JPH05121991A - Reflection bank type unidirectional saw device - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a reflective bank type unidirectional SAW device in which electrodes can be easily formed in a high frequency region. [Structure] Three pairs of positive and negative IDT1 using double electrodes
A reflector bank type unidirectional SAW device having a plurality of reflectors 4 _{1 to} 4 ₃ between _{1 to} 3 ₂
It is obtained by removing one 3 ₂ double electrode adjacent to _1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called reflection bank type unidirectional SAW device in which electrodes can be easily formed.

[0002]

2. Description of the Related Art A plurality of reflectors are provided between a pair of IDTs having double electrodes, the distance between the reflectors is set to be similar to that of the IDTs, and the entire reflectors are arranged on either side of the IDTs by λ. SA excited by IDT by shifting / 8
So-called reflection bank type unidirectional SA that gives unidirectionality to W
There is a W device. The unidirectionality of this device is equivalent to that of other unidirectional devices, such as those of three-phase unidirectionality or group type unidirectionality, but with a normal S configuration.
Similar to the AW filter, the electrode can be formed by one-time vapor deposition and photoetching process, and it has a feature that it is simple because no phase shifter is used outside. Furthermore, by using the double electrode as the IDT, the acoustic triple reflection wave (TT) generated when this IDT is a normal single electrode IDT
The in-passband ripple of the filter according to E) can be eliminated. This effect is obtained even in a filter in which two unidirectional IDTs of this type are made to face each other.
The same applies to the type of filter in which the unidirectional IDTs of this type are arranged on both sides of.

However, the positive / negative IDT as described above
In a reflection bank type unidirectional IDT using a double electrode, the distance between the reflector and one of the double electrodes adjacent to the reflector is λ / 16 due to the electrode structure (where λ is a positive / negative electrode exciting S
(AW wavelength), and there is a drawback that manufacturing becomes difficult or impossible when the frequency becomes high.

[0004]

SUMMARY OF THE INVENTION The present invention is difficult to manufacture in the conventional reflection bank type unidirectional SAW device as described above because the gap between the reflector and one of the double electrodes adjacent thereto is narrow. The present invention has been made to solve the drawbacks, and an object thereof is to provide a reflection bank type unidirectional SAW device in which electrodes can be easily formed in a high frequency region.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, one of the double electrodes adjacent to a reflector is removed in the present invention.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on the embodiments shown in the drawings. Prior to the description of the embodiments, in order to help understanding of the present invention, a conventional reflection bank type unidirectional SAW is used.
The electrode configuration of the device will be briefly described. FIG. 2 is a diagram showing a basic electrode configuration of a reflection bank type unidirectional SAW device, which is a so-called normal type IDT array section (three IDTs 1, 2, and 3 are set as one set) and λ / a plurality of reflectors 4 _1, 2 interval 4 _2, ..., 4 _n insert the this reflector 4 _1, 4 _2, ..., 4 _n set as a whole by lambda / 8 to the left or right of the normal type IDT of It was sent to. As a result, it goes without saying that the edge distance between the IDT 3 (which is always the ground electrode) and the reflector 4 ₁ becomes λ / 8. However, when this type of device is used as a filter, ripples occur in the pass band. Therefore, as shown in FIG. 3, the IDTs _{1, 2} and 3 should be double electrodes 1 _{1 to} 3 ₂ to suppress the ripples. Is being done. However, when such an electrode structure is adopted, the edge distance between the reflector 4 ₁ and _one of the double electrodes 3 ₂ which is the ground electrode becomes λ / 16, which makes it impossible to manufacture in the high frequency region. is there.

In order to solve this problem, the reflection bank type SAW device of the present invention eliminates the double electrode 3 ₂ adjacent to the reflector 4 ₁ . Where double electrode 2
_{Since 1} and 2 ₂ are positive electrodes and 1 ₁ and 3 ₁ are negative electrodes, there are negative electrodes 1 ₂ and 3 _{1 on} the left side of the positive electrode 2 ₁ and the right side of the positive electrode 2 ₂ , respectively, so that SAW It can be considered that the excitation efficiency does not decrease. In order to confirm this by an experiment, a filter in which the directions in which the SAWs that excite each of the two devices are emphasized was made to be a prototype, and its characteristics were examined. The results shown in FIG. 4 were obtained. .. This satisfies the specifications of the IF filter for digital car phones, and the validity of the above-mentioned electrode construction method was verified.

[0008]

Since the reflection bank type unidirectional SAW device of the present invention is constructed as described above,
It has characteristics equivalent to those of a conventional general positive / negative IDT having double electrodes, and since the electrodes can be easily formed, it is extremely effective when applied to various filters for communication devices in recent years when the frequency is remarkably high. ..

[0009]

[Brief description of drawings]

FIG. 1 is a plan view showing an electrode configuration of a reflection bank type unidirectional SAW device of the present invention.

FIG. 2 is a plan view showing a basic electrode configuration of a conventional reflection bank type unidirectional SAW device.

FIG. 3 is a plan view showing another electrode configuration of a conventional reflection bank type unidirectional SAW device.

FIG. 4 is a diagram of experimental results showing the characteristics of a filter configured using the reflection bank type unidirectional SAW device of the present invention.

[Explanation of symbols]

1 ₁ 3 ₂ Double electrode was IDT 4 ₁ to 4 ₃ reflector

Claims (1)

[Claims] 1. A plurality of reflectors are provided between a set of double-electrode IDTs, and the distance between the reflectors is the same as that of the IDTs, and the entire reflectors are arranged on either side of the IDTs by λ. SAW excited by IDT by shifting / 8
A reflection bank type unidirectional SAW device, characterized in that one of the double electrodes adjacent to the reflector is removed in the SAW device having unidirectionality.