JPH07240657A - Unidirectional surface acoustic wave transformer - Google Patents

Abstract

PURPOSE:To unnecessitate the preparation of a superfine electrode even when the interdigital transformer (IDT) of a high frequency area by a basic wave operation is prepared by making the constitutions of an electrode pair differ from the constitutions of other electrode pair. CONSTITUTION:A disposal is performed so as to differ the conductive film of electrode fingers 2a and 3a constituting the nth electrode pair or either one of the electrode fingers from the kinds or film thickness of the conductive film of electrode fingers 2b and 3b constituting the mth electrode pair or either one of the electrode fingers. A dispolsal is performed so as to differ the width of the electrode fingers 2a and 3a constituting nth electrode pair or either one of the electrode fingers or the center distance of the electrode fingers 2b and 3b from the width of the electrode fingers 2b and 3b constituting the mth electrode pair or either one of the electrode pair or the center distance of the electrode fingers 2b and 3b. If this one-directional IDT is used, a surface acoustic wave device with low insertion loss can be obtained without using an external phase converter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a unidirectional surface acoustic wave converter.

[0002]

2. Description of the Related Art Conventionally, a transversal surface acoustic wave (hereinafter referred to as SAW) filter has been widely used as a wide band low loss filter in a high frequency region of VHF to UHF band. However, transversal type S
The AW filter is an interdigital converter (hereinafter,
There is a loss of 6 dB or more due to the bidirectional loss (denoted as IDT), and it is necessary to use the unidirectional IDT in order to reduce the loss.

Therefore, various types of unidirectional IDTs have been conventionally proposed, and improved unidirectional IDTs have also been proposed. For example, (a) a three-phase unidirectional IDT is known in which signals having a phase difference of zero degrees, 120 degrees, and 240 degrees are applied to three types of IDT electrode fingers, respectively.
No. 25510 discloses an improved unidirectional IDT. (B) A group-type unidirectional IDT in which a meander line is provided between the fingers of a general IDT electrode and is grounded has been proposed, and an improved unidirectional IDT is disclosed in Japanese Patent Laid-Open No. 64-27306. Has been done. (C) I
Various internal reflection type unidirectional IDTs in which an open type or a short type floating electrode is arranged between the positive and negative electrode fingers of the DT have been proposed, and are disclosed in JP-A-3-119815 and JP-A-3-13.
An improved unidirectional IDT is proposed in 3209. A manufacturing method is disclosed in Japanese Patent Laid-Open No. 3-16309.

[0004]

However, (a)
The multi-phase unidirectional IDT of (1) has the drawbacks that it is extremely difficult to manufacture and requires an external phase shifter. Further, the group type unidirectional IDT of (b) also requires a 90-degree phase shifter (specifically, a coil), the total length of the meander line becomes long, and the insertion loss of the filter due to ohmic loss is large. There was a drawback that Further, the internal reflection type unidirectional IDT of (c) does not require a phase shifter, but has a large number of electrode fingers in a unit section represented by the fundamental operating wavelength, and the ID in a high frequency region due to the fundamental wave operation.
In the case of producing T, there is a drawback that it is necessary to produce an ultrafine electrode, and neither was satisfactory.

Therefore, the present invention does not require an external phase shifter in the unidirectional surface acoustic wave converter, minimizes the number of electrode fingers in a unit section represented by the fundamental operating wavelength, and realizes the fundamental wave operation. Another object of the present invention is to provide a unidirectional IDT structure that does not require the production of ultrafine electrodes even when producing an IDT in the high frequency region.

[0006]

DISCLOSURE OF THE INVENTION The present invention is a device for receiving an acoustic surface wave that has been excited or propagated by arranging an interdigital transducer on a piezoelectric substrate or a substrate having a piezoelectric thin film. The unidirectional surface acoustic wave converter is characterized in that the configuration of the electrode pair is different from the configurations of the other electrode pairs. More specifically, a conductive thin film of two electrode fingers forming one electrode pair or one of the electrode fingers, and two electrode fingers forming another electrode pair or one of the electrode fingers A unidirectional surface acoustic wave converter characterized in that the type or thickness of the conductive thin film is different, and further, the two electrode fingers forming a certain electrode pair or the width of either one of the electrode fingers or Unidirectionality characterized in that the distance between the centers of two electrode fingers is different from the width of the two electrode fingers forming another electrode pair or the width of one of the electrode fingers or the distance between the centers of the two electrode fingers. It is a surface acoustic wave converter.

In carrying out the present invention, the piezoelectric substrate or the substrate having the piezoelectric thin film is not limited, but Li ₂ B
₄ O ₇ single crystal substrate, LiNbO ₃ single crystal substrate, LiTa
O ₃ single crystal substrate, crystal substrate, Bi ₁₂ GeO ₂₀ single crystal substrate, bulk piezoelectric substrate such as GaAs substrate or sapphire substrate having AlN thin film, sapphire substrate having LiNbO ₃ thin film, sapphire substrate having LiTaO ₃ thin film,
Sapphire substrate with Li ₂ B ₄ O ₇ thin film, PbTiO
Sapphire substrate with ₃ thin films, sapphire substrate with ZnO thin film, sapphire substrate with CdS thin film, Si substrate with AlN thin film, Si substrate with LiNbO ₃ thin film,
Si substrate with LiTaO ₃ thin film, Si substrate with Li ₂ B ₄ O ₇ thin film, Si substrate with PbTiO ₃ thin film, Z
Si substrate with nO thin film, Si substrate with CdS thin film,
GaAs substrate with AlN thin film, GaAs substrate with LiNbO ₃ thin film, GaAs substrate with LiTaO ₃ thin film, GaAs substrate with Li ₂ B ₄ O ₇ thin film, PbTi
GaAs substrate with O ₃ thin film, GaA with ZnO thin film
s substrate, GaAs substrate with CdS thin film, MgO substrate with AlN thin film, MgO substrate with LiNbO ₃ thin film,
MgO substrate with LiTaO ₃ thin film, MgO substrate with Li ₂ B ₄ O ₇ thin film, MgO substrate with PbTiO ₃ thin film, MgO substrate with ZnO thin film, M with CdS thin film
gO substrate, glass substrate with ZnO thin film, quartz substrate with ZnO thin film, SrTiO ₃ substrate with AlN thin film, L
SrTiO ₃ substrate with iNbO ₃ thin film, LiTaO ₃
SrTiO ₃ substrate having a thin film, SrTiO ₃ substrate with Li ₂ B ₄ O ₇ thin, SrTi with PbTiO ₃ film
O ₃ substrate, SrTiO ₃ substrate with ZnO thin film, CdS
A SrTiO ₃ substrate having a thin film or the like is used.

The conductive film forming the IDT electrode is not limited, but is a pure metal thin film such as aluminum, copper, titanium, platinum, or gold, or Si, Cu, W, P on aluminum or the like.
A metal thin film made of a two-element metal containing d, Ti, Sn or the like, or a non-metal conductive film such as indium titanium oxide is used. Regarding these conductive films, the type and film thickness of the conductive film forming a certain electrode pair may be different from the conductive film and film thickness forming the other electrode pair. For example, the electrode fingers (2a, 2a,
3a) may be made of a conductive film containing aluminum as a main component, and the conductive film of the electrode fingers (2b, 3b) forming another electrode pair may be made of gold or platinum. It may be configured that the film thickness of the electrode is not equal to the film thickness of the conductive film of the other electrode finger.

The material of the conductive film forming the electrode fingers may be the same, and the film thickness of the conductive film of one electrode finger may be different from the film thickness of the conductive film of another electrode finger. It may be configured such that the width of the electrode finger and the distance between the centers of the electrode fingers of a certain electrode pair and another electrode pair are different. That is, it is important that the configuration of one electrode pair is different from the configuration of another electrode pair. The electrode pairs having different configurations may be adjacent to each other or may be consecutive, but at least one pair is present in one device.

[0010]

EXAMPLES Next, the present invention will be described in more detail by way of examples. FIG. 1 shows an embodiment of the present invention, in which a device for receiving a surface acoustic wave which excites or propagates a surface acoustic wave by disposing an interdigital transducer on a substrate 1 having a piezoelectric substrate or a piezoelectric thin film. , An electrode pair, that is, the configuration of the n-th electrode pair including the electrode finger 2a and the electrode finger 3a, and another electrode pair, that is, the electrode finger 2
The structure of the m-th electrode pair consisting of b and 3b is arranged so as to be different. More specifically, the electrode finger 2a and the electrode finger 3a forming the nth electrode pair or the conductive thin film of either one of the electrode fingers and the electrode finger 2b or the electrode finger forming the mth electrode pair. 3b or one of the electrode fingers is arranged so that the type or thickness of the conductive thin film is different. Furthermore, the electrode fingers 2 that form the nth electrode pair
a and the width of the electrode finger 3a or one of the electrode fingers, or the center distance between the electrode finger 2a and the electrode finger 3a and the electrode finger 2b and / or the electrode finger 3b forming the m-th electrode pair. Electrode finger width or electrode finger 2a and electrode finger 3
It is arranged so that the center-to-center distances of a are different. Where n
Indicates electrode fingers 2a and 3a, 4a and 5a ...
m indicates the electrode fingers 2b and 3b, 4b and 5b ... It is desirable to have two electrode fingers in order to simplify the electrode pair.

In FIG. 2, the film thicknesses of the electrode fingers 4a and 5a are different from the film thicknesses of the electrode fingers 4b, 5b, 4c and 5c. In FIG. 3, the electrode fingers 6a and 7a are made of an aluminum film, and the electrode fingers 6b, 7b, 6c, and 7c are made of a gold film. Are different. In FIG. 4, the type and thickness of the conductive film forming the electrode fingers are the same for all the electrode fingers, but the width 10 of the electrode finger 9a and the electrode finger 8a are the same.
Width 12 and distance 11 between electrode fingers 9a-8a, electrode finger 8
Taking the distance 13 between a-9b as a reference, the width 14 of the electrode finger 9b, the width 16 of the electrode finger 8b, the distance 15 between the electrode fingers 9b-8b, and the distance 17 between the electrode fingers 8b-9d are different. . Further, the width 18 of the electrode finger 9c, the width 20 of the electrode finger 8c, the distance 19 between the electrode fingers 9c-8c, and the distance 21 between the electrode fingers 8c-9e are different.

The width of these electrode fingers and the distance between the electrode fingers are not limited, but can be changed within the range of Table 1,
It can be preferably changed within the range shown in parentheses. It is important that the sum of the width of the electrode fingers and the distance between the electrode fingers in each electrode pair be equal to the wavelength of SAW.
As an example for explaining the effect of the one-way IDT according to the present invention, FIG. 5 shows a frequency transmission characteristic when a filter is configured. An insertion loss of 1.21 dB is obtained, which confirms the effectiveness of the present invention. It is a thing.

[0013]

[Table 1]

[0014]

By using the unidirectional IDT according to the present invention, the external phase shifter is not used, and the ultrafine electrode for producing the IDT in the high frequency region by the fundamental wave operation is not required. A directional IDT can be manufactured, and a surface acoustic wave device with low insertion loss can be obtained.

[Brief description of drawings]

FIG. 1 (a) is a plan view showing an embodiment of a unidirectional IDT according to the present invention, and FIG. 1 (b) is a sectional view.

FIG. 2 (a) is a plan view showing an embodiment of a unidirectional IDT according to the present invention, and FIG. 2 (b) is a sectional view.

FIG. 3 (a) is a plan view showing an embodiment of a unidirectional IDT according to the present invention, and FIG. 3 (b) is a sectional view.

4 (a) is a plan view showing an embodiment of a unidirectional IDT according to the present invention, and FIG. 4 (b) is a sectional view.

FIG. 5 is a frequency transmission characteristic of a SAW filter according to an embodiment of a unidirectional IDT according to the present invention.

[Explanation of symbols]

1 substrate 2, 3 positive / negative IDT electrodes 2a, 2b, 3a, 3b positive / negative IDT electrode fingers 4, 5 positive / negative IDT electrodes 4a, 4b, 5a, 5b positive / negative IDT electrode fingers 6, 7 positive / negative IDT electrodes 6a, 6b, 7a, 7b positive / negative IDT electrode fingers 8, 9 Positive / negative IDT electrodes 8a, 8b, 8c, 9a, 9b, 9c, 9d, 9e
Positive and negative IDT electrode fingers

Claims (3)

[Claims] 1. A device for arranging an interdigital transducer on a piezoelectric substrate or a substrate 1 having a piezoelectric thin film to receive a surface acoustic wave which excites or propagates a surface acoustic wave, and a structure of a certain electrode pair, and others. Unidirectional surface acoustic wave converter characterized in that different electrode pairs have different configurations 2. The two electrode fingers forming a certain electrode pair, or the conductive thin film of one of the electrode fingers, and the two electrode fingers forming another electrode pair according to claim 1. One-way surface acoustic wave converter characterized in that the type or thickness of the conductive thin film of one of the electrode fingers is different. 3. The width of one of the two electrode fingers constituting one electrode pair or the distance between the centers of the two electrode fingers, and the other electrode pair according to claim 1. A unidirectional surface acoustic wave converter characterized in that the width of two electrode fingers or one of the two electrode fingers or the distance between the centers of the two electrode fingers is different.