JPH04317208A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To provide technique for preventing the influence of the bulk wave generated from one of surface acoustic wave elements when two small pieces of piezo-electric circuit board on which the surface acoustic wave element is formed are bonded to each other so that the face on which the element is formed on one circuit board can face the opposite side to the surface on which the element is formed on another circuit board. CONSTITUTION:When two small pieces 2 of circuit board on which a surface acoustic wave element is formed are bonded to each other so that the face on which the element is formed on one circuit board can face the opposite side to the surface on which the element is formed on another circuit board, an acoustic material is sandwiched and between and bonded to the two small pieces 2 of piezo-electric circuit board.

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 element used in an electric circuit.

0002

2. Description of the Related Art In the prior art, the back sides of small pieces of piezoelectric substrates were simply adhered to each other without using any sound absorbing material.

0003

[Problem to be Solved by the Invention] In the above-mentioned conventional technology, unnecessary bulk waves due to mode conversion generated from a small piece of one surface acoustic wave element are reflected at the joint with a small piece of the other substrate, resulting in a change in characteristics. The problem was that it had a negative impact.

[0004] Furthermore, there is a problem in that unnecessary bulk waves that are transmitted without being reflected at the joint between the small pieces of the two substrates also have an adverse effect on the characteristics of the other surface acoustic wave element.

An object of the present invention is to bond two small pieces of piezoelectric substrates each having a surface acoustic wave element formed thereon so that the surfaces opposite to the surface on which the element is formed face each other. The present invention provides a technology for preventing the influence of bulk waves generated from elements.

[0006]

[Means for Solving the Problems] The above object is achieved by bonding two small pieces of piezoelectric substrates each having a surface acoustic wave element formed thereon so that the surfaces opposite to the surface on which the element is formed face each other. This is achieved by sandwiching and adhering a sound absorbing material between the small pieces of the piezoelectric substrate.

[0007]

[Operation] Unnecessary waves such as bulk waves generated by one of the surface acoustic wave elements are absorbed by the sound absorbing material coated at the joints of the small pieces of the piezoelectric substrate, and do not affect the characteristics.

[0008]

[Example] Fig. 1 shows a stem 3 and a shell 4 in which two small pieces 2 of piezoelectric substrates on which surface acoustic wave elements are formed are pasted together with a sound absorbing material applied to the surface where the elements are not formed. This is an example of a case where the device is housed in a cylindrical package consisting of.

FIG. 1 is a side view, and is drawn so that the interior can be seen through the shell.

[0010] For example, quartz crystal or lithium tantalate is used as the piezoelectric substrate. After several patterns of surface acoustic wave elements are formed on this substrate using a conductive metal such as aluminum, the piezoelectric substrate is cut into small pieces 3 using a dicing machine or the like. Then, the sound absorbing material and adhesive 1 are applied to the back surface of the small piece 3 of the piezoelectric substrate, that is, the surface on which no pattern is formed.

[0011] After the adhesion is completed, the lead wire and the small piece of the piezoelectric substrate are fixed by a method such as conductive paste or soldering. Here, a can-shaped case is used in which the lead wire passes through the stem 3 and is fixed thereto.

In the above example, the small pieces of the two substrates to be pasted together were both piezoelectric substrates on which surface acoustic wave elements were formed, but one of the two substrates was not necessary and was made of silicon on which a semiconductor circuit was formed. It may be a substrate or a gallium arsenide substrate.

FIG. 2 is a diagram of FIG. 1 viewed from direction A. Two small pieces of piezoelectric substrates are glued together with sound-absorbing material sandwiched between them, and these are fixed to the lead wires. In addition, in this figure, the small piece 2 of the piezoelectric substrate, the sound absorbing material, and the adhesive layer 1 are drawn with wavy lines because they are seen through the stem.

Furthermore, since there are lead wires 5 for the upper element and for the lower element, a total of four lead wires are required. The required number may be provided depending on the number of wave elements. FIG. 3 is an example showing the application of the adhesive and sound absorbing material of the present invention. Generally, an adhesive and a sound absorbing material may be used in combination, but if the mixture is used, the aging characteristics will deteriorate due to deterioration or the like, then the example shown in FIG. 3 is used. First, an adhesive is applied to the back side of the small piece 2 of the piezoelectric substrate, that is, near the outer periphery of the surface on which the surface acoustic wave element is not formed, and then a sound absorbing material is applied to the inside thereof. Then, the back sides of the small pieces of the piezoelectric substrate are glued together.

FIG. 4 shows an example in which adhesive layers and sound absorbing material layers are applied alternately. Even in this case, unnecessary waves such as bulk waves can be canceled to some extent. This embodiment is used for the purpose of maintaining adhesive strength when the surface acoustic wave element is used in a place where vibrations are severe.

FIG. 5 shows the frequency characteristics of the surface acoustic wave filter before and after implementing the present invention.

A phenomenon in which the passband was slightly wavy was observed in the case 8 before the present invention was implemented, which is indicated by a dotted line, but the wavy phenomenon in the passband was no longer observed in the case 9 after the present invention was implemented, which was indicated by a solid line.

Although surface acoustic wave filters have been described above, the characteristics of these filters can also be improved for elements to which surface acoustic waves are applied, such as resonators and delay elements.

[0019]

According to the present invention, when two small pieces of piezoelectric substrates each having a surface acoustic wave element formed thereon are pasted together so that the surfaces opposite to the surfaces on which the surface acoustic wave elements are formed face each other, the piezoelectric By sandwiching and adhering the sound absorbing material between the small pieces of the substrate, it is possible to prevent the influence of bulk waves, etc., and has the effect of improving the characteristics compared to the case without the sound absorbing material.

[Brief explanation of the drawing]

FIG. 1 is a side view of one embodiment of the present invention.

FIG. 2 is a front view of an embodiment of the present invention seen from below.

FIG. 3 is a front view showing an embodiment of the method for adhering small pieces of a piezoelectric substrate according to the present invention.

FIG. 4 is a side view showing a second embodiment of the invention.

FIG. 5 is a diagram showing frequency characteristics before and after implementation of the present invention.

[Explanation of symbols]

1. Sound absorbing material and adhesive layer 2 Small piece of piezoelectric substrate 3 Stem 4 Shell 5 Lead wire 6. Adhesive 7 Sound absorbing material 8 Characteristics before implementation of the invention 9 Characteristics after implementation of the present invention

Claims (3)

[Claims] 1. In a structure in which two small pieces of a piezoelectric substrate on which a surface acoustic wave element is formed are pasted together with their surfaces opposite to the surface on which the element is formed, a sound absorbing material is placed between the small pieces of the piezoelectric substrate. A surface acoustic wave element characterized by sandwiching and bonding. 2. One of the small pieces of the substrate is a small piece of a piezoelectric substrate on which a surface acoustic wave element is formed,
The surface acoustic wave device according to claim 1. 3. The surface acoustic wave element according to claim 1, wherein the sound absorbing material is an adhesive.