JPS60236313A - Elastic surface wave element - Google Patents

Abstract

PURPOSE:To suppress effectively the undesired waves by using an absorbing agent to cover a part or whole of the area between an electrode finger of the maximum cross width of a comb-shaped electrode at the input side and the final electrode finger of an electrode at the output side. CONSTITUTION:The layers 10 and 10 covered by an undesired wave absorbing agent is provided at a part of the area between an electrode finger of the maximum cross width of a comb-shaped electrode 2 at the input side of an elastic surface wave element and an electrode finger of an electrode 3 at the output side at a point closest to the electrode 2 as shown in a figure (a). The layers 10 and 10 are provided at a part of the position corresponding to the position of the electrode 3 as shown in a figure (b). Furthermore both layers 10 and 10 are provided at a part of the area between both electrodes 2 and 3 as shown in a figure (c). Thus undesired waves can be suppressed effectively owing to the layers 10 formed at such positions.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a surface acoustic wave element that can be suitably used for, for example, a filter, a resonator, a delay element, and the like.

(Prior Art) It is well known that surface acoustic wave elements have been applied to filters, resonators, delay elements, etc. because they have the advantages of being small and thin, requiring no adjustment.

FIG. 6 shows a piezoelectric substrate or a piezoelectric film and at least a comb-shaped (
This figure shows an example of the configuration of a filter in which a surface acoustic wave element having an electrode structure (interdigital type) is applied to a filter. ,Zn
It is a substrate made of a piezoelectric material such as 0t crystal (a film made of a piezoelectric material may also be used. In the following explanation, it may be described as a piezoelectric substrate or a piezoelectric film), and 2 is a substrate on the input side. Electrode 3 is the output side electrode.

The input-side electrode 2 and the output-side electrode 3 are formed by forming a thin film of metal such as aluminum or gold on the piezoelectric substrate (or piezoelectric film) 1, and then using a photo-etching method or the like. Depending on the application, it can be constructed in a predetermined pattern, such as with intersecting electrode fingers.

The electrodes 2 on the input side and the electrodes 3 on the output side are provided with electrode bases 2a, 2b, and 38.3b that are arranged facing each other, respectively, and protrude from each of the electrode bases 2a, 2b, 3a, and 3b. Provided electrode fingers 2al, 2b1, 3
each electrode finger 2 al, 2 bt, in each electrode 2, 3,
Transmission and reception of surface acoustic waves is performed in the range where 3aL3bl overlap each other (intersection width of electrodes). In addition, 4g, 4b
shows a sound-absorbing coating layer to absorb unnecessary reflected waves.

That is, in the filter using the surface acoustic wave element shown in FIG. 6, when an AC voltage is applied to the input terminals 5a+5b of the electrode 2 on the input side, the voltage from the electrode 2 on the input side as shown by the arrows Sr and SQ in FIG. Although surface acoustic waves are generated on both sides of the electrode 2 on the input side, only the surface acoustic waves indicated by the arrow Sr are received by the electrode 3 on the output side, so that the surface acoustic wave element shown in FIG. This results in a filter that exhibits filter characteristics as shown in the figure.

The filter characteristics exhibited by the surface acoustic wave element described above are determined by the shape of the input side electrode 2 and the output side electrode 3, for example.
It is determined by the width of the electrode fingers, the number of electrode fingers, the crossing width of the electrode fingers, etc. Generally, the comb-shaped electrode required to obtain the required filter characteristics is determined by Fourier transform of the required filter characteristics. The shape of is determined.

However, even if a surface acoustic wave device is actually manufactured.

The presence of secondary effects such as wave reflection, diffraction, and interference, and the mode of waves generated in surface acoustic wave elements may be complex waves with bulk waves or Lamb waves other than the specified Rayleigh wave, etc. For these reasons, it is extremely difficult to produce a surface acoustic wave device that exhibits the same characteristics as the designed values.

As a measure to eliminate the deviation in characteristics due to the second-order effect in the surface acoustic wave element described above, various solutions have been proposed in the past, such as devising the structure of the electrode fingers and using sound absorbing materials. ing.

Figures (a) to (o) in Figure 8 show typical examples of various solutions that have been proposed in the past for the above-mentioned problem. This is a filter in which a sound-absorbing coating layer 4a is provided on a portion of the input-side electrode 2 other than the intersection portion where the filter is applied, in order to improve side lobes and ripples that appear in the characteristics of the filter. In addition, as shown in FIG. 8(b), a sound-absorbing coating layer 4a is provided at the intersection of the weighted input electrodes 2 to eliminate side lobes and ripples that appear on the filter characteristics. In addition to improving the characteristics of
FIG. 8(c) shows a resonator in which triangular resist coating layers 4a and 4b are provided on the reflective grating 7.7 to improve spurious resonance characteristics. FIG. 8(d) shows a filter having a configuration in which a multi-strip coupler 8 is interposed between the input side electrode 2 and the output side electrode 3, and the wave interference between the upper stage and the lower stage is suppressed. In order to prevent this, a sound absorbing material coating layer 4c is provided at the boundary between the upper and lower stages, and (e) in FIG.
) is one in which a correction electrode 9 is provided in order to eliminate unnecessary waves generated at the electrode finger at the end of the weighted input side electrode 2 near the output side electrode 3 (No. 8).
In (e) of the figure, an enlarged view of the part surrounded by the dot-dash dots is shown below).

(Problems to be Solved by the Invention) According to the conventional solutions to the problems of the surface acoustic wave element described with reference to (8) in FIG. 8 to (8) in FIG.
Although each improvement effect can be obtained depending on the purpose, in order to obtain a surface acoustic wave element with characteristics closest to the design values, it is necessary to perform the steps (a) to (e) in Fig. 8. Since it was not sufficient to implement the conventional solutions referred to and described, a solution was sought.

(Means for Solving the Problems) The present invention provides a piezoelectric substrate or a piezoelectric film and at least a comb-shaped (
In a surface acoustic wave device configured with electrodes having an electrode structure (interdigital type), the position of the electrode finger with the maximum crossing width on the comb-shaped electrode on the input side and the final electrode finger on the output side electrode The object of the present invention is to provide a surface acoustic wave element in which a part or all of the portion between the position and the position is coated with an unnecessary wave absorber.

(Example) Hereinafter, specific details of the surface acoustic wave device of the present invention will be described with reference to the accompanying drawings. Figure 1 (, l) ~ 1st
(c) of the figure is a plan view of different actual image aspects of the surface acoustic wave element of the present invention, and in (a) of FIG. 1 to (C) of FIG. a) to (e in Figure 8)
) to each corresponding component in the conventional surface acoustic wave element described above with reference to (,) to
The same drawing numerals as those used in FIG. 8(e) are used.

In the surface acoustic wave element of the present invention shown in FIGS. 1(a) to 1(C), 10 is the maximum crossover at the comb-shaped electrode 2 on the input side of the surface acoustic wave element. A coating layer made of an unnecessary wave absorber provided so as to cover a part (or even the whole part) of the part between the width electrode finger position and the final electrode finger position on the output side electrode 3. In the surface acoustic wave element shown in FIG. 1(a).

The coating layers io and to made of unnecessary wave absorbers are located at the position of the electrode finger with the maximum crossing width on the comb-shaped electrode 2 on the input side in the surface acoustic wave element, and the electrode finger closest to the input side electrode 2 on the output side electrode 3. In addition, in the surface acoustic wave element shown in FIG. 1(b), a coating layer 10.
is provided in a part of the surface acoustic wave element at a position corresponding to the position of the output side electrode 3.

Furthermore, in the surface acoustic wave element shown in FIG. It is provided in a part of the middle between 3.

In the surface acoustic wave elements shown in FIGS. 1(a) to 1(e), the component portion 2C that is continuous with the electrode terminal 2b of the input-side electrode 2 is electric%2
It acts as an electrostatic shielding member between the electrode 3 on the output side and the electrode 3 on the output side.

2 (,) to 2 (c) are the positions of the electrode fingers with the maximum crossing width on the comb-shaped electrode 2 on the input side and the final position on the electrode 3 on the output side in the surface acoustic wave device of the present invention. Unwanted wave absorption when the coating layer 10 made of an unnecessary wave absorber is provided so as to cover a part of the area between the position of the electrode finger and the position of the electrode finger. FIG. 3 is a plan view showing an example of the structure of a coating layer 10.10 made of an agent.

In the surface acoustic wave device of the present invention, the portion between the position of the electrode finger with the maximum crossing width on the comb-shaped electrode 2 on the input side and the position of the final electrode finger on the output side electrode 3 in the surface acoustic wave device. The coating layer 10 made of an unnecessary wave absorber should be provided so as to cover a part (or the whole part) of the
For example, silicone, varnish, epoxy resin, rubber, or resist agent can be used as the unnecessary wave absorber, and the coating layer 10 made of the above-mentioned unnecessary wave absorber can be formed by brush-coating the unnecessary wave absorber, for example. The coating layer 10 of the unwanted wave absorber may be formed in a predetermined pattern by applying a coating method using a spray coating method or a printing coating method. Alternatively, after the entire surface is coated with the unwanted wave absorber by a spinner coating method, a coating layer 10 of the unwanted wave absorber in a predetermined pattern is formed by a photolithography method. You may also do so.

A coating layer 10 made of a line-shaped or dot-shaped unnecessary wave absorber as shown in FIG. 2(a) to FIG. 2(C)
Needless to say, this can be easily constructed by applying the photolithography method described above.

The area and thickness of the coating layer 10 made of an unnecessary wave absorber to be formed on the surface acoustic wave element described above are 5. Taking into consideration the permissible range of decrease in output level that occurs when the surface acoustic wave element is coated W10 with an unnecessary wave absorber by implementing the present invention, and the degree of reduction in side load and ripple, the unnecessary wave absorber The thickness of the coating layer 10 and the coating layer 1 made of the unnecessary wave absorber.
For example, 2000 is approximately inversely proportional to the area of 0.
It is preferable that the thickness be appropriately selected within the range of angstroms to 300 micrometers.

In carrying out the present invention, the portion between the position of the electrode finger with the maximum crossing width on the comb-shaped electrode 2 on the input side and the position of the final electrode finger on the output side electrode 3 in the surface acoustic wave element is As a guideline for the thickness and area of the coating layer 10 made of an unwanted wave absorber to be formed by partially (or all) '8f-ell, Comparing the amplitude characteristics when the coating layer 10 is formed and the amplitude characteristics of the surface acoustic wave device without forming the coating layer 10 made of an unnecessary wave absorber, it is found that the surface acoustic wave device is improved by implementing the present invention. The amplitude when the coating layer 10 made of the unwanted wave absorber is formed is 2 dB in amplitude characteristics compared to the amplitude in the surface acoustic wave element without the coating layer 10 formed by the unwanted wave absorber.
One guideline is to set the thickness and area to such an extent that the amplitude decreases within Compared to the amplitude of the surface acoustic wave element in which the surface acoustic wave element 10 is not formed, the amplitude when the surface acoustic wave element is formed with the coating layer 10 made of an unnecessary wave absorber according to the present invention is 0.5 in terms of amplitude characteristics. When a coating layer 10 made of an unwanted wave absorber is formed with a thickness and V area that causes a dB amplitude reduction, it has almost no effect on the overall filter characteristics, and moreover, it can reduce side lobes. A filter using a surface acoustic wave element that satisfactorily reduces ripples has been obtained.

FIG. 3 shows that after the comb-shaped electrode 2 on the input side and the electric current f@3 on the output side are adhered and formed on the glass substrate 11, a piezoelectric film 12, for example, a two-layer structure made of one ZnO film with a thickness of about 2 μm, is formed. The counter electrodes 13.14 (the counter electrodes 13.14 are made of the ZnO film 1 and are in contact with each other, but the other parts are not connected to each other). An example of an elastic surface wave element in which the present invention is applied to a surface acoustic wave element having a configuration in which the present invention is connected (in a connected state and in an electrically floating neutral state) FIG. 2 is a side sectional view of a surface wave element.

In FIG. 3, 10 is a part (or may be the entire part) of the part between the position of the electrode finger with the maximum crossing width on the comb-shaped electrode 2 on the input side and the position of the final electrode finger on the output side electrode 3. ) is coated with an unwanted wave absorber, and the structure of the coating layer 10 made of an unnecessary wave absorber in the surface acoustic wave element shown in the embodiment of FIG. Material, shape and thickness of the coating layer 10 made of the unnecessary wave absorber.

The area and the like are the same as in the embodiment of the surface acoustic wave device of the present invention described with reference to FIGS. 1 and 2.

In addition, as a surface acoustic wave element constructed using a piezoelectric film, 1, the input side electrode 2 and the output side electrode 3 are provided on the glass substrate 11, or the input side electrode 2 and the output side electrode 3 is provided on the top surface of the piezoelectric film 12, and whether or not the counter electrodes 13 and 14 are provided. Including the surface acoustic wave element having the configuration shown in FIG. 3, a total of four types of surface acoustic wave elements can be made. Of course, the present invention can be equally well applied to any of the four types of surface acoustic wave elements.

FIG. 4 shows a surface acoustic wave element having the configuration shown in FIG. 3 (the shape of the coating layer 10 made of an unnecessary wave absorber is shown in
In the case shown in a), the input side electrode 2 is made up of 72 weighted pairs of electrode fingers, and the output side electrode 3 is made up of 14 pairs of weighted electrode fingers. FIG. 4 is a frequency-amplitude characteristic curve diagram of a surface acoustic wave element used as an output-side electrode 3 consisting of electrode fingers as a band-pass filter for a video intermediate frequency signal for a television receiver; The curve (solid line) shown in FIG.
1 shows for reference the frequency amplitude characteristic curve of a surface acoustic wave element in a state where the coating layer 10 made of an unnecessary wave absorber is not formed.

Looking at FIG. 4, it can be seen that by implementing the present invention, the ripple in the main passband is reduced, and the ripple is reduced by 60.25
It can be seen that the response in the sidelobe part that exists near NHZ and the sidelobe part that exists above it is reduced (the frequency amplitude shown by the solid line curve in Fig. 4). Although the characteristic curve is not shown, it shows values very close to the design values).

Next, FIG. 5 shows a surface acoustic wave element having the configuration shown in FIG.
J), the input side electrode 2 is made up of 126 pairs of electrode fingers weighted in a 5inx/x type, and
The output side electrode 3 is made up of four pairs of electrode fingers so that the output side electrode 3 has a sufficiently wide band, and the center frequency is 46M.
5 is a diagram showing a frequency amplitude characteristic curve and a group delay characteristic curve of a filter using a surface acoustic wave element used as a Hz filter, and in FIG. 5 shows a frequency amplitude characteristic curve of a filter using a surface acoustic wave element, and the curve (2) indicated by a dotted line in FIG. The frequency-amplitude characteristic curve is shown for reference.Furthermore, in FIG. Furthermore, the dotted line curve in FIG. 5 is a group delay characteristic curve of a filter using a surface acoustic wave element without the coating layer 10 formed of an unwanted wave absorber for reference.

Looking at FIG. 5, it is clear that various characteristics such as ripple, sidelobe, and group delay characteristics are greatly improved by implementing the present invention.

In other words, if you look at Figure 5, the ripple is 2°5 above.
dB has been improved to ±1 dB, and the site lobe has been improved to 17
It can be seen that the dB is improved to 29 dB, and the group delay ripple is further improved from ±450S to ±20ns within the -3 dB band.

Although the reason for the improved characteristics of the surface acoustic wave device of the present invention as described above is not clear at present, the inventors believe that unnecessary waves propagating on the very surface of the surface acoustic wave device are It is speculated that this is because the waves are well suppressed by the coating layer 10 made of a wave absorbing agent.

In the embodiments so far, cases have been explained in which the surface acoustic wave device invented by Filter Banji is applied, but it is obvious that the present invention can be similarly applied to resonators and delay circuits. Needless to say, when the present invention is applied to a resonator, for example, there is a The spurious characteristics can be improved by providing a coating layer 10 made of an unnecessary wave absorber.

The present invention can be equally effective even if the crossing state, length, width, and type of piezoelectric material of the electrodes are different.

(Effects) As is clear from the detailed explanation above, the surface acoustic wave element of the present invention includes a piezoelectric substrate or a piezoelectric film, and an electrode having at least a comb-shaped (interdigital type) electrode structure. In the constructed surface acoustic wave element, part or all of the part between the position of the electrode finger of the maximum crossing width on the comb-shaped electrode on the input side and the position of the final electrode finger on the output side electrode is unnecessary. Since the surface acoustic wave element of the present invention is coated with a wave absorbing agent.

Part or all of the part between the position of the electrode finger of the maximum crossing width on the comb-shaped electrode on the input side and the final IT electrode finger position on the output side electrode is coated with an unnecessary wave absorber. The layers can effectively suppress unnecessary waves that propagate to the very surface of the surface acoustic wave device, so the amplitude frequency characteristics and group delay characteristics of the surface acoustic wave device can be improved compared to conventional surface acoustic wave devices. This can be greatly improved, and it becomes possible to easily provide a surface acoustic wave element with characteristics close to the designed values.

[Brief explanation of the drawing]

1 and 2 are plan views of the surface acoustic wave element of the present invention,
FIG. 3 is a side sectional view of the surface acoustic wave device of the present invention, FIGS. 4, 5, and 7 are characteristic curve side views, and FIGS. 6 and 8 are of conventional surface acoustic wave devices. FIG. DESCRIPTION OF SYMBOLS 1... Piezoelectric substrate, 2... Input side electrode, 3... Output side electrode, 4a* 4b... Sound absorbing material coating layer, 7.
...Reflection grating, 8...Multi-strip coupler, 10...Covering layer with unnecessary wave absorber, 11...
・Glass substrate.

Claims (1)

[Claims] 1. In a surface acoustic wave element configured with a piezoelectric substrate or a piezoelectric film and an electrode having at least a comb-shaped (interdigital type) electrode structure, the comb-shaped electrode on the input side A surface acoustic wave element 2, as a piezoelectric film, in which part or all of the part between the position of the electrode finger of the maximum crossing width and the position of the final electrode finger on the output side electrode is coated with an unnecessary wave absorber. A surface acoustic wave element 3 according to claim 1 which uses a ZnO film, and a patent claim which uses any one of silicone, a plastic film, an epoxy resin, a rubber, and a resist agent as an unnecessary wave absorber. The surface acoustic wave element 4 according to claim 1, wherein a predetermined portion is coated with a resist agent having an unnecessary wave absorption effect using a photolithography method in a predetermined pattern. Surface wave element 5, a surface acoustic wave element according to claim 1, in which the pattern of the coating with the unnecessary wave absorber is linear or dot-shaped.