JPH03128518A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To prevent discharging from being destroyed by a pyroelectric effect and to improve the characteristic of an element by providing a short circuit pattern to short-circuit the both mutually faced electrodes of an interdigital transducer(IDT) in the manner of a direct current and forming this pattern with specified thickness and length. CONSTITUTION:IDT 2 and 3 are respectively composed of comb-shaped electrodes 2a, 2b, 3a and 3b, which are mutually incoming and outgoing, and further, the above mentioned electrodes 2a and 2b or the electrodes 3a and 3b are short-circuited through a short circuit pattern in the manner of the direct current. This short circuit pattern 7 is sufficiently thinned out and equipped with a fixed guide component. Otherwise, the thickness and length is set so that a power reflection factor due to the synthetic admittance of the both short circuit pattern and the IDT can be made small in comparison with the power reflection factor due to the admittance of the IDT. Thus, not only during a manufacture process but also during real use, discharging can be prevented from being destroyed by the pyroelectric effect and simultaneously, the characteristic of the element can satisfactorily be corrected.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a surface acoustic wave device.

[Conventional technology]

FIG. 12 is a plan view showing the basic configuration of a well-known surface acoustic wave filter among surface acoustic wave elements. In the figure, 1 is a piezoelectric substrate that serves as a propagation medium for surface acoustic waves, and 2 and 3 are interdigital transducers (hereinafter referred to as "interdigital transducers") on the input and output sides that convert electrical signals into surface acoustic waves or convert surface acoustic waves into electrical signals, respectively. rI
DTj). Input and output IDT
23 are comb-tooth-shaped electrodes 2a and 2b and comb-tooth-shaped electrodes 3a and 3b, in which "comb-tooth-shaped" portions are inserted into each other, respectively.
, and are not electrically connected to each other.

For this reason, in conventional surface acoustic wave devices, if the piezoelectric material of the substrate has pyroelectric properties, the pyroelectric effect causes "comb-like" parts to get into each other when subjected to sudden temperature changes. Comb-shaped electrodes 2a and 2b or comb-shaped electrode 3a
Charges of opposite signs are induced in and 3b. As a result, a high voltage is generated between the comb-shaped electrodes 2a and 2b or between 3a and 3b, and when the voltage reaches the insulation limit or higher, a discharge occurs and the comb-shaped electrode is destroyed. Sometimes.

This phenomenon often occurs at various times, such as during the manufacturing process, during environmental testing, or when it is actually incorporated into a circuit and used, and in some cases, it occurs at a fairly high rate, making it a major problem. was.

As a conventional example that improved this point, for example,
The structure of the surface acoustic wave device shown in Publication No. 7890 is the first
Shown in Figure 3.

The basic configuration of the surface acoustic wave device shown in FIG. 13 is the same as that shown in FIG. 12, with a piezoelectric substrate 1. Input and output IDT
2.3, the input side and output side IDT
2 and 3 are a comb-like electrode 2a2b and a comb-like electrode 3a, 3b, respectively, in which comb-like parts are inserted into each other.
It consists of Furthermore, in the surface acoustic wave device shown in FIG. 13, electrical connections are made between the puff cage base 4 that fixes the piezoelectric substrate 1 and each of the comb-like electrodes 2a, 2b, 3a, and 3b via the resistive paste 5. There is a short circuit.

In the surface acoustic wave device shown in FIG. 13, even if a pyroelectric effect occurs due to a rapid temperature change, the charges generated in each comb-shaped electrode are discharged through the resistive paste 5 and the package base 4.

However, it is difficult to form the resistive paste 5 into a thin shape with good reproducibility, and it is impossible to stably secure an appropriate electrical induction component for the frequency band used. For this reason, if the comb-shaped electrodes 2a and 2b or 3a and 3b, in which the comb-shaped portions are inserted into each other, are both short-circuited to the package base 4, the insertion loss of the element increases significantly, making it useless. Furthermore, at the stage of the manufacturing process on the wafer before the resistor paste 5 is applied, it is vulnerable to discharge destruction due to the pyroelectric effect, like conventional elements.

Next, as another conventional example, a surface acoustic wave element disclosed in Japanese Patent Application Laid-Open No. 59-8420 is shown in FIG. this is,
This shows the state before three surface acoustic wave device chips are cut, and the chips are cut into three identical chips by cutting along the cutting line 6 shown by the dotted line. The basic configuration of each chip is the same as the previous example, with a piezoelectric substrate l
, an input side and an output side IDT 2.3, and comb-like electrodes 2a, 2b and 3a, 3b that go in and out of each other. Furthermore, in this element, the input side and output side IDT
are the input end or output side ID of the adjacent chip, respectively.
It is electrically short-circuited through T and short-circuit pattern 7,
Furthermore, the comb-shaped electrodes 2a and 2b and 3a and 3b which go in and out of each other are patterned so that they are short.

However, in this element, when the element is cut into a chip shape, the short circuit pattern is cut off, and the comb-like electrodes are arranged so as to be electrically isolated. For this reason,
In the case of this device, it is effective to prevent discharge damage due to the pyroelectric effect during the manufacturing process of the wafer shape before cutting into chips, but during assembly after cutting into chips and subsequent environmental tests, No measures are taken against the pyroelectric effect at each stage, such as during actual use.

[Problem to be solved by the invention]

As mentioned above, in conventional surface acoustic wave elements,
There is nothing that can prevent discharge damage caused by the pyroelectric effect during the manufacturing process and in all conditions after the device is completed.
Moreover, there has been no method that can prevent discharge destruction due to the pyroelectric effect while maintaining good characteristics of the device.

The present invention has been made in view of these points, and its purpose is to prevent discharge destruction due to the pyroelectric effect during the entire process from the manufacturing process to assembly and after completion of the device. An object of the present invention is to stably and easily obtain a surface acoustic wave device whose characteristics can be corrected to good ones.

[Means to solve the problem]

In order to achieve such an objective, the present invention includes a short circuit pattern that directly shorts both opposing electrodes of an interdigital transducer, and the short circuit pattern is set to a frequency band that the short circuit pattern exhibits for the frequency band used. The power reflection factor due to the composite admittance of the admittance and the admittance that the interdigital transducer exhibits for the operating frequency band when it does not have a short circuit pattern is the power reflection factor that the interdigital transducer exhibits for the operating frequency band when it does not include the short circuit pattern. The pattern is designed to have a thickness and length that are smaller than the power reflectance due to admittance.

Further, the interdigital transducer is provided with a short-circuit pattern that short-circuits both opposing electrodes in a DC manner, and this short-circuit pattern is made to be a thin pattern that exhibits inductivity in the frequency band used.

Further, a short-circuit pattern is provided that short-circuits both opposing electrodes of the interdigital transducer, and this short-circuit pattern is arranged at a constant angle with respect to the comb-like electrodes of the interdigital transducer.

[Effect]

In the surface acoustic wave device according to the present invention, discharge due to the pyroelectric effect can be prevented not only during the manufacturing process but also during use, and the characteristics of the device can be favorably corrected.

〔Example〕

FIG. 1 is a plan view showing one embodiment of a surface acoustic wave device according to the present invention. In the figure, l is a piezoelectric substrate, 2.
3 are input and output side IDTs, and the IDTs 2.3 each have comb-shaped electrodes 2a, 2 that go in and out of each other.
b, 3a, and 3b. Further, the comb-shaped electrodes 2a and 2b or 3a and 3b that go in and out of each other are short-circuited via a short-circuit pattern 7. Here, by making this short circuit pattern 7 sufficiently thin,
It is possible to have a constant induced component for the frequency band used. In this case, due to the above-mentioned inductive component, it will have a predetermined impedance for the frequency used,
There is no possibility that the electrodes (2a and 2b or 3a and 3b) of the IDT are short-circuited at the frequency used. In the case where the inductive component is not considered for the short circuit pattern, if the short circuit pattern 7 is connected to both poles of the interdigitated electrodes that go in and out of each other, it will also be short-circuited at the operating frequency, so that will not be able to connect. On the other hand, in the case of this example, even when actually used, although it is short-circuited in terms of DC, it is not short-circuited at the operating frequency, so the characteristics of the element are not impaired, and the characteristics of the element are not impaired. Since it is short-circuited, it also serves to prevent discharge damage caused by the pyroelectric effect. Alternatively, this short circuit pattern 7 can be used as an I
The thickness and length can be set such that the power reflection rate due to the combined admittance of both the short circuit pattern and the IDT is smaller than the power reflection rate due to the attance of the DT. In this case, the short-circuit pattern 7 serves as a matching circuit, so it is possible to improve device characteristics such as reducing insertion loss and reducing the voltage standing wave ratio of input/output terminals for the frequency band used. .

Therefore, in this example, since the DC short circuit is performed not only during the manufacturing process but also during actual use, it is possible to prevent discharge damage due to the pyroelectric effect, and at the same time, to satisfactorily correct the characteristics of the element. be able to.

In addition, this short circuit pattern 7 can be manufactured simultaneously with other patterns such as comb-like electrodes by the same manufacturing method and the same process, so that it can be easily manufactured without increasing the conventional manufacturing process.

Furthermore, since the short-circuit pattern 7 is formed using photolithography, it is more stable and can be formed with good reproducibility compared to methods such as applying resistive paste, so that element characteristics can be stably corrected.

FIG. 2 is a plan view showing a second embodiment of the invention.

In the figure, the necessary length is ensured by making the short circuit pattern 7 meander.

In addition, in the embodiments shown in FIGS. 1 and 2, the input side EDT
and output side IDT 75 (one case is shown, but the third
The figure is a plan view showing a third embodiment in which there is one IDT 2 on the input side and two IDTs 3 on the output side.

Furthermore, FIG. 4 is a plan view showing a fourth embodiment of the present invention, which is a surface acoustic wave element having a two-terminal resonator structure and equipped with a grating reflector 8.

Furthermore, FIG. 5 is a plan view showing a fifth embodiment of the present invention, and similarly to FIG. show.

1 and 2 for the embodiments shown in FIGS. 3 to 5.
The same effect as the embodiment shown in the figure is achieved.

FIG. 6 is a plan view showing a sixth embodiment of the surface acoustic wave device according to the present invention. In the figure, 1 is a piezoelectric substrate;
2 and 3 are input and output side IDTs, rDT
2 and 3 are comb-shaped electrodes 2 that penetrate into each other.
Consists of a, 2b and 3a3b. moreover,
Both opposing electrodes of each IDT 2.3 are short-circuited by a short-circuit pattern 9. Here, the short circuit pattern 9 is not arranged parallel to the comb-shaped electrodes 2a, 2b and 3a, 3b, but is arranged obliquely so as to form a certain angle.

As a result, as shown by arrows 10 and 1), the surface acoustic waves propagating from the input side IDT 2, even if reflected by the short circuit pattern 9, propagate in a direction different from that of the output side IDT 3, or Even when the wavefront of the surface acoustic wave reaches the IDT 3, the wavefront of the surface acoustic wave reaches the comb-shaped electrodes 3a and 3b of the output side IDT 3.
Since it is not parallel to the output side IDT 3, it is not converted into an electrical signal at the output side IDT 3.

Therefore, in this embodiment, since no unnecessary signal propagates by reflecting off the short-circuit pattern, it is possible to obtain an element without deterioration of characteristics due to in-band ripples, increases in time axis spurious, etc.

FIG. 7 is a plan view showing a seventh embodiment of the present invention,
The shape of the short circuit pattern 9 is slightly different from the embodiment shown in FIG.

FIG. 8 is a plan view showing an eighth embodiment of the present invention, in which the short circuit pattern 9 is meandered to ensure the necessary length.

Further, FIG. 9 is a plan view showing a ninth embodiment of the present invention, and shows an embodiment in which there is one IDT 2 on the input side and two IDTs 3 on the output side.

Furthermore, FIG. 10 is a plan view showing a tenth embodiment of the present invention, and shows an embodiment in the case of a surface acoustic wave element having a two-terminal resonator structure equipped with a grating reflector 8.

Further, Fig. 1) is a plan view showing the embodiment of 1) of the present invention, and similarly to Fig. 10, it is a surface acoustic wave element with a four-terminal resonator structure equipped with a grating reflector 8. An example is shown.

These 7th to 1st) embodiments also have the same effects as the 6th embodiment shown in FIG.

〔Effect of the invention〕

As explained above, the present invention provides a short-circuit pattern between the opposite poles of the comb-shaped electrodes, thereby making the short-circuit pattern sufficiently thin so that it exhibits inductive properties in the frequency band used. By doing so, it is possible to prevent short circuits between the two poles of the comb-shaped electrode at the operating frequency, and to prevent discharge breakdown due to the pyroelectric effect, not only during the manufacturing process but also during actual use. This has the effect of making it possible to easily and stably obtain a surface acoustic wave device with good reproducibility without impairing the characteristics of the device.

Furthermore, by appropriately setting the thickness and length of the short-circuit pattern, it is possible to reduce the power reflectance, and at the same time, it is possible to improve the characteristics of the device.

Furthermore, by arranging the short-circuit pattern diagonally at a certain angle, instead of arranging it parallel to the comb-shaped electrode,
Since it is possible to eliminate unnecessary signals caused by surface acoustic waves reflecting and propagating in the short-circuit pattern, there is an effect that a surface acoustic wave element with good characteristics can be obtained.

[Brief explanation of the drawing]

Figures 1 to 1) show the first diagram of the surface acoustic wave device according to the present invention.
12 to 14 are plan views showing conventional surface acoustic wave elements. l...Piezoelectric substrate, 2...Input terminal IDT, 2a,
'1b, 3a, 3b... comb-shaped electrode, 3... output side IDT, 7... short circuit pattern.

Claims (3)

[Claims] (1) A piezoelectric substrate that serves as a propagation medium for surface acoustic waves, and an interdigital transducer that is provided on the surface of this piezoelectric substrate and converts electrical signals into surface acoustic waves or surface acoustic waves into electrical signals. The surface acoustic wave element includes a short-circuit pattern that short-circuits both opposing electrodes of the interdigital transducer in a direct current manner, and the short-circuit pattern has an admittance that the short-circuit pattern exhibits for a frequency band used, and the short-circuit pattern. The power reflectance due to the combined admittance with the admittance that the interdigital transducer exhibits for the frequency band in use when it is not equipped with the short circuit pattern is the power due to the admittance that the interdigital transducer exhibits for the frequency band in use when it does not include the short circuit pattern. A surface acoustic wave element characterized by a pattern having a thickness and length such that the reflectance is small compared to the reflectance. (2) A piezoelectric substrate that serves as a propagation medium for surface acoustic waves, and an interdigital transducer that is provided on the surface of this piezoelectric substrate and converts electrical signals into surface acoustic waves or surface acoustic waves into electrical signals. The surface acoustic wave element is provided with a short circuit pattern that DC shorts both opposing electrodes of the interdigital transducer, and the short circuit pattern is a thin pattern that exhibits inductive properties in the frequency band used. Characteristic surface acoustic wave device. (3) It has a piezoelectric substrate that serves as a propagation medium for surface acoustic waves, and comb-like electrodes that are provided on the surface of this piezoelectric substrate and that penetrate into each other. A surface acoustic wave element comprising an interdigital transducer that converts the interdigital transducer into A surface acoustic wave element characterized in that it is arranged at a constant angle with respect to the surface acoustic wave element.