JPS63115410A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To eliminate distortions on the surface of a surface acoustic wave SAW caused by the difference of SAW speeds between an electrode part and a non-electrode part and therefore to improve daterioration of characteristics due to said SAW distortions with a SAW device, by using an electrode plate containing many small non-electrode gaps at an area equivalent to a conventional dummy electrode. CONSTITUTION:A mesh electrode part 5 is provided between a weighting electrode part 4 and a draw-out electrode part 6. The part 5 contains many non-electrode gaps 7 in a mesh form and these gaps 7 are formed so that the even value is secured among metallic parts serving as electrodes in the SAW transmitting direction. Thus the total SAW transmitting speed is kept at a constant level to eliminate distortions produced on the SAW surface and therefore no deterioration of characteristics is caused. In addition, the small holes 7 are periodically formed or the sizes of these holes 7 are set smaller enough that the SAW length. As a result, the SAW reflection is reduced and therefore the deterioration of characteristics due to the SAW reflection is extremely reduced. Furthermore the defects due to disconnections of electrodes are greatly reduced in comparison with a conventional case where both the electrode 4 and a dummy electrode are formed in the electrode pieces since the electrode 5 is formed in a mesh form. Then the production yield is improved with a SAW device.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a surface acoustic wave device used in video equipment such as television receivers and video tape recorders, and public transport equipment.

(Prior art) A surface acoustic wave device is a type of electromechanical vibrator.
As illustrated in Figure (A), on the top surface of a piezoelectric substrate a made of lithium niobate single crystal or the like, a transmitting electrode and a receiving electrode C each having a shape of incorporating comb-like electrode fingers are provided. Therefore, when AC No. 42 is applied to the sending electrode, due to the piezoelectric effect of the electrode finger pair of the sending electrode)) S A W (
A surface acoustic wave (surface acoustic wave) is generated, propagates left and right, and AC No. 42 by SAW propagating from the receiving electrode C is extracted. When this is used as a filter, a so-called weighted electrode pattern is used in which the crossing width W of the electrode fingers and the electrode finger interval λ are appropriately changed in order to obtain desired frequency characteristics. In addition, since the propagation speed of the SAW differs depending on whether or not there is a metal plate on the propagation medium, that is, the surface, for example, as shown in The wavefront is distorted and the output frequency characteristics deteriorate. Therefore, as shown in Fig. 2 (b), a dummy electrode finger f3 is provided at each point t where no electrode finger is provided for weighting, and the 5AWO propagation velocity is simulated/stamped. (See the conventional example described in JP-A-61-81013), a split-type electrode finger in which the elongated electrode finger is further divided into two (see the conventional example described in JP-A-61-81013);
(See the conventional example described in Publication No. 2) is known.

(Problems to be solved by the investigation) A device simply provided with dummy electrode fingers cannot solve the problem of increased SAW reflected waves due to an increase in the number of electrode fingers.
This causes a new problem of characteristic deterioration. In addition, when the electrode fingers (including dummy electrode fingers) are split-type electrode fingers, the reflections from each electrode finger cancel each other out, so the problem of reflected waves is solved, but the width of the electrode finger Since the electrode fingers are rounded, they become very thin, and especially when the length of the electrode fingers is long, defects due to breakage of the electrode fingers are likely to occur, and the yield during manufacturing is likely to decrease.

(Means for Solving the Problems) Therefore, the present invention provides a surface acoustic wave device that solves the above-mentioned problems. In a surface acoustic wave device equipped with a facing electrode made of a metal thin film, the facing part of the electrode is formed into a comb-like electrode finger according to the desired characteristics, and the surface acoustic wave is formed in the part other than the electrode finger. This device is characterized by providing an electrode plate having a large number of small-area non-electrode gaps so that the area ratio of electrode portions to non-electrode portions in the propagation direction is approximately uniform.

Therefore, the amount of metal along the east direction of SAW propagation becomes the same by providing a large number of non-electrode gaps, which solves the problem of characteristic deterioration due to differences in SAW propagation speed.

Furthermore, when providing a large number of non-electrode voids, by making the formation locations non-periodic, or by making the size of each void sufficiently small, it is possible to prevent characteristic deterioration due to SAW reflection, and Since the electrode is plate-shaped, defects due to disconnection are also reduced.

(Example) Next, embodiments of the present invention will be described based on the drawings.

An embodiment of the present invention is shown in FIG. 1, in which a transmitting electrode 2 and a receiving electrode 3 are provided on a piezoelectric substrate 1 as in the conventional case, and the weighting of the transmitting electrode 2ζ is on the electrode part. 4, consists of a mesh electrode part 5 and an extraction electrode part 6, and weighting is applied to the electrode part 4
(It consists of a group of paired comb-shaped electrode fingers with a length determined according to the desired characteristics, and is arranged on both sides of the electrode 2 and connected to the outside. The mesh electrode section 5, which is connected to the connection terminal, is provided between the weighted T4 pole section 4 and the extraction electrode section 6, and is formed into a mesh shape by providing a large number of non-electrode gaps 7. Therefore, the propagation speed of the SAW is different between the electrode portion and the non-electrode portion, and this causes the propagation wave of the SAW to be distorted. If the SAW is formed so that its appearance is uniform, the propagation speed of the SAW as l-tal will be constant)
) Since there is no distortion of the SAW wavefront, there is no characteristic deterioration due to this. In addition, if the small holes 7 are provided non-periodically or are made sufficiently smaller than the wavelength of the SAW to be used, the SA
Since the reflection of W can be reduced, the deterioration of characteristics due to SAW reflection can be greatly reduced. Furthermore, since the mesh electrode section 5 is constructed in a mesh-like manner as a whole, the weighting significantly reduces defects due to electrode breakage compared to the conventional structure in which electrode fingers are used for both the electrode 4 and the dummy electrode. Therefore, the manufacturing yield is improved accordingly.

(Effects of the Invention) As described above, the present invention provides a surface acoustic wave device in which the part corresponding to the conventional dummy electrode is replaced with an electrode plate having a large number of small-area non-electrode gaps, and the SAW used By appropriately determining the shape, size, and position of the non-electrode gap according to the wavelength, etc., it is possible to eliminate distortion of the SAW wavefront due to the difference in SAW speed between the electrode part and the non-electrode part, and to improve the deterioration of characteristics caused by this. In addition, the three problems of preventing characteristic deterioration due to SAW reflected waves and reducing defects due to disconnection are simultaneously solved.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a surface acoustic wave filter embodying the present invention. FIGS. 2(a) and 2(b) show the same conventional example. 1 is the substrate 2 is the transmitter = electrode 3 is the receiver TAtlii 4 is the weighted electrode section 5 is the dummy electrode section 6 (the extraction electrode section 7 is the non-electrode gap

Claims (1)

[Claims] In a surface acoustic wave device in which a counter electrode made of a metal thin film is disposed on a piezoelectric substrate, the opposing portions of the electrodes are formed into comb-like interlocking electrode fingers according to the desired characteristics, and the portions other than the electrode fingers are formed. A surface acoustic wave device comprising an electrode plate having a large number of small-area non-electrode gaps so that the area ratio of electrode portions to non-electrode portions in the propagation direction of a surface acoustic liquid is approximately uniform.