JPH0946169A - Surface acoustic wave element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily obtain a SAW device with a desired characteristic by adopting a gentle shape for a cross section of a reflecting groove end. SOLUTION: An input electrode 3 and a reflection groove 11 of a surface acoustic wave element 1 are formed on a piezoelectric substrate 2. A gentle projection is adopted for the shape of cross section of the input electrode 3. A gentle shape is adopted for the cross section of a groove end 11a of the reflection groove 11. Through the gentle shape adopted for the cross section of the end of the input electrode 3 and the groove end 11a of the reflection groove 11, reflection opportunity of the generated surface acoustic wave at the end face of the electrode 3 is decreased and the opportunity of the conversion of the confined surface acoustic wave into a bulk wave at the groove end is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device, and more particularly to the structure of its electrode.

[0002]

2. Description of the Related Art Conventionally, SAW (surf using surface acoustic waves)
As a method of reducing the loss in the ace acoustic wave device, an interdigital transducer (ID) is used.
T) is a method of unidirectionalizing itself, and ITD is bidirectional and a method of reducing loss by a reflector or other means (resonator filter or the like) is known.

A resonator type surface acoustic wave element 50 using a resonator filter is shown in FIG. Resonator type surface acoustic wave element 50
The input side electrode 3 and the output side electrode 5 are provided on the substrate surface, and the reflection electrode 7 and the reflection electrode 8 are provided on both sides of the both electrodes. Resonator type surface acoustic wave element 50
In, the surface acoustic waves generated at the input side electrode 3 and the output side electrode 5 are repeatedly reflected between the reflection electrodes 7 and 8 to become a standing wave. In this way, the loss can be reduced by providing the reflection electrodes 7 and 8 in the portion corresponding to the antinode of the standing wave.

[0004]

However, the resonator type surface acoustic wave element 50 has the following problems. With higher frequency, electrodes are becoming finer and thinner. The reflection electrodes 7 and 8 may be destroyed by the stress generated during reflection.

In order to prevent such damage of the reflection electrode due to stress, it is possible to form a reflection groove instead of the reflection electrode as shown in FIG. However, a separate photolithography process is required for such a reflection groove forming process.

In addition, the reflection groove 11,
When forming 12, sputter etching is generally performed. At the time of this sputter etching, the heat generated may harden the resist and make it impossible to peel it off, or the resist may peel off to form a groove at an unnecessary portion.

Further, in the etching using the photoresist, as shown in FIG.
The groove ends of 1 and 12 have a steep shape. Therefore, the surface acoustic wave to be confined may be converted into a bulk wave at the groove end portion and may be attenuated. It is an object of the present invention to provide a surface acoustic wave element and a method for manufacturing the same, which are free from such attenuation.

[0008]

According to another aspect of the surface acoustic wave device of the present invention, the reflection groove has a cross-sectional shape in which the groove end is gentle.

In the surface acoustic wave device according to a second aspect of the present invention, the electrode is made of one or more metals.
At least one of the metals forming the electrode is characterized in that a cross section in a direction perpendicular to the substrate has a gentle convex shape.

In the method of manufacturing a surface acoustic wave device according to a third aspect of the present invention, when the electrode is formed on the surface of the substrate, the focused ion beam is selectively irradiated on the surface of the substrate with energy capable of vapor deposition, When forming a reflection groove for reflecting a surface acoustic wave generated on the surface of the substrate, the focused ion beam is selectively irradiated on the surface of the substrate with energy capable of forming the groove.

In the method of manufacturing a surface acoustic wave device according to a fourth aspect, the speed is reduced near the surface of the substrate,
The focused ion beam is irradiated with energy capable of vapor deposition.

[0012]

In the surface acoustic wave device according to the first aspect of the present invention, the cross-sectional shape of the reflection groove has a gentle groove end. Therefore, the confined surface acoustic waves are less likely to be converted into bulk waves at the groove ends, and the wave attenuation is reduced. This makes it possible to easily provide a surface acoustic wave device having desired characteristics.

In the surface acoustic wave device according to a second aspect of the present invention, the electrode is made of one or more metals.
At least one of the metals forming the electrode has a gentle convex cross section in a direction perpendicular to the substrate. Therefore, the generated surface acoustic waves are less reflected on the end faces of the electrodes and are transmitted on the substrate surface. As a result, it is possible to easily obtain a surface acoustic wave element having desired characteristics.

In the method of manufacturing a surface acoustic wave device according to a third aspect of the present invention, when the electrode is formed on the surface of the substrate, the focused ion beam is selectively applied to the surface of the substrate with vaporizable energy. . On the other hand, in the case of forming a reflection groove for reflecting the surface acoustic wave generated on the surface of the substrate, the focused ion beam is formed with groove formable energy,
The surface of the substrate is selectively irradiated. Therefore,
The electrodes and the reflection grooves can be formed only by irradiating the focused ion beams having different energies. This makes it possible to easily provide a surface acoustic wave device having desired characteristics.

In the method of manufacturing a surface acoustic wave device according to a fourth aspect, by decelerating near the surface of the substrate,
The focused ion beam is irradiated with energy that can be deposited. Therefore, it is possible to irradiate the focused ion beam at an accurate position with the energy capable of vapor deposition without being affected by the fluctuation of the electric field. This makes it possible to easily provide a surface acoustic wave device having desired characteristics.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a cross-sectional view of an essential part of a resonator type surface acoustic wave device 1 according to the present invention. Resonator type surface acoustic wave device 1
In FIG. 1, the input side electrode 3 and the reflection groove 11 which is a reflection groove are formed on the piezoelectric substrate 2. The cross-sectional shape of the input-side electrode 3 is a gentle convex shape. Further, the cross-sectional shape of the reflecting groove 11 is the groove end portion 1
1a has a gentle shape. Although not shown in FIG. 1, the cross-sectional shape of the output side electrode 5 also has a gentle convex shape, and the cross-sectional shape of the reflection groove 12 also has a gentle shape at the groove end. There is.

As described above, since the ends of the input / output side electrodes and the groove ends of the reflection groove are gentle,
It is possible to prevent the generated surface acoustic wave from being converted into a bulk wave at the end face.

An outline of an apparatus for manufacturing the resonator type surface acoustic wave element 1 will be described. The focused ion beam direct vapor deposition apparatus 10 shown in FIG. 2 has a vacuum chamber 20, and the focused ion beam direct vapor deposition and groove formation are performed in the vacuum chamber 20 as follows.

For the liquid metal ion source 21, for example, Al
-Au-Ge alloy tip is set,
Generates ion species such as u ⁺ and Al ⁺ . The generated metal ions are accelerated to 20 keV by the acceleration electrode 22 and focused by the condenser lens 23. Since the ion beam generated in the liquid metal ion source 21 contains various kinds of ion species, only the desired ion source is selected by the mass analyzer for the beam containing the various kinds of ion species. This selection is performed by the mass filter 24. The ion beam that has passed through the beam aperture 25 is deflected by the deflection electrode 26. The ion beam is focused on the objective lens 27 and applied to the substrate 31 mounted on the stage 28. The substrate 31 on the stage 28 is in an electrically floating state by the insulator 32. Therefore, by applying a deceleration voltage of 0 to 20 KV to the stage 28 by the deceleration power supply 12, the final energy of the focused ion beam continuously changes in a wide range of 0 to 20 KeV.
For example, if 19.9KV is applied as the deceleration potential, 20K
The metal ions accelerated to eV were decelerated to 100 eV when they reached the substrate. Thus, by decelerating the once focused ion beam and irradiating it on the piezoelectric substrate 2, the metal ions can be directly vapor-deposited, whereby the input / output electrodes are formed without using a resist. be able to.

On the other hand, if the deceleration voltage is not applied, the focused ion beam reaches the substrate surface without deceleration. As a result, a groove is formed on the surface of the substrate.

As described above, in the focused ion beam direct vapor deposition apparatus 10, electrode formation and groove formation can be easily switched depending on whether or not the deceleration voltage is applied.

A method of manufacturing the resonator type surface acoustic wave element 1 will be specifically described with reference to FIG. First, as shown in FIG. 3A, a quartz ST-cut piezoelectric substrate 2 is prepared.
Next, the surface of the piezoelectric substrate 2 is selectively irradiated without decelerating the focused ion beam. In this embodiment,
Irradiation was performed at 20 KeV as irradiation energy. As a result, the focused ion beam forms a groove having a width of 0.1 μm. This was scanned to obtain a groove having a depth of 500 Å and a width of 0.9 μm. As a result, FIG.
As shown in FIG. 3, the groove end 11 a was formed gently, and the reflection groove 11 was formed on the surface of the piezoelectric substrate 2.

The reason why the groove end portion 11a becomes gentle is that the ion distribution of the focused ion beam to be irradiated has a Gaussian distribution. Further, as shown in FIG. 1, the groove 11 has a flat bottom surface because the focused ion beam is scanned.

Next, as shown in FIG. 3B, the piezoelectric substrate 2 is irradiated with a focused ion beam whose energy is decelerated. In this way, the electrode is formed by irradiating the focused ion beam with the energy capable of vapor deposition.

In this embodiment, the film is vapor-deposited by irradiating with 200 eV, and has a line width of 0.9 μm and a film thickness of 80
A 0 angstrom aluminum input / output electrode was obtained.
As a result, a resonator type filter in the 800 MHz band was obtained.

Even if the focused ion beam is decelerated before being irradiated on the piezoelectric substrate 2, its ion distribution becomes a Gaussian distribution. Therefore, an electrode having a convex shape with a gentle cross-section is formed on the piezoelectric substrate 2.

Since the ends 11a of the reflection groove and the electrode 3 thus formed are not steep, it is possible to prevent wasteful bulk conversion loss.

As described above, by forming the reflection groove and the input / output electrode using the focused ion beam direct vapor deposition device 10, without using a resist mask.
Reflection grooves and input / output electrodes can be formed. As a result, the photolithography process in the electrode forming process and the reflection groove forming process can be reduced.

Although the input / output side electrode is formed after the reflection groove is formed in this example, the reflection groove may be formed after the input / output side electrode is formed first.

Further, since no resist pattern is used, it is possible to prevent pattern defects due to peeling defects and missing resist patterns.

Further, in this embodiment, since the input / output electrodes are formed by using the focused ion beam direct vapor deposition device 10 as described above, the following effects are also obtained. Since the electrodes can be formed in a one-step process, a plurality of resist mask processes are unnecessary. In particular, SAW devices are manufactured in small quantities and in a large variety of products, so that there is a great merit that a resist mask is unnecessary.

Further, a device or material (organic solvent, gas device) such as dry etching is unnecessary. In addition, unlike the case where the dry etching method is used, there is no possibility that the surface of the power generation substrate is damaged or damaged. Especially in the case of a SAW device, since an electric signal is transmitted using surface acoustic waves,
Since the damage to the surface can be avoided, there is no possibility that the characteristics will change.

Further, since the resist mask is not used, it is not necessary to consider the mask shift, so that the electrode with high accuracy can be formed.

In the case of a SAW device, the input / output electrodes may be formed of different metals. For example, the input side electrode is made of aluminum and the output side electrode 5 is made of gold. In such a case, when using a conventional resist mask,
It is necessary to separately perform the input side electrode forming step and the output side electrode forming step, and the number of steps is doubled. However, in the focused ion beam direct vapor deposition apparatus 10, since only the desired ion species can be selected by the mass filter 24, different kinds of ion species can be selected to form electrodes of different kinds of metal in the same process. can do.

Further, in the SAW device, as shown in FIG.
As shown in A, the input / output electrodes may be three-dimensionally formed. This is because a reflection phase is changed by forming a metal such as chrome on a part of the aluminum electrode 113 to prevent reflection at the electrode end face. Even in this case,
As shown in FIG. 4B, the upper electrode (gold) 14 can be easily formed on the lower electrode (aluminum) 13. As described above, even when one or both of the input and output electrodes are made of two or more different metals, at least one of the metals is formed into a gentle convex shape in the cross section in the direction perpendicular to the substrate. It is possible to more effectively prevent reflection at the electrode end face.

In this example, a single crystal piezoelectric substrate 2 such as LiTaO ₃ was used as the substrate having piezoelectricity.
However, as the material of the piezoelectric substrate 2, LiNbO ₃ , Li ₂ B
A single crystal substrate such as ₄ O ₇ or quartz may be used. Further, instead of the piezoelectric substrate itself, a glass substrate or a sapphire substrate (AL ₂ O ₃ ) on which a piezoelectric thin film is formed may be used.

In this embodiment, the case where the SAW device is applied as the surface acoustic wave device has been described. However, the surface acoustic wave is not limited to this, and SSBW is used.
(Surface skimming bulk wave) or SBW (shall
ow bulk wave) may be used. These waves are SH (shear horizontal) wave type bulk waves whose main displacement is parallel to the substrate surface, so compared with the case where Rayleigh waves are used.
Propagation speed is as high as 1.5 times or more, and it has excellent frequency-temperature characteristics.

In this embodiment, the focused ion beam direct vapor deposition apparatus shown in FIG. 2 was used to form an electrode having a gentle convex cross section as shown in FIG. However, the electrode is not limited to this, and may be any electrode as long as it has a convex shape with a gentle cross section as shown in FIG.

Further, in the present embodiment, the energy of the focused ion beam is decelerated near the surface of the piezoelectric substrate 2 so that the once focused ion beam is decelerated to the energy capable of vapor deposition. But,
The manufacturing method is not limited to this, and any other manufacturing method may be used as long as it is a method capable of selectively irradiating a focused ion beam on the surface of the substrate with energy capable of vapor deposition.

In this embodiment, the metal ions are generated from the liquid ion source and then focused. However, the method is not limited to this, and any method may be used as long as it can obtain a focused ion beam.

FIG. 5 shows another embodiment. This example is
This is an embodiment in which a reflection groove is provided in the image repeating filter. As described above, the present invention is not limited to the resonator type surface acoustic wave element, but can be applied to a surface acoustic wave element that uses a reflector with the IDT as bidirectional.

FIG. 6 shows another embodiment. This is an embodiment in which the reflecting groove is formed in a tapered shape. Thus, by gradually changing the depth of the reflection groove, it is possible to reduce the conversion loss to the bulk mode.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional view of a main part of a resonator type surface acoustic wave device 1 according to the present invention.

FIG. 2 is a conceptual diagram illustrating a focused ion beam direct vapor deposition device 10.

FIG. 3 is a diagram for explaining a process of forming a reflection groove and an electrode by using the focused ion beam direct vapor deposition device 10.

FIG. 4 is a diagram showing a state in which another kind of electrode is formed.

FIG. 5 is a conceptual diagram showing an example in which a reflection groove is provided in an image repeating filter.

FIG. 6 is a cross-sectional view of main parts showing another embodiment.

FIG. 7 is a conceptual diagram illustrating a conventional resonator type surface acoustic wave element 50.

FIG. 8 is a cross-sectional view of a main part of a resonator type surface acoustic wave element 51 having reflection grooves 11 and 12 formed therein.

[Explanation of symbols]

 1 ... Surface acoustic wave element 2 ... Piezoelectric substrate 3 ... Input side electrode 5 ... Output side electrode 10 ... Focused ion beam direct vapor deposition device 11 ... ..Reflecting grooves 12 .... Reflecting grooves

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shinji Nagamachi, No. 1 Nishinokyo Kuwabara-cho, Nakagyo-ku, Kyoto City, Kyoto Prefecture Shimadzu Corporation Co., Ltd. Within

Claims (4)

[Claims] 1. An elastic surface comprising: a substrate having piezoelectricity; an electrode formed on the substrate; and a reflection groove provided adjacent to the electrode for reflecting a surface acoustic wave generated on the surface of the substrate. In the wave element, a surface acoustic wave element characterized in that a cross-sectional shape of the reflection groove has a gentle groove end portion. 2. The surface acoustic wave device according to claim 1, wherein the electrode is made of one or more metals, and at least one of the metals constituting the electrode is perpendicular to the substrate. A surface acoustic wave device characterized by having a gentle convex cross-section in the direction. 3. A method for manufacturing a surface acoustic wave device by irradiating a piezoelectric substrate with an focused ion beam, wherein the focused ion beam is used when an electrode is formed on the substrate surface. In the case of forming a reflection groove that selectively irradiates the surface of the substrate with the energy capable of vapor deposition and reflects the surface acoustic wave generated on the surface of the substrate, the focused ion beam is generated with the energy capable of forming the groove. A method for manufacturing a surface acoustic wave device, characterized in that the substrate surface is selectively irradiated. 4. The surface acoustic wave device according to claim 3, wherein the focused ion beam is irradiated with energy capable of vapor deposition by decelerating in the vicinity of the surface of the substrate. Wave element manufacturing method.