JPS5829626Y2 - surface wave filter - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a surface wave filter, and particularly aims to provide an electrode structure that can change impedance values without affecting frequency characteristics.

The piezoelectric substrate material used for the elastic wave filter is LiT.
It is made of a single crystal material such as aO3, and an input electrode that converts an electrical signal into a surface wave and an output electrode that converts the surface wave into an electrical signal are formed on the surface.

This electrode is made of a metal, for example, an aluminum vapor-deposited film, formed in the form of a pair of interdigitated electrode metals.

The things that form the surface wave filter impedance are radiation resistance, capacitance, electrode resistance, acoustic susceptance, etc., and when using a surface wave filter as a set, the most problematic one is It is capacitance.

What determines this capacitance is the capacitance per pair of electrodes.
It is extremely difficult to change the number of effective pairs, crossing width, etc. without affecting the frequency characteristics, and therefore it cannot be said that the filter has sufficient compatibility with other surface wave filters.

The present invention has been developed in consideration of this point, and provides a surface wave filter in which the capacitance can be easily changed without substantially affecting the frequency characteristics.

That is, the auxiliary electrode is electrically connected to the input electrode or the output electrode and formed in parallel on the substrate without changing the input electrode button or the output electrode at all.

By setting the capacitance of such an auxiliary electrode to an arbitrary value, the capacitance of the input electrode or the capacitance of the output electrode is controlled.

However, the surface waves generated at the auxiliary electrodes pose a problem, and as a countermeasure, a sound-absorbing layer or grooves and a sound-absorbing layer formed in the substrate are provided between the input/output electrodes and the auxiliary electrodes. This prevents any influence on the characteristics of the wave filter.

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, an input electrode 2 and an output electrode 3 are formed on a substrate 1 by metal, for example, an aluminum vapor deposited film, in the shape of a comb that intersects with each other.
An auxiliary electrode 4 is formed from an aluminum vapor-deposited film, extending outward from the edge toward the end surface of the substrate and intersecting inward.

Next, a sound absorbing layer 5 is formed on the side of the input electrode 2, and the output electrode 3
A sound absorbing layer 6 is formed between the auxiliary electrode 4 and the auxiliary electrode 4 .

Since the auxiliary electrode is thus formed and electrically connected to the outside of the output electrode, the capacitance can be easily increased without affecting the frequency characteristics.

If the capacitance of the auxiliary electrode of the octopus is set to a predetermined value, there will be no need for a capacitor as a separate member to accommodate the conventional surface acoustic wave filter, which will improve manufacturing and It is extremely useful when used as a device.

Although the auxiliary electrode is formed by connecting the output electrode to the output electrode in the above example, the auxiliary electrode 8 may be formed separately from the output electrode 3 as shown in FIG. A groove 7 may be formed in the substrate between them, and the output electrode 3 and the auxiliary electrode 8 may be connected to a bonding wire 9 for electrical connection.

Needless to say, in this case as well, the sound absorbing layer 10 is provided between the output electrode 3 and the auxiliary electrode 8.

Although the auxiliary electrode is formed on the outside of the output electrode in the above example, the auxiliary electrode may be formed on the outside of the substrate end surface of the input electrode 2 in addition to what is shown in the drawings. It may be formed on the upper or lower substrate, and various modified structures can be obtained according to the gist of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a plan view of one embodiment of the present invention, and FIG. 2 is a plan view of another embodiment of the present invention. 1...Substrate, 2...Input electrode, 3...
...Output electrode, 4.8...Auxiliary electrode, 5,
6, 10...Sound absorption layer, 7...Groove, 9.
...Bonding wire.

Claims (1)

[Scope of utility model registration request] In a surface wave filter comprising an input electrode and an output electrode made of a metal vapor deposited film on a piezoelectric substrate, an auxiliary electrode is formed by being electrically connected to the outside of the input electrode or the output electrode, and the auxiliary electrode and the input electrode or A surface wave filter comprising a sound absorbing layer formed between an output electrode and an output electrode.