JPH09181558A - Piezoelectric element and resin sealed piezoelectric part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element itself with moisture resistance and to suppress the variation of characteristics due to humidity or dew condensation by applying water repellent processing to the surface of a piezoelectric element. SOLUTION: The piezoelectric element 10 is constituted of a polarized piezoelectric ceramic substrate (piezoelectric substrate) 1, electrodes 2, 3 formed on both the main faces of the substrate 1 and an water repellent coat 4. The substrate 1 coated with the electrodes 2, 3 is also coated with the water repellent coat 4 as water repellent processing. The coat 4 is formed by applying a fluorine polymer solution diluted by a solvent and drying the applied solution. The film thickness of the coat 4 is about 0.1μm, and since the coat 4 does not act as an insulating coat, the electrodes 2, 3 can be electrically connected to an external circuit without generating any trouble. Since the piezoelectric element 10 can repulse water, humidity or the like even in the sticking state of humidity or water, dew condensation is not generated on the surface of the element 10 even in a state generating dew condensation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a repellent-processed piezoelectric element and a resin-encapsulated piezoelectric component containing the same in a container.

[0002]

2. Description of the Related Art Conventionally, a piezoelectric element is an element using a piezoelectric substrate having a piezoelectric effect (electrostrictive effect), and examples thereof include a resonator and a filter. Further, such a piezoelectric element is housed in a container in which an electrode led out to the outside is formed and mounted on a printed wiring board or the like. The state in which the piezoelectric element is housed in a container is called a piezoelectric component.

Further, there are piezoelectric elements that use bulk waves of the piezoelectric substrate and those that use elastic waves generated on the surface of the piezoelectric substrate.

For example, in the former case, a piezoelectric ceramic substrate such as PZT (lead zirconate titanate) or PT (lead titanate) which is polarized, or a piezoelectric substrate such as a piezoelectric single crystal substrate utilizing a predetermined crystal orientation such as quartz crystal. In addition, the electrodes facing each other in the thickness direction of the piezoelectric substrate were formed.

A piezoelectric component having such a piezoelectric element is
One of the plate-shaped substrate and the casing-shaped substrate forming the container is fixed so as to electrically connect the externally derivable electrode and the electrode of the piezoelectric element, and the plate-shaped substrate and the casing-shaped substrate are sealed. It was formed by joining with members. Examples of the material of the container include resins and ceramics,
Examples of the material of the sealing member include resin, glass, solder and the like.

However, when a resin is used as a sealing member in a piezoelectric component used under severe operating conditions, water will infiltrate from this sealing portion, causing condensation and icing on the piezoelectric element. There is a problem that stable vibration characteristics cannot be obtained.

For this reason, ceramics are used for the flat plate-like substrate and the casing-like substrate, and low melting point glass or the like is used for the sealing member. However, it is necessary to perform heat treatment at 360 to 400 ° C. at the time of glass sealing processing using low melting point glass for the bonding member.

At this time, since the Curie point of the piezoelectric substrate may be exceeded and the piezoelectric characteristics disappear, the piezoelectric element of the glass-sealed piezoelectric component has been exclusively used as the piezoelectric single crystal piezoelectric element. Further, in order to perform the above-mentioned heat treatment, it is necessary to use, for example, an expensive polyimide conductive resin paste for joining the piezoelectric element and the electrode for external lead formed on the container.

In the above-mentioned piezoelectric component having improved moisture resistance,
The same applies to not only the piezoelectric element using the bulk wave but also the one using the elastic wave generated on the surface of the piezoelectric substrate.

That is, in order to improve the moisture resistance reliability of the piezoelectric component, it is necessary to hermetically seal the structure of the container, in particular, glass sealing or the like, and the heat treatment at the time of sealing is performed. It was necessary to sufficiently consider the characteristics of the piezoelectric element regarding the temperature.

The present invention has been devised in view of the above-mentioned problems, and an object thereof is to provide a piezoelectric element itself with moisture resistance, thereby suppressing fluctuations in characteristics due to humidity and condensation. It is to provide a piezoelectric element capable of

Another object of the present invention is to provide an inexpensive and easy-to-handle piezoelectric component by using this piezoelectric element, which simplifies the construction of the container, especially the treatment of the sealing member.

[0013]

According to the first invention, an electrode for generating a piezoelectric effect is formed on at least one main surface of a piezoelectric substrate, and a water repellent film is formed on the surfaces of the piezoelectric substrate and the electrode. It is a piezoelectric element.

Here, when the electrodes of the piezoelectric element are formed on at least one main surface, for example, in the case of a piezoelectric element using a bulk wave generated on a piezoelectric substrate, a part of the piezoelectric substrate is opposed to both main surfaces. It is necessary to form matching electrodes, and in a piezoelectric element using elastic waves generated on the surface, electrodes are formed only on one main surface.

Further, such a piezoelectric element is housed in a container composed of a flat plate-shaped substrate and a housing-shaped substrate, and as a bonding member between the flat-plate-shaped substrate and the housing-shaped substrate, a resin-sealed resin is used. Type piezoelectric component.

[0016]

According to the first aspect of the present invention, since the surface of the piezoelectric element is covered with the water repellent film, regardless of the structure of the container, even if the moisture diffused in the container tries to adhere to the surface of the piezoelectric element, This moisture can be effectively repelled, and dew condensation does not occur on the surface of the element. Therefore, it is possible to effectively suppress the variation of the characteristics (frequency) of the piezoelectric element caused by the alteration of the piezoelectric substrate, the corrosion of the electrode, and the change of the mass.

According to the second aspect of the invention, in order to improve the humidity resistance reliability of the piezoelectric element itself, a flat plate-shaped substrate forming a container,
It is not necessary to consider moisture resistance in the material of the housing-like substrate and the material for joining the both, and in particular, a resin that can be processed at low temperature can be used as the sealing member. By using this resin, the heat treatment temperature for sealing can be processed at a low temperature, so there is no restriction on the piezoelectric elements that can be used,
The resin-encapsulated piezoelectric component is inexpensive and easy to handle, and the encapsulation process is simple, and the cost is low as a whole.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The piezoelectric element of the present invention will be described below with reference to the drawings.

FIG. 1 is an external perspective view of the piezoelectric element of the present invention. A piezoelectric ceramic substrate is used as the piezoelectric element, and a thickness sliding oscillator in which electrodes are formed on both main surfaces of the piezoelectric substrate will be described as an example.

In FIG. 1, reference numeral 10 denotes a piezoelectric element. This piezoelectric element 10 is a piezoelectric ceramic substrate (hereinafter referred to as a piezoelectric substrate) 1 that has been polarized, and electrodes 2 and 3 formed on both main surfaces of the piezoelectric substrate 1. , And the water repellent film 4.

The piezoelectric substrate 1 is made of PZT (lead zirconate titanate) or the like, and is polarized in the thickness direction.

Electrodes 2 and 3 made of Ag or the like are formed on both main surfaces of the piezoelectric substrate 1 by a thin film technique.

The electrode 2 is adhered and formed on the one main surface of the piezoelectric substrate 1 from one end of the short side to the center thereof.
The electrode 3 is attached and formed on the other main surface of the piezoelectric substrate 1 from the other end of the short side to the center. As a result, in the vicinity of the central portion of the piezoelectric substrate 1, the electrode 2 and the electrode 3 face each other with a predetermined area.

On the piezoelectric substrate 1 on which the electrodes 2 and 3 are adhered and formed, a water repellent film 4 is adhered and formed as a water repellent treatment.

The water repellent film 4 is formed by applying a fluoropolymer solution diluted with a solvent and drying it.
For example, the piezoelectric substrate 1 is dipped in a fluoropolymer solution diluted with a solvent, the excess solution is removed by a centrifuge, and
It is formed by a drying treatment at 150 ° C. Also,
The piezoelectric substrate 1 may be applied by spin coating or printing and then dried.

The water-repellent coating 4 thus formed has a thickness of about 0.1 μm, and since the coating does not act as an insulating coating, the electrodes 2, 3 and the external circuit are electrically connected. Connection can be done without any problems.

The water-repellent coating 4 is formed by forming a copolymer of (meth) acrylate containing a polyfluoroalkyl group and methacrylate containing a water distribution group, or under reduced pressure. SiO using CVD method
It can also be formed by forming _two films or a chlorosilicone film.

According to the piezoelectric element 10 described above, the piezoelectric element 1
Even if moisture or moisture tries to adhere to the surface of No. 0, the moisture, moisture, etc. can be effectively repelled, and dew condensation occurs due to the humidity inside the container that houses the piezoelectric element 10 and the temperature difference between the inside and the outside air. Even in the state, due to the surface water repellent action of the piezoelectric element 10, it does not occur on the surface of the piezoelectric element 10, but can occur on the inner wall side of the container.

With these, it is possible to prevent the deterioration of the piezoelectric substrate 1, the deterioration of the electrodes 2 and 3, and the corrosion.
It is possible to derive stable characteristics for a long period of time, in which the oscillation frequency of 0 does not change.

Further, since the moisture resistance of the piezoelectric element 10 itself is improved by the water repellent film 4, it is not necessary to use a highly airtight structure or a highly airtight material for the container, which is inexpensive. It can be a piezoelectric component.

In the above description, as the piezoelectric substrate 1, a piezoelectric element using a bulk wave is taken as an example. However, in the piezoelectric element using an elastic wave on the surface of the piezoelectric substrate, one main surface of the piezoelectric substrate has a gap. Although a very narrow comb-teeth-shaped electrode is formed, the water repellent film 4 is formed on such a piezoelectric element, which is very effective in preventing migration of the vibrating electrode material. Further, as an example of alteration of the piezoelectric substrate, a lithium tetraborate substrate or the like can be exemplified. That is, the composition of this substrate changes due to moisture,
As a result, the predetermined characteristic may not be derived, but this does not occur at all.

FIG. 2 shows a piezoelectric component of the second invention.

The piezoelectric component 20 includes the above-described piezoelectric element 10, the flat plate-shaped substrate 21, the housing-shaped substrate 24 in which the area for accommodating the piezoelectric element 10 is formed, and the terminal electrodes 22 connected to the electrodes 2 and 3 of the piezoelectric element 10. , 23, a sealing member 25 for sealing the two substrates 21 and 24, and connecting means 26 and 27.

The plate-shaped substrate 21 and the housing-shaped substrate 24 are made of ceramic, epoxy resin, liquid crystal polymer resin, or the like, and one of them is a terminal electrode 22 for bonding to a printed wiring board and connecting with an external circuit. , 23 are formed. In FIG. 2, the flat substrate 21 is formed over the end portion, that is, the front surface, the end surface, and the back surface.

Such terminal electrodes 22 and 23 are formed, for example, by baking a conductive paste such as Ag on the surface of the substrate 21, or when a flat metal plate member is integrally formed when forming the substrate. It is formed at the same time.

In the embodiment, the terminal electrodes 22 and 23 extend to positions corresponding to both ends of the piezoelectric element 10 arranged on the flat substrate 21 in the longitudinal direction, and are connected to the extended portions. It is electrically connected and mechanically joined via the members 26 and 27.

The connecting members 26 and 27 are formed by applying and drying, for example, using a conductive resin paste in which a conductive powder such as Ag is kneaded. In particular, the piezoelectric element 1
As a method of ensuring a vibration space between the substrate 0 and the flat substrate 21, a gap material may be mixed in the conductive paste as needed. When the terminal electrodes 22 and 23 are formed of a metal flat plate member, the thickness of the metal flat plate member may be used.

In this manner, the piezoelectric element 10 is arranged, and the four flat plate-shaped substrate 21 is provided on the housing-shaped substrate 24 and the piezoelectric element 1.
They are joined and sealed so as to cover 0. The housing-like substrate 24 is formed with a recess for accommodating the piezoelectric element 10.

The flat plate-shaped substrate 21 and the housing-shaped substrate 24 are bonded to each other by a bonding member 25 on the peripheral surface of the recess of the housing-shaped substrate 24.
It is sealed through.

Examples of the sealing member 25 include a thermosetting resin such as an epoxy resin and an ultraviolet curing resin.

Conventionally, in order to attach great importance to the airtightness of the container (the flat plate-shaped substrate 21 and the housing-shaped substrate 24), a flat plate-shaped substrate made of ceramics and a ceramic housing-shaped substrate are used, and a low melting point glass or the like is used as a joining member between them. It was used and glass-sealed at a high temperature of 300 ° C. or higher. In addition, a seam welding process is performed by forming a metallized layer on the joint surface portion. further,
A metal flat plate substrate and a metal housing substrate were used to weld them together.

On the other hand, in the present invention, the flat substrate 2
The joint between 1 and the housing-like substrate 24 is sealed with a resin sealing member 25. For sealing, for example, a resin to be the sealing member 25 is applied to the joint portion between the flat plate-shaped substrate 21 and the housing-shaped substrate 24, primary curing (about 80 ° C.) is performed, and then both are temporarily joined, It was cured (150 to 200 ° C.) and completely bonded.

Therefore, in the piezoelectric component 20, the sealing member 25
Since the resin is used for the heat treatment, the heat treatment temperature in the bonding step is about 200 ° C. at most. Therefore, even if the piezoelectric substrate 1 is polarized, for example, the polarization of the piezoelectric substrate 1 does not disappear and The characteristics can be derived stably.

The electrodes of the piezoelectric layer 1 and the terminal electrodes 22, 2
Regarding the connection means 26, 27 for achieving the connection with 3,
Since the heat applied to the connecting means 26, 27 is low, the range of selection of the material such as solder joint and conductive resin is widened.

Furthermore, the resin sealing member 25 makes the material of the joining member inexpensive, and the manufacturing process is simplified because it is achieved by a simple joining process, resulting in an inexpensive piezoelectric component 20.

Since the joining member 25 is made of resin, the moisture resistance reliability at the joining portion is lowered, but since the water repellent coating 4 is formed on the piezoelectric element 1, the moisture resistance of the entire piezoelectric component 20 is reduced. It prevents the deterioration of reliability.

Therefore, in addition to the sealing member 25, it is not necessary to use a ceramic material or a metal material as the material of the flat plate-shaped substrate 21 and the housing-shaped substrate 24 which form the container, so that the piezoelectric component 20 is further improved. It will be cheap.

FIG. 3 is a sectional view of a piezoelectric component 30 using the piezoelectric element 10 utilizing surface acoustic waves or elastic waves in the vicinity of the surface of the piezoelectric substrate.

In the figure, the piezoelectric element 10 is directly attached to the surface of the flat substrate 21 via a resin adhesive or the like.

The input / output pads connected to the respective vibrating electrodes of the piezoelectric element 10 are connected to the terminal electrodes 22 and 23 extending on the surface of the base substrate 21 by connecting means 26 and 27 such as wire bonding thin wires. To be done.

After that, the housing-like substrate 24 is bonded via the resin bonding member 25.

As described above, according to the present invention, since the water repellent film 4 is formed on the piezoelectric element 10 to perform the water repellent treatment, the moisture resistance reliability of the piezoelectric element 10 itself is greatly improved, which results in Thus, it is possible to prevent the frequency variation of the piezoelectric element 10 and to effectively prevent the electrodes 2 and 3 from being corroded or migrated.

In the above-described embodiment, the piezoelectric element 10 is an element in which the vibrating electrodes 2 and 3 are formed on both main surfaces of a strip-shaped piezoelectric substrate 1, and a comb is formed on one main surface of the flat piezoelectric substrate 1. Although the element in which the vibrating electrode having the shape of a tooth electrode is formed is shown as an example, a piezoelectric substrate made of a tuning fork type quartz material may be used.

Further, in FIG. 2 and FIG. 3, the piezoelectric element 10 is arranged on the flat base substrate 21.
2, 23 are formed on the side of the housing substrate 24, and the housing substrate 24
After accommodating the piezoelectric element 10 in the above, the plate-shaped substrate 21 may be covered and bonded.

[0055]

As described above, according to the present invention, since the surface of the piezoelectric element is subjected to the water repellent treatment, the piezoelectric vibrator itself can be made to have moisture resistance. It is possible to suppress variations in characteristics.

Further, since the piezoelectric element itself can be made to have moisture resistance, even if the humidity resistance reliability of the container for connecting the piezoelectric element and the outside and connecting the piezoelectric element is lowered, the entire piezoelectric component can be reduced. Since the moisture resistance reliability does not deteriorate, the range of choices for the material of the container, the structure of the container, the material of the joining means, the structure, etc. can be widened, and as a result, it is inexpensive as a piezoelectric component, and the connection method and handling are very easy. This is a resin-sealed piezoelectric component that can be easily manufactured.

[0057]

[Brief description of the drawings]

FIG. 1 is an external perspective view of a piezoelectric element of the present invention.

FIG. 2 is a sectional view of a resin-sealed piezoelectric component using the piezoelectric element shown in FIG.

FIG. 3 is a cross-sectional view of another resin-sealed piezoelectric component of the present invention.

[Explanation of Codes] 10 ... Piezoelectric element 1 ... Piezoelectric substrate 2, 3 ... Electrode 4 ... Water repellent coating 20, 30 ... Resin-sealed piezoelectric component 21 ... Flat substrate 22, 23 ... Terminal electrode 24 ... Enclosure-like substrate 25 ... Joining member 26, 27 ... Connecting means

Claims (2)

[Claims] 1. A piezoelectric element, wherein an electrode for generating a piezoelectric effect is formed on at least one main surface of a piezoelectric substrate, and a water repellent film is formed on the surfaces of the piezoelectric substrate and the electrode. 2. The piezoelectric element according to claim 1 is housed in a container composed of a flat substrate and a housing substrate having an element housing area, and the flat substrate and the housing substrate are joined by resin. A resin-sealed piezoelectric component, which is encapsulated.