JP2008177750A - Piezoelectric thin film device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To render a piezoelectric thin film device low-profile without providing an insulation portion as essential constitution between a substrate and a piezoelectric thin film. <P>SOLUTION: A piezoelectric vibrating resonator 1 is provided with the substrate 2 made of an insulating material, the piezoelectric thin film 3 formed on the substrate 2, and upper and lower electrodes 41 and 42 which are formed on the substrate 2 and opposite to top and reverse surfaces 31 and 32 of the piezoelectric thin film 3, the lower electrode 42 being interposed between the substrate 2 and piezoelectric thin film 3. The lower electrode 42 comprises a driven electrode portion 421 opposed to the upper electrode 41 with the piezoelectric thin film 3 interposed, and a connection electrode portion 422 for making an external electric connection. A cavity 23 is formed in the substrate 2 and the driven electrode portion 421 of the lower electrode 42 is disposed in the cavity 23 while exposed. An adjusting section 51 for oscillation frequency adjustment is provided in a portion of the driven electrode portion 421 of the lower electrode 42 where the adjusting section is exposed at least from the cavity 23. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric thin film device.

  In recent years, with the increase in frequency used for wireless communication and electric circuits, electronic devices used for these electric vibrations are also required to support higher frequencies.

  For example, among electronic devices, there is a piezoelectric thin film device (piezoelectric thin film resonator) having an FBAR (Film Bulk Acoustic Resonator) structure using bulk wave vibration. In this piezoelectric thin film device, a piezoelectric thin film is used as a piezoelectric material ( See Patent Document 1 below).

  In the piezoelectric thin film resonator described in Patent Document 1, a silicon oxide film is provided on the surface of a substrate made of silicon, and an oxide sandwiched between a lower electrode and an upper electrode made of aluminum is formed on the silicon oxide film. A piezoelectric thin film made of zinc is provided.

As described above, in Patent Document 1, zinc oxide is used as the piezoelectric thin film, and a silicon oxide film made of an insulating material is used between the piezoelectric thin film and the substrate.
Japanese Patent Publication No. 1-31728

  By the way, at present, thinning, that is, low profile is promoted in the piezoelectric thin film device. Therefore, in the case of the piezoelectric thin film resonator described in Patent Document 1, it is conceivable to reduce the height by omitting the silicon oxide film from the configuration. However, since the silicon substrate is not a perfect insulating material, it is necessary to interpose a silicon oxide film of an insulating material between the piezoelectric thin film, and this silicon oxide film cannot be omitted from the configuration.

  Therefore, in order to solve the above problems, the present invention aims to reduce the height of the piezoelectric thin film device without providing an insulating part (insulating film, insulating layer, etc.) as an essential component between the substrate and the piezoelectric thin film. An object is to provide a piezoelectric thin film device.

  In order to achieve the above object, a piezoelectric thin film device according to the present invention is formed on a substrate, a piezoelectric thin film formed on the substrate, and formed on the substrate and facing the front and back surfaces of the piezoelectric thin film. In the piezoelectric thin film device in which the paired upper and lower electrodes are provided in a stacked state, and the lower electrode is interposed between the substrate and the piezoelectric thin film, the upper and lower electrodes sandwich the piezoelectric thin film, respectively. The substrate is made of an insulating material, and a cavity is formed in the substrate and the lower electrode is formed in the cavity. The excitation electrode portion is disposed so as to be exposed, and at least a portion of the excitation electrode portion of the lower electrode that is exposed from the cavity is provided with an adjustment portion that performs oscillation frequency adjustment. And features.

  According to the present invention, the upper and lower electrodes are composed of the excitation electrode portion and the connection electrode portion, the substrate is made of an insulating material, and the excitation electrode of the lower electrode is formed in the cavity formed in the substrate. Since the adjustment portion is provided at least in a portion of the excitation electrode portion of the lower electrode exposed from the cavity, the piezoelectric thin film, the upper and lower electrodes, and the substrate are provided. It is not necessary to provide an insulating material. Therefore, it is possible to reduce the height of the piezoelectric thin film device. In particular, the design of the piezoelectric thin film device corresponding to high frequency is facilitated.

  Moreover, in a general FBAR structure piezoelectric thin film device, the upper and lower electrodes of a preset amount cannot be formed to adjust the oscillation frequency after manufacturing the piezoelectric thin film device. The upper and lower electrodes are composed of the excitation electrode portion and the connection electrode portion, the substrate is made of an insulating material, and the excitation electrode portion of the lower electrode is exposed in the cavity formed in the substrate. And since the said adjustment part is provided in the site | part exposed from the said cavity at least among the said excitation electrode parts of the said lower electrode, it becomes possible to adjust the oscillation frequency after manufacture of the said piezoelectric thin film device. Specifically, the oscillation frequency can be adjusted even after the upper and lower electrodes are formed on the substrate.

  Further, when the present invention is compared with the configuration shown in Patent Document 1 as the prior art, unlike the present invention, in the configuration shown in Patent Document 1, the lower electrode is not exposed from the cavity. That is, in Patent Document 1, a cavity is formed in a substrate, but the bottom surface member of the cavity is made of a thin substrate. Therefore, according to the configuration of Patent Document 1, it is necessary to consider the reduction of the oscillation frequency due to the thickness of the thin substrate. In Patent Document 1, an oscillation frequency adjustment thin film (frequency adjustment film) is provided in the cavity to adjust the oscillation frequency. The thickness of the frequency adjustment film is the thickness of a thin substrate. Therefore, the adjustment of the oscillation frequency using the frequency adjusting film cannot be widened. On the other hand, in the present invention, since the adjustment unit is configured as a part of the excitation electrode unit, it is possible to adjust the oscillation frequency without limiting the film thickness of the adjustment unit used to adjust the oscillation frequency. It becomes possible to have a width.

  The said structure WHEREIN: Furthermore, the additional adjustment part which adjusts an oscillation frequency may be provided in the said cavity.

  In this case, since the additional adjusting portion is provided in the cavity, not only can the oscillation frequency be adjusted even after the upper and lower electrodes are formed on the substrate, but further in combination with the adjusting portion. It is possible to provide a wide range of adjustment of the oscillation frequency.

  In the above configuration, the substrate is made of quartz, the excitation electrode portion is made of molybdenum, the connection electrode portion is made of chrome and gold, the adjustment portion is made of gold, and the piezoelectric thin film is made of the lower electrode. It may be made of aluminum nitride.

  In this case, since the substrate has a thermal expansion coefficient close to that of the material of the lower electrode, it is possible to avoid a bonding failure between the substrate and the connection electrode portion due to a different thermal expansion coefficient, It is possible to improve the bonding strength between the excitation electrode portion and the vibration region. In addition, the excitation electrode portion of the lower electrode is made of molybdenum that is not easily milled, but the adjustment electrode is provided in a portion of the excitation electrode portion of the lower electrode that is exposed from the cavity. It is possible to adjust the oscillation frequency even after forming the lower electrode on the substrate in a state where molybdenum is used.

  In the above configuration, the substrate may be made of a Z plate crystal (XY ′ cut), the side surface of the cavity may be tapered, and the inclination angle of the side surface may be 35 degrees with respect to the main surface of the substrate.

  In this case, since the side surface of the cavity is tapered and the inclination angle of the side surface is about 35 degrees with respect to the main surface of the substrate, it is exposed in the cavity as compared with the case where silicon is used for the substrate. It is suitable for adjusting the oscillation frequency using the excitation electrode. Specifically, general silicon used for an IC chip or the like is an anisotropic material, and a Si (111) surface having a taper surface with an inclination angle of about 55 degrees. Therefore, with silicon, it is difficult to adjust the oscillation frequency without laying down the tapered surface as shown in the present invention. In addition, since the inclination angle of the side surface of the cavity is 35 degrees with respect to the surface of the substrate, the lower electrode interposed between the substrate and the piezoelectric thin film even when the thin substrate is used. It is possible to expose the excitation electrode portion of the cavity from the cavity. Further, the physical surface of the lower electrode exposed by the cavity is uniformly applied to the entire surface of the lower electrode by laying the inclined surface of the side surface of the cavity with respect to the surface of the substrate (chemically). It is possible to adjust the oscillation frequency by etching or the like (with processing added). As a result, it is possible to suppress the generation of a plurality of frequencies due to the difference in mass and density at each portion of the excitation electrode portion where longitudinal vibration of the piezoelectric thin film device occurs. In particular, the upper and lower electrodes (especially the excitation electrode part) are relatively thin in the high frequency region that has been developed recently, but according to this configuration, the entire excitation electrode part (adjustment part) On the other hand, since the oscillation frequency is adjusted uniformly by milling or etching using a reactive gas, it can be effectively used for the thin lower electrode. In addition, it is possible to suppress fluctuations in the characteristics of the piezoelectric vibrating device due to non-uniform layer thickness after adjusting the oscillation frequency.

  According to the present invention, it is possible to reduce the height of the piezoelectric thin film device without providing an insulating portion as an essential component between the substrate and the piezoelectric thin film.

  Embodiments of the present invention will be described below with reference to the drawings. In the following examples, the present invention is applied to a piezoelectric thin film resonator as a piezoelectric thin film device.

  The piezoelectric thin film resonator 1 according to the present embodiment has an FBAR structure as shown in FIGS. 1 and 13 and is formed on the substrate 2, the piezoelectric thin film 3 formed on the substrate 2, and the substrate 2. A pair of an upper electrode 41 and a lower electrode 42 formed to face the front and back surfaces 31 and 32 of the piezoelectric thin film 3 are provided. In the piezoelectric thin film resonator 1, a substrate 2, a lower electrode 42, a piezoelectric thin film 3, and an upper electrode 41 are laminated, and the lower electrode 42 is interposed between the substrate 2 and the piezoelectric thin film 3.

  The upper electrode 41 includes an excitation electrode portion 411 that is opposed to the lower electrode 42 with the piezoelectric thin film 3 interposed therebetween, and a connection electrode portion 412 that is electrically connected to the outside. The excitation electrode portion 411 of the upper electrode 41 has a circular shape, and is arranged at a position corresponding to a closed end face 26 of the cavity 23 described below, as shown in FIG. Of the upper electrode 41, the excitation electrode portion 411 is made of molybdenum, and the connection electrode portion 412 is made of an electrode made of molybdenum and an electrode formed by laminating chromium and gold. The thickness of the upper electrode 41 is, for example, 200 nm, and this thickness is adjusted according to desired characteristics such as the oscillation frequency.

  The lower electrode 42 includes an excitation electrode portion 421 that is opposed to the upper electrode 41 with the piezoelectric thin film 3 interposed therebetween, and a connection electrode portion 422 that is electrically connected to the outside. In the lower electrode 42, the excitation electrode portion 421 and the connection electrode portion 422 are partially overlapped, and the excitation electrode portion 421 is disposed in the cavity 23 so as to be exposed. An adjustment portion 51 that adjusts the oscillation frequency is provided at least in a portion of the excitation electrode portion 421 that is exposed from the cavity 23. Note that a part of the connection electrode part 422 and the adjustment part 51 are made of the same material, and the materials of the excitation electrode part 421 and a part of the connection electrode part 422 are different. Specifically, the excitation electrode part 421 is made of molybdenum, the connection electrode part 422 is made of an electrode made of molybdenum and an electrode made by laminating chromium and gold, and the adjusting part 51 is made of laminating chromium and gold. It becomes. The part of the connection electrode portion 422 here refers to an electrode formed by laminating chromium and gold. Further, as shown in FIGS. 1 and 13, the excitation electrode portion 421 of the lower electrode 42 has a rectangular shape having a size (dimension in plan view) larger than the excitation electrode portion 411 of the upper electrode 41 described above. Further, the thickness of the excitation electrode portion 421 is, for example, 200 nm, and this thickness is adjusted by desired characteristics such as an oscillation frequency. Note that the etching rate of an electrode formed by stacking chromium and gold is higher than that of an electrode made of molybdenum.

  The piezoelectric thin film 3 is made of aluminum nitride. The piezoelectric thin film 3 includes a vibration region 33 between the upper and lower electrodes 41 and 42 formed to face the front and back surfaces 31 and 32 and another region 34 other than the vibration region 33. The thickness of the vibration region of the piezoelectric thin film 3 is 2 μm, and this thickness is adjusted by desired characteristics such as the oscillation frequency.

  The substrate 2 is made of a Z plate crystal that is an insulating material, and its maximum thickness is 80 μm. Both main surfaces 21 and 22 of the substrate 2 are mirror-finished to suppress the surface roughness when the substrate 2 is molded. Here, the Z plate crystal means a crystal plate composed of an XY plane perpendicular to the Z axis of the crystal axis of the crystal, and in this embodiment, a Z plate rotated by +1 to 2 degrees around the X axis. Crystal is used. Moreover, the surface roughness at the time of mirror surface processing here means the thing of 1-3 micrometers by the surface roughness 10 point average method, for example. The mirror finishing is preferable because the surface state of the upper electrode 41 and the lower electrode 42 formed on the substrate 2 can be improved, and the piezoelectric thin film 3 having good characteristics can be obtained. Further, a cavity 23 is formed in the substrate 2, and an excitation electrode portion 421 of the lower electrode 42 is disposed corresponding to the cavity 23, and the adjustment portion 51 is disposed in the cavity 23 so as to be exposed. Further, the side surface 24 of the cavity 23 is tapered, and the inclination angle of the side surface 24 is inclined by about 35 degrees with respect to the surface of the substrate 2. When the cavity 23 is formed by etching, this inclination angle depends on the rotation angle around the X axis of the Z-plate crystal and may be set to a value around 35 degrees. The open end face 25 and the closed end face 26 of the cavity 23 are formed in a circular shape or a substantially triangular shape.

  Next, the manufacturing process of the piezoelectric thin film resonator 1 according to this embodiment will be described with reference to the drawings (FIGS. 1 to 13).

  First, a plurality of crystal wafers (not shown) are formed from a crystal ingot (not shown). Both main surfaces of the crystal wafer molded from the crystal ingot are polished and polished, and then cleaned to flatten both main surfaces of the crystal wafer. Chromium is formed on both flat main surfaces of the quartz wafer, and gold is laminated on the upper surface to form a metal layer made of chromium and gold (hereinafter referred to as Cr—Au metal layer 61 (see FIG. 2)). The Cr—Au metal layer 61 is coated with a resist (not shown), exposed and developed to form the outer pattern of the substrate 2 and the pattern of the cavity 23, and the Cr—Au metal layer 61 is formed into a predetermined pattern. Metal etch into shape. Then, the resist is peeled off, and the cavity 23 is etched in the substrate 2 as shown in FIG.

  After forming the cavity 23 as shown in FIG. 2, a resist 64 is applied on the Cr—Au metal layer 61 formed on the main surface 21 on the surface side of the substrate 2 (see FIG. 3). Then, the applied resist 64 is exposed and developed to form a part of the electrodes of the connection electrode portions 411 and 422 of the upper and lower electrodes 41 and 42 and the pattern of the adjustment portion 51 (see FIG. 4), and Cr—Au metal The layer 61 is metal etched into a predetermined pattern shape (see FIG. 5). Then, after the Cr—Au metal layer 61 is subjected to metal etching, the resist 64 is peeled off as shown in FIG. 6 to form part of the connection electrode portions 411 and 422 of the upper and lower electrodes 41 and 42 and the adjustment portion 51. .

  As shown in FIG. 7, a metal layer made of molybdenum (hereinafter referred to as Mo metal layer 62) is laminated on the substrate 2 in the state shown in FIG. And the resist 64 is apply | coated on the Mo metal layer 62 formed in the main surface 21 at the surface side of the board | substrate 2 (refer FIG. 8). Then, the applied resist 64 is exposed and developed to form the pattern of the excitation electrodes 421 of the lower electrode 42 and the remaining electrodes of the connection electrode 422 (see FIG. 9), and the Mo metal layer 62 is formed into a predetermined pattern. Metal etching is performed to the shape (see FIG. 10). Then, after metal etching of the Mo metal layer 62, the resist 64 is peeled off as shown in FIG. 11, and the excitation electrode portion 421 of the lower electrode 42 and the remaining electrodes of the connection electrode portion 422 are formed to form the lower electrode 42. To do.

  An AlN layer 63 made of aluminum nitride is stacked on the substrate 2 in the state shown in FIG. Then, a resist (not shown) is applied on the AlN layer 63 formed on the main surface 21 on the surface side of the substrate 2, and the applied resist is exposed and developed to form an outer pattern of the piezoelectric thin film 3. The AlN layer 63 is metal etched into a predetermined pattern shape. Then, after the AlN layer 63 is metal etched, the resist is peeled off to form the piezoelectric thin film 3 as shown in FIG.

  A metal layer made of molybdenum (hereinafter, Mo metal layer 62) is laminated on the substrate 2 in the state shown in FIG. Then, a resist (not shown) is applied on the Mo metal layer 62 formed on the main surface 21 on the surface side of the substrate 2. Then, the applied resist is exposed and developed to form the pattern of the excitation electrode portion 411 of the upper electrode 41 and the remaining electrode of the connection electrode portion 412, and the Mo metal layer 62 is metal etched into a predetermined pattern shape. Then, after the metal etching of the Mo metal layer 62, the resist is peeled off, and the upper electrode 41 is formed by forming the excitation electrode portion 411 of the upper electrode 41 and the remaining electrode of the connection electrode portion 412 as shown in FIG. The piezoelectric thin film resonator 1 is obtained.

  According to the above-described piezoelectric thin film resonator 1 according to the present embodiment, the upper and lower electrodes 41 and 42 are constituted by the excitation electrode portions 411 and 421 and the connection electrode portions 412 and 422, and the substrate 2 is made of an insulating material. 2, the excitation electrode portion 421 of the lower electrode 42 is disposed so as to be exposed, and the adjustment portion 51 is provided at least in a portion exposed from the cavity 23 in the excitation electrode portion 421 of the lower electrode 42. Therefore, it is not necessary to provide an insulating material between the piezoelectric thin film 3 and the upper and lower electrodes 41 and 42 and the substrate 2. Therefore, the piezoelectric thin film resonator 1 can be reduced in height. In particular, the design of the piezoelectric thin film resonator 1 corresponding to high frequency is facilitated.

  In addition, in a general FBAR structure piezoelectric thin film device, it is not possible to adjust the oscillation frequency after manufacturing the piezoelectric thin film device by forming a predetermined amount of upper and lower electrodes. The electrodes 41 and 42 are composed of excitation electrode portions 411 and 421 and connection electrode portions 412 and 422, and the substrate 2 is made of an insulating material, and the excitation electrode portion 421 of the lower electrode 42 in the cavity 23 formed in the substrate 2. Is provided, and the adjustment portion 51 is provided at least in the portion of the excitation electrode portion 421 of the lower electrode 42 that is exposed from the cavity 23. Therefore, the oscillation frequency after the manufacture of the piezoelectric thin film resonator 1 is adjusted. be able to. Specifically, the oscillation frequency can be adjusted even after the upper and lower electrodes 41 and 42 are formed on the substrate 2.

  Further, when this example is compared with the conventional configuration as shown in Patent Document 1, in the configuration shown in Patent Document 1, the lower electrode is not exposed from the cavity. That is, in Patent Document 1, a cavity is formed in a substrate, but the bottom surface member of the cavity is made of a thin substrate. Therefore, according to the configuration of Patent Document 1, it is necessary to consider the reduction of the oscillation frequency due to the thickness of the thin substrate. In Patent Document 1, an oscillation frequency adjustment thin film (frequency adjustment film) is provided in the cavity to adjust the oscillation frequency. The thickness of the frequency adjustment film is the thickness of a thin substrate. Therefore, the adjustment of the oscillation frequency using the frequency adjusting film cannot be widened. On the other hand, according to the present embodiment, since the adjustment unit 51 is configured as a part of the excitation electrode unit 421, the oscillation frequency is not limited without limiting the film thickness of the adjustment unit 51 used to adjust the oscillation frequency. The width of the adjustment can be increased.

  In the case of the piezoelectric thin film resonator that does not have the other region 34 of the piezoelectric thin film 3 of the present embodiment among the conventional piezoelectric thin film resonators, the distance between the upper and lower electrodes with the reduction in the height of the piezoelectric thin film resonator. Becomes very close and the upper and lower electrodes are connected to each other, so that a short circuit is likely to occur. However, according to this embodiment, a short circuit between the upper and lower electrodes 41 and 42 can be avoided by the other region 34 of the piezoelectric thin film 3.

  From the above, according to the piezoelectric thin film resonator 1 according to the present example, spurious can be suppressed while maintaining a high Q value, and further, the problem of the DLD characteristic can be made difficult to occur.

  In addition, since the substrate 2 has a thermal expansion coefficient close to that of the material of the lower electrode 42, it is possible to avoid a bonding failure between the substrate 2 and the connection electrode portion 422 due to a difference in the thermal expansion coefficient, and the excitation electrode portion. The bonding strength between 421 and the vibration region 33 can be improved. Further, although molybdenum that is difficult to be milled is used for the excitation electrode portion 421 of the lower electrode 42, the adjustment portion 51 is provided in a portion of the excitation electrode portion 421 of the lower electrode 42 that is exposed from the cavity 23. The oscillation frequency can be adjusted even after the lower electrode 42 is formed on the substrate 2 in the state where molybdenum is used for 421.

  Further, since the side surface of the cavity 23 is tapered and the inclination angle of the side surface is about 35 degrees with respect to the surface of the substrate 2, the excitation electrode exposed in the cavity 23 is compared with the case where silicon is used for the substrate 2. And is suitable for adjusting the oscillation frequency. Specifically, general silicon used for an IC chip or the like is an anisotropic material, and a Si (111) surface having a taper surface with an inclination angle of about 55 degrees. Therefore, with silicon, it is difficult to adjust the oscillation frequency without laying down the tapered surface as shown in the present embodiment. In addition, since the inclination angle of the side surface 24 of the cavity 23 is 35 degrees with respect to the surface of the substrate 2, even when the thin substrate 2 is used, the lower surface interposed between the substrate 2 and the piezoelectric thin film 3 is used. The excitation electrode portion 421 of the electrode 42 can be exposed from the cavity 23. Also, physical milling and reaction gas were used uniformly over the entire portion of the lower electrode 42 exposed by the cavity 23 by laying the inclined surface of the side surface of the cavity 23 against the surface of the substrate 2 (chemical) Oscillation frequency can be adjusted by etching or the like. As a result, it is possible to suppress the generation of a plurality of frequencies due to the difference in mass and density at each portion of the excitation electrode portion 421 where longitudinal vibration of the piezoelectric thin film resonator 1 occurs. In particular, the upper and lower electrodes 41 and 42 (especially the excitation electrode portions 411 and 421) are relatively thin in the high frequency region that has been developed recently, but according to this configuration, the excitation electrode portion 421 (adjustment portion) 51) Since the oscillation frequency is adjusted uniformly by milling, etching using a reactive gas, or the like, the thin lower electrode 42 can be used effectively. In addition, fluctuations in characteristics of the piezoelectric resonator 1 due to non-uniform layer thickness after adjustment of the oscillation frequency can be suppressed.

  In this embodiment, the open end face 25 and the closed end face 26 of the cavity 23 are formed in a circular shape. However, the present invention is not limited to this, and a Z-plate crystal is used for the substrate 2. The closed end face 26 may be formed in a triangular shape. Note that the triangular sides referred to here may be curved. When the closed end face 26 of the cavity 23 is formed in a triangular shape, the shape of the excitation electrode portion 411 of the upper electrode 41 may be triangular according to the shape of the closed end face 26 of the cavity 23.

  In this embodiment, molybdenum is used for the excitation electrode portion 421 and the upper electrode 41 of the lower electrode 42. However, this is a preferred example and is not limited to this. For example, aluminum, titanium or gold Or platinum or tungsten. Moreover, you may employ | adopt the structure which formed gold | metal | money on the molybdenum base in a part of connection electrode 411,421 of the upper and lower electrodes 41,42.

  Further, in this embodiment, aluminum nitride is used for the piezoelectric thin film 3, but this is a preferred example and is not limited to this. For example, zinc oxide may be used.

  In this embodiment, a Z plate crystal rotated by +1 to 2 degrees around the X axis is used as the substrate 2, but this rotation angle is not limited to this, for example, a Z plate that does not rotate around the X axis It is arbitrarily set according to the use such as using a crystal or a Z-plate crystal rotated by 2 degrees or more.

  In the present embodiment, the thickness of the vibration region 33 and the thickness of the other region 34 are set to the same thickness, but the present invention is not limited to this. For example, as shown in FIG. The thickness of the other region 34 may be set to 1/2 or less of the thickness of 33. In the example shown in FIG. 14, the thickness of the vibration region 33 of the piezoelectric thin film 3 is 2 μm, and the thickness of the other region 34 is 1 μm. These thicknesses are adjusted according to desired characteristics such as the oscillation frequency. Is done. In this case, longitudinal vibration of the piezoelectric thin film 3 sandwiched between the upper and lower electrodes 41 and 42 can be performed while suppressing leakage of vibration energy. The thickness of the other region 34n in this embodiment is preferably thinner than 1 μm. The thinner the thickness, the smaller the vibration energy leakage (piezoelectric leakage wave), and the unnecessary vibration of the piezoelectric vibration resonator 1 is suppressed. Improved characteristics.

  In the present embodiment, the adjustment unit 51 is provided as a configuration of the lower electrode 42, but is not limited to this, and additional adjustment for newly adjusting the oscillation frequency to the cavity 23 of the piezoelectric thin film resonator 1 is performed. A part 52 may be provided. That is, the addition adjusting unit 52 may be added to the piezoelectric thin film resonator 1. The additional adjustment unit 52 shown in FIG. 15 is made of gold and is electrically connected to the excitation electrode unit 421 of the lower electrode 42. Thus, by providing the additional adjustment portion 52 in the cavity 23, not only can the oscillation frequency be adjusted even after the upper and lower electrodes 41, 42 are formed on the substrate 2, but also together with the adjustment portion 51. Further, it is possible to provide a wide range for adjusting the oscillation frequency.

  Further, in this embodiment, the lower electrode 42 is formed by overlapping a part of the electrode made of molybdenum and the electrode formed by laminating chromium and gold. This configuration is not limited to the present embodiment, and if different materials are formed to overlap, the excitation electrode portion 421 and the connection electrode portion 422 of the lower electrode 42 are made of different materials, and these excitations are made. A part of the electrode part 421 and the connection electrode part 422 may overlap each other. That is, the material required for the excitation electrode portion 421 (Mo metal layer 62 in this embodiment) and the material required for the connection electrode portion 422 (Cr—Au metal layer 61 in this embodiment) overlap each other. It only has to be.

  It should be noted that the present invention can be implemented in various other forms without departing from the spirit, gist, or main features. For this reason, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  It can be used for a piezoelectric thin film device using quartz as a substrate.

FIG. 1 is a schematic plan view of a piezoelectric thin film resonator according to this example. FIG. 2 is a schematic side view of the substrate on which the cavity is formed in the manufacturing process of the piezoelectric thin film resonator according to this example. FIG. 3 is a schematic side view of the substrate showing a subsequent process of the manufacturing process shown in FIG. 2 among the manufacturing processes of the piezoelectric thin film resonator according to the present example. FIG. 4 is a schematic side view of the substrate showing the subsequent process of the manufacturing process shown in FIG. 3 among the manufacturing processes of the piezoelectric thin film resonator according to the present example. FIG. 5 is a schematic side view of the substrate showing a subsequent process of the manufacturing process shown in FIG. 4 among the manufacturing processes of the piezoelectric thin film resonator according to the present example. FIG. 6 is a schematic side view of the substrate showing a subsequent process of the manufacturing process shown in FIG. 5 among the manufacturing processes of the piezoelectric thin film resonator according to the present example. FIG. 7 is a schematic side view of the substrate showing a subsequent process of the manufacturing process shown in FIG. 6 among the manufacturing processes of the piezoelectric thin film resonator according to the present example. FIG. 8 is a schematic side view of the substrate showing the subsequent process of the manufacturing process shown in FIG. 7 among the manufacturing processes of the piezoelectric thin film resonator according to the present example. FIG. 9 is a schematic side view of the substrate showing a subsequent process of the manufacturing process shown in FIG. 8 among the manufacturing processes of the piezoelectric thin film resonator according to the present example. FIG. 10 is a schematic side view of the substrate showing the subsequent process of the manufacturing process shown in FIG. 9 among the manufacturing processes of the piezoelectric thin film resonator according to the present example. FIG. 11 is a schematic side view of the substrate in a state where the lower electrode is formed on the substrate, showing a subsequent step of the manufacturing step shown in FIG. 10 among the manufacturing steps of the piezoelectric thin film resonator according to the present example. FIG. 12 is a schematic side view of the substrate in which the lower electrode and the piezoelectric thin film are formed on the substrate, showing a subsequent step of the manufacturing step shown in FIG. 11 among the steps of manufacturing the piezoelectric thin film resonator according to the present example. . FIG. 13 is a schematic side view of the piezoelectric thin film resonator according to the present example. FIG. 14 is a schematic side view of a piezoelectric thin film resonator according to another example of the present embodiment. FIG. 15 is a schematic side view of a piezoelectric thin film resonator according to another example of the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric thin film resonator 2 Substrate 23 Cavity 24 Cavity side surface 3 Piezoelectric thin films 31, 32 Front and back surfaces of piezoelectric thin film 33 Vibration region 34 Other region 41 Upper electrode 42 Lower electrode 411, 421 Excitation electrode portion 412, 422 Connection electrode portion 51 Adjustment Part 52 Additional adjustment part

Claims (4)

A substrate, a piezoelectric thin film formed on the substrate, and a pair of upper and lower electrodes formed on the substrate and opposed to the front and back surfaces of the piezoelectric thin film are provided in a stacked state, In the piezoelectric thin film device in which the lower electrode is interposed between the substrate and the piezoelectric thin film,
The upper and lower electrodes are each composed of an excitation electrode portion facing each other with the piezoelectric thin film interposed therebetween, and a connection electrode portion that performs electrical connection with the outside,
The substrate is made of an insulating material, and a cavity is formed in the substrate, and the excitation electrode portion of the lower electrode is exposed and disposed in the cavity.
A piezoelectric thin film device, wherein an adjustment portion for adjusting an oscillation frequency is provided at least in a portion exposed from the cavity in the excitation electrode portion of the lower electrode.   The piezoelectric thin film device according to claim 1, further comprising an additional adjustment unit that adjusts an oscillation frequency in the cavity. The substrate is made of quartz,
In the lower electrode, the excitation electrode portion is made of molybdenum, and the connection electrode portion is a laminate of chromium and gold,
The adjustment unit is made of gold,
The piezoelectric thin film device according to claim 1, wherein the piezoelectric thin film is made of aluminum nitride. The substrate is made of Z-plate crystal,
4. The piezoelectric thin film device according to claim 1, wherein a side surface of the cavity is tapered, and an inclination angle of the side surface is 35 degrees with respect to a main surface of the substrate.

Images