JP3114459B2 - Method for manufacturing piezoelectric element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a piezoelectric element for joining and integrating a piezoelectric ceramic and a substrate.

[0002]

2. Description of the Related Art FIG. 5 shows a method of bonding and integrating a piezoelectric ceramics 1 and a substrate 2 made of silicon or the like using anodic bonding. The anodic bonding generally joins the glass plate 4 and the silicon substrate 2 as shown in FIG. 4. The substrate 2 and the glass plate 4 are overlapped, and the substrate 2 is When a voltage of several hundred volts is applied between the glass plates 4, mobile ions of the glass layer move, and the two materials adhere to each other due to electrostatic attraction between the glass layer and the silicon substrate. By bonding oxygen and Si of the silicon substrate, the substrate 2 and the glass plate 4 are joined and integrated.

In order to join the piezoelectric ceramics 1 and the silicon substrate 2 using the above-described anodic bonding, as shown in FIG. 5, a glass layer 4 is formed as an inorganic adhesive layer on the joining surface of the piezoelectric ceramics 1, and The substrate 2 and the piezoelectric ceramics 1 are superimposed on each other via the glass layer 4, and several hundred volts are applied between the substrate 2 and the glass layer 4 by a power source 6 in a high-temperature furnace at 300 to 600 ° C.
Anodic bonding between the substrate 2 and the glass layer 4 is performed by applying
And a substrate 2 are integrated to produce a piezoelectric element.

[0004]

In the method of joining the piezoelectric ceramics 1 and the substrate 2 by anodic joining, the joining temperature is as high as 400 ° C. or 500 ° C., and therefore, after the anodic joining, the temperature is cooled to room temperature. During the process, a large internal strain remains in the piezoelectric element, and there is a problem that the residual strain lowers the mechanical strength of the piezoelectric element and degrades the characteristics of the element.

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a method of manufacturing a piezoelectric element in which residual stress of the element caused by high-temperature anodic bonding is reduced as much as possible. It is in.

[0006]

The present invention is configured as follows to achieve the above object. That is, the present invention provides a method for manufacturing a piezoelectric element in which a piezoelectric ceramic and a substrate are joined and integrated via an adhesive layer, wherein an inorganic adhesive layer is formed on a joint surface of the piezoelectric ceramic, and the substrate is interposed via the inorganic adhesive layer. And piezoelectric ceramics
The piezoelectric ceramics and the substrate are joined and integrated by applying a voltage between the substrate and the piezoelectric ceramics in a bonding temperature atmosphere.

[0007]

In the present invention having the above structure, when the piezoelectric ceramic is bonded to the substrate via the inorganic adhesive layer, a voltage is applied between the substrate and the piezoelectric ceramic.
Even if the thickness of the inorganic adhesive layer is reduced, dielectric breakdown of the inorganic adhesive layer is less likely to occur, and accordingly, the applied voltage can be increased as compared with a case where the applied voltage is directly applied to the inorganic adhesive layer. The temperature can be lowered, and the residual internal strain of the piezoelectric element decreases as much as the bonding temperature decreases.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In this embodiment, too, the piezoelectric ceramics 1 and the substrate 2 are joined by anodic bonding. However, a characteristic different from the conventional example shown in FIG. 5 is that the voltage applied between the substrate and the glass layer 4 at the time of anodic bonding is different. That is, the voltage is applied between the piezoelectric ceramics 1 and the substrate 2 instead of being applied between them.

In FIG. 1, lead zircon titanate Pb
Both surfaces of the (Zr _x Ti _1-x ) O ₃ -based piezoelectric ceramic 1 are polished, and a glass layer of Pyrex glass or the like having a thickness of several μm (2 μm in this embodiment) is formed on the bonding surface by sputtering or the like. 4 is formed as an inorganic adhesive layer,
On the opposite surface, a metal electrode 5a is formed by vapor deposition or the like.

On the other hand, a metal electrode 5b is formed on the electrode forming surface of the silicon substrate 2 by vapor deposition or the like. When the piezoelectric ceramics 1 and the substrate 2 are anodic-bonded, the bonding surface of the substrate 2 and the piezoelectric ceramics 1 are overlapped via the glass layer 4 and, for example, in an atmosphere at a bonding temperature of 400 ° C., the piezoelectric 500 between ceramics 1 and substrate 2
A voltage of V is applied. Then, the glass layer 4 and the substrate 2
Are anodically bonded to each other, and the piezoelectric ceramics 1 and the substrate 2 are integrally bonded to each other to produce a piezoelectric element.

In this embodiment, the voltage applied at the time of bonding is applied between the piezoelectric ceramics 1 and the substrate 2, that is, between the glass layer 4 and the substrate 2 via the piezoelectric ceramics 1. The following effects can be obtained. First, as a first effect, the withstand voltage of the glass layer 4 with respect to the applied voltage is increased, and the safety against dielectric breakdown is enhanced. In the method in which a voltage is directly applied to the glass layer 4 as in the conventional example shown in FIG. 5, there is a concern that an increase in the applied voltage may cause a dielectric breakdown of the glass layer. The broken portion is in a short-circuit state, and current flows through the insulating broken portion and the glass layer 4 and the silicon substrate 2
Therefore, there arises a problem that a voltage for anodic bonding cannot be obtained and anodic bonding cannot be performed.

On the other hand, in this embodiment, since a voltage is applied to the glass layer 4 via the piezoelectric ceramics 1,
Since the applied voltage is applied to the entire flat surface of the glass layer 4, the withstand voltage is increased. Further, as shown in FIG. Because piezoelectric ceramics are formed in series with 4,
Since the current flowing through the dielectric breakdown location 7 is blocked by the insulation resistance of the piezoelectric ceramic, the voltage required for anodic bonding between the glass layer 4 and the substrate 2 is secured except for the local location where the dielectric breakdown has occurred, and there is no trouble. Anodic bonding can be achieved.

Second, by increasing the withstand voltage of the glass layer 4 as described above, it is possible to apply a higher voltage than in the conventional example, and it is possible to obtain the effect of reducing the bonding temperature. The present inventors have demonstrated this effect by experiments. An example of this experimental result is shown in Table 1. For example, when the applied voltage is as low as 300 V, the junction temperature is set at 500 V.
The anodic bonding is obtained when the temperature is as high as ℃, and the anodic bonding cannot be performed at a lower bonding temperature of, for example, 400 ℃. In contrast, the applied voltage is 50
When the voltage is increased to 0 V, anodic bonding can be performed even when the bonding temperature is reduced to 400 ° C.

[0014]

[Table 1]

Examination of the above experimental results shows that the higher the applied voltage and the higher the bonding temperature, the higher the possibility of anodic bonding. The reason is that as the applied voltage is higher and the bonding temperature is higher, the mobile ions in the glass layer are more likely to move, and the electrostatic attraction between the glass layer 4 and the silicon substrate 2 increases, resulting in anodic bonding. It seems that the likelihood of this will increase.

In other words, the higher the applied voltage, the lower the bonding temperature can be, and the lower the bonding temperature, the lower the internal residual strain. This has the effect of increasing the mechanical strength due to the internal strain and preventing the deterioration of the device characteristics due to the internal strain.

As described above, in this embodiment, the voltage applied during the anodic bonding is not directly applied to the glass layer 4 but is applied to the glass layer 4 via the piezoelectric ceramics 1.
Even if a voltage is applied to the glass layer 4 indirectly via the piezoelectric ceramic 1 as described above, the piezoelectric ceramic 1 has a higher dielectric constant than the glass layer 4, so that a sufficiently high voltage necessary for anodic bonding is applied to the glass. It can be applied to layer 4. This can be explained as follows. An equivalent circuit at the anode junction of this embodiment can be represented as shown in FIG. Here V _E is the power supply voltage, V _P is the voltage applied to the piezoelectric ceramic 1, the V _g shows the voltage applied to the glass layer 4.
The capacitance C _P of the piezoelectric ceramic 1 is C _P = ε ₀ ε _P s
/ D _P , and the capacitance C _g of the glass layer 4 is C _g = ε
_It is expressed as ₀ ε _g s / d _g . Here, ε ₀ is the dielectric constant in a vacuum, ε _P is the relative dielectric constant of the piezoelectric ceramics 1, ε _g
Is the relative dielectric constant of the glass layer 4, d _P is the thickness of the piezoelectric ceramic 1, d _g is the thickness of the glass layer 4, s is the plane area of the piezoelectric ceramic 1 and the glass layer 4, Since the areas are equal, they are represented by the same symbol s.

When a voltage of V _E from the power supply voltage 6 is applied, the voltage V _g applied to the glass layer 4 becomes V _g = (1 / C
_g ) V _E / {(1 / C _P ) + (1 / C _g )} = C _P · V
_E / (C _P + C _g ) = (ε _P / d _P ) V _E / ｛(ε _P /
d _P ) + (ε _g / d _g )}.

The relative permittivity of the piezoelectric ceramic 1 of this embodiment is 1000 to 5000, and the relative permittivity ε _g of the glass layer 4 is about 5
, And the thickness of the piezoelectric ceramic 1 is 300 to 500 [mu] m, the thickness d _g of the glass layer 4 is 2 [mu] m, the voltage of V _g is by substituting these values into equation for the V _g sought, will be 2/3 the voltage of the V _g to about supply voltage V _E is applied, the as, by the withstand voltage of the glass layer 4 is sufficiently increased, it possible to increase the power supply voltage V _E Even if a voltage is applied via the piezoelectric ceramics 1, a high voltage can be applied to the glass layer 4 without any problem.

The present invention is not limited to the above embodiment, but can take various embodiments. For example, in the above embodiment, glass was used as the inorganic adhesive layer and silicon was used as the material of the substrate 2, but these inorganic adhesive layer and the material of the substrate may be other materials as long as they can be subjected to anodic bonding. .

The values of the junction temperature and the applied voltage shown in the present embodiment do not limit the present invention in any way, and it goes without saying that anodic bonding can be performed at other junction temperatures and applied voltages. is there.

[0022]

According to the present invention, the voltage applied to the inorganic adhesive layer in the bonding temperature atmosphere is not directly applied to the inorganic adhesive layer.
Since the voltage is applied via the piezoelectric ceramics, the breakdown voltage of the inorganic adhesive layer can be increased, and the applied voltage can be increased accordingly. By increasing the applied voltage, the joining temperature can be reduced accordingly, so that the generation of thermal stress and the internal residual strain of the thermal stress become smaller, so that the mechanical strength against the internal strain of the piezoelectric element becomes stronger, Further, it is possible to obtain an excellent effect that a reduction in characteristics due to internal strain of the piezoelectric element can be prevented with a decrease in residual internal strain.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the effect of increasing the withstand voltage of the glass layer 4 in this embodiment.

FIG. 3 is an equivalent circuit diagram for explaining a relationship between a junction temperature and an applied voltage in the present embodiment.

FIG. 4 is an explanatory view of a conventional general anodic bonding.

FIG. 5 is an explanatory view showing a conventional bonding example of a piezoelectric ceramic and a silicon substrate using anodic bonding.

[Description of Signs] 1 piezoelectric ceramics 2 substrate 4 glass layer

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Claims (1)

(57) [Claims] In a method of manufacturing a piezoelectric element, wherein a piezoelectric ceramic and a substrate are joined and integrated via an adhesive layer, an inorganic adhesive layer is formed on a joint surface of the piezoelectric ceramic, and the substrate is connected to the substrate via the inorganic adhesive layer. A method for manufacturing a piezoelectric element in which piezoelectric ceramics and a substrate are joined together by applying a voltage between the substrate and the piezoelectric ceramics in a bonding temperature atmosphere by superposing the piezoelectric ceramics.