JP2006121259A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device comprising a surface acoustic wave element on the IC-forming layer of a semiconductor substrate, where the generation of noise is prevented by isolating the IC and the surface acoustic wave element. <P>SOLUTION: The surface acoustic wave device comprises a semiconductor substrate 10, an IC forming layer 11 formed on the semiconductor substrate 10, a reflecting layer 20 formed on the IC formation layer 11, a piezoelectric thin-film layer 30 formed on the reflecting layer 20, and a surface acoustic wave element 31 formed on the piezoelectric thin-film layer 30, wherein the thickness d1 of the reflecting layer 20 is set equal to one-fourth the wavelength of an elastic wave propagating through the reflecting layer 20, in order to reflect the surface acoustic waves excited from the surface acoustic wave element 31 on the reflecting layer 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface acoustic wave device including an integrated circuit (IC) formed on a semiconductor substrate, a piezoelectric thin film laminated thereon, and a surface acoustic wave element.

  2. Description of the Related Art Conventionally, a surface acoustic wave device in which an IC is formed on a semiconductor substrate and a surface acoustic wave element is provided thereon is known. In such a surface acoustic wave device in which an IC and a surface acoustic wave element are integrated, there is a concern about the generation of noise due to the interaction between the IC and the surface acoustic wave element, and proposals have been made to prevent the generation of noise. . For example, as shown in Patent Document 1, an IC forming layer and a surface acoustic wave element are separately disposed in the same semiconductor substrate, an electrode is formed so as to surround the surface acoustic wave element, and the electrode is interposed between the electrode and the semiconductor substrate. A structure is disclosed in which a surface acoustic wave element and an IC are separated by applying a bias voltage.

Japanese Examined Patent Publication No. 3-3411 (Fig. 2)

However, a surface acoustic wave element normally uses a Rayleigh wave in which a longitudinal wave and a transverse wave are combined as an elastic wave, and this longitudinal wave component (vertical component) is mostly at a depth within one wavelength from the surface. Energy is concentrated. For this reason, when a surface acoustic wave element is provided on the IC formation layer, the acoustic wave propagates to the IC formation layer, stress is applied to the wiring, and resistance and capacitance change, causing noise. Concerned.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a surface acoustic wave device including a surface acoustic wave device in which a piezoelectric thin film is laminated on an IC formation layer, and includes a surface acoustic wave and an IC. An object of the present invention is to provide a surface acoustic wave device that separates elements between elements and prevents noise from being generated.

  In order to solve the above problems, a surface acoustic wave device according to the present invention includes a semiconductor substrate, an IC formation layer formed on the semiconductor substrate, a reflection layer laminated above the IC formation layer, and the reflection A piezoelectric thin film layer formed on the layer, and a surface acoustic wave element formed on the piezoelectric thin film layer, and the thickness of the reflective layer is determined when the acoustic wave propagates through the reflective layer. It is characterized by being formed to a thickness that is ¼ of the wavelength.

  According to this configuration, the thickness of the surface acoustic wave device is obtained by forming the reflective layer to a thickness of ¼ of the wavelength when the acoustic wave excited from the surface acoustic wave element propagates through the reflective layer. The elastic wave propagating in the direction can be reflected in the reflection layer and confined in the reflection layer. As a result, propagation of the elastic wave to the IC formation layer can be prevented, element separation between the IC and the surface acoustic wave element can be performed, and generation of noise due to interaction can be prevented.

  In the surface acoustic wave device of the present invention, the reflective layer formed to have a thickness of ¼ of the wavelength when the acoustic wave propagates through the reflective layer may have a multilayer structure.

  Thus, if the reflective layer has a multilayer structure, for example, the adjacent reflective layers are stacked so that the difference in acoustic impedance is large, the elastic wave can be effectively confined in the reflective layer.

  In the surface acoustic wave device of the present invention, the reflective layer formed to a thickness of ¼ of the wavelength when the acoustic wave propagates through the reflective layer includes a conductive film.

  In this way, the reflective layer can have both the effect of confining the elastic wave in the reflective layer and the effect of electromagnetically shielding the IC by the conductive film, reducing the noise of the surface acoustic wave device due to the influence of the elastic wave and electromagnetic wave. can do.

  Further, in the surface acoustic wave device of the present invention, a conductive film is further provided between the reflective layer and the IC forming layer formed to a thickness of ¼ of the wavelength when the acoustic wave propagates through the reflective layer. It is characterized by providing.

  According to this configuration, the IC can be electromagnetically shielded by the conductive film. From this, the noise of the surface acoustic wave device due to the influence of the elastic wave and the electromagnetic wave can be reduced.

  The surface acoustic wave device of the present invention is formed on a semiconductor substrate, an IC formation layer formed on the semiconductor substrate, a reflection layer stacked above the IC formation layer, and the reflection layer. At least a piezoelectric thin film layer and a surface acoustic wave element formed on the piezoelectric thin film layer, and the thickness of the reflective layer is ½ of the wavelength when the acoustic wave propagates through the reflective layer It is characterized by being formed to a certain thickness.

  According to this configuration, the thickness of the surface acoustic wave device is obtained by forming the reflective layer to a thickness that is ½ of the wavelength when the acoustic wave excited from the surface acoustic wave element propagates through the reflective layer. The elastic wave propagating in the direction can be reflected in the reflection layer and canceled in the reflection layer. As a result, propagation of the elastic wave to the IC formation layer can be prevented, element separation between the IC and the surface acoustic wave element can be performed, and generation of noise due to interaction can be prevented.

  In the surface acoustic wave device of the present invention, the reflective layer formed to have a thickness of ½ of the wavelength when an acoustic wave propagates through the reflective layer may have a multilayer structure.

  In this way, if the reflective layer has a multilayer structure, for example, the adjacent reflective layers are stacked so that the difference in acoustic impedance is large, the elastic wave can be effectively canceled in the reflective layer.

  In the surface acoustic wave device of the present invention, the reflective layer formed to have a thickness of ½ of a wavelength when an acoustic wave propagates through the reflective layer includes a conductive film.

  In this way, the reflective layer can have both the effect of canceling the elastic wave in the reflective layer and the effect of electromagnetically shielding the IC by the conductive film, reducing the noise of the surface acoustic wave device due to the influence of the elastic wave and electromagnetic wave. can do.

  Further, in the surface acoustic wave device of the present invention, a conductive film is further provided between the reflective layer and the IC forming layer formed to have a thickness of ½ of the wavelength when the acoustic wave propagates through the reflective layer. It is characterized by providing.

  According to this configuration, the IC can be electromagnetically shielded by the conductive film. From this, the noise of the surface acoustic wave device due to the influence of the elastic wave and the electromagnetic wave can be reduced.

  In the surface acoustic wave device of the present invention, the surface acoustic wave device functions as a resonator or a frequency filter.

  According to the present invention, since the surface acoustic wave device functions as a resonator or a frequency filter, it is possible to prevent the occurrence of noise due to the interaction between the IC and the surface acoustic wave element, which is obtained due to the above configuration, Characteristics can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)

FIG. 1 is a perspective view showing a schematic configuration of a surface acoustic wave device according to this embodiment.
The surface acoustic wave device 1 includes an IC formation layer 11 on a semiconductor substrate 10, and a reflective layer 20 is laminated via an insulating film 12. A piezoelectric thin film layer 30 is provided on the reflective layer 20, and a surface acoustic wave element 31 is formed on the piezoelectric thin film layer 30. The surface acoustic wave element 31 includes a comb-shaped IDT electrode 32 and is disposed so that the two IDT electrodes 32 mesh with each other.
As described above, the surface acoustic wave device 31 is provided on the IC forming layer 11 to constitute the surface acoustic wave device 1 in which the IC and the surface acoustic wave device 31 are integrated.

FIG. 2 is a schematic cross-sectional view of the surface acoustic wave device 1 taken along the line AA in FIG.
A semiconductor substrate 10 made of Si or the like is provided with an IC forming layer 11 in which an integrated circuit is formed, and an insulating film 12 made of SiO ₂ is provided on the IC forming layer 11. The IC formation layer 11 includes an oscillation circuit for exciting the surface acoustic wave element 31. A reflective layer 20 made of W (tungsten) is provided on the insulating film 12, and a piezoelectric thin film layer 30 made of ZnO is provided on the reflective layer 20. Further, on the piezoelectric thin film layer 30, a comb-shaped IDT electrode 32 formed of a conductor such as Al constituting the surface acoustic wave element 31 is provided.

  In order to increase the reflection coefficient of the elastic wave in the reflection layer 20, the reflection layer 20 is configured so that the difference in acoustic impedance between the adjacent layer materials becomes large. In the present embodiment, the acoustic impedance of the reflective layer 20 has a relatively high acoustic impedance with respect to the insulating film 12 and the piezoelectric thin film layer 30. Further, the thickness d1 of the reflective layer 20 is formed with a thickness of ¼ of the wavelength when the elastic wave excited from the surface acoustic wave element 31 propagates through the reflective layer 20. The wavelength at which the elastic wave propagates through the reflective layer 20 is determined by the speed of sound passing through the material used as the reflective layer 20 and the frequency of the elastic wave, and the wavelength differs depending on the material used.

In addition to Si, Ge, SiGe, SiC, SiSn, PbS, GaAs, InP, GaN, ZnSe, or the like can be used as a material for the semiconductor substrate 10. In addition to W, Al, Mo, Au, Pt, Ir, Si, SiO ₂ , Diamond, etc. can be used as the material of the reflective layer 20. Further, as the material of the piezoelectric thin film layer 30, AlN or the like can be used in addition to ZnO.
These materials are appropriately selected in consideration of the acoustic impedance and lattice matching of the adjacent layer materials. For example, a configuration in which the piezoelectric thin film layer 30 is ZnO and the reflective layer 20 is W, or a configuration in which the piezoelectric thin film layer 30 is AlN and the reflective layer 20 is Mo can be given.
Note that a planarization layer may be provided between the insulating layer 12 and the reflective layer 20 for the purpose of planarizing a layer stacked on the insulating layer 12. In this way, the reflective layer 20 and the piezoelectric thin film layer 30 can be formed flat, and the surface acoustic wave element 31 can be manufactured with high accuracy.

  In the surface acoustic wave device 1 configured as described above, when a surface acoustic wave is excited from the surface acoustic wave element 31, the longitudinal wave component of the acoustic wave propagates in the thickness direction of the surface acoustic wave device 1. The elastic wave propagates through the piezoelectric thin film layer 30 and enters the reflective layer 20. Since the thickness d1 of the reflective layer 20 is formed to be ¼ of the wavelength when the elastic wave propagates through the reflective layer 20, the reflective layer 20 has a reflective layer on the lower surface (the surface in contact with the insulating film 12). An elastic wave that has advanced by a quarter wavelength (90 °) with respect to the upper surface of 20 reaches. Here, the elastic wave is reflected (phase-inverted), and the elastic wave advanced 360 ° with respect to the incident elastic wave reaches the upper surface of the reflective layer 20 (the surface in contact with the piezoelectric thin film layer 30). Furthermore, an elastic wave is reflected on the upper surface of the reflective layer 20, and thereafter reflection is repeated in the reflective layer 20. For this reason, the elastic wave is confined in the reflective layer 20 and does not enter the IC forming layer 11.

As described above, the reflective layer 20 is provided under the piezoelectric thin film layer 30 on which the surface acoustic wave element 31 is disposed, and the thickness d1 of the reflective layer 20 is equal to the wavelength when the acoustic wave propagates through the reflective layer 20. By forming the ¼ thickness, it is possible to prevent the elastic wave from entering the IC forming layer 11. Therefore, element separation between the IC and the surface acoustic wave element can be performed, and noise due to interaction can be prevented. Further, if the reflective layer 20 is formed of a conductive film as in the present embodiment, the IC formed on the IC forming layer 11 can be electromagnetically shielded.
(Second Embodiment)

Further, the thickness d1 of the reflective layer 20 in FIG. 2 may be formed to a thickness of ½ of the wavelength when the elastic wave propagates through the reflective layer 20.
In this case, the acoustic wave excited from the surface acoustic wave element 31 enters the reflective layer 20 through the piezoelectric thin film layer 30. The thickness d1 of the reflective layer 20 is ½ of the wavelength when the elastic wave propagates through the reflective layer 20, so that the lower surface of the reflective layer 20 is ½ of the upper surface of the reflective layer 20. An elastic wave that reaches a wavelength (180 °) arrives. Here, the elastic wave is reflected (phase inversion), and an elastic wave that has advanced by 540 ° (with a phase shift of 180 °) reaches the upper surface of the reflective layer 20. That is, the incident elastic wave and the reflected elastic wave work so as to cancel each other out in the reflection layer 20. For this reason, the elastic waves cancel each other in the reflective layer 20 and do not enter the IC forming layer 11.

As described above, the reflective layer 20 is provided under the piezoelectric thin film layer 30 on which the surface acoustic wave element 31 is disposed, and the thickness d1 of the reflective layer 20 is equal to the wavelength when the acoustic wave propagates through the reflective layer 20. By forming the ½ thickness, the elastic wave can be prevented from entering the IC forming layer 11. Therefore, element separation between the IC and the surface acoustic wave element can be performed, and noise due to interaction can be prevented. Further, if the reflective layer 20 is formed of a conductive film, the IC formed on the IC forming layer 11 can be electromagnetically shielded.
(Third embodiment)

  Next, an embodiment in which the reflective layer has a multilayer structure will be described as a third embodiment. FIG. 3 is a schematic cross-sectional view showing a configuration of a surface acoustic wave device having two reflective layers, and FIG. 4 is a schematic cross-section showing a configuration of a surface acoustic wave device having four reflective layers. FIG.

In FIG. 3, the surface acoustic wave device 2 includes a semiconductor substrate 10 made of Si, an IC formation layer 11 having an integrated circuit formed on the semiconductor substrate 10, and an SiO ₂ on the IC formation layer 11. An insulating film 12 is provided. The IC formation layer 11 includes an oscillation circuit for exciting the surface acoustic wave element 31. A reflective layer 20 in which a first reflective layer 21 and a second reflective layer 22 are laminated is provided on the insulating film 12. The first reflective layer 21 is made of W, and the second reflective layer 22 is made of SiO ₂ .
The first reflective layer 21 and the second reflective layer 22 are configured so that the difference in acoustic impedance between the layer materials in contact with each other is large. The first reflective layer 21 has a relatively high acoustic impedance with respect to the insulating layer 12 and the second reflective layer 22. The second reflective layer 22 has a relatively low acoustic impedance with respect to the first reflective layer 21 and the piezoelectric thin film layer 30.

A piezoelectric thin film layer 30 made of ZnO is provided on the reflective layer 20. Further, on the piezoelectric thin film layer 30, a comb-shaped IDT electrode 32 formed of a conductor such as Al constituting the surface acoustic wave element 31 is provided.
The thickness d2 of the reflective layer 20 is formed with a thickness of ¼ of the wavelength when the elastic wave excited from the surface acoustic wave element 31 propagates through the reflective layer 20. The wavelength that propagates through the reflective layer 20 is determined by the speed of sound and the frequency of elastic waves that pass through the material used as the reflective layer 20, and the wavelength varies depending on the material used. For example, the upper surface of the second reflective layer 22 ( The elastic wave incident from the surface in contact with the piezoelectric thin film layer 30, and the first reflective layer 21 so that the wavelength advanced by 1/4 wavelength reaches the lower surface of the first reflective layer 21 (surface in contact with the insulating film 12). Each thickness of the second reflective layer 22 is designed.

In addition to Si, Ge, SiGe, SiC, SiSn, PbS, GaAs, InP, GaN, ZnSe, or the like can be used as a material for the semiconductor substrate 10. In addition to W, Al, Mo, Au, Pt, Ir, Si, SiO ₂ , Diamond, etc. can be used as the material of the reflective layer 20. Further, as the material of the piezoelectric thin film layer 30, AlN or the like can be used in addition to ZnO.

  In the surface acoustic wave device 2 configured as described above, when a surface acoustic wave is excited from the surface acoustic wave element 31, the longitudinal wave component of the acoustic wave propagates in the thickness direction of the surface acoustic wave device 2. The elastic wave propagates through the piezoelectric thin film layer 30 and enters the reflective layer 20. Since the thickness d2 of the reflective layer 20 is formed to be ¼ of the wavelength when the elastic wave propagates through the reflective layer 20, the lower surface of the first reflective layer 21 in the reflective layer 20 has a thickness of the reflective layer 20. An elastic wave that has advanced by a quarter wavelength (90 °) with respect to the upper surface of the second reflective layer 22 arrives. Here, the elastic wave is reflected (phase inversion), and the elastic wave advanced 360 ° relative to the incident elastic wave reaches the upper surface of the second reflective layer 22 in the reflective layer 20. Furthermore, an elastic wave is reflected on the upper surface of the second reflective layer 22, and thereafter reflection is repeated in the reflective layer 20. Thus, the elastic wave is confined in the reflective layer 20 and does not enter the IC forming layer 11.

Moreover, even if it is the structure which formed the reflection layer into four layers as shown in FIG. 4, it can implement.
The surface acoustic wave device 3 in FIG. 4 differs from the surface acoustic wave device 2 described in FIG. 3 only in the configuration of the reflective layer 20, and thus the same reference numerals are given to the same configurations and the description thereof is omitted.
The reflective layer 20 includes a first reflective layer 23, a second reflective layer 24, a third reflective layer 25, and a fourth reflective layer 26. The first reflective layer 23 and the third reflective layer 25 are formed of a Mo film, and the second reflective layer 24 and the fourth reflective layer 26 are formed of a Si film.
The first reflective layer 23 to the fourth reflective layer 26 are configured so that the difference in acoustic impedance between the layer materials in contact with each other becomes large. The first reflective layer 23 has a relatively high acoustic impedance with respect to the insulating layer 12 and the second reflective layer 24. The second reflective layer 24 has a relatively low acoustic impedance with respect to the first reflective layer 23 and the third reflective layer 25. The third reflective layer 25 has a relatively high acoustic impedance with respect to the second reflective layer 24 and the fourth reflective layer 26. Further, the fourth reflective layer 26 has a relatively low acoustic impedance with respect to the third reflective layer 25 and the piezoelectric thin film layer 30.
The thickness d3 of the reflective layer 20 is formed with a thickness of ¼ of the wavelength when the elastic wave excited from the surface acoustic wave element 31 propagates through the reflective layer 20.

  In the surface acoustic wave device 3 configured as described above, when a surface acoustic wave is excited from the surface acoustic wave element 31, a longitudinal wave component of the elastic wave propagates in the thickness direction of the surface acoustic wave device 3. The elastic wave propagates through the piezoelectric thin film layer 30 and enters the reflective layer 20. Then, an elastic wave propagates from the fourth reflective layer 26 to the first reflective layer 23. Since the thickness d3 of the reflective layer 20 is formed to be ¼ of the wavelength when the elastic wave propagates through the reflective layer 20, the lower surface of the first reflective layer 23 in the reflective layer 20 has a thickness of the reflective layer 20. An elastic wave that has advanced by a quarter wavelength (90 °) with respect to the upper surface of the fourth reflective layer 26 arrives. Here, the elastic wave is reflected (phase inversion), and the elastic wave advanced 360 ° with respect to the incident elastic wave reaches the upper surface of the fourth reflective layer 26 in the reflective layer 20. Further, the elastic wave is reflected on the upper surface of the fourth reflective layer 26, and thereafter the reflection is repeated in the reflective layer 20. Thus, the elastic wave is confined in the reflective layer 20 and does not enter the IC forming layer 11.

As described with reference to FIGS. 3 and 4, the following effects can be obtained by forming the reflective layer 20 in a multilayer structure.
The reflective layer 20 having a multilayer structure is provided under the piezoelectric thin film layer 30 on which the surface acoustic wave element 31 is disposed, and the thicknesses d2 and d3 of the reflective layer 20 are measured when the acoustic wave propagates through the reflective layer 20. By forming the thickness to ¼ of the wavelength, it is possible to prevent the elastic wave from entering the IC forming layer 11. In particular, the first reflective layer 21 and the second reflective layer 22 are configured such that the difference in acoustic impedance between the layer materials in contact with each other is increased, so that the traveling elastic wave is effectively reflected and the elastic wave is effectively reflected. It can be confined in the reflective layer 20. And element isolation | separation between IC and a surface acoustic wave element is enabled, and generation | occurrence | production of the noise by interaction can be prevented. In addition, by including a conductive film in the reflective layer 20 having a multilayer structure as in the present embodiment, it is possible to electromagnetically shield the IC formed in the IC forming layer 11.
(Fourth embodiment)

Further, the thicknesses d2 and d3 of the reflective layer 20 in FIGS. 3 and 4 may be formed to a thickness of ½ of the wavelength when the elastic wave propagates through the reflective layer 20.
In this case, the acoustic wave excited from the surface acoustic wave element 31 enters the reflective layer 20 through the piezoelectric thin film layer 30. The thicknesses d2 and d3 of the reflective layer 20 are formed to be ½ of the wavelength when the elastic wave propagates through the reflective layer 20, so that the lower surface of the reflective layer 20 is 1 with respect to the upper surface of the reflective layer 20. An elastic wave that has advanced by two wavelengths (180 °) reaches. Here, the elastic wave is reflected (phase inversion), and an elastic wave that has advanced by 540 ° (with a phase shift of 180 °) reaches the upper surface of the reflective layer 20. That is, the incident elastic wave and the reflected elastic wave work so as to cancel each other in the reflection layer 20. As described above, the elastic waves cancel each other in the reflection layer 20 and do not enter the IC formation layer 11.

Thus, the reflective layer 20 having a multilayer structure is provided under the piezoelectric thin film layer 30 on which the surface acoustic wave element 31 is disposed, and the acoustic waves propagate through the reflective layer 20 with the thicknesses d2 and d3 of the reflective layer 20 being provided. In this case, the elastic wave can be prevented from being incident on the IC formation layer 11 by forming the film to a thickness that is ½ of the wavelength at the time. In particular, by configuring the reflective layer 20 having a multilayer structure so that the difference in acoustic impedance between the layer materials in contact with each other is increased, the traveling elastic wave is effectively reflected, and the elastic wave is effectively reflected in the reflective layer 20. Can be countered. And element isolation | separation between IC and a surface acoustic wave element is enabled, and generation | occurrence | production of the noise by interaction can be prevented. Further, by including a conductive film in the reflective layer 20 having a multilayer structure, it is possible to electromagnetically shield the IC formed in the IC formation layer 11.
(Fifth embodiment)

Next, an embodiment in which a conductive film is provided under the reflective layer will be described.
FIG. 5 is a schematic cross-sectional view showing the configuration of the surface acoustic wave device of this embodiment.
The surface acoustic wave device 4 includes a semiconductor substrate 10 made of Si or the like, an IC formation layer 11 in which an integrated circuit is formed on the semiconductor substrate 10, and an insulating film 12 made of SiO ₂ on the IC formation layer 11. I have. A conductive film 40 made of Al or the like and having a thickness of at least about 5 nm is provided on the insulating film 12. A reflective layer 20 made of Si is provided on the conductive film 40, and a piezoelectric thin film layer 30 made of ZnO is provided on the reflective layer 20. Further, on the piezoelectric thin film layer 30, a comb-shaped IDT electrode 32 formed of a conductor such as Al constituting the surface acoustic wave element 31 is provided.
The thickness d1 of the reflective layer 20 is formed with a thickness of ¼ of the wavelength when the elastic wave excited from the surface acoustic wave element 31 propagates through the reflective layer 20.

  In the surface acoustic wave device 4 configured as described above, an elastic wave is confined in the reflective layer 20 as in the first embodiment, and no elastic wave is incident on the IC forming layer 11. Further, when the reflective layer 20 does not include a conductive film, the conductive film 40 is provided between the reflective layer 20 and the insulating layer 12 to electromagnetically shield the IC formed on the IC forming layer 11. Is possible.

As described above, the reflective layer 20 is provided under the piezoelectric thin film layer 30 on which the surface acoustic wave element 31 is disposed, and the thickness d1 of the reflective layer 20 is equal to the wavelength when the acoustic wave propagates through the reflective layer 20. By forming the ¼ thickness, it is possible to prevent the elastic wave from entering the IC forming layer 11. And element isolation | separation between IC and a surface acoustic wave element is enabled, and generation | occurrence | production of the noise by interaction can be prevented. Further, when the reflective layer 20 does not include a conductive film as in the present embodiment, an IC formed on the IC forming layer 11 by providing the conductive film 40 between the reflective layer 20 and the insulating layer 12 is provided. Electromagnetic shielding is possible.
(Sixth embodiment)

Further, the thickness d1 of the reflective layer 20 in FIG. 5 may be formed to a thickness of ½ of the wavelength when the elastic wave propagates through the reflective layer 20.
In this case, similarly to the first embodiment, elastic waves cancel each other in the reflective layer 20, and no elastic waves are incident on the IC forming layer 11. In addition, when the reflective layer 20 does not include a conductive film, the conductive film 40 having a thickness of at least about 5 nm is provided between the reflective layer 20 and the insulating layer 12 to form the IC forming layer 11. The shielded IC can be electromagnetically shielded.

  As described above, the reflective layer 20 is provided under the piezoelectric thin film layer 30 on which the surface acoustic wave element 31 is disposed, and the thickness d1 of the reflective layer 20 is equal to the wavelength when the acoustic wave propagates through the reflective layer 20. By forming the ½ thickness, the elastic wave can be prevented from entering the IC forming layer 11. And element isolation | separation between IC and a surface acoustic wave element is enabled, and generation | occurrence | production of the noise by interaction can be prevented. Further, when the reflective layer 20 does not include a conductive film, the conductive film 40 functions as a layer for electromagnetically shielding the IC, and the same effect as described above can be obtained.

Furthermore, the surface acoustic wave device described above can function as a resonator or a frequency filter.
In this way, by using the surface acoustic wave device as a resonator or a frequency filter, it is possible to prevent the generation of noise due to the interaction between the IC and the surface acoustic wave element, and to obtain good characteristics as a resonator or a frequency filter. Can do.

1 is a perspective view showing a schematic configuration of a surface acoustic wave device according to an embodiment of the present invention. 1 is a schematic cross-sectional view illustrating a configuration of a surface acoustic wave device according to an embodiment. 1 is a schematic cross-sectional view showing a configuration of a surface acoustic wave device according to an embodiment in which a reflective layer has a multilayer structure. 1 is a schematic cross-sectional view showing a configuration of a surface acoustic wave device according to an embodiment in which a reflective layer has a multilayer structure. The schematic cross section which shows the structure of the surface acoustic wave apparatus provided with the electrically conductive film under the reflection layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2, 3, 4 ... Surface acoustic wave apparatus, 10 ... Semiconductor substrate, 11 ... IC formation layer, 12 ... Insulating layer, 20 ... Reflective layer, 30 ... Piezoelectric thin film layer, 31 ... Surface acoustic wave element, 32 ... IDT Electrode, 40 ... conductive film, d1, d2, d3 ... thickness of the reflective layer.

Claims (9)

A semiconductor substrate;
An IC forming layer formed on the semiconductor substrate;
A reflective layer laminated above the IC forming layer;
A piezoelectric thin film layer formed on the reflective layer;
A surface acoustic wave element formed on the piezoelectric thin film layer;
Comprising at least
2. A surface acoustic wave device according to claim 1, wherein the thickness of the reflective layer is set to a thickness that is 1/4 of a wavelength when the elastic wave propagates through the reflective layer.   2. The surface acoustic wave device according to claim 1, wherein the reflective layer has a multilayer structure.   3. The surface acoustic wave device according to claim 1, wherein the reflective layer includes a conductive film.   3. The surface acoustic wave device according to claim 1, further comprising a conductive film between the reflective layer and the IC forming layer. A semiconductor substrate;
An IC forming layer formed on the semiconductor substrate;
A reflective layer laminated above the IC forming layer;
A piezoelectric thin film layer formed on the reflective layer;
A surface acoustic wave element formed on the piezoelectric thin film layer;
Comprising at least
2. The surface acoustic wave device according to claim 1, wherein the thickness of the reflective layer is set to a thickness that is ½ of a wavelength when the elastic wave propagates through the reflective layer.   6. The surface acoustic wave device according to claim 5, wherein the reflective layer has a multilayer structure.   7. The surface acoustic wave device according to claim 5, wherein the reflective layer includes a conductive film.   The surface acoustic wave device according to claim 5, further comprising a conductive film between the reflective layer and the IC forming layer. The surface acoustic wave device according to any one of claims 1 to 8, wherein the surface acoustic wave device functions as a resonator or a frequency filter.

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