JP2000196408A - Surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode structure for a small sized surface acoustic wave element where defect of an interdigital transducer is suppressed due to a discharge caused by a pyroelectric effect in the manufacture process. SOLUTION: In the small sized surface acoustic wave element where interdigital transducers 111, 121, 131 are formed on a major side of a wafer made of a piezoelectric crystal, comb-line electrodes 141, 142 are combined so that electrode fingers of the comb-line electrode 142 are placed interdigitally between the electrode fingers of the comb-line electrode 141, and the element is provided with a discharge electrode 140 where the comb-line electrode 141 is electrically connected to the interdigital transducers 111, 121, 131 and the comb-line electrode 142 is connected to nowhere. Thus, even in the case that electrostatic charges are produced in the manufacture process and the surface of the wafer of the small sized surface acoustic wave element not connected to an external circuit is charged, the discharge is caused in the discharge electrode 140. Thus, a damage of the interdigital transducers 111, 121, 131 due to the discharge can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device, and more particularly, to an electrode structure of a surface acoustic wave device that suppresses discharge in an interdigital transducer.

[0002]

2. Description of the Related Art A surface acoustic wave device is an interdigital transducer (hereinafter referred to as I) formed of a metal film such as aluminum on a wafer surface.
It is called DT. )) And an element utilizing the propagation characteristics of a surface acoustic wave generated by applying a high frequency thereto. I
Various characteristics can be provided depending on the shape of the DT, and it is applied to various kinds of electronics such as a real-time correlator such as a pulse expander / compressor and a matched filter, a fast Fourier transformer, a spectrum analyzer, a radar, and a spread spectrum communication device. ing.

[0003] The wafer material of the surface acoustic wave device is LiTa.
A piezoelectric crystal having a large electromechanical coupling coefficient such as O3 or LiNbO3 is often used. In these materials, charge is induced on the surface by a change in temperature (this is called a pyroelectric effect). Therefore, when a temperature change due to heating, cooling, or the like occurs during the manufacturing process, electric charges are accumulated in the IDT on the wafer due to the pyroelectric effect, and a discharge occurs, which may damage the IDT. Damage to the IDT is more likely to occur as the width of the electrode finger becomes narrower, and a large degree of damage leads to poor characteristics of the element and poor insulation.

[0004] As a method of suppressing damage to the IDT due to discharge, a method of providing a discharge gap between a shield electrode and an input / output IDT is disclosed in Japanese Patent Application Laid-Open No. 60-240207.

As another conventional example, Japanese Patent Laid-Open No. 7-46077 discloses a method in which a dummy electrode is arranged to make the potential difference between IDTs caused by the pyroelectric effect substantially zero, thereby suppressing discharge. No. 6,086,045.

[0006]

However, the method of providing the discharge gap affects the electrical characteristics (capacitance, inductance, etc.) of the element. For this reason,
For example, when used as a resonator, the Q value (an amount indicating the sharpness of resonance) may be reduced.

The method of arranging dummy electrodes to make the potential difference between IDTs caused by the pyroelectric effect substantially zero is specific to a specific IDT pattern. Therefore, when the shape of the IDT is changed, the arrangement and shape of the dummy electrode must be reconsidered from the beginning.

The present invention relates to an electrode structure for suppressing damage to an IDT caused by a discharge caused by a pyroelectric effect in a manufacturing process, and can be used for an IDT having an arbitrary shape.
It is another object of the present invention to provide an electrode structure of a surface acoustic wave device that does not affect the characteristics of the surface acoustic wave device.

[0009]

A surface acoustic wave device according to the present invention is a surface acoustic wave device in which at least one IDT is formed on a main surface of a wafer made of a piezoelectric crystal. The electrode fingers of the second comb-shaped electrode are combined so that the electrode fingers of the second comb-shaped electrode enter between the electrode fingers of the electrode, the first comb-shaped electrode is electrically connected to the IDT, and the second comb-shaped electrode is electrically connected to anywhere. And at least one discharge electrode.

According to the present invention, even if an electrostatic charge is generated in the manufacturing process and the surface of the surface acoustic wave element not connected to the circuit is charged, the discharge occurs at the discharge electrode. Therefore, it is possible to suppress the IDT from being damaged by the discharge, and the yield is improved.

In addition, the discharge electrodes are made of IDTs of various shapes.
And does not affect the characteristics of the surface acoustic wave element.

[0012]

FIG. 1 is a plan view showing a first embodiment of a surface acoustic wave device according to the present invention.

On a wafer 101 made of a piezoelectric crystal, three terminals IN1, OUT1 and G1, three surface acoustic wave resonators 110, 120 and 130, and a discharge electrode 140
And the wiring 150 are formed. Surface acoustic wave resonator 1
10 is connected to the terminal IN1, and the surface acoustic wave resonator 120
Is connected to the terminal G1, and the surface acoustic wave resonator 130 is connected to the terminal OUT1. The surface acoustic wave resonators 110, 120, and 130 and the discharge electrode 140 are connected to each other via a wiring 150. The three surface acoustic wave resonators 110, 120, and 130 are arranged in parallel with each other so as not to affect the propagation of the surface acoustic wave generated by each surface acoustic wave resonator. Discharge electrode 14
Numeral 0 is disposed at a position distant from the propagation path of the surface acoustic wave generated by each surface acoustic wave resonator.

The surface acoustic wave resonator 110 includes a comb-shaped electrode 11
The grating reflectors 112 and 113 are arranged on both sides of the IDT 111 having a structure in which the electrode fingers of the comb-shaped electrode 115 are inserted between the four electrode fingers. The comb electrode 114 is connected to the terminal IN1, and the comb electrode 115 is connected to the wiring 150.

The surface acoustic wave resonator 120 includes the comb-shaped electrode 12
The grating reflectors 122 and 123 are arranged on both sides of the IDT 121 having a structure in which the electrode fingers of the comb-shaped electrode 125 are inserted between the four electrode fingers. The comb electrode 124 is connected to the wiring 150, and the comb electrode 125 is connected to the terminal G1.

The surface acoustic wave resonator 130 includes the comb-shaped electrode 13
The grating reflectors 132 and 133 are arranged on both sides of the IDT 131 having a structure in which the electrode fingers of the comb-shaped electrode 135 are inserted between the four electrode fingers. The comb electrode 134 is connected to the wiring 150, and the comb electrode 135 is connected to the terminal OUT1.

The discharge electrode 140 is composed of comb electrodes 141 and 142 formed of a metal film of Al or the like, and is combined so that the electrode fingers of the comb electrode 142 are inserted between the electrode fingers of the comb electrode 141. Having. Comb electrodes 141,
The distance between the electrode fingers of 142 is the IDT of each surface acoustic wave resonator.
Is smaller than the distance between the electrode fingers of the comb-shaped electrode. Therefore, this 2
The inter-electrode distance between two comb-shaped electrodes depends on the I
It is smaller than the distance between the electrodes of the DT. Comb electrode 14
1 is connected to the wiring 150. The comb-shaped electrode 142 is not connected anywhere.

The comb electrodes 114, 115, 124,
125, 134, 135, terminals IN1, OUT1, G
1 and the wiring 150 are formed of a metal film such as Al. Also, the grating reflectors 112, 113, 12
Reference numerals 2, 123, 132, and 133 are formed by dielectric ridges, etching by ion milling or the like, arrangement of metal strips of Al or the like, and the like.

By providing the discharge electrodes as described above, even if static charges are generated in the manufacturing process, more charges are accumulated in the discharge electrodes than in the IDT, and the distance between the discharge electrodes is reduced. Therefore, dielectric breakdown is likely to occur. For this reason, in most cases, discharge occurs at the discharge electrode. As a result, it is possible to prevent the IDT from being damaged by electric discharge.

Further, since the discharge electrode is provided at a position distant from the surface acoustic wave propagation path, it does not affect the propagation characteristics of the surface acoustic wave. Also, since it is not electrically connected, the characteristics of the surface acoustic wave element are not affected.

FIG. 2 is a plan view showing a second embodiment of the surface acoustic wave device according to the present invention.

On a wafer 201 made of a piezoelectric crystal,
Four terminals IN2, OUT2, G20, G21, two IDTs 210, 220, and two discharge electrodes 230, 24
0 and wirings 250 and 260 are formed. IDT2
10 is connected to terminal G21, and IDT220 is connected to terminal OU.
Connected to T2. The IDT 210 and the discharge electrode 230 are connected to the terminal IN2 via the wiring 250, and the IDT 220 and the discharge electrode 240 are connected to the terminal G20 via the wiring 260. IDT210,2
Reference numerals 20 are arranged such that the propagation paths of the surface acoustic waves generated in the respective IDTs overlap each other, and interact with each other via the surface acoustic waves. The discharge electrodes 230 and 240 are arranged at locations away from the propagation path of the surface acoustic wave generated in each IDT.

The IDT 210 includes comb electrodes 211 and 212
And the interdigital electrode 21 between the electrode fingers of the interdigital electrode 211.
It has a structure combined so that two electrode fingers can enter.
The comb-shaped electrode 211 is connected to the terminal G21,
2 is connected to the wiring 250.

The IDT 220 has comb electrodes 221 and 222
And a comb-shaped electrode 22 between electrode fingers of the comb-shaped electrode 221.
It has a structure combined so that two electrode fingers can enter.
The comb-shaped electrode 221 is connected to the terminal OUT2,
Reference numeral 22 is connected to the wiring 260.

The discharge electrode 230 comprises comb electrodes 231 and 232 formed of a metal film such as Al.
It has a structure in which the electrode fingers of the comb-shaped electrode 232 are inserted between the 31 electrode fingers. Comb electrodes 231 and 23
The interval between the two electrode fingers is smaller than the interval between the electrode fingers of the comb-shaped electrodes of each IDT. Therefore, the inter-electrode distance between the two comb-shaped electrodes is smaller than the inter-electrode distance between the combined comb-shaped electrodes of each IDT. The comb electrode 231 is connected to the wiring 250. The comb electrode 232 is not connected anywhere.

The discharge electrode 240 comprises comb electrodes 241 and 242 formed of a metal film such as Al.
It has a structure in which the electrode fingers of the comb-shaped electrode 242 are inserted between the 41 electrode fingers. Comb electrodes 241, 24
The interval between the two electrode fingers is smaller than the interval between the electrode fingers of the comb-shaped electrodes of each IDT. Therefore, the inter-electrode distance between the two comb-shaped electrodes is smaller than the inter-electrode distance between the combined comb-shaped electrodes of each IDT. The comb electrode 241 is connected to the wiring 260. The comb electrode 242 is not connected anywhere.

The comb electrodes 211, 212, 221,
222, the terminals IN2, OUT2, G20, G21, and the wirings 250, 260 are formed of a metal film such as Al.

By providing the discharge electrodes 230 and 240 in this manner, even if an electrostatic charge is generated in the manufacturing process, more charge is accumulated in the discharge electrode than in the IDT.
Since the distance between the discharge electrodes is narrow, dielectric breakdown is likely to occur. For this reason, in most cases,
Discharge occurs at the discharge electrode. As a result, it is possible to prevent the IDT from being damaged by electric discharge.

Further, since the discharge electrodes 230 and 240 are provided at positions away from the surface acoustic wave propagation path, they do not affect the surface acoustic wave propagation characteristics.
Since the elements 2 and 242 are not electrically connected when the element is incorporated in the case, the characteristics of the surface acoustic wave element are not affected.

[0030]

As described above, according to the present invention, even if an electrostatic charge is generated in the manufacturing process and the surface of the surface of the surface acoustic wave device not connected to the circuit is charged, the IDT does not cause any problem. Also, a large amount of charge is accumulated on the discharge electrode. Since the distance between the electrodes of the discharge electrode is smaller than the distance between the electrodes of the IDT, dielectric breakdown is likely to occur. Thus, in most cases, the discharge occurs at the discharge electrode. Therefore, it is possible to suppress the IDT from being damaged by the discharge, and the yield is improved.

The discharge electrode is provided at a position distant from the propagation path of the surface acoustic wave generated in the IDT, and has one of two comb-shaped electrodes constituting the discharge electrode.
When the element is incorporated in the case, it is not connected anywhere, so that the characteristics of the surface acoustic wave element are not affected.

Further, the discharge electrode can be used regardless of the shape of the IDT, regardless of the shape of the IDT.

[Brief description of the drawings]

FIG. 1 is a plan view showing a first embodiment of a surface acoustic wave device according to the present invention.

FIG. 2 is a plan view showing a second embodiment of the surface acoustic wave device according to the present invention.

[Explanation of symbols]

 Reference Signs List 101 wafer 110 surface acoustic wave resonator 111 IDT 112 grating reflector 113 grating reflector 114 comb electrode 115 comb electrode 120 surface acoustic wave resonator 121 IDT 122 grating reflector 123 grating reflector 124 comb electrode 125 comb electrode 130 surface acoustic wave Resonator 131 IDT 132 Grating reflector 133 Grating reflector 134 Comb electrode 135 Comb electrode 140 Discharge electrode 141 Comb electrode 142 Comb electrode 150 Wiring IN1 terminal OUT1 terminal G1 terminal 201 Wafer 210 IDT 211 Comb electrode 212 Comb electrode 220 IDT22 Electrode 222 Comb electrode 230 Discharge electrode 231 Comb electrode 232 Comb electrode 240 Discharge electrode 241 Comb electrode 242 Form electrodes 250 wire 260 wire IN2 terminal OUT2 terminal G20 pin G21 pin

Claims (3)

[Claims] 1. A surface acoustic wave device having at least one interdigital transducer formed on a main surface of a wafer made of a piezoelectric crystal, wherein a second comb electrode is disposed between electrode fingers of the first comb electrode. Combined such that electrode fingers enter, the first comb electrode is electrically connected to the interdigital transducer, and the second comb electrode is not electrically connected anywhere,
A surface acoustic wave device comprising at least one discharge electrode. 2. The surface acoustic wave according to claim 1, wherein a distance between the first comb electrode and the second comb electrode is smaller than a distance between the electrodes of the interdigital transducer. element. 3. The surface acoustic wave device according to claim 1, wherein the discharge electrode is provided at a position away from a propagation path of a surface acoustic wave generated by the interdigital transducer.