JPS5830216A - Acoustic wave device - Google Patents

Abstract

PURPOSE:To remarkably suppress an end face reflection signal of an acoustic wave, by shifting a position of a propagation path end part, by >=1 stage by width of lambda/4XN(N=1,3,5-, and lambda denotes the wavelength of the acoustic wave), and also setting the overall length of the propagation path end part to half of the whole. CONSTITUTION:An electric signal is converted to an acoustic wave by the first reedlike electrode 2 or 3, and the surface acoustic wave is converted to the electric signal again by the second bamboo blind-like electrode 3 or 2. A position of a propagation path end part of the acoustic wave is formed by shifting at least 1 stage by width of lambda/4XN (N=1,3,5-, and lambda denotes the wavelength of the acoustic wave), and the overall length of the propagation path end part which has been shifted and formed is set to 1/2 of the whole. When each half of the propagation path end part for reflecting the acoustic wave is shifted by lambda/4X N from each other, reflected waves from the respective end parts negate each phase, no reflection signal appears in the second reedlike electrode, and a satisfactory frequency characteristic of only a main signal can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an elastic wave device, and more particularly, to an elastic wave device that suppresses reflection from the end face of a substrate and has a frequency of *a.

There are two types of elastic wave devices: boundary acoustic wave devices and surface acoustic wave devices.The former has interdigital electrodes 2.5 provided on the piezoelectric substrate 1, as shown in Figure 1 (α) (b) K. j! On top of that, there is a piezoelectric substrate 1 and a thin film having different elastic constants or densities.
[4t-formed. With this structure, almost all of the energy is concentrated on the boundary 1ii5 between the piezoelectric substrate 2 and the thin layer 1[4], generating waves similar to piezoelectric Stoneley waves, which can be transmitted through filters and delay lines. It is applied to various electronic devices such as.

However, in such a boundary acoustic wave device, as shown in FIG.
The signal propagates in both left and right directions as shown by arrows A and B, and a portion of it is received by the output interdigital electrode 3 as a main signal. However, in addition to this, elastic waves A' and B' reflected at the end face of the piezoelectric substrate 1, that is, at the end 6.7 of the boundary surface 5, are also received by the output interdigital electrode 3. This elastic wave A',
The electrical signal generated by the output interdigital electrode 3 based on B' is delayed in phase with respect to the main signal and becomes a good signal, which causes the problem that it appears as a ripple in terms of frequency characteristics.

A phenomenon similar to that described above also occurs in acoustic wave surface devices. As a means for suppressing reflected waves from the end faces of the piezoelectric substrate, a method is generally used in which a surface acoustic wave absorbing material is coated on the surface of the substrate near the end faces of the piezoelectric substrate.

However, in the boundary acoustic wave device, as mentioned above, almost all of the energy is concentrated on the interface 5 between the piezoelectric substrate 1 and the thin film 4, and the energy on the surface of the device is measured. 1? '
! ' Since it is equal to zero, as in the case of surface acoustic wave devices,
Even if an elastic wave absorbing material is applied to the surface of the thin layer 1[4 near the piezoelectric substrate end 6.7, it hardly contributes to suppressing the reflected wave of the elastic wave as the objective. Therefore, in putting the boundary acoustic wave device into practical use, effectively suppressing the reflected acoustic waves from the end face of the substrate becomes a major problem. Furthermore, in surface acoustic wave devices, there have been expectations for the development of means for more effectively suppressing reflected waves.

The present invention was devised in view of the drawbacks of the conventional elastic wave devices, and an object of the present invention is to improve the conventional problems and provide an elastic wave device having good frequency characteristics.

The elastic wave device of the present invention converts an electric signal into an elastic wave.
sl, a second interdigital electrode that converts the elastic wave into an electric signal again, and a propagation path for the elastic wave, and the position of the end of the propagation path is λ74. X# (N
= 1j, 5..., λ is the wavelength of the elastic wave).

The ends of the propagation path that reflect the elastic waves are λ/4 each other.
If they are shifted by xN, the reflected waves from each end will cancel each other in phase, and no reflected signal will appear on the sagging electrode of the output terminal 2, and only the main signal will be in good condition. It becomes possible to obtain frequency characteristics.

The present invention will be described in more detail below with reference to embodiments shown in the accompanying drawings.

FIG. 3 shows an embodiment of the present invention, in which a filter used in the intermediate frequency stage of a television receiver is formed using the boundary acoustic wave device of the present invention. As the piezoelectric substrate 1, lithium onipate with 128° rotation and Y-axis cut was used, and the propagation direction of the boundary acoustic waves was set to be along the X-axis. Interdigital electrode 2.3
The center frequency is 57 MHz, the number of electrode pairs is 15,
A piezoelectric substrate was fabricated by using double electrodes with an electrode width of 8 and weighted electrodes with varying electrode crossing widths and electrode spacing, and photoetching a full Z nicum vapor deposited film of 05 μm for each electrode. 1.

9. As for the thin film 4, a 30 μm film was formed on the p-substrate by silicon dioxide t-CVD method, and half of it was deposited on each of the interface end faces 8.9 as shown in Fig. The interface end faces 8' and 9' were machined so that the end face positions were shifted by λ/4 (λ=64μ).

FIG. 4 is a diagram showing the frequency characteristics of the embodiment shown in FIG. 3. As shown in the figure, the ripple 10 that occurs in the conventional boundary acoustic wave device is eliminated by the ripple 10 according to the present invention! As shown in 111, the reflected signal level is almost suppressed to 135 tLB or less compared to the main signal.

Exactly the same effect can be obtained even if the boundary surface edges 8 and 9f are divided into five or more parts according to the above technical idea, and the positional deviation of each part of 9.9' is made an odd multiple of tλμ. I will open with what I can get.

Furthermore, in the embodiment shown in FIG.
As for the combination, if at least one of the substances has piezoelectricity, the above-mentioned boundary acoustic wave can be excited, and in this case also, the present invention has a similar end face reflection suppressing effect.

Although the above embodiments were related to boundary acoustic wave devices, they can be applied in exactly the same manner (applicable to surface acoustic wave devices that receive and receive surface acoustic waves instead of boundary acoustic waves, and reflected surface acoustic waves can also be applied). It becomes possible to suppress it.

As is clear from the above description, according to the present invention, it is possible to significantly suppress end face reflection signals of elastic waves and provide an elastic wave device having good frequency characteristics.

[Brief explanation of the drawing]

FIG. 1(α) is a plan view showing a conventional boundary acoustic wave device, FIG. 1(A) is a side sectional view showing a conventional boundary acoustic wave device,
##2 Figure 2 is an explanatory diagram showing the state of end face reflection of boundary acoustic waves in a conventional boundary acoustic wave device, Figure 3 is a plan view showing an embodiment of the present invention, Figure 4 is W, Figure 3 is It is a figure which shows the frequency characteristic of the example shown. 1... Piezoelectric substrate 2.3... Interdigital electrode 4
...Thin film 5...Boundary surface 6, 7.8.8
' , 9.9'...Boundary surface edge agent Benbushi Usui
1) Toshiyukidai 1 Saeq (6L) Figure 2 Figure 5 Figure 40 ” 54-56 #6θ bz
”Namimotoba FIHz)

Claims (1)

[Scope of Claims] (1) A first interdigital electrode that converts an electric signal into an elastic wave, a second interdigital electrode that converts the acoustic wave tube back into an electric signal, and a propagation system in which the elastic wave propagates. Be prepared with a road.
, and the position of the end of the propagation path of the elastic wave is λ74
(N== 1.5.5..., where λ is the wavelength of the elastic wave), and the total length of the shifted propagation path end is the entire i
An elastic wave device that is characterized by the ability to (2) The elastic wave device according to claim (1), wherein the elastic wave is a boundary acoustic wave. (6) Claim 111E, wherein the elastic wave is a surface acoustic wave.