JPH06164013A - Method for heating and joining piezoelectric body and substrate - Google Patents

Abstract

PURPOSE:To provide a method for heating and joining a piezoelectric body and a substrate without any warpage and crack and characteristic deterioration in a joint body even if they are cooled to normal temperatures after they are heated and joined. CONSTITUTION:The temperature dependency of average expansion coefficients of a piezoelectric body (PZT (1) and PZT (2)) which is heated and joined to Si substrate and the Si substrate from normal temperatures is obtained. In the case of the piezoelectric body PZT (1), the average expansion coefficient from the normal temperatures matches that of the Si substrate from the normal temperatures near 500 deg.C. On the other hand, in the case of the piezoelectric body PZT (2), it approaches the average expansion coefficient of the Si substrate from the normal temperatures near 300 deg.C. When the piezoelectric body PZT (1) is heated and joined to the Si substrate near 500 deg.C and the piezoelectric body PZT (2) is heated and joined near 300 deg.C, the heat shrinkable deformation of the piezoelectric body and that of the Si substrate are nearly equal when they are cooled to the normal temperatures thus preventing warpage and crack of a joined body and deterioration of characteristics of the piezoelectric body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of a piezoelectric body assembly for use in sensors such as pressure sensors, acceleration sensors, gyros and the like, and electromechanical interconversion devices such as piezoelectric actuators, and more particularly to piezoelectric bodies and substrates. The present invention relates to a heat bonding method.

[0002]

2. Description of the Related Art FIG. 3 shows the structure of a conventional method for heating and joining a piezoelectric body and a substrate. The bonding method shown in FIG. 3A is generally called glass bonding. For example, a glass layer 3 having a low melting point is formed on the surface of a Si substrate 2, and a piezoelectric body 1 is stacked on the glass layer 3 so that the piezoelectric body 1 side is formed. The piezoelectric body 1 is bonded to the Si substrate 2 by heating the whole while applying pressure.
The joining temperature at this time is 400 to 700 ° C. Also, FIG.
The bonding method shown in (b) is called anodic bonding. For example, as in the glass bonding method, the glass layer 3 is formed on the surface of the Si substrate 2, and the piezoelectric body 1 is superposed on the glass layer 3. An electrode 4 is provided on the piezoelectric body 1, and a voltage is applied between the Si substrate 2 and the piezoelectric body 1 to cause electrostatic attraction to both interfaces between the Si substrate 2 and the glass layer 3 and between the glass layer 3 and the piezoelectric body 1. Are bonded by chemical bonding. The bonding temperature at this time is 300 to 600 ° C.

[0003]

By the way, the piezoelectric body 1 is made of PZT composed of lead zirconate titanate or the like and having a different composition.
Although there are (1) and PZT (2), as shown in FIG. 2, the piezoelectric body PZT (1) is different from the thermal expansion coefficient of the Si substrate.
And the piezoelectric body PZT (2) have large thermal expansion coefficients, and the piezoelectric body 1 and the S
When the i substrate 2 is bonded, the bonding temperature needs to be 300 ° C. or higher. Therefore, when the bonded body is cooled to room temperature from the temperature of 300 ° C. or higher, the thermal expansion coefficient of the piezoelectric body 1 and the Si substrate 2 becomes Due to the difference, stress may be generated in the bonded body of the piezoelectric body 1 and the Si substrate 2, and the bonded body may be warped and cracked. When warp cracks occur, there are problems such as deterioration of the properties of the bonded body.

The present invention has been made in order to solve the above problems, and an object thereof is to prevent warping cracks and deterioration of characteristics of a bonded body even if the piezoelectric body and a substrate are heated and bonded and then cooled to room temperature. A method for heating and joining a piezoelectric body and a substrate is provided.

[0005]

In order to achieve the above object, the present invention is constructed as follows. That is, according to the present invention, in the heating and bonding method of the piezoelectric body and the substrate, in which the piezoelectric body is superposed on the substrate and heated to bond the piezoelectric body and the substrate, the thermal contraction deformation of the substrate and the piezoelectric body from the bonding temperature to the room temperature is the same. Alternatively, the bonding temperature is set so as to be close to each other, and the piezoelectric body and the substrate are bonded by heating.

[0006]

When the piezoelectric body and the substrate are heat-bonded, the temperatures at which the average expansion coefficients of the piezoelectric body and the substrate are equal or close to each other are set, and the piezoelectric body and the substrate are heat-bonded at this set temperature. Then cool to room temperature. As a result, the heat shrinkage deformations of the piezoelectric body and the substrate can be matched or made close to each other, and warpage cracking of the bonded body can be prevented. This prevents the characteristic deterioration of the piezoelectric body.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. In the description of the present embodiment, the same reference numerals will be given to the same names as those in the conventional example, and detailed description thereof will be omitted.

This embodiment is similar to the conventional example in that a piezoelectric body is superposed on a substrate and heated to bond the piezoelectric body and the substrate. The characteristic feature of this embodiment is that the piezoelectric body and the substrate are joined together. The joining temperature is set so that the heat shrinkage deformation from the joining temperature to the room temperature is equal to or close to each other, and the piezoelectric body 1 and the Si substrate 2 are heated and joined at this joining temperature.

FIG. 2 shows the temperature dependence of the coefficient of thermal expansion between the piezoelectric body and the Si substrate. In the figure, the coefficient of thermal expansion of the piezoelectric bodies PZT (1) and PZT (2) having different compositions greatly differs depending on the temperature, which is completely different from the curve of the coefficient of thermal expansion of the Si substrate, but they match in a certain temperature range. . The coefficient of thermal expansion tends to decrease near the Curie point of the piezoelectric body, and thereafter the coefficient of thermal expansion tends to increase.

By the way, when the piezoelectric body 1 and the Si substrate 2 are bonded at the bonding temperature T _b and cooled to room temperature T _m , the stress σ applied to the piezoelectric body 1 of the bonded body can be expressed as follows.

Σ ₁ = ε ₁ E ₁ / (1-ν) = (α ₁ −α ₂ ) (T _b −T _m ) E ₁ / (1-ν)

Here, ε ₁ is strain of the piezoelectric material, E ₁ is Young's modulus of the piezoelectric material, ν is Poisson's ratio, α ₁ is thermal expansion coefficient of the piezoelectric material, α ₂ is thermal expansion coefficient of Si substrate, T _b Is the junction temperature,
T _m is room temperature. Since T _m , E ₁ , and ν are constant, T _b
It can be seen that the stress increases as the difference between the thermal expansion coefficients of the piezoelectric body and the Si substrate increases with increasing. From this, it is understood that if the difference between the thermal expansion coefficient of the piezoelectric body and the thermal expansion coefficient of the Si substrate is made small, the stress becomes small.

As described above, if the difference in the coefficient of thermal expansion between the piezoelectric body 1 and the Si substrate 2 can be made small, the stress σ applied to the piezoelectric body 1 becomes small. By the way, as shown in FIG. 2, for example, the coefficient of thermal expansion of the Si substrate 2 and the coefficient of thermal expansion of the piezoelectric body PZT (1) are almost the same at around 350 ° C. Returning to 1, since the thermal expansion coefficient of the piezoelectric body 1 and the Si substrate 2 is greatly different from the bonding temperature to the room temperature, a large difference occurs in the thermal contraction deformation between the piezoelectric body 1 and the Si substrate 2, and the stress applied to the bonded body is reduced. It cannot be made smaller.

Therefore, the inventors have found that when the piezoelectric body 1 and the Si substrate 2 have the same average expansion coefficient from room temperature to the joining temperature, the heat shrinkage deformation becomes similar when the joint temperature is returned to the room temperature. Focusing on the fact that the stress applied to the bonded body becomes small, the average expansion coefficient of the piezoelectric body 1 and the Si substrate 2 from room temperature was calculated as shown in FIG. Piezoelectric PZT (1)
The average expansion coefficient from room temperature is around 500 ° C, which is the same as the average expansion coefficient of the Si substrate 2, and the piezoelectric PZT (2) has an average expansion coefficient of 300 ° C.
It is close to the average expansion coefficient of the Si substrate 2.

Therefore, based on the data of the average expansion coefficient of the piezoelectric body 1 and the Si substrate 2 from room temperature, the piezoelectric body 1 and Si
The substrate 2 was bonded by the anodic bonding method shown in FIG. 3B to form a bonded body. A low melting point glass layer 3 is formed on the surface of the Si substrate 2, and the piezoelectric body 1 (PZ
T (1) or PZT (2) are superposed, and the piezoelectric body 1 and the Si substrate 2 are anodically bonded. At this time, the piezoelectric body P
In the case of ZT (1), the joining is performed at a joining temperature near 500 ° C,
In the case of the piezoelectric body PZT (2), the joining was performed at a joining temperature near 300 ° C.

According to this embodiment, the piezoelectric body 1 and the Si substrate 2 are
Since the piezoelectric body 1 and the Si substrate 2 are bonded at a bonding temperature at which the average expansion coefficient from the room temperature is equal to or close to that of the room temperature, the heat of the piezoelectric body 1 and the Si substrate 2 is reduced when the bonded body is cooled to room temperature. Since the shrinkage deformations are equal to or close to each other, there is no problem such as warpage cracking of the bonded body, and there is almost no stress applied to the piezoelectric body 1, so that characteristic deterioration of the piezoelectric body 1 can be prevented.

The present invention is not limited to the above-mentioned embodiment, and various embodiments can be adopted. For example, in the above embodiment, P such as lead zirconate titanate is used as the piezoelectric body.
Although the ZT-based material is used, for example, a lead titanate-based material may be used, and the material is not limited as long as it is a piezoelectric material.

Further, in the above embodiment, the anodic bonding method was used for bonding the piezoelectric body and the Si substrate, but for example, the glass bonding method may be used as shown in the conventional example, and if it is the heating bonding method, the bonding is performed. The method does not matter.

Further, in the above embodiment, the substrate bonded to the piezoelectric body 1 is the Si substrate 2, but this substrate is, for example,
A ceramic substrate may be used, and any material may be used as long as it can be heat-bonded to the piezoelectric body 1.

[0020]

According to the present invention, when the piezoelectric body and the substrate are joined by heating, the joining temperature is set so that the thermal contraction deformation of the piezoelectric body and the substrate from the joining temperature to room temperature are the same or close to each other. Since they are heat-bonded to each other, there is no problem such as warpage cracking of the bonded body, and there is almost no stress applied to the piezoelectric body, so that deterioration of the characteristics of the piezoelectric body can be prevented.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the temperature dependence of the average expansion coefficient of a piezoelectric body and a Si substrate of this embodiment from room temperature.

FIG. 2 is an explanatory diagram showing temperature dependence of thermal expansion coefficients of the piezoelectric body and the Si substrate.

FIG. 3 is an explanatory diagram of various bonding configurations of a piezoelectric body and a Si substrate.

[Explanation of symbols]

 1 Piezoelectric substance 2 Si substrate 3 Glass layer 4 Electrode

Claims (1)

[Claims] 1. A method for heating and joining a piezoelectric body and a substrate, wherein a piezoelectric body is superposed on a substrate and heated to join the piezoelectric body and the substrate, in which the thermal contraction deformation of the substrate and the piezoelectric body is the same from the joining temperature to room temperature. A method for heating and joining a piezoelectric body and a substrate, wherein the joining temperature is set so as to be close to each other and the piezoelectric body and the substrate are joined together by heating.