JPS60153631A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To improve the accuracy in forming an electrode by coating a metallic conductor electrode layer and an insulation oxide layer of the same metal to the surface of a substrate having a piezoelectric effect and imbedding the electrode layer to the oxide layer so as to attain ease of manufacture of the imbedded electrode structure. CONSTITUTION:A metallic layer 8 is formed by vapor-depositing Al or Ti having a high conductivity to the entire surface of the substrate 1 having the piezoelectric effect. Then a resist film 9 is formed selectively by coating, and a part not covered by the film 9 is selected so as to form the metallic electrode layer 8a and the oxide layer 8b made of the same metal as that of the electrode layer 8a. Then the electrode layer 8a is formed at the same time while it is imbedded to the oxide layer 8b so as to attain ease of manufacture of the surface acoustic wave element of the electrode structure thereby improving the accuracy in forming the electrodes.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a surface acoustic wave (SAW) device which is a telecommunication device using surface acoustic waves.

Conventional technology Focusing on surface acoustic waves that propagate on solid surfaces, an electrode layer of a predetermined shape is formed on a substrate with a piezoelectric effect to skillfully convert electrical signals and surface acoustic waves for telecommunications. Elastic surface coating W (hereinafter referred to as SAW element), which is an element, can be applied to a wide range of applications such as delay elements, filters, and oscillators.
It has the potential to easily realize stable circuits in the range from several hundred MHz to several GHz.

Fig. 1 explains an example of a structure used as a wave device, in which interdigital electrodes (2) and (3) are adhered and formed on the surface of a substrate (1) having a piezoelectric effect, and one interdigital electrode (
2) by inputting an electrical signal e to generate a surface acoustic wave on the substrate (1), which is converted into an electrical signal by the other interdigital electrode (3), which is filtered at a constant resonant frequency. The configuration is such that output E is taken out. In the same figure, (
4) (4) is a damping substance.

FIG. 2 shows the device used as a resonator.

When interdigital grating reflectors (5) (5) are formed on the surface of a substrate (1) having a piezoelectric effect at a distance that is an integral multiple of the half wavelength of the surface acoustic wave, the surface acoustic wave will be transmitted between the two reflectors. It repeats reflection and becomes a standing wave. A resonator can be constructed by providing a blind-shaped electrode (ff) at the antinode of the standing wave.

Therefore, the blind-shaped electric current tl (
2)(3)(5) and the grating reflector (5) are formed by depositing a metal film (6) on the surface of a substrate (1) having a piezoelectric effect, as shown in FIG. This formation is performed by a lift-off method or an etching method.

In the lift-off method, a photoresist Iff is formed on the substrate surface except for the area where the metal film is to be formed, and after metal evaporation is performed on the entire surface, the photoresist film is removed together with the metal film deposited on top of the photoresist film, and the metal film is formed only in the necessary areas. It leaves behind.

In addition, the etching method deposits a metal film on the entire surface of the substrate.
Thereon, a photoresist film is formed over the portion where the electrode is to be formed by photolithography, and the photoresist 11? is etched. Gold nF having a predetermined shape is formed by removing the portion where j is not formed.

However, the metal film formed by the above method has a stepped shape protruding from the substrate (1) as shown in FIG. For this reason, there is a problem in that loss occurs when the surface acoustic waves travel back and forth between the metal films, and the resonance sharpness Q cannot be made large, making it impossible to obtain sufficient characteristics.

Therefore, as an attempt to improve the characteristics such as improving the electro-mechanical coupling efficiency and increasing the resonance sharpness Q, a buried electrode (7) as shown in Fig. 4 was developed on February 15, 1982.
Published in Nikkei Electronics P186-P187 published by Japan.

However, in order to form the buried electrode (7) as described above, a mask is formed using a photoresist or the like excluding the electrode formation area, a groove is formed in the substrate (1) by etching, and then a metal electrode layer is formed in the groove. A complicated process of embedding must be performed, which increases the number of man-hours, reduces production efficiency, and makes it difficult to improve the accuracy of electrode formation.

In view of the complexity of the manufacturing process for forming the buried electrodes, the present invention aims to provide an improved product that has a similar structure to the buried electrodes and can be manufactured in a simple process. .

20 Structure of the Invention The present invention involves forming a metal electrode layer of a predetermined shape on the surface of a substrate having a piezoelectric effect, and forming an oxide layer of the same metal as the metal electrode layer on the part where the metal electrode layer is not formed. It is characterized by being formed by adhering to it.

According to the above configuration, the electrodes of the SAV/element can be formed by oxidizing the gold hJta deposited on the entire surface of the substrate except for the electrode forming part, so manufacturing is easy and the shape is also that of the buried electrode. The result is similar to (good characteristics can be obtained).

E, Example An embodiment of the present invention will be described according to its manufacturing process.

First, a substrate having a piezoelectric effect is prepared. The material of this substrate is, for example, lithium tantalate (Li Ta 03 ).
, lithium niobate (LiNb, crystal piezoelectric ceramic, etc.).As shown in Figure 5, the entire surface of this substrate is coated with a metal that is easily compatible with the substrate (1), has high conductivity, and becomes a good insulator during oxidation. , for example aluminum (/l),
Metal Ji (8) is formed by depositing titanium (Ti), tantalum (Ta), etc. by metal vapor deposition or the like. Next, as shown in FIG. 6, a resist 11tH9) is selectively deposited on the portion where the electrode is to be formed by photolithography or the like. Next, it is placed in a light-permeable environment that oxidizes it, for example, an oxidizing atmosphere, and the portions not covered by the resist film (9) are selectively oxidized and converted into oxide 71 (8a). If the first metal deposited is aluminum (/l),
This oxide layer (8a) is alumina (8I1203”)
It is. Thereafter, the resist film (9) is removed using a predetermined solvent. As a result, as shown in FIG. 7, a metal electrode layer (8b) having a structure similar to that of a buried electrode can be obtained surrounded by an oxide layer (8a).

03) If you want to form the writing oxide layer with good precision, you can perform an anodizing treatment as shown in Figure 9. That is, the metal layer (8) and the resist film (9) are deposited and formed. The substrate (1) which has been prepared is immersed in an electrolytic solution (10), and a DC voltage V is applied between the oxidizing electrode (11) placed in the electrolytic solution and the metal layer (8) with the fully bent layer side as the anode. When added, a predetermined portion can be oxidized at high speed and with high precision.

Effects of the Invention The SAW device of the present invention forms electrodes (including grating electrodes) having the same structure as buried electrodes by a simple method by selectively oxidizing the metal layer deposited on the substrate. be able to. Therefore, it is possible to manufacture a SAW element having good characteristics such as high electromechanical conversion efficiency and large resonance sharpness Q at low cost.

[Brief explanation of the drawing]

1 and 2 are perspective views showing structural examples of SAW elements, with FIG. 1 showing a filter and FIG. 2 showing a resonator. 3 and 4 are cross-sectional views showing examples of conventional electrode structures, and FIGS. 5 to 8 are cross-sectional views sequentially showing manufacturing steps of an embodiment of the present invention.
FIG. 9 is a cross-sectional view illustrating anodizing treatment that can be employed in manufacturing the device of the present invention. (1)...Substrate having a piezoelectric effect, (8a)...Metal electrode layer, (8b)...Oxide layer.

Claims (1)

[Claims] (1) A metal conductive electrode layer and an insulating oxide layer of the same metal are deposited on the surface of a substrate having a piezoelectric effect, and the electrode layer is embedded in the oxide layer. surface acoustic wave device.