JP2007228011A - Surface acoustic wave device, surface acoustic wave device, and electronic device - Google Patents

Abstract

A surface acoustic wave device, a surface acoustic wave device, and a so-called impact-resistant improved surface acoustic wave device that suppresses stress concentration at a connecting portion between a piezoelectric substrate such as a quartz substrate and a storage container and withstands external impacts. Electronic devices using them are provided.
A surface acoustic wave element 10 includes a quartz substrate 1 as a piezoelectric substrate, IDT electrodes 2 and reflector electrodes 3a and 3b formed on a surface 1a of the quartz substrate 1, and a back surface 1b of the quartz substrate 1. And a diamond layer 5 as a reflecting portion formed thereon. The diamond layer 5 has a function of reflecting the propagated pseudo longitudinal wave type surface acoustic wave.
[Selection] Figure 1

Description

  The present invention relates to a surface acoustic wave element, a surface acoustic wave device using a pseudo longitudinal wave type leaky surface acoustic wave, and an electronic apparatus using the surface acoustic wave device.

Surface acoustic wave devices are used in communication equipment and the like as circuit elements such as resonators and filters. Examples of the surface acoustic wave used in the surface acoustic wave device include a Rayleigh wave and a leaky surface acoustic wave.
A Rayleigh wave is a surface wave that propagates on the surface of an elastic body, and its energy propagates without radiating into the piezoelectric substrate. There are three types of volume waves (bulk waves) in the piezoelectric substrate: “slow transverse wave”, “fast transverse wave”, and “longitudinal wave”, but this Rayleigh wave has a slower phase velocity than “slow transverse wave”. Propagate.
The leaky surface acoustic wave is a surface acoustic wave that propagates while radiating energy in the depth direction of the elastic body (piezoelectric body), and can be used in a specific cutting angle and propagation direction of the piezoelectric substrate. This leaky surface acoustic wave propagates at a phase velocity between a “slow transverse wave” and a “fast transverse wave”.

  The characteristics of surface acoustic wave devices depend on the propagation characteristics of surface acoustic waves propagating through piezoelectric substrates, and the use of surface acoustic waves with a high phase velocity is required in order to cope with the higher frequency of surface acoustic wave devices. Yes. In recent years, the theory of leaky surface acoustic waves has been developed, and most of the displacement on the substrate surface is composed of longitudinal wave components, and while emitting two transverse wave components inside the piezoelectric substrate as volume waves, “fast transverse waves” and “longitudinal waves” The use of a quasi-longitudinal-type leaky surface acoustic wave propagating at a high phase velocity between “waves” in a surface acoustic wave device is disclosed (see Patent Document 1).

  A conventional surface acoustic wave device using a quasi-longitudinal wave type leaky surface acoustic wave will be described with reference to FIG. FIG. 9 is a front sectional view showing a conventional surface acoustic wave device. In the surface acoustic wave device 100, the quartz substrate 102 as an example of the piezoelectric substrate on which the IDT electrode 103 and the like are formed is bonded so that the IDT electrode 103 faces the opening of the storage container 106 (in FIG. 9, upward). The container 107 is connected via the agent 107. An electrode (not shown) on the quartz substrate 102 is connected to an electrode (not shown) of the storage container 106 via a bonding wire 104. The quartz substrate 102 using the quasi-longitudinal wave type leaky surface acoustic wave needs to be thin in order to improve the characteristics. For example, in the case of using Rayleigh waves, the thickness of the quartz substrate 102 is 50 μm in order to realize the 2 GHz quartz substrate 102 having a thickness of about 400 μm using a high-speed pseudo longitudinal wave type leaky surface acoustic wave. It will be about.

  The quartz substrate 102 is provided with a reinforcing portion 108 along the outer peripheral portion on the back side thereof, and a concave portion 105 is formed on the back side of the quartz substrate 102 by the reinforcing portion 108. In the quartz substrate 102, the reinforcing portion 108 is connected to the storage container 106 via an adhesive 107 (see Patent Document 2). The recess 105 is formed so as to correspond at least to the formation range of the IDT electrode 103 on the quartz substrate 102. As a result, the quasi-longitudinal wave type leaky surface acoustic wave propagating to the back side of the quartz substrate 102 is accommodated in the recess 105, and the storage container 106 in the reinforcing portion 108 without leakage of the quasi-longitudinal wave type leaky surface acoustic wave. Can be connected.

JP 2004-215227 A JP 2004-215226 A

  However, since the crystal substrate 102 and the storage container 106 are joined only at the reinforcing portion 108, the connection area is reduced, and stress concentration due to an impact applied to the surface acoustic wave device 100 from the outside is caused. It tends to occur at the connection part. In particular, as described above, the quartz substrate 102 using the quasi-longitudinal wave type leaky surface acoustic wave is weak in strength because it is necessary to reduce the thickness, and the quartz substrate 102 may be damaged from this connection portion. Had the problem of being.

  The present invention has been made in order to solve the above-described problems, and suppresses stress concentration generated in a connection portion between a piezoelectric substrate such as a quartz crystal substrate and a storage container, and has a so-called impact resistance that can withstand an impact applied from the outside. An object of the present invention is to provide an improved surface acoustic wave device, a surface acoustic wave device, and an electronic apparatus using them.

  The surface acoustic wave device according to the present invention is a surface acoustic wave device including a piezoelectric substrate and an IDT electrode for exciting a pseudo longitudinal wave type leakage surface acoustic wave formed on the piezoelectric substrate, wherein the IDT electrode is formed. A reflection part having an acoustic impedance different from the acoustic impedance of the piezoelectric substrate is formed on the back surface of the piezoelectric substrate in a relation between the surface and the back surface.

  According to the surface acoustic wave device of the present invention, the leakage wave that leaks to the back surface side of the piezoelectric substrate along with the propagation of the pseudo-longitudinal wave type surface acoustic wave is reflected by the reflection portion, so that the leakage of energy to the outside of the piezoelectric substrate is prevented. It becomes possible to prevent. As a result, it is possible to support the piezoelectric substrate using the entire reflection portion, and the connection area for the support can be increased. That is, since stress concentration at the support portion is less likely to occur, the piezoelectric substrate can be prevented from being damaged, and so-called impact resistance can be improved.

  In addition, it is desirable that the acoustic impedance of the reflecting portion is larger than the acoustic impedance of the piezoelectric substrate.

  In this way, the reflection efficiency of the leaky wave generated along with the propagation of the quasi-longitudinal wave type leaky surface acoustic wave becomes higher, and the leakage of energy to the holding part can be reduced. As a result, it is possible to suppress the deterioration of characteristics such as the Q value of the surface acoustic wave element due to the leaky wave generated along with the propagation of the pseudo longitudinal wave type leaky surface acoustic wave.

  Moreover, it is desirable that the boundary between the piezoelectric substrate and the reflecting portion is bonded by anodic bonding or direct bonding.

  In this way, it is possible to reliably reflect the leaky wave generated along with the propagation of the pseudo longitudinal wave type leaky surface acoustic wave. As a result, it is possible to suppress the deterioration of characteristics such as the Q value of the surface acoustic wave element due to the leaky wave generated along with the propagation of the pseudo longitudinal wave type leaky surface acoustic wave.

  Moreover, it is desirable that the reflection portion is formed of a thin film.

  In this way, it is possible to reliably reflect the leaky wave generated along with the propagation of the pseudo longitudinal wave type leaky surface acoustic wave. As a result, it is possible to suppress the deterioration of characteristics such as the Q value of the surface acoustic wave element due to the leaky wave generated along with the propagation of the pseudo longitudinal wave type leaky surface acoustic wave.

  Further, the reflecting portion has the same shape as the plane of the piezoelectric substrate, or a plane area equal to or larger than the plane area of the piezoelectric substrate.

  In this way, the connection area between the reflecting portion and the holding portion can be increased and ensured reliably.

  The surface acoustic wave device of the present invention is a surface acoustic wave device including a piezoelectric substrate and an IDT electrode for exciting a pseudo longitudinal wave type leaky surface acoustic wave formed on the piezoelectric substrate, the IDT electrode On the back surface of the piezoelectric substrate that is in a front-to-back relationship with the surface on which the surface is formed, the reflective portion is formed to have an acoustic impedance different from the acoustic impedance of the piezoelectric substrate, and is formed in contact with the reflective portion And a holding portion.

  According to the surface acoustic wave device of the present invention, the leakage wave that leaks to the back surface side of the piezoelectric substrate along with the propagation of the pseudo-longitudinal wave type surface acoustic wave is reflected by the reflection portion, thereby preventing leakage of energy to the holding portion. It becomes possible to do. Therefore, the piezoelectric substrate can be connected to the holding portion over the entire reflection portion, and the connection area can be increased. That is, even when an external impact is applied to the surface acoustic wave device, stress concentration is less likely to occur, and damage to the piezoelectric substrate can be prevented. Accordingly, a surface acoustic wave device with improved so-called impact resistance can be provided.

  In addition, it is desirable that the acoustic impedance of the reflecting portion is larger than the acoustic impedance of the piezoelectric substrate.

  If it does in this way, the reflection efficiency of the leaky wave produced with propagation of the propagated pseudo longitudinal wave type leaky surface acoustic wave becomes higher, and the leakage of energy to the holding part can be reduced. As a result, it is possible to suppress the deterioration of characteristics such as the Q value of the surface acoustic wave device due to the leaky wave generated along with the propagation of the pseudo longitudinal wave type leaky surface acoustic wave.

  Moreover, it is desirable that the boundary between the piezoelectric substrate and the reflecting portion is bonded by anodic bonding or direct bonding.

  In this way, it is possible to reliably reflect the leaky wave generated along with the propagation of the pseudo longitudinal wave type leaky surface acoustic wave. As a result, it is possible to suppress the deterioration of characteristics such as the Q value of the surface acoustic wave element due to the leaky wave generated along with the propagation of the pseudo longitudinal wave type leaky surface acoustic wave.

  Moreover, it is desirable that the reflection portion is formed of a thin film.

  In this way, it is possible to reliably reflect the leaky wave generated along with the propagation of the pseudo longitudinal wave type leaky surface acoustic wave. As a result, it is possible to suppress the deterioration of characteristics such as the Q value of the surface acoustic wave element due to the leaky wave generated along with the propagation of the pseudo longitudinal wave type leaky surface acoustic wave.

  Further, the reflecting portion has the same shape as the plane of the piezoelectric substrate, or a plane area equal to or larger than the plane area of the piezoelectric substrate.

  In this way, the connection area between the reflecting portion and the holding portion can be increased and ensured reliably.

  The electronic apparatus according to the present invention is a surface acoustic wave device including a piezoelectric substrate and an IDT electrode for exciting a pseudo longitudinal wave type leaky surface acoustic wave formed on the piezoelectric substrate, the IDT electrode A surface acoustic wave device in which a reflection part having an acoustic impedance different from the acoustic impedance of the piezoelectric substrate is formed on the back surface of the piezoelectric substrate in a relation between the front surface and the back surface. And

  According to the electronic device of the present invention, since the surface acoustic wave device with improved impact resistance is used, it is possible to provide an electronic device that can withstand an impact applied to the electronic device.

Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)

  1A and 1B show a schematic configuration of a surface acoustic wave element according to this embodiment. FIG. 1A is a perspective view, and FIG. 1B is a cross-sectional view taken along line AA in FIG.

  As shown in FIG. 1, a surface acoustic wave element 10 includes a quartz crystal substrate 1 as a piezoelectric substrate, IDT electrodes 2 and reflector electrodes 3a and 3b formed on the surface 1a of the quartz crystal substrate 1, and a quartz crystal substrate 1 And a diamond layer 5 as a reflecting portion formed on the back surface 1b. In FIG. 1, t is the thickness of the quartz substrate 1, P is the pitch of the IDT electrodes 2, λ is the IDT wavelength, and h is the thickness of the IDT electrode 2 and the reflector electrodes 3a and 3b. The quartz substrate 1 is cut out at a cut-out angle corresponding to each piezoelectric material so that the pseudo longitudinal wave type leaky surface acoustic wave is excited, and the thickness t is adjusted to a predetermined thickness.

  The IDT electrode 2 and the reflector electrodes 3a and 3b are made of a metal mainly composed of aluminum, and are formed on the surface 1a of the quartz substrate 1. The IDT electrode 2 has a function of exciting a pseudo-longitudinal wave type leaky surface acoustic wave by supplying a driving voltage and outputting a vibration having a predetermined frequency. The reflector electrodes 3 a and 3 b are formed so as to sandwich the IDT electrode 2, reflect the propagation of the pseudo longitudinal wave type surface acoustic wave excited by the IDT electrode 2 toward the outer peripheral portion, and the IDT electrode 2. Has the function of confining surface wave energy.

  The diamond layer 5 is a layer mainly composed of diamond formed on the back surface 1b of the quartz substrate 1 by a hot filament CVD method or the like. The diamond layer 5 is excited by the IDT electrode 2, reflects a pseudo longitudinal wave type leaky surface acoustic wave propagating in the direction of the back surface 1 b of the crystal substrate 1, and simulates a pseudo longitudinal wave type leaky elastic surface from the back surface 1 b of the crystal substrate 1. It has a function to prevent wave leakage.

  Here, this function will be described. When the acoustic impedance on the incident side is Z1 and the acoustic impedance on the outgoing side is Z2 with respect to the adjacent interface (in this example, quartz and diamond), the acoustic reflection ratio of this interface (the sound pressure of the incident wave and the reflected wave) Is expressed by R = (Z2−Z1) / (Z2 + Z1). If Z1 <Z2, R is positive and the phase of the reflected wave is normal, and if Z1> Z2, R is negative and the phase of the reflected wave is inverted. The acoustic impedance is expressed as a product of density and sound speed. As described above, if the acoustic impedances of the piezoelectric substrate and the reflecting portion are made different, the leaked leak wave is reflected along with the propagation of the pseudo longitudinal leaky surface acoustic wave at the interface. That is, by forming the diamond layer 5 having different acoustic impedance on the back surface 1b of the quartz substrate 1, the leakage wave is reflected, and the vibration displacement is lost on the back surface 1c of the diamond layer 5. Can be prevented.

  The thickness of the diamond layer 5 is 1λ (λ (IDT wavelength) = V (sound speed) / f (oscillation frequency) as shown in the displacement distribution of the pseudo longitudinal wave type leaky surface acoustic wave in FIG. The thickness of (1)) is sufficient, and the function of sufficiently reflecting the propagated pseudo longitudinal wave type leaky surface acoustic wave is provided. For example, when a quartz substrate (sound velocity V = 5700 m / sec) is used and the oscillation frequency (f) is 2 GHz (gigahertz), from equation (1), λ = 2.85 μm, so the thickness of the diamond layer 5 Is 2.85 μm.

  Here, the graph shown in FIG. 2 shows the displacement distribution of the pseudo longitudinal wave type surface acoustic wave when the thickness of the diamond layer 5 is 1λ, and the graph shown in FIG. 3 shows the case where the thickness of the diamond layer 5 is 10λ. The displacement distribution of the pseudo longitudinal wave type leaky surface acoustic wave is shown. The graph shown in FIG. 4 shows the displacement distribution of the pseudo longitudinal wave type leaky surface acoustic wave when the diamond layer 5 is not formed as a comparative example. Here, the vertical axis shown in FIGS. 2 to 4 represents the displacement of the pseudo longitudinal wave type leaky surface acoustic wave, and the horizontal axis represents the depth (thickness) of the quartz substrate 1 by n × λ. . For example, 20 on the horizontal axis is a depth of 20 × λ (IDT wavelength). 2 to 4, u1 is a longitudinal wave component (displacement in the X axis direction), u2 is a depth direction component (displacement in the Z axis direction), and u3 is a transverse wave component (displacement in the Y axis direction). Is shown.

  FIG. 2 shows a displacement distribution of a pseudo longitudinal wave type leaky surface acoustic wave when a diamond layer 5 having a thickness of 1λ is formed on the back surface of a quartz substrate 1 having a thickness of 20λ. In this case, as shown in FIG. 2, the displacement of the pseudo longitudinal wave type leaky surface acoustic wave is hardly observed in the portion of 20λ or more. That is, it can be seen that the leakage wave generated along with the propagation of the quasi-longitudinal-wave type leaky surface acoustic wave is reflected by the diamond layer 5 having a thickness of 1λ, and no leakage of energy occurs outside the diamond layer 5.

  FIG. 3 shows a displacement distribution of a pseudo longitudinal wave type leaky surface acoustic wave when a diamond layer 5 having a thickness of 10λ is formed on the back surface of the quartz substrate 1 having a thickness of 20λ. In this case, as in the case of 1λ shown in FIG. 2, almost no displacement of the quasi-longitudinal wave type surface acoustic wave is observed in the portion of 20λ or more. That is, even when the diamond layer 5 having a thickness of 10λ is formed, the leakage wave generated along with the propagation of the quasi-longitudinal wave type leaky surface acoustic wave is reflected, and no energy leakage occurs outside the diamond layer 5. I understand that.

  FIG. 4 shows a displacement distribution of the pseudo longitudinal wave type leaky surface acoustic wave when the diamond layer 5 is not formed on the back surface of the quartz substrate 1 as a comparative example. In this case, as shown in FIG. 4, almost no attenuation of the quasi-longitudinal wave type leaky surface acoustic wave is observed, and the back surface of the quartz substrate 1 also has vibration displacement.

  As shown in FIGS. 2 and 3, if the thickness of the diamond layer 5 as a reflection portion adjacent to the quartz substrate 1 is larger than 1λ, the leakage wave of the pseudo longitudinal wave type leakage surface acoustic wave is reflected, and the diamond layer 5 On the outer side, no leakage of energy occurs. Therefore, even if an adhesive or the like as a holding portion is attached to the entire back surface 1c of the diamond layer 5, the characteristics are not deteriorated due to leakage, and the quartz substrate 1 can be supported by the entire back surface 1c of the diamond layer 5.

  Thus, since the area for supporting the quartz substrate 1 can be increased, stress concentration can be made difficult to occur, and damage to the quartz substrate 1 can be prevented. In addition, it is possible to provide a surface acoustic wave element with improved so-called impact resistance, in which the diamond layer 5 functions as a reinforcing layer of the quartz substrate 1.

  In addition, although the diamond layer 5 was demonstrated as an example as a reflection part above, a reflection part is not restricted to this. For example, a material having an acoustic impedance different from that of a piezoelectric substrate such as sapphire, molybdenum, or tungsten may be used. Furthermore, a material having an acoustic impedance larger than the acoustic impedance of the piezoelectric substrate is suitable for increasing the reflection efficiency.

In the above description, the hot filament CVD method is used to form the diamond layer 5. However, the present invention is not limited to this, and the crystal substrate 1 and the diamond layer 5 may be bonded at the molecular level or atomic level. The leakage wave of the quasi-longitudinal wave type leaky surface acoustic wave can be reflected. As another bonding method, for example, an anodic bonding method, a eutectic method, a direct bonding method, or the like may be used.
(Second embodiment)

  Next, the surface acoustic wave device according to this embodiment will be described with reference to FIG. FIG. 5 is a front sectional view showing an outline of a surface acoustic wave device in which the surface acoustic wave element described in the first embodiment is accommodated in a storage container.

  As shown in FIG. 5, the surface acoustic wave device 20 includes a storage container 28, a surface acoustic wave element 30, and a lid 29. The storage container 28 formed of ceramics or the like is provided with a recess having an open bottom and a bottom surface 26 and a bottom surface 27. In this recess, a surface acoustic wave element 30 made of a quartz substrate 21 as a piezoelectric substrate is accommodated so that the IDT electrode 22 faces upward (the opening side of the recess). The quartz substrate 21 uses one surface of the diamond layer 23 as a reflection portion formed by a hot filament CVD method or the like on the opposite surface (back surface) to the IDT electrode 22 formation surface, and an adhesive layer 24 as a holding portion. To the bottom surface 27 of the recess. Since this diamond layer 23 is the same as that of the first embodiment described above, description thereof is omitted here. The quartz substrate 21 is electrically connected to an electrode (not shown) on the surface on which the IDT electrode 22 is formed, a wiring electrode (not shown) on the bottom surface 26 of the recess, and the like by a wire wiring 25 or the like. A lid 29 is sealed on the upper surface of the storage container 28 while keeping the inside in a vacuum atmosphere or an inert gas atmosphere to form a packaged surface acoustic wave device 20.

As described above, the surface acoustic wave device 20 of the present embodiment has the surface acoustic wave element 30 on the bottom surface 27 of the storage container 28 through the diamond layer 23 as a reflection part of the leakage wave of the pseudo longitudinal wave type leakage surface acoustic wave. Is connected. The diamond layer 23 reflects the leakage wave of the quasi-longitudinal wave type leaky surface acoustic wave, and energy does not leak to the outside of the diamond layer 23, that is, to the adhesive layer 24 and the bottom surface 27. Connection can be made. In this way, since the connection area of the surface acoustic wave element 30 can be increased, stress concentration can be made difficult to occur, damage to the quartz substrate 21 can be prevented, and so-called impact resistance is improved. It is possible to provide the surface acoustic wave device 20.
(Third embodiment)

  Next, the surface acoustic wave device according to the present embodiment will be described with reference to FIG. FIG. 6 is a front sectional view showing an outline of a surface acoustic wave device in which the surface acoustic wave element described in the first embodiment is accommodated in a storage container.

  As shown in FIG. 6, the surface acoustic wave device 50 includes a storage container 55 and a surface acoustic wave element 60. The storage container 55 formed of ceramics or the like is provided with a recess that is open on one side. A surface acoustic wave element 60 comprising a quartz crystal substrate 51 as a piezoelectric substrate and a diamond layer 53 as a reflecting portion is placed in the concave portion of the storage container 55 with the IDT electrode 52 facing downward (bottom side of the concave portion), and gold bumps. It is mounted via 54, and electrical connection and mechanical connection are achieved simultaneously. The storage container 55 is filled with a filler 56 as a holding portion made of resin or the like except for the formation surface of the IDT electrode 52, protects the surface acoustic wave device 60, and is packaged with the surface acoustic wave device 50 packaged. Become.

As described above, the surface acoustic wave device 50 according to the present embodiment has the surface acoustic wave element 60 as a holding portion via the diamond layer 53 as a reflection portion that reflects the leakage wave of the pseudo longitudinal wave type leakage surface acoustic wave. Covered with a filler 56. The diamond layer 53 reflects the leakage wave of the quasi-longitudinal wave type leaky surface acoustic wave, and since the energy does not leak to the outside of the diamond layer 53, that is, the filler 56, the entire surface of the diamond layer 53 is covered with the filler 56. It becomes possible. Thus, since the back surface side of the surface acoustic wave element 60 is covered with the filler 56, the connection area becomes large, and stress concentration can be made difficult to occur. Thereby, it becomes possible to prevent the quartz substrate 51 from being damaged, and it is possible to provide the surface acoustic wave device 50 with improved so-called impact resistance.
(Fourth embodiment)

  Next, the surface acoustic wave device according to the present embodiment will be described with reference to FIG. FIG. 7 is a front sectional view schematically showing the surface acoustic wave device according to the fourth embodiment.

As shown in FIG. 7, in the surface acoustic wave device 70, a surface acoustic wave element 77 is connected on a substrate 75 made of ceramic or the like, and a mold resin 76 as a holding portion is provided so as to cover the periphery of the element. It is configured in the so-called CSP form provided.
The surface acoustic wave element 77 includes a crystal substrate 71 as a piezoelectric substrate, a diamond layer 73 as a reflection portion, an IDT electrode 72 formed on the surface of the crystal substrate 71, and the like.
The surface acoustic wave element 77 is mounted via a gold bump 74 in a state where the IDT electrode 72 faces the substrate 75, and achieves electrical connection and mechanical connection simultaneously.
A mold resin 76 made of epoxy resin or the like is provided in a state excluding the formation surface of the IDT electrode 72 to protect the surface acoustic wave element 77 and form a packaged surface acoustic wave device 70.

In the surface acoustic wave device 70 of the present embodiment, the surface acoustic wave element 77 is covered with a mold resin 76 via a diamond layer 73 as a reflection part that reflects the leakage wave of the pseudo longitudinal wave type leakage surface acoustic wave. The diamond layer 73 reflects the leakage wave of the pseudo-longitudinal wave type leaky surface acoustic wave, and energy does not leak to the outside of the diamond layer 73, that is, to the mold resin 76. Therefore, the entire surface of the diamond layer 73 is covered with the mold resin 76. It becomes possible. Thus, since the back surface side of the surface acoustic wave element 77 is covered with the mold resin 76, the connection area is increased, and stress concentration is less likely to occur. As a result, it is possible to prevent the quartz substrate 71 from being damaged. In addition, since the storage container is unnecessary, it is possible to reduce the size. Accordingly, it is possible to provide a small surface acoustic wave device 70 with improved impact resistance.
(Fifth embodiment)

  Next, an electronic device according to an embodiment of the present invention will be described as a fifth embodiment. FIG. 8 is a configuration diagram illustrating a configuration of the electronic device. The electronic device 80 includes the surface acoustic wave device 90 (the surface acoustic wave devices 20, 50, and 70 shown in FIGS. 5, 6, and 7) as described in the first to fourth embodiments. I have. Examples of the electronic device according to this embodiment include a mobile phone and a keyless entry system. In the case of a mobile phone, the surface acoustic wave device 90 is used as a frequency selection filter for the mobile phone. In the case of a keyless entry system, the surface acoustic wave device 90 is used as an oscillator resonator.

  As described above, the electronic device 80 according to this embodiment includes the surface acoustic wave device 90 using a pseudo longitudinal wave type leaky surface acoustic wave as a filter, a resonator, or an oscillator. The electronic device 80 having such a configuration includes the surface acoustic wave device 90 with improved impact resistance, and can provide the electronic device 80 with good performance that can withstand external shocks.

  In the above-described embodiment, the quartz substrate is used as an example of the piezoelectric substrate, but the present invention is not limited to this. For example, a piezoelectric substrate such as a lithium tantalate substrate, a lithium niobate substrate, or a lithium tetraborate substrate may be used, and the effect is the same.

The schematic structure of the surface acoustic wave element of 1st embodiment is shown, (a) is a perspective view, (b) is AA sectional drawing of (a). The graph which shows the displacement distribution of the pseudo longitudinal wave type | mold leaky surface acoustic wave of an example of 1st embodiment. The graph which shows the displacement distribution of the pseudo longitudinal wave type | mold leaky surface acoustic wave of an example of 1st embodiment. The graph which shows the displacement distribution of the pseudo longitudinal wave type | mold leaky surface acoustic wave as a comparative example. The front sectional view showing the outline of the surface acoustic wave device of the second embodiment. The front sectional view showing the outline of the surface acoustic wave device of the third embodiment. The front sectional view showing the outline of the surface acoustic wave device of a fourth embodiment. The block diagram which shows the outline of the electronic device of 5th embodiment. FIG. 3 is a front sectional view showing a conventional surface acoustic wave device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Quartz substrate as a piezoelectric substrate, 1a ... The surface of a quartz substrate, 1b ... The back surface of a quartz substrate, 1c ... The back surface of a diamond layer, 2 ... IDT electrode, 3a, 3b ... Reflector electrode 10, 30, 60, 77 ... surface acoustic wave element, 5 ... diamond layer as reflection part, 20, 50, 70 ... surface acoustic wave device, 80 ... electronic equipment, t ... thickness of piezoelectric substrate, h ... electrode thickness, λ ... IDT wavelength, P ... IDT electrode pitch.

Claims (11)

A surface acoustic wave device comprising a piezoelectric substrate and an IDT electrode for exciting a pseudo longitudinal wave type surface acoustic wave formed on the piezoelectric substrate,
A surface acoustic wave characterized in that a reflective portion having an acoustic impedance different from the acoustic impedance of the piezoelectric substrate is formed on the back surface of the piezoelectric substrate having a front-back relationship with the surface on which the IDT electrode is formed. element. The surface acoustic wave device according to claim 1,
The surface acoustic wave device according to claim 1, wherein an acoustic impedance of the reflecting portion is larger than an acoustic impedance of the piezoelectric substrate. In the surface acoustic wave device according to claim 1 or 2,
A surface acoustic wave device, wherein a boundary between the piezoelectric substrate and the reflecting portion is bonded by anodic bonding or direct bonding. The surface acoustic wave device according to any one of claims 1 to 3,
The surface acoustic wave device, wherein the reflection portion is formed of a thin film. The surface acoustic wave element according to any one of claims 1 to 4,
The surface acoustic wave device according to claim 1, wherein the reflecting portion has the same shape as the plane of the piezoelectric substrate or a plane area equal to or larger than the plane area of the piezoelectric substrate. A surface acoustic wave device comprising: a piezoelectric substrate; and an IDT electrode that excites a quasi-longitudinal wave type leaky surface acoustic wave formed on the piezoelectric substrate,
A reflection portion formed on the back surface of the piezoelectric substrate having a front-back relationship with the surface on which the IDT electrode is formed, and having an acoustic impedance different from that of the piezoelectric substrate;
A surface acoustic wave device comprising: a holding portion formed so as to be in contact with the reflecting portion. The surface acoustic wave device according to claim 6,
The surface acoustic wave device according to claim 1, wherein an acoustic impedance of the reflecting portion is larger than an acoustic impedance of the piezoelectric substrate. The surface acoustic wave device according to claim 6 or 7,
A surface acoustic wave device, wherein a boundary between the piezoelectric substrate and the reflecting portion is bonded by anodic bonding or direct bonding. The surface acoustic wave device according to any one of claims 6 to 8,
The surface acoustic wave device according to claim 1, wherein the reflecting portion is formed of a thin film. The surface acoustic wave device according to any one of claims 6 to 9,
The surface acoustic wave device according to claim 1, wherein the reflecting portion has the same shape as the plane of the piezoelectric substrate or a plane area equal to or larger than the plane area of the piezoelectric substrate. A surface acoustic wave device comprising a piezoelectric substrate and an IDT electrode for exciting a quasi-longitudinal wave type leaky surface acoustic wave formed on the piezoelectric substrate, the relationship between the surface on which the IDT electrode is formed and the front and back An electronic apparatus comprising: a surface acoustic wave device in which a reflection portion having an acoustic impedance different from the acoustic impedance of the piezoelectric substrate is formed on a back surface of the piezoelectric substrate.

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