JPH04138707A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To prevent short-circuit between electrode fingers caused in the case of high frequency processing of the surface acoustic wave element and to cancel a reflecting wave in a transducer by adopting a structure such that a slot is provided to a piezoelectric substrate at an interval of 1/4 wavelength each and the electrode fingers are bridged over the slot. CONSTITUTION:A slot 2 if provided to a piezoelectric substrate 1 made of a piezoelectric material such as a crystal or a lithium tantalate at an interval of 1/4 wavelength each. Then an electrode finger 3 made of a metallic material such as aluminum is formed in the slot 2 and on the piezoelectric substrate 1. That is, at first a resist 10 is patterned onto the piezoelectric substrate 1. Then dry etching or wet etching is applied to etch a part without the resist to form the slot 2. Moreover, a resist 11 is formed on the piezoelectric substrate 1. Then electrode fingers 3,3' are formed by vapor-depositing or sputtering an electrode metal. Then the electrode is formed by removing the resist 11. A reflecting wave is caused at an edge of the electrode finger 3 on the piezoelectric substrate 1 and an edge of the slot 2. However, since the phases of the reflecting waves are deviated by l80 deg., they are canceled together and no effect is caused on the traveling wave.

Description

[Detailed description of the invention] <Purpose of the invention> "Industrial application field" The present invention relates to a surface acoustic wave element suitable for high frequencies.

"Prior Art" Conventionally, the electrode fingers of a transducer of a surface acoustic wave element are arranged to intersect at 1/4 wavelength intervals.

However, when the electrode fingers are arranged at 1/4 wavelength intervals, reflected waves are generated by reflection at the electrode finger edges, and this reflected wave makes the frequency characteristics of the main vibration steep.

Therefore, the electrode fingers are arranged at 1/4 wavelength intervals as shown in FIG. Two electrode fingers are excited to the same potential in pairs. With this arrangement, as shown in FIG. 5, a reflected wave is generated at each edge of the electrode finger with respect to the traveling wave shown by the solid line. The reflected wave is
Since reflected waves of opposite phase are generated for every 1/4 wavelength, they cancel each other out and have no effect on the traveling wave. However, with such electrode fingers, when increasing the frequency, it is necessary to narrow the spacing between the electrode fingers in the transducer, but the spacing is half that of the conventional one, and there is a risk of a short circuit between the electrode fingers.

``Problem to be Solved by the Invention'' If the aforementioned transducer electrode is made less susceptible to the effects of reflected waves, there is a risk of electrode short-circuiting when the frequency increases, so there is a need for an electrode with a structure that is less likely to short-circuit.

[Object of the Invention] An object of the present invention is to provide a surface acoustic wave element that eliminates the above-mentioned drawbacks, reduces reflected waves from a transducer that occur when the frequency is increased, and does not have steep characteristics.

Structure of the Present Invention>"Means for Solving the Problems" Therefore, in the present invention, first, a groove is provided on the piezoelectric substrate, and an electrode finger is provided so as to straddle the groove. Second, the grooves on the piezoelectric substrate are diagonal, and electrode fingers are provided in these grooves.

"Function" In the present invention, the reflected waves generated at the edges of the electrode fingers and the reflected waves generated at the edges of the groove cancel each other out, so that the influence of the reflected waves is eliminated. That is, by arranging the edges of the electrode fingers and the edges of the grooves so as to be shifted by 1/4 wavelength, the reflected waves cancel each other out.

"First Example" FIG. 1(a) is a sectional view showing an example of the surface acoustic wave element of the present invention. FIG. 1(b) is a graph showing traveling waves and reflected waves.

Grooves 2 are formed every 1/4 wavelength in a piezoelectric substrate 1 made of a piezoelectric material such as crystal or lithium tantalate. Then, electrode fingers 3 made of a metal material such as aluminum are formed in the groove 2 and on the piezoelectric substrate 1. Since FIG. 1(a) is a cross-sectional view, the electrode finger 3
The length direction of is perpendicular to the plane of the drawing and extends.

FIGS. 3(a) to 3(e) show an example of the electrode forming method of this embodiment. First, a resist 10 is patterned on the piezoelectric substrate 1. (FIG. 3a) Next, dry etching or wet etching is performed to etch the portions where there is no resist and form grooves 2. (FIG. 3b) Furthermore, a resist 11 is formed on the piezoelectric substrate 1.

(FIG. 3C) Electrode fingers 3.3' are formed thereon by vapor deposition or sputtering of electrode metal. (FIG. 3d) Then, when the resist 11 is removed, electrodes are formed. (Fig. 3e) With the electrode formed in this way, the electrode on the piezoelectric substrate and the electrode finger in the groove immediately next to it are at the same potential. Although this embodiment uses a lift-off method to form electrode fingers, other methods may be used to form grooves and electrodes.

FIG. 1(b) is a graph representing traveling waves and reflected waves,
Reflected waves are generated at the edges of the electrode fingers 3 and the grooves 2 on the piezoelectric substrate 1. However, since the reflected waves are 180 degrees out of phase, they cancel each other out and have no effect on the traveling wave.

[Second Embodiment] FIG. 4 is a sectional view showing another embodiment, in which the grooves 20 are formed obliquely from the surface of the piezoelectric substrate. As a method of forming such grooves, a resist is applied to the portions other than the grooves, and a beam is applied obliquely to the grooves by dry etching. Further, depending on the piezoelectric material, it can be formed by taking advantage of the anisotropy of the crystal axis and the fact that the etching rate differs depending on the axial direction.

After the grooves are formed, metal electrode fingers 21 are formed by vapor deposition or sputtering. Although the electrodes are formed in the grooves in FIG. 4, they may be formed only in the grooves, or the electrode fingers may extend on the surface of the piezoelectric substrate.

In this example, the edge 20' of the obliquely formed groove 20 and the edge 21' of the electrode finger 21 are formed to have a wavelength of 174.
Reflected waves are generated at each edge, but their phases are opposite to each other and cancel each other out.

INDUSTRIAL APPLICATION This invention is used for a surface acoustic wave filter, a surface acoustic wave oscillator, a delay element, etc.

Effects of the Present Invention> The present invention can prevent short circuits between electrode fingers that occur when the frequency of a surface acoustic wave element is increased, and can also prevent reflected waves within the transducer from becoming elastic so that the frequency characteristics do not become steep. We were able to realize a surface wave device.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view showing this example, FIG. 1(b) is a graph showing traveling waves and reflected waves, and FIGS. 2(a) to (e) show the method of forming grooves and electrode fingers. 3 and 4 are sectional views showing other embodiments, FIG. 5(a) is a sectional view showing a conventional electrode finger, and FIG. 5(b) is a sectional view showing a conventional electrode finger. FIG. 5C is a plan view showing a conventional electrode finger. 1...Piezoelectric substrate, 2...Groove, 3...Electrode finger

Claims (3)

[Claims] (1) A surface acoustic wave element in which transducer electrode fingers made of metal are arranged on a piezoelectric substrate, characterized in that a groove is provided on the piezoelectric substrate, and the electrode finger is provided so as to straddle the groove. surface wave element. (2) A surface acoustic wave element in which transducer electrode fingers made of metal are arranged on a piezoelectric substrate, characterized in that an inclined groove is provided on the piezoelectric substrate, and the electrode finger is provided at least in the groove. surface wave element. (3) The surface acoustic wave device according to claim 1 or 2, wherein the edge of the electrode finger and the edge of the groove are provided at an interval of 1/4 wavelength.