JPH03127505A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To suppress migration of an electrode metal at application of large power and to prevent destruction due to a short-circuit of electrode fingers by providing a floating electrode having electrode fingers at both ends between electrode fingers of interdigital electrodes and constituting a couple of electrode fingers with each electrode finger of the floating electrode and each electrode finger of the interdigital electrodes. CONSTITUTION:Input side interdigital electrodes 2-1, 2-2 and output side interdigital electrodes 3-1-3-2 are arranged alternately in the propagation direction of a surface acoustic wave. Then each of the input side interdigital electrodes 2-1, 3-2 has a signal electrode 10 receiving an electric signal 10, a ground electrode 11 whose one end connects to ground, and a floating electrode 9 having electrode fingers at both ends and placed between the signal electrode 10 and the ground electrode 11, and the electrode fingers of the signal electrode 10 are in pairs with the electrode fingers at one end of the floating electrode 9 and the electrode fingers of the earth electrode 11 are in pairs with the electrode fingers at the other end of the floating electrode 9. Thus, the migration of the electrode metal is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a surface acoustic wave device with high power resistance.

(Prior Art) FIG. 2 is a schematic plan view showing an example of a conventional surface acoustic wave device, in which an input for converting an electric signal into a surface acoustic wave signal is applied to the surface of a piezoelectric substrate 1 consisting of a surface acoustic wave element. Side interdigital electrodes 7-1, 7-2 and output side interdigital electrodes 8-1 to 8-3, which convert surface acoustic wave signals into electrical signals, are arranged alternately in the propagation direction of surface acoustic waves. (For example, Japanese Patent Laid-Open No. 115-1983). Here, 4 is an input terminal for inputting an electric signal, and 5 is an output terminal for taking out an electric signal.

The electrical signal supplied to the input terminal 4 is distributed to each input side interdigital electrode 7-1, 7-2, and excites a surface acoustic wave 6 on the piezoelectric substrate 1. This surface acoustic wave 6 is transmitted from both sides of the input end interdigital electrode 7-1, 7-2 to the output side interdigital electrode 8-1.
~8-3, perpendicular to the electrode fingers of the input side interdigital electrodes 7-1, 7-2. When the surface acoustic wave 6 reaches the output side interdigital electrodes 8-1 to 8-3, a potential difference is generated between the electrode fingers. This potential difference is taken out from the output terminal 5 as an electrical signal.

In the surface acoustic wave filter shown in FIG. 2, when an electrical signal is supplied from the output terminal 5, the electrical signal can be extracted from the input terminal 4 in the same manner as described above. In this case, the output blind-shaped electrodes 8-1 to 8-1 in FIG.
8-3 operates as an input-side interdigital electrode, and input-side interdigital electrodes 7-1 and 7-2 operate as output-side interdigital electrodes.

(Problem to be Solved by the Invention) However, in the surface acoustic wave device having the above configuration, the voltage supplied to the input terminal 4 is directly applied to the input side interdigital electrode 7.
-1.7-2, input side interdigital electrode 7-1.
The amplitude of the surface acoustic wave 6 excited at 7-2 depends on the voltage applied between the electrode fingers of input-side interdigital electrodes 7-1 and 7-2. Therefore, when a large power is applied to the input terminal 4, the voltage between the input side interdigital electrodes 7-1 and 7-2 becomes large, and the input side interdigital electrodes 7-1 and 7-2 are excited. Then, the amplitude of the surface acoustic waves received by the output-side interdigital electrodes 8-1 to 8-3 becomes considerably large, and the migration of the electrode metal in the interdigital electrodes increases, causing a short circuit between the electrode fingers. The problem is that a large current flows through the device and it eventually breaks down, making it impossible to apply large amounts of power.

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface acoustic wave device with excellent power durability, which suppresses the migration of electrode metal during application of high power as described above, and prevents destruction of electrode fingers due to yoke.

(Means for solving the problem) In order to achieve the above-mentioned object, the present invention has been devised to solve the problem. A floating electrode with electrode fingers at both ends is provided between the electrode fingers of the two electrodes, and each electrode finger of the floating electrode and each electrode finger of the interdigital electrode constitute a pair of electrode fingers. It was designed to do so.

(Function) The voltage of the electric signal input to the surface acoustic wave device is applied to the input end interdigital flih. The applied voltage is decomposed by the floating electrode, and a surface acoustic wave having an amplitude corresponding to the decomposed voltage is excited on the piezoelectric substrate. That is, the amplitude of the surface acoustic wave is reduced, and migration of the electrode metal is suppressed. The excited surface acoustic waves propagate on the piezoelectric substrate and reach the input end interdigital transducer. The input end interdigital electrode has the same configuration as the output side interdigital electrode, and the arriving surface acoustic wave is converted into an electric signal having a voltage of approximately the original magnitude, and is output.

(Embodiment) FIG. 1 is a schematic plan view showing a first embodiment of the present invention. In FIG. 1, 1 is a piezoelectric substrate of a surface acoustic wave element, 2 is a piezoelectric substrate of a surface acoustic wave element;
-1.2-2 is an input side interdigital electrode, 3-1 to 3-3 are output side interdigital electrodes, 4 is an input terminal, 5 is an output terminal, and the input side interdigital electrode 2-1.2 -2 and the output side interdigital electrodes 3-1 to 3-3 are arranged alternately in the propagation direction of the surface acoustic wave, and the input end interdigital electrodes 2-1 and 2-2 are connected to the input terminal 4 in parallel with each other. , output side interdigital electrode 3
-1 to 3-3 are connected to the output terminal 5 in parallel with each other.

Figure 3 shows the input side interdigital electrode 2-1.2- shown in Figure 1.
FIG. 2 is an enlarged plan view of FIG. This input end interdigital electrode has a signal electrode 10 to which an electric signal 12 is applied, a ground electrode 11 whose one end is grounded, and electrode fingers at both ends, and between the signal electrode 10 and the ground electrode 11. The electrode finger of the signal electrode 10 and the electrode finger at one end of the floating electrode 9 form a pair, and the electrode finger of the ground electrode 11 and the electrode finger at the other end of the floating electrode 9 form a pair. is doing. This is a state in which two interdigital electrodes are connected electrically in series and acoustically in parallel.

Note that the output side blinds 7 ([3-1 to 3-3-
3 also has a configuration similar to that of the input end interdigital electrode shown in FIG.

Next, the operation of this embodiment will be explained based on FIGS. 1 and 3. The voltage of the electric signal applied to the input terminal 4 is directly supplied to the input end interdigital electrode 2-1.2-2. Input end stray electrodes 2-1, . When voltage is supplied to 2-2, induced charges are induced on the floating electrode 9 shown in FIG. An electric field is generated. The magnitude of these electric fields is the same as that of the signal electrode 1 when the floating electrode 9 is not installed.
17 of the magnitude of the electric field generated between 0 and the earth electrode 11
It is 2. Therefore, the amplitude of the electrode finger between the signal electrode 10 and the floating electrode 9 and the electrode finger between the floating electrode 9 and the ground electrode 11 corresponds to 1/2 of the voltage of the supply voltage 1 and 2, respectively. A surface acoustic wave 6 having the following value is excited. That is, the input end interdigital electrodes 2-1 and 2-2 of this embodiment generate a surface acoustic wave having an amplitude that is 1/2 of the surface acoustic wave excited by a conventional input end interdigital electrode that does not have a floating electrode. 6 will be excited in twice the excitation area.

The excited surface acoustic waves 6 are transmitted to the output side interdigital electrodes 3-1 to 3-1.
3-3, the potential difference between the signal electrode and the floating electrode, and between the floating electrode and the ground electrode is 1/2 of the potential difference between the conventional output-side interdigital electrodes that do not have a floating electrode. A potential difference of the same magnitude is generated, and a potential difference equal to the sum of the potential differences appears between the signal electrode and the ground electrode, and is taken out from the output terminal 5 as an output signal.

Therefore, -C1 According to this embodiment, it is possible to apply a larger power to the input terminal than in the conventional case without causing migration of the electrode metal.

According to an actual measurement example of a stretchable surface wave device in the 835 MHz band,
In the conventional surface acoustic wave device shown in FIG. 2, the electrodes were destroyed by applying current with an output of 2 W, whereas in the surface acoustic wave device of this embodiment shown in FIG. 1, it is possible to apply power with an output of 3 W or more. . Note that FIG. 4 is a block diagram of the FLL constant system used in the above-mentioned measurement, in which the surface acoustic wave device 16 is the measurement target, and the input power of the surface acoustic wave device 16 is determined by the Ap1 constant value of the power meter A and the power Based on the difference between the measured values of meter B, the output power can be determined from the Al11 constant value of power meter C.

FIG. 5 is a schematic plan view showing a second embodiment of the present invention. In FIG. 5, the input side interdigital electrode 20-1.20
-2 and the output side interdigital electrodes 21-1 to 21-3 are each provided with two floating electrodes in series between the signal electrode and the ground electrode, and are different from the conventional one shown in FIG. Three interdigital electrodes are connected electrically in series and acoustically in parallel. Therefore, according to this embodiment, it is possible to apply and extract a larger amount of power than in the case of the first embodiment of the present invention shown in FIG. In FIG. 5, 1 is a piezoelectric substrate, 4 is an input terminal, and 5 is an output terminal.

(Effects of the Invention) As described above in detail, according to the present invention, since the floating electrode is provided between the electrode fingers of the interdigital electrode,
The voltage between the electrode fingers is divided by the floating electrode, the amplitude of an attractive surface wave excited on the piezoelectric substrate is reduced, and migration of the electrode metal is suppressed.

Therefore, it becomes possible to apply power greater than that which can be applied to conventional surface acoustic wave devices.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of the first embodiment of the present invention, FIG. 2 is a schematic plan view of a conventional surface acoustic wave device, and FIG. 3 is an enlarged plan view of the input side interdigital electrode shown in FIG. 1. , FIG. 4 is a block diagram of an output band pj constant system of a surface acoustic wave device, and FIG. 5 is a schematic plan view of a second embodiment of the present invention. 1... Piezoelectric substrate, 2-1.2-2.20-1°20-
2... Input side interdigital electrode, 3-1 to 3-3゜21-
1-21-3... Output side interdigital electrode, 4... Input terminal, 5... Output terminal, 9... Floating electrode, 10... Signal electrode, 11... Earth electrode.

Claims (1)

[Claims] A floating electrode having electrode fingers at both ends is provided between the electrode fingers of the interdigital electrodes, and each electrode finger of the floating electrode and each electrode finger of the interdigital electrode constitute a pair of electrode fingers. A surface acoustic wave device characterized by: