JPH06314947A - Crystal vibrator and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the small sized and highly stable crystal vibrator. CONSTITUTION:A vibration crystal plate 1 is formed to be a crystal vibrator fixed through direct bonding to a substrate 2 via a buffer plate 3 whose thermal expansion rate is an intermediate rate between that of a crystal and that of the substrate 2. In the manufacture method, the vibration crystal plate 1, the buffer plate 3 and the substrate 2 are made in contact with through hydrophilic processing and heat treatment is applied to the crystal within a temperature range at which the crystal indicates piezoelectricity to bond directly the vibration crystal plate 1, the buffer plate 3 and the substrate 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small and highly stable crystal oscillator and a method for manufacturing the same.

[0002]

2. Description of the Related Art Crystal oscillators have high stability,
It is used as an important device indispensable for information communication. With the development of satellite communication and mobile phones in recent years,
One of the major goals is to reduce the size and increase the performance of each device, but crystal units are no exception.

Crystal oscillators are required to have strict frequency stability. 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 oscillator, there is one in which an AT-cut crystal plate is supported by a metallic support frame. Figure 6
Shows an example of these crystal oscillators. In FIG. 6, 1
Reference numeral 5 is an AT-cut crystal plate, and electrodes 4 are formed on both surfaces of the crystal plate 1 by vapor deposition. The crystal plate 1 is held by a holding unit 16, and the holding unit 16 and the crystal plate 15 are held.
Are bonded with a conductive adhesive 17. The electrodes 4 are electrically connected to different holding portions via the conductive adhesive 17.

As described above, in the conventional crystal unit,
In order to hold the crystal plate 15, a metal holder 16 is usually used.
And the conductive adhesive 17 is used. FIG. 7 shows an example of the manufacturing process of this crystal unit. In this manufacturing process, the crystal plate is cut, and then the crystal plates that have been individually cut are polished. Next, an electrode is vapor-deposited on the cut quartz plate and bonded to the holding portion. Further, a conductive adhesive is attached, the frequency is adjusted, and the package is hermetically sealed with a metal package.

FIG. 8 shows how to solve the problem of thermal stress of the holding portion (Japanese Patent Laid-Open No. 2-261210). This is an exciting electrode 1 on both sides of the vibrating crystal piece 18.
9 is vapor deposited, and the vibrating crystal piece 18 is held by the crystal piece 20 having substantially the same thermal expansion. The crystal piece 20 is arranged on a base 21, and the vibrating crystal piece 18 and the holding crystal piece 20 are fixed by a conductive adhesive 22. The holding crystal piece 20 and the base 21
Are bonded with an adhesive 23. And the crystal piece for vibration 1
8 and the fixing direction of the holding crystal piece 20 (XX direction) and the fixing direction of the holding crystal piece 20 and the base 21 (ZZ) are orthogonal to each other.

Further, as a product to which the crystal unit is applied, there are a crystal oscillator, a temperature-compensated crystal oscillator (TCXO), a voltage controlled crystal oscillator (VCXO) and the like. General TC in Figure 9
The external view of XO is shown. Here, for the sake of easy understanding, a state in which a part of the case is removed is shown. As shown in the figure, the case 26 has a configuration in which a crystal oscillator 24 and a control circuit 25 including an oscillation circuit, a voltage control circuit, a temperature sensor, and the like are combined and housed.

[0008]

However, when the metal holding portion 16 is used as shown in FIG. 6, the coefficient of thermal expansion is different from that of the crystal plate 15, so that the temperature of the crystal resonator changes. Then, thermal stress is generated between the holding portion 16 and the crystal plate 15. Since the oscillation frequency of the crystal plate 15 largely depends on the stress in the crystal, such a holding method results in a crystal oscillator that is unstable with respect to temperature changes. for that reason,
A large gap must be provided between the electrode 4 and the holding portion 16 so that stress is not applied to the vibrating portion of the crystal plate 15. Moreover, since the conductive adhesive 17 is used, the stress due to the expansion and contraction of the conductive adhesive 17 at the time of bonding is applied to the crystal plate 15, and the thermal expansion is caused by the difference in the coefficient of thermal expansion between the conductive adhesive 17 and the crystal plate 15. There is a problem that stress is generated, that the adhesive strength is not sufficient and a large adhesive area is required, and that there is a problem in the heat resistance of the conductive adhesive 17, so that only a low temperature process can be performed in soldering. The stability of the crystal resonator is deteriorated due to the release of gas accompanying the curing of the agent 17, insufficient stability against mechanical vibration, and the problem of deterioration of the conductive adhesive 17. There is also 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 the manufacturing method shown in FIG. 7, if a crystal plate is cut into small pieces in order to produce a small crystal resonator, a very small crystal plate is handled in the polishing process.
A sophisticated polishing apparatus must be used to polish such a minute quartz plate. Therefore, it is difficult to use this manufacturing method to accurately manufacture a smaller crystal unit. Further, it is necessary to individually handle the cut crystal plates, and the crystal plates are required to have a certain size or more in order to apply the conductive adhesive. Due to the above-mentioned reasons related to cutting and polishing, and reasons related to conductive adhesives, in a crystal unit having such a structure, the crystal plate is usually 2 mm or more in width and 5 mm or more in length.
It was difficult to create a highly stable crystal unit. Further, since the crystal plate itself is large and it must be mounted in a separate container for hermetic sealing, a considerable size is required for the crystal unit as a whole.

Next, in the structure shown in FIG. 8, the holding crystal piece 20 has a free end in the longitudinal direction, and can be expanded and contracted with respect to heat so that stress is not generated. Further, the vibrating crystal piece 18 has its longitudinal direction aligned with the same direction as the crystal piece 20 and has its both ends fixed. Therefore, the expansion and contraction of the vibrating crystal piece 18 in the longitudinal direction is affected by the holding crystal piece 20, but the same material has the same coefficient of thermal expansion and does not generate stress due to heat. By so doing, it is possible to prevent frequency changes due to thermal expansion and obtain good temperature characteristics. However, since the vibrating crystal piece 18 and the holding crystal piece 20 are fixed using the conductive adhesive, various problems caused by the conductive adhesive and stress due to expansion and contraction of the adhesive at the time of bonding are caused. Is a crystal piece for vibration 1
8 problem, thermal stress occurs due to the difference in thermal expansion coefficient between the adhesive and the vibrating crystal blank 18, the adhesive strength is not sufficient and a large adhesive area is required, and the heat resistance of the conductive adhesive is high. The problem of soldering is that it can only be processed at low temperature during soldering, gas is released when the conductive adhesive is hardened, it is not sufficiently stable against mechanical vibration, and the problem of adhesive deterioration is solved. Not done. for that reason,
Even this crystal unit cannot have sufficient stability in terms of temperature characteristics and deterioration.

Further, in the TCXO shown in FIG. 9, the crystal unit 24 and the control circuit unit 25, which are separately manufactured, are combined and housed in the case 26. It was very difficult to reduce the size.

As described above, in the conventional crystal unit,
Due to the conductive adhesive for bonding the crystal plate and the holding part, the stress due to the expansion and contraction of the adhesive during bonding causes the crystal, the problem of reduced adhesive strength due to vibration, etc., the reliability of heating during soldering There was a problem of the property, the problem of the gas release, the problem of the deterioration of the adhesive, etc., and the characteristics were unstable with respect to aging and mechanical vibration. In addition, there is a fundamental problem due to the structure of the crystal unit and the products to which it is applied, which are miniaturized.

The present invention overcomes the above-mentioned drawbacks of a crystal unit, and provides a small-sized and highly stable crystal unit and a method for manufacturing the same.

[0014]

In order to solve the above-mentioned problems, the present invention is a crystal in which a vibrating crystal plate is fixed by direct bonding to a substrate through a buffer plate having a coefficient of thermal expansion intermediate between that of the crystal and the substrate material. Use the oscillator configuration. Further, the manufacturing method thereof, the vibrating crystal plate, the buffer plate, and the surface of the substrate are subjected to hydrophilic treatment and brought into contact with each other, and heat treatment is performed within the temperature range in which the crystal exhibits piezoelectricity even after the heat treatment, The method is to directly bond the vibrating crystal plate, the buffer plate, and the substrate.

[0015]

By virtue of the above-described structure and manufacturing method, that is, the vibrating crystal plate is fixed by direct bonding without using an adhesive, the adhesive strength is strong and the stability against vibration is improved. Also, it is stable and does not deteriorate with respect to heat caused by soldering, and does not generate gas so that vibration characteristics do not deteriorate. Moreover, the crystal plate for vibration is
Since it is fixed to the substrate at the correct position together with the buffer plate, the space at the time of sealing can be reduced and the crystal oscillator as a whole can be easily miniaturized. When glass is used as the buffer plate, it is inexpensive and easy to process by etching or the like. Further, the vibrating crystal plate and the 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, so that a crystal oscillator integrated into one chip, T
Since CXO and VCXO can be manufactured, these products can be easily miniaturized.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a perspective view of a crystal unit according to the present embodiment. In this figure, 1 is a vibrating crystal plate, 2 is a silicon substrate, and a buffer glass plate 3 having a coefficient of thermal expansion not larger than that of the vibrating crystal plate 1 but larger than that of the silicon substrate 2 is interposed between them. ing. An excitation electrode 4 is provided on the vibrating crystal plate 1, and an electrode lead-out portion 5 is provided from the excitation electrode 4 to a terminal 6 on the silicon electrode 2.

In this embodiment, a part of the vibrating crystal plate 1 in the vicinity of the periphery thereof is fixed to the buffer glass plate 3 by direct bonding, and one part of the vibrating crystal plate 1 of the buffer glass plate 3 is fixed. The portion is fixed to the silicon substrate 2 by direct bonding.

Here, the direct joining will be described. Direct bonding refers to the crystal surface constituent atoms on the non-fixed surface of the substrate and the crystal surface constituent atoms of the other substrate without the interposition of an adhesive between the silicon substrates, the silicon substrate and the glass plate, the glass plate and the crystal plate, etc. With the technique of directly fixing using a covalent bond between, the silicon substrate, glass plate, crystal plate, etc. that have been subjected to polishing, washing, and hydrophilic group formation treatment are brought into contact in a clean atmosphere, and heat treatment is performed. It is to obtain a strong fixation. This fixing strength shows a value of about several tens of kgw / cm ² even in the initial stage just after being contacted after the hydrophilic group forming treatment, but the value increases to several hundred kgw / cm ² or more by the heat treatment. To do.

Specifically, such a bond is formed as follows. After the hydrophilic group formation treatment, in the initial stage where they are only brought into contact with each other, the non-adhesive substrates are bonded to each other through the hydrogen bond between the hydrophilic group formed on the surface and the water molecule existing between the non-adhesive surfaces. ing. By performing heat treatment from 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. For this reason, in fixing using direct bonding, the fixing strength is high and no adhesive is used, so that it is resistant to heat treatment, vibration, etc., and unnecessary gas is not emitted. However, since direct bonding requires heat treatment, it is not possible to directly bond those having a large coefficient of thermal expansion. A
The thermal expansion coefficient of T-cut quartz plate is approximately 9 in the largest direction.
The thermal expansion coefficient of the silicon substrate is approximately 6 × 10 −6, while the thermal expansion coefficient is approximately 10 × 6. For this reason, a large tension is applied to the silicon substrate during the heat treatment, and the silicon substrate is broken without being affected by the tension.

However, the coefficient of thermal expansion of glass can be variously changed depending on the components and proportions constituting the glass. For example, a certain type of glass plate called borosilicate glass has a coefficient of thermal expansion of 6 to 8 × 10 −6, which is an intermediate value between the coefficient of thermal expansion of quartz and the coefficient of thermal expansion of silicon. When this glass and silicon or glass and crystal are directly bonded, since the coefficient of thermal expansion of glass is between silicon and crystal, a smaller stress is applied than when silicon and crystal are directly bonded.

By thus selecting the coefficient of thermal expansion, the vibration crystal plate 1 and the buffer glass plate 3 are directly joined,
The direct bonding of the buffer glass plate 3 and the silicon substrate 2 is possible without breaking each substrate. Further, since the buffer glass plate 3 is made of glass, the cost is low and the processing such as etching is easy.

After forming the crystal unit, it is necessary to reflow at 200 ° C. or more for soldering on the substrate.
However, when a conductive adhesive is used, the reliability against solder reflow is poor, and the resonance frequency generally fluctuates by 2 to 3 ppm before and after solder reflow. 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. For example, as a concrete example, the vibration crystal plate is 1 m.
An AT-cut crystal plate having a size of m × 3 mm, a borosilicate glass plate having a size of 1 mm × 1 mm as the holding glass plate, and a P-type single crystal plate having a size of 3 mm × 4.5 mm as the silicon substrate. A crystal unit having the structure described in this example was manufactured. For comparison, a comparative crystal unit having a structure in which the vibrating crystal plate having a size of 1 mm × 3 mm is adhered to a conventional metal holding portion with a conductive adhesive is also prepared. The solder reflow characteristics of the frequency of the crystal unit were measured. As a result, the amount of fluctuation 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, a crystal oscillator, TCXO or V, which is made into one chip, can be incorporated.
It enables the production of CXO. FIG. 2 shows a perspective view of the TCXO which is made into one chip. In this figure, 1 is a vibrating crystal plate, 2 is a silicon substrate, 3 is a buffer glass plate, 4
Is an excitation electrode, 5 is an electrode extraction portion, and 7 is a control circuit. (Embodiment 2) FIG. 3 is a perspective view of a crystal unit according to this embodiment. In this figure, 1 is a crystal plate for vibration, 8 is Z
The cut LiTaO3 substrate, 3 are not as large as the vibrating crystal plate 1, but have a larger coefficient of thermal expansion than the LiTaO3 substrate, a buffer glass plate, 4 is an excitation electrode, 5 is an electrode lead portion, and 6 is a terminal.

In this embodiment, a part of the vibrating crystal plate 1 in the vicinity of the periphery is fixed to the buffer glass plate 3 by direct bonding, and one part of the vibrating crystal plate 1 of the buffer glass plate 3 is fixed. The portion is fixed to the LiTaO3 substrate 8 by direct bonding. AT cut crystal plate and Z cut L
When the iTaO3 substrate is directly bonded, the thermal expansion coefficient of the AT-cut quartz plate is about 9 × 10 −6 in the largest direction, while the thermal expansion coefficient of the Z-cut LiTaO3 substrate is 4 × 10 in the smallest direction. Since it is -6, a large tension is applied to the LiTaO3 substrate during the heat treatment,
A phenomenon occurs in which the aO3 substrate is constantly destroyed by tension and is destroyed.

However, the coefficient of thermal expansion of glass can be variously changed depending on the components and proportions constituting the glass. For example, the thermal expansion coefficient of a certain type of glass plate called borosilicate glass is 6 to 8 × 10 −6, which is an intermediate value between the thermal expansion coefficient of quartz and the thermal expansion coefficient of LiTaO 3.
When this glass and LiTaO3 or glass and quartz are directly bonded, since the coefficient of thermal expansion of glass is between that of LiTaO3 and quartz, a smaller stress is applied than when LiTaO3 and quartz are directly bonded.

By selecting the coefficient of thermal expansion in this manner, the vibration crystal plate 1 and the buffer glass plate 3 are directly joined,
The direct bonding of the buffer glass plate 3 and the LiTaO3 substrate 8 is possible without breaking each substrate. Further, since the buffer glass plate is made of glass, the cost is low, and processing such as etching is easy.

After forming the crystal unit, it is necessary to reflow at a temperature of 200 ° C. or more for soldering on the substrate.
However, when a conductive adhesive is used, the reliability against solder reflow is poor, and the resonance frequency generally fluctuates by 2 to 3 ppm before and after solder reflow. 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. For example, as a concrete example, the vibration crystal plate is 1 m.
This embodiment uses an AT-cut crystal plate having a size of m × 3 mm, a borosilicate glass plate having a size of 1 mm × 1 mm as the holding glass plate, and a Z-cut plate having a size of 3 mm × 4.5 mm as the LiTaO3 substrate. A crystal unit having the structure described in the example was manufactured. For comparison, a comparative crystal unit having a structure in which the vibrating crystal plate having a size of 1 mm × 3 mm is adhered to a conventional metal holding portion with a conductive adhesive is also prepared,
Frequency solder reflow characteristics of the crystal unit and the comparative crystal unit were measured. As a result, the amount of fluctuation of 2 ppm or more due to the solder reflow was less than half that of the comparative crystal oscillator.

Further, in this embodiment, a silicon substrate was used as the substrate and a glass plate was used as the buffer plate. However, even if a GaAs substrate or LiTaO3 substrate is used as these materials, the vibrating quartz plate and the substrate material have the same coefficient of thermal expansion. It is obvious that the same effect can be obtained by using one or more layers of buffer plates having an intermediate value for the same adhesion. (Embodiment 3) Hereinafter, a third embodiment of the present invention will be described in detail with reference to the drawings. Fig. 4- (a), Fig. 4-
(B), FIG. 4- (c), FIG. 4- (d), FIG. 4- (e),
And FIG. 4- (f) is a figure which shows the manufacturing method of the crystal oscillator of this invention. In these drawings, 1 is a vibrating crystal plate, 2 is a silicon substrate, 3 is a buffer glass plate having a coefficient of thermal expansion not larger than that of the vibrating crystal plate and larger than silicon, 4 is an excitation electrode, and 5 is an electrode lead portion. , 9 is a crystal blank,
10 is a glass substrate, and 11 is a silicon base plate.

In this embodiment, the crystal blank 9 has a thickness of 3
AT-cut quartz crystal plate having a size of 50 μm and a size of 3 inches, the glass substrate 10 has a thickness of 350 μm, and a borosilicate glass substrate having a size of 3 inches has a plane orientation (100) and a thickness of 450 μm for the silicon base plate 11. A P-type single crystal silicon substrate having a size of 3 inches was used.

The quartz crystal plate 9 is etched to a depth of 80 μm by leaving a large number of shapes of the vibrating crystal plate 1, and the glass substrate 10 has a depth of leaving a large number of shapes of the buffer glass plate 3. It was removed by etching up to 50 μm. At this time, all the vibrating crystal plates 1 remaining on the quartz crystal plate 9 and all the buffer glass plates 3 remaining on the glass substrate 10 may be brought into contact with each other at desired positions. The position of each was determined. The surfaces of the quartz crystal plate 9 and the glass substrate 10 were mirror-polished, and the surfaces were made hydrophilic by using a solution obtained by heating a mixed solution of ammonia water, hydrogen peroxide solution and water to 60 ° C., and washed with water. . Then, it was washed carefully so that dust was not present at the portion where the vibrating crystal plate 1 and the buffer glass plate 3 were in contact with each other. Next, the crystal blank 9 and the glass substrate 10 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. This state is shown in FIG. 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 set to 870 ° C. or higher. Therefore, in this embodiment, the heat treatment temperature is set to 500 ° C., for example.

In order to separate the buffer glass plates 3 one by one, the glass substrate 10 directly bonded to the crystal plate 9 was polished while holding the crystal plate 9. This state is shown in FIG.

In order to directly bond the silicon base plate 11 and the buffer glass plate 3 formed on the crystal base plate 9, their surfaces are mirror-polished, and further, ammonia water and hydrogen peroxide solution are used. The surface was hydrophilized using a solution obtained by heating a mixed solution of water and water at 60 ° C., and washed with water. afterwards,
The surface of the buffer glass plate 3 and the silicon base plate 11 formed on the crystal base plate 9 was carefully washed so that no dust was present. Next, the silicon base plate 11 and the buffer glass plate 3 formed on the crystal base plate 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. This state is shown in FIG. For the same reason as above, the heat treatment temperature cannot be heated to 870 ° C. or higher, but the glass can be heated to a relatively high temperature because the coefficient of thermal expansion of glass is between silicon and quartz. Therefore, in this embodiment, the heat treatment temperature is set to 500 ° C., for example.

The silicon base plate 11 fixed by the buffer glass plate 3 directly bonded to the crystal base plate 9.
Is polished by holding the crystal blank 9, and further etching is performed from the side of the silicon blank 11 where the buffer glass plate 3 is not directly bonded to form an opening to form a silicon substrate 2. . Figure 4-
It shows in (d).

After that, the quartz crystal plate 9 fixed by the buffer glass plate 3 directly bonded to the silicon substrate 2 is polished by holding the silicon substrate 2, and the vibrating quartz plate 1 is obtained. Separated individually. The state is shown in FIG.

A pair of the excitation electrodes 4 are formed so as to face the quartz crystal plate 9 substantially in the vicinity of the center of the vibrating quartz plate 1. At this time, the electrode lead-out portion 5 was also formed at the same time. In the case of the present embodiment, these were formed by vacuum-depositing chromium to a thickness of 200 Å and gold to a thickness of 500 Å. The state is shown in FIG.

Finally, the silicon substrates 2 were separated one by one to obtain crystal oscillators. Since the vibration crystal plate 1, the buffer glass plate 3 and the silicon substrate 2 are processed with very precise dimensions by applying semiconductor processing techniques such as photolithography and etching, they are very precise. A compact, high-precision, high-performance crystal unit can be obtained. Further, since the buffer glass plate 3 is made of glass, the cost is low and the processing such as etching is easy.

Further, in this embodiment, a silicon substrate is used as a substrate and a glass plate is used as a buffer plate. However, even if a GaAs substrate or a LiNbO3 substrate is used as these materials, the vibrating quartz plate and the substrate material have the same coefficient of thermal expansion. It is obvious that the same effect can be obtained by using one or more layers of buffer plates having an intermediate value for the same adhesion. (Embodiment 4) Hereinafter, a fourth embodiment of the present invention will be described in detail with reference to the drawings. FIG. 5 is a cross-sectional view of a crystal unit obtained by the manufacturing method of the present invention. In this figure, 1 is a vibrating crystal plate, 2 is a silicon substrate, 3 is a buffer glass plate which is not as large as the vibrating crystal plate 1 and has a coefficient of thermal expansion larger than that of silicon, 4 is an excitation electrode, and 5 is an electrode lead portion. , 6 are terminals, 12 is a silicon substrate for the lid, 13
Is a silicon substrate for a base, and 14 is a low melting point glass.

In this embodiment, the vibrating crystal plate 1,
The silicon substrate 2, the buffer glass plate 3, and the excitation electrode 4 have the same configuration as the crystal oscillator of the first embodiment. The vibrating crystal plate 1 is vacuumed or sealed with an inert gas so that the silicon substrate 2 is sandwiched between the lid silicon substrate 12 and the base silicon substrate 13. As a sealing method, in the present embodiment, for example, only the peripheral portion of the electrode lead-out portion 5 is sealed with the low-melting glass 14, and the other portions are sealed by direct bonding to the lid silicon substrate 12 and the base. The silicon substrate 13 seals with nitrogen gas.

In this way, the lid portion and the base portion are also directly joined to the silicon substrate, whereby the positions of the vibrating crystal plate 1, the lid silicon substrate 12, and the base silicon substrate 13 are set. The relationship can be absolutely determined, without disturbing the vibration of the vibrating crystal plate 1,
Moreover, since the space required for sealing can be made very small,
The effect that the size of the entire crystal unit can be made extremely small is obtained. For example, as a specific example, when the size of the vibrating crystal plate is 1 mm × 3 mm, the size of the crystal resonator manufactured by the conventional method is 3 mm × 6 mm as a space, and the case has a thickness of 1 mm.
Since it is necessary to have a size of mm, the size will be 4 mm × 7 mm as a whole. On the other hand, in the case of the crystal unit having the structure of the present embodiment, the size of the vibrating crystal plate is also 1 mm × 3 mm, and the size of the buffer glass plate is 1 mm.
mm x 1 mm, the size of the silicon substrate is 2 mm
When it is set to 5 mm, the size of the space may be almost the same as that of the vibrating crystal plate, and the size of the lid silicon substrate 12 and the base silicon substrate 13 is 2 mm.
Since 4.5 mm is sufficient, it is very effective for miniaturization.

Also, using silicon, which is a semiconductor, as a substrate,
Moreover, as described above in the first embodiment, since the sealing is performed by using it, it has good compatibility with an integrated circuit and can be easily applied to integration with an oscillator or the like.

Further, although a silicon substrate is used as a substrate and a glass plate is used as a buffer plate in the present embodiment, even if a GaAs substrate or a LiTaO3 substrate is used as these materials, the vibrating quartz plate and the substrate material have the same coefficient of thermal expansion. It is obvious that the same effect can be obtained by using one or more layers of buffer plates having an intermediate value for the same adhesion.

In the examples, the heat treatment temperature in direct bonding is set to 500 ° C., but the present invention is not limited to this. 100 ° C to 350 ° C,
350 ° C-500 ° C, 500 ° C-570 ° C, 570 ° C-
The adhesive strength of quartz and silicon was also examined at 860 ° C, but the higher the temperature, the greater the adhesive strength.
The heat treatment temperature may be selected within a temperature range in which the quartz exhibits piezoelectricity even after the heat treatment and the properties of the buffer glass plate do not significantly change.

Further, in the embodiment, the buffer crystal plate is set to 1
Although examples of layers are described, the present invention is not limited to this. Even when the buffer crystal plate is made of two layers, three layers, or more layers, it is possible to reduce the thermal stress by selecting the coefficient of thermal expansion of the glass between the silicon and the crystal. It becomes possible to do.

Further, in the embodiment, the glass plate is used as the buffer plate, and the silicon substrate and LiTaO3 are used as the substrate. However, as the substrate, various substrates such as GaAs substrate and LiNiO3 can be used. It is obvious that the same effect can be obtained by selecting a material having a coefficient of thermal expansion during the period.

[0045]

As is apparent from the above description of the embodiments, since the vibrating crystal plate and the buffer plate and the buffer plate and the substrate do not differ greatly in the coefficient of thermal expansion in the present invention, direct bonding is possible. Yes, because fixing does not use an adhesive or the like, the stress due to expansion and contraction of the adhesive at the time of adhesion will be applied to the crystal, and sufficient adhesive strength is not sufficient and a large adhesive area is required. 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 There are no problems, such as instability in characteristics with respect to temperature and mechanical vibration, and it is possible to manufacture a highly stable crystal oscillator suitable for miniaturization.

Furthermore, by using a silicon substrate as the substrate, a circuit for driving and controlling the vibrating crystal plate can be incorporated on the silicon substrate, so that a crystal oscillator, TCXO or VCX integrated into one chip.
O can be produced. In addition, since the crystal plate for vibration, the glass plate for buffer, and the silicon substrate can be precisely processed by applying semiconductor processing technology, a very small and highly accurate, high-performance crystal resonator can be obtained. .

Further, by using glass as the buffer plate, processing such as etching is inexpensive and easy.

[Brief description of drawings]

FIG. 1 is a perspective view of a crystal unit according to a first embodiment of the invention.

FIG. 2 is a perspective view of a one-chip TCXO.

FIG. 3 is a perspective view of a crystal unit according to a second embodiment of the present invention.

FIG. 4 is a process diagram showing a method of manufacturing a crystal unit according to a third embodiment of the present invention.

FIG. 5 is a sectional view of a crystal unit according to a fourth embodiment of the present invention.

FIG. 6 is a perspective view showing a conventional crystal unit.

FIG. 7 is a manufacturing process diagram of a conventional crystal unit.

FIG. 8 is a perspective view showing a conventional crystal unit.

FIG. 9: External view of TCXO

[Explanation of symbols]

 1 Crystal plate for vibration 2 Silicon substrate 3 Glass plate for buffer 4 Excitation electrode 5 Electrode extraction part 6 Terminal

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

Claims (6)

[Claims] 1. A vibrating crystal plate, a substrate, and a buffer plate having one or more layers, wherein the coefficient of thermal expansion of the buffer plate has a value between that of the vibrating crystal plate and the substrate, and the vibrating crystal plate. And the buffer plate are fixed by direct bonding, and the buffer plate and the substrate are fixed by direct bonding. 2. The crystal unit according to claim 1, wherein a silicon substrate is used as the substrate. 3. A vibrating crystal plate, a substrate, and a buffer plate having one or more layers, wherein the coefficient of thermal expansion of the buffer plate has a value between that of the vibrating crystal plate and the substrate, and the vibrating crystal plate. And, the surface of the buffer plate and the substrate is subjected to hydrophilic treatment and brought into contact with each other,
A method of manufacturing a crystal resonator, wherein the vibrating crystal plate, the buffer plate and the substrate are directly bonded by performing heat treatment within a temperature range where the crystal exhibits piezoelectricity even after the heat treatment. 4. The method of manufacturing a crystal resonator according to claim 3, wherein a silicon substrate is used as the substrate. 5. A vibrating crystal plate, a substrate, and a buffer plate having one or more layers, wherein the coefficient of thermal expansion of the buffer plate has a value between that of the vibrating crystal plate and the substrate. Is held by the buffer plate, the buffer plate is fixed to the substrate by direct bonding, and the crystal plate for vibration and the buffer plate are sealed by the substrate. 6. The crystal unit according to claim 5, wherein a silicon substrate is used as the substrate.