JPS60212019A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To decrease remarkably a ripple of a group delay characteristic and a ripple of a frequency characteristic by using an absorbing member being a mixture of niobium oxide powder to a silicone group resin so as to improve the suppressing effect of an unnecessary surface wave. CONSTITUTION:Absorbing members 4, 5 are provided by screen print to a region to absorb the unnecessary surface wave on the surface wave substrate 1, e.g., between input/output electrodes 2, 3 and each substrate edge. The absorbing members 4, 5 are constituted with the silicone group resin, e.g., a material mixing niobium oxide (NbO, Nb2O3 or Nb2O5) powder to the silicone rubber, preferably in the weight ratio of 5:1-1:1 of the silicone rubber and the niobium oxide powder. The group delay characteristic suppresses the ripple to a small value <=100ns.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to surface wave devices, and more particularly to improvements in absorbers for damping unwanted surface waves.

In general, a surface wave device is configured to form an interdigital transducer on a piezoelectric substrate and to excite or receive surface waves with this transducer. For example, in the case of a surface wave filter, an input (excitation)
The transmission transducer and the output (reception) transducer are spaced apart by t equivalents. In such a surface wave filter, the surface waves excited by the input transducer propagate in two directions, of which the surface waves in one direction propagate to the output transducer, and half of the surface waves are picked up by the output transducer. However, the remaining surface waves pass through and are reflected as unnecessary waves at the edge of the substrate. Furthermore, the surface waves propagating in the other direction are also reflected by the end face of the substrate and become unnecessary waves, which are extracted as unnecessary signals by the output side transducer. Reflections at these end faces or transducer electrodes appear as frequency characteristic ripples or group delay ripples, but since group delay ripples are more noticeable than frequency characteristic ripples, this specification will focus on them. ) shows the evaluation results of group delay.

In order to dampen such unnecessary surface waves, conventionally, on the substrate outside the input/output transducer,
An absorbent material made of silicone rubber or epoxy adhesive is coated or printed. However, when silicone rubber or epoxy adhesive is printed in this way, it is still insufficient to suppress unnecessary signals, particularly ripples in the head of frequency characteristics and group delay characteristics. For example, if silicone rubber is printed on a surface wave substrate,
As shown in Figure 2 (C), the group delay characteristic (G
DT) has a ripple of 1@s or more.

The present invention eliminates the above-mentioned conventional drawbacks, and aims to provide a surface acoustic wave device that can suppress unnecessary surface waves, in particular, sufficiently reduce ripples in frequency characteristics and ripples in group delay characteristics. The gist is that an absorbing material made of silicone adhesive mixed with niobium oxide powder is provided on the surface wave substrate in a region for absorbing unnecessary surface waves.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 1, numeral 1 denotes a surface wave substrate, which is composed of PZT lamics, single crystal, ZnO film on a glass substrate, etc. On this surface wave substrate 1, there are interdigital electrodes 2 on the input side and Interdigital electrodes 3 are formed at appropriate intervals.

On this surface wave substrate 1, an absorbing material 4.5 is formed by screen printing or the like in a region for absorbing unnecessary surface waves, for example, between the input/output electrode 2.3 and the edge of each substrate. It is provided. These absorbers 4.5 are silicone resins such as silicone rubber and niobium oxide (Nb
The material is preferably a mixture of silicone rubber and niobium oxide powder in a weight ratio of 5:1 to 1:1. For example, znO on a glass substrate
A VIF filter for a television receiver is constructed using a surface wave substrate made of a film, and the absorption material has a weight ratio of silicone rubber:niobium powder=5:1 and silicone rubber:niobium powder=1:1. When screen printing was performed, the group delay characteristics became as shown in FIGS. 2(a) and 2(b).

As is clear from the figure, the ripple could be suppressed to 10 Dos or less. If the weight ratio of niobium oxide powder is less than 5:1, the ripple suppression effect will be reduced, and if the weight ratio exceeds 1:1 and a large amount of niobium oxide powder is mixed, the viscosity of the material will increase. This would make screen printing difficult, and would be a practical problem for mass production.

As explained above, since the present invention uses an absorbing material made of a silicone resin mixed with niobium oxide powder, the effect of suppressing unnecessary surface waves is great, especially ripples in group delay characteristics and frequency Characteristic ripples can be significantly reduced.

[Brief explanation of drawings]

Fig. 1 is a plan view showing an embodiment of the surface wave device according to the present invention, Fig. 2 (a) and (b) are group delay characteristic diagrams based on the present invention, and Fig. 2 (C) is a group delay characteristic diagram based on the conventional example. It is a delay characteristic diagram. 1 is a surface wave substrate, 2.3 is an electrode, and 4.5 is an absorbing material. Patent applicant Murata Manufacturing Co., Ltd. Figure 117

Claims (1)

[Claims] A surface wave device characterized in that an absorbing material made of silicone resin mixed with niobium oxide powder is provided on a surface wave substrate in a region for absorbing unnecessary surface waves.