JPH10178330A - Surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration and alternation of piezoelectric thin film caused by external atmosphere by covering the forming area of the piezoelectric thin film with a protective member so as to perfectly isolate the piezoelectric thin film from external atmosphere to prevent the entering of moisture and foreign matters. SOLUTION: IDT electrodes 2, 3 and fetching electrodes 2a, 2b, 3a and 3b consisting of aluminum thin films are formed on one main surface of a substrate 1 and the piezoelectric thin film 5 consisting of Zno is formed by a sputtering method so as to cover the forming area of the IDT electrodes 2 and 3 from the upper side of these. Then a protective film 6 consisting of ceramics such as SiO2 , sapphire, etc., is formed by the sputtering method or a depositing method so as to cover the film 5. The film 6 is the protective member for disconnecting the film 5 from external atmosphere, is provided with an area a little larger than the outer peripheral of the film 5 so as to perfectly cover the film 5 and is formed on the substrate 1 so as to expose the tip parts of the electrodes 2a, 2b, 3a and 3b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device having an IDT electrode formed on an insulative substrate, and more particularly, to a chip-like surface mountable chip having sufficient moisture resistance and corrosion resistance. The present invention relates to a surface acoustic wave device.

[0002]

2. Description of the Related Art As a surface acoustic wave device having an electrode formed on a substrate and a piezoelectric thin film formed thereon, there is known a surface acoustic wave device having a structure as shown in FIG. FIG. 3A is a plan view of the surface acoustic wave element, and FIG. 3B is a cross-sectional view.

In this surface acoustic wave device, IDT electrodes 2 and 3 made of an aluminum thin film are formed on one main surface of an insulating substrate 1, and are connected to the IDT electrodes 2 and 3 to take out electrodes 2a, 2b and 2b. 3a and 3b are formed, and a piezoelectric thin film 5 such as a ZnO film is formed by a sputtering method so as to cover the IDT electrodes 2, 3 and the like from above. The piezoelectric thin film 5 in this configuration forms a layer that propagates a surface acoustic wave, and the characteristics of the surface acoustic wave element are greatly affected by the thickness and characteristics of the piezoelectric thin film 5.

Conventionally, such a surface acoustic wave element has been fixed to a metal base or a base substrate such as alumina by an adhesive or soldering, and a metal cap has been joined to the metal base or the base substrate. It is used sealed in a package consisting of a substrate and a metal cap.

By the way, in recent years, in order to realize miniaturization, cost reduction, and simplification of mounting work of devices, a bare chip is mounted on a mounting board without storing the surface acoustic wave element in a package such as a hermetic case. A method of implementing it as is is under consideration.

[0006]

However, when the above conventional surface acoustic wave element is used as a bare chip,
The piezoelectric thin film is not shielded from the external atmosphere, and there is a problem that the piezoelectric thin film is deteriorated or deteriorated by the external atmosphere at the time of solder mounting or use, and the characteristics of the surface acoustic wave element are deteriorated. For example, in a corrosion resistance test, in particular, in an SO ₂ atmosphere test, there is a problem that the piezoelectric thin film is corroded, and the characteristics deteriorate rapidly.

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface acoustic wave device which can be mounted on a bare chip and can realize necessary and sufficient reliability with a simple structure without being housed in a package.

[0008]

In order to achieve the above object, the invention according to claim 1 comprises forming electrodes such as IDT electrodes on a substrate and forming a piezoelectric thin film on these electrodes. In the surface acoustic wave device, a region where the piezoelectric thin film is formed is covered with a protective member.

According to a second aspect of the present invention, in the surface acoustic wave device according to the first aspect, the protection member is formed in a film shape on the piezoelectric thin film.

According to a third aspect of the present invention, in the surface acoustic wave device according to the first aspect, the protection member has a cap shape.

According to the above configuration, since the piezoelectric thin film is covered with the protective member and completely shielded from the external atmosphere, the invasion of moisture and foreign substances is prevented, and the deterioration and deterioration of the piezoelectric thin film due to the external atmosphere are prevented. Is prevented. In other words, moisture resistance and corrosion resistance can be greatly improved without being housed in a package, and thus sufficient and sufficient reliability can be realized with a small and simple structure. The chip can be surface-mounted on a mounting substrate as it is.

The protection member is formed in a film shape or a cap shape. In particular, if the protection member is formed in a film shape, the protection member can be formed at lower cost.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings showing embodiments thereof. FIG. 1 shows the structure of a surface acoustic wave device according to a first embodiment of the present invention. FIG. 1A is a plan view of a surface acoustic wave device, and FIG. 1B is a cross-sectional view.

The surface acoustic wave device according to the present embodiment includes an insulating substrate 1 made of glass or the like. On one main surface of the substrate 1, IDT electrodes 2 and 3 made of an aluminum thin film and IDT electrodes 2 and 3 are provided. Connected extraction electrodes 2a, 2b, 3a, 3b
Are formed, and the extraction electrodes 2a, 2b, 3
A piezoelectric thin film 5 made of ZnO is formed by a sputtering method so as to cover the region where the IDT electrodes 2 and 3 are formed except for a part of a and 3b.

The IDT electrodes 2 and 3 are formed to face each other at appropriate intervals in the longitudinal direction of the substrate 1 and take out electrodes 2a and 2a.
b, 3a, 3b are formed extending from both ends of the respective IDT electrodes 2, 3 to one end of the substrate 1 in the longitudinal direction.

The piezoelectric thin film 5 in this configuration forms a layer that propagates a surface acoustic wave.
The surface acoustic wave element is formed so as to cover a major part of the surface acoustic wave element such as a surface acoustic wave propagation path and the like, and the characteristics of the surface acoustic wave element are greatly affected by the thickness and characteristics of the piezoelectric thin film 5.

In the surface acoustic wave device according to the present embodiment, a protective film 6 made of ceramics such as SiO 2 or sapphire is formed by a sputtering method or a vapor deposition method so as to cover a region where the piezoelectric thin film 5 is formed. The protective film 6 functions as a protective member for shielding the piezoelectric thin film 5 from the external atmosphere, and has an area slightly larger than the outer periphery of the piezoelectric thin film 5 so as to completely cover the piezoelectric thin film 5.
Further, it is formed on the substrate 1 so as to expose the ends of the extraction electrodes 2a, 2b, 3a, 3b.

In this embodiment, the substrate 1 has a thickness of about 800 μm.
m, IDT electrodes 2 and 3 are about 10 μm, and piezoelectric thin film 5 is about 2 μm.
The protective film 6 is formed with a thickness of about 0.8 μm. The thickness, material, and the like of the protective film 6 are appropriately set according to the required values of reliability such as required moisture resistance and corrosion resistance.

In the surface acoustic wave device of this embodiment, the piezoelectric thin film 5 formed on the substrate 1 is entirely covered with the protective film 6, and the piezoelectric thin film 5 is completely shielded from the external atmosphere by the protective film 6. Therefore, the moisture resistance and corrosion resistance of the piezoelectric thin film 5 are greatly improved, and the deterioration and deterioration of the piezoelectric thin film due to an external atmosphere are prevented. That is, since the necessary and sufficient reliability is secured by the protective film 6, it is not necessary to provide an exterior component such as a package other than the protective film 6.

Since such a surface acoustic wave device is generally formed by forming a large number of devices on a mother substrate and then dividing the device into individual devices by cutting, the protective member is formed in a film shape as in this embodiment. Then, as described above, a protective film can be simultaneously formed on a large number of elements simultaneously by sputtering, vapor deposition, printing, or the like, and the protective member can be formed at low cost.

Further, in the surface acoustic wave device of this embodiment,
In the exposed portions of the extraction electrodes 2a, 2b, 3a, 3b,
For example, it is possible to form a solder bump and perform surface mounting on a mounting substrate by face-down bonding.
That is, the surface acoustic wave device of the present embodiment can be mounted on a mounting board as it is as a so-called bare chip.

Alternatively, die bonding may be performed with the surface on which the protective film is formed facing upward, and each extraction electrode and the electrode of the mounting substrate may be mounted by wire bonding.

Note that the protective film is not limited to the above-described embodiment, and a resin material having good corrosion resistance and moisture resistance such as polyimide is used as the protective film, and this resin is formed on the piezoelectric thin film by screen printing or the like. You may do so.

FIG. 2 is a sectional view of a surface acoustic wave device according to a second embodiment of the present invention. In the surface acoustic wave element of this embodiment, a box-shaped protective cap 7 made of plastic is adhered and fixed with an adhesive 8 so as to seal the area where the piezoelectric thin film 5 is formed. Except for forming a protective cap 7 instead of a protective film as a protective member, the configuration is the same as that described in the first embodiment, and a description thereof will be omitted.

Although the height of the protective cap 7 is about 2 mm in this embodiment, it is preferable to use a protective cap having a height as low as possible in the case of face-down surface mounting.

The material of the protective cap is not limited to plastic, but may be any material having good moisture resistance, corrosion resistance and heat resistance.

Also in this configuration, since the piezoelectric thin film 5 is hermetically sealed by the protective cap 7 and completely shielded from the external atmosphere, the same effect as that described in the first embodiment can be obtained.

In each of the above embodiments, the configuration of the transversal type filter has been described as an example. However, the present invention can be applied to a resonator type filter and other oscillators.

[0029]

As described above, according to the surface acoustic wave device according to the present invention, the piezoelectric thin film is covered with the protective member such as the protective film and the protective cap and is completely shielded from the external atmosphere. Therefore, the moisture resistance and corrosion resistance of the piezoelectric thin film are greatly improved, and the deterioration of the piezoelectric thin film due to an external atmosphere can be prevented.

Further, when the protective member is formed in a film shape, the protective member can be formed at lower cost.

Therefore, according to the present invention, a necessary and sufficient reliability can be realized by the protection member, and no external components such as a package are required, and a small, inexpensive, surface acoustic wave element which can be mounted on a bare chip can be easily obtained. be able to.

[Brief description of the drawings]

FIG. 1A is a plan view of a surface acoustic wave device according to a first embodiment of the present invention, and FIG. 1B is a cross-sectional view thereof.

FIG. 2 is a sectional view of a surface acoustic wave device according to a second embodiment of the present invention.

FIG. 3A is a plan view of a conventional surface acoustic wave device, and FIG. 3B is a cross-sectional view thereof.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2, 3 IDT 5 Piezoelectric thin film 6 Protective film 7 Protective cap

Claims (3)

[Claims] 1. A surface acoustic wave device in which electrodes such as IDT electrodes are formed on a substrate and a piezoelectric thin film is formed on these electrodes, wherein the formation region of the piezoelectric thin film is covered with a protective member. Characteristic surface acoustic wave element. 2. The surface acoustic wave device according to claim 1, wherein the protection member is formed in a film shape on the piezoelectric thin film. 3. The surface acoustic wave device according to claim 1, wherein the protection member has a cap shape.