JP2010200197A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave (SAW) device which has a high manufacturing yield and high reliability by suppressing the warpage of a substrate du to temperature changes. <P>SOLUTION: A first piezoelectric substrate 11 and a second piezoelectric substrate 13 are constituted of the same kind of piezoelectric materials having anisotropy in thermal expansion coefficient. The first piezoelectric substrate 11 includes an interdigital electrode 15, exciting a SAW on one principal surface; another principal surface bonded to one principal surface of a supporting substrate 12; and the other principal surface of the support substrate 12 bonded to one principal surface of the second piezoelectric substrate 13. In a SAW propagation direction, the thermal expansion coefficient of the supporting substrate 12 is made smaller than that of the first piezoelectric substrate 11, a direction in which the thermal expansion coefficient of the first piezoelectric substrate 11 in a planar direction is great is made identical to the direction in which the thermal expansion coefficient of the second piezoelectric substrate 13 in a plane direction is large. Furthermore, the thickness of the support substrate 12 is made larger than the sum of the thickness of the piezoelectric substrate 11 and the thickness of the second piezoelectric substrate 13. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave device mainly used in mobile communication equipment.

  Hereinafter, a conventional surface acoustic wave device will be described with reference to the drawings.

  FIG. 3 shows a schematic diagram of a conventional surface acoustic wave device. In FIG. 3, reference numeral 1 denotes a piezoelectric substrate made of a lithium tantalate single crystal of 36 ° rotation Y-cut X propagation. Reference numeral 2 denotes a comb-shaped electrode made of a conductor disposed on one main surface of the piezoelectric substrate 1, and a surface acoustic wave is excited on the surface of the piezoelectric substrate 1 by applying a voltage to the comb-shaped electrode 2. A support substrate 3 is bonded to the other main surface of the piezoelectric substrate 1, and a bonded body of the support substrate 3 and the piezoelectric substrate 1 constitutes the bonded substrate 4.

  Then, by making the thermal expansion coefficient of the support substrate 3 smaller than the thermal expansion coefficient of the piezoelectric substrate 1 in the propagation direction of the surface acoustic wave, the thermal expansion due to the temperature change of the piezoelectric substrate 1 in the propagation direction of the surface acoustic wave is suppressed. As a result, the fluctuation of the frequency characteristic due to the temperature change of the surface acoustic wave device is suppressed.

For example, Patent Document 1 and Patent Document 2 are known as prior art document information relating to the invention of this application.
JP 2007-150931 A JP 2002-9584 A

  However, the conventional surface acoustic wave device shown in FIG. 3 suppresses dimensional changes due to temperature changes by bonding and restraining the piezoelectric substrate 1 having a large thermal expansion coefficient to the support substrate 3 having a small thermal expansion coefficient. As a result, the difference in thermal expansion coefficient between the piezoelectric substrate 1 and the support substrate 3 becomes large, and as a result, a relatively large warp occurs when the temperature rises. In general, since a surface acoustic wave device passes through a thermal history of room temperature to 260 ° C. in the manufacturing process and the mounting process, the bonding substrate 4 has a convex shape on the side of the piezoelectric substrate 1 having a large thermal expansion coefficient when the temperature rises. The bonding substrate 4 has a problem that the bonding substrate 4 is cracked by the warp and the manufacturing yield is lowered. Further, even when the surface acoustic wave device is used, there is a problem that the bonding substrate 4 warps when a temperature change occurs, and this warping causes cracks in the bonding substrate 4 and impairs reliability. Was.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a surface acoustic wave device having a good manufacturing yield and high reliability by suppressing the warpage of the substrate due to a temperature change. .

  In order to achieve the above object, the present invention has the following configuration.

  According to a first aspect of the present invention, in the surface acoustic wave device including the first piezoelectric substrate, the support substrate, and the second piezoelectric substrate, the first piezoelectric substrate, the second piezoelectric substrate, The first piezoelectric substrate has a comb-shaped electrode for exciting a surface acoustic wave on one main surface, and the other main surface is supported by the first piezoelectric substrate. Bonded to one main surface of the substrate, the other main surface of the support substrate is bonded to one main surface of the second piezoelectric substrate, and the coefficient of thermal expansion of the support substrate in the propagation direction of the surface acoustic wave A direction in which the thermal expansion coefficient is smaller than that of the first piezoelectric substrate, the thermal expansion coefficient in the planar direction of the first piezoelectric substrate is large, and a direction in which the thermal expansion coefficient in the planar direction of the second piezoelectric substrate is large. In the same direction, and the thickness of the support substrate is the first direction The thickness of the electric substrate is larger than the total thickness of the second piezoelectric substrate. According to this configuration, the first piezoelectric substrate and the second piezoelectric substrate have anisotropy in thermal expansion coefficient. Composed of the same kind of piezoelectric material, the first piezoelectric substrate has a comb-shaped electrode for exciting a surface acoustic wave on one main surface, and the other main surface is bonded to one main surface of the support substrate, The other main surface of the support substrate is bonded to one main surface of the second piezoelectric substrate, and the thermal expansion coefficient of the support substrate is set to be the thermal expansion coefficient of the first piezoelectric substrate in the propagation direction of the surface acoustic wave. The direction in which the thermal expansion coefficient in the planar direction of the first piezoelectric substrate is large and the direction in which the thermal expansion coefficient in the planar direction of the second piezoelectric substrate is large are the same direction, and The thickness of the first piezoelectric substrate and the thickness of the second piezoelectric substrate Since the total thickness of the plates is larger, the stress in the vertical direction caused by the difference in thermal expansion coefficient between the first piezoelectric substrate and the support substrate is reduced by the thermal expansion coefficient between the second piezoelectric substrate and the support substrate. It can be offset by the reverse stress caused by the difference, thereby suppressing the warpage of the substrate due to the temperature change, so that it is possible to prevent the substrate from cracking due to the warp at the time of use, and at the time of use It has the effect that the fall of the reliability by curvature can also be suppressed.

  According to a second aspect of the present invention, in the surface acoustic wave device including the first piezoelectric substrate, the second piezoelectric substrate, and the third piezoelectric substrate, the first piezoelectric substrate and the second piezoelectric substrate. The substrate and the third piezoelectric substrate are made of the same kind of piezoelectric material having anisotropy in thermal expansion coefficient, and the first piezoelectric substrate has a comb-shaped electrode for exciting a surface acoustic wave on one main surface, And the other main surface is directly bonded to one main surface of the second piezoelectric substrate, the other main surface of the second piezoelectric substrate is directly bonded to one main surface of the third piezoelectric substrate, The direction in which the thermal expansion coefficient in the planar direction of the first piezoelectric substrate is large, the direction in which the thermal expansion coefficient in the planar direction of the second piezoelectric substrate is small, and the thermal expansion coefficient in the planar direction of the third piezoelectric substrate are The larger direction is the same direction, and the thickness of the second piezoelectric substrate is set to the first direction. The thickness of the piezoelectric substrate is larger than the total thickness of the third piezoelectric substrate. According to this configuration, the first piezoelectric substrate, the second piezoelectric substrate, and the third piezoelectric substrate are thermally expanded. The first piezoelectric substrate has a comb-shaped electrode for exciting a surface acoustic wave on one main surface, and the other main surface is the second piezoelectric substrate. The other main surface of the second piezoelectric substrate is directly bonded to one main surface of the third piezoelectric substrate, and thermal expansion in the plane direction of the first piezoelectric substrate is performed. The direction in which the coefficient is large, the direction in which the coefficient of thermal expansion in the plane direction of the second piezoelectric substrate is small, and the direction in which the coefficient of thermal expansion in the plane direction of the third piezoelectric substrate is large are the same direction. The thickness of the piezoelectric substrate is set to the thickness of the first piezoelectric substrate and the third pressure. Since it is larger than the total thickness of the substrate, it is possible to suppress the warpage of the substrate at the time of temperature change, thereby suppressing the cracking of the substrate and the deterioration of the reliability, and the first piezoelectric element. Since the acoustic impedance of the bonding surface between the substrate and the second piezoelectric substrate can be matched, noise due to reflection of leaky bulk waves at this bonding surface can be suppressed, and as a result, an elastic surface with good electrical characteristics. It has the effect that a wave device can be provided.

  As described above, the surface acoustic wave device according to the present invention is the surface acoustic wave device including the first piezoelectric substrate, the support substrate, and the second piezoelectric substrate, and the first piezoelectric substrate and the second piezoelectric substrate. And the first piezoelectric substrate has a comb-shaped electrode for exciting a surface acoustic wave on one main surface, and the other main surface is Bonded to one main surface of the support substrate, the other main surface of the support substrate is bonded to one main surface of the second piezoelectric substrate, and the thermal expansion coefficient of the support substrate in the propagation direction of the surface acoustic wave In which the thermal expansion coefficient in the planar direction of the first piezoelectric substrate is large and the thermal expansion coefficient in the planar direction of the second piezoelectric substrate is large. And the thickness of the support substrate Since the thickness of the first piezoelectric substrate and the total thickness of the second piezoelectric substrate are larger, the stress in the vertical direction caused by the difference in thermal expansion coefficient between the first piezoelectric substrate and the support substrate is This can be offset by the reverse stress caused by the difference in the thermal expansion coefficient between the second piezoelectric substrate and the support substrate, thereby suppressing the warpage of the substrate due to the temperature change. It is possible to prevent the substrate from being cracked and to produce an excellent effect that the decrease in reliability due to warpage during use can also be suppressed.

(Embodiment 1)
Hereinafter, the first aspect of the present invention will be described with reference to the first embodiment.

  FIG. 1 is a schematic diagram of a surface acoustic wave device according to Embodiment 1 of the present invention.

  In FIG. 1, reference numeral 11 denotes a first piezoelectric substrate that forms an element for exciting surface acoustic waves on the surface thereof. This first piezoelectric substrate 11 adapts a lithium tantalate single crystal to the propagation of surface acoustic waves. Thus, it is cut and configured to have a normal direction rotated by an angle in the range of 36 ° from the Y axis to the Z axis direction around the X axis, and its thickness is about 25 μm, An element for exciting a surface acoustic wave having a traveling direction in the X-axis direction is formed on the surface. In addition to lithium tantalate single crystals, there are piezoelectric single crystals such as lithium niobate single crystals and quartz crystals, which are generally different in thermal expansion coefficient. It has directionality. In the case of the lithium tantalate single crystal described above, the thermal expansion coefficient in the X-axis direction and the Y-axis direction is 16 ppm / ° C., whereas the thermal expansion coefficient in the Z-axis direction is 4 ppm / ° C., which excites surface acoustic waves. The coefficient of thermal expansion in the X-axis direction is large.

  Reference numeral 12 denotes a support substrate. This support substrate 12 is made of a sapphire single crystal having a thermal expansion coefficient of 7 ppm / ° C., a Young's modulus of 470 GPa, and a bending strength of 690 MPa, and the plate thickness is about 0.3 mm. The support substrate 12 is bonded to the surface of the first piezoelectric substrate 11 opposite to the surface for exciting the surface acoustic wave via an adhesive (not shown). In this way, the propagation direction of the surface acoustic wave of the first piezoelectric substrate 11 is obtained by bonding the support substrate 12 having a smaller thermal expansion coefficient than that of the first piezoelectric substrate 11 in the propagation direction of the surface acoustic wave. Therefore, it is possible to restrain a change in frequency characteristics due to a temperature change of the surface acoustic wave device.

  As the material of the support substrate 12, low thermal expansion glass, alumina ceramic, silicon carbide, silicon nitride, silicon or the like can be used in addition to sapphire single crystal, and the thermal expansion of the first piezoelectric substrate 11 is mechanically performed. It is only necessary to appropriately select a substance having a rigidity and a bending strength for restraining and having a small coefficient of thermal expansion according to a temperature change characteristic of a required frequency.

  Reference numeral 13 denotes a second piezoelectric substrate. The second piezoelectric substrate 13 is a normal direction obtained by rotating a lithium tantalate single crystal around the X axis at an angle in the range of 36 ° from the Y axis to the Z axis. The thickness is about 25 μm. The second piezoelectric substrate 13 has an adhesive (not shown) on the surface of the support substrate 12 opposite to the surface to which the first piezoelectric substrate 11 is bonded, and the first piezoelectric substrate. The X-axis direction of 11 and the X-axis direction of the second piezoelectric substrate 13 are joined in the same direction. The joined body of the first piezoelectric substrate 11, the support substrate 12, and the second piezoelectric substrate 13 constitutes a joined substrate 14.

  Reference numeral 15 denotes a comb-shaped electrode in which a plurality of electrode fingers are arranged in the X-axis direction of the first piezoelectric substrate 11 on the surface of the bonding substrate 14 that excites the surface acoustic wave, that is, the exposed surface of the first piezoelectric substrate 11. The comb-shaped electrode 15 is made of a metal whose main component is aluminum, and excites a surface acoustic wave propagating in the X-axis direction by applying an AC voltage. The mode of the surface acoustic wave to be excited may be a Rayleigh wave or a leaky wave. In the bonding substrate 14, a surface acoustic wave device is manufactured by forming an interdigital electrode 15 and other conductive circuits (not shown) and then sealing an excitation space.

  As described above, in the first embodiment of the present invention, the first support substrate 12 having a thermal expansion coefficient smaller than that of the first piezoelectric substrate 11 in the propagation direction of the surface acoustic wave is bonded. Since the thermal expansion of the piezoelectric substrate 11 in the surface acoustic wave propagation direction is constrained, the change in the frequency characteristics due to the temperature change of the surface acoustic wave device can be suppressed.

  Further, on the opposite surface of the first piezoelectric substrate 11 across the support substrate 12, a second piezoelectric substrate 13 having the same type of piezoelectric material as the first piezoelectric substrate 11 and having the same thickness is disposed on the first piezoelectric substrate 11. Bonding is performed so that the X-axis direction, which is the direction with the largest thermal expansion coefficient in the planar direction, and the X-axis direction, which is the direction with the largest thermal expansion coefficient in the planar direction, of the second piezoelectric substrate 13 are the same direction. Therefore, the thermal expansion coefficient of the first piezoelectric substrate 11 and the thermal expansion coefficient of the second piezoelectric substrate 13 in the direction of the X axis in which the surface acoustic wave travels and the direction perpendicular to the X axis in the plane direction are As a result, the shape becomes substantially symmetric about the support substrate 12. The vertical stress generated by the difference in thermal expansion coefficient between the first piezoelectric substrate 11 and the support substrate 12 is the reverse stress generated by the difference in thermal expansion coefficient between the second piezoelectric substrate 13 and the support substrate 12. Therefore, the warpage of the bonding substrate 14 due to the temperature change can be suppressed.

  In addition, since the warpage due to thermal expansion of the bonding substrate 14 can be suppressed in the thermal history of room temperature to 260 ° C. in the manufacturing process and the mounting process of the surface acoustic wave device, damage such as cracking due to the warping of the bonding substrate 14 is possible. Thus, the production yield of the surface acoustic wave device can be improved.

  Furthermore, even when the temperature of the surface acoustic wave device rises during its operation, the occurrence of cracks due to the warp of the substrate can be prevented, so that the reliability can be improved.

  Here, the fact that the first piezoelectric substrate 11 and the second piezoelectric substrate 13 are the same kind of piezoelectric material means that the main composition components are the same. Further, the method of bonding the support substrate 12 to the first piezoelectric substrate 11 and the second piezoelectric substrate 13 may be bonding via metal or direct bonding in addition to bonding by an adhesive. .

  In the first embodiment of the present invention described above, the thickness of the first piezoelectric substrate 11 and the thickness of the second piezoelectric substrate 13 are the same 25 μm. However, the first piezoelectric substrate 11 has the same thickness to minimize the degree of warping. It is also possible to provide a slight difference between the thickness of the piezoelectric substrate 11 and the thickness of the second piezoelectric substrate 13, and it is suitable for optimizing the frequency temperature characteristics or optimizing the reliability. It is also possible to provide a difference between the thickness of the first piezoelectric substrate 11 and the thickness of the second piezoelectric substrate 13 so that slight warping occurs. For example, when the frequency change of the frequency is particularly small, the thickness of the second piezoelectric substrate 13 is made larger than the thickness of the first piezoelectric substrate 11 and slightly increases toward the first piezoelectric substrate 11 when the temperature rises. A concave warp may be generated.

  In the first embodiment of the present invention described above, the thickness of the support substrate 12 is set to 0.3 mm, which is six times the total thickness of the first piezoelectric substrate 11 and the second piezoelectric substrate 13 being 50 μm. However, the relationship between the thickness of the first piezoelectric substrate 11 and the total thickness of the second piezoelectric substrate 13 and the thickness of the support substrate 12 is to restrict the thermal expansion of the first piezoelectric substrate 11 effectively. Requires that the thickness of the support substrate 12 be larger than the sum of the thickness of the first piezoelectric substrate 11 and the second piezoelectric substrate 13, and the ratio is a frequency required in the surface acoustic wave device. What is necessary is just to set suitably according to the level of the temperature change characteristic.

(Embodiment 2)
The second aspect of the present invention will be described below with reference to the second embodiment.

  The second embodiment is different from the first embodiment of the present invention described above in that a piezoelectric substrate of the same type as a piezoelectric substrate that propagates a surface acoustic wave is used as the support substrate, and is used as the support substrate. The direction of the piezoelectric substrate to be used is that the direction with the smallest thermal expansion coefficient is parallel to the propagation direction of the surface acoustic wave, and the piezoelectric substrate that propagates the surface acoustic wave and the piezoelectric substrate used as the support substrate are joined by direct joining. is there.

  FIG. 2 shows a schematic diagram of a surface acoustic wave device according to Embodiment 2 of the present invention.

  In FIG. 2, reference numeral 21 denotes a first piezoelectric substrate that forms an element for exciting surface acoustic waves on the surface thereof. The first piezoelectric substrate 21 adapts a lithium tantalate single crystal to the propagation of surface acoustic waves. Thus, it is cut and configured to have a normal direction rotated by an angle in the range of 36 ° from the Y axis to the Z axis direction around the X axis, and its thickness is about 25 μm, Then, an element for exciting a surface acoustic wave having a traveling direction in the X-axis direction is formed on the surface.

  Reference numeral 22 denotes a second piezoelectric substrate. The second piezoelectric substrate 22 is formed by cutting a lithium tantalate single crystal so that the Y axis has a normal direction, and the thickness thereof is about 0. .3 mm. The second piezoelectric substrate 22 has an X axis that is a propagation direction of the surface acoustic wave of the first piezoelectric substrate 21 on a surface opposite to the surface of the first piezoelectric substrate 21 that excites the surface acoustic wave. Direct bonding is performed in such a direction that the direction (thermal expansion coefficient 16 ppm / ° C.) and the Z-axis direction (thermal expansion coefficient 4 ppm / ° C.) having the smallest thermal expansion coefficient in the second piezoelectric substrate 22 are the same direction. Is. By performing such bonding, the thermal expansion in the propagation direction of the surface acoustic wave of the first piezoelectric substrate 21 can be constrained by the second piezoelectric substrate 22, so that the frequency characteristics due to the temperature change of the surface acoustic wave device. It is possible to suppress this change.

  Reference numeral 23 denotes a third piezoelectric substrate. The third piezoelectric substrate 23 is a normal direction obtained by rotating a lithium tantalate single crystal around the X axis at an angle in the range of 36 ° from the Y axis to the Z axis. The thickness is about 25 μm. The third piezoelectric substrate 23 is formed on the surface of the second piezoelectric substrate 22 opposite to the surface to which the first piezoelectric substrate 21 is bonded, in the X-axis direction of the first piezoelectric substrate 21. The third piezoelectric substrate 23 is directly bonded in such a direction that the X-axis directions are the same. A joined body of the first piezoelectric substrate 21, the second piezoelectric substrate 22, and the third piezoelectric substrate 23 constitutes a joined substrate 24.

  In this way, the third piezoelectric substrate 23 having the same material and thickness as the first piezoelectric substrate 21 is disposed on the opposite surface of the first piezoelectric substrate 21 with the second piezoelectric substrate 22 in between. By joining so that the direction in which the thermal expansion coefficient in the planar direction of the substrate 21 is large and the direction in which the thermal expansion coefficient in the planar direction of the third piezoelectric substrate 23 is large are in the same direction, the first piezoelectric substrate 21 and Since the stress in the vertical direction in the bonding substrate 24 generated by the difference in thermal expansion coefficient with the second piezoelectric substrate 22 can be canceled by the third piezoelectric substrate 23, the warp due to temperature change can be suppressed. It is.

  Reference numeral 25 denotes a comb-shaped electrode in which a plurality of electrode fingers are arranged in the X-axis direction of the first piezoelectric substrate 21 on the surface for exciting the surface acoustic wave in the bonding substrate 24, that is, the exposed surface of the first piezoelectric substrate 21. The comb electrode 25 is made of a metal mainly composed of aluminum, and excites a surface acoustic wave propagating in the X-axis direction by applying an alternating voltage. In the bonding substrate 24, a comb-shaped electrode 25 and other circuits (not shown) are formed, and then the excitation space is sealed to manufacture a surface acoustic wave device.

  As described above, in the second embodiment of the present invention, the second piezoelectric substrate 22 having a smaller thermal expansion coefficient than that of the first piezoelectric substrate 21 in the propagation direction of the surface acoustic wave is bonded. Since the thermal expansion of the first piezoelectric substrate 21 in the propagation direction of the surface acoustic wave is constrained, the change in frequency characteristics due to the temperature change of the surface acoustic wave device can be suppressed.

  Further, a third piezoelectric substrate 23 having the same thickness as that of the first piezoelectric substrate 21 is formed on the opposite surface of the first piezoelectric substrate 21 with the second piezoelectric substrate 22 interposed therebetween. The direction of the X axis, which is the direction in which the thermal expansion coefficient in the planar direction of the substrate 21 is large, and the direction of the X axis, which is the direction in which the thermal expansion coefficient in the planar direction of the third piezoelectric substrate 23 is large, are the same direction. Since the bonding is performed, the thermal expansion coefficient of the first piezoelectric substrate 21 and the thermal expansion coefficient of the third piezoelectric substrate 23 in the X-axis direction in which the surface acoustic wave travels and the direction perpendicular to the X-axis in the planar direction are Are equal to each other, so that the second piezoelectric substrate 22 has a substantially symmetric shape. The vertical stress caused by the difference in thermal expansion coefficient between the first piezoelectric substrate 21 and the second piezoelectric substrate 22 causes the difference in thermal expansion coefficient between the third piezoelectric substrate 23 and the second piezoelectric substrate 22. Therefore, the warpage of the bonding substrate 24 due to a temperature change can be suppressed.

  In addition, since the warpage due to thermal expansion of the bonding substrate 24 can be suppressed in the thermal history of room temperature to 260 ° C. in the manufacturing process of the surface acoustic wave device, damage such as cracking due to the warpage of the bonding substrate 24 is prevented. Thus, the production yield of the surface acoustic wave device can be improved.

  Furthermore, even when the temperature of the surface acoustic wave device rises during its operation, the occurrence of cracks due to the warp of the substrate can be prevented, so that the reliability can be improved.

  Furthermore, in the second embodiment of the present invention, the first piezoelectric substrate 21 that excites the surface acoustic wave and the second piezoelectric substrate 22 that restrains the thermal expansion of the first piezoelectric substrate 21 are the same kind of piezoelectric material. Therefore, the acoustic impedance matching at the joint surface can be improved, and reflection of the acoustic wave at the joint surface can be reduced.

  This is a part of the surface acoustic wave excited on the surface of the first piezoelectric substrate 21, and becomes a leaky bulk wave that travels in the depth direction of the substrate. It is possible to suppress the reflection at the bonding surface between the first piezoelectric substrate 21 and the second piezoelectric substrate 22 and returning to the surface to become a noise component, thereby improving the electrical characteristics of the surface acoustic wave device. Is. In addition, since this is particularly likely to cause a leaky bulk wave in a surface acoustic wave device using a leaky wave, the influence thereof is large. In particular, the surface acoustic wave device is thinned and the thickness of the first piezoelectric substrate 21 is reduced. It has a big influence when you do it.

  In the second embodiment of the present invention, the second piezoelectric substrate 22 and the third piezoelectric substrate 23 are made of a single crystal made of the same kind of piezoelectric material and are directly bonded. The acoustic impedance of the bonding surface between the substrate 22 and the third piezoelectric substrate 23 can be matched, thereby suppressing the reflection of the leaky bulk wave at the bonding surface. It is possible to further improve the electrical characteristics.

  In the above-described second embodiment of the present invention, the thickness of the first piezoelectric substrate 21 and the thickness of the third piezoelectric substrate 23 are the same 25 μm. However, the first piezoelectric substrate 21 has the same thickness to minimize the degree of warpage. It is also possible to provide a slight difference between the thickness of the piezoelectric substrate 21 and the thickness of the third piezoelectric substrate 23, which is suitable for optimizing the frequency temperature characteristics or for optimizing the reliability. It is also possible to provide a difference between the thickness of the first piezoelectric substrate 21 and the thickness of the third piezoelectric substrate 23 so that slight warping occurs.

  In the second embodiment of the present invention described above, the thickness of the second piezoelectric substrate 22 is 6 times the total thickness of the first piezoelectric substrate 21 and the third piezoelectric substrate 23 being 50 μm. Although the thickness of the first piezoelectric substrate 21 is 3 mm, the relationship between the total thickness of the first piezoelectric substrate 21 and the third piezoelectric substrate 23 and the thickness of the second piezoelectric substrate 22 is effective for the thermal expansion of the first piezoelectric substrate 21. In order to constrain, the thickness of the second piezoelectric substrate 22 needs to be larger than the total thickness of the first piezoelectric substrate 21 and the third piezoelectric substrate 23, and the ratio is What is necessary is just to set suitably according to the level of the temperature change characteristic of the frequency required in a surface acoustic wave device.

  The surface acoustic wave device according to the present invention improves the manufacturing yield and reliability by suppressing the warpage of the substrate due to temperature change. The surface acoustic wave filter and the surface acoustic wave mainly used in mobile communication equipment. This is useful in a surface acoustic wave device such as a duplexer.

Schematic diagram of surface acoustic wave device according to Embodiment 1 of the present invention Schematic diagram of a surface acoustic wave device according to Embodiment 2 of the present invention Schematic diagram of a conventional surface acoustic wave device

DESCRIPTION OF SYMBOLS 11 1st piezoelectric substrate 12 Support substrate 13 2nd piezoelectric substrate 15 Comb electrode 21 1st piezoelectric substrate 22 2nd piezoelectric substrate 23 3rd piezoelectric substrate 25 Comb electrode

Claims (2)

In a surface acoustic wave device including a first piezoelectric substrate, a support substrate, and a second piezoelectric substrate, the first piezoelectric substrate and the second piezoelectric substrate are of the same kind having anisotropy in thermal expansion coefficient. The first piezoelectric substrate includes a comb-shaped electrode that excites a surface acoustic wave on one main surface, and the other main surface is bonded to one main surface of the support substrate, and the support The other principal surface of the substrate is joined to one principal surface of the second piezoelectric substrate, and the thermal expansion coefficient of the support substrate in the propagation direction of the surface acoustic wave is greater than the thermal expansion coefficient of the first piezoelectric substrate. The direction in which the thermal expansion coefficient in the planar direction of the first piezoelectric substrate is large and the direction in which the thermal expansion coefficient in the planar direction of the second piezoelectric substrate is large are the same direction, and the thickness of the support substrate is further reduced. The thickness of the first piezoelectric substrate and the second piezoelectric substrate The surface acoustic wave device is made larger than the sum of the thickness. In a surface acoustic wave device including a first piezoelectric substrate, a second piezoelectric substrate, and a third piezoelectric substrate, the first piezoelectric substrate, the second piezoelectric substrate, and the third piezoelectric substrate have a thermal expansion coefficient. The first piezoelectric substrate has a comb-shaped electrode for exciting a surface acoustic wave on one main surface, and the other main surface is the second piezoelectric substrate. The other main surface of the second piezoelectric substrate is directly bonded to one main surface of the third piezoelectric substrate, and thermal expansion in the plane direction of the first piezoelectric substrate is performed. The direction in which the coefficient is large, the direction in which the coefficient of thermal expansion in the plane direction of the second piezoelectric substrate is small, and the direction in which the coefficient of thermal expansion in the plane direction of the third piezoelectric substrate is large are the same direction. The thickness of the first piezoelectric substrate and the thickness of the third piezoelectric substrate. The surface acoustic wave device is made larger than the sum of the thickness of the plate.

Images