JPS61220514A - Surface acoustic wave resonator - Google Patents

Abstract

PURPOSE:To realize a high reflecting efficiency and to improve the resonance Q by setting the center interval between the electrode finger of a converter and a reflector where two kinds of surface acoustic wave reflectors having positive/negative reflecting efficiencies are arranged in a pitch of lambda/4 to the length of lambda/4. CONSTITUTION:The 1st surface acoustic wave reflecting strip 2 made of a gold thin film having a film thickness of lambda/200 with a width of lambda/8 and the 2nd surface acoustic wave reflecting strip 3 made of an aluminum thin film having a film thickness of lambda/50 the same width as that of the strip 2 are arranged alternately on a crystal substrate 1 in a pitch of lambda/4 to form two grating reflectors 6. Further, an interdigital converter 7 of the same structure as that of the 1st and 2nd surface acoustic wave reflecting strips 2, 3 is provided. Moreover, the center interval between the reflecting strip 2 or 3 at the end of the reflector 6 opposite to the converter 7 and the electrode finger 4 or 5 at the end of the converter 7 opposite to the reflector 6 is set to lambda/4, where lambda is a wavelength of the surface acoustic wave propagated on the substrate 1.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a resonator using surface acoustic waves.

[Technical background of the invention and its problems]

The basic structure of the conventionally widely known surface acoustic wave resonator was invented by Clin, Sylvester Hartman, et al.
It is based on Japanese Patent Publication No. 56-4-6289). That is, as shown in FIG. 14, a large number of surface acoustic wave reflecting strips 22 having a width λ/4 are arranged on a piezoelectric substrate 21, where λ is the wavelength of the surface acoustic wave propagating on the substrate 21.
a grating reflector 26 arranged with a period of /2;
An interdigital transducer 27 consisting of electrode fingers 23 having a width of /I/4 is provided.

By the way, since the characteristics of such a surface acoustic wave resonator are mainly determined by the grating reflector, improving the characteristics of the grating reflector is an extremely important issue. in general,
Surface acoustic wave reflector 1 such as strip, ridge, group, etc.
When the true reflectance ε is large, the number of reflectors may be small, but as ε becomes smaller, the number of reflectors becomes more necessary.

Peter Cross is published in Reference 1: IEFE Trans
.

on 5onics & Ultrason, (vo
l 5u-23, NO, 4ρD, 255-262)
[7G states that in order to obtain a sufficient reflector, the number of reflectors in the grating reflector must be N#3/ε or more.

For example, a reflector with ε40.01 requires a large number of gratings, 300 or more, and considering that two or more grating reflectors are generally used in a resonator, the entire resonator becomes extremely large. The problem is that it becomes.

On the other hand, in order to increase ε per anti-body,
~As the lip thickness, ridge height, and group depth are increased, the mode conversion from surface acoustic waves to bulk waves increases accordingly, leading to a decrease in the Q of the resonator due to the conversion loss. .

As a means to solve these problems, the inventors have developed an ultrasonic research group of the Institute of Electronics and Communication Engineers (Reference 2: Telecommunications Institute Technical Report US8).
4-30 (September 1980), two types of reflectors with opposite reflection coefficients were alternately λ/5 with a width of 2778 for the surface wave wavelength λ of the frequency used.
We have proposed a grating reflector arranged in four periods. In a grating reflector with this structure, the reflected wave from the reflector with a positive reflection coefficient and the reflected wave from the reflector with a negative reflection coefficient are added, so that the reflector is
Compared to a conventional general grating reflector arranged in two periods, the amount of reflection per unit length increases nearly twice. On the other hand, the mode conversion loss to bulk waves only increases by 1.4 times. Therefore, if compared with the conventional one with the same amount of reflection, mode conversion loss to bulk waves will be reduced.

However, the effect of suppressing mode conversion loss to bulk waves in the grating reflector occurs only in the central part 24, as shown in FIG. 14(b), and in the vicinity of the end part 25 facing the interdigital converter. No suppression effect can be obtained. That is, in the central part 24 of the grating reflector where the reflectors are arranged periodically with a period of λ/4, the acoustic impedance can be considered to have a substantially infinite period, so the radiated bulk waves (J cancel each other out), while the grating reflection At the end part 2!'), the distance between the electrode fingers of the adjacent interdigital transducer () is λ/4L:l, and the reflector arrangement period at the center of the grating reflector is a different value. Therefore, the acoustic impedance no longer appears to have an infinite period, so a radiated bulk wave remains, causing mode conversion loss.

In this way, a grating reflector made of silk with a reflection coefficient of one anti-q has a high reflection efficiency, can be made compact, and can change the mode from surface acoustic waves to bulk waves inside the reflector. Although it had the characteristic of low conversion loss, the mode conversion loss at the end of the reflector could not be suppressed, and this was a major hindrance to realizing a high Q surface acoustic wave resonator. [.

[Purpose of the invention]

The present invention was made in view of the above-mentioned problems, and has a basic structure in which two types of surface acoustic wave reflectors having positive and negative reflection coefficients are arranged at a period of 1/4 of the surface acoustic wave wavelength. By using a high grating reflector and effectively suppressing mode conversion loss from surface acoustic waves to bulk waves not only inside the grating reflector but also at its edges, it is possible to generate surface acoustic waves that are small and have a high Q value. The purpose is to provide a resonator.

(Summary of the Invention) The present invention provides a surface acoustic wave resonator comprising a small number of grating reflectors on a piezoelectric substrate and at least one interdigital transducer formed between these grating reflectors. , a grating reflector is arranged on a piezoelectric substrate, and two types of surface acoustic wave reflectors having positive and negative reflection coefficients for surface acoustic waves and at least one of which is made of a conductive material are alternately arranged, and the wavelength of the surface acoustic wave is The interdigital transducer is constructed by arranging two types of reflectors used in these grating reflectors and two types of electrode fingers of the same structure alternately, and at approximately the wavelength of surface acoustic waves. Furthermore, a reflector at the end of the grating reflector facing the interdigital converter, and an electrode (J) at the end facing the grating reflector of the interdigital converter. It is characterized in that the center-to-center spacing between the finger and the finger is set to 1/4 of the wavelength of the surface acoustic wave.

(Effects of the Invention) In the surface acoustic wave resonator according to the present invention, the grating reflector alternately arranges two types of surface acoustic wave reflectors having positive and negative reflection coefficients on the piezoelectric substrate at 1/4 of the surface acoustic wave wavelength. Since it has a basic structure arranged with a period of , it has high reflection efficiency by adding the reflected waves from both slips 1 to 1. That is, the amount of reflection of surface acoustic waves per unit length increases, and mode conversion loss from surface acoustic waves to bulk waves inside the grating reflector is relatively reduced.

Furthermore, in the present invention, the grating reflector has a C
The structures of the N-pole fingers in the grating reflector and the interdigital converter are the same, and the arrangement periods of these reflectors and electrode fingers are approximately the same, and Since the center-to-center spacing between the reflector and electrode fingers is approximately equal to the arrangement period of the reflector and electrode fingers, the periodicity of the acoustic perturbation effect is maintained over the entire region where surface acoustic waves are confined as standing waves. . Of course, the acoustic impedance becomes infinitely periodic not only inside the grating reflector but also at the ends of the grating reflector. Therefore, conversion loss of surface acoustic waves to bulk waves is suppressed not only inside the grating reflector but also at the ends of the grating reflector, and the Q of the resonator can be effectively increased.

As described above, according to the present invention, it is small and QI+fJ
A surface acoustic wave resonator with high performance is realized.

(Example of the invention) An example of the invention will be described with reference to the drawings. Fig. 1 shows the structure of a surface acoustic wave resonator according to an example of the invention, and it is used as a piezoelectric substrate. A film thickness of λ/200 (1
In the case of 00MHz, the first surface acoustic wave reflection by the gold thin film (equivalent to 1600 people) -10 = Slip 1 to Lip 2, line width λ, /8 and film thickness λ, , / 50
(equivalent to 6,400 people in the case of 100MH7) second surface acoustic wave reflection screen (~ lip 3) by an aluminum thin film
Toga/! Two grating reflectors 6 arranged in a pattern with a period of The electrode fingers have the same structure as the lips 2 and 3, namely, the first electrode finger 4 is made of a gold thin film with a line width λ7/8 and a film thickness II/200, and the first electrode finger 4 is made of an aluminum thin film with a line width λ/8 and a film thickness λ150. An interdigital transducer 7 consisting of a second electrode finger 5 is provided.

More specifically, each grating reflector 6
The total number of the first and second surface acoustic wave reflecting slips 2 and 3 is, for example, 150, and in this case, the length of the grating reflector 6 in the surface acoustic wave propagation direction is 75λ. It is. On the other hand, the total number of first and second electrode fingers 4 and 5 in the interdigital converter 7 is 100, and strictly speaking, the arrangement period is set so as to obtain a good resonance state. , grating reflector 6
For the arrangement period (λ/4) of anti-q4-slib in ()
This is about a 5% reduction. In addition, the grating reflector 6
The reflective strip (2 or 3) at the end opposite the interdigital transducer 7 and the N8i finger (4 or 5) at the end opposite the grating reflector 6 of the interdigital transducer 7. The center-to-center spacing is set to 1/4 of the wavelength of the surface acoustic wave. Generalizing the arrangement period of the electrode fingers 4 and 5 in the interdigital transducer 7, when the length of the interdigital transducer 7 in the surface acoustic wave propagation direction (propagation path length) is nλ, λ/4 ・( 1-1/4n).

The film thickness dependence of the reflectance of the surface acoustic wave reflection slips 1 to 1 through the gold thin film and aluminum thin film formed on the quartz substrate is shown by solid lines and broken lines in FIG. As we will see, the reflectance is negative for reflective strips made of thin gold films;
In the case of a reflective strip made of a thin aluminum film, the positive and negative values are opposite to each other, and the film thickness dependence is four times larger for a thin gold film than that for a thin aluminum film.

Therefore, in order to have the same reflectance in absolute value, the thickness of the gold thin film may be 1/4 of the thickness of the aluminum thin film.

In addition, in the above, the cut angle of the crystal substrate 1 is selected so that the peak temperature is around room temperature with the gold thin film and aluminum thin film formed on the surface, but this depends on the thickness of each of the gold and aluminum thin films. It is necessary to decide accordingly.

With such a structure, the reflectance of surface acoustic waves per unit length of the grating reflector 6 becomes high, making it possible to downsize the grating reflector 6 and the interdigital converter 7. Since there are reflective strips and electrode fingers with approximately λ/4 period throughout the entire structure, bulk waves are suppressed well and a resonator with high Q can be obtained.

This effect will be explained more specifically. The surface acoustic wave resonator of this example and the conventional structure of λ/4 shown in FIG.
Reflection by an aluminum thin film with a line width] Lips and electrode fingers are used for grating reflectors and interdigital transducers, and surface acoustic wave reflections with an aluminum thin film thickness of λ1509] ~ Number of lips: 150, number of electrode fingers: 1
Comparing the Q value with a surface acoustic wave resonator prototyped under the same conditions as this example, the Q value is 2000 in this example.
While it exceeds 0, it is less than 10,000 with the conventional structure, and an improvement of more than twice in Q value was observed.

On the other hand, as a comparative example, the grating reflector is composed of reflective strips made of aluminum and gold thin films as in the present embodiment, and the interdigital converter is composed of λ
We prototyped a surface acoustic wave resonator using electrode fingers made of aluminum thin film with a line width of /4, but in this case as well, the Q was 15,000.
It never exceeded.

The reason why a surface acoustic wave resonator constructed using a reflective strip made of an aluminum thin film and electrode fingers has a low Q is because the reflectance of the reflective strip made of an aluminum thin film alone is not large enough. This is thought to be because a portion of the grating leaks out of the grating reflector, increasing the loss. Reflection is the best way to improve your Q! ~Number of lips 200
However, in that case, the size of the resonator would become extremely large as described above.

Furthermore, in the surface acoustic wave resonator of the comparative example in which the interdigital transducer is composed only of electrode fingers made of thin aluminum films, the grating reflector is made of reflective slips made of thin films of aluminum and gold. is sufficient, and losses caused by surface acoustic waves leaking out of the grading reflector are significantly reduced. However, the periodicity of the acoustic perturbation effect occurs at the boundary between the interdigital transducer and the grating reflector. Because of the large difference, there is a mode conversion loss from surface acoustic waves to radiation bulk waves, and Q is not sufficiently improved as described above.

In contrast, in the embodiment of the present invention, the periodicity of the acoustic perturbation effect of the reflective strip electrode fingers is sufficiently maintained over the entire region where the surface acoustic waves are confined as standing waves. Therefore, it is thought that the mode conversion loss to the radiated bulk wave is suppressed to a small level, thereby significantly increasing Q(a).

Regarding the degree of uniformity of the arrangement period of the reflective strips and electrode fingers, for example, if the uniformity at the boundary is shifted, that is, the reflection strip at the end of the grating reflector]~ If the center-to-center distance between the lip and the electrode fingers at the end of the interdigital transducer is increased from λ/4, the effect of the present invention is sufficient up to about 5%;
It was confirmed that when it exceeds 0%, there is no effect of suppressing mode conversion loss at the boundary.

Next, an example of the manufacturing process of the surface acoustic wave resonator shown in FIG. 1 will be explained using FIG. 3.

First, as shown in FIG. 3(a), on the crystal substrate 1,
A thin gold film 2' is deposited by vapor deposition or J sputtering method. At this time, a thin gold film 2 was added for the purpose of improving the quality of the food.
A base layer made of a very thin layer of chrome or titanium may be placed under the .

Next, as shown in FIG. 3(b) using a photolithography technique, a first surface acoustic wave reflecting strip 2 and a first electrode finger 4 made of a thin gold film with a line width λ/82 and a period λ/2 are formed.
form. If there is an underlying layer, it is also removed by etching at the same time as the gold thin film.

Next, as shown in FIG. 3(C), a thin aluminum film 3' is formed over the entire surface to a thickness approximately four times that of the thin gold film 2'.
It is attached by vapor deposition or sputtering method. At this time,
The surface of the aluminum thin film 3' is sufficiently flat because the thickness of the first surface acoustic wave reflecting strip 2 formed by the underlying gold thin film is extremely small, less than 1/20 of the line width.

As shown in FIG. 3(d), a second surface acoustic wave reflecting strip 3 and a second surface acoustic wave reflecting strip 3 made of an aluminum thin film with a line width λ/81 and a period λ/2 are formed by photolithography.
The N-pole resin 5 is formed so as to be located approximately in the middle of each of the first surface acoustic wave reflecting strip 2 and the first electrode finger 4 made of a thin gold film. Note that the aluminum thin film 3'
3(d), the first surface acoustic wave reflection slip 1-slip 2 and the first electrode finger 4 made of the gold thin film underneath become invisible. 3(b), a mask alignment mark 8 is formed outside the grating reflector formation area in the process shown in FIG. 3(b), and furthermore, in the process shown in FIG. It is necessary that the area where the mark 8 is formed is not covered with the aluminum thin film.

FIG. 4 shows an embodiment in which the grating reflector 6 is modified from the embodiment shown in FIG. and are also electrically connected to each other. When the piezoelectric substrate is the crystal substrate 1, the electro-mechanical coupling coefficient is very small, so even if the surface acoustic wave reflecting strip 2.3 is electrically short-circuited in this way, it is operationally electrically open. It is almost the same as in the case of The same applies even if only one of the first and second surface acoustic wave reflective strips 2.3 is electrically short-circuited, or both are short-circuited but not electrically connected to each other. It is.

In the above embodiment, it was explained that a 32° rotated Y plate was used as the crystal substrate '1, but it is not necessarily limited to this angle. The intended purpose of the present invention can be achieved by slightly changing the thickness ratio of the thin film. In addition, when surface acoustic waves are called surface acoustic waves, they generally refer to Rayleigh waves, but are not necessarily limited to this vibration mode.For example, surface acoustic waves propagate at right angles to the It can also be applied to a surface acoustic wave resonator using a pseudo bullet 110 surface wave or a pseudo surface acoustic wave propagating on the Y and X axes with a rotation of 105°±10°. In particular, in pseudo surface acoustic waves, there are many modes in which part of the energy is radiated inside the substrate in a propagation path where nothing exists on the surface. However, if periodic perturbations such as reflective slips and electrode fingers are present on the surface, energy tends to concentrate on the surface and is no longer radiated. In this regard, the surface acoustic wave resonator according to the present invention has a structure in which periodic perturbations exist in all regions where pseudo surface acoustic waves exist, so it utilizes pseudo surface acoustic waves, which conventionally could not be realized with large Q. This surface acoustic wave resonator also has the advantage of being able to achieve a high Q.

Further, in the above explanation, a quartz substrate was used in all cases, but the same effect can be obtained by using a 1:Ta03W plate, for example.

FIG. 5 shows only a portion of the grating reflector 6 for explaining the embodiment, in which a 1iTaQ3 substrate 1 is used as the piezoelectric substrate instead of a quartz substrate, and a gold thin film is formed on this substrate 1. One surface acoustic wave reflecting strip 1 to lip 2 and a second surface acoustic wave reflecting strip 1 to lip 3 made of an aluminum thin film are formed. In this case, the process is basically the same as the case of the crystal substrate, but since the electro-mechanical coupling coefficient of the l-1Ta03 substrate is larger than that of the crystal substrate, the first elastic surface made of a thin gold film is used as shown in the figure. Although the wave reflecting strip 2 is electrically isolated, it is more desirable to electrically short-circuit the second surface acoustic wave reflecting strip 3 made of an aluminum thin film in order to increase the reflectance as much as possible.

In this case, the interdigital converter 6 may also have a structure in which the electrode fingers 4 made of a thin gold film are electrically isolated and the electrode fingers 5 made of a thin aluminum film are electrically short-circuited, as shown in FIG.

1! T a O3'A plate (X cut - 112°Y
Plate) Top (71) Line width λ due to gold and aluminum thin film
Examining the reflectance per slip of the /8 surface acoustic wave reflective strip, as shown in Figure 7, the reflection coefficients are in opposite phases to each other, and that of the gold thin film is higher than that of the aluminum thin film. The dependence of reflectance on film thickness is approximately twice as large. However, as shown in FIG. 5, this characteristic is obtained when the first surface acoustic wave reflecting strip 2 made of a thin gold film is electrically open.
This is a case where the second surface acoustic wave reflection slip 1 and the slip 3 formed by the aluminum film are electrically short-circuited. According to this,
The film thickness of the first surface acoustic wave reflecting strips 1 to 2 made of a gold thin film can be approximately 1/2 of that of the second surface acoustic wave reflecting strips 1 to 3 made of an aluminum thin film. .

In the following embodiments, a single-bore type surface acoustic wave resonator having one interdigital transducer has been described. This can also be applied to a multi-port surface acoustic wave resonator with It is also possible.

FIG. 9 shows a surface acoustic wave resonator according to yet another embodiment of the present invention, in which a surface acoustic wave resonator with a line width of λ/8 is mounted on a crystal substrate 1 consisting of a 36° rotated Y plate as a piezoelectric substrate. Film thickness λ1
50 (equivalent to 6400 people in the case of 100MHz +7)) and a recess formed by removing the surface of the substrate 1 with the same dimensions, that is, a width λ/8 and a depth. Grating reflectors 6 are provided in which surface acoustic wave reflection groups 1o of λ/50 are arranged alternately at a period of λ/4, and further located between these grating reflectors 6, the above-mentioned reflection strips 3 and Electrode finger 5 with the same structure as reflection group 1o
, 11 is provided.

The film thickness dependence of the reflectance of the surface acoustic wave reflection slips 1 to 14 formed on the aluminum thin film formed on the crystal substrate and the dependence of the reflectance of the surface acoustic wave reflection group 14 on the group depth are shown in FIG. Indicated by solid and broken lines. As shown below, the reflectance (positive for the reflective strip made of aluminum thin film and negative for the reflective group) is opposite to each other, and when the film thickness and depth are approximately equal,
The magnitude of the reflectance is also the same.

An example of the manufacturing process of the surface acoustic wave resonator of this embodiment will be explained using FIG. 11.

First, as shown in FIG. 11(a), a real aluminum thin film 3' is deposited on the entire surface of the crystal substrate 1 by vapor deposition or sputtering.

Next, as shown in FIG. 11(b), a resist 12 is formed, and a photolithography technique is used to form a group 1o and a group (electrode fingers) 11, as shown in FIG. 11(c). After removing the aluminum thin film in the part, as shown in FIG. 2(d), the surface of the crystal substrate 1 in the part where the aluminum thin film was removed in the steps (b) and (c) is etched to have a width of λ/89. Groups 10.11 with a period λ/2 are formed. At this time, the resist 12 used in the steps (b) and (c) may be left as is and the crystal substrate 1 may be etched.
Peel off the aluminum thin film 3' to group 10.11
It is also possible to substitute the resists 1 to 1 during formation.

The crystal substrate 1 may be etched by wet etching using a solution such as hydrofluoric acid or antimony fluoride, or by dry etching using a gas such as CF4.

Next, as shown in FIG. 11(e), a new regimen 1 to
is coated, exposed and visualized, and finally the reflective slips 1 to 3 and electrode fingers 5 are coated with an aluminum thin film.
A resistor of -13 is left only in the part where . Next, as shown in FIG. 3(f), unnecessary portions of the aluminum thin film 3' are etched away using a resist 13 to form reflective strips 3 and electrode fingers 5.

-31: L7 In the manufacturing process, the strip 3. is made of aluminum thin film. Group 1 before electrode finger 5
0.11, but strips 3. The electrode fingers 5 may be formed first.

FIG. 12 shows only the grating reflector 6 of a surface acoustic wave resonator according to an embodiment that is a further modification of the embodiment shown in FIG. 5 and the surface of the crystal substrate 1 other than group 10 and group (electrode finger) 11,
This embodiment differs from the embodiment shown in FIG. 9 in that a very thin chromium or titanium film 14 of about several hundred layers is formed. Even with such a structure, the characteristics as a surface acoustic wave resonator are basically the same as those shown in FIG. 1.

FIG. 13 shows the manufacturing process of the surface acoustic wave resonator of FIG. 11. First, as shown in (a), a chromium or titanium thin film 14' and an aluminum thin film 3' are sequentially deposited on the entire surface of the crystal substrate 1. Formed by vapor deposition or sputtering. Next, as shown in FIG. 13(b), the thin films 3' and 14' in the regions where the groups 10.11 will finally be formed are removed by photolithography. And the 13th
As shown in Figure (C), a resist 15 is formed, and this resist 15 is used to form reflective slips 1-3 and electrode fingers 5 made of aluminum thin films by photolithography as shown in Figure (D). After R, a surface acoustic wave reflection group 10 is formed on the crystal substrate 1 using a chromium or titanium thin film 14 instead of the resist 1 as shown in FIG. 13(e).

The advantage of this embodiment is that group 10 in FIG. 13(e).
If etching of the crystal substrate 1 is performed by a dry process in the forming step 11, the groups 10 and 11 can be formed in depth one after another while monitoring the characteristics with the elastic surface and the plane wave resonator in operation. That is, it is possible to form groups 10 and 11 while monitoring characteristics such as resonance frequency and Q, and is extremely effective as a manufacturing method that allows trimming.

In addition to the embodiments described above, the present invention can be implemented with various modifications as follows.

26-For example, the gold thin film and aluminum thin film used in the examples are
There is no problem even if a trace amount of additives of several percent or less are included.

In particular, doping aluminum with 0.1 to 4% by weight of copper or silicon can suppress metal migration and contribute to improving the power resistance characteristics (excitation resistance strength) of the surface acoustic wave resonator.

Further, the aluminum thin film can be replaced with a silicon oxide thin film whose elastic properties closely resemble those of the aluminum thin film. Silicon oxide film is sputtered.

It can be formed by CVD method or the like. However, if a silicon oxide film is used for one surface acoustic wave reflector and electrode fingers, the other surface acoustic wave reflector (
strips) and electrode fingers must be made of conductive bamboo material, such as a thin gold film.

Furthermore, in the embodiments shown in FIGS. 9 and 12, a silicon single-crystal substrate made of the same silicon atoms may be used instead of the crystal substrate as the piezoelectric substrate, which means that surface acoustic waves propagating thereon may be used as piezoelectric substrates. On the other hand, any material may be used as long as the reflective strip made of an aluminum thin film or silicon oxide thin film has a positive reflection coefficient, and the reflective group has a negative reflection coefficient.

In addition, the line width of the strip used for the surface acoustic wave reflector and the electrode finger, or the width of the group, should be λ/8.
It does not need to be defined precisely; generally, the amount of reflection of surface acoustic waves is 10% of these line widths or group widths.
Since the amount of reflection changes by only 8% due to the deviation of
Deviations in width up to a certain degree are allowed.

Generally speaking, in each of the above embodiments, all two types of surface acoustic wave reflectors and electrode fingers are arranged without interruption, but this is not necessary, and any reflector can be used without changing the positional relationship. Even a structure in which the electrode fingers are thinned out does not change the gist of the present invention.

In other words, standing waves of surface acoustic waves caused by resonance,
A sudden shift in the positional relationship between the reflector and the electrode fingers is the cause of the generation of radiated bulk waves, so as long as the positional relationship is correct, even if any reflector or electrode finger is removed, the radiated bulk wave will still be generated. Wave generation will not increase significantly.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the structure of a surface acoustic wave resonator according to an embodiment of the present invention, and FIG. 2 is a perspective view showing the structure of a surface acoustic wave resonator according to an embodiment of the present invention. Figure 3 is a process diagram for explaining the manufacturing process of the surface acoustic wave resonator of the same example, and Figures 4 to 6 are A perspective view showing the configuration of the main parts in an embodiment modified from the embodiment shown in FIG. 1, and FIG. A diagram showing the film thickness dependence of the reflectance of a surface acoustic wave reflective strip.
FIG. 8 is a perspective view showing an embodiment in which the present invention is applied to a multi-port surface acoustic wave resonator, and FIG. 9 is a perspective view showing an embodiment in which groups are used as a surface acoustic wave reflector and a part of the electrode fingers. Figure 10 shows the film thickness dependence of the reflectance of the surface acoustic wave reflection l-slip and the group depth of the reflectance of the reflection group by the aluminum = 29-nium thin film formed on the quartz crystal substrate in the same example. FIG. 11 is a process diagram for explaining the manufacturing process of the surface acoustic wave resonator of the embodiment shown in FIG. 9, and FIG. 12 is a diagram showing the dependence on A perspective view showing the configuration of the main parts, FIG. 13 is a process diagram for explaining the manufacturing process of the surface acoustic wave resonator of the embodiment shown in FIG. 12, and FIGS. 1 is a perspective view showing the basic configuration of a wave resonator and a sectional view of a portion of its grating reflector. 1... Piezoelectric substrate, 2... Surface acoustic wave reflecting strip (surface acoustic wave reflector) made of a gold thin film. , 3... Surface acoustic wave reflecting slip I/slip (surface acoustic wave reflector) made of aluminum thin film, 4... Electrode finger made of gold thin film, 5...
Electrode fingers made of aluminum thin film, 6... grating reflector, 7... interdigital converter, 8...
Mask alignment mark, 9... Shield electrode, 10...
- Group (surface acoustic wave reflector), 11... Group (electrode finger), 12.13... Resist, 14... Chromium or titanium thin film, 15... Resist 1-. . Figure 2 Figure 3 Figure 6 Figure 7 Figure 10 Figure 11 Figure 12 Figure 13

Claims (7)

[Claims] (1) In a surface acoustic wave resonator comprising a plurality of grating reflectors and at least one interdigital transducer formed between these grating reflectors on a piezoelectric substrate, the gray The Teing reflector comprises alternating two types of surface acoustic wave reflectors on the piezoelectric substrate, each of which has positive and negative reflection coefficients for surface acoustic waves propagating on the substrate, and at least one of which is made of a conductive material. The interdigital transducer is configured such that the two types of reflectors and the two types of electrode fingers having the same structure are arranged alternately at a period of 1/4 of the wavelength of the surface acoustic wave. and a reflector at an end of the grating reflector facing the interdigital converter; The center-to-center spacing between the electrode fingers at the opposing ends is approximately 1/1/2 of the wavelength of the surface acoustic wave.
4. A surface acoustic wave resonator characterized in that the surface acoustic wave resonator is set to 4. (2) A crystal substrate is used as the piezoelectric substrate, and one of the two types of surface acoustic wave reflectors having a positive reflection coefficient is formed of a thin film mainly composed of aluminum, and has a negative reflection coefficient. 2. The surface acoustic wave resonator according to claim 1, wherein the reflector is formed of a thin film containing gold as a main component. (3) A surface acoustic wave according to claim 1 or 2, characterized in that a 105°±10° rotated Y plate is used as the piezoelectric substrate, and a pseudo surface acoustic wave is used as the vibration mode. resonator. (4) Using a LiTaO_3 substrate as a piezoelectric substrate,
Of the two types of surface acoustic wave reflectors, the reflector having a positive reflection coefficient was formed from a thin film containing aluminum as a main component, and the reflector having a negative reflection coefficient was formed from a thin film containing gold as a main component. Claim 1 characterized in that
The surface acoustic wave resonator described in . (5) A crystal substrate is used as the piezoelectric substrate, and one of the two types of surface acoustic wave reflectors having a positive reflection coefficient is formed of a thin film mainly composed of aluminum or a silicon oxide thin film, and a negative 2. The surface acoustic wave resonator according to claim 1, wherein the reflector having a reflection coefficient is formed by a group on the crystal substrate. (6) Using a silicon single crystal substrate as a piezoelectric substrate,
Of the two types of surface acoustic wave reflectors, the reflector having a positive reflection coefficient is formed of a thin film mainly composed of aluminum or a silicon oxide thin film, and the reflector having a negative reflection coefficient is formed on the silicon single crystal substrate. A surface acoustic wave resonator according to claim 1, characterized in that the surface acoustic wave resonator is formed by a group of: (7) The thin film mainly composed of an aluminum thin film is a thin film in which aluminum is doped with at least one of copper and silicon.
The surface acoustic wave resonator according to any one of Item 6.