JPH0640610B2 - Surface acoustic wave resonator - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a resonator to which surface acoustic waves are applied.

[Technical background of the invention and its problems]

The substrate structure of a surface acoustic wave resonator that has been widely known in the past is based on the invention by Clinton Sylvester Hartmann et al. (Japanese Patent Publication No. 56-46289). That is, as shown in FIG. 14, assuming that the wavelength of the surface acoustic wave propagating on the substrate 21 is λ, a large number of surface acoustic wave reflection strips 22 having a width λ / 4 are provided on the piezoelectric substrate 21. Two
Grating reflectors 26 arranged in a cycle and having a width λ
An in-digital converter 27 including / 4 electrode fingers 23 is provided and configured.

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 reflectors 1 such as strips, ridges, and groups
When the reflectance ε per line is large, the number of reflectors may be small, but as ε becomes smaller, a large number of reflectors are required. Peter Cross, Document 1: IEEE Tran
s.on Sonics & Ultrason. (vol su-23, N0.4pp.255-26
2) In 1976, it is stated that the number of reflectors in the grating reflector must be N≈3 / ε or more to obtain a sufficient reflection amount. This means that for a reflector of ≈0.01, a large number of 300 or more is required,
Generally, considering that two or more grating reflectors are used in a resonator, there is a problem that the entire resonator becomes very large.

On the other hand, if the strip thickness, ridge height, and group depth are increased in order to increase ε per reflector, the mode conversion from surface acoustic wave to bulk wave increases accordingly. The conversion loss causes the Q of the resonator to decrease.

As a means for solving these problems, the inventors of the present invention have conducted an ultrasonic research group of the Institute of Electronics and Communication Engineers (reference 2: Technical Report US84
-30 September 1984), a grating reflection in which two types of reflectors having a λ / 8 width and a reflection coefficient opposite to each other with respect to the surface wave wavelength λ of the used frequency are alternately arranged at a λ / 4 period. I suggest a vessel. In the grating reflector having this structure, the reflected wave at the reflector having a positive reflection coefficient and the reflected wave at the reflector having a negative reflection coefficient are added, so that the reflector has a λ / 2 cycle. The amount of reflection per unit length is almost doubled as compared with the arranged conventional general grating reflector. On the other hand, the loss of mode conversion to bulk wave is only 1.4 times. Therefore, when the amount of reflection is the same as that of the conventional general one, the mode conversion loss to the bulk wave is reduced.

However, the effect of suppressing the mode conversion loss to the bulk wave in the grating reflector occurs only in the central portion 24 as shown in FIG. 14 (b), and near the end portion 25 facing the interdigital converter. No suppression effect is obtained. That is, in the central portion 24 of the grating reflector in which the reflectors are periodically arranged at λ / 4 period, the radiated bulk waves are canceled out because the acoustic impedance can be regarded as a substantially infinite period, while the grating reflector is cancelled. At the end portion 25, the distance between the electrode fingers of the adjacent interdigital converters is λ / 4 or less, which is different from the reflector array period at the central portion of the grating reflector, and the acoustic impedance cannot be regarded as an infinite period. Because it disappears
The radiated bulk wave remains, resulting in mode conversion loss.

In this way, a grating reflector that combines reflectors with positive and negative reflection coefficients has high reflection efficiency and can be miniaturized, and there is little mode conversion loss from surface acoustic wave to bulk wave inside the reflector. However, the mode conversion loss at the end of the reflector could not be suppressed, which was a major obstacle to the realization of a surface acoustic wave resonator having a high Q.

[Object of the Invention]

The present invention has been 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 cycle of ¼ of the surface acoustic wave wavelength. Using a high-grating reflector and effectively suppressing the mode conversion loss from the surface acoustic wave to the bulk wave not only inside the grating reflector but also at the end, it is a small surface acoustic wave with a high Q value. The purpose is to provide a resonator.

[Outline of Invention]

The present invention provides a surface acoustic wave resonator having a plurality of grating reflectors and at least one interdigital converter formed between the grating reflectors on a piezoelectric substrate. Two types of surface acoustic wave reflectors having positive and negative reflection coefficients for the surface acoustic wave and at least one of which is made of a conductive material are alternately arranged on the piezoelectric substrate, and the surface acoustic wave has a wavelength of ¼ of the surface acoustic wave. The interdigital transducers are arranged in a periodic manner, and the electrode fingers cross each other at a half period of the wavelength of the surface acoustic wave. The interdigital converter has the same structure as the two kinds of reflectors used in these grating reflectors. A reflector at the end facing the interdigital converter of the grating reflector, which is configured by alternately arranging the electrode fingers of the seed and at a period of about 1/4 of the wavelength of the surface acoustic wave. The center-to-center spacing between the electrode fingers at the ends facing the grating reflector of the interdigital transducer, and wherein the set to 1/4 of a wavelength of approximately SAW.

〔The invention's effect〕

In the surface acoustic wave resonator according to the present invention, the grating reflector has two kinds of surface acoustic wave reflectors having positive and negative reflection coefficients alternately arranged on the piezoelectric substrate at a period of ¼ of the surface acoustic wave wavelength. , And the electrode finger is 1/2 the wavelength of the surface acoustic wave.
Since it has a basic structure of intersecting with each other at a period of, the reflection waves from these two reflectors are added, so that a high reflection efficiency is obtained. That is, the reflection amount of the surface acoustic wave per unit length increases, and the mode conversion loss from the surface acoustic wave to the bulk wave inside the grating reflector is relatively reduced.

Further, in the present invention, the structure of the reflector in the grating reflector and the electrode fingers in the interdigital converter are the same, and the arrangement periods of the reflector and the electrode fingers are substantially the same, and the grating reflector and the interdigital converter are the same. Since the center-to-center spacing between the reflector and the electrode finger at the boundary of the digital converter is also almost equal to the array period of the reflector and the electrode finger, the acoustic perturbation effect over the entire area where the surface acoustic wave is confined as a standing wave. The synchronism of is maintained. That is, the acoustic impedance can be regarded as an infinite period not only inside the grating reflector but also at the end of the grating reflector. Therefore, the conversion loss of the surface acoustic wave into the bulk wave is suppressed not only inside the grating reflector but also at the end of the grating reflector,
The Q of the resonator can be effectively increased.

As described above, according to the present invention, a small-sized surface acoustic wave resonator having a high Q value is realized.

Example of Invention

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the structure of a surface acoustic wave resonator according to an embodiment of the present invention, which propagates on a quartz substrate 1 made of a 32 ° rotating Y plate as a piezoelectric substrate. The wavelength of the surface acoustic wave is λ, and the film thickness is λ / 200 (100 MHz
In the case of, the first surface acoustic wave reflection strip 2 made of a gold thin film of 1600 Å) and the film thickness λ / 50 (100
In the case of MHz, the second surface acoustic wave reflection strips 3 made of an aluminum thin film of 6400 Å) are alternately arranged with a λ / 4 period to provide two grating reflectors 6, and these grating reflectors 6 Electrode fingers of the same structure as the first and second surface acoustic wave reflection strips 2 and 3, that is, the first electrode fingers 4 made of a gold thin film having a line width λ / 8 and a film thickness λ / 200. And the line width λ / 8
The second electrode finger 5 made of an aluminum thin film with a thickness of λ / 50
An inter-digital converter 7 consisting of and is provided. Further, the first electrode fingers 4 and the second electrode fingers 5 in the interdigital converter 7 are alternately arranged at a cycle of λ / 4 as shown in the figure, and intersect at a cycle of λ / 2. .

More specifically, each grating reflector 6
The total number of the first and second surface acoustic wave reflection strips 2 and 3 in is, for example, 150, and in this case, the length of the grating reflector 6 in the surface acoustic wave propagation direction is
It is 75λ. On the other hand, the total number of the first and second electrode fingers 4 and 5 in the interdigital converter 7 is 100, and the array period is strictly a grating reflector in order to obtain a good resonance state. It is shortened by about 5% with respect to the arrangement period (λ / 4) of the reflecting strips within 6. Further, a reflection strip (2 or 3) which is an end of the grating reflector 6 facing the interdigital converter 7, and an electrode finger (4 or 5) at an end of the interdigital converter 7 facing the grating reflector 6 )
The center-to-center spacing between and is set to approximately 1/4 of the wavelength of the surface acoustic wave. When the array period of the electrode fingers 4 and 5 in the interdigital converter 7 is generalized and shown, when the length (propagation path length) in the surface acoustic wave propagation direction of the interdigital converter 7 is nλ, λ / 4 · That is (1-1 / 4n).

The thickness dependence of the reflectance of the surface acoustic wave reflection strip formed by the gold thin film and the aluminum thin film formed on the quartz substrate is shown by the solid line and the broken line in FIG. As can be seen, the reflectance is negative for the reflection strip made of the gold thin film and positive for the reflection strip made of the aluminum thin film, and the film thickness dependence is 4 for the gold thin film as compared to that for the aluminum thin film. Twice as big. Therefore, in order to obtain 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.

Further, in the above description, the cut angle of the quartz substrate 1 is selected so that the apex temperature is near room temperature with the gold thin film and the aluminum thin film formed on the surface. It is necessary to make a corresponding decision.

With such a structure, the reflectance of the surface acoustic wave per unit length in the grating reflector 6 is increased, which enables downsizing, and at the same time, the grating reflector 6 and the interdigital converter 7 Since the reflecting strips and the electrode fingers are present at approximately λ / 4 period all over, bulk waves are well suppressed and a resonator having a high Q is obtained.

This effect will be described more specifically. The surface acoustic wave resonator of this embodiment and the conventional structure λ / 4 shown in FIG.
The aluminum strip thin film of thickness and the electrode fingers are used for the grating reflector and interdigital converter, and the thickness of the aluminum thin film is λ / 50, the number of surface acoustic wave reflection strips is 150, and the number of electrode fingers is 100. Comparing the Q value with a surface acoustic wave resonator manufactured under the same conditions as in the example, the Q value in this embodiment exceeds 20000, whereas the Q value in the conventional structure is 10000 or less, and the Q value is 2
A more than double improvement was observed.

On the other hand, as a comparative example, the grating reflector is composed of a reflecting strip made of an aluminum and gold thin film as in the case of this embodiment, and the interdigital converter has a λ as in the conventional case.
A surface acoustic wave resonator using electrode fingers made of / 4 line width aluminum thin film was prototyped, but in this case also, Q did not exceed 15,000.

The reason why the surface acoustic wave resonator configured by using the reflection strip and the electrode fingers made of the aluminum thin film has a low Q is that the reflectance is not sufficiently high only by the reflection strip made of the aluminum thin film. Is likely to leak out of the grating reflector and increase the loss. In order to improve Q, the number of reflective strips needs to be 200 to 300, but in that case, the size of the resonator becomes extremely large as described above.

Further, in the surface acoustic wave resonator of the comparative example in which the interdigital converter is composed only of the electrode fingers made of the aluminum thin film, the grating reflector is made of the reflecting strip made of the aluminum and gold thin films, so that the reflection efficiency is sufficient. The loss due to surface acoustic waves leaking out of the grating reflector is also greatly reduced, but the synchronicity of the acoustic perturbation effect is significantly different at the boundary between the interdigital converter and the grating reflector. Therefore, there is a mode conversion loss of the surface acoustic wave into the radiated bulk wave, and Q is not sufficiently improved as described above.

On the other hand, in the example of the present invention, the acoustic perturbation effect of the reflective strip and the electrode fingers is sufficiently maintained over the entire area where the surface acoustic wave is confined as a standing wave. It is considered that the mode conversion loss to the radiated bulk wave is suppressed to a small value, and thereby the Q value is greatly increased.

To what extent the uniformity of the arrangement period of the reflecting strips and the electrode fingers is allowed, for example, if the uniformity at the boundary is shifted, that is, the reflecting strip at the end of the grating reflector and the When the distance between the centers of the electrodes of the digital converter and the electrode fingers is shifted from λ / 4, the effect of the present invention is sufficient up to about 5%, and when it exceeds 10%, the effect of suppressing mode conversion loss at the boundary is achieved. It was confirmed that the

Next, an example of a manufacturing process of the surface acoustic wave resonator shown in FIG. 1 will be described with reference to FIG.

First, as shown in FIG. 3 (a), on the entire surface of the quartz substrate 1,
A gold thin film 2'is attached by vapor deposition or sputtering. At this time, the gold thin film 2'for the purpose of improving the adhesiveness.
An underlayer consisting of an extremely thin layer of chrome or titanium may be attached underneath.

Next, as shown in FIG. 3 (b), a first surface acoustic wave reflection strip 2 and a first electrode finger 4 made of a gold thin film having a line width λ / 8 and a period λ / 2 are formed by a photolithography technique.
To form. If there are underlying layers, they are also removed by etching at the same time as the gold thin film.

Then, as shown in FIG. 3 (c), an aluminum thin film 3'is deposited on the entire surface by vapor deposition, sputtering, or the like so as to have a thickness approximately four times that of the gold thin film 2 '. At this time, the surface of the aluminum thin film 3'is sufficiently flat because the film thickness of the first surface acoustic wave reflection strip 2 made of the gold thin film located therebelow is 1/20 or less of the line width, which is extremely small.

Then, as shown in FIG. 3D, the second surface acoustic wave reflection strip 3 and the second surface acoustic wave reflection strip 3 made of an aluminum thin film having a line width λ / 8 and a period λ / 2 are formed by photolithography.
The electrode finger 5 is formed so as to be located substantially in the middle of each of the first surface acoustic wave reflection strip 2 made of a gold thin film and the first electrode finger 4. The aluminum thin film 3 '
When the film is formed, the first surface acoustic wave reflection strip 2 and the first electrode finger 4 formed by the gold thin film thereunder cannot be seen. Therefore, for the purpose of facilitating mask alignment in the step of FIG. 3 (d), In the step of FIG. 3 (b), the mark 8 for mask alignment is formed outside the area where the grating reflector is formed, and in the step of FIG. 3 (c), at least the mark 8 on the quartz substrate 1 is formed. It is necessary that the exposed area is not covered with the aluminum thin film.

FIG. 4 shows a modified embodiment of the grating reflector 6 in the embodiment of FIG. 1, in which the first and second surface acoustic wave reflection strips 2 and 3 are electrically short-circuited,
And they are also electrically connected to each other. When the piezoelectric substrate is the quartz substrate 1, since the electromechanical coupling coefficient is very small, even if the surface acoustic wave reflection strips 2 and 3 are electrically short-circuited in this way, they are electrically opened in operation. It is almost the same as the case of. The same applies when only one of the first and second surface acoustic wave reflection strips 2 and 3 is electrically short-circuited, or when both are short-circuited but not electrically connected to each other. Is.

In the above embodiment, the crystal substrate 1 is rotated by 32 °
Although it has been described that a plate is used, it is not necessarily limited to this angle, and a quartz substrate having another cutting angle can achieve the intended object of the present invention by slightly changing the film thickness ratio of the gold thin film and the aluminum thin film. You can In addition, when it is called a surface acoustic wave, it generally refers to a Rayleigh wave, but it is not necessarily limited to this vibration mode, for example, −50.5 of a quartz substrate.
The present invention can also be applied to a pseudo surface acoustic wave propagating on a ° rotation Y plate at right angles to the X axis, a 105 ° ± 10 ° rotation Y plate, and a surface acoustic wave resonator using a pseudo surface wave propagating on the X axis. In particular, in the case of pseudo surface acoustic waves, there are many modes in which some of the energy is radiated inside the substrate in the propagation path where nothing exists on the surface.
However, if there is a periodic perturbation such as a reflective strip or an electrode finger on the surface, energy tends to concentrate on the surface and not radiate. On the other hand, since the surface acoustic wave resonator according to the present invention has a structure in which the periodic perturbation exists in all regions where the pseudo surface acoustic wave exists, the pseudo surface acoustic wave which cannot be realized with a large Q in the related art is used. Also in the surface acoustic wave resonator described above, there is an advantage that a high Q can be achieved.

Furthermore, although a quartz substrate is used in all of the above explanations, the same effect can be obtained by using a LiTaO ₃ substrate, for example.
FIG. 5 shows only the portion of the grating reflector 6 for explaining the embodiment. A LiTaO ₃ substrate 1 is used instead of a quartz substrate as a piezoelectric substrate, and a gold thin film is formed on this substrate 1. A first surface acoustic wave reflecting strip 2 and a second surface acoustic wave reflecting strip 3 made of an aluminum thin film are formed. In this case, the crystal substrate may be basically the same, but the LiTaO ₃ substrate has a larger electro-mechanical coupling coefficient than that of the crystal substrate, and thus the first surface acoustic wave reflection by the gold thin film is as shown in the figure. Although the strip 2 has an electrically isolated shape, it is more desirable to electrically short-circuit the second surface acoustic wave reflection 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 gold thin film are electrically isolated and the electrode fingers 5 made of an aluminum thin film are electrically short-circuited, as shown in FIG. Also in this case, the first electrode fingers 4 and the second electrode fingers 5 in the interdigital converter 6 are alternately arranged at a cycle of λ / 4 and intersect at a cycle of λ / 2. To do.

The reflectance per strip of the surface acoustic wave reflection strip having a line width of λ / 8 formed by the gold and aluminum thin films on the LiTaO ₃ substrate (X-cut 112 ° Y plate) was examined, and as shown in FIG. Are opposite phases to each other, and the film thickness of the reflectance is about twice as large as that of the gold thin film as compared to that of the aluminum thin film. However, as shown in FIG. 5, this characteristic is obtained when the first surface acoustic wave reflection strip 2 made of a gold thin film is electrically opened and the second surface acoustic wave reflection strip 3 made of an aluminum thin film is electrically short-circuited. Is. According to this, the film thickness of the first surface acoustic wave reflection strip 2 made of a gold thin film is about 1 / each of that of the second surface acoustic wave reflection strip 3 made of an aluminum thin film.
2 is good.

In the above embodiments, the one-port surface acoustic wave resonator having one interdigital converter has been described.
The present invention can be applied to a multi-port surface acoustic wave resonator having a plurality of interdigital converters 7 as shown in FIG. In this case, a shield electrode 9 having the same structure as the grating reflector 6 is provided between both interdigital converters 7.
It is also conceivable to provide (or a coupling electrode).

FIG. 9 shows a surface acoustic wave resonator according to another embodiment of the present invention, which has a line width λ / 8 on a quartz substrate 1 made of a 36 ° rotating Y plate as a piezoelectric substrate. Film thickness λ / 50
A surface acoustic wave reflection strip 3 made of an aluminum thin film (corresponding to 6400Å in the case of 100 MHz) and a concave portion formed by removing the surface of the substrate 1 to the same size, that is, a width λ.
A surface acoustic wave reflection group 10 having a width of / 8 and a surface acoustic wave reflection group 10 having a depth of λ / 50 is alternately arranged at a period of λ / 4.
An interdigital converter 7 consisting of electrode fingers 5 and 11 having the same structure as the above-mentioned reflective strip 3 and reflective group 10 is provided between them.

The thickness dependence of the reflectance of the surface acoustic wave reflection strip by the aluminum thin film formed on the quartz substrate and the dependence of the reflectance of the surface acoustic wave reflection group on the group depth are shown by the solid line and the broken line in FIG. Indicated. As can be seen, the reflectivity is positive for the aluminum strip and negative for the reflective group.
Moreover, when the film thickness and the depth are almost the same, the magnitudes of the reflectances are also the same.

An example of the manufacturing process of the surface acoustic wave resonator of this embodiment will be described with reference to FIG.

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

Next, as shown in FIG. 11B, a resist 12 is formed, and finally a group 10 and a group (electrode fingers) are formed by a photolithography technique as shown in FIG.
By removing the aluminum thin film in the portion to be 11 and subsequently etching the surface of the quartz substrate 1 in the portion where the aluminum thin film is removed in the steps (b) and (c) as shown in FIG. Groups 10 and 11 each having λ / 8 and a period λ / 2 are formed. At this time, the quartz substrate 1 may be etched while leaving the resist 12 used in the steps (b) and (c) as it is, but the resist 12 is peeled off to form the aluminum thin film 3 ′ when the groups 10 and 11 are formed. Etching of the quartz substrate 1, which may be used as a resist, may be wet etching with a solution of hydrofluoric acid, antimony fluoride or the like, or dry etching using a gas such as CF ₄ .

Next, as shown in FIG. 11E, a resist is newly coated, exposed and developed, and the resist 13 is left only in the portions where the reflective strip 3 and the electrode fingers 5 of the aluminum thin film are finally formed. Next, as shown in FIG. 3 (f), unnecessary portions of the aluminum thin film 3'are etched and removed using the resist 13 to form the reflective strips 3 and the electrode fingers 5.

In the manufacturing process described above, the groups 10 and 11 are formed before the strip 3 and the electrode finger 5 made of an aluminum thin film, but the strip 3 and the electrode finger 5 may be formed first.

FIG. 12 shows only a part of the grating reflector 6 of the surface acoustic wave resonator according to an embodiment obtained by further modifying the embodiment shown in FIG. 9, and the lower part of the reflecting strip 3 and the electrode finger 5 made of an aluminum thin film. And on the surface of the crystal substrate 1 other than the groups 10 and 11 (electrode fingers) 11,
This embodiment differs from the embodiment shown in FIG. 9 in that a chromium or titanium thin film 14 having an extremely thin film thickness of about 100 Å is formed. Even with such a structure, the characteristics of the surface acoustic wave resonator are basically the same as those shown in FIG.

FIG. 13 shows a manufacturing process of the surface acoustic wave resonator shown in FIG. 11. First, as shown in (a), a chromium or titanium thin film 14 ′ and an aluminum thin film 3 ′ are sequentially formed on the entire surface of the quartz substrate 1. It is 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 and 11 are finally formed are removed by photolithography. Then, a resist 15 is formed as shown in FIG. 13 (c), and the resist 15 is used to form the reflective strip 3 and the electrode finger 5 made of an aluminum thin film by the photolithography method in FIG. 13 (d). Finally, as shown in FIG. 13 (e), a chromium or titanium thin film 14 is used instead of the resist,
The surface acoustic wave reflection group 10 is formed on the crystal substrate 1.

The advantage of this embodiment is that the group 10 in FIG.
If the crystal substrate 1 is etched by a dry process in the step of forming 11, the groups 10 and 11 can be sequentially formed deeper while monitoring the characteristics while the surface acoustic wave resonator is operating. That is, the groups 10 and 11 can be formed while monitoring the characteristics such as the resonance frequency and the Q, which is extremely effective as a manufacturing method capable of trimming.

The present invention can be implemented by variously modifying as follows other than the embodiment described above.

For example, the gold thin film and aluminum thin film used in the examples are
It does not matter even if a trace amount of additive of several% or less is contained.
In particular, if aluminum is doped with copper or silicon in an amount of 0.1 to 4% by weight, metal migration can be suppressed, and the power withstand characteristics (excitation strength) of the surface acoustic wave resonator can be improved.

Further, the aluminum thin film can be replaced with a silicon oxide thin film whose elastic property is very similar to that of the aluminum thin film. The silicon oxide film can be formed by sputtering, CVD method or the like. However, when a silicon oxide film is used for one surface acoustic wave reflector and electrode fingers, the other surface acoustic wave reflector (strip) and The electrode fingers need to be formed of a conductive material such as a gold thin film.

Further, in the embodiment shown in FIGS. 9 and 12, a silicon single crystal substrate composed of the same silicon atoms may be used as the piezoelectric substrate instead of the quartz substrate. In short, a surface acoustic wave propagating on the substrate may be used. On the other hand, any material may be used as long as the reflection strip made of an aluminum thin film or a silicon oxide thin film has a positive reflection coefficient and the reflection group has a negative reflection coefficient.

Also, regarding the line width of the strip used for the surface acoustic wave reflector and the electrode fingers, or the width of the group, λ / 8
It is not necessary to be specified accurately, and generally, for these line widths or group widths, the reflection amount of surface acoustic waves changes by 8% with a deviation of 10%, so up to several tens of% Deviations in width are allowed.

Furthermore, 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 always necessary, and any reflector and Even the structure in which the electrode fingers are thinned out does not change the gist of the present invention. That is, because the standing wave of the surface acoustic wave generated by the resonance and the positional relationship between the reflector and the electrode finger are abruptly displaced are the causes of the radiated bulk wave, so if only the positional relationship is correctly arranged, The generation of radiated bulk waves does not increase significantly if any reflector or electrode finger is removed.

[Brief description of drawings]

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 surface acoustic wave reflection strip made of a gold and aluminum thin film formed on a quartz substrate in FIG. FIG. 3 is a view showing the film thickness dependence of reflectance, FIG. 3 is a process drawing for explaining the manufacturing process of the surface acoustic wave resonator of the same embodiment, and FIGS. 4 to 6 are the embodiments of FIG. FIG. 7 is a perspective view showing the structure of the main part of the modified embodiment, and FIG. 7 shows the reflectance of the surface acoustic wave reflection strip formed by the gold and aluminum thin films formed on the LiTaO ₃ substrate used in FIGS. 5 and 6. FIG. 8 is a diagram showing the film thickness dependence, 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 groove on a surface acoustic wave reflector and a part of an electrode finger. FIG. 10 is a perspective view showing an embodiment using the same, FIG. And FIG. 11 shows the dependence of the reflectance of the surface acoustic wave reflection strip by the aluminum thin film formed on the quartz substrate on the film thickness and the dependence of the reflectance of the reflection groove on the groove depth in FIG. FIG. 12 is a perspective view showing the construction of the main part in an embodiment in which the embodiment of FIG. 9 is modified, and FIG. 13 is FIG. 14 (a) and 14 (b) are perspective views showing the basic structure of a conventional surface acoustic wave resonator and a grating reflector of the same. It is a sectional view of a part. 1 ... Piezoelectric substrate, 2 ... Surface acoustic wave reflection strip (surface acoustic wave reflector) made of gold thin film, 3 ... Surface acoustic wave reflection strip made of aluminum thin film (surface acoustic wave reflector), 4 ... Gold thin film Electrode fingers by 5 ... Electrode fingers by aluminum thin film, 6 ... Grating reflector, 7 ...
... interdigital converter, 8 ... mask alignment mark, 9 ... shield electrode, 10 ... groove (surface acoustic wave reflector), 11 ... groove (electrode finger), 12, 13
...... Resist, 14 …… Chromium or titanium thin film, 15
…… Resist.

Continued Front Page (72) Hiroaki Sato Inventor Hiromu Sato 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Inside the Toshiba Research Institute Co., Ltd. (56) References IEICE Technical Report US84-30 “Having positive and negative reflection coefficients” Surface acoustic wave grating reflector and resonator consisting of reflective elements "

Claims (7)

[Claims] 1. A surface acoustic wave resonator having a plurality of grating reflectors and at least one interdigital converter formed between the grating reflectors on a piezoelectric substrate. The reflector has two kinds of surface acoustic wave reflectors, which have positive and negative reflection coefficients with respect to surface acoustic waves propagating on the piezoelectric substrate and at least one of which is made of a conductive material, and alternately. The interdigital converter is formed by arranging at a period of ¼ of the wavelength of the surface acoustic wave, and the interdigital converter alternately includes two kinds of electrode fingers having the same structure as the two kinds of surface acoustic wave reflectors, and The electrodes are arranged at a cycle of ¼ of the wavelength of the surface acoustic wave, and the electrode fingers are arranged to intersect at a cycle of ½ of the wavelength of the surface acoustic wave. Distance between the surface acoustic wave reflector at the end facing the reflector and the electrode finger at the end facing the grating reflector of the interdigital converter is 1/4 of the wavelength of the surface acoustic wave. A surface acoustic wave resonator characterized by being set. 2. A quartz substrate is used as a piezoelectric substrate, and a reflector having a positive reflection coefficient of the two types of surface acoustic wave reflectors is formed of a thin film containing aluminum as a main component.
The surface acoustic wave resonator according to claim 1, wherein the reflector having a negative temperature coefficient is formed of a thin film containing gold as a main component. 3. The piezoelectric substrate is rotated 105 ° ± 10 ° Y
The surface acoustic wave resonator according to claim 1 or 2, wherein a plate is used and a pseudo surface acoustic wave is used as a vibration mode. 4. A LiTaO ₃ substrate is used as the piezoelectric substrate, and a reflector having a positive reflection coefficient of the two types of surface acoustic wave reflectors is formed of a thin film containing aluminum as a main component, and a negative The surface acoustic wave resonator according to claim 1, wherein the reflector having a reflection coefficient is formed of a thin film containing gold as a main component. 5. A quartz substrate is used as the piezoelectric substrate,
A reflector having a positive reflection coefficient of the two types of surface acoustic wave reflectors is formed of a thin film containing aluminum as a main component or a silicon oxide thin film, and a reflector having a negative reflection coefficient is formed on the quartz substrate. The surface acoustic wave resonator according to claim 1, wherein the surface acoustic wave resonator is formed of a group. 6. A silicon single crystal substrate is used as the piezoelectric substrate, and a reflector having a positive reflection coefficient of the two types of surface acoustic wave reflectors containing aluminum as a main component or a silicon oxide thin film. The surface acoustic wave resonator according to claim 1, wherein the reflector having a negative reflection coefficient is formed by a groove on the silicon single crystal substrate. 7. The thin film containing aluminum as a main component,
The surface acoustic wave resonator according to any one of claims 2 to 6, which is a thin film in which aluminum is doped with at least one of copper and silicon.