JP2010251827A - Surface acoustic wave element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave element having improved manufacturing efficiency. <P>SOLUTION: The surface acoustic wave element includes: (a) a piezoelectric substrate 10 having a pair of main surfaces 10a, 10b which are parallel to each other; (b) an element pattern formed on the one main surface 10a of the piezoelectric substrate 10 and including an IDT electrode 20; and (c) a supporting layer 16 formed on the other main surface 10b of the piezoelectric substrate 10 and having a linear expansion coefficient smaller than that of the piezoelectric substrate 10. A groove 12 extending in parallel to the direction where a surface acoustic wave is propagated is formed so that a step difference 12x may be formed near the boundary between a portion opposing a vibration region where the surface acoustic wave propagates and a portion adjacent to the portion out of the other main surface 10b of the piezoelectric substrate 10 when viewed in the direction where the surface acoustic wave propagates by the IDT electrode 20. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a surface acoustic wave element, and more particularly to a method for manufacturing a surface acoustic wave element in which a support layer is formed on a piezoelectric substrate.

  A surface acoustic wave element such as a filter or a resonator using a surface acoustic wave needs to have a thin piezoelectric substrate in order to obtain desired characteristics. In order to reduce the thickness of the piezoelectric substrate, for example, a manufacturing method shown in a sectional view of FIG. 7 has been proposed.

  That is, as shown in FIG. 7A, after bonding the piezoelectric substrate 111A and the silicon support substrate 112A, as shown in FIG. 7B, a part 111C of the piezoelectric substrate 111A is cut and polished. The piezoelectric substrate 111B having a desired thickness is formed by removing. Next, as shown in FIG. 7C, an IDT electrode (IDT: interdigital transducers) 113, an electrode pad 114, and a conductive pattern 101a including a wiring pattern are formed on the piezoelectric substrate 111B, and a bump 108 is formed on the electrode pad 114. To do. Next, as shown in FIG. 7D, a part 112C of the support substrate 112A is removed by cutting and polishing to form a support substrate 112B having a desired thickness. Next, as shown in FIG. 7E, the piezoelectric substrate 111B and the support substrate 112B are cut so that the conductive patterns 101a are separated, thereby separating the surface acoustic waves separated into pieces as shown in FIG. The element 110, that is, the surface acoustic wave element 110 in which the support layer 112 is formed on the piezoelectric substrate 111 is manufactured (for example, see Patent Document 1).

JP 2004-297893 A

  However, it is difficult to process the entire surface of the piezoelectric substrate thinly and uniformly, and the piezoelectric substrate may be cracked during processing, so that it is difficult to manufacture efficiently. In addition, since the entire surface of the piezoelectric substrate is processed, a portion that needs to be thinned and a portion that does not need to be thinned are processed.

  In view of such circumstances, the present invention intends to provide a surface acoustic wave device capable of improving manufacturing efficiency.

  In order to solve the above problems, the present invention provides a surface acoustic wave device configured as follows.

  The surface acoustic wave element includes: (a) a piezoelectric substrate having a pair of main surfaces parallel to each other; (b) an element pattern including an IDT electrode formed on one of the main surfaces of the piezoelectric substrate; And a support layer formed on the other main surface of the piezoelectric substrate and having a linear expansion coefficient smaller than that of the piezoelectric substrate. When viewed in the direction in which the surface acoustic wave is propagated by the IDT electrode, a portion of the other principal surface of the piezoelectric substrate that faces the vibration region where the surface acoustic wave propagates and a portion adjacent to the portion A groove extending in parallel with the direction in which the surface acoustic wave propagates is formed so that a step is formed in the vicinity of the boundary.

  In the above configuration, the expansion and contraction accompanying the temperature change of the piezoelectric substrate is suppressed by the support layer having a smaller linear expansion coefficient than that of the piezoelectric substrate. Therefore, the temperature characteristics of the surface acoustic wave element can be improved.

  In the above configuration, the groove formed in the portion of the other principal surface of the piezoelectric substrate facing the vibration region when viewed in the direction in which the surface acoustic wave due to the IDT electrode propagates extends in the direction in which the surface acoustic wave propagates. And it may be formed also in parts other than the part which opposes a vibration area | region beyond the part which opposes a vibration area | region.

  According to the above configuration, a groove may be partially formed on the other main surface of the piezoelectric substrate, and the piezoelectric substrate is processed as compared with the case where the entire surface of the other main surface of the piezoelectric substrate is processed to have the same thickness. Hard to break inside.

  Further, when viewed in the direction in which the surface acoustic wave due to the IDT electrode propagates, the thickness of the piezoelectric substrate differs between the part facing the vibration region and the other part depending on the presence or absence of the groove. Therefore, the processing method, the processing accuracy, and the processing shape can be changed between the portion facing the vibration region and the other portion of the other main surface of the piezoelectric substrate. Therefore, the other main surface of the piezoelectric substrate can be processed more efficiently than the case where the entire surface of the other main surface of the piezoelectric substrate is processed into the same processed shape with the same processing accuracy with the same processing method.

  Therefore, it can process efficiently and the temperature characteristic improvement effect can be acquired.

  In a preferred aspect, the groove faces a vibration region in which the surface acoustic wave due to the IDT electrode propagates in the other main surface of the piezoelectric substrate when viewed in the direction in which the surface acoustic wave due to the IDT electrode propagates. It is formed only in the part to be.

  In this case, the piezoelectric substrate is thinned by forming a groove in a portion facing the vibration region. When thinning the piezoelectric substrate in order to obtain desired characteristics, it is only necessary to process the portion facing the vibration region, so that it can be processed efficiently.

  In another preferable aspect, when the groove is viewed in a direction in which the surface acoustic wave due to the IDT electrode propagates, in the vibration region where the surface acoustic wave due to the IDT electrode propagates in the other main surface of the piezoelectric substrate. It is formed only in parts other than the opposing part.

  In this case, the portion of the piezoelectric substrate that opposes the vibration region is contracted by a temperature change in the direction in which the surface acoustic wave propagates, and is formed near the boundary between the portion that opposes the vibration region and the portion adjacent to the portion. It is limited by the support layer composed of a low thermal expansion coefficient through the step. Therefore, the temperature characteristics can be further improved.

  In each of the above configurations, preferably, a plurality of the grooves are formed.

  In this case, the characteristics of the surface acoustic wave element can be improved by changing the direction in which the bulk wave is reflected on the other principal surface of the piezoelectric substrate depending on the location and weakening the bulk wave.

  The surface acoustic wave device of the present invention can improve manufacturing efficiency.

It is sectional drawing of a surface acoustic wave element. (Example 1) It is a partial cross-sectional perspective view of a surface acoustic wave element. (Example 1) It is sectional drawing which shows the manufacturing process of a surface acoustic wave element. (Example 1) It is sectional drawing of a surface acoustic wave element. (Example 1) It is sectional drawing of a surface acoustic wave element. (Example 2) It is sectional drawing of a surface acoustic wave element. (Example 3) It is sectional drawing which shows the manufacturing process of a surface acoustic wave element. (Conventional example)

  Embodiments of the present invention will be described below with reference to FIGS.

  <Example 1> A surface acoustic wave element 2 according to Example 1 will be described with reference to FIGS.

  FIG. 1 is a cross-sectional view of the surface acoustic wave element 2. FIG. 2 is a perspective view schematically showing the configuration of the surface acoustic wave element 2.

  As shown in FIGS. 1 and 2, an element pattern including an IDT electrode 20 is formed on the surface 10 a which is one main surface of the piezoelectric substrate 10. The IDT electrode 20 is configured by a pair of comb-shaped electrodes each having a plurality of electrode fingers 22 that are interleaved with each other, and one end of the electrode finger 22 is connected to the bus bar 21. A support layer 16 is formed on the back surface 10 b which is the other main surface of the piezoelectric substrate 10. The support layer 16 has a linear expansion coefficient smaller than that of the piezoelectric substrate 10.

  As indicated by an arrow 28 in FIG. 2, the surface acoustic wave generated by the IDT electrode 20 propagates in the vertical direction to the electrode finger 22 of the IDT electrode 20. FIG. 1 is a cross-sectional view taken along the electrode finger 22 of the IDT electrode 20, and the surface acoustic wave generated by the IDT electrode 20 propagates in the direction perpendicular to the paper surface of FIG. As shown in FIG. 1, when viewed in the direction in which the surface acoustic wave due to the IDT electrode 20 propagates, the IDT electrode is formed on the back surface 10 b of the piezoelectric substrate 10 facing the vibration region where the surface acoustic wave due to the IDT electrode 20 propagates. A groove 12 extending in parallel with the direction in which the surface acoustic wave propagates due to the surface 20 is formed, and a step is formed near the boundary between the portion facing the vibration region where the surface acoustic wave due to the IDT electrode 20 propagates and the portion adjacent to the portion. 12x is formed. The groove 12 is processed so that the thickness between the surface 10a of the piezoelectric substrate 10 and the groove bottom surface 12a of the groove 12 has a predetermined dimension corresponding to a desired frequency characteristic.

  Since the groove 12 only needs to be processed on the portion of the back surface 10b of the piezoelectric substrate 10 that faces the vibration region, the piezoelectric substrate 10 can be processed efficiently. That is, if the grooves 12 are partially formed on the back surface 10b of the piezoelectric substrate 10, the piezoelectric substrate 10 is less likely to be cracked during processing than when processing the entire back surface 10b of the piezoelectric substrate 10 to have the same thickness. In addition, the processing method, processing accuracy, and processing shape can be changed between the portion where the groove 12 is processed and the other portion of the back surface 10b of the piezoelectric substrate 10, and the same processing method is applied to the entire back surface of the piezoelectric substrate 10. Thus, the back surface of the piezoelectric substrate 10 can be processed more efficiently than when processing into the same processing shape with the same processing accuracy. Since the piezoelectric substrate 10 on the back surface of the IDT electrode 20 can be thinned, the temperature characteristics are improved.

  In addition, the groove | channel 12 may be formed also in parts other than the part which opposes a vibration area | region beyond the part which opposes a vibration area | region. For example, when a reflector is formed on the surface 10 a of the piezoelectric substrate 10 together with the IDT electrode, and the surface acoustic wave generated by the IDT electrode 20 is confined between the reflectors, the groove 12 is formed by the surface acoustic wave generated by the IDT electrode 20. It may be formed on both sides of the portion facing the vibration region so as to pass through the portion facing the vibration region in parallel with the direction in which the light propagates.

  The temperature characteristics of the surface acoustic wave element 2 are improved by the support layer 16 having a smaller linear expansion coefficient than the piezoelectric substrate 10. That is, when the portion of the piezoelectric substrate 10 facing the vibration region expands and contracts as the temperature changes, the expansion and contraction of the groove bottom surface 12a of the groove 12 formed on the back surface 10b of the piezoelectric substrate 10 is configured with a low thermal linear expansion coefficient. Limited by the support layer 16. When the support layer 16 restricts expansion and contraction in the direction in which the surface acoustic wave propagates in the vibration region of the piezoelectric substrate 10, changes in the vibration propagation state are suppressed, fluctuations in frequency characteristics are reduced, and temperature characteristics are improved. .

  For example, as shown in the cross-sectional view of FIG. 4, when the simulation is performed on the case where the groove 12 is formed in the piezoelectric substrate 10, the linear expansion coefficient in the direction in which the surface acoustic wave propagates at the center 10 c of the vibration region is 9.62 ppm / ° C. there were. On the other hand, when the groove 12 was not formed in the piezoelectric substrate 10, the linear expansion coefficient in the direction in which the surface acoustic wave at the center 10c of the vibration region propagated was 13.36 ppm / ° C. It can be seen that the temperature characteristic can be further improved because the linear expansion coefficient is reduced by forming the groove 12.

  The dimensions and the like of each part of FIG. 4 used for the simulation are as follows.

  The width W1 of the piezoelectric substrate 10 was 0.8 mm, and the thickness T1 was 40 μm. The total thickness T0 of the piezoelectric substrate 10 and the support layer 16 was 150 μm. When the groove 12 was formed, the groove width W2 was 0.4 mm, the width W3 on both sides of the groove 12 was 0.2 mm, and the thickness T2 of the portion of the piezoelectric substrate 10 where the groove 12 was formed was 20 μm. The distance (L) between the center point 10c of the surface 10a of the piezoelectric substrate 10 and a point 0.05 mm away from the center point 10c in the direction in which the surface acoustic wave propagates (in the direction perpendicular to the paper surface) increases with a temperature increase of 100 ° C. The linear expansion coefficient was calculated by λ / (L × 100) based on the dimension (λ) to be extended.

  Next, a method for manufacturing the surface acoustic wave element 2 will be described with reference to FIG. FIG. 3 is a cross-sectional view schematically showing the manufacturing process of the surface acoustic wave element 2.

(A) Pattern Formation Step First, as shown in FIG. 3A, an element pattern including the IDT electrode 20 is formed on the surface 10a of the wafer-like piezoelectric substrate 10.

Specifically, on the surface 10a of the piezoelectric substrate 10 such as a lithium tantalate (LiTaO ₃ ) substrate or a lithium niobate (LiNbO ₃ ) substrate, an IDT electrode 20, a pad (not shown), and between the IDT electrode and the pad are provided. An element pattern including a wiring (not shown) for connecting is formed. The element pattern is formed by processing a metal film into a predetermined pattern on the surface 10a of the piezoelectric substrate 10 by a thin film forming method such as a vapor deposition method, a sputtering method, or a CVD method using a photolithography technique or an etching technique.

(B) Substrate Thinning Step Next, as shown in FIG. 3B, the back surface 10b of the piezoelectric substrate 10 is processed to make the piezoelectric substrate 10 thinner.

  Specifically, with the surface 10a of the piezoelectric substrate 10 fixed through a bonding material such as an adhesive tape or wax, the back surface 10b of the piezoelectric substrate 10 is subjected to removal processing such as grinding (grinding) or polishing (lapping). The piezoelectric substrate 10 is thinned.

(C) Groove Formation Step Next, as shown in FIG. 3C, the groove 12 is processed on the back surface 10b of the piezoelectric substrate 10 by half-cutting or sandblasting.

  In the case of half-cutting, the groove 12 is formed by cutting a dicing grade cutting edge into the back surface 10b of the piezoelectric substrate 10 to a predetermined depth. In the case of sandblasting, sandblasting is performed in a state where the back surface 10b of the piezoelectric substrate 10 is covered except for the portion where the groove 12 is formed. Half cut and sandblasting may be combined.

(D) Support Layer Formation Step Next, as shown in FIG. 3 (d), the support layer 16 is formed on the back surface 10 b of the piezoelectric substrate 10.

Specifically, the support layer 16 is formed by film formation such as thermal spraying. In particular, by thermal spraying, the support layer 16 can be easily formed on the back surface 10b of the piezoelectric substrate 10 on which irregularities are formed by the grooves 12. The support layer 16 is formed using a material having a sufficiently small linear expansion coefficient relative to the linear expansion coefficient of the piezoelectric substrate 10 such as lithium tantalate or lithium niobate, such as Si, Al ₂ O ₃ , or SiO ₂ .

(E) Substrate dividing step Next, after the bonding material is peeled off by UV irradiation or chemical cleaning, the integrally formed piezoelectric substrate 10 and support layer 16 are divided by dicing or the like, and the surface acoustic wave shown in FIG. A piece of element 2 is formed.

  According to the manufacturing method described above, the surface acoustic wave elements 2 can be efficiently manufactured in batches in a wafer state, but can also be manufactured one by one from the beginning.

  Example 2 A surface acoustic wave element 2a according to Example 2 will be described with reference to FIG.

  The surface acoustic wave element 2a according to the second embodiment is configured in substantially the same manner as the surface acoustic wave element 2 according to the first embodiment. In the following, the same reference numerals are used for the same components as in the first embodiment, and differences from the first embodiment will be mainly described.

  FIG. 5 is a cross-sectional view showing the configuration of the surface acoustic wave element 2a according to the second embodiment, and is a cross-sectional view taken along the electrode finger 22 of the IDT electrode 20 similarly to FIG.

  In the surface acoustic wave element 2a according to the second embodiment, the support layer 18 is formed on the back surface 10b of the piezoelectric substrate 10 when viewed in the direction in which the surface acoustic waves from the IDT electrode 20 propagate as shown in FIG. A groove 14 is formed on the back surface 10b of the piezoelectric substrate 10 so as to extend in parallel with the direction in which the surface acoustic wave due to the IDT electrode 20 propagates.

  However, unlike the first embodiment, the groove 14 is formed on the back surface 10b of the piezoelectric substrate 10 other than the portion facing the vibration region where the surface acoustic wave due to the IDT electrode 20 propagates. In the piezoelectric substrate 10, both sides of the portion facing the vibration region are made thinner than the portion facing the vibration region by the groove 14, and a step 14 x is formed near the boundary between the portion facing the vibration region and the portion adjacent to the portion. Is formed.

  A portion of the piezoelectric substrate 10 facing the vibration region is contracted by a temperature change in the direction in which the surface acoustic wave propagates, and a step 14x formed near the boundary between the portion facing the vibration region and a portion adjacent to the portion. It is limited by the support layer 18 composed of a low coefficient of thermal expansion through. Accordingly, the temperature characteristics are further improved.

  Example 3 A surface acoustic wave element 2b of Example 3 will be described with reference to FIG.

  The surface acoustic wave element 2b according to the third embodiment is configured in substantially the same manner as the surface acoustic wave element 2 according to the first embodiment. In the following, the same reference numerals are used for the same components as in the first embodiment, and differences from the first embodiment will be mainly described.

  FIG. 6 is a cross-sectional view showing the configuration of the surface acoustic wave element 2b according to the third embodiment, and is a cross-sectional view taken along the electrode finger 22 of the IDT electrode 20 similarly to FIG.

  When the surface acoustic wave element 2b according to the third embodiment is viewed in the direction in which the surface acoustic waves from the IDT electrode 20 propagate as shown in FIG. 6, the support layer 17 is provided on the back surface 10b of the piezoelectric substrate 10 as in the first embodiment. A groove 13 extending in parallel with the direction in which the surface acoustic wave due to the IDT electrode 20 propagates is formed in a portion of the back surface 10b of the piezoelectric substrate 10 facing the vibration region where the surface acoustic wave due to the IDT electrode 20 propagates. A step 13x is formed in the vicinity of the boundary between the portion formed and opposed to the vibration region and the portion adjacent to the portion. However, unlike Example 1, a plurality of grooves 13 are formed.

  When a plurality of grooves 13 are formed as in the third embodiment, the direction in which the bulk wave is reflected on the back surface 10b side of the piezoelectric substrate 10 varies depending on the location. Accordingly, the bulk wave can be weakened as compared with the case where the back surface 10b side of the piezoelectric substrate 10 is a flat surface and the reflection direction of the bulk wave is uniform, so that the characteristics of the surface acoustic wave element can be improved.

  <Summary> As described above, manufacturing efficiency can be improved by forming a groove on the back surface of the piezoelectric substrate.

  The present invention is not limited to the above embodiment, and can be implemented with various modifications.

  For example, the cross-sectional shape of the groove is arbitrary. For example, the cross section of the groove may be V-shaped or U-shaped. The bottom surface of the groove is not limited to a flat surface, and may be rough or rough, such as a zigzag cross section. When there are a plurality of IDT electrodes, a plurality of grooves corresponding to the individual IDT electrodes may be formed.

2, 2a, 2b, 2x Surface acoustic wave element 10 Piezoelectric substrate 10a Surface (one main surface)
10b Back side (the other main side)
12, 13, 14 Groove 16, 17, 18 Support layer 20 IDT electrode 21 Bus bar 22 Electrode finger

Claims (4)

A piezoelectric substrate having a pair of main surfaces parallel to each other;
An element pattern including an IDT electrode formed on one main surface of the piezoelectric substrate;
A support layer formed on the other principal surface of the piezoelectric substrate and having a linear expansion coefficient smaller than that of the piezoelectric substrate;
In a surface acoustic wave device comprising:
When viewed in the direction in which the surface acoustic wave is propagated by the IDT electrode, a portion of the other principal surface of the piezoelectric substrate that faces the vibration region where the surface acoustic wave propagates and a portion adjacent to the portion A surface acoustic wave element, wherein a groove extending in parallel with a direction in which the surface acoustic wave propagates is formed so that a step is formed in the vicinity of the boundary.   The groove is formed only in a portion of the other main surface of the piezoelectric substrate facing a vibration region where the surface acoustic wave due to the IDT electrode propagates when viewed in a direction in which the surface acoustic wave due to the IDT electrode propagates. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is provided.   The groove is a portion of the other principal surface of the piezoelectric substrate other than a portion facing a vibration region in which the surface acoustic wave due to the IDT electrode propagates when viewed in a direction in which the surface acoustic wave due to the IDT electrode propagates. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is formed only on the surface.   The surface acoustic wave device according to claim 1, wherein a plurality of the grooves are formed.

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