JP2010259005A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device that improves temperature characteristics without processing a piezoelectric substrate itself. <P>SOLUTION: The surface acoustic wave device 4 is equipped with a plurality of surface acoustic wave element portions 12, 14, 16, 18 having an IDT electrode which are formed on a same main surface 10a of the piezoelectric substrate 10. The surface acoustic wave device 4 is equipped with constrained layers 20, 22, 24 formed on the main surface 10a of the piezoelectric substrate 10 by using a material whose linear expansion coefficient is smaller than that of the piezoelectric substrate 10, the constrained layers 20, 22, 24 that are extended in parallel with a direction to which the surface acoustic wave transmits, and face the surface acoustic wave element portions 12, 14, 16, 18 on both external sides of a vibration region where the surface acoustic wave is transmitted by the IDT electrodes of the surface acoustic wave elements 12, 14, 16, 18 with respect to at least one of surface acoustic wave element portions 12, 14, 16 18. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave device, and more particularly, to a surface acoustic wave device composed of a filter, a resonator, or the like that uses a surface acoustic wave on a surface of a piezoelectric substrate.

Conventionally, for example, in a mobile communication system in which a frequency difference between a transmission band and a reception band is small, lithium tantalate (LiTaO ₃ ; LT), lithium niobate (LiNbO ₃ ; LN), etc. are used to secure attenuation in the reception band. A surface acoustic wave filter using a piezoelectric substrate having a large electromechanical coupling coefficient is used. However, when the frequency temperature coefficient (TCF) of the LT substrate or the LN substrate is large and the manufacturing variation is taken into consideration, the transmission / reception band interval becomes substantially very small. Therefore, improvement of temperature characteristics is desired.

  As a measure for improving temperature characteristics, it has been proposed that a piezoelectric substrate is bonded to a support substrate having higher strength and elasticity than the piezoelectric substrate.

For example, in Patent Document 1, as shown in the configuration diagram of FIG. 11 and the cross-sectional view of FIG. 12, an IDT resonator 2 is formed in a blank area around an IDT (interdigital transducer) resonator 2 on the surface of the LT substrate 1. A rectangular protective film 3 is formed so as to surround the substrate, and the protective film 3 is formed of quartz (SiO ₂ ) having a smaller thermal expansion coefficient than that of the LT substrate 1 and the expansion and contraction of the substrate 1 is limited by the protective film 3. It is disclosed.

  In Patent Document 2, as shown in the cross-sectional view of FIG. 13, after bonding a relatively thick piezoelectric substrate 111A and silicon substrate 112A, the substrates 111A and 112A are cut and polished (FIG. 13 ( b) and (c) (see cutting / deleting portions 111C and 112C), it is disclosed that the piezoelectric substrate 111B thinned to a desired level and the silicon substrate 112B are joined.

JP 2003-17980 A JP 2004-297893 A

  However, the structure in which the protective film 3 is formed on the stepped portion of the surface of the piezoelectric substrate 1 as shown in FIG. 12 requires a step of partially processing the surface of the piezoelectric substrate 1.

  Further, in the configuration in which the support substrate is bonded to the piezoelectric substrate as shown in FIG. 13, the step of thinning the piezoelectric substrate is necessary in order to obtain the temperature characteristic improvement effect unless the piezoelectric substrate is thinned.

  In view of such circumstances, the present invention intends to provide a surface acoustic wave device that can improve temperature characteristics without processing the piezoelectric substrate itself.

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

  In the surface acoustic wave device, a plurality of surface acoustic wave element portions including IDT electrodes are formed on the same main surface of a piezoelectric substrate. The surface acoustic wave device includes a constraining layer formed on the main surface of the piezoelectric substrate using a material having a linear expansion coefficient smaller than that of the piezoelectric substrate. The constraining layer extends parallel to the direction in which the surface acoustic wave propagates on both outer sides of the vibration region in which the surface acoustic wave from the IDT electrode of the surface acoustic wave element portion propagates with respect to at least one surface acoustic wave element portion. And the surface acoustic wave element portion is formed so as to face each other.

  In the above configuration, in the vibration region, expansion and contraction due to a temperature change in the direction in which the surface acoustic wave propagates is suppressed by the constraining layers disposed on both outer sides of the vibration region. As a result, the surface acoustic wave device has improved temperature characteristics.

  According to the above configuration, the piezoelectric substrate does not need to be thin or have a step. Therefore, a special process for processing the piezoelectric substrate itself is not necessary.

  Preferably, if the length in the direction in which the surface acoustic wave propagates in the vibration region is a, and the length in the direction in which the surface acoustic wave propagates in the portion of the constraining layer adjacent to the vibration region is b, b / a is 0.7 or more.

  An IDT electrode is disposed at the center portion of the vibration region, and the expansion and contraction of this portion has a great influence on the frequency characteristics. When b / a is 0.7 or more, at least the central portion of the vibration region that has a dominant influence on the temperature characteristics can suppress expansion and contraction due to temperature change, and effectively improve the temperature characteristics. be able to.

  If the constraining layer is adjacent to the entire vibration region, that is, if b / a is 1 or more, the expansion and contraction due to temperature change can be constrained by the constraining layer for the entire vibration region that affects the temperature characteristics, so the temperature characteristics are further improved. More preferred.

  Preferably, the constraining layer surrounds the entire outer periphery of the surface acoustic wave element portion.

  In this case, the sealing performance can be maintained when the surface acoustic wave device is mounted by flip chip bonding. That is, when the connection electrode is formed on the main surface of the piezoelectric substrate on which the surface acoustic wave element portion and the constraining layer are formed, and the connection electrode of the surface acoustic wave device is flip-chip bonded to the substrate or the package, the surface acoustic wave device The surface acoustic wave element is opposed to the substrate and the package and is surrounded by a constraining layer to be protected.

  The surface acoustic wave device of the present invention can improve temperature characteristics without processing the piezoelectric substrate itself. Since a special process for processing the piezoelectric substrate itself is unnecessary, it can be easily manufactured.

It is (a) top view and (b) sectional view of a surface acoustic wave device. (Example 1) It is a graph of the linear expansion coefficient of a surface acoustic wave device. (Example 1) It is a top view of a surface acoustic wave device. (Example 2) It is a top view of a surface acoustic wave device. (Specific example 1) 1 is a schematic diagram showing a circuit configuration of a surface acoustic wave device. (Specific example 1) It is a top view of a surface acoustic wave device. (Specific example 2) 1 is a schematic diagram showing a circuit configuration of a surface acoustic wave device. (Specific example 2) It is a top view of a surface acoustic wave device. (Specific example 3) 1 is a schematic diagram showing a circuit configuration of a surface acoustic wave device. (Specific example 3) It is a top view of a surface acoustic wave device. (Example 3) It is a perspective view of a surface acoustic wave device. (Conventional example 1) It is sectional drawing of a surface acoustic wave device. (Conventional example 1) It is sectional drawing which shows the manufacturing process of a surface acoustic wave device. (Conventional example 2)

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  Example 1 A surface acoustic wave device 4 of Example 1 will be described with reference to FIGS. 1 and 2.

  FIG. 1A is a plan view schematically showing the basic configuration of the surface acoustic wave device 4. FIG.1 (b) is sectional drawing which shows typically the cross section cut | disconnected along line AA of Fig.1 (a).

  As shown in FIG. 1, the surface acoustic wave device 4 includes four surface acoustic wave element portions 12, 14, 16, 18, constraining layers 20, 22, 24, and a wiring pattern 11 on the surface 10 a of the piezoelectric substrate 10. And are formed.

  The piezoelectric substrate 10 is an LT substrate or an LN substrate. The four surface acoustic wave element units 12, 14, 16, and 18 are connected by the wiring pattern 11, and constitute, for example, a longitudinally coupled resonator type filter. Each of the surface acoustic wave element units 12, 14, 16, and 18 includes one or more IDT electrodes and reflectors, and the surface acoustic wave excited by the IDT electrodes propagates between the reflectors. That is, the surface acoustic wave element units 12, 14, 16, and 18 are formed in a vibration region in which the surface acoustic wave by the IDT electrode propagates. The surface acoustic waves generated by the IDT electrodes of the surface acoustic wave element units 12, 14, 16, and 18 propagate in the left-right direction in FIG.

The constraining layers 20, 22, and 24 are formed using a material having a smaller linear expansion coefficient than that of the piezoelectric substrate 10. For example, after a conductive pattern including an IDT electrode and a wiring pattern 11 is formed on the surface 10a of the piezoelectric substrate 10, a protective film such as a resist is formed on the IDT electrode and the electrode pad, and a film forming method such as thermal spraying or sputtering is used. Then, the constraining layers 20, 22, and 24 are formed by depositing a material such as Si, Al ₂ O ₃ , or SiO ₂ having a smaller linear expansion coefficient than that of the piezoelectric substrate 10 such as the LT substrate or the LN substrate. In the case of thermal spraying, the film forming speed is fast, which is advantageous in terms of cost, and a thick film is easily formed.

  The constraining layers 20, 22, and 24 may be formed using a mask instead of a protective layer such as a resist. Further, through holes may be formed in the constraining layers 20, 22 and 24 using a laser or the like to expose the electrode pads, and input / output may be taken out.

  The constraining layers 20, 22, and 24 are formed on both outer sides of the surface acoustic wave element units 12, 14, 16, and 18. The constraining layers 20, 22, and 24 extend in parallel with the direction in which the surface acoustic waves from the IDT electrodes of the surface acoustic wave element units 12, 14, 16, and 18 propagate, that is, in the left-right direction in FIG. The surface acoustic wave element portions 12, 14, 16 and 18 are formed so as to face each other.

  Since the surface acoustic wave element portions 12, 14, 16, and 18 are disposed between the constraining layers 20, 22, and 24, the surface 10a of the piezoelectric substrate 10 expands and contracts with a temperature change in the direction in which the surface acoustic waves propagate. Is restricted by the constraining layers 20, 22, and 24, the change in the state in which the surface acoustic wave propagates is suppressed, and the change in the frequency characteristic becomes small. Therefore, the surface acoustic wave device 4 has improved temperature characteristics.

  The surface 10 a of the piezoelectric substrate 10 is constrained along the surface 10 a by the constraining layers 20, 22, and 24 in the direction in which the surface acoustic wave propagates. Therefore, the temperature characteristic can be improved without reducing the thickness of the piezoelectric substrate 10 or processing the groove on the surface 10a of the piezoelectric substrate 10.

  By forming the constraining layer 24 on the wiring pattern 11 as shown in FIG. 1B, the surface acoustic wave element portions 12, 14, 16, and 18 can be constrained individually, so that high temperature characteristics are improved. An effect is obtained.

  By limiting the range in which the constraining layers 20, 22, and 24 are formed, the constraining force on the surface acoustic wave element portions 12, 14, 16, and 18 is increased, and temperature characteristics can be effectively improved.

  By reducing the distance between the center of the IDT electrode of the surface acoustic wave element portions 12, 14, 16, and 18 and the constraining layers 20, 22, and 24, the restraint on the IDT electrode is easily transmitted, and a high temperature characteristic improvement effect is obtained. .

  Since it is not necessary to form a groove on the surface 10a of the piezoelectric substrate 10, the manufacturing process is simplified. Further, by not forming grooves on the surface 10a of the piezoelectric substrate 10, the constraining layers 20, 22, and 24 having a low linear expansion coefficient can be formed without considering the wiring portion.

  FIG. 2 is a graph showing the result of calculating the linear expansion coefficient of the surface 10 a of the piezoelectric substrate 10 of the surface acoustic wave element unit 12. In FIG. 2, the horizontal axis is b / a, and the vertical axis is the linear expansion coefficient. As shown in FIG. 1A, the length of the surface acoustic wave element portion 12 in the direction in which the surface acoustic wave propagates is a, and the surface acoustic waves are transmitted to the constraining layers 20 and 22 facing the surface acoustic wave element portion 12. The linear expansion coefficient of the surface 10a of the piezoelectric substrate 10 at the center of the surface acoustic wave element unit 12 was calculated with the length in the propagation direction being b.

  From FIG. 2, as the constraint width b of the constraint layers 20 and 22 with respect to the surface acoustic wave element unit 12 increases, the constraint force with respect to the surface acoustic wave element unit 12 increases and the linear expansion coefficient of the surface 10 a of the piezoelectric substrate 10 decreases. I understand.

  When b / a is smaller than 1, that is, when b is smaller than a, the linear expansion coefficient deteriorates rapidly. Therefore, b / a is preferably 1 or more.

  However, when an electrode pad is provided near the surface acoustic wave element portion as in the configuration example described later, b may not be larger than a, and b / a may not be 1 or more. Even in such a case, if b / a is 0.7 or more, the linear expansion coefficient is improved to some extent, and at least the expansion and contraction accompanying the temperature change in the central portion of the vibration region that has a dominant influence on the temperature characteristics. Since it can suppress, a temperature characteristic can be improved effectively.

  Example 2 A surface acoustic wave device 5 of Example 2 will be described with reference to FIG.

  FIG. 3 is a plan view schematically showing the basic configuration of the surface acoustic wave device 5.

  As shown in FIG. 3, in the surface acoustic wave device 5 of the second embodiment, the first surface acoustic wave element units 12, 14 and 2 in the surface acoustic wave device 4 of the first embodiment shown in FIG. The constraining layer 22 formed between the stage surface acoustic wave element portions 16 and 18 is eliminated.

すなわち、表１は、図３の実施例２の構成（モデル１）と、図１（ａ）の実施例１の構成（モデル２）とについて、それぞれの弾性表面波素子部１２，１４，１６，１８のＩＤＴ電極の中心部（ＩＤＴ１〜ＩＤＴ４）における圧電基板１０の表面１０ａの線膨張係数を計算した結果を示す。 Table 1 below shows the results of calculating the linear expansion coefficient for Examples 1 and 2.

That is, Table 1 shows the surface acoustic wave element sections 12, 14, and 16 for the configuration of the second embodiment in FIG. 3 (model 1) and the configuration of the first embodiment in FIG. 1A (model 2). , 18 shows the result of calculating the linear expansion coefficient of the surface 10a of the piezoelectric substrate 10 at the center (IDT1 to IDT4) of the IDT electrodes.

  From Table 1, it can be seen that the effect of improving the temperature characteristics can also be obtained by the configuration of FIG. 3 (model 1) in which the two surface acoustic wave element portions 12, 16; 14, 18 are sandwiched between the pair of constraining layers 20, 24.

  However, the configuration (model 2) in FIG. 1A in which the surface acoustic wave element portions 12, 14, 16, and 18 are individually sandwiched between the constraining layers 20, 22, and 24 has two surface acoustic wave element portions 12, 16; 14 and 18 are sandwiched between a pair of constraining layers 20 and 24, and the linear expansion coefficient is smaller than that of the configuration of FIG.

  Next, a configuration example of the surface acoustic wave device will be described.

  <Configuration Example 1> FIG. 4 is a plan view of the surface acoustic wave device 6 according to the configuration example 1, and FIG. 5 is a schematic diagram schematically showing a circuit configuration of the surface acoustic wave device 6 according to the configuration example 1.

  As shown in FIGS. 4 and 5, the surface 10 a of the piezoelectric substrate 10 has six electrode pads 30 to 35, four surface acoustic wave element portions 12, 14, 16, 18, and constraining layers 20, 22, 24a and 24b are formed.

  An unbalanced signal is input to the electrode pad 31. A balanced signal is output from the electrode pads 33 and 35. The electrode pads 30, 32, and 34 are connected to the ground.

  As shown in FIG. 5, the surface acoustic wave element units 12, 14, 16, and 18 include three IDT electrodes 50, 52, and 54 and two reflectors 60 and 62, respectively. Three IDT electrodes 50, 52, 54 are arranged between the two reflectors 60, 62, and the three IDT electrodes 50, 52, 54 and the two reflectors 60, 62 propagate the surface acoustic wave. The surface acoustic waves propagate in the vibration region between the reflectors.

  The electrode pad 31 to which an unbalanced signal is input is connected to the IDT electrode at the center of the surface acoustic wave element units 12 and 14 at the first stage. The electrode pads 33 and 35 to which the balanced signal is output are connected to the IDT electrodes at the center of the second stage surface acoustic wave element portions 16 and 18. The IDT electrodes on both sides of the first stage surface acoustic wave element units 12 and 14 and the IDT electrodes on both sides of the second stage surface acoustic wave element units 12 and 14 are connected to each other.

  <Configuration Example 2> FIG. 6 is a plan view of the surface acoustic wave device 7 of the configuration example 2, and FIG. 7 is a schematic diagram schematically showing a circuit configuration of the surface acoustic wave device 4 of the configuration example 2.

  As shown in FIGS. 6 and 7, on the surface 10a of the piezoelectric substrate 10, six electrode pads 30a to 35a, four surface acoustic wave element portions 12a, 14a, 16a, 18a, constraining layers 20k, 22k, 22q, 22p, and 24k are formed.

  An unbalanced signal is input to the electrode pad 31a. A balanced signal is output from the electrode pads 33a and 35a. The electrode pads 30a, 32a, 34a are connected to the ground.

  The constraining layers 20k, 22k, 22q, 22p, and 24k and the surface acoustic wave element portions 12a, 14a, 16a, and 18a are alternately formed in a line.

  As shown in FIG. 7, the surface acoustic wave element units 12a, 14a, 16a, and 18a include the three IDT electrodes 50, 52, and two reflectors 60 and 62, respectively, as in the configuration example 1. A surface acoustic wave propagates in the vibration region between the reflectors.

  The electrode pad 31a to which an unbalanced signal is input is connected to the IDT electrode at the center of the first stage surface acoustic wave element portions 14a and 16a. One electrode pad 33a from which a balanced signal is output is connected to the center IDT electrode of one surface acoustic wave element portion 12a in the second stage. The other electrode pad 35a from which the balanced signal is output is connected to the center IDT electrode of the other surface acoustic wave element portion 18a in the second stage.

  <Configuration Example 3> FIG. 8 is a plan view of the surface acoustic wave device 8 of the configuration example 3, and FIG. 9 is a schematic diagram schematically showing a circuit configuration of the surface acoustic wave device 8 of the configuration example 3.

  As shown in FIGS. 8 and 9, on the surface 10a of the piezoelectric substrate 10, six electrode pads 30b to 35b, four surface acoustic wave element portions 12b, 14b, 16b, and 18b, constraining layers 20s, 22s, 22t and 24s are formed.

  The electrode pads 30b, 32b, 33b are connected to the ground. An unbalanced signal is input to the electrode pad 31b. A balanced signal is output from the electrode pads 34b and 35b.

  The surface acoustic wave element portions 12b, 14b, 16b, and 18b and the constraining layers 20s, 22s, 22t, and 24s are alternately formed and arranged in a line.

  As shown in FIG. 9, the surface acoustic wave element portions 12b, 14b, 16b, and 18b include three IDT electrodes 50, 52, and 54 and two reflectors 60 and 62, respectively. Surface acoustic waves propagate in the vibration region between them.

  The electrode pad 31b to which the unbalanced signal is input is connected to the IDT electrode at the center of the first stage surface acoustic wave element portions 12b and 14b. One electrode pad 34b from which a balanced signal is output is connected to the center IDT electrode of one surface acoustic wave element portion 16b in the second stage. The other electrode pad 35b from which the balanced signal is output is connected to the center IDT electrode of the other surface acoustic wave element portion 18b in the second stage.

  <Example 3> A surface acoustic wave device 9 of Example 3 will be described with reference to FIG.

  FIG. 10 is a plan view schematically showing the basic configuration of the surface acoustic wave device 9. As shown in FIG. 10, the surface acoustic wave device 9 has four surface acoustic wave element portions 12, 14, 16, 18, a constraining layer 26, and a wiring pattern (not shown) on the surface 10 a of the piezoelectric substrate 10. Is formed. The constraining layer 26 is formed so as to surround the entire circumference of each surface acoustic wave element portion 12, 14, 16, 18.

  Although not shown, bumps are formed on the surface 10a of the piezoelectric substrate 10, and the surface acoustic wave device 9 can be mounted on a substrate or a package by flip chip bonding.

  When the surface acoustic wave device 9 is mounted on a substrate or a package by flip chip bonding, the surface acoustic wave element portion 10 faces the substrate or the package and is surrounded by a constraining layer 26, so that the surface acoustic wave element The parts 12, 14, 16, 18 are individually protected. Therefore, the sealing performance can be maintained when mounted by flip chip.

  <Summary> As described above, the temperature characteristics can be improved without processing the piezoelectric substrate itself. Since a special process for processing the piezoelectric substrate itself is unnecessary, it can be easily manufactured.

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

4-9 Surface acoustic wave device 10 Substrate 10a Surface (main surface)
12, 12a, 12b Surface acoustic wave element section 14, 14a, 14b Surface acoustic wave element section 16, 16a, 16b Surface acoustic wave element section 18, 18a, 18b Surface acoustic wave element section 20, 20a, 20k, 20s Constraining layer 22 , 22a, 22k, 22p, 22q, 22s, 22t Constrained layer 24, 24a, 24b, 24k, 24s Constrained layer 26 Constrained layer

Claims (3)

A surface acoustic wave device in which a plurality of surface acoustic wave element units including IDT electrodes are formed on the same main surface of a piezoelectric substrate,
A constraining layer formed on the main surface of the piezoelectric substrate using a material having a linear expansion coefficient smaller than that of the piezoelectric substrate;
The constraining layer is formed on at least one of the surface acoustic wave element portions on both outer sides of a vibration region in which the surface acoustic wave is propagated by the IDT electrode of the surface acoustic wave element portion in parallel with the direction in which the surface acoustic waves propagate. A surface acoustic wave device characterized in that:   Assuming that the length in the direction in which the surface acoustic wave propagates in the vibration region is a, and the length in the direction in which the surface acoustic wave propagates in the portion of the constraining layer facing the vibration region is b, b / a is 0. A surface acoustic wave device, wherein the surface acoustic wave device is 7 or more.   The surface acoustic wave device according to claim 1, wherein the constraining layer surrounds the entire circumference of the surface acoustic wave element unit.

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