JP2001111377A - Surface acoustic wave device and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave device for making satisfactory uni-directionality, and for reducing an insertion loss, and for simplifying manufacturing. SOLUTION: An interdigital electrode 3 is formed on a substrate 2 constituted of an insulating body, a dielectric, or a piezoelectric body, and a piezoelectric thin film 4 is formed so that at least the electrode fingers of the interdigital electrode 3 can be covered, and a reflector having plural protrusions 4a-4c for reflecting surface waves is constituted on the surface of the piezoelectric thin film 4, and the centers of the protrusions 4a-4c are shifted from the excitation centers of the corresponding electrode fingers of the interdigital electrode to the opposite side of the center of an element by about λ/8 in the surface wave propagating direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface acoustic wave device used as, for example, a bandpass filter or a resonator, and a method of manufacturing the same, and more particularly, to a one-way surface acoustic wave device and a method of manufacturing the same.

[0002]

2. Description of the Related Art In a surface acoustic wave device, at least one IDT electrode is formed on a piezoelectric substrate. By applying a voltage to the IDT electrode, a surface wave is excited, and the surface wave propagates toward both sides of the IDT electrode. That is, since the conventional surface acoustic wave device is bidirectional, there is a problem that the loss is large.

In order to reduce the loss, various unidirectional surface acoustic wave devices have been proposed. For example, Japanese Patent Application Laid-Open No. 9-260993 discloses a unidirectional surface acoustic wave device shown in FIGS.

In a one-way surface acoustic wave device 51 shown in FIGS. 5A and 5B, an IDT electrode 53 is formed on a piezoelectric substrate 52. The IDT electrode 53 has electrodes 53a and 53b that are electrically separated from each other.
The electrodes 53a and 53b have electrode fingers 53a ₁ and 53b ₁ interposed therebetween, respectively. In FIG. 5, the electrode finger 5
3a ₁ , 53a ₂ and 53b ₁ are shown.

In FIGS. 5A and 5B, the IDT
Although only a part of the electrode 53 is shown, in FIG. 5, the direction toward the right side indicates the element center direction, and the surface acoustic wave device 51 is configured such that surface acoustic waves can propagate in the element center direction. ing.

That is, the surface acoustic wave device 51 shown in FIG.
In this case, the dielectric thin film 54 has the electrode fingers 53a ₁ , 53a ₂ ,
It is formed so as to cover the 53b _1. However, grooves 54a and 54b are formed on the upper surface of dielectric thin film 54. A reflector is constituted by the grooves 54a and 54b, and is configured such that the surface wave propagates only in the element center direction.

In FIG. 5B, the hatched portions indicate the deepest portions of the grooves 54a and 54b. The center of reflection is determined by these combined steps.

In the surface acoustic wave device 61 shown in FIG. 6, an IDT electrode 63 is formed on a piezoelectric substrate 62. The IDT electrode 63 is an electrically separated electrode 6
3a, has a 63 b, IDT electrodes 63a, 63b has an electrode finger 63a _1, 63 b ₁ to interdigitate with each other.

In order to realize unidirectionality, the electrode fingers 63a ₁ , 63b ₁ , 63a ₂ are partially covered.
Striped dielectric thin films 64a to 64c are formed. Dielectric 64a~64c is formed by a thin film forming method, from the electrode fingers 63a _1, 63 b _1, a side of 63a _2, the element center of the edge of the electrode fingers 63a _1, 63b _1, 63a ₂ The electrode fingers are formed so as to reach the upper surface of each electrode finger.

In the surface acoustic wave devices 51 and 61, as described above, the grooves 54a and 54b and the stripe-shaped dielectric material are formed on the dielectric thin films 54 and 64 in order to form a reflection surface for reflecting the surface wave. Thin films 64a to 64c are formed.

In the surface acoustic wave devices 51 and 61 described in the prior art, the distances g _{1 to} g ₄ between the center of the electrode finger and the reflection center of the reflector formed as described above are set to λ.
It is said that the unidirectionality is realized by setting / 8.

[0012]

In the conventional surface acoustic wave device 51, in order to realize unidirectionality, the dielectric thin film 5 is used.
4, the grooves 54a and 54b are precisely formed,
It was necessary to accurately form the centers of a and 54b so as to be separated by λ / 8 from the center of the electrode finger.

Here, in the surface acoustic wave device 51, a dielectric material is used.
A thin film 54 is formed, and an electrode finger 53a is formed. ₁, 53b₁Patter
Using photolithography,
Grooves 54a and 54b are formed. These grooves 54a, 5
In forming 4b, exposure is performed from the back side of piezoelectric substrate 52.
Needed. Therefore, the piezoelectric substrate 52 and the dielectric thin film 5
As 4, a translucent material must be used.
There was about. In addition, the thickness of the dielectric thin film 54 is increased.
In such a case, the position accuracy of the grooves 54a and 54b is reduced.
There was a problem.

Further, a dielectric thin film 54 is formed on the piezoelectric substrate 52.
After forming the grooves, the grooves 54a and 54b are formed by etching. Therefore, unevenness occurs in the height direction of the grooves 54a and 54b due to uneven etching, and there is a problem that the characteristics are not stable.

Further, since the pattern of the IDT electrode 53 is used in forming the grooves 54a and 54b, the distance g ₃ g between the center of excitation, that is, the center of the electrode finger, and the reflection center.
There is also a problem that it is difficult to set ₄ exactly to λ / 8.

On the other hand, the surface acoustic wave device 61 shown in FIG.
Are striped dielectric thin films 64a on the piezoelectric substrate 62.
To 64c, the surface acoustic wave device 51
In comparison, the formation of the dielectric thin films 64a to 64c is easier.
You. However, the dielectric thin films 64a to 64c are piezoelectric
From the upper surface of the substrate 62, the electrode fingers 63a₁, 63b₁, 63a
_TwoIt is configured to ride on. Therefore,
The excitation center, that is, the electrode finger 63a₁, 63b₁, 6
3a_TwoCenter and reflection center, that is, striped dielectric
Distance g between centers of body thin films 64a to 64c₁, G_Two,
g_ThreeWas difficult to accurately set to λ / 8.

In addition, the above prior art does not mention the case of an electrode finger composed of a so-called split electrode in which the electrode finger is constituted by two electrodes. In the case where the electrode finger is a split electrode, if the pattern of the IDT electrode 53 is used for forming the groove as described in the above-mentioned prior art, the center of excitation, that is, the center of the electrode finger, and the center of reflection, that is, the center of the groove do not shift. Direction cannot be realized.

An object of the present invention is to precisely control the distance between the excitation center of the interdigital transducer and the reflection center of the thin film formed to constitute the reflector so as to cover the electrode fingers of the interdigital transducer. It is an object of the present invention to provide a surface acoustic wave device which can realize a unidirectionality reliably and can be easily manufactured, and a method of manufacturing the same.

[0019]

According to the present invention, there is provided a surface acoustic wave device comprising: a substrate made of an insulator, a dielectric, or a piezoelectric;
At least one interdigital electrode formed on one surface of the substrate and having a plurality of electrode fingers interposed between each other, and a piezoelectric element formed on the substrate so as to cover at least the electrode fingers of the interdigital electrode Comprising a body thin film or a dielectric thin film, a plurality of protrusions for reflecting surface waves on the surface of the piezoelectric thin film or the dielectric thin film are formed,
The center of the ridge is shifted from the center of excitation of each electrode finger of the interdigital electrode by about λ / 8 in a direction opposite to the center of the element.

In a specific aspect of the present invention, the electrode fingers of the interdigital transducer are solid electrodes, and the width of the electrode fingers is λ /
8 and the width of the ridge formed on the piezoelectric thin film or the dielectric thin film is at most λ / 4, and the center of the ridge is separated from the excitation center of the electrode finger of the interdigital electrode by surface acoustic waves. It is offset by λ / 8 in the opposite direction to the center of the device.

In another specific aspect of the present invention, each electrode finger of the interdigital transducer is a split electrode composed of two electrodes, and a width of a ridge formed on the piezoelectric thin film or the dielectric thin film Is at most λ / 4, and the center of the ridge is shifted by λ / 8 in the surface wave propagation direction in the direction opposite to the center of the surface acoustic wave device with respect to the excitation center of the electrode finger.

In the surface acoustic wave device according to the present invention, preferably, the width of the electrode fingers of the interdigital transducer is about 3λ / 8. The method for manufacturing a surface acoustic wave device according to the present invention includes a step of forming an interdigital electrode on a substrate made of an insulator, a dielectric or a piezoelectric substance, and the step of forming an interdigital electrode on the substrate surface on which the interdigital electrode is formed. A first piezoelectric thin film or a dielectric thin film is formed so as to fill a region between the electrode fingers of the electrode and on the upper surface of the electrode finger of the interdigital electrode on which the protrusion is formed, and the electrode of the interdigital electrode is formed. A step of forming a projection by a piezoelectric thin film or a dielectric thin film on a finger, and filling an area between the electrode fingers of the interdigital electrode, and an upper surface portion of the electrode finger of the interdigital electrode on which the protrusion is formed. A second piezoelectric thin film or a dielectric thin film having a uniform thickness is formed so as to cover the portion, and the protrusions are formed by portions of the second piezoelectric thin film or the dielectric thin film which cover the projections. And a process To.

In a specific aspect of the method of manufacturing the surface acoustic wave device according to the present invention, the step of forming the projections by the piezoelectric thin film or the dielectric thin film on the electrode fingers of the interdigital electrode is performed by a uniform thin film forming method. Forming a first piezoelectric thin film or dielectric thin film having a thickness, and covering the region between the electrode fingers of the interdigital electrode and the electrode finger surface of the interdigital electrode with the first piezoelectric thin film or the dielectric thin film; The first piezoelectric thin film or dielectric thin film is processed by photolithography and etching, and the first piezoelectric thin film or dielectric thin film on the electrode finger surface of the interdigital transducer is partially removed to remove the protrusion. Forming.

In another specific aspect of the method for manufacturing a surface acoustic wave device according to the present invention, the step of forming a projection by a piezoelectric thin film or a dielectric thin film on the electrode finger of the interdigital electrode comprises the step of interfacing the substrate. A mask is brought into contact with the surface on which the electrode is formed, and a first piezoelectric thin film or a dielectric thin film is formed by a thin film forming method, whereby the piezoelectric thin film or the dielectric thin film is interposed between the electrode fingers of the interdigital electrode. Is formed, and a protrusion made of the piezoelectric thin film or the dielectric thin film is partially formed on the surface of the electrode finger of the interdigital electrode.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be clarified by describing a surface acoustic wave device according to an embodiment of the present invention and a method of manufacturing the same with reference to the drawings.

FIG. 1A is a plan view for explaining an interdigital electrode of the surface acoustic wave device according to the first embodiment of the present invention, and FIG. It is sectional drawing of the surface acoustic wave device in the part which follows the -B line. The surface acoustic wave device 1 has a structure in which an interdigital electrode 3 is formed on an upper surface of a substrate 2 made of a dielectric or an insulator. IDT 3
Has electrodes 3a and 3b that are electrically separated.
Interdigital electrodes 3a has an electrode finger 3a ₁ to 3 A ₄ which is extended in a direction orthogonal to the surface wave propagation direction, interdigital electrodes 3b were extended in a direction orthogonal to the surface wave propagation direction electrode with a finger 3b ₁ ~3b _5. The electrode fingers 3a ₁ to 3 A
_4, the electrode fingers 3b ₁ ~3b _5, are arranged so as interdigitated with each other.

Although not shown in FIG. 1A, a piezoelectric thin film 4 is formed so as to cover the IDT 3 (see FIG. 1B). The material forming the insulating substrate 2 is not particularly limited, but for example, an insulating ceramic such as alumina can be used. Further, a dielectric substrate may be used instead of the insulating substrate 2.

Further, the interdigital electrode 3 can be formed using an appropriate metal material such as Al. As the piezoelectric thin film 4, a ZnO thin film, a Ta ₂ O ₅ thin film, or the like can be used.

Further, in the surface acoustic wave device 1 of this embodiment,
Although only the interdigital transducer 3 is shown, another interdigital transducer (not shown) is formed on the upper surface of the insulating substrate 2 to the left of the interdigital transducer 3. That is, in the surface acoustic wave device 1, the center of the element is on the left side of the illustrated portion. Accordingly, in FIG. 1, the arrow D is the element center direction.

In the surface acoustic wave device 1, a reflector composed of a plurality of ridges 4 a to 4 c is formed on the surface of the piezoelectric thin film 4 in order to impart unidirectionality to the IDT 3. This will be described more specifically with reference to FIG.

As shown in FIG. 1B, the electrode fingers 3a ₃ ,
The width of 3a ₄ and 3b ₄ is set to 3λ / 8. In addition,
λ indicates the wavelength of the surface wave excited by the IDT 3. Normally, when a regular interdigital electrode is formed, the width of the electrode fingers is set to λ / 4, the width of the region between adjacent electrode fingers is also set to λ / 4, and the electrode fingers are set at λ / 2 pitch. Are located.

On the other hand, in the surface acoustic wave device 1 of the present embodiment, the electrode fingers 3a ₃ , 3b ₄ , 3a ₄ are arranged at a pitch of λ / 2, but each of the electrode fingers 3a ₃ , 3b _4. , 3a
The width of ₄ is 3λ / 8, which is larger than λ / 4.

On the other hand, on the upper surface of the piezoelectric thin film 4, ridges 4a to 4c extending in a direction perpendicular to the surface wave propagation direction are formed to constitute a reflector. The ridges 4a to 4c are
Above the electrode fingers _{3a 3, 3b 4, 3a 4} , the electrode fingers 3a _3, 3b _4, 3a ₄ are arranged and to partially overlap. Further, both ends in the length direction of the protrusions 4a to 4c end at positions equal to both ends of the electrode finger intersection region. However, the ridges 4a to 4c may extend outside a region where the electrode fingers of the interdigital transducer 3 intersect in a direction perpendicular to the surface wave propagation direction.

That is, a grating-type reflector is formed by forming the ridges 4 a to 4 c on the upper surface of the piezoelectric thin film 4. The width (the dimension in the direction orthogonal to the surface propagation direction) of the ridges 4a to 4c is equal to the electrode finger 3a.
₃ , 3b ₄ , 3a ₄ are narrower than the width (= 3λ / 8), so that the deviation between the center of excitation of the interdigital transducer 3 and the center of reflection of the reflector can be approximately λ / 8. It is easy. Therefore, unidirectionality is realized and the insertion loss is improved. This will be clarified by describing the manufacturing method with reference to FIG.

In the following description with reference to FIG. 2, only the main part of the interdigital transducer 3 in the surface acoustic wave device 1 will be described. On the left side of the electrode 3, another interdigital electrode is formed.

In manufacturing the surface acoustic wave device 1, first, an insulating substrate 2 is prepared (see FIG. 2A). Next, the interdigital electrode 3 is formed on the upper surface of the insulating substrate 2.
(B)). The interdigital electrodes 3 can be formed by forming a metal film on the entire upper surface of the insulating substrate 2 by a thin film forming method such as vapor deposition, plating, or sputtering, and patterning the metal film. Alternatively, the IDTs 3 may be formed by bringing a mask into contact with the upper surface of the insulating substrate 2 and depositing a metal material.

Next, after the interdigital electrode 3 is formed, a first piezoelectric thin film 4A is formed by a thin film forming method such as vapor deposition, plating or sputtering. The first piezoelectric thin film 4A is formed to have a uniform film thickness by the above thin film forming method. The thickness of the first piezoelectric thin film 4 </ b> A is equal to or smaller than the thickness of the IDT 3. As a result, as shown in FIG. 2C, the first electrode 3a ₃ , 3b ₄ , 3a ₄ in the interdigital transducer 3 and the upper surface of the electrode fingers 3a ₃ , 3b ₄ , 3a ₄ Is formed.

Next, the electrode fingers 3 of the first piezoelectric thin film 4A are formed using photolithography-etching technology.
The piezoelectric thin films on a ₃ , 3b ₄ and 3a ₄ are etched to form protrusions 4B, 4B and 4B. The protrusion 4B extends in a direction perpendicular to the surface propagation direction and is formed to have the same width and height as the finally formed protrusions 4a to 4c (FIG. 1B).

In forming the projections 4B, 4B, 4B, etching may be performed in accordance with one edge of the underlying electrode fingers 3a ₃ , 3b ₄ , 3a ₄ , ie, the right edge. Therefore, the projections 4B, 4B, 4B can be formed accurately.

Next, a second piezoelectric thin film is formed on the upper surface of the insulating substrate 2 by a thin film forming method such as vapor deposition, plating or sputtering to form a piezoelectric thin film 4. The protrusion 4B, 4B, since 4B are previously formed on the electrode fingers _{3a 3, 3b 4, 3a 4} , to form a second piezoelectric thin film, the protrusion 4B, 4B, the upper part 4B is formed A projection 4a having the same width and height as the projections 4B, 4B, 4B.
To 4c are formed.

The width of the ridges 4a to 4c can be accurately determined only by adjusting the width of etching when forming the above-mentioned projections 4B, 4B, 4B. Therefore, according to the manufacturing method of this embodiment, the electrode fingers 3a ₃ and 3b
₄ and 3a ₄ are set to 3λ / 8, which is larger than λ / 4,
By adjusting the width of the etching, the ridges 4a to
4c can be easily adjusted. Therefore, FIG.
As shown in (b), the distance along the surface propagation direction between the excitation center of the interdigital transducer 3 and the reflection center of the reflector can be easily set to λ / 8, thereby realizing unidirectionality. The insertion loss is reduced.

In FIG. 1B, the dashed line X indicates the excitation center, and the broken line Y indicates the reflection center. Here, the excitation center X corresponds to the center position of the electrode fingers 3a ₃ , 3b ₄ , 3a ₄ , and the reflection center Y is the ridge 4 forming the reflector.
It is located at the center in the width direction of a to 4c. That is, the electrode finger 3
Taking b ₄ and protrusions 4b as an example, since the element center direction is to the left of FIG. 1, with respect to the excitation center X of the electrode fingers 3b _4, the reflection center Y of projection 4b provided above the Are separated by about λ / 8 in a direction opposite to the element center direction. Therefore, the surface wave can be propagated only in the element center direction by the reflection effect of the ridge 4b, and the insertion loss can be reduced.

Also, by setting the width of the electrode fingers 3a ₃ , 3b ₄ , 3a ₄ to 3λ / 8 and the width of the etching to λ / 4, the center Z by the etching is shifted with respect to the excitation center of the corresponding electrode finger. Λ / 16 in the element center direction. Therefore, as a result, the reflection center Y of the ridges 4a to 4c is shifted to the opposite side from the element center direction by λ / 8 suitable for one direction with respect to the excitation center X of the IDT.

In the manufacturing method described with reference to FIG. 2, after the interdigital electrode 3 is formed, the first piezoelectric thin film 4 is formed.
A was formed, and the projections 4B, 4B, 4B were formed by photolithography-etching. After the interdigital electrode 3 was formed, a mask was brought into contact with the insulating substrate 2,
The first piezoelectric thin film may be formed by vapor deposition, plating, sputtering, or the like, thereby immediately obtaining the structure shown in FIG. 2D from the state shown in FIG. 2B.

As described above, in the surface acoustic wave device 1 according to the present embodiment, after the interdigital electrode 3 is formed, the one side edge of the protrusion 4B, 4B, 4B is formed on one side edge of the electrode finger of the interdigital electrode 3. Are formed so as to match each other, and the second piezoelectric thin film having a uniform thickness is formed by the thin film forming method, whereby the reflector having the above-described ridges 4a to 4c can be easily configured. In addition, when forming the projections 4B, 4B, 4B, the width thereof can be easily adjusted.
As described above, the electrode fingers 3a ₃ , 3
b ₄ and 3a ₄ are made larger than λ / 4, and the electrode fingers 3a ₃ and 3a
b _4, projections 4B to be narrower than 3a _4, 4B, 4
Only form a B, and the reflection center of the projection 4 a to 4 c, the electrode 3a _3, 3b _4, can be moved in a direction opposite to the element center than the excitation center 3a _4. Therefore, ridge 4a
4c can be reliably shifted by about λ / 8 from the corresponding electrode finger to the side opposite to the element center direction by an amount suitable for one-way direction.

In this case, the center of etching may be moved in the range of λ / 32 to λ / 8 with respect to the center of excitation of the corresponding electrode finger. The thickness of the interdigital electrode 3 and the height of the ridges 4a to 4c are not particularly limited, but may be generally in the range of 0.2 to 3% with respect to λ.

As described above, when the ridges 4a to 4c are shifted by λ / 8 to the opposite side to the element center direction with respect to the excitation centers of the corresponding electrode fingers 3a ₃ , 3b ₄ , 3a _4. As shown in FIG. 3, the insertion loss can be effectively improved. That is, the solid line in FIG. 3, the reflection center Y ridges 4a~4c is, the corresponding electrode fingers 3a _3, 3b _4, with respect to the excitation center X of 3a _4, lambda / 8 on the side opposite to the element center direction The insertion loss versus frequency characteristic of the surface acoustic wave device of the shifted embodiment is shown, and the dashed line is the same as above except that no ridges 4a-4c are formed, ie, no reflector is formed. Loss vs. frequency characteristics of the surface acoustic wave device configured as described above. As is clear from the comparison between the characteristics of the solid line and the dashed line, it is clear that the insertion loss can be improved by 3 dB or more compared to the bidirectional surface acoustic wave device by configuring the reflector according to the present embodiment. .

FIG. 4 is a sectional view for explaining a surface acoustic wave device according to a second embodiment of the present invention, and is a diagram corresponding to FIG. 1B showing the first embodiment. . Second
In the surface acoustic wave device 11 of this embodiment, the IDT 13
Are constituted by a so-called split electrode composed of two electrodes. That is, the interdigital electrodes 13 are formed on the insulating substrate 12. The interdigital electrodes 13 include electrically separated interdigital electrodes arranged so that the electrode fingers of each other are interposed. Each electrode finger of each IDT is in the form of a split electrode composed of two electrodes. As shown in FIG. 4, the electrode fingers 23a ₃ has electrodes 23a _31, 23a _32. Similarly, the electrode fingers 23b _4, 23a _4, having two electrodes _{23b 41, 23b 42, 23a 41} , 23a 42.

Reference numeral 24 denotes a piezoelectric thin film, and the piezoelectric thin film 2
4, on the upper surface of the ridges 24a to 24c as in the first embodiment.
Are formed, and ridges 24a to 24c are formed. When the interdigital electrodes 3 having electrode fingers made of such a split electrodes, when realizing the one-way as in the first embodiment, the width of each electrode 23a ₃₁ ~23a ₄₂ is λ
/ 8. The width of the ridges 24a to 24c is λ / 4.
It is said. And the ridges 24a to 24c are respectively
It is arranged above one electrode of the corresponding electrode finger.
For example, taking the electrode fingers 23a ₃ as an example, protrusions 24a are formed on the electrode 23a ₃₂ located on the opposite side to the element center direction. In the case of an electrode finger in the form of a split electrode, the excitation center of the electrode finger is located at the center between the two electrodes. That is, taking the electrode fingers 23a ₃ as an example, the excitation center X is located between the electrode 23a ₃₁ and the electrode 23a _32.

Therefore, the reflection center Y of the ridges 24a to 24c is
Is shifted by λ / 8 in the direction opposite to the element center with respect to the excitation center X of the corresponding electrode fingers 23a ₃ , 23b ₄ , 23a ₄ , as in the case of the first embodiment. Characteristics can be realized, and insertion loss can be reduced.

Also in this case, the ridges 24a to 24c
In the same manner as in the first embodiment, after forming the IDT 23, a first piezoelectric thin film is formed, and the first piezoelectric thin film is formed.
The projections can be formed by patterning the piezoelectric thin film described above, and the second piezoelectric thin film can be easily formed by laminating the second piezoelectric thin film.

In this embodiment, the electrode fingers 23a ₃ and 23a
b _4, 23a ₄ of the width of each electrode 23a ₃₁ ~23a ₄₂ λ /
If it is in the range of 32 to λ / 4, the width of the etching is λ / 3.
By adjusting in the range of 2 to λ / 4, the ridges 24 a to 24
The reflection center Y of 24c is set to the corresponding electrode fingers 23a ₃ , 23
The excitation center of b ₄ and 23a ₄ can be shifted by λ / 8 in the direction opposite to the center of the element.

The insertion loss of the surface acoustic wave device of the second embodiment constructed in the same manner as in the first embodiment except that the electrode fingers of the IDT are constituted by the split electrodes as described above. The frequency characteristics are shown by broken lines in FIG. As is clear from FIG. 3, the surface acoustic wave device of the second embodiment also
As compared with the bidirectional surface acoustic wave device (the surface acoustic wave device having the characteristics indicated by the dashed line), the insertion loss can be improved by 3 dB or more, and it can be seen that the device has good unidirectionality.

In the first and second embodiments, the unidirectionality is realized by forming the interdigital electrodes and the piezoelectric thin film on the insulating substrate and forming the ridges on the piezoelectric thin film. However, in the present invention, an interdigital electrode is formed on a piezoelectric substrate, a piezoelectric thin film or a dielectric thin film is formed on the upper surface thereof, and ridges and grooves are formed on the surface of the piezoelectric thin film or the dielectric thin film as described above. It may be formed.

[0055]

In the surface acoustic wave device according to the present invention, the piezoelectric thin film or the dielectric thin film is laminated so as to cover at least the electrode fingers of the interdigital electrode formed on the substrate.
A plurality of ridges for reflecting surface waves is formed on the surface of the piezoelectric thin film or the dielectric thin film, and the center of the ridge is opposite to the center of the element with respect to the excitation center of the corresponding electrode finger. Is shifted by about λ / 8 in the surface wave propagation direction, so that most of the excited surface waves propagate only to the center of the element, so that good unidirectionality can be realized. It is possible to reduce the insertion loss of the device.

In the surface acoustic wave device according to the present invention, the electrode finger of the interdigital transducer is a solid electrode, the width of the electrode finger is larger than λ / 8, and the protrusion formed on the piezoelectric thin film or the dielectric thin film is formed. When the width of the strip is λ / 8 and the etching center is shifted by λ / 8 at the maximum from the center of the electrode finger toward the element center, the electrode center is thereby shifted with respect to the excitation center of the electrode finger. The center of the corresponding ridge is reliably shifted by λ / 8 to the opposite side to the element center in the surface wave propagation direction. Therefore, it is possible to easily configure the surface acoustic wave device according to the present invention that can realize good unidirectionality.

In the surface acoustic wave device according to the present invention, the electrode fingers of the interdigital transducer are the split electrodes, and the width of the groove between the ridges formed on the piezoelectric thin film or the dielectric thin film is at most λ / 4. When the etching center is shifted by λ / 8 at the maximum from the center of the electrode finger toward the element center, the center of the ridge corresponding to the electrode finger is shifted with respect to the excitation center of the electrode finger. It is surely shifted by λ / 8 to the side opposite to the element center in the surface wave propagation direction. Therefore, it is possible to easily configure the surface acoustic wave device according to the present invention that can realize good unidirectionality.

In the method of manufacturing a surface acoustic wave device according to the present invention, the interdigital transducer is formed on the substrate, and the interdigital transducer of the interdigital transducer is filled with the interdigital electrode. A first piezoelectric thin film or a dielectric thin film is formed on the upper surface of the electrode finger, a projection made of the piezoelectric thin film or the dielectric thin film is formed on the electrode finger, and a second thin film having a uniform thickness is formed.
By laminating the piezoelectric thin film or the dielectric thin film, the ridge is reliably and easily formed above the portion where the protrusion is formed. Therefore, it is possible to easily provide the surface acoustic wave device according to the present invention, which has good unidirectionality and can greatly reduce the insertion loss.

In the method of manufacturing a surface acoustic wave device according to the present invention, after forming the interdigital transducer, a first piezoelectric thin film or a dielectric thin film having a uniform thickness is formed, and then photolithography and etching are performed. In the case of forming the protrusions by processing as described above, the protrusions can be formed at a desired width and position only by adjusting the etching width. Therefore, by laminating the second piezoelectric thin film or the dielectric thin film, the ridge can be easily formed at a desired position.

When a mask is brought into contact with the surface on which the IDTs are formed, a first piezoelectric thin film or a dielectric thin film is formed by a thin film forming method. By increasing the accuracy, the position of the protrusion can be set accurately. Therefore, by stacking the second piezoelectric thin film or the dielectric thin film, the ridge can be easily formed at a desired position on the projection.

[Brief description of the drawings]

FIGS. 1A and 1B are a partially cutaway plan view showing an electrode structure of a surface acoustic wave device according to a first embodiment of the present invention, and a partially cutaway sectional view showing a main part, respectively. Sectional drawing of the part corresponding to BB line of).

FIGS. 2A to 2E are cross-sectional views illustrating a method of manufacturing the surface acoustic wave device according to the first embodiment.

FIG. 3 is a diagram showing insertion loss-frequency characteristics of the surface acoustic wave device prepared for the first embodiment, the second embodiment, and a comparison.

FIG. 4 is a sectional view for explaining a main part of a surface acoustic wave device according to a second embodiment.

FIGS. 5A and 5B are a partially cutaway sectional view and a schematic plan view showing an example of a conventional surface acoustic wave device.

FIGS. 6A and 6B are a partially cutaway sectional view and a schematic plan view for explaining another example of a conventional surface acoustic wave device.

[Explanation of symbols]

1 ... the surface acoustic wave device 2 ... insulating substrate 3 ... IDT 3a ₁ to 3 A ₄ ... electrode finger 3b ₁ ~3b ₅ ... electrode fingers 4 ... piezoelectric thin film 4 a to 4 c ... projections 4A ... first piezoelectric thin film 4B ... projections 11 ... surface acoustic wave device 12 ... insulating substrate 13 ... IDT _{13a 3, 13a 4, 13b 4} ... electrode finger _{13a 31, 13a 32, 13b 41} , 13b 42, 13a 41,
13a ₄₂ ... electrode

Claims (6)

[Claims] 1. A substrate made of an insulator, a dielectric, or a piezoelectric material, at least one interdigital electrode formed on one surface of the substrate and having a plurality of electrode fingers interposed between each other; A piezoelectric thin film or a dielectric thin film formed on the substrate so as to cover at least the electrode fingers of the electrode, and a plurality of protrusions for reflecting surface waves on the surface of the piezoelectric thin film or the dielectric thin film. Wherein the center of the ridge is shifted by about λ / 8 in the opposite direction to the center of the element with respect to the center of excitation of each electrode finger of the interdigital transducer. apparatus. 2. The method according to claim 1, wherein the electrode fingers of the interdigital transducer are solid electrodes, the width of the electrode fingers is larger than λ / 8, and the width of the ridge formed on the piezoelectric thin film or the dielectric thin film is large. 2. The elastic surface according to claim 1, wherein the center of the ridge is shifted by λ / 8 from the center of excitation of the electrode fingers of the interdigital transducer in a direction opposite to the center of the surface acoustic wave device. Wave device. 3. The method according to claim 1, wherein each electrode finger of the interdigital transducer is a split electrode composed of two electrodes, and the width of a ridge formed on the piezoelectric thin film or the dielectric thin film is λ /
The center of the protrusion is shifted by λ / 8 in a surface wave propagation direction in a direction opposite to a center of the surface acoustic wave device with respect to an excitation center of the electrode finger. Surface acoustic wave device. 4. On a substrate made of a dielectric material or a piezoelectric material,
A step of forming an interdigital electrode, on the surface of the substrate on which the interdigital electrode is formed, so as to fill an area between the electrode fingers of the interdigital electrode, and on the upper surface of the electrode finger of the interdigital electrode, Forming a first piezoelectric thin film or a dielectric thin film at a position where it is to be formed, and forming a projection with the piezoelectric thin film or the dielectric thin film on the electrode finger of the interdigital electrode; After forming a piezoelectric thin film or a dielectric thin film so as to form the protrusion between the interdigital transducers and on the interdigital transducer, a second thin film having a uniform thickness is formed so as to cover the exposed portions of the interdigital transducer electrode fingers. Forming a piezoelectric thin film or a dielectric thin film, and forming the ridge by a portion of the second piezoelectric thin film or the dielectric thin film that covers the projection. Claim 1
3. The method for manufacturing a surface acoustic wave device according to claim 1. 5. The step of forming a projection by a piezoelectric thin film or a dielectric thin film on an electrode finger of the interdigital transducer comprises forming a first piezoelectric thin film or a dielectric thin film having a uniform thickness by a thin film forming method. Covering the region between the electrode fingers of the interdigital electrode and the surface of the electrode finger of the interdigital electrode with a first piezoelectric thin film or a dielectric thin film; and photolithography the first piezoelectric thin film or the dielectric thin film. 5. The elastic surface according to claim 4, further comprising a step of processing by etching to partially remove the first piezoelectric thin film or the dielectric thin film on the electrode finger surface of the interdigital electrode, thereby forming the protrusion. Method of manufacturing wave device. 6. A step of forming a projection by a piezoelectric thin film or a dielectric thin film on an electrode finger of the interdigital electrode comprises contacting a mask with the surface of the substrate on which the interdigital electrode is formed, and forming a thin film. By forming the first piezoelectric thin film or the dielectric thin film by the method, the piezoelectric thin film or the dielectric thin film is formed between the electrode fingers of the interdigital electrode, and the first thin film or the dielectric thin film is formed on the surface of the electrode finger of the interdigital electrode. The method for manufacturing a surface acoustic wave device according to claim 4, wherein the method is performed by partially forming a protrusion made of a piezoelectric thin film or a dielectric thin film.