than that of the vibrating piezoelectric plate and the substrate. A method for manufacturing a piezoelectric component having a smaller Young's modulus having a larger expansion coefficient, wherein a voltage is applied between the vibration damping piezoelectric plate and the substrate having a larger thermal expansion coefficient and the stress buffer plate. In the same state, the piezoelectric plate is heat-treated within a temperature range in which the piezoelectric plate shows piezoelectricity even after the heat treatment, and one of the vibration-use piezoelectric plate and the substrate having a larger thermal expansion coefficient and the stress buffer plate are anodically bonded. Then, one of the piezoelectric plate for vibration and the substrate having a smaller coefficient of thermal expansion is brought into contact with the surface of the stress buffer plate by applying a hydrophilic treatment, and in that state, the piezoelectric plate shows piezoelectricity even after heat treatment. Within temperature range A method of manufacturing a piezoelectric component, which comprises heat-treating and directly joining one of the vibration piezoelectric plate and the substrate having a smaller coefficient of thermal expansion and the stress buffer plate.