JP5188714B2 - Surface acoustic wave device - Google Patents

Description

  The present invention relates to a surface acoustic wave device, and more particularly to a surface acoustic wave device that can be suitably used for a SAW (Surface Acoustic Wave) filter having a comb-tooth electrode and a reflective electrode on the surface of a piezoelectric substrate. .

  FIG. 4 shows an example of a conventional surface acoustic wave device 101. In the conventional surface acoustic wave device 101, as shown in FIG. 4, one or more pairs of comb electrodes (in FIG. 4, arranged in a line in the vertical direction) on the piezoelectric surface 102a of the piezoelectric substrate 102. 2 pairs of comb-tooth electrodes) 103 and a reflective electrode 104 at a position sandwiching the comb-tooth electrodes 103. Since the piezoelectric substrate 102 has piezoelectricity, when electricity is applied to the piezoelectric substrate 102, the piezoelectric substrate 102 expands and contracts, and when stress is applied to the piezoelectric substrate 102, electricity is generated in the piezoelectric substrate 102. Further, the comb electrode 103 serves as an electrical gateway for the piezoelectric substrate 102. By using this piezoelectric characteristic, the surface acoustic wave device 101 is used as a SAW filter or a transformer (see Patent Document 1).

  Here, as a material used for the conventional comb electrode 103 and the reflective electrode 104, Al, Cu, Ag, Au, or the like, or a metal mainly composed of one element thereof is selected. In particular, when considering the migration resistance and ease of formation of the comb electrode 103 and the reflective electrode 104, Al was selected. In addition, Cu is selected when it is desired to improve the power resistance of the comb-tooth electrode 103 and the reflective electrode 104.

JP 2005-5853 A

  However, when Al having high migration resistance is used for the comb-tooth electrode 103 and the reflective electrode 104, Al power is poor, so when the voltage is increased, Al atoms vibrate vigorously and Al is scattered. As a result, the comb electrode 103 or the reflective electrode 104 may be disconnected.

  On the other hand, when Cu having high power durability is used for the comb-tooth electrode 103 and the reflective electrode 104, other electrode fingers 105 and 106 of the comb-tooth electrode 103 and the reflective electrode 104 are used as shown in FIGS. When a voltage is applied between the adjacent electrode fingers 105A and 106A adjacent to the electrode fingers 105 and 106 of the comb electrode 103 or the reflective electrode 104 and the other adjacent electrode fingers 105A and 106A, Cu migration resistance Therefore, migration 109 may occur between the adjacent electrode fingers 105A and 106A.

  In addition, since a voltage is applied between the adjacent electrode fingers 105A and 106A during the manufacturing process of the surface acoustic wave device 101, the surface acoustic wave device 101 has already been destroyed at the stage of manufacturing the surface acoustic wave device 101. Therefore, a product incorporating the surface acoustic wave device 101 may cause an initial failure.

  Accordingly, the present invention has been made in view of these points, and it is an object of the present invention to provide a surface acoustic wave device capable of improving the power durability of each electrode while preventing the occurrence of migration in each electrode. The purpose is.

In order to achieve the above-described object, a surface acoustic wave device according to the present invention includes, as a first aspect, a piezoelectric substrate having a piezoelectric surface, and electrode fingers arranged in a comb shape on the surface of the piezoelectric substrate. And two or more pairs of comb electrodes arranged in a row or in a row formed by alternately arranging electrode fingers, and arranged in a fence shape on the surface of the piezoelectric substrate A pair of reflective electrodes each having an electrode finger and formed at positions sandwiching two or more pairs of comb-shaped electrodes arranged in a pair or in a row, In the electrode finger of the electrode and the reflective electrode, the adjacent electrode finger adjacent to the electrode finger of the other comb-teeth electrode or the reflective electrode is made of the first metal that has better migration resistance than the electrode fingers other than the adjacent electrode finger. Formed, and a pair of comb electrode electrodes The electrode fingers other than the adjacent electrode fingers in the finger is characterized by being formed with a second metal having excellent power durability than the first metal. In addition, since the electrode fingers other than the adjacent electrode fingers are not required to have migration resistance or power resistance in the electrode fingers of the reflective electrode, either the first metal or the second metal may be used, or another metal is used. May be.

  According to the surface acoustic wave device of the first aspect of the present invention, it is possible to improve the migration resistance of the adjacent electrode fingers that are the places where the migration occurs, and the electrode fingers other than the adjacent electrode fingers that do not become the places where the migration occurs. Power durability can be improved.

  The surface acoustic wave device according to the second aspect of the present invention is the surface acoustic wave device according to the first aspect, wherein the adjacent electrode finger is the outermost electrode facing the electrode finger of the other comb-tooth electrode or the reflective electrode. It is characterized by being a finger.

  According to the surface acoustic wave device of the second aspect of the present invention, by setting the adjacent electrode finger using the fact that the electrode finger that is the location of occurrence of migration is the outermost electrode finger, It is possible to efficiently improve the migration resistance and power resistance of the reflective electrode.

  The surface acoustic wave device according to the third aspect of the present invention is characterized in that, in the surface acoustic wave device according to the first or second aspect, the first metal is a metal containing Al as a main component.

  According to the surface acoustic wave device of the third aspect of the present invention, not only the migration resistance but also the ease of forming the electrode fingers can be improved. Further, migration resistance can be drastically improved by adding a small amount of an additive element.

  A surface acoustic wave device according to a fourth aspect of the present invention is the surface acoustic wave device according to any one of the first to third aspects, wherein the second metal is a metal containing Cu as a main component. Yes.

  According to the surface acoustic wave device of the fourth aspect of the present invention, when Cu is used for the electrode fingers, for example, power durability can be drastically improved as compared with the case where Al is used for the electrode fingers.

  According to the surface acoustic wave device of the present invention, since the material used for the electrode finger is selected depending on whether or not the electrode finger is a migration occurrence location, There is an effect that it is possible to improve the power resistance of the.

  Hereinafter, the surface acoustic wave device of the present invention will be described with reference to FIGS. 1 to 3 according to an embodiment thereof.

  FIG. 1 shows a plan view of a surface acoustic wave device 1 of the present embodiment. As shown in FIG. 1, the surface acoustic wave device 1 of the present embodiment includes a piezoelectric substrate 2, a comb electrode 3, and a reflective electrode 4.

  The piezoelectric substrate 2 is formed in a flat plate shape so that its surface 2a has piezoelectricity. Specifically, the piezoelectric substrate 2 of the present embodiment may be formed in a flat plate shape using a piezoelectric metal oxide such as PbTiO3, BaTiO3, LiNbO3, LiTiO3, KNbO3, LiTaO3, LiB4O7, or the like. Alternatively, the surface of a sapphire sapphire substrate or diamond substrate may be coated with a piezoelectric metal oxide.

  As shown in FIG. 1, the comb-teeth electrodes 3 each have electrode fingers 5 arranged in a comb-teeth shape on the surface 2 a of the piezoelectric substrate 2. The dimensions and the number of the electrode fingers 5 of the comb-teeth electrode 3 are appropriately changed according to the electric signals input and output from the comb-teeth electrode 3. Similarly, the number of comb electrodes 3 formed is appropriately changed according to the electric signals input and output from the comb electrodes 3. In the comb-tooth electrode 3 of this embodiment, four pieces are formed on the surface 2a of the piezoelectric substrate 2, and the electrode fingers 5 are alternately arranged. When the two comb-teeth electrodes 3 in which the electrode fingers 5 are alternately arranged are defined as a pair of comb-teeth electrodes 3, the surface 2a of the piezoelectric substrate 2 of the present embodiment has one row (in FIG. Two pairs of comb electrodes 3 arranged in a row are formed, and electrode pads 7 are formed using the first metal or the second metal for each pair of comb electrodes 3. The first metal and the second metal will be described later.

  Further, the comb electrode 3 of the present embodiment is formed by different materials for each electrode finger 5. Of the electrode fingers 5 of the pair of comb-teeth electrodes 3, the adjacent electrode fingers 5A adjacent to the electrode fingers 5 and 6 of the other comb-teeth electrode 3 or the reflective electrode 4 are the first metal excellent in migration resistance. It is formed using. Only the surface of the adjacent electrode finger 5A may be formed using the first metal. The adjacent electrode finger 5A may be two to three electrode fingers 5 from the outside, but the adjacent electrode finger 5A of the comb electrode 3 of this embodiment is the electrode finger 5 of another comb electrode 3 or the reflective electrode 4. , 6 is the outermost electrode finger 5C. Further, as the first metal, a pure metal having high migration resistance such as Al, Pt, Pd, and Fe or a metal improved in migration resistance by alloying such as AlCu, AlScCu, and AlSi can be selected. In the first metal of the present embodiment, a metal mainly composed of Al, such as an Al pure metal or an alloy obtained by adding a small amount (for example, about 4 wt%) of Cu to Al, is used.

  On the other hand, the remaining electrode fingers 5B other than the adjacent electrode finger 5A (the outermost electrode finger 5C in the present embodiment) are formed using a second metal that has better power durability than the first metal. Yes. As the second metal, a metal having high power resistance such as Cu, CuAg, CuAl, or CuSi can be selected. Cu is used in the second metal of the present embodiment.

  Two reflecting electrodes 4 are formed, one at each end of the comb-like electrode 3 paired on the surface 2 a of the piezoelectric substrate 2. As shown in FIG. 1, in this embodiment, since two pairs of comb-teeth electrodes 3 are arranged in one row, the reflective electrode 4 is located at a position between the two pairs of comb-teeth electrodes 3 arranged in one row. Each is formed. Moreover, the reflective electrode 4 has the electrode finger 6 arrange | positioned at the fence shape, respectively. The dimensions and number of the electrode fingers 6 of the reflective electrode 4 are appropriately changed according to the electric signal input / output from the comb-tooth electrode 3.

  Of all the electrode fingers 6 of the reflective electrode 4, the adjacent electrode finger 6 </ b> A adjacent to the electrode finger 5 of the comb electrode 3 is formed using a first metal having excellent migration resistance. Similar to the adjacent electrode finger 5A of the comb electrode 3 described above, the adjacent electrode finger 6A may be two to three electrode fingers 6 from the outside, but the adjacent electrode finger 6A of the reflective electrode 4 of the present embodiment is a comb. The outermost electrode finger 6 </ b> C is opposed to the electrode finger 5 of the tooth electrode 3. Further, since the remaining electrode fingers 6B other than the adjacent electrode finger 6A (in the present embodiment, the outermost electrode finger 6C) in the reflective electrode 4 are not required to have migration resistance or power resistance, the first metal or the first metal finger Any of two metals may be used, and other metals may be used.

  2 and 3, the adjacent electrode finger 5A of the comb electrode 3 (the outermost electrode finger 5C in the present embodiment) and the adjacent electrode finger 6A of the reflective electrode 4 (the outermost electrode finger in the present embodiment) are used. Two examples relating to the method of forming the outer electrode finger 6C) will be described. FIG. 2 shows a first example forming method of forming the adjacent electrode fingers 5A of the comb-teeth electrode 3 and the adjacent electrode fingers 6A of the reflective electrode 4 using only the first metal in the order of AC. Shows the formation method of the second example in which the first metal is coated on the surface of the second metal to form the adjacent electrode finger 5A of the comb electrode 3 and the adjacent electrode finger 6A of the reflective electrode 4 in the order of AC. Yes.

  First, the formation method of the first example will be described. The forming method of the first example mainly includes three steps. In the first step, as shown in FIG. 2A, a second metal film (not shown) is formed on the surface 2a of the piezoelectric substrate 2 by vapor deposition or sputtering. Thereafter, patterning (“patterning” means a series of steps by resist coating, exposure, and development) is performed on the second metal film, and the comb electrode 3 and the reflective electrode are formed on the surface 2 a of the piezoelectric substrate 2. The remaining electrode fingers 5B and 6B other than the adjacent electrode fingers 5A and 6A according to 4 are formed.

  In the second step, as shown in FIG. 2B, a resist film 10 is formed on the surface 2a of the piezoelectric substrate 2 and the remaining electrode fingers 5B and 6B related to the comb electrode 3 and the reflective electrode 4. Thereafter, by patterning the rectangular long holes 10 h in the resist film 10, portions where the adjacent electrode fingers 5 </ b> A and 6 </ b> A related to the comb-tooth electrode 3 and the reflective electrode 4 are formed are exposed from the resist film 10.

  In the final third step, the first metal is deposited or sputtered on the surface 2a of the piezoelectric substrate 2 exposed from the rectangular long hole 10h of the resist film 10 as shown in FIG. 2B, as shown in FIG. 2C. Then, adjacent electrode fingers 5A and 6A related to the comb electrode 3 and the reflective electrode 4 are formed on the surface 2a of the piezoelectric substrate 2. Thereafter, the resist film 10 is removed with a resist remover.

  Next, a forming method of the second example will be described. The forming method of the second example mainly includes three steps. In the first step, as shown in FIG. 3A, a second metal film is deposited or sputtered on the surface 2a of the piezoelectric substrate 2 and then patterned to form comb-like electrodes on the surface 2a of the piezoelectric substrate 2. 3 and electrode fingers 5 and 6 of the reflective electrode 4 are formed. Unlike the formation method of the first example (see FIG. 2A), in this first step, the main bodies 5Aa and 6Aa of the adjacent electrode fingers 5A and 6A related to the comb electrode 3 and the reflective electrode 4 are formed using the second metal. Has been.

  In the second step, as shown in FIG. 3B, a resist film 10 is formed on the surface 2 a of the piezoelectric substrate 2 and the electrode fingers 5 and 6 of the comb electrode 3 and the reflective electrode 4. Thereafter, by patterning the rectangular long holes 10h in the resist film 10, the surfaces and side surfaces of the main bodies 5Aa and 6Aa of the adjacent electrode fingers 5A and 6A related to the comb electrode 3 and the reflective electrode 4 are exposed from the resist film 10. .

  In the final third step, the first metal is deposited or sputtered on the surfaces and side surfaces of the main bodies 5Aa and 6Aa of the adjacent electrode fingers 5A and 6A exposed from the rectangular long hole 10h of the resist film 10 as shown in FIG. 3B. Thus, as shown in FIG. 3C, a first metal film is formed on the surfaces and side surfaces of the main bodies 5Aa and 6Aa so as to cover the main bodies 5Aa and 6Aa of the adjacent electrode fingers 5A and 6A. Thereafter, the resist film 10 is removed with a resist remover.

  Next, the operation of the surface acoustic wave device 1 according to the present embodiment will be described with reference to FIG.

  Migration occurs due to the potential difference between the electrodes. That is, in the surface acoustic wave device 1, no potential difference is generated between the electrode fingers 5 in the same comb-tooth electrode 3 and between the electrode fingers 6 in the same reflective electrode 4, so that there is no possibility of migration. . On the other hand, the outer two or three electrode fingers 5, 6 adjacent to each other between the comb electrode 3 and the reflective electrode 4 and between the two pairs of comb electrodes 3, that is, the respective adjacent electrodes Since there is a potential difference between the fingers 5A and 6A, migration may occur. Therefore, the adjacent electrode fingers 5A and 6A are locations where migration occurs (see FIGS. 5 and 6).

  Therefore, in the surface acoustic wave device 1 of the present embodiment, as shown in FIG. 1, the adjacent electrode fingers 5A and 6A of the comb electrode 3 and the reflective electrode 4 are formed using a first metal having excellent migration resistance. In addition, the electrode fingers 5 and 6 other than the adjacent electrode fingers 5A and 6A are formed using a second metal having excellent power durability. Therefore, as shown in FIG. 1, the migration resistance of the adjacent electrode fingers 5A and 6A can be improved by the first metal, and the remaining electrode fingers 5B other than the adjacent electrode fingers 5A and 6A that do not become the places where the migration occurs. 6B, the power durability can be improved by the second metal. Thereby, the electric power resistance can be improved without deteriorating the migration resistance of the comb-tooth electrode 3 and the reflective electrode 4.

  As described above, since the adjacent electrode fingers 5A and 6A are locations where migration occurs, migration may occur from some of the electrode fingers 5 and 6 outside the comb electrode 3 and the reflective electrode 4. However, it is often the case that only the outermost electrode fingers 5C and 6C among all the electrode fingers 5 and 6 are the locations where migration actually occurs (see FIGS. 5 and 6). Therefore, in the comb-tooth electrode 3 and the reflective electrode 4 of this embodiment, the adjacent electrode fingers 5A and 6A are limited to the outermost electrode fingers 5C and 6C only, and the first metal having excellent migration resistance is the outermost electrode finger. While being used only for the electrode fingers 5C and 6C, the second metal having excellent power durability is used for the remaining electrode fingers 5B and 6B. As a result, it is possible to efficiently improve the power durability while suppressing the occurrence of migration in the comb electrode 3 and the reflective electrode 4.

  Here, in the first metal of the present embodiment, a metal containing Al as a main component is used. Since the metal containing Al as a main component has been used not only for migration resistance but also conventionally, the electrode fingers 5 and 6 can be easily formed. In addition, migration resistance can be drastically improved by adding a small amount of an additive element to Al, such as when a small amount of Cu is added to Al.

  In the second metal of this embodiment, a metal containing Cu as a main component is used. When Cu is used for the electrode fingers 5 and 6, the power durability can be dramatically improved as compared with the case where Al is used for the electrode fingers 5 and 6. Moreover, Cu has a low unit price, and can form the comb electrode 3 and the reflective electrode 4 excellent in power durability at low cost.

  That is, according to the surface acoustic wave device 1 of the present embodiment, since the material used for the electrode fingers 5 and 6 is selected according to whether or not the electrode fingers 5 and 6 are locations where migration occurs, There exists an effect | action that the electric power durability of each electrode can be improved, preventing generation | occurrence | production of migration.

  In addition, this invention is not limited to embodiment mentioned above etc., A various change is possible as needed.

The top view which shows the surface acoustic wave device of this embodiment The top view which shows the 1st formation method which concerns on the comb-tooth electrode and reflective electrode of this embodiment in order of AC The top view which shows the 2nd formation method which concerns on the comb-tooth electrode and reflective electrode of this embodiment in order of AC Plan view showing a conventional surface acoustic wave device The top view which shows the state which the migration generate | occur | produced between the conventional comb-tooth electrode and the reflective electrode The top view which shows the state which the migration generate | occur | produced between the conventional comb-tooth electrodes

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface acoustic wave device 2 Piezoelectric substrate 3 Comb electrode 4 Reflective electrode 5 Electrode finger (of comb electrode) 5A Adjacent electrode finger (of comb electrode) 5B Electrode finger other than adjacent electrode finger (of comb electrode) 5C Outermost electrode finger (of the comb electrode) 6 Electrode finger (of the reflective electrode) 6A Adjacent electrode finger (of the reflective electrode) 6B Electrode finger other than the adjacent electrode finger (of the reflective electrode) 6C Outermost electrode finger (of the reflective electrode) Electrode finger

Claims (4)

A piezoelectric substrate having a piezoelectric surface;
Each of the piezoelectric substrates has electrode fingers arranged in a comb-like shape on the surface, and two or more pairs arranged in one row or in a row formed by alternately arranging the electrode fingers. A comb electrode;
Each set has electrode fingers arranged like a fence on the surface of the piezoelectric substrate, and each pair is formed at a position sandwiching two or more pairs of comb-shaped electrodes arranged in one or a row. And a reflective electrode,
In a pair of comb-shaped electrodes and electrode fingers of the reflective electrode, adjacent electrode fingers adjacent to the electrode fingers of the other comb-shaped electrode or the reflective electrode are more resistant to migration than electrode fingers other than the adjacent electrode fingers . It is formed using the first metal excellent in
A surface elasticity characterized in that in the electrode fingers of the pair of comb-teeth electrodes, the electrode fingers other than the adjacent electrode fingers are formed by using a second metal having a higher power durability than the first metal. Wave device. The surface acoustic wave device according to claim 1, wherein the adjacent electrode finger is an outermost electrode finger facing an electrode finger of the other comb-tooth electrode or the reflective electrode. The surface acoustic wave device according to claim 1, wherein the first metal is a metal containing Al as a main component. The surface acoustic wave device according to any one of claims 1 to 3, wherein the second metal is a metal containing Cu as a main component.

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