JPH0444409A - Surface acoustic wave device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) The present invention relates to a surface acoustic wave device, and particularly to a surface acoustic wave device suitable for an IF circuit of a satellite broadcasting receiver.

(Prior Art) Surface acoustic wave devices have been widely used as filters and the like for various devices. As one such surface acoustic wave device, a so-called dual type surface acoustic wave device is known, which includes a plurality of pairs of comb-shaped electrodes having different frequency characteristics. Such surface acoustic wave devices are mainly used in IF circuits of satellite broadcast receivers and the like.

FIG. 8 shows the configuration of an example of such a conventional dual type surface acoustic wave device. In the figure, reference numeral 1 indicates an envelope of a surface acoustic wave filter element, and inside this envelope 1, an input side electrode 2 consisting of a comb-shaped electrode and an output side electrode 3 are provided.
a and 3b are provided.

The input electrode 2 is connected to an input terminal 4.5, and the output electrodes 3a, 3b are connected to an external switching circuit 6. The switching circuit 6 is composed of diodes 7a, 7b, amplifiers ga, sb, resistor 9, etc., and selects one of the output side electrodes 3a, 3b by switching the voltage applied to the control terminal 10. The output terminals 11a and llb are configured to obtain outputs with desired characteristics.

(Problem to be Solved by the Invention) However, in the conventional surface acoustic wave device described above, in order to switch the frequency characteristics, an external switching circuit using a diode or the like is required, which increases the number of components. Additionally, there is a problem in that characteristics vary due to stray capacitance due to the routing of the PC board pattern.

The present invention has been made in response to such conventional circumstances, and it is possible to reduce the number of parts and reduce costs compared to the conventional method, and also to reduce stray capacitance due to the routing of PC board patterns compared to the conventional method. It is an object of the present invention to provide a surface acoustic wave device that can be reduced in size and have uniform characteristics.

[Structure of the Invention] (Means for Solving the Problems) That is, the surface acoustic wave device of the present invention includes an insulating substrate, a plurality of pairs of comb-shaped electrodes formed on the insulating substrate, and a structure that covers the comb-shaped electrodes. a surface acoustic wave filter element made of a formed zinc oxide compound thin film and configured to be able to obtain at least two types of outputs having different frequency characteristics; and a conductive thin film formed at a distance on the insulating substrate. and a plurality of voltage dependent resistance elements made of the zinc oxide compound thin film formed to be interposed between the electrode pairs, and the voltage applied to the voltage dependent resistance elements is switched. , characterized in that the frequency characteristic of the output of the surface acoustic wave filter element is selected.

(Function) In the surface acoustic wave device of the present invention having the above configuration, a switching circuit using a voltage-dependent resistance element and a surface acoustic wave filter element are arranged on the same chip. Furthermore, since a zinc oxide compound thin film is used as the surface acoustic wave propagation medium and the material of the voltage-dependent resistance element, it is possible to simultaneously form a switching circuit using the voltage-dependent resistance element and a surface acoustic wave filter element. .

Therefore, by accommodating the switching circuit and the surface acoustic wave filter element in the same package, it is possible to reduce the number of parts and the number of manufacturing steps, thereby lowering costs. Capacity can be reduced,
Characteristics can be made uniform.

(Example) Hereinafter, details of the present invention will be described with reference to the drawings.

FIGS. 1 and 2 show the configuration of a surface acoustic wave device according to an embodiment of the present invention.

In the surface acoustic wave device of this embodiment, first, an aluminum thin film (conductive thin film) is formed on a glass substrate 20 as an insulating substrate.
By vapor deposition, the input side electrode 21 and output side electrodes 22a, 22b of the surface acoustic wave filter element consisting of comb-shaped electrodes, and the electrode pair 23a and the electrode pair 23b for constructing the voltage dependent resistance element are formed.

Thereafter, ZnO as a surface acoustic wave propagation medium and voltage-dependent resistance element material is deposited by sputtering through an appropriate mask to form a Zno thin film 24 on the input side electrode 21 and output side electrodes 22a and 22b. At the same time, Zn was added between the electrode pair 2311 and the electrode pair 23b.
An O thin film 25a125b is formed, and a surface acoustic wave filter element 26 and voltage dependent resistance elements 27a and 27b are simultaneously formed.

In FIG. 1, 28a and 28b are input bonding pads, 29g and 29b are output bonding pads, and 30 is a control bonding pad, which are formed on the glass substrate 20 together with each electrode.

Here, 27g of voltage-dependent resistance elements using a ZnO thin film
, 27b, as shown in FIG.
It has a structure in which a (25b) is interposed. Such an element has characteristics as shown in the graph of FIG. 4, with the vertical axis representing current and the horizontal axis representing voltage. That is, for example, when the cross-sectional area of the electrodes is 500 μm 2 and the distance between the electrodes is 300 μm, a current flows by applying an external voltage of 1.5 V or more between the electrodes.

In the surface acoustic wave device of this embodiment, by utilizing the above characteristics, as shown in FIG.
A bias voltage of +1.5V is always applied from the switch 32 to the control terminal 33.
Turns on/off a voltage of +3v or more through the resistor 34.
loFF ) to select the output.

That is, when the switch 32 is turned on, the control terminal 3
If a voltage of 3 to +3v or more is applied, the IC of the external circuit
Since bias voltages of +1 and 5v are always applied from 31a and 31b, the potential difference becomes +1.5v or more, and a current flows through the voltage-dependent resistance element 27b, resulting in a short circuit. For this reason, the output side electrode 22b also becomes short-circuited,
Input from input terminal 35a135b, input side electrode 21
The waves propagated from are received only by the output side electrode 22a,
An output is generated at output terminal 36a.

Conversely, when the switch 32 is turned off and the control terminal 33 is operated unattended, a current flows through the voltage-dependent resistance element 27a due to the bias voltage from the ICs 31a and 31b, and an output is generated at the output terminal 36b.

In this way, ZnO is used as the material of the propagation medium of the surface acoustic wave filter element 26 and the voltage-dependent resistance elements 27a and 27b.
By using a thin film, the voltage dependent resistance element 27a,
27b and the surface acoustic wave filter element 26 are configured on the same chip (glass substrate 20),
It becomes possible to store them in the same package 37. Therefore, compared to the conventional surface acoustic wave device shown in FIG. 8, the number of diodes 7a and 7b in the external circuit can be reduced. Further, along with this, it is possible to reduce stray capacitance due to the routing of PC board patterns in the switching circuit, and it is possible to reduce variations in characteristics due to stray capacitance.

Note that if a differential amplifier 31 is used in the external circuit as shown in FIG. 5, induction can be eliminated and the number of parts can be further reduced.

Further, in the above embodiment, one input side electrode 21 and 2
A surface acoustic wave filter element 2 that realizes two different frequency characteristics by the claw output side electrodes 22a, 22b.
6 has been described, but since the surface acoustic wave filter element 26 is a reversible element, as shown in FIG.
Input side electrode 21a.

Two electrodes 21b and one output electrode 22 may be provided.

Further, as shown in FIG. 7, two input side electrodes 21a,
21b and two output side electrodes 22a, 22b are provided, the present invention can be similarly applied. In this way, by using one pair of input side electrode 21g and output side electrode 22a, and one pair of input side electrode 21b and output side electrode 22b for each frequency characteristic, it is possible to electrically separate each pair, and the two Mutual interference of different frequency characteristics can be eliminated.

[Effects of the Invention] As explained above, according to the surface acoustic wave device of the present invention, the number of parts can be reduced and costs can be lowered compared to the conventional method, and the PC board pattern can be reduced compared to the conventional method. Stray capacitance due to routing can be reduced and characteristics can be made more uniform.

[Brief explanation of the drawing]

1 and 2 are diagrams showing the configuration of a surface acoustic wave device according to an embodiment of the present invention, FIG. 3 is a diagram showing the configuration of a voltage-dependent resistance element, and FIG. 4 is a diagram showing the configuration of a voltage-dependent resistance element. Graphs showing the characteristics, FIGS. 5 to 7 are diagrams showing the configuration of surface acoustic wave devices of other embodiments, and FIG. 8 is a diagram showing the configuration of a conventional surface acoustic wave device. 20・・・・・・・・・・・・・・・・・・Glass substrate 21・・・・・・・・・・・・・・・・・・
Input side electrodes 22g, 22b...Output side electrode 23
a, 23b... Electrode pair 24.......Zn
O thin film 25a, 25b--ZnO thin film 26...Surface acoustic wave filter element 27a, 27b... ...Voltage-dependent resistance element Applicant: Toshiba Corporation Applicant: Toshiba Electronic Device Engineering Co., Ltd.

Claims (1)

[Claims] It consists of an insulating substrate, a plurality of pairs of comb-shaped electrodes formed on the surface of the insulating substrate, and a zinc oxide compound thin film formed to cover these comb-shaped electrodes, and is capable of obtaining at least two types of outputs with different frequency characteristics. A surface acoustic wave filter element configured as follows, an electrode pair made of a conductive thin film formed at a distance on the insulating substrate surface, and the zinc oxide compound thin film formed to be interposed between the electrode pair. and a plurality of voltage-dependent resistance elements, and is configured to select the frequency characteristic of the output of the surface acoustic wave filter element by switching the voltage applied to the voltage-dependent resistance elements. Surface acoustic wave device.