JP2005244184A - Thin-film piezoelectric element and method of manufacturing the thin-film piezoelectric element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin-film piezoelectric element which can improve the electromechanical coupling factor of a piezoelectric film. <P>SOLUTION: The thin-film piezoelectric element comprises an amorphous metal film 22 on a substrate 11 and a piezoelectric film 15 oriented perpendicularly to the surface of the amorphous metal film 22. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a thin film piezoelectric element using a piezoelectric body, and more particularly to a thin film piezoelectric element used in a high frequency band and a method for manufacturing the thin film piezoelectric element.

  In recent years, wireless communication systems such as mobile communication devices such as mobile phones and wireless local area network (LAN) systems that transfer data between computers at high speed use a high frequency band of GHz or higher. Thin film piezoelectric elements have attracted attention as high frequency (RF) elements used in high frequency band electronic devices such as such wireless communication systems. As a thin film piezoelectric element, for example, a resonator, a variable capacitor, a microswitch, or the like is desired. In particular, a thin film piezoelectric element by micro electro mechanical system (MEMS) technology is manufactured by thin film microfabrication in the same manner as a manufacturing process of a semiconductor device such as a metal / insulating film / semiconductor (MIS) integrated circuit (IC). Therefore, it is possible to integrate the MEMS thin film piezoelectric element and the semiconductor device on the same semiconductor substrate.

  For example, a surface acoustic wave (SAW) element is generally used as a high frequency band resonator. However, the resonance frequency of the SAW element is inversely proportional to the inter-comb electrode distance, and in a frequency region exceeding 1 GHz, the inter-comb electrode distance is 1 μm or less. It has become difficult to respond to computerization.

  As a resonator that has recently attracted attention in place of the SAW element, there is a thin film piezoelectric resonator (FBAR) using a longitudinal vibration mode in the thickness direction of the piezoelectric film. An FBAR using a piezoelectric film is also referred to as a bulk acoustic wave (BAW) element or the like. In FBAR, the resonance frequency is determined by the sound speed and film thickness of the piezoelectric body. For example, the piezoelectric film usually corresponds to the 2 GHz band with a film thickness of 1 to 2 μm, and corresponds to the 5 GHz band with a film thickness of 0.4 to 0.8 μm. Furthermore, by reducing the thickness of the piezoelectric film, it is possible to increase the frequency up to several tens of GHz.

  Non-Patent Document 1 discloses that a ladder-type filter using FBAR can be used as an RF filter of a mobile communication device. In the ladder filter, a plurality of FBARs are arranged so as to be connected in series and in parallel. The FBAR can be used as a voltage controlled oscillator (VCO) of a mobile communication device in combination with a variable capacitance capacitor and an amplifier.

  In the current typical FBAR structure, a piezoelectric film such as aluminum nitride (AlN) or zinc oxide (ZnO) is sandwiched between opposed lower and upper electrodes. For high performance, the FBAR resonator is placed above the cavity. A manufacturing process of an FBAR having a cavity is disclosed (for example, see Patent Document 1). For example, a depression is formed on a silicon (Si) substrate by anisotropic etching. Next, a sacrificial layer that is easy to etch, such as boron and phosphorus doped silicate glass (BPSG), is embedded in the recess and planarized. A lower electrode, a piezoelectric film, and an upper electrode are sequentially deposited on the planarized sacrificial layer. Thereafter, holes are drilled from the upper electrode formed on the sacrificial layer until the sacrificial layer is reached. The sacrificial layer is removed by selective etching to form a cavity.

  The piezoelectric characteristics of the piezoelectric film used for FBAR depends on the orientation. For example, in an AlN piezoelectric film, it is known that there is a strong correlation between the c-axis orientation half width of an AlN crystal and the electromechanical coupling coefficient (see, for example, Non-Patent Document 1). In order to obtain good piezoelectric characteristics, it is necessary to form the hexagonal AlN piezoelectric film so that the c-axis direction is oriented along the opposing direction of the lower and upper electrodes. However, the orientation of the AlN piezoelectric film formed on the sacrificial layer is limited, and there is a problem that the electromechanical coupling coefficient is small.

  In order to improve the orientation of the piezoelectric crystal, a method of manufacturing an FBAR by epitaxially growing an AlN piezoelectric film on a substrate is disclosed (for example, see Patent Document 2). In the method disclosed in Patent Document 2, an AlN piezoelectric film is epitaxially grown in the (0001) direction, that is, the c-axis direction on a (111) -oriented Si substrate. An upper electrode is formed on the AlN piezoelectric film. Thereafter, the Si substrate is anisotropically etched from the back side of the substrate until the AlN piezoelectric film is exposed, and a via hole is formed. After the AlN piezoelectric film is exposed, a lower electrode is formed from the back side of the substrate. In this way, a resonator using the epitaxial AlN piezoelectric film is formed on the cavity.

  In the FBAR manufacturing method described above, it is necessary to use a Si substrate with a (111) orientation in order to make the AlN piezoelectric film c-axis oriented. There is also a problem that is different from the (100) -oriented Si substrate used in the manufacture of general semiconductor devices.

  In addition, in a thin film piezoelectric element such as a capacitance variable capacitor or a microswitch, a movable electrode provided on an actuator beam supported at one end in the air on the substrate, and a fixed electrode provided on the substrate surface facing the actuator Is provided. The actuator changes the distance between the movable electrode and the fixed electrode. As a driving force, a piezoelectric actuator using an electrostrictive effect or a reverse piezoelectric effect of a piezoelectric film has been studied.

  As a piezoelectric film having a large electrostrictive effect, lead zirconate titanate (PZT) is known. In PZT, in order to obtain a good film quality, it is necessary to anneal at about 600 ° C. after film formation at room temperature. Since volume shrinkage occurs by annealing, the residual strain of the PZT piezoelectric film inevitably increases. The piezoelectric actuator has a long and thin beam structure including a piezoelectric layer supported in the air and sandwiched between upper and lower electrodes. For this reason, it becomes difficult to suppress the warpage generated in the PZT piezoelectric film due to the residual strain.

Since a piezoelectric film such as AlN or ZnO can be formed near room temperature, the residual stress can be controlled more precisely depending on the film forming conditions than the PZT piezoelectric film. However, AlN, ZnO, and the like have a smaller electrostrictive effect than PZT. Therefore, the electromechanical coupling coefficient of the piezoelectric film is small, and the driving range of the piezoelectric actuator may be insufficient.
JP 2000-69594 A JP 2001-94373 PR Rajan S. Naik et al., “Measurements of Bulk, c-Axis Electromechanical Coupling Constant as a Function of AlN Film Quality ”, IEEE Transactions on ultrasonics, Ferroelectrics, and Frequency Control, January 2000, Vol. 47 , No. 1, p. 292-296

  The present invention provides a thin film piezoelectric element capable of improving the electromechanical coupling coefficient of the piezoelectric film and a method for manufacturing the thin film piezoelectric element.

  In order to solve the above-described problems, the first aspect of the present invention includes (a) an amorphous metal film on a substrate and (b) an amorphous metal film perpendicular to the surface of the amorphous metal film. The gist of the invention is a thin film piezoelectric element including a piezoelectric film oriented in a direction.

  The second aspect of the present invention is: (a) an amorphous metal film is formed on a substrate, and (b) a piezoelectric material oriented in a direction perpendicular to the surface of the amorphous metal film on the amorphous metal film. The gist of the present invention is a method of manufacturing a thin film piezoelectric element including forming a film and (c) forming an upper metal film facing the amorphous metal film with the piezoelectric film sandwiched between the surfaces of the piezoelectric film.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the manufacturing method of the thin film piezoelectric element which can improve the electromechanical coupling coefficient of a piezoelectric film, and a thin film piezoelectric element.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

The piezoelectric film 15 used in the thin film piezoelectric element according to the first and second embodiments of the present invention is provided on the surface of the base layer of the amorphous metal film 22 provided on the substrate 11 as shown in FIG. It is done. A piezoelectric material such as AlN or ZnO is used for the piezoelectric film 15. As the substrate 11, a semiconductor substrate such as Si is used. A metal such as aluminum tantalum (Al _x Ta _1-x ), titanium diboride (TiB ₂ ), or the like is used for the amorphous metal film 22. When an Al _x Ta _1-x alloy is deposited near the room temperature by, for example, sputtering or the like by X-ray diffraction (XRD) or backscattered electron diffraction (RHEED), the Al composition x is about 0.1 To about 0.9, it is confirmed that the material is amorphous.

The performance of the piezoelectric film 15 can be expressed by an electromechanical coupling coefficient k _t ² that is an index of the magnitude of the piezoelectric effect, a quality coefficient Q that is an index of the sharpness of mechanical vibration at the resonance frequency, and the like. In order to increase the electromechanical coupling coefficient of the piezoelectric film 15, it is important to align the polarization axis of the piezoelectric crystal in the thickness direction of the piezoelectric film 15. Moreover, a large quality factor Q can be obtained by using a high-purity piezoelectric crystal and aligning the crystal orientation of the piezoelectric film with the polarization direction.

  For example, in an RF filter or VCO using a thin film piezoelectric element, the band can be broadened as the electromechanical coupling coefficient of the piezoelectric film increases. The quality factor Q is related to the insertion loss of the RF filter and the purity of the VCO oscillation. The quality factor Q is related to various phenomena that absorb elastic waves. Also, in the piezoelectric actuator, the driving range increases as the electromechanical coupling coefficient of the piezoelectric film increases, so that low voltage driving and a wide variable range of the actuator can be realized.

  A piezoelectric crystal such as AlN or ZnO used as the piezoelectric film 15 belongs to the hexagonal system. Hexagonal crystals inherently have the property of being easily c-axis oriented. The polarization axes can be aligned by unidirectionally aligning the piezoelectric film 15 in the c-axis which is the polarization direction of the piezoelectric crystal, that is, the (0001) direction. As a result, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 can be ensured.

AlN and ZnO piezoelectric films are formed on various underlayers, and the orientation of the piezoelectric films is evaluated using X-ray diffraction (XRD) or the like. The underlayer and the piezoelectric film are deposited at room temperature by magnetron sputtering or the like. The film thickness of the piezoelectric film is about 500 nm. As shown in FIG. 2, in samples A and B using an Al _0.4 Ta _0.6 amorphous metal film as an underlayer, the AlN piezoelectric film and the ZnO piezoelectric film have an alignment half-value width of 2.3 ° and 2.6 °, respectively. And highly oriented in the c-axis direction. In Samples C and D using a TiB ₂ amorphous metal film as an underlayer, the AlN piezoelectric film and the ZnO piezoelectric film are highly oriented in the c-axis direction with half-widths of 1.9 ° and 1.8 °, respectively. doing.

In Samples E to H using an amorphous insulating layer such as silicon oxide (SiO ₂ ) and alumina (Al ₂ O ₃ ) as an underlayer, the AlN piezoelectric film and the ZnO piezoelectric film are c-axis oriented. Yes. The alignment half-value width is 4.1 ° to 5.1 °, which is wider than Sample A to Sample D, and the orientation is poor. Furthermore, in Samples I to L using Al polycrystalline metal or polycrystalline Si semiconductor (poly-Si) as an underlayer, the AlN piezoelectric film and the ZnO piezoelectric film become polycrystalline films without being unidirectionally oriented. . As described above, the effect of the amorphous metal underlayer on the high orientation of the piezoelectric film is very large.

  The surface of a polycrystalline metal is composed of crystal planes having various orientations, and there are many irregularities depending on crystal grains. On the other hand, the amorphous metal is formed with an amorphous surface having a uniform surface. Further, the mean square roughness detected by a surface roughness meter, an atomic force microscope (AFM) or the like is 3 nm or more on a polycrystalline metal surface, but is 3 nm or less on an amorphous metal surface. . As described above, since an extremely flat and uniform surface is obtained with an amorphous metal, the layer is oriented to the c-plane [0001], which is the original crystal habit plane of a hexagonal crystal such as AlN or ZnO. Easy to grow. As a result, the orientation of a piezoelectric film such as AlN or ZnO formed on the amorphous metal film can be improved.

In addition, the surface energy of the amorphous metal is generally larger than that of the amorphous insulating layer as compared with an amorphous insulating layer such as SiO ₂ ordinarily used as an underlayer or sacrificial layer on the substrate surface. The crystal growing on the amorphous metal film grows in layers and has the property of reducing the surface energy. Therefore, it is considered that the orientation is further improved on the amorphous metal film.

  As shown in FIG. 3, the piezoelectric film 15 is laminated on the surface of the orientation metal film 23 provided on the surface of the base layer of the amorphous metal film 22. The orientation metal film 23 is highly oriented on the surface of the amorphous metal film 22. As the orientation metal film 23, Al, copper (Cu), gold (Au), silver (Ag), iridium (Ir), nickel (Ni), and platinum that can be highly oriented on the (111) crystal habit plane. A face-centered cubic lattice (fcc) metal such as (Pt) or a body-centered cubic lattice (bcc) metal such as molybdenum (Mo) or tungsten (W) that can be highly oriented on the crystal habit plane of (110) orientation is used. It is possible. Highly oriented Al (111), Cu (111), Au (111), Ag (111), Ir (111), Ni (111), Pt (111), Mo (110), W (110), etc. A highly oriented piezoelectric film 15 such as AlN (0001) or ZnO (0001) can be formed on the oriented metal film 23 by inheriting the orientation.

An Al metal film and an AlN piezoelectric layer are formed on various underlayers, and the orientation of the piezoelectric film is evaluated by XRD or the like. The underlayer, the metal film, and the piezoelectric film are all deposited at room temperature by magnetron sputtering. The film thickness of the piezoelectric film is about 500 nm. As shown in FIG. 4, in the sample M using an Al _0.4 Ta _0.6 amorphous metal film as an underlayer, the Al metal film and the AlN piezoelectric film have an alignment half width of 1.0 ° and 1.5 °, respectively ( 111) and highly oriented in the c-axis direction. Further, in the sample N using the TiB ₂ amorphous metal film as the underlayer, the Al metal film and the AlN piezoelectric film have an alignment half width of 1.6 ° and 1.9 °, respectively, in the (111) and c-axis directions. Highly oriented.

In Sample O and Sample P in which an amorphous insulating layer such as SiO ₂ and Al ₂ O ₃ is used as an underlayer, the Al metal film has an alignment half width of 4.2 ° and 4.0 ° (111 And the AlN piezoelectric film is c-axis oriented with orientation half widths of 4.6 ° and 4.1 °. The alignment half-value widths of the Al metal film and the AlN piezoelectric film of the sample O and the sample P are wider than the sample M and the sample N, and the orientation is inferior. Furthermore, in Sample Q and Sample R using Al polycrystalline metal or poly-Si as an underlayer, the Al metal film and the AlN piezoelectric film are not oriented in a single orientation but become a non-oriented or low-oriented polycrystalline film. .

  Thus, by interposing the highly oriented metal film 23 between the amorphous metal film 22 and the piezoelectric film 15, the piezoelectric film can be further highly oriented.

(First embodiment)
As shown in FIG. 5, the thin film piezoelectric element according to the first embodiment of the present invention is provided on the lower electrode 14 of the amorphous metal film 22 provided on the surface of the substrate 11 and on the surface of the lower electrode 14. The piezoelectric film 15 and an upper electrode (upper metal film) 16 provided on the surface of the piezoelectric film 15 are provided. The resonance part 20 is defined by the region where the lower and upper electrodes 14 and 16 face each other and the piezoelectric film 15 sandwiched between the lower and upper electrodes 14 and 16 which face each other.

Further, as shown in FIG. 6, a barrier layer 13 is provided with a cavity 17 provided on the substrate 11 interposed therebetween. The resonating unit 20 is disposed on the cavity 17. The lower electrode 14 is provided to extend from the surface of the substrate 11 to the surface of the barrier layer 13. For example, the substrate 11 is a Si semiconductor substrate having a high resistance of about 1000 Ω · cm or more. The barrier layer 13 is a SiO ₂ film or the like. The lower electrode 14 is an amorphous metal film such as AlTa. The piezoelectric film 15 is made of AlN or the like. The upper electrode 16 is a metal film such as Al.

  In the piezoelectric film 15 of the resonance unit 20, a high frequency signal is transmitted by resonance of the bulk acoustic wave excited by the high frequency signal applied to the lower electrode 14 or the upper electrode 16. For example, a high frequency signal in the GHz band applied from the lower electrode 14 is transmitted to the upper electrode 16 via the piezoelectric film 15 of the resonance unit 20. On the amorphous metal lower electrode 14, the piezoelectric film 15 is highly oriented in the c-axis, which is the polarization direction of the piezoelectric crystal. Therefore, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 can be ensured.

  According to the first embodiment, the piezoelectric film 15 can be highly oriented on the c-axis, and the electromechanical coupling coefficient and the quality factor Q can be improved. As a result, it is possible to realize good resonance characteristics of the resonance part 20 of the thin film piezoelectric element.

  Next, a method for manufacturing the thin film piezoelectric element according to the first embodiment will be described with reference to process cross-sectional views shown in FIGS. Here, in the process cross-sectional view used for the description, a cross-section corresponding to the line AA shown in FIG. 5 is shown.

For example, a strontium / ruthenium oxide (SrRuO ₃ ) layer is formed to a thickness of about 1 μm on the surface of the substrate 11 such as Si by RF magnetron sputtering or the like. As shown in FIG. 7, the sacrificial layer 12 is formed by selectively removing the SrRuO ₃ layer by photolithography, wet etching, or the like. Thereafter, for example, a SiO ₂ layer is formed with a thickness of about 50 nm on the surface of the substrate 11 on which the sacrificial layer 12 is formed by RF magnetron sputtering or the like. The barrier layer 13 is formed by selectively removing the SiO ₂ layer by photolithography, wet etching, or the like.

An amorphous metal layer such as Al _0.4 Ta _{0.6 is formed} on the substrate 11 by RF magnetron sputtering or the like. As shown in FIG. 8, the lower electrode 14 is formed by selectively removing the amorphous metal layer by photolithography and reactive ion etching (RIE) using a fluoride gas.

  A piezoelectric layer such as AlN is formed to a thickness of 1.4 μm on the substrate 11 by reactive RF magnetron sputtering or the like. As shown in FIG. 9, the piezoelectric layer 15 is formed so as to cover one end of the lower electrode 14 by selectively removing the piezoelectric layer by photolithography and RIE using a chloride gas. Thereafter, a metal layer such as Al is formed on the substrate 11 by RF magnetron sputtering or the like. The metal layer is selectively removed by photolithography, RIE, or the like, and the upper electrode 16 is formed so as to extend to one end side of the lower electrode 14 covered with the piezoelectric film 15.

Further, as shown in FIG. 10, the sacrificial layer 12 is exposed on the substrate 11 by etching using, for example, 3% concentration of cerium ammonium nitrate (Ce (NH ₄ (NO ₃ ) ₆ )) ( Then, the sacrificial layer 12 is selectively removed to form the cavity 17. In this way, the lower electrode 14, the piezoelectric film 15 and the upper electrode 16 are formed on the cavity 17, as shown in FIG. The resonating part 20 is formed.

  In the method of manufacturing the thin film piezoelectric element according to the first embodiment, an amorphous metal film is used as the lower electrode 14. In the resonance unit 20, the piezoelectric film 15 is formed on the surface of the lower electrode 14. As a result, the piezoelectric film 15 of the resonating unit 20 is highly oriented on the c-axis that is the polarization direction.

  The frequency characteristics of the manufactured thin film piezoelectric element are measured by a network analyzer or the like. For example, the resonance frequency of the thin film piezoelectric element according to the first embodiment is about 2.1 GHz. Further, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 are evaluated from the resonance characteristics of the thin film piezoelectric element. For example, the electromechanical coupling coefficient is 6.4%, and the quality factor Q is 700 at the resonance point and 620 at the anti-resonance point. It has been confirmed that the electromechanical coupling coefficient and the quality factor Q are comparable to those of a thin film piezoelectric element using an epitaxially grown single crystal piezoelectric film. Thus, good piezoelectric characteristics are realized in the piezoelectric film 15 of the thin film piezoelectric element according to the first embodiment.

  According to the first embodiment, the piezoelectric film 15 can be highly oriented on the c-axis without using an expensive and complicated growth technique such as an epitaxial growth method, and the electromechanical coupling coefficient and the quality factor are improved. A thin film piezoelectric element can be realized.

(First modification of the first embodiment)
As shown in FIG. 11, the thin film piezoelectric element according to the first modification of the first embodiment of the present invention includes a lower electrode 14 provided on an insulating film 32 on the surface of the substrate 11, and a lower electrode 14. A piezoelectric film 15 provided on the surface of the piezoelectric film 15 and an upper electrode 16 provided on the surface of the piezoelectric film 15. The resonance part 20 is disposed on the cavity 17 between the amorphous metal film 22 and the lower electrode 14 provided on the surface of the insulating film 32. The insulating film 32 is a SiO ₂ film, a silicon nitride (Si ₃ N ₄ ) film, or a composite film of a SiO ₂ film and a Si ₃ N ₄ film. The lower electrode 14 is an oriented metal film such as Mo. The amorphous metal film 22 is AlTa or the like. The upper electrode 16 is a metal film such as Mo.

  In the first modification of the first embodiment, the amorphous metal film 22 is provided so as to face the lower electrode 14 of the highly oriented metal film with the cavity 17 in between. It is different from the form. Other configurations are the same as those of the first embodiment, and thus redundant description is omitted.

  For example, a metal such as Al that can be selectively etched with respect to the metal material used for the lower electrode 14 is provided on the amorphous metal film 22. On the amorphous metal film 22, the Al metal film can be highly oriented in the (111) direction in a direction perpendicular to the surface of the amorphous metal film 22. Mo used for the lower electrode 14 is highly oriented in the (110) orientation on the (111) oriented Al metal film. (110) On the highly oriented lower electrode 14, the piezoelectric film 15 is highly oriented in the c-axis which is the polarization direction of the piezoelectric crystal. Therefore, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 can be ensured.

  Next, a method for manufacturing a thin film piezoelectric element according to a first modification of the first embodiment will be described with reference to process cross-sectional views shown in FIGS.

As shown in FIG. 12, an insulating film 32 such as SiO ₂ is formed on the surface of the substrate 11 with a thickness of about 1 μm by thermal oxidation or the like. An amorphous metal film 22 such as Al _0.4 Ta _{0.6 is} formed to a thickness of 0.2 μm on the surface of the insulating film 32 by RF magnetron sputtering or the like.

  A metal layer of Al or the like is formed to a thickness of about 1 μm by RF magnetron sputtering or the like. As shown in FIG. 13, the sacrificial layer 12a is formed by selectively removing the Al metal layer by photolithography and RIE using a chloride gas.

  A metal layer such as Mo is formed by RF magnetron sputtering or the like. As shown in FIG. 14, the Mo metal layer is selectively removed to form the lower electrode 14 by photolithography and RIE using a fluoride gas.

  A piezoelectric layer such as AlN is formed to a thickness of about 1.4 μm by reactive RF magnetron sputtering or the like. As shown in FIG. 15, the piezoelectric film 15 is formed by selectively removing the AlN piezoelectric layer by photolithography and RIE using a chloride gas. Further, a metal layer such as Mo is formed on the piezoelectric film 15 by RF magnetron sputtering or the like. The upper electrode 16 is formed by selectively removing the Mo metal layer by photolithography, RIE, or the like.

  As shown in FIG. 16, the sacrificial layer 12a is selectively removed from the portion where the Al sacrificial layer is exposed on the substrate (not shown), for example, by wet etching using hydrochloric acid having a concentration of about 10%. Thus, the cavity 17 is formed. Thus, as shown in FIG. 11, the resonance part 20 having the lower electrode 14, the piezoelectric film 15, and the upper electrode 16 is formed on the cavity 17.

  In the first modification of the first embodiment, the sacrificial layer 12a on the amorphous metal film 22 is made a highly oriented film, so that the highly oriented piezoelectric film 15 is formed even in the periphery of the resonance part 20. Is done. As a result, it is possible to form the piezoelectric film 15 with high orientation on the c-axis over the entire area of the cavity 17, and to improve the mechanical strength of the piezoelectric film 15.

  The frequency characteristics of the thin film piezoelectric element thus manufactured are measured. For example, the resonance frequency is 2.1 GHz. Further, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 are evaluated from the resonance characteristics of the thin film piezoelectric element. For example, the electromechanical coupling coefficient and the quality factor Q are improved by 6.5%, the quality factor Q is 800 at the resonance point, and 750 at the antiresonance point. As described above, in the piezoelectric film 15 of the thin film piezoelectric element according to the first modification of the first embodiment, even better piezoelectric characteristics are realized.

  According to the first modification of the first embodiment, the piezoelectric film 15 can be highly oriented in the c-axis without using an expensive and complicated growth technique such as an epitaxial growth method, and the electromechanical coupling coefficient and A thin film piezoelectric element with improved quality factor can be realized.

(Second modification of the first embodiment)
As shown in FIG. 17, the thin film piezoelectric element according to the second modification of the first embodiment of the present invention includes an amorphous metal film 22 provided on the surface of the insulating film 32, and an amorphous metal film. 22 includes a lower electrode 14 having an orientation metal film 23 provided on the surface. The lower electrode 14, the piezoelectric film 15, and the upper electrode 16 are supported by the substrate 11 and the insulating film 32 provided with a cavity 17a. The resonance unit 20 is defined by the lower electrode 14, the piezoelectric film 15, and the upper electrode 16 disposed on the cavity 17 a. The cavity 17 a has inclined side walls whose opening width becomes narrower from the back surface of the substrate 11 toward the insulating film 32.

  The amorphous metal film 22 of the lower electrode 14 is, for example, AlTa. The oriented metal film 23 is an oriented metal film such as Al that is (111) oriented in a direction perpendicular to the surface of the amorphous metal film 22.

In the second modification of the first embodiment, on the surface of the insulating film 32, a cavity 17 a in which the lower electrode 14 having the amorphous metal film 22 and the oriented metal film 23 is provided in the substrate 11 and the insulating film 32. The point arranged above is different from the first embodiment and the first modification of the first embodiment. Other configurations are the same as those of the first embodiment and the first modification of the first embodiment, and thus redundant description is omitted.

  In the second modification of the first embodiment, an orientation metal film 23 such as Al oriented in the (111) orientation is provided on the amorphous metal film 22 of the lower electrode 14. The piezoelectric film 15 provided on the oriented metal film 23 can be highly oriented along the c axis. Therefore, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 can be ensured. Further, since the lower electrode 14 extends over the insulating film 32 beyond the entire surface of the cavity 17a, the mechanical strength of the piezoelectric film 15 can be structurally improved. Further, no step due to the end of the lower electrode 14 is formed in the piezoelectric film 15 above the cavity 17a. Therefore, the deterioration of the orientation of the piezoelectric film 15 is prevented in the vicinity of the resonating portion 20, and the occurrence of spurious vibrations can be suppressed in the resonance characteristics of the thin film piezoelectric element.

  Next, a method for manufacturing a thin film piezoelectric element according to a second modification of the first embodiment will be described with reference to process cross-sectional views shown in FIGS.

As shown in FIG. 18, an insulating film 32 such as SiO ₂ is formed to a thickness of 1 μm on the surface of the substrate 11 by thermal oxidation or the like. An amorphous metal film 22 such as Al _0.4 Ta _{0.6 is formed to} a thickness of about 0.2 μm by RF magnetron sputtering or the like.

  As shown in FIG. 19, an orientation metal film 23 such as Al is formed by RF magnetron sputtering or the like. The lower electrode 14 is formed by selectively removing the oriented metal film 23 and the amorphous metal film 22 by photolithography and RIE using a chloride gas or a fluoride gas.

  As shown in FIG. 20, a piezoelectric film 15 such as AlN is formed to a thickness of 1.7 μm by reactive RF magnetron sputtering or the like. The piezoelectric film 15 is selectively removed by photolithography or RIE using a chloride gas. Further, a metal layer such as Al is formed on the piezoelectric film 15 by RF magnetron sputtering or the like. The upper electrode 16 is formed by selectively removing the Al metal layer by photolithography, RIE, or the like.

The insulating film 32 on the back surface of the substrate 11 is selectively removed by photolithography, etching, or the like to form an opening where the back surface of the substrate 11 is exposed below the lower electrode 14. As shown in FIG. 21, the exposed substrate 11 is selectively removed by anisotropic etching or the like using the opening on the back surface as a mask to form the opening. The cavity 17a is formed by selectively removing the insulating film 32 under the lower electrode 14 through the opening of the substrate 11 by wet etching using an ammonium fluoride (NH ₄ F) solution. In this way, as shown in FIG. 17, the resonance part 20 having the lower electrode 14, the piezoelectric film 15, and the upper electrode 16 is formed on the cavity 17a.

  In the second modification of the first embodiment, a flat amorphous metal film 22 is formed on the surface of the insulating film 32. On the surface of the flat amorphous metal film 22, an oriented metal film 23 such as Al can be formed with a high orientation in the (111) direction. As a result, the piezoelectric film 15 can be formed with high orientation on the c-axis. Further, since the lower electrode 14 is formed so as to cover the cavity 17a, the mechanical strength of the piezoelectric film 15 can be improved. Further, the end of the lower electrode 14 deviates from the region above the cavity 17a. Therefore, the piezoelectric film 15 can be uniformly formed with high orientation above the cavity 17a.

  The frequency characteristics of the thin film piezoelectric element thus manufactured are measured. For example, the resonance frequency is 2.1 GHz. Further, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 are evaluated from the resonance characteristics of the thin film piezoelectric element. For example, the electromechanical coupling coefficient and the quality factor Q are improved to 6.8%, the quality factor Q is 950 at the resonance point, and 900 at the antiresonance point. Thus, good piezoelectric characteristics are realized in the piezoelectric film 15 of the thin film piezoelectric element according to the third modification of the first embodiment.

  According to the second modification of the first embodiment, the piezoelectric film 15 can be highly oriented in the c-axis without using an expensive and complicated growth technique such as an epitaxial growth method, and the electromechanical coupling coefficient and A thin film piezoelectric element with improved quality factor can be realized.

(Third modification of the first embodiment)
As shown in FIG. 22, a thin film piezoelectric element according to a third modification of the first embodiment of the present invention includes an amorphous metal film 22 provided on the surface of the insulating film 32, and an amorphous metal film. 22 includes a lower electrode 14 having an orientation metal film 23 provided on the surface. The lower electrode 14, the piezoelectric film 15, and the upper electrode 16 are supported by the substrate 11 having the cavity 17b and the insulating film 32. The resonance unit 20 is defined by the lower electrode 14, the piezoelectric film 15, and the upper electrode 16 disposed on the cavity 17 b. The cavity 17 b has substantially vertical sidewalls from the back surface of the substrate 11 toward the insulating film 32.

  The amorphous metal film 22 of the lower electrode 14 is, for example, AlTa. The oriented metal film 23 is an oriented metal film such as Pt that is (111) oriented in a direction perpendicular to the surface of the amorphous metal film 22.

In the third modification of the first embodiment, on the surface of the insulating film 32, the cavity 17 b in which the lower electrode 14 having the amorphous metal film 22 and the oriented metal film 23 is provided in the substrate 11 and the insulating film 32. The point arrange | positioned above differs from the 2nd modification of 1st Embodiment. Other configurations are the same as those of the second modification example of the first embodiment, and thus redundant description is omitted.

  In the third modification of the first embodiment, an orientation metal film 23 such as Pt oriented in the (111) orientation is provided on the amorphous metal film 22 of the lower electrode 14. The piezoelectric film 15 provided on the oriented metal film 23 can be highly oriented along the c axis. Therefore, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 can be ensured. Further, since the lower electrode 14 extends over the insulating film 32 beyond the entire surface of the cavity 17b, the mechanical strength of the piezoelectric film 15 can be structurally improved. Further, no step due to the end of the lower electrode 14 is formed in the piezoelectric film 15 above the cavity 17b. Therefore, the deterioration of the orientation of the piezoelectric film 15 is prevented in the vicinity of the resonating portion 20, and the occurrence of spurious vibrations can be suppressed in the resonance characteristics of the thin film piezoelectric element.

  Next, a method for manufacturing a thin film piezoelectric element according to a third modification of the first embodiment will be described with reference to process cross-sectional views shown in FIGS.

As shown in FIG. 23, an insulating film 32 such as SiO ₂ is formed to a thickness of 1 μm on the surface of the substrate 11 by thermal oxidation or the like. An amorphous metal film 22 such as Al _0.4 Ta _{0.6 is formed to} a thickness of about 0.2 μm by RF magnetron sputtering or the like.

  A metal layer such as Pt is formed by RF magnetron sputtering or the like. As shown in FIG. 24, the lower electrode 14 is formed by selectively removing the metal layer and the amorphous metal film 22 by photolithography and RIE using a chlorine-based gas or a fluoride-based gas.

  A piezoelectric layer such as AlN is formed to a thickness of 1.7 μm by reactive RF magnetron sputtering or the like. As shown in FIG. 25, the piezoelectric film 15 is formed by selectively removing the AlN piezoelectric layer by photolithography, RIE using a chloride gas, or the like. Further, a metal layer such as Pt is formed on the piezoelectric film 15 by RF magnetron sputtering or the like. The upper electrode 16 is formed by selectively removing the Pt metal layer by photolithography, RIE, or the like.

Polishing is performed from the insulating film 32 on the back surface of the substrate 11 until the thickness of the substrate 11 becomes about 200 μm. As shown in FIG. 26, the substrate 11 is selectively and vertically removed by photolithography and RIE using a fluoride gas to form an opening. The cavity 17b is formed by selectively removing the insulating film 32 under the lower electrode 14 through the opening of the substrate 11 by wet etching using an NH ₄ F solution or the like. In this way, as shown in FIG. 22, the resonance part 20 having the lower electrode 14, the piezoelectric film 15, and the upper electrode 16 is formed on the cavity 17b.

  In the third modification of the first embodiment, a flat amorphous metal film 22 is formed on the surface of the insulating film 32. On the surface of the flat amorphous metal film 22, an oriented metal film 23 such as Pt can be formed with a high orientation in the (111) direction. As a result, the piezoelectric film 15 can be formed with high orientation on the c-axis. Moreover, since the lower electrode 14 is formed so as to cover the cavity 17b, the mechanical strength of the piezoelectric film 15 can be improved. Further, the end of the lower electrode 14 deviates from the region above the cavity 17b. Therefore, the piezoelectric film 15 can be uniformly formed with high orientation above the cavity 17b.

  The frequency characteristics of the thin film piezoelectric element thus manufactured are measured. For example, the resonance frequency is 2.1 GHz. Further, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 are evaluated from the resonance characteristics of the thin film piezoelectric element. For example, the electromechanical coupling coefficient and the quality factor Q are improved to 6.7%, the quality factor Q is 900 at the resonance point, and 950 at the antiresonance point. Thus, good piezoelectric characteristics are realized in the piezoelectric film 15 of the thin film piezoelectric element according to the third modification of the first embodiment.

  According to the third modification of the first embodiment, the piezoelectric film 15 can be highly oriented in the c-axis without using an expensive and complicated growth technique such as an epitaxial growth method, and the electromechanical coupling coefficient and A thin film piezoelectric element with improved quality factor can be realized.

(Fourth modification of the first embodiment)
As shown in FIG. 27, a thin film piezoelectric element according to a fourth modification of the first embodiment of the present invention includes an amorphous metal film 22 extending on a cavity 17 provided in the substrate 11, A lower electrode 14 having an orientation metal film 23 provided on the surface of the amorphous metal film 22 is provided. The resonance unit 20 is disposed on the cavity 17 and is defined by the opposed lower and upper electrodes 14 and 16 and the piezoelectric film 15 between the lower and upper electrodes 14 and 16.

  The amorphous metal film 22 of the lower electrode 14 is, for example, AlTa. The oriented metal film 23 is an oriented metal film such as Pt that is (111) oriented in a direction perpendicular to the surface of the amorphous metal film 22.

  In the fourth modification of the first embodiment, one end of the lower electrode 14 is disposed on the cavity 17 provided in the substrate 11, and the second and third of the first embodiment are the same. This is different from the modified example. Other configurations are the same as those of the second and third modifications of the first embodiment, and thus redundant description is omitted.

  In the fourth modification of the first embodiment, an orientation metal film 23 such as Pt oriented in the (111) orientation is provided on the amorphous metal film 22 of the lower electrode 14. The piezoelectric film 15 provided on the oriented metal film 23 can be highly oriented along the c axis. Therefore, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 can be ensured. In addition, since one end of the lower electrode 14 is disposed on the cavity 17, formation of a capacitor structure in which the piezoelectric film 15 is sandwiched between the lower and upper electrodes 14 and 16 in a region other than the resonance portion 20 is suppressed. . Therefore, it is possible to suppress the deterioration of the resonance characteristics in the high frequency band of the thin film piezoelectric element.

  Next, a method for manufacturing a thin film piezoelectric element according to a fourth modification of the first embodiment will be described with reference to process cross-sectional views shown in FIGS.

  As shown in FIG. 28, the substrate 11 is selectively removed by photolithography and RIE using a fluoride-based gas to form an opening 27 having a depth of about 1 μm.

As shown in FIG. 29, a sacrificial layer 12 such as SiO ₂ is formed to a thickness of about 1.2 μm on the surface of the substrate 11 having the opening 27 by plasma enhanced chemical vapor deposition (CVD) or the like. As shown in FIG. 30, the sacrificial layer 12 is planarized and polished by chemical mechanical polishing (CMP) or the like so that the surface of the substrate 11 is exposed. As the sacrificial layer 12, a semiconductor such as germanium (Ge) and poly-Si, a metal such as Mo, Al, and W, or an insulator such as BPSG and Si ₃ N ₄ can be used.

As shown in FIG. 31, an amorphous metal film 22 such as Al _0.4 Ta _{0.6 is} formed to a thickness of 0.2 μm on the surface of the substrate 11 with the sacrificial layer 12 embedded by RF magnetron sputtering or the like. An oriented metal film 23 such as Pt is formed by RF magnetron sputtering or the like. The lower electrode 14 is formed by selectively removing the oriented metal film 23 and the amorphous metal film 22 by photolithography and RIE using a chloride gas or a chloride gas.

  As shown in FIG. 32, a piezoelectric film 15 such as AlN is formed to a thickness of 1.7 μm by reactive RF magnetron sputtering or the like. The piezoelectric film 15 is selectively removed by photolithography or RIE using a chloride gas. Further, a metal layer such as Ir is formed on the piezoelectric film 15 by RF magnetron sputtering or the like. The upper electrode 16 is formed by selectively removing the Ir metal layer by photolithography and RIE using a fluoride gas.

Via holes (not shown) are formed by photolithography and RIE using a chloride gas so that a part of the sacrificial layer 12 is exposed. As shown in FIG. 33, the sacrificial layer 12 is selectively dissolved from the via hole by wet etching using an NH ₄ F solution or the like to form the cavity 17.

  In the fourth modification of the first embodiment, a flat amorphous metal film 22 is formed on the surface of the substrate 11 that is flattened with the sacrificial layer 12 embedded therein. On the surface of the flat amorphous metal film 22, an oriented metal film 23 such as Pt can be formed with a high orientation in the (111) direction. As a result, the piezoelectric film 15 can be formed with high orientation on the c-axis. Further, the end of the lower electrode 14 deviates from the region above the cavity 17. Therefore, the piezoelectric film 15 can be uniformly formed with high orientation above the cavity 17.

  The frequency characteristics of the thin film piezoelectric element thus manufactured are measured. For example, the resonance frequency is 2.1 GHz. Further, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 are evaluated from the resonance characteristics of the thin film piezoelectric element. For example, the electromechanical coupling factor and the quality factor Q are 6.9%, the quality factor Q is 1100 at the resonance point, and 1150 at the antiresonance point. Thus, good piezoelectric characteristics are realized in the piezoelectric film 15 of the thin film piezoelectric element according to the fourth modification of the first embodiment.

  According to the fourth modification of the first embodiment, the piezoelectric film 15 can be highly oriented in the c-axis without using an expensive and complicated growth technique such as an epitaxial growth method, and the electromechanical coupling coefficient and A thin film piezoelectric element with improved quality factor can be realized.

(Fifth modification of the first embodiment)
In the thin film piezoelectric element according to the fifth modification of the first embodiment of the present invention, as shown in FIG. 34, the lower electrode 14, the piezoelectric film 15 and the piezoelectric film 15 are formed on the acoustic reflection layer 38 provided on the substrate 11. An upper electrode 16 is disposed. The resonance unit 20 is defined by the lower and upper electrodes 14 and 16 facing each other on the acoustic reflection layer 38 and the piezoelectric film 15 between the lower and upper electrodes 14 and 16.

In the acoustic reflection layer 38, the first acoustic impedance layers 36a and 36b having a high acoustic impedance and the second acoustic impedance layers 37a and 37b having a low acoustic impedance are alternately laminated. The film thickness of each of the first and second acoustic impedance layers 36 a, 37 a, 36 b, and 37 b is about ¼ of the wavelength of the bulk acoustic wave excited by the resonance unit 20. The bulk acoustic wave is reflected by the first and second acoustic impedance layers 36a, 37a, 36b, and 37b that are periodically arranged with a thickness of about ¼ of the wavelength of the acoustic wave. The acoustic impedance is determined by the density and elastic constant of the material. For example, as a material having high acoustic impedance, insulators such as AlN, tantalum oxide (Ta ₂ O ₅ ), Al ₂ O ₃ , and metals such as W, Mo, Pt, Ir, Ru, rhodium (Rh), and Ta Is preferred. As materials having low acoustic impedance, insulators such as SiO ₂ and Si ₃ N ₄ , semiconductors such as Si, and metals such as Al and titanium (Ti) are suitable.

  The acoustic reflection layer 38 is laminated with first and second acoustic impedance layers 36a, 36b, 37a, 37b. However, the number of stacked acoustic reflection layers 38 is not limited. The number of layers may be determined so as to improve the quality factor Q most depending on the material to be used.

  The fifth modification example of the first embodiment differs from the fourth modification example of the first embodiment in that the resonance unit 20 is disposed on the acoustic reflection layer 38 on the substrate 11. . Other configurations are the same as those of the fourth modified example of the first embodiment, and thus redundant description is omitted.

  In the fifth modification of the first embodiment, the piezoelectric vibration excited by the piezoelectric film 15 is reflected and efficiently confined in the resonance unit 20 by the acoustic reflection layer 38 provided under the resonance unit 20. . Therefore, deterioration of the resonance characteristics of the resonance unit 20 can be suppressed. In addition, an oriented metal film 23 is provided on the amorphous metal film 22 of the lower electrode 14. The piezoelectric film 15 provided on the oriented metal film 23 can be highly oriented along the c axis. Therefore, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 can be ensured. Since the lower electrode 14 is disposed on the flat acoustic reflection layer 38, the mechanical strength of the piezoelectric film 15 can be structurally improved.

  Next, a method for manufacturing a thin film piezoelectric element according to a fifth modification of the first embodiment will be described with reference to process cross-sectional views shown in FIGS.

  As shown in FIG. 35, the first acoustic impedance layer 36a, the second acoustic impedance layer 37a, the first acoustic impedance layer 36b, and the second acoustic impedance are sequentially formed on the surface of the substrate 11 by sputtering or CVD. The layer 37b is formed, and the acoustic reflection layer 38 is formed. In order to ensure the flatness of the surface of the acoustic reflection layer 38, the surface of the acoustic reflection layer 38 may be planarized by CMP or the like. It is desirable to use an insulator for at least the second acoustic impedance layer 37b as the uppermost layer.

As shown in FIG. 36, an amorphous metal film 22 of Al _0.5 Ta _0.5 or the like is formed to a thickness of about 20 nm on the surface of the acoustic reflection layer 38 by DC magnetron sputtering or the like. Subsequently, an oriented metal film 23 of Ni or the like is formed to a thickness of about 250 nm by DC magnetron sputtering or the like. The lower electrode 14 is formed by selectively removing the oriented metal film 23 and the amorphous metal film 22 by photolithography, etching, or the like.

  As shown in FIG. 37, a piezoelectric layer such as AlN is formed to a thickness of about 2 μm by reactive RF magnetron sputtering or the like. The piezoelectric film 15 is formed by selectively removing the piezoelectric layer by photolithography and RIE using a chloride gas.

  As shown in FIG. 38, a metal layer such as Mo is formed on the piezoelectric film 15 by DC magnetron sputtering or the like. The upper electrode 16 is formed by selectively removing the Mo metal layer by photolithography, wet etching, or the like.

  Note that the orientation of the Ni-oriented metal film 23 formed on the surface of the amorphous metal film 22 is measured by XRD. As a result of the measurement, it is confirmed that the Ni-oriented metal film 23 is highly oriented in the (111) orientation with an orientation half-value width of about 0.7 °.

  In the fifth modification of the first embodiment, a flat amorphous metal film 22 is formed on the surface of the flat acoustic reflection layer 38. On the surface of the flat amorphous metal film 22, an oriented metal film 23 such as Ni can be formed with a high orientation in the (111) direction. As a result, the piezoelectric film 15 can be formed with high orientation on the c-axis. Further, since the lower electrode 14 is formed on the flat acoustic reflection layer 38, the mechanical strength of the piezoelectric film 15 can be structurally improved.

  The frequency characteristics of the thin film piezoelectric element thus manufactured are measured. For example, the resonance frequency is about 2 GHz. Further, the electromechanical coupling coefficient and the quality factor Q of the piezoelectric film 15 are evaluated from the resonance characteristics of the thin film piezoelectric element. For example, the electromechanical coupling coefficient is about 6.5% to about 6.7%, the quality factor Q is about 900 to about 1000 at the resonance point, and about 800 to about 900 at the antiresonance point. Q is improving. Thus, good piezoelectric characteristics are realized in the piezoelectric film 15 of the thin film piezoelectric element according to the fifth modification of the first embodiment.

  According to the fifth modification of the first embodiment, the piezoelectric film 15 can be highly oriented in the c-axis without using an expensive and complicated growth technique such as an epitaxial growth method, and the electromechanical coupling coefficient and A thin film piezoelectric element with improved quality factor can be realized.

(Application example of the first embodiment)
As an application example of the thin film piezoelectric element according to the first embodiment of the present invention, a phase locked loop (PLL) circuit that generates a reference frequency of a frequency synthesizer used in a mobile phone system or the like will be described.

  As shown in FIG. 39, the PLL circuit includes a VCO 141 including a frequency variable filter 130, an amplifier 131, and a buffer amplifier 132, a frequency divider 142, a phase comparator 143, a charge pump 144, a loop filter 145, A noise amplifier (LNA) 146, a frequency variable filter 130a, and a mixer 147 are provided.

  As shown in FIG. 40, the VCO 141 feeds back only the frequency component that has passed through the frequency variable filter 130 to the input of the amplifier 131. The VCO 141 uses a plurality of thin film piezoelectric elements 120a, 120b, 120c and 120d, and variable capacitance capacitors C1 and C2. The thin film piezoelectric elements according to the first embodiment and the first to seventh modifications of the first embodiment are used for the thin film piezoelectric elements 120a to 120d.

  For example, as shown in FIG. 41, in the frequency variable filter 130, the thin film piezoelectric elements 120a and 120b are connected in series from the input side to the output side. The thin film piezoelectric elements 120c and 120d are connected in parallel from the respective output sides of the thin film piezoelectric elements 120a and 120b connected in series to a common line.

  For example, as shown in FIG. 42, the thin film piezoelectric element 120 a connected to the input wiring 122 is connected in series to the thin film piezoelectric element 120 b connected to the output wiring 124 via the connection line 126. The thin film piezoelectric element 120 c connected to the connection wiring 126 is connected to the common wiring 128. The thin film piezoelectric element 120 d connected to the output wiring 124 is connected to the common wiring 128.

  The PLL circuit shown in FIG. 39 detects the frequency difference between the oscillation frequency and the desired frequency when the oscillation frequency of the VCO 141 is larger or smaller than the desired frequency, and uses the VCO 141 as the DC control voltage Vctrl. Feedback is made to the variable capacitance element C1 in the frequency variable filter 130. Therefore, when the feedback loop operates normally and reaches a stable state and the phase is locked, the oscillation frequency of the VCO 141 can be matched with a desired frequency.

  The PLL circuit uses the same frequency variable filter 130a as the frequency variable filter 130 of the VCO 141 as a passband filter for filtering communication signals. For example, the input high frequency signal is transmitted to the LNA 146. The output signal amplified by the LNA 146 is input to the frequency variable filter 130a. The output signal filtered by the frequency variable filter 130a is input to one of the input terminals of the down-conversion mixer 147.

  On the other hand, the reference signal generated by the VCO 141 is input to the other input terminal of the mixer 147 as a local oscillation signal (LO). In this way, the high frequency signal is frequency converted into a baseband signal.

  In the application example of the first embodiment, the same DC control voltage Vctrl generated by the loop filter 145 is applied to both the frequency variable filter 130 a and the frequency variable filter 130 in the VCO 141. As a result, the oscillation frequency of the VCO 141 can be matched with the center frequency of the pass band of the frequency variable filter 130a.

(Second Embodiment)
As shown in FIG. 43, the variable capacitance capacitor as the thin film piezoelectric element according to the second embodiment of the present invention includes a piezoelectric actuator 40 and a fixed electrode 46. As shown in FIG. 44, the fixed end 48 of the piezoelectric actuator 40 is fixed to an anchor 42 provided on the surface of the insulating film 32 on the substrate 11. The action end portion 49 of the piezoelectric actuator 40 is provided so as to face the fixed electrode 46 provided on the surface of the insulating film 32. The piezoelectric actuator 40 is opposed to the lower electrode 14 with the lower electrode 14 provided extending from the anchor 42 surface above the fixed electrode 46, the piezoelectric film 15 provided on the surface of the lower electrode 14, and the piezoelectric film 15 interposed therebetween. An upper electrode 16 and a support film 19 provided on the upper electrode 16. The fixed electrode 46 includes a dielectric film 45 and a conductor film 44 covered with the dielectric film 45.

For the anchor 42, the support film 19, and the dielectric film 45, an insulator such as Si ₃ N ₄ or SiO ₂ is used. An amorphous metal such as AlTa is used for the lower electrode 14. A piezoelectric material such as AlN or ZnO is used for the piezoelectric film 15. The material of the upper electrode 16 and the conductor film 44 is preferably a metal with low resistance and easy processing, such as Al, Au, Pt, Cu, Ir, W, and Mo.

  The piezoelectric actuator 40 of the thin film piezoelectric element according to the second embodiment is different from the structure of the thin film piezoelectric element according to the first embodiment in that a support film 19 is provided on the upper electrode 16. Since the structures of the lower electrode 14, the piezoelectric film 15, and the upper electrode 16 are the same as those in the first embodiment, overlapping descriptions are omitted.

  The thin film piezoelectric element according to the second embodiment uses a capacitance Cvar between the conductor film 44 and the working end 49 of the lower electrode 14. The capacitance Cvar changes corresponding to a change in the distance between the fixed electrode 46 and the lower electrode 14 that is a movable electrode.

  When a voltage is applied between the lower electrode 14 and the upper electrode 16 of the piezoelectric actuator 40, the piezoelectric film 15 is distorted and expands and contracts due to the piezoelectric effect. Since the support film 19 provided on the upper electrode 16 does not exhibit a piezoelectric effect, the piezoelectric actuator 40 is displaced in a direction perpendicular to the surface of the substrate 11 by the expansion and contraction of the piezoelectric film 15. For example, when a tensile stress is generated by the applied voltage and the piezoelectric film 15 extends, the piezoelectric actuator 40 bends in a direction away from the surface of the substrate 11. On the other hand, when the piezoelectric film 15 contracts due to compressive stress, the piezoelectric actuator 40 bends toward the surface of the substrate 11.

  The driving range of the piezoelectric actuator 40 depends on the electromechanical coupling coefficient of the piezoelectric film 15. When the electromechanical coupling coefficient is large, in the piezoelectric actuator 40, the action end portion 49 can be largely displaced with a low driving voltage.

  In the piezoelectric actuator 40 according to the second embodiment, since the piezoelectric film 15 is provided on the surface of the lower electrode 14 of the amorphous metal film, it is highly oriented along the c-axis that is the polarization direction. As a result, the electromechanical coupling coefficient increases and the driving range of the piezoelectric actuator 40 increases. Therefore, the variable width of the variable capacitor using the piezoelectric actuator 40 can be improved.

  Next, a method for manufacturing a thin film piezoelectric element according to the second embodiment will be described with reference to process cross-sectional views shown in FIGS.

As shown in FIG. 45, an insulating film 32 such as SiO ₂ is formed on the surface of the substrate 11 by thermal oxidation or the like. The anchor 42 is formed by selectively removing the insulator layer such as Si ₃ N ₄ formed on the surface of the insulating film 32 by CVD or the like by photolithography and etching using NH ₄ F solution.

Further, the conductor film 44 is formed by selectively removing a metal layer such as Al formed on the surface of the insulating film 32 by sputtering or the like by photolithography, etching, or the like. A dielectric film 45 is formed so as to cover the conductor film 44 by selectively removing the dielectric layer such as Si ₃ N ₄ formed on the insulating film 32 by photolithography and etching. In this way, the fixed electrode 46 is formed.

  As shown in FIG. 46, a sacrificial layer 12b such as poly-Si is conformally formed on the surface of the insulating film 32 having the anchor 42 and the fixed electrode 46 by CVD or the like. The sacrificial layer 12b is planarized and polished so that the surface of the anchor 42 is exposed by CMP or the like.

An amorphous metal layer such as Al _0.4 Ta _0.6 , a piezoelectric layer such as AlN, a metal layer such as Al, and an insulator layer such as SiO ₂ are formed on the surface of the sacrificial layer 12b by magnetron sputtering or the like. As shown in FIG. 47, the insulator layer, the metal layer, the piezoelectric layer, and the amorphous metal layer are selectively removed by photolithography, RIE, or the like, so that the lower electrode 14, the piezoelectric film 15, and the upper electrode 16 are removed. The piezoelectric actuator 40 having the support film 19 is formed.

  As shown in FIG. 48, poly-Si is selectively removed by dry etching using xenon fluoride (XeF2) or the like. In this manner, a thin film piezoelectric element having the piezoelectric actuator 40 fixed to the anchor 42 and extending above the fixed electrode 46 is manufactured.

  In the second embodiment, a flat amorphous metal film lower electrode 14 is provided on the surface of the sacrificial layer 12 b flattened at the level of the surface of the anchor 42. On the surface of the lower electrode 14 of a flat amorphous metal film, the piezoelectric film 15 can be highly oriented along the c axis. With respect to the formed piezoelectric film 15, the half width of orientation is measured by XRD. As a result of the measurement, the half width of orientation is about 2.1 °, and it can be seen that the piezoelectric film 15 highly oriented on the c-axis is formed.

  The capacity variable characteristics of the thin film piezoelectric element manufactured in this way are measured. For example, the control voltage of the piezoelectric actuator 40 is applied between the lower and upper electrodes 14 and 16 in the range of 0V to 3V. The capacitance between the fixed electrode 46 and the lower electrode 14 varies in a range from a minimum of 0.34 pF to a maximum of 51 pF. The ratio between the maximum capacity and the minimum capacity is about 150, and a large variable capacity width is obtained.

  According to the second embodiment, the piezoelectric film 15 can be highly oriented along the c-axis without using an expensive and complicated growth technique such as an epitaxial growth method, and the variable capacitance width can be improved by driving at a low control voltage. A thin film piezoelectric element can be realized.

  In the second embodiment, a variable capacitance capacitor is formed by using a conductor film 44 covered with a dielectric film 45 as the fixed electrode 46 of the thin film piezoelectric element. For example, if only a conductive film is used as the fixed electrode, it can function as a microswitch.

(Modification of the second embodiment)
As shown in FIG. 49, a microswitch as a thin film piezoelectric element according to a modification of the second embodiment of the present invention includes a piezoelectric actuator 40a and a fixed electrode 46a. As shown in FIG. 50, the fixed end portion 48 of the piezoelectric actuator 40 a is fixed to an anchor 42 provided on the surface of the insulating film 32 on the substrate 11. The working end portion 49 of the piezoelectric actuator 40a is provided so as to face the fixed electrode 46a provided on the surface of the insulating film 32. The piezoelectric actuator 40a is opposed to the lower electrode 14 with the lower electrode 14 provided extending from the anchor 42 surface above the fixed electrode 46a, the piezoelectric film 15 provided on the surface of the lower electrode 14, and the piezoelectric film 15 interposed therebetween. An upper electrode 16 and a support film 19 provided on the upper electrode 16. The lower electrode 14 has an amorphous metal film 22 and an orientation metal film 23.

  An amorphous metal such as AlTa is used for the amorphous metal film 22 of the lower electrode 14. For the orientation metal film 23, a metal that is easily oriented in the (111) direction or the (110) direction, such as an fcc metal or a bcc metal, is used. The fixed electrode 46a is a metal with low resistance, such as Al, Au, Pt, Cu, Ir, W, and Mo, which is easy to process.

  A piezoelectric actuator 40a of a thin film piezoelectric element according to a modification of the second embodiment is that the lower electrode 14 has an amorphous metal film 22 and an oriented metal film 23, as compared with the second embodiment. And different. Since other structures are the same as those of the second embodiment, overlapping descriptions are omitted.

  When a voltage is applied between the lower electrode 14 and the upper electrode 16 of the piezoelectric actuator 40a, the piezoelectric film 15 is distorted and expanded due to the piezoelectric effect. For example, when compressive stress is generated by the applied voltage and the piezoelectric film 15 contracts, the piezoelectric actuator 40a bends toward the surface of the substrate 11. The lower electrode 14 of the piezoelectric actuator 40a contacts the fixed electrode 46a, and the thin film piezoelectric element becomes conductive.

  The driving range of the piezoelectric actuator 40 a depends on the electromechanical coupling coefficient of the piezoelectric film 15. When the electromechanical coupling coefficient is large, in the piezoelectric actuator 40a, the action end portion 49 can be largely displaced with a low driving voltage.

  In the piezoelectric actuator 40a according to the modification of the second embodiment, the piezoelectric film 15 is provided on the surface of the oriented metal film 23 that is highly oriented in the (111) direction or the (110) direction on the amorphous metal film 22. Therefore, it is highly oriented in the c-axis which is the polarization direction. As a result, the electromechanical coupling coefficient increases and the movable range of the piezoelectric actuator 40a increases. Therefore, the microswitch using the piezoelectric actuator 40a can be driven with a low control voltage.

  Next, a method for manufacturing a thin film piezoelectric element according to a modification of the second embodiment will be described with reference to process cross-sectional views shown in FIGS.

As shown in FIG. 51, an insulating film 32 such as SiO ₂ is formed on the surface of the substrate 11 by thermal oxidation or the like. The anchor 42 is formed by selectively removing the insulator layer such as Si ₃ N ₄ formed on the surface of the insulating film 32 by CVD or the like by photolithography and etching using NH ₄ F solution. Also, a fixed electrode 46a is formed by selectively forming a metal film such as Au formed on the surface of the insulating film 32 by sputtering and a lift-off process.

  As shown in FIG. 52, a sacrificial layer 12b such as poly-Si is conformally formed on the surface of the insulating film 32 having the anchor 42 and the fixed electrode 46a by CVD or the like. The sacrificial layer 12b is planarized and polished so that the surface of the anchor 42 is exposed by CMP or the like.

By magnetron sputtering or the like, the surface of the sacrificial layer 12b is made of an amorphous metal layer such as Al _0.4 Ta _0.6 , a lower metal layer such as Al, a piezoelectric layer such as AlN, an upper metal layer such as Al, and an insulation such as SiO _2. A body layer is formed. As shown in FIG. 53, the insulator layer, the upper metal layer, the piezoelectric layer, the lower metal layer, and the amorphous metal layer are selectively removed by photolithography, RIE, etc., and the amorphous metal film 22 is obtained. And a piezoelectric actuator 40 a having the lower electrode 14 having the orientation metal film 23, the piezoelectric film 15, the upper electrode 16, and the support film 19.

  As shown in FIG. 54, poly-Si is selectively removed by dry etching or the like using xenon fluoride (XeF2). In this manner, a thin film piezoelectric element having the piezoelectric actuator 40a fixed to the anchor 42 and extending to above the fixed electrode 46a is manufactured.

  In the modification of the second embodiment, a flat amorphous metal film 22 is provided on the surface of the sacrificial layer 12b flattened at the level of the surface of the anchor 42. On the surface of the flat amorphous metal film 22, an oriented metal film 23 such as Al can be formed with a high orientation in the (111) direction. As a result, the piezoelectric film 15 can be formed with high orientation on the c-axis. With respect to the formed piezoelectric film 15, the half width of orientation is measured by XRD. As a result of the measurement, the orientation half width is about 2.4 °, and it can be seen that the piezoelectric film 15 highly oriented in the c-axis is formed.

  The electrical characteristics of the thin film piezoelectric element thus manufactured are measured. For example, the control voltage is applied between the lower and upper electrodes 14 and 16 of the piezoelectric actuator 40a, and the insulation resistance and the on-resistance are evaluated at a frequency of 2 GHz. The control voltage is 0V, and the insulation resistance between the fixed electrode 46a and the lower electrode 14 is about 28 dB. The control voltage is 3V, and the on-resistance between the fixed electrode 46a and the lower electrode 14 is about 0.3 dB. As described above, the thin film piezoelectric element according to the modification of the second embodiment can be driven with a low control voltage, and can realize a small on-resistance and a good insulation resistance in a high-frequency band.

  According to the second embodiment, the piezoelectric film 15 can be highly oriented on the c-axis without using an expensive and complicated growth technique such as an epitaxial growth method, and the high-frequency characteristics are improved by driving at a low control voltage. A thin film piezoelectric element can be realized.

  In the modification of the second embodiment, a metal film is used as the fixed electrode 46a. For example, if the fixed electrode 46 having the conductor film 44 covered with the dielectric film 45 shown in FIG. 57 is used instead of the fixed electrode 46a, the thin film piezoelectric element can function as a capacitance variable capacitor.

(Other embodiments)
As described above, the first and second embodiments of the present invention have been described. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, embodiments and operational techniques will be apparent to those skilled in the art.

  As described above, the present invention naturally includes various embodiments that are not described herein. Accordingly, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

It is sectional drawing which shows an example of the piezoelectric film which concerns on embodiment of this invention. It is a figure which shows an example of evaluation of the orientation of the piezoelectric film which concerns on embodiment of this invention. It is sectional drawing which shows the other example of the piezoelectric film which concerns on embodiment of this invention. It is a figure which shows the other example of evaluation of the orientation of the piezoelectric film which concerns on embodiment of this invention. It is a top view which shows an example of the thin film piezoelectric element which concerns on the 1st Embodiment of this invention. It is sectional drawing along the AA line of the thin film piezoelectric element shown in FIG. It is sectional drawing (the 1) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 1st Embodiment of this invention. It is sectional drawing (the 2) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 1st Embodiment of this invention. It is sectional drawing (the 3) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 1st Embodiment of this invention. It is sectional drawing (the 4) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows an example of the thin film piezoelectric element which concerns on the 1st modification of the 1st Embodiment of this invention. It is sectional drawing (the 1) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 1st modification of the 1st Embodiment of this invention. It is sectional drawing (the 2) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 1st modification of the 1st Embodiment of this invention. It is sectional drawing (the 3) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 1st modification of the 1st Embodiment of this invention. It is sectional drawing (the 4) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 1st modification of the 1st Embodiment of this invention. It is sectional drawing (the 5) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 1st modification of the 1st Embodiment of this invention. It is sectional drawing which shows an example of the thin film piezoelectric element which concerns on the 2nd modification of the 1st Embodiment of this invention. It is sectional drawing (the 1) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 2nd modification of the 1st Embodiment of this invention. It is sectional drawing (the 2) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 2nd modification of the 1st Embodiment of this invention. It is sectional drawing (the 3) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 2nd modification of the 1st Embodiment of this invention. It is sectional drawing (the 4) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 2nd modification of the 1st Embodiment of this invention. It is sectional drawing which shows an example of the thin film piezoelectric element which concerns on the 3rd modification of the 1st Embodiment of this invention. It is sectional drawing (the 1) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 3rd modification of the 1st Embodiment of this invention. It is sectional drawing (the 2) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 3rd modification of the 1st Embodiment of this invention. It is sectional drawing (the 3) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 3rd modification of the 1st Embodiment of this invention. It is sectional drawing (the 4) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 3rd modification of the 1st Embodiment of this invention. It is sectional drawing which shows an example of the thin film piezoelectric element which concerns on the 4th modification of the 1st Embodiment of this invention. It is sectional drawing (the 1) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 4th modification of the 1st Embodiment of this invention. It is sectional drawing (the 2) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 4th modification of the 1st Embodiment of this invention. It is sectional drawing (the 3) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 4th modification of the 1st Embodiment of this invention. It is sectional drawing (the 4) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 4th modification of the 1st Embodiment of this invention. It is sectional drawing (the 5) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 4th modification of the 1st Embodiment of this invention. It is sectional drawing (the 6) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 4th modification of the 1st Embodiment of this invention. It is sectional drawing which shows an example of the thin film piezoelectric element which concerns on the 5th modification of the 1st Embodiment of this invention. It is sectional drawing (the 1) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 5th modification of the 1st Embodiment of this invention. It is sectional drawing (the 2) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 5th modification of the 1st Embodiment of this invention. It is sectional drawing (the 3) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 5th modification of the 1st Embodiment of this invention. It is sectional drawing (the 4) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 5th modification of the 1st Embodiment of this invention. It is a block diagram which shows an example of the phase locked loop circuit based on the application example of the 1st Embodiment of this invention. It is a block diagram which shows an example of the voltage control transmitter which concerns on the application example of the 1st Embodiment of this invention. It is a block diagram which shows an example of the connection of the thin film piezoelectric element used for the frequency variable filter which concerns on the application example of the 1st Embodiment of this invention. It is a figure which shows an example of arrangement | positioning of the thin film piezoelectric element used for the frequency variable filter which concerns on the application example of the 1st Embodiment of this invention. It is a top view which shows an example of the thin film piezoelectric element which concerns on the 2nd Embodiment of this invention. It is sectional drawing along the BB line of the thin film piezoelectric element shown in FIG. It is sectional drawing (the 1) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 2nd Embodiment of this invention. It is sectional drawing (the 2) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 2nd Embodiment of this invention. It is sectional drawing (the 3) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 2nd Embodiment of this invention. It is sectional drawing (the 4) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 2nd Embodiment of this invention. It is a top view which shows an example of the thin film piezoelectric element which concerns on the modification of the 2nd Embodiment of this invention. It is sectional drawing along CC line of the thin film piezoelectric element shown in FIG. It is sectional drawing (the 1) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 2nd Embodiment of this invention. It is sectional drawing (the 2) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 2nd Embodiment of this invention. It is sectional drawing (the 3) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 2nd Embodiment of this invention. It is sectional drawing (the 4) which shows an example of the manufacturing method of the thin film piezoelectric element which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Board | substrate 12,12a, 12b Sacrificial layer 13 Barrier layer 14 Lower electrode 15 Piezoelectric film 16 Upper electrode 17, 17a, 17b Cavity 19 Support film 20 Resonance part 22 Amorphous metal film 23 Oriented metal film 24 Lower electrode 27 Opening part 32 Insulating film 36a, 36b First acoustic impedance layer 37a, 37b Second acoustic impedance layer 38 Acoustic reflection layer 40, 40a Piezoelectric actuator 42 Anchor 44 Conductor film 45 Dielectric film 46, 46a Fixed electrode 48 Fixed end 49 Working end Part 120a-120d Thin film piezoelectric element 122 Input wiring 124 Output wiring 126 Connection wiring 128 Common wiring 130, 130a Frequency variable filter 130a Frequency variable filter 131 Amplifier 132 Buffer amplifier 141 VCO
142 frequency divider 143 phase comparator 144 charge pump 145 loop filter 146 LNA
147 mixer

Claims (16)

An amorphous metal film on the substrate;
And a piezoelectric film oriented in a direction perpendicular to the surface of the amorphous metal film on the amorphous metal film.   The thin film piezoelectric element according to claim 1, wherein the piezoelectric film is provided on a surface of the amorphous metal film.   The thin film piezoelectric element according to claim 1, further comprising an orientation metal film between the amorphous metal film and the piezoelectric film.   The thin film piezoelectric element according to claim 3, wherein the oriented metal film is one of a face-centered cubic lattice metal and a body-centered cubic lattice metal.   The thin film piezoelectric element according to claim 1, further comprising an upper metal film provided on a surface of the piezoelectric film.   The thin film piezoelectric element according to claim 1, wherein the amorphous metal film is an aluminum tantalum alloy.   The thin film piezoelectric element according to claim 1, wherein the piezoelectric film is one of aluminum nitride and zinc oxide.   A region defined by the opposing amorphous metal film and the upper metal film and the piezoelectric film between the amorphous metal film and the upper metal film is disposed in the air apart from the substrate. The thin film piezoelectric element according to claim 1, wherein:   8. The amorphous metal film according to claim 1, wherein one end of the amorphous metal film is fixed on the substrate and the other end is disposed in the air apart from the substrate surface. Thin film piezoelectric element.   The thin film piezoelectric element according to claim 9, wherein the other end faces a fixed electrode disposed on the surface of the substrate. Forming an amorphous metal film on the substrate;
Forming a piezoelectric film oriented in a direction perpendicular to the surface of the amorphous metal film on the amorphous metal film;
An upper metal film facing the amorphous metal film is formed on the surface of the piezoelectric film with the piezoelectric film interposed therebetween. A method of manufacturing a thin film piezoelectric element, comprising:   12. The method of manufacturing a thin film piezoelectric element according to claim 11, further comprising forming an orientation metal film on the surface of the amorphous metal film before forming the piezoelectric film. 13. The method for manufacturing a thin film piezoelectric element according to claim 12, wherein the oriented metal film is one of a face-centered cubic lattice metal and a body-centered cubic lattice metal.   Before forming the amorphous metal, an acoustic reflection layer in which a first acoustic impedance layer having a high acoustic impedance and a second acoustic impedance layer having a low acoustic impedance are alternately stacked is formed on the substrate. The method for manufacturing a thin film piezoelectric element according to claim 11, further comprising:   The first and second acoustic impedance layers are resonant defined by the opposing amorphous metal film and upper metal film, and the piezoelectric film between the amorphous metal film and the upper metal film. The method of manufacturing a thin film piezoelectric element according to claim 14, wherein the thickness is about ¼ of the wavelength of the bulk acoustic wave excited at the portion. Before forming the amorphous metal film, a sacrificial layer is formed on the substrate,
The method of manufacturing a thin film piezoelectric element according to claim 11, further comprising selectively removing the sacrificial layer after forming the upper metal layer.

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