Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a piezoelectric device including a thin film of a piezoelectric single crystal and a method for manufacturing the piezoelectric device. 
     2. Description of the Related Art 
     Currently, there are various piezoelectric devices including single-crystalline piezoelectric substrates. In particular, there are surface acoustic wave and plate wave devices including IDT (Interdigital Transducer) electrodes (also referred to as comb-shaped electrodes). Plate waves are those which have vibration displacements on both surfaces of an elastic substance and which propagate along the surfaces. An example of the plate waves is shown in, for example, FIG. 1.19 of Danseiha Soshi Gijutsu Handobukku. Among plate waves propagating in anisotropic crystals such as LiTaO 3  and LiNbO 3  single crystals are not only pure SH waves (a u 2  component only) and Lamb waves (a u 1  component and a u 3  component only) but also modes propagating with displacement components such as u 1  u 2 , and u 3  being combined (that is, SH waves having a slight u 1  component and a slight u 3  component and Lamb waves having a slight u 2  component). 
     A conventional piezoelectric device including such IDT electrodes has, for example, a structure disclosed in Japanese Unexamined Patent Application Publication No. 2007-251910. In particular, the conventional piezoelectric device includes a composite piezoelectric substrate including a piezoelectric thin-film and a support bonded thereto and also includes IDT electrodes formed on a surface of the piezoelectric thin-film that is located opposite to the support. In order not to inhibit the vibration of a region of the piezoelectric thin-film that has the IDT electrodes formed therein, a space is formed on the side of bonded surfaces of the piezoelectric thin-film and the support so as to correspond to the IDT electrode-formed region. 
     However, the conventional piezoelectric device, which includes the IDT electrodes as disclosed in Japanese Unexamined Patent Application Publication No. 2007-251910, is configured such that the IDT electrodes are exposed at the surface of the conventional piezoelectric device. Therefore, there are various problems as described below. 
     In back-end steps of a process for manufacturing a module for mounting the piezoelectric device, metal powders and the like may adhere to a surface thereof. This causes short circuits between electrode fingers of the IDT electrodes. If an insulating layer made of SiO 2  or SiN is formed on an IDT electrode-formed surface for the purpose of preventing such a short-circuit failure, the vibration of the piezoelectric thin-film will be inhibited by the insulating layer. 
     If organic contaminants adhere thereto, gases will possibly be generated from the contaminants because of the thermal history of the back-end steps. The generated gases corrode the IDT electrodes to vary the excitation mode thereof and therefore adversely affect properties thereof. Particularly, in a sensor which includes IDT electrodes and which operates to detect the mass applied to a piezoelectric thin-film portion (membrane) not supported by a support, such corrosion leads to the deterioration of detection performance and therefore seriously reduces functions of the sensor. 
     In particular, for a plate wave device, the frequency thereof is significantly affected by the thickness of a piezoelectric thin-film defining a membrane. Therefore, when the piezoelectric thin-film is polished for frequency adjustment, the IDT electrodes are also ground or milled, whereby properties thereof are deteriorated. Likewise, when the thickness of the piezoelectric thin-film is adjusted by ion milling, the electrodes are ground or milled. When the membrane has an opening facing a support, a surface of the piezoelectric thin-film that faces a surface having the IDT electrode can be polished or milled. However, a boundary portion near the support cannot be polished or milled to a uniform thickness because a recessed portion is ground or milled. This causes differences in properties. 
     SUMMARY OF THE INVENTION 
     Thus, preferred embodiments of the present invention provide a piezoelectric device that solves various problems resulting from the use of IDT electrodes as described above and also provide a method for manufacturing the piezoelectric device. 
     According to a preferred embodiment of the present invention, a piezoelectric device includes a piezoelectric thin-film supported by a support. In the piezoelectric device, IDT electrodes are located on a support side of the piezoelectric thin-film and a space is provided over an IDT electrode region of the piezoelectric thin-film that is located on the support side such that the IDT electrodes are not in contact with the support. 
     In this configuration, the IDT electrodes are not located on the piezoelectric device but are located in the piezoelectric device. As a result, no metal powder or organic contaminant adheres to the IDT electrodes. Since the IDT electrode-formed region is not in contact with the support, the vibration of a membrane is not inhibited. This can prevent failure due to attached substances and negative influences thereof on properties without deteriorating structural properties of devices. 
     A method for manufacturing a piezoelectric device according to another preferred embodiment of the present invention includes a step of forming an ion-implanted layer by implanting ions into a principal surface of a piezoelectric substrate, a step of forming IDT electrodes on an ion implantation surface of the piezoelectric substrate, a step of providing a support on the ion implantation surface of the piezoelectric substrate, a step of etching the support to expose the IDT electrodes, and a step of delaminating a piezoelectric thin-film from the piezoelectric substrate. 
     In the manufacturing method, after the IDT electrodes are formed on a surface of the piezoelectric substrate that is to be the piezoelectric thin-film, the support is provided on the IDT electrode-formed surface. The support corresponding to a region in which the IDT electrodes are formed is removed by etching and the piezoelectric thin-film is delaminated from the piezoelectric substrate, whereby a membrane is formed. Therefore, the addition of a complex, complicated manufacturing step is not necessary and the piezoelectric device can be manufactured so as to have the above-described effective configuration. 
     A method for manufacturing a piezoelectric device according to a further preferred embodiment of the present invention includes a step of forming an ion-implanted layer by implanting ions into a principal surface of a piezoelectric substrate, a step of forming IDT electrodes on an ion implantation surface of the piezoelectric substrate, a step of forming a sacrificial layer in a sacrificial layer-forming region including a region in which the IDT electrodes are formed and which is disposed in the ion implantation surface of the piezoelectric substrate, a step of providing a support on the ion implantation surface of the piezoelectric substrate, a step of delaminating a piezoelectric thin-film from the piezoelectric substrate, and a step of removing the sacrificial layer. 
     In this manufacturing method, after the IDT electrodes are formed on a surface of the piezoelectric substrate that is to define the piezoelectric thin-film, the sacrificial layer is formed on the IDT electrode-formed surface and the support is further provided thereon. Subsequently, the piezoelectric thin-film is delaminated from the piezoelectric substrate and the sacrificial layer is removed. A space (void) is formed between the piezoelectric thin-film and the support by the removal of the sacrificial layer and the IDT electrodes are arranged in the space. Therefore, the addition of a complex, complicated manufacturing step is not necessary and the piezoelectric device can be manufactured so as to have an effective configuration. 
     A method for manufacturing a piezoelectric device according to yet another preferred embodiment of the present invention includes a step of forming an ion-implanted layer by implanting ions into a principal surface of a piezoelectric substrate, a step of forming IDT electrodes on a support, a step of bonding an IDT electrode-formed surface of the support to an ion implantation surface of the piezoelectric substrate, a step of etching the support to expose the IDT electrodes, and a step of delaminating a piezoelectric thin-film from the piezoelectric substrate. 
     In this manufacturing method, unlike the above manufacturing methods, after the IDT electrodes are formed on a surface of the support, the support and the piezoelectric substrate are bonded together. The support corresponding to a region in which the IDT electrodes are formed is removed by etching and the piezoelectric thin-film is delaminated from the piezoelectric substrate, whereby a membrane is formed. Therefore, the addition of a complex, complicated manufacturing step is not necessary and the piezoelectric device can be manufactured so as to have an effective configuration. 
     A method for manufacturing a piezoelectric device according to a further preferred embodiment of the present invention includes a step of forming an ion-implanted layer by implanting ions into a principal surface of a piezoelectric substrate, a step of forming a sacrificial layer on a support, a step of forming IDT electrodes in a sacrificial layer-forming region of the support, a step of bonding an IDT electrode-formed surface of the support to an ion implantation surface of the piezoelectric substrate, a step of delaminating a piezoelectric thin-film from the piezoelectric substrate, and a step of removing the sacrificial layer. 
     In this manufacturing method, unlike the above manufacturing methods, after the sacrificial layer and the IDT electrodes are formed on a surface of the support, the piezoelectric substrate and the support are bonded together. The piezoelectric thin-film is delaminated from the piezoelectric substrate and the sacrificial layer is then removed. A space (void) is formed between the piezoelectric thin-film and the support by the removal of the sacrificial layer and the IDT electrodes are arranged in the space. Therefore, the addition of a complex, complicated manufacturing step is not necessary and the piezoelectric device can be manufactured so as to have an effective configuration. 
     According to various preferred embodiments of the present invention, the following problems can be solved: problems which affect the deterioration of properties of piezoelectric devices including IDT electrodes and which occur in back-end steps and the like because of the use of the IDT electrodes. Furthermore, according to various preferred embodiments of the present invention, a piezoelectric device having such a configuration can be readily manufactured. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  include a plan view of a piezoelectric device according to a first preferred embodiment of the present invention, a sectional view thereof, and a schematic sectional view of a piezoelectric device having another configuration. 
         FIG. 2  is a flowchart illustrating a method for manufacturing the piezoelectric device having a configuration shown in  FIGS. 1A and 1B . 
         FIGS. 3A-3E  are schematic views illustrating steps of manufacturing the thin film-type piezoelectric device in accordance with the flowchart shown in  FIG. 2 . 
         FIGS. 4A-4D  are schematic views illustrating steps of manufacturing the thin film-type piezoelectric device in accordance with the flowchart shown in  FIG. 2 . 
         FIG. 5  is a flowchart illustrating a manufacturing method according to a second preferred embodiment of the present invention. 
         FIGS. 6A-6E  are schematic views illustrating steps of manufacturing a thin film-type piezoelectric device in accordance with the flowchart shown in  FIG. 5 . 
         FIGS. 7A-7D  are schematic views illustrating steps of manufacturing the thin film-type piezoelectric device in accordance with the flowchart shown in  FIG. 5 . 
         FIG. 8  is a flowchart illustrating a manufacturing method according to a third preferred embodiment of the present invention. 
         FIGS. 9A-9E  are schematic views illustrating steps of manufacturing a thin film-type piezoelectric device in accordance with the flowchart shown in  FIG. 8 . 
         FIGS. 10A-10D  are schematic views illustrating steps of manufacturing the thin film-type piezoelectric device in accordance with the flowchart shown in  FIG. 8 . 
         FIG. 11  is a flowchart illustrating a manufacturing method according to a fourth preferred embodiment of the present invention. 
         FIGS. 12A-12E  are schematic views illustrating steps of manufacturing a thin film-type piezoelectric device in accordance with the flowchart shown in  FIG. 11 . 
         FIG. 13  is a flowchart illustrating a manufacturing method according to a fifth preferred embodiment of the present invention. 
         FIGS. 14A-14D  are schematic views illustrating steps of manufacturing a thin film-type piezoelectric device in accordance with the flowchart shown in  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A piezoelectric device according to a first preferred embodiment of the present invention and a method for manufacturing the piezoelectric device will now be described with reference to the accompanying drawings. The piezoelectric device is described below using a plate wave device as an example. The plate wave device includes IDT electrodes and generates waves which have vibration displacements on both surfaces of a tabular elastic substance (in this preferred embodiment, a piezoelectric thin-film  10 ) and which propagate along the surfaces. A configuration and manufacturing method below can be applied to a piezoelectric device including other IDT electrodes. 
       FIG. 1A  is a plan view of the piezoelectric device  10 D according to this preferred embodiment and  FIG. 1B  is a sectional view of the piezoelectric device  10 D taken along the line A-A′ of  FIG. 1A .  FIG. 1C  is a schematic sectional view of a piezoelectric device  10 D′ having another configuration. 
     As shown in  FIGS. 1A-1C , the piezoelectric device  10 D includes the piezoelectric thin-film  10 , which has a predetermined thickness, for example, about 1 μm, and a support  30 B. The piezoelectric thin-film  10  includes a piezoelectric single crystal substance such as an LT substrate, an LN substrate, an LBO (Li 2 B 4 O 7 ), or a langasite (La 3 Ga 5 SiO 14 ) substrate. The thickness of the piezoelectric thin-film  10  is preferably set depending on each material such that the piezoelectric device  10 D has a target frequency. The support  30 B is preferably made of Si or glass or is made from a piezoelectric substrate with a linear expansion coefficient equal or similar to that of the piezoelectric thin-film. The piezoelectric thin-film  10  and the support  30 B are bonded to each other with an adhesive layer  30 A made of an insulating material such as an organic material or a SiN and so on. IDT electrodes  60  and interconnect electrodes  61  are located on the support  30 B side of the piezoelectric thin-film  10 . The piezoelectric thin-film  10  has conductive through-holes  62 . The conductive through-holes  62  are connected to end portions of the interconnect electrodes  61  that are opposite to end portions of the interconnect electrodes  61  that are connected to the IDT electrodes  60 . Bumps  90  serving as external connection terminals are provided on a surface of the piezoelectric thin-film  10  that is opposite to an IDT electrode-formed surface  12  of the piezoelectric thin-film  10  so as to correspond to the positions of the conductive through-holes  62 . 
     The IDT electrode-formed surface  12  of the piezoelectric thin-film  10  includes a region in which the IDT electrodes  60  are provided and no support  30 B is disposed but an opening  31  is formed on the IDT electrode  60 -formed region. That is, the support  30 B supports a region of the piezoelectric thin-film  10  that is other than the IDT electrode  60 -formed region and is not in contact with the IDT electrodes  60  or a portion of the piezoelectric thin-film  10  that corresponds to the IDT electrode  60 -formed region. 
     In the case of mounting the piezoelectric device  10 D on a circuit board, the support  30 B is attached to the circuit board. That is, the bump  90 -formed surface of the piezoelectric thin-film  10  corresponds to the front surface of the piezoelectric device  10 D and the IDT electrode-formed surface  12  is located in the piezoelectric device  10 D. 
     Therefore, even if a metal powder adheres to the piezoelectric device  10 D in a back-end step of assembling the piezoelectric device  10 D and another circuit board into a module, the metal powder adheres to the bump-formed surface and does not adhere to the IDT electrode-formed surface  12 . Thus, short-circuit failure due to the metal powder can be prevented. Alternatively, even if an organic contaminant adheres thereto to generate gas, this phenomenon occurs on the bump-formed surface and does not affect the IDT electrode-formed surface  12 , which is opposite to the bump-formed surface of the piezoelectric thin-film  10 . Thus, the IDT electrodes  60  are not corroded by the gas and therefore properties thereof can be prevented from being deteriorated. When the frequency of the plate wave device is adjusted, the surface (the bump-formed surface) of the piezoelectric thin-film  10  that is opposite to the IDT electrode-formed surface  12  thereof can be readily and uniformly ground or milled by ion milling before the bumps  90  are formed. The IDT electrodes  60  are not ground or milled by milling. Thus, the piezoelectric thin-film  10  can be readily ground or milled without unnecessarily grinding or milling the IDT electrodes. This allows a plate wave device having good properties to be accurately and readily achieved. 
     In the piezoelectric device  10 D, the IDT electrode  60 -formed region of the piezoelectric thin-film  10  is open as shown in  FIGS. 1A and 1B . The above advantageous effects can be achieved using the piezoelectric device  10 D′, which has a configuration in which a void  80  is formed on a region which is located on the side of a junction between a piezoelectric thin-film  10  and a support  30 B and in which IDT electrodes  60  are formed, as shown in  FIG. 1C . 
     The method for manufacturing the piezoelectric device is described below. 
       FIG. 2  is a flowchart illustrating method for manufacturing the piezoelectric device, which has the configuration shown in  FIGS. 1A and 1B , according to this preferred embodiment.  FIGS. 3A-3E  and  4 A- 4 D are schematic views illustrating steps of manufacturing the piezoelectric device in accordance with the flowchart shown in  FIG. 2 . 
     A single-crystalline piezoelectric substrate  1  having a predetermined thickness and an area sufficient to arrange or form a plurality of piezoelectric devices is prepared. As shown in  FIG. 3A , hydrogen ions are implanted into the single-crystalline piezoelectric substrate  1 , whereby an ion-implanted layer  100  is formed (S 101  in  FIG. 2 ). In this step, a substrate having a plurality of discretely arranged piezoelectric devices is preferably used as the single-crystalline piezoelectric substrate  1 . If, for example, an LT substrate is used as the single-crystalline piezoelectric substrate  1 , the ion-implanted layer  100  is formed in such a manner that hydrogen ions are implanted into the substrate at a dose of approximately 1.0×10 17  atoms/cm 2  with an acceleration energy of about 150 keV such that a hydrogen ion layer is formed at a depth of about 1 μm from an ion implantation surface  12 . 
     As shown in  FIG. 3B , the IDT electrodes  60  and the interconnect electrodes  61  are formed on the ion implantation surface  12  of the single-crystalline piezoelectric substrate  1  (S 102  in  FIG. 2 ). The ion implantation surface  12  corresponds to the IDT electrode-formed surface and is referred to as “IDT electrode-formed surface” in this preferred embodiment to a third preferred embodiment. As shown in  FIG. 3C , the adhesive layer  30 A, which is made of the insulating material such as an organic material or a SiN, is formed on the IDT electrode-formed surface  12  (S 103  in  FIG. 2 ). In this step, the adhesive layer  30 A is formed so as to have a thickness not less than the thickness of the IDT electrodes  60  or the interconnect electrodes  61  and is planarized by CMP or the like so as to have a flat surface. 
     The support  30 B, which is made of an appropriately selected material such as Si, glass, or a piezoelectric material identical to the single-crystalline piezoelectric substrate, is prepared. As shown in  FIG. 3D , the support  30 B is bonded to the IDT electrode-formed surface  12  side of the single-crystalline piezoelectric substrate  1  (S 104  in  FIG. 2 ). In this step, the support  30 B is cleanly bonded to the adhesive layer  30 A and is thereby bonded to the single-crystalline piezoelectric substrate  1 . 
     As shown in  FIG. 3E , the support  30 B and the adhesive layer  30 A are etched such that the IDT electrodes  60  on the single-crystalline piezoelectric substrate  1  are exposed from the support  30 B, whereby the opening  31  is formed (S 105  in  FIG. 2 ). 
     A complex prepared by bonding the support  30 B to the single-crystalline piezoelectric substrate  1  is heated to, for example, 500° C. This allows the ion-implanted layer  100  to serve as a delamination surface, whereby the piezoelectric thin-film is delaminated from the single-crystalline piezoelectric substrate  1  and a composite piezoelectric substrate is formed as shown in  FIG. 4A  (S 106  in  FIG. 2 ). Polarization electrodes are provided on the IDT electrode-formed surface  12  of the piezoelectric thin-film  10  and a surface of the piezoelectric thin-film  10  that is opposite to the IDT electrode-formed surface  12  thereof using a liquid electrode. The piezoelectric thin-film  10  is polarized by applying an electric field thereto. 
     Perforations are formed in portions of the piezoelectric thin-film  10  that correspond to the end portions of the interconnect electrodes  61  that are opposite to the end portions of the interconnect electrodes  61  that are connected to the IDT electrodes  60 . A conductor is filled in the perforations, whereby the conductive through-holes  62  are formed as shown in  FIG. 4B  (S 107  in  FIG. 2 ). 
     A surface of the piezoelectric thin-film  10  that is opposite to the IDT electrode-formed surface  12  thereof is ground or milled for frequency adjustment. This treatment is performed for each piezoelectric device. The piezoelectric thin-film  10  is ground or milled with an ion beam in such a manner that each piezoelectric device is measured for frequency by applying a driving signal to the piezoelectric device through the conductive through-holes  62  and the grinding allowance is calculated from the difference between the target frequency and the measurement. This allows a target frequency to be achieved. Since the surface opposite to the IDT electrode-formed surface  12  is ground or milled as described above, the IDT electrodes  60  are not ground or milled and therefore the deterioration of properties can be prevented. 
     After frequency adjustment is performed as described above, the bumps  90  are formed on the surface of the piezoelectric thin-film  10  that is opposite to the IDT electrode-formed surface  12  thereof so as to be connected to the conductive through-holes  62  as shown in  FIG. 4C  (S 109  in  FIG. 2 ). Through these steps, multiple piezoelectric devices can be manufactured. The multiple piezoelectric devices are separated into pieces, whereby the piezoelectric device shown in  FIGS. 4D ,  1 A, and  1 B can be manufactured. 
     Through the above steps, a configuration in which the IDT electrodes  60  are not formed on the piezoelectric device  10 D but are formed therein can be readily achieved. 
     A method for manufacturing a piezoelectric device according to a second preferred embodiment will now be described. The manufacturing method according to this preferred embodiment corresponds to a method for manufacturing the piezoelectric device  10 D′ having the configuration shown in  FIG. 1C . 
       FIG. 5  is a flowchart illustrating the manufacturing method according to this preferred embodiment.  FIGS. 6A-6E  and  7 A- 7 D are schematic views illustrating steps of manufacturing the piezoelectric device in accordance with the flowchart shown in  FIG. 5 . 
     In the manufacturing method according to this preferred embodiment, ion implantation and the formation of IDT electrodes and interconnect electrodes preferably are the same or substantially the same as those described in the first preferred embodiment and will not be described in detail (S 201  and S 202  in  FIG. 5  and  FIGS. 6A and 6B ). 
     After the IDT electrodes  60  and the interconnect electrodes  61  are formed, sacrificial layers  40  are formed on a IDT electrode-formed surface  12  of a single-crystalline piezoelectric substrate  1  so as to each entirely cover a region in which the IDT electrodes  60  are formed as shown in  FIG. 6C  (S 203  in  FIG. 5 ). The sacrificial layers  40  may be made of a material that can be removed by a treatment below without affecting the IDT electrodes  60 . In the case of using oxygen plasma etching or a NMP etching solution, the IDT electrodes  60  may be made of Al, Cu, Au, Pt, Ti, W, Mo, Ni, or Ta and the sacrificial layers  40  may be made of a resin material, the etching ratio of the resin material to a material used to form the IDT electrodes  60  being about 10000 or more. 
     As shown in  FIG. 6D , a supporting layer  302 B is formed on the IDT electrode-formed surface  12  of the single-crystalline piezoelectric substrate  1  that has the IDT electrodes  60 , the interconnect electrodes  61 , and the sacrificial layers  40  (S 204  in  FIG. 5 ). The supporting layer  302 B is made of an insulating material such as SiN and has a flat surface polished by CMP or the like. 
     A parent member  301 B, made of an appropriately selected material such as Si, glass, or a piezoelectric material identical to the single-crystalline piezoelectric substrate, for forming a support  30 B is prepared. As shown in  FIG. 6E , the parent member  301 B is cleanly bonded to the supporting layer  302 B (S 205  in  FIG. 5 ). This results in the formation of a complex including, the support  30 B made of the parent member  301 B and the supporting layer  302 B, and the single-crystalline piezoelectric substrate  1 . 
     The complex is heated as described in the first preferred embodiment. This allows an ion-implanted layer  100  to serve as a delamination surface, whereby a piezoelectric thin-film  10  is delaminated from the single-crystalline piezoelectric substrate  1  and a composite piezoelectric substrate is formed as shown in  FIG. 7A  (S 206  in  FIG. 5 ). 
     A surface of the piezoelectric thin-film  10  delaminated as described above is planarized by a polishing process such as CMP. Polarization electrodes are provided on the piezoelectric thin-film  10  and the piezoelectric thin-film  10  is polarized by applying an electric field thereto as described in the first preferred embodiment. 
     A resist is applied to a surface of the piezoelectric thin-film  10  that is opposite to the IDT electrode-formed surface  12  thereof and is then patterned. The piezoelectric thin-film  10  is etched by RIE or the like, whereby etching windows  71  and through-holes  72  are formed as shown in  FIG. 7B  (S 207  in  FIG. 5 ). The etching windows  71  are formed in regions in which sacrificial layers  40  are formed and no IDT electrodes  60  are formed. The through-holes  72  are formed at the positions of end portions of the interconnect electrodes  61  that are opposite to end portions of the interconnect electrodes  61  that are connected to the IDT electrodes  60 . The resist used to form the etching windows  71  and the through-holes  72  is removed before or after a step of forming the sacrificial layers  40  and the piezoelectric thin-film  10  may be then surface-cleaned. 
     An etching solution is introduced into the etching windows  71 , whereby the sacrificial layers  40  are removed and voids  80  are thereby formed as shown in  FIG. 7C  (S 208  in  FIG. 5 ). This eliminates the sacrificial layers  40  from the IDT electrodes  60  and a surface of the piezoelectric thin-film  10  that has the IDT electrodes  60  and allows a configuration in which the IDT electrodes  60  are not in direct contact with the support  30 B to be achieved. 
     As shown in  FIG. 7D , a conductor is filled in the through-holes  72 , whereby conductive through-holes  62  are formed (S 209  in  FIG. 5 ). Milling is performed for frequency adjustment as described in the first preferred embodiment, whereby bumps  90  are formed on the surface of the piezoelectric thin-film  10  that is opposite to the IDT electrode-formed surface  12  so as to be connected to the conductive through-holes  62  (S 210  in  FIG. 5 ). 
     Through these steps, multiple piezoelectric devices can be manufactured. The multiple piezoelectric devices are separated into pieces, whereby a piezoelectric device shown in  FIG. 1C  can be manufactured. 
     A method for manufacturing a piezoelectric device according to a third preferred embodiment will now be described. In the manufacturing method according to this preferred embodiment, sacrificial layers  40  are formed in a support  30 B. 
       FIG. 8  is a flowchart illustrating the manufacturing method according to the third preferred embodiment.  FIGS. 9A-9E  and  10 A- 10 D are schematic views illustrating steps of manufacturing the piezoelectric device in accordance with the flowchart shown in  FIG. 8 . 
     In the manufacturing method according to this preferred embodiment, ion implantation and the formation of IDT electrodes and interconnect electrodes preferably are the same or substantially the same as those described in the first and second preferred embodiments and will not be described in detail (S 301  and S 302  in  FIG. 8  and  FIGS. 9A and 9B ). 
     After the IDT electrodes  60  and the interconnect electrodes  61  are formed, an adhesive layer  30 A is formed on a IDT electrode-formed surface  12  of a single-crystalline piezoelectric substrate  1  so as to entirely cover the IDT electrode-formed surface  12  as shown in  FIG. 9C  (S 303  in  FIG. 8 ). The adhesive layer  30 A is made of an insulating material capable of being etched as described below and has a thickness sufficient to entirely cover the IDT electrodes  60  and the interconnect electrodes  61 . 
     As shown in  FIG. 9D , the sacrificial layers  40  and a supporting layer  302 B are formed on a parent member  301 B (S 304  in  FIG. 8 ). The sacrificial layers  40  are preferably formed from the same material as that used to from the sacrificial layers  40  described in the second preferred embodiment. The sacrificial layers  40  are formed in zones including regions in which the IDT electrodes  60  are to be formed in such a state that the support  30 B including the parent member  301 B and the supporting layer  302 B is bonded to the single-crystalline piezoelectric substrate  1 . 
     As shown in  FIG. 9E , the support  30 B having the sacrificial layers  40  is cleanly bonded to the IDT electrode-formed surface  12  of the single-crystalline piezoelectric substrate  1  having the IDT electrodes  60 , the interconnect electrodes  61 , and the adhesive layer  30 A (S 305  in  FIG. 8 ). This results in the formation of a complex including the support  30 B and the single-crystalline piezoelectric substrate  1 . 
     The complex is heated as described in the first preferred embodiment. This allows an ion-implanted layer  100  to serve as a delamination surface, whereby a piezoelectric thin-film  10  is delaminated from the single-crystalline piezoelectric substrate  1  and a composite piezoelectric substrate is formed as shown in  FIG. 10A  (S 306  in  FIG. 8 ). 
     A surface of the piezoelectric thin-film  10  delaminated as described above is planarized by a polishing process such as CMP. Polarization electrodes are provided on the piezoelectric thin-film  10  and the piezoelectric thin-film  10  is polarized by applying an electric field thereto as described in the first preferred embodiment. 
     A resist is applied to a surface of the piezoelectric thin-film  10  that is opposite to the IDT electrode-formed surface  12  thereof and is then patterned. The piezoelectric thin-film  10  is etched by RIE or the like, whereby etching windows  71  and through-holes  72  are formed as shown in  FIG. 10B  (S 307  in  FIG. 8 ). The etching windows  71  and the through-holes are formed preferably under the same or substantially the same conditions as those described in the second preferred embodiment. 
     An etching solution is introduced into the etching windows  71 , whereby the sacrificial layers  40  and the adhesive layer  30 A are removed and voids  80  are thereby formed as shown in  FIG. 10C  (S 308  in  FIG. 8 ). This eliminates the sacrificial layers  40  from the IDT electrodes  60  and a surface of the piezoelectric thin-film  10  that has the IDT electrodes  60  and allows a configuration in which the IDT electrodes  60  are not in direct contact with the support  30 B to be achieved. 
     As shown in  FIG. 10D , a conductor is filled in the through-holes  72 , whereby conductive through-holes  62  are formed (S 309  in  FIG. 8 ). Milling is performed for frequency adjustment as described in the first preferred embodiment, whereby bumps  90  are formed on the surface of the piezoelectric thin-film  10  that is opposite to the IDT electrode-formed surface  12  so as to be connected to the conductive through-holes  62  (S 310  in  FIG. 8 ). 
     Through these steps, multiple piezoelectric devices can be manufactured. The multiple piezoelectric devices are separated into pieces, whereby a piezoelectric device can be manufactured. 
     A method for manufacturing a piezoelectric device according to a fourth preferred embodiment will now be described. 
     In the piezoelectric device-manufacturing methods according to the first to third preferred embodiments, the IDT electrodes  60  and the interconnect electrodes  61  are formed on the single-crystalline piezoelectric substrate  1  as described above. In each of this preferred embodiment and a fifth preferred embodiment below, a method for forming IDT electrodes  60  and interconnect electrodes  61  are formed on a support  30 B is described. In each of this preferred embodiment and the fifth preferred embodiment, since the IDT electrodes  60  are formed on the support  30 B, a surface of a single-crystalline piezoelectric substrate  1  that is subjected to ion implantation is referred to as an ion implantation surface  12 . 
       FIG. 11  is a flowchart illustrating the manufacturing method according to the fourth preferred embodiment.  FIGS. 12A-12E  are schematic views illustrating steps of manufacturing the piezoelectric device in accordance with the flowchart shown in  FIG. 11 . A step of forming a composite piezoelectric substrate and steps subsequent thereto (S 407  and steps subsequent thereto in  FIG. 11 ) preferably are the same or substantially the same as those of the manufacturing method according to the first preferred embodiment and will not be described in detail or shown in these figures. 
     A single-crystalline piezoelectric substrate  1  having a predetermined thickness and an area sufficient to arrange or form a plurality of piezoelectric devices is prepared as described in the first preferred embodiment. As shown in  FIG. 12A , hydrogen ions are implanted into the single-crystalline piezoelectric substrate  1 , whereby an ion-implanted layer  100  is formed (S 401  in  FIG. 11 ). 
     The support  30 B is prepared separately from the single-crystalline piezoelectric substrate  1 . The support  30 B is made of an appropriately selected material such as a piezoelectric material identical to the single-crystalline piezoelectric substrate. As shown in  FIG. 12B , the IDT electrodes  60  and the interconnect electrodes  61  are formed on a surface of the support  30 B (S 402  in  FIG. 11 ). As shown in  FIG. 12B , an adhesive layer  30 A made of an insulating material such as an organic material or a SiN is formed on the IDT electrode-formed surface of the support  30 B (S 403  in  FIG. 11 ). In this step, the adhesive layer  30 A is formed so as to have a thickness not less than the thickness of the IDT electrodes  60  or the interconnect electrodes  61  and is planarized by CMP or the like so as to have a flat surface. 
     As shown in  FIG. 12C , the support  30 B is cleanly bonded to the IDT electrode-formed surface  12  of the single-crystalline piezoelectric substrate  1  with the adhesive layer  30 A disposed therebetween (S 404  in  FIG. 11 ). 
     As shown in  FIG. 12D , the support  30 B and the adhesive layer  30 A are etched such that the IDT electrodes  60  on the single-crystalline piezoelectric substrate  1  are exposed from the support  30 B, whereby openings  31  are formed (S 405  in  FIG. 11 ). 
     Heating and delamination are performed as described in the first preferred embodiment. This allows the ion-implanted layer  100  to serve as a delamination surface, whereby a piezoelectric thin-film  10  is delaminated from the single-crystalline piezoelectric substrate  1  and a composite piezoelectric substrate is formed as shown in  FIG. 12E  (S 406  in  FIG. 11 ). 
     A configuration in which the IDT electrodes  60  are not formed on the piezoelectric device but are formed therein can be readily achieved even by the manufacturing method, in which the IDT electrodes  60  and the interconnect electrodes  61  are formed on the support  30 B as described above. 
     A method for manufacturing a piezoelectric device according to a fifth preferred embodiment will now be described. The manufacturing method according to this preferred embodiment is preferably the same as the manufacturing method according to the third preferred embodiment and the other thirds except that IDT electrodes  60  and interconnect electrodes  61  are formed on a support  30 B. 
       FIG. 13  is a flowchart illustrating the manufacturing method according to the fifth preferred embodiment.  FIGS. 14A-14D  are schematic views illustrating steps of manufacturing the piezoelectric device in accordance with the flowchart shown in  FIG. 13 . A step of forming a composite piezoelectric substrate and steps subsequent thereto (S 507  and steps subsequent thereto in  FIG. 13 ) are preferably the same as those of the manufacturing method according to the third preferred embodiment and will not be described in detail or shown in these figures. 
     A single-crystalline piezoelectric substrate  1  having a predetermined thickness and an area sufficient to arrange or form a plurality of piezoelectric devices is prepared as described in the above-mentioned preferred embodiments. As shown in  FIG. 14A , hydrogen ions are implanted into the single-crystalline piezoelectric substrate  1 , whereby an ion-implanted layer  100  is formed (S 501  in  FIG. 13 ). 
     A parent member  301 B made of an appropriately selected material such as a piezoelectric material identical to the single-crystalline piezoelectric substrate is prepared separately from the single-crystalline piezoelectric substrate  1 . As shown in  FIG. 14B , sacrificial layers  40  and a supporting layer  302 B are formed on a surface of the parent member  301 B (S 502  in  FIG. 13 ). As shown in  FIG. 14B , in the parent member  301 B having the sacrificial layers  40  and supporting layer  302 B, the IDT electrodes  60  are formed on a surface of each sacrificial layer  40  and the interconnect electrodes  61  are formed on a surface of the sacrificial layer  40  and a surface of the supporting layer  302 B (S 503  in  FIG. 13 ). As shown in  FIG. 14C , an adhesive layer  30 A made of an insulating material such as an organic material or a SiN is formed over the sacrificial layers  40  and the supporting layer  302 B (S 504  in  FIG. 13 ). In this step, the adhesive layer  30 A is formed so as to have a thickness not less than the thickness of the IDT electrodes  60  or the interconnect electrodes  61  and is planarized by CMP or the like so as to have a flat surface. 
     As shown in  FIG. 14D , the support  30 B, which includes the supporting layer  302 B and the parent member  301 B, having the sacrificial layers  40  is cleanly bonded to an ion implantation surface  12  of the single-crystalline piezoelectric substrate  1  with the adhesive layer  30 A disposed therebetween (S 505  in  FIG. 13 ). 
     Heating and delamination are performed as described in the above-mentioned preferred embodiments. This allows the ion-implanted layer  100  to serve as a delamination surface, whereby a piezoelectric thin-film  10  is delaminated from the single-crystalline piezoelectric substrate  1  and a composite piezoelectric substrate is formed (S 506  in  FIG. 13 ). A configuration in which the IDT electrodes  60  are not formed on the piezoelectric device but are formed therein can be readily achieved even by the manufacturing method, in which the sacrificial layers  40  are formed on the support  30 B and the IDT electrodes  60  are formed on the sacrificial layers  40  as described above. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.

Technology Category: 4