JPH0119457Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave resonator, and particularly to a surface acoustic wave resonator provided with a reflective electrode having good reflection characteristics.

For example, in VTR, depending on the viewer's preference,
The method used is to receive television radio waves sent in the UHF and VHF ranges, record them, and then connect the recorded signals to the empty channel of the television receiver and play them back when necessary. For this reason, a device that oscillates the same carrier wave as the carrier wave of the empty channel must be installed inside the VTR, and an RF converter is inevitably installed.

For example, in Japan, the Kanto region uses the second channel (97.25MHz) and the Kansai region uses the first channel (91.25MHz), so RF converters for two different frequencies are usually used.

Conventionally, RF converters required a complex circuit consisting of a crystal resonator, a multiplier circuit, an amplifier, a harmonic removal circuit, and a VSB circuit, but with the development of a surface acoustic wave resonator that directly oscillates, surface acoustic wave Very simple RF converters are now available that connect the resonator directly to the VSB circuit.

Next, an example of a surface acoustic wave resonator is shown in Figures 1 and 2.
This will be explained using figures.

That is, on one main surface of a piezoelectric substrate 1 made of LiTaO ₃ , LiNbO ₃ , crystal, ceramics, etc., an excitation electrode 2 consisting of an interdigital electrode 2 ₁ is arranged at a predetermined interval on both sides of this excitation electrode 2 . The reflective electrodes 3 and 4 each include a plurality of grating electrodes 3 ₁ and 4 ₁ , and only a signal voltage of a predetermined frequency applied between the terminals 2 a and 2 b of the excitation electrode 2 is applied to the interface of the excitation electrode 2 . Digital electrode 2 ₁
Then, using the surface waves of the piezoelectric substrate 1, it is reflected by the reflective electrodes on both sides and the grating electrodes 3 ₁ and 4 ₁ and fed back to the excitation electrode 2 again, so that direct oscillation is performed at a predetermined frequency. It's summery.

Such a surface acoustic wave resonator usually has a piezoelectric substrate 1.
Aluminum is deposited on one principal surface by vapor deposition and then photoetched. In this case, as shown in FIG. 2, the aluminum near the end of the photoresist film 5 shown by the broken line is overetched. A hollow part 6 is formed, and the vicinity of the piezoelectric substrate 1 is underetched, so that the piezoelectric substrate 1 in the side surface part 7, which is the most important part for a surface acoustic wave element, is underetched.
Not only is it not possible to maintain a predetermined distance between the grating electrodes 3 ₁ , 4 ₁ or between the grating electrodes 3 ₁ , 4 ₁ and the interdigital electrodes at the portions 8 in contact with the electrodes 2 ₁ , 3 ₁ , 4 ₁ , the internal angle θ ₁ of the portion 8 in contact with the piezoelectric substrate 1 of the side surface 7 tends to be an acute angle, which has the disadvantage of worsening the reflection characteristics as described in Japanese Patent Publication No. 54-24811. The reason for this is thought to be that since the interior angle θ ₁ is an acute angle, the layer of soft metal such as aluminum in this portion 8 becomes thinner, reducing the surface wave reflection efficiency.

The present invention was devised in view of the various drawbacks of the conventional surface acoustic wave resonators, and an object of the present invention is to provide a surface acoustic wave resonator with extremely good reflection efficiency.

Next, an embodiment of the surface acoustic wave resonator of the present invention will be explained with reference to FIGS. 3 and 4.

That is, an excitation electrode 12 formed of an interdigital electrode 12 ₁ on one main surface of a piezoelectric substrate 11 made of LiTaO ₃ , LiNbO ₃ , crystal, ceramics, etc.
and a plurality of grating electrodes 1 arranged at predetermined intervals on both sides of the excitation electrode 12.
The excitation electrode 12 consists of reflective electrodes 13 and 14 consisting of 3 ₁ and 14 ₁ , and receives only a signal voltage of a predetermined frequency applied between the terminals 12a and 12b of the excitation electrode 12.
interdigital electrode 12 ₁ to piezoelectric substrate 11
The surface wave is reflected by the grating electrodes 13 ₁ , 14 ₁ of the reflective electrodes 13 , 14 on both sides, and fed back to the excitation electrode 12 again to directly oscillate at a predetermined frequency. , is almost the same as a conventional surface acoustic wave resonator, but in this embodiment, the grating electrodes 13 ₁ ,
14 ₁ and the side surface 17 of the interdigital electrode 12 ₁ are characterized in that the internal angle θ ₂ of the portion 18 where the interdigital electrode 12 1 contacts the piezoelectric substrate 11 is an obtuse angle.

By forming the electrodes 12 ₁ , 13 ₁ , and 14 ₁ in this manner, the soft metal such as aluminum in the portion 18 becomes thicker, making it possible to increase the surface wave reflection efficiency.

The method for forming the electrodes 12 ₁ , 13 ₁ , 14 ₁ described above is to deposit aluminum or the like on one main surface of the piezoelectric substrate 11 by vapor deposition, and to form the electrodes by a photoetching method, which has recently been used for etching semiconductors. ing. It can be formed by using a so-called lift-off method.

In the embodiment described above, the grating electrode 1
3 ₁ , 14 ₁ and the interdigital electrode 12 ₁ both have an obtuse internal angle θ ₂ at the portion 18, but this may be done only for the grating electrodes 13 ₁ and 14 ₁ .

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing an example of a conventional surface acoustic wave resonator. Figure 1 is a plan view, and Figure 2 is a view of Figure 1 taken along line A-A. 3 and 4 are views showing an embodiment of the surface acoustic wave resonator of the present invention, FIG. 3 is a plan view, and FIG. 4 is a cross-sectional view of FIG. FIG. 2 is an enlarged sectional view of a main part taken along a line. 1, 11... Piezoelectric substrate, 2, 12... Excitation electrode, 2 ₁ , 12 ₁ ... Interdigital electrode, 3,
4, 13, 14...Reflecting electrode, 3 ₁ , 4 ₁ , 13 ₁ ,
14 ₁ ... grating electrode, 5, 15 ... photoresist film, θ ₁ , θ ₂ ... interior angle.

Claims (1)

[Claims for Utility Model Registration] An excitation electrode composed of at least an interdigital electrode formed on one main surface of a piezoelectric substrate, and reflective electrodes arranged on both sides of this excitation electrode and each composed of a plurality of grating electrodes. In the surface acoustic wave resonator provided with the surface acoustic wave resonator, an internal angle θ ₂ of a portion where at least the side surface of the grating electrode contacts the piezoelectric substrate among the side surface of the grating electrode and the side surface of the interdigital electrode is determined by a reflection characteristic. A surface acoustic wave resonator characterized by a good obtuse angle.