JPH0435515A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To obtain a large capacity without enlarging an area of a substrate by providing a conductor film facing at least one of input/output electrodes on the reverse side of the substrate, and forming the capacity between at least one of the input/output electrodes and the conductor film of the reverse side of the substrate. CONSTITUTION:A conductor film 13 facing at least one of input/output electrodes 11, 12 is provided on the reverse side of a substrate, and the capacity is formed between at least one of the input/output electrodes 11, 12 and the conductor film 13 of the reverse side of the substrate. In such a state, when thickness of the substrate 10 is made small, the capacity can be obtained by opposing inter-digital electrodes 11, 12 and the electrode of the reverse side. Since the inter-digital electrodes 11, 12 have a comparatively wide area, it is also possible to obtain a comparatively large capacity. The conductor film of the reverse side of the substrate is connected to a stem of a TO can, etc.,k and by connecting it to the ground potential, the capacity is formed in parallel to the inter-digital electrodes, and grounded. In such a way, the capacity being effective for adjusting a characteristic can be formed in the device without enlarging an area of the substrate 10.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electrode structure for a surface acoustic wave device, and particularly to an electrode structure for a surface acoustic wave device equipped with a matching electrode for use as a filter or the like. It is related to.

[Prior art]

Surface acoustic wave devices have various uses such as filters, resonators, and delay lines. In addition, the frequency band used is several hundred MHz.
It extends to z or more. In particular, it is used in various fields as a filter.

When using a surface acoustic wave device as a filter or the like, it is often necessary to add capacitance, inductance, etc. to adjust impedance in order to obtain matching between input and output. For this purpose, external components are used or conductive patterns are formed on the surface of the board.

Furthermore, multi-mode filters, which have been attracting attention recently, are required to obtain broadband characteristics by matching the resonant frequencies and anti-resonant frequencies of the two modes. However, as shown in FIG. 4, there may be a difference between the anti-resonant frequency f1 and the resonant frequency frZ. In this case, the antiresonant frequency f
In order to lower at, it is necessary to add a capacitor C in parallel as shown in the equivalent circuit of FIG. To this end, capacitance is obtained by attaching an external matching element or by placing conductor patterns facing each other on the surface of the substrate.

〔assignment〕

However, if external parts are required, the device becomes larger and the cost of the puff cage and the like also increases.

Furthermore, even when forming on the surface of a substrate, a large area is required to obtain a large capacitance, and if an attempt is made to use a small area, a sufficient capacitance cannot be obtained.

The present invention provides a surface acoustic wave device that can obtain a large capacity without increasing the area of the substrate.

[Means to solve the problem]

The present invention solves the above problems by forming a capacitance between an interdigital electrode and a conductor film on the back surface of a substrate.

That is, in a surface acoustic wave device including input and output electrodes of interdigital electrodes on a substrate having piezoelectricity, a conductor film is provided on the back surface of the substrate facing at least one of the input and output electrodes, and It is characterized in that a capacitance is formed between it and the conductor film on the back surface of the substrate.

In addition, in a surface acoustic wave device that includes an interdigital electrode on a piezoelectric substrate and a reflector arranged in the propagation direction of the surface acoustic wave excited by the interdigital electrode, the interdigital electrode is placed opposite to the interdigital electrode on the back side of the substrate. It is characterized by a capacitance being formed between the interdigital electrode and the conductive film on the back surface of the substrate, and is characterized by the fact that a capacitance is formed between the interdigital electrode and the conductive film on the back surface of the substrate. A capacitor may be formed between one interdigital electrode and a conductive film on the back surface of the substrate.

[Effect]

By reducing the thickness of the substrate, capacitance can be obtained by making the interdigital electrodes and the back electrodes face each other. Since the interdigital electrode has a relatively large area, it is also possible to obtain a relatively large capacitance.

The conductor film on the back side of the board is connected to the stem of 70 cans, etc.
Connected to ground potential. As a result, a capacitor is formed in parallel with the interdigital electrode and grounded.

〔Example〕

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

FIG. 1 shows an example of a transversal filter, in which (a) is a plan view and (b) is a front view. Interdigital electrodes 11.12 are formed on the surface of a piezoelectric substrate 10 made of quartz, lithium tantalate, or the like by two conductor patterns facing each other in a comb-teeth pattern. In this case, the interdigital electrode 11 is an input electrode, and the interdigital electrode 12 is an input electrode.
is the output electrode.

The two interdigital electrodes are each connected to an input/output terminal, and the input electrical signal is converted into a surface acoustic wave by the interdigital electrode 11.
2 converts the surface acoustic waves into output electrical signals.

A conductor film 13 is formed on the back surface of the substrate 10.

In this example, it is formed only in the portion facing the interdigital electrode 11 on the input side. If this conductive film is formed not only on the comb teeth portion of the interdigital electrode but also on the bus bar portion, a larger capacitance can be obtained.

In this example, the conductive film was formed only on the part facing the interdigital electrode on the input side, but it could also be formed on the output side.
It may be formed entirely.

FIG. 2 shows an example of a multimode resonator filter, in which (a) is a plan view and (b) is a front view. Interdigital electrodes 21 are formed on the surface of a piezoelectric substrate 20 made of crystal or the like, connected in series by two conductor patterns facing each other in a comb-teeth shape. In this case, one of the interdigital electrodes 21 becomes an input electrode, and the other interdigital electrode becomes an output electrode. The two interdigital electrodes are each connected to an input/output terminal, and the input electrical signal is converted into a surface acoustic wave by the interdigital electrode 21, and is multiple reflected by the reflectors 24 arranged in a grid pattern, thereby trapping the energy. , becomes a resonator. The vibration modes of the two resonators are combined, and an output having a predetermined passband characteristic is obtained from one end of the interdigital electrode 21.

A conductor film 23 is formed on the back surface of the substrate 10.

In this example, it is formed only in the portion facing the interdigital electrode 21 on the input side. If this conductive film is formed not only on the comb teeth portion of the interdigital electrode but also on the bus bar portion, a larger capacitance can be obtained.

Although it is the same in the above example, the conductor film 23 on the back surface of the substrate is T
It is glued to the stem of an O-can or the like and connected to ground potential. Thereby, the device can be bonded and connected at the same time.

FIG. 3 is a plan view showing another example of the transversal filter. Interdigital electrodes 31 and 32 are formed on the surface of a piezoelectric substrate 30 made of crystal, lithium tantalate, or the like by two conductor patterns facing each other in a comb-teeth pattern. In this case, interdigital electrode 31 is an input electrode, and interdigital electrode 32 is an output electrode. The two interdigital electrodes are each connected to an input/output terminal, and the interdigital electrode 31 converts an input electrical signal into a surface acoustic wave, and the interdigital electrode 32 converts the surface acoustic wave into an output electrical signal.

In this example, the width of the bus bar 35 of the input interdigital electrode 31 is made wider than usual.

A conductive film 33 is formed on the back surface of the substrate 30. In this example, it is formed only in the portion facing the interdigital electrode 31 on the input side. This conductor film is formed to extend not only to the comb-teeth portion of the interdigital electrode but also to the bus bar portion whose width is wider than in the above example, and a large capacitance can be obtained.

〔effect〕

According to the present invention, a capacitance effective for adjusting characteristics can be formed in a surface acoustic wave device without increasing the area of the substrate. Therefore, it is possible to downsize the surface acoustic wave device.

This also simplifies the matching circuit, which is advantageous in terms of cost and the like.

Furthermore, there is an advantage that the conductive film can also be used for die bonding, shielding, etc.

[Brief explanation of the drawing]

FIGS. 1 and 2 show embodiments of the present invention, respectively (a
l is a plan view, (bl is a front view. Fig. 3 is a plan view showing another embodiment of the present invention, Fig. 4 is an explanatory diagram of the characteristics of the multimode filter, and Fig. 5 is an equivalent circuit diagram thereof. It is.

Claims (6)

[Claims] (1) In a surface acoustic wave device having input/output electrodes of interdigital electrodes on a substrate having piezoelectricity, a conductive film facing at least one of the input/output electrodes is provided on the back surface of the substrate, and at least one of the input/output electrodes is provided. A surface acoustic wave device characterized in that a capacitance is formed between the substrate and a conductor film on the back surface of the substrate. (2) In a surface acoustic wave device equipped with an interdigital electrode on a piezoelectric substrate and a reflector arranged in the propagation direction of the surface acoustic wave excited by the interdigital electrode, the interdigital electrode is placed on the back side of the substrate. A surface acoustic wave device comprising opposing conductor films, and a capacitance is formed between the interdigital electrode and the conductor film on the back surface of the substrate. (3) In a surface acoustic wave device equipped with a plurality of interdigital electrodes on a piezoelectric substrate and a reflector arranged in the propagation direction of the surface acoustic wave excited by the interdigital electrodes, an interdigital A surface acoustic wave device comprising a conductor film facing at least one of the electrodes, and a capacitance is formed between the interdigital electrode and the conductor film on the back surface of the substrate. (4) The surface acoustic wave device according to claim 1, 2 or 3, wherein the bus bar width of the interdigital electrode is widened so that the conductive film on the back surface of the substrate also faces the bus bar. (5) The surface acoustic wave device according to claim 4, wherein the interdigital electrode and the external circuit are connected by wire bonding to the bus bar. (6) The surface acoustic wave device according to claim 1, 2 or 3, wherein the electrode on the back surface of the substrate is bonded to a metal surface connected to ground potential.