Patent Publication Number: US-2021193901-A1

Title: Piezoelectric transducer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2018-230899 filed on Dec. 10, 2018 and is a Continuation Application of PCT Application No. PCT/JP2019/032100 filed on Aug. 16, 2019. The entire contents of each application are hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a piezoelectric transducer. 
     2. Description of the Related Art 
     Japanese Unexamined Patent Application Publication No. 2014-515214 discloses a configuration of a piezoelectric transducer. The piezoelectric transducer described in Japanese Unexamined Patent Application Publication No. 2014-515214 includes a substrate and a plurality of cantilevered beams. The cantilevered beams are adjacent to each other and tapered. Each of the plurality of cantilevered beams defines a beam base portion, a beam tip portion, and a beam body portion. The beam body portion is disposed between the beam base portion and the beam tip portion. Each of the plurality of cantilevered beams is disposed such that the beam tip portion extends toward a common imaginary point. Each of the plurality of cantilevered beams is coupled to the substrate along the beam base portion, and is free from the substrate along the beam body portion. 
     In a piezoelectric transducer according to the related art, a pattern of a piezoelectric layer or the like is formed on a front surface side of a substrate. Further, a recessed portion is provided for the substrate by deep reactive ion etching (Deep RIE), wet etching, or other processing from a back surface side of the substrate. In a case where an alignment error occurs between the processing on the front surface side and the processing on the back surface side of the substrate, lengths of movable portions of a plurality of beam portions may vary. Accordingly, when the piezoelectric transducer is driven, mechanical characteristics, such as a resonant frequency and a deformation amount of each of the plurality of beam portions, are different from each other, and thus the input/output characteristics of the piezoelectric transducer deteriorate. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide piezoelectric transducers each having improved input/output characteristics by equalizing lengths of movable portions of a plurality of beam portions. 
     A piezoelectric transducer according to a preferred embodiment the present invention includes a base portion, a plurality of beam portions, and at least one fixing portion. Each of the plurality of beam portions is supported by the base portion at an end portion, and extends in a direction away from the base portion at a position above the base portion. Each of the plurality of beam portions includes a plurality of layers. Each of the plurality of beam portions includes a piezoelectric layer, an upper electrode layer disposed on an upper side of the piezoelectric layer, and a lower electrode layer disposed facing at least a portion of the upper electrode layer with the piezoelectric layer interposed therebetween. The fixing portion is disposed on the beam portion so as to sandwich the end portion of each of the plurality of beam portions between the fixing portion and the base portion. The fixing portion overlaps at least a portion of the base portion in an up-down direction, and extends so as to protrude from the base portion in an extending direction of the beam portion. 
     According to preferred embodiments of the present invention, it is possible to improve the input/output characteristics of the piezoelectric transducers by equalizing the length of the movable portion of each of the plurality of beam portions. 
     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 
         FIG. 1  is a plan view illustrating a configuration of a piezoelectric transducer according to Preferred Embodiment 1 of the present invention. 
         FIG. 2  is a sectional view of the piezoelectric transducer illustrated in  FIG. 1  taken along line II-II and viewed from a direction denoted by arrow. 
         FIG. 3  is a sectional view illustrating a state in which a lower electrode layer is provided on an upper surface of an active layer in a method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. 
         FIG. 4  is a sectional view illustrating a state in which a piezoelectric layer is provided on an upper surface of the lower electrode layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. 
         FIG. 5  is a sectional view illustrating a state in which an upper electrode layer is provided on an upper surface of the piezoelectric layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. 
         FIG. 6  is a diagram illustrating a state in which the upper electrode layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. 
         FIG. 7  is a diagram illustrating a state in which the piezoelectric layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. 
         FIG. 8  is a diagram illustrating a state in which the lower electrode layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. 
         FIG. 9  is a diagram illustrating a state in which the active layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. 
         FIG. 10  is a diagram illustrating a state in which a fixing portion is provided on the upper surface of the piezoelectric layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. 
         FIG. 11  is a diagram illustrating a state in which a recessed portion is formed in a lower base portion in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. 
         FIG. 12  is a sectional view of a piezoelectric transducer according to an example of a preferred embodiment of the present invention. 
         FIG. 13  is a sectional view of a piezoelectric transducer according to a comparative example. 
         FIG. 14  is a plan view illustrating a configuration of a piezoelectric transducer according to a modified example of Preferred Embodiment 1 of the present invention. 
         FIG. 15  is a sectional view of the piezoelectric transducer illustrated in  FIG. 14  taken along line XV-XV and viewed from a direction denoted by arrow. 
         FIG. 16  is a sectional view of the piezoelectric transducer illustrated in  FIG. 14  taken along line XVI-XVI and viewed from a direction denoted by arrow. 
         FIG. 17  is a plan view illustrating a configuration of a piezoelectric transducer according to Preferred Embodiment 2 of the present invention. 
         FIG. 18  is a sectional view illustrating a configuration of a piezoelectric transducer according to Preferred Embodiment 3 of the present invention. 
         FIG. 19  is a sectional view illustrating a state in which a lower electrode layer is provided on an upper surface of an active layer in a method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. 
         FIG. 20  is a sectional view illustrating a state in which a fixing portion is provided on an upper surface of the lower electrode layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. 
         FIG. 21  is a sectional view illustrating a state in which a piezoelectric layer is provided on an upper surface of the lower electrode layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. 
         FIG. 22  is a sectional view illustrating a state in which an upper electrode layer is provided on an upper surface of a piezoelectric layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. 
         FIG. 23  is a diagram illustrating a state in which the upper electrode layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. 
         FIG. 24  is a diagram illustrating a state in which the piezoelectric layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. 
         FIG. 25  is a diagram illustrating a state in which the lower electrode layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. 
         FIG. 26  is a diagram illustrating a state in which the active layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. 
         FIG. 27  is a diagram illustrating a state in which a recessed portion is formed in a lower base portion in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. 
         FIG. 28  is a plan view illustrating a configuration of a piezoelectric transducer according to Preferred Embodiment 4 of the present invention. 
         FIG. 29  is a sectional view of the piezoelectric transducer illustrated in  FIG. 28  taken along line XXIX-XXIX and viewed from a direction denoted by arrow. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, piezoelectric transducers according to preferred embodiments of the present invention will be described with reference to the drawings. In the following description of the preferred embodiments, the same or corresponding portions and elements in the drawings are denoted by the same reference numerals, and description thereof will not be repeated. 
     Preferred Embodiment 1 
       FIG. 1  is a plan view illustrating a configuration of a piezoelectric transducer according to Preferred Embodiment 1 of the present invention.  FIG. 2  is a sectional view of the piezoelectric transducer illustrated in  FIG. 1  taken along line II-II and viewed from a direction denoted by arrow. 
     As illustrated in  FIG. 1  and  FIG. 2 , a piezoelectric transducer  100  according to Preferred Embodiment 1 of the present invention includes a base portion  110 , a plurality of beam portions  120 , and at least one fixing portion  130 . In the present preferred embodiment, four fixing portions  130  are provided. 
     As illustrated in  FIG. 2 , the base portion  110  is located on a lower side of the end portion  121  of each of the plurality of beam portions  120 . Thus, the base portion  110  has an annular outer shape when the piezoelectric transducer  100  is viewed from above, and specifically, has a rectangular or substantially rectangular annular outer shape, similar to the end portion  121  of each of the plurality of beam portions  120  illustrated in  FIG. 1 . 
     As illustrated in  FIG. 2 , in the present preferred embodiment, the base portion  110  has a sectional shape that extends in an up-down direction with a constant or substantially constant width. Note that the base portion  110  may have a sectional shape in which the width becomes wider toward an upper side. 
     The base portion  110  includes a lower base portion  111  and an upper base portion  112 . The upper base portion  112  is layered on the upper portion of the lower base portion  111 . In the present preferred embodiment, the lower base portion  111  is preferably made of Si, for example. The upper base portion  112  is preferably made of SiO 2 , for example. 
     As illustrated in  FIG. 1  and  FIG. 2 , each of the plurality of beam portions  120  is supported by the base portion  110  at the end portion  121 , and extends in a direction away from the base portion  110  at a position above the base portion  110 . 
     Each of the plurality of beam portions  120  has an outer shape that is tapered in an extending direction of the beam portion  120  when the piezoelectric transducer  100  is viewed from above. Specifically, each of the plurality of beam portions  120  preferably has, for example, a triangular or substantially triangular outer shape when the piezoelectric transducer  100  is viewed from above. In the present preferred embodiment, the triangular or substantially triangular shape is an isosceles triangle shape, for example. 
     Note that when the piezoelectric transducer  100  is viewed from above, each of the plurality of beam portions  120  may have an outer shape having a constant width in the extending direction of the beam portion  120 , or may have an outer shape such that the width thereof gradually increases in the extending direction of the beam portion  120 . Each of the plurality of beam portions  120  may have a rectangular or substantially rectangular outer shape, for example. A piezoelectric transducer according to a modified example in which the shape and the arrangement of the beam portions  120  are different will be described later. 
     As illustrated in  FIG. 1 , in the present preferred embodiment, the piezoelectric transducer includes four beam portions  120 . The plurality of beam portions  120  are disposed so as to be point-symmetrical to each other with respect to an imaginary center point C of the piezoelectric transducer  100  when the piezoelectric transducer  100  is viewed from above. In the present preferred embodiment, the four beam portions  120  are each disposed such that, when the piezoelectric transducer  100  is viewed from above, extending directions of adjacent beam portions  120  are different from each other by about 90° while extending in different directions from each other. 
     In the present preferred embodiment, the extending directions of the plurality of beam portions  120  extend toward the imaginary center point C when the piezoelectric transducer  100  is viewed from above. Note that the extending direction of each of the plurality of beam portions  120  may extend away from the imaginary center point, or may not necessarily be directed toward the imaginary center point C. 
     As illustrated in  FIG. 1  and  FIG. 2 , each of the plurality of beam portions  120  is configured such that the end portions  121  of adjacent beam portions  120  are continuous with each other. As described above, the end portions  121  of the plurality of beam portions  120  are configured to be continuous to have an annular outer shape when the piezoelectric transducer  100  is viewed from above, and specifically, preferably have a rectangular or substantially rectangular annular outer shape. 
     The plurality of beam portions  120  are spaced away from each other with a gap  101  interposed therebetween. In the present preferred embodiment, the gap  101  located between the plurality of beam portions  120  extends radially from the imaginary center point C when the piezoelectric transducer  100  is viewed from above. In the extending direction of the gap  101 , a width of the gap  101  is constant or substantially constant. 
     As illustrated in  FIG. 1  and  FIG. 2 , in the present preferred embodiment, a tip portion of each of the plurality of beam portions  120  is a free end spaced apart from the base portion  110 . Note that the tip portion of each of the plurality of beam portions  120  may be connected to a plate-shaped portion that vibrates up and down when the piezoelectric transducer  100  is driven. A piezoelectric transducer according to a modified example having a plate-shaped portion will be described later. 
     As illustrated in  FIG. 2 , each of the plurality of beam portions  120  includes a plurality of layers. Each of the plurality of beam portions  120  includes a piezoelectric layer  122 , an upper electrode layer  123 , and a lower electrode layer  124 . 
     In the present preferred embodiment, the piezoelectric layer  122  is positioned over the entire or substantially the entire length from the end portion  121  side to the tip portion side in the extending direction of the beam portion  120 . Further, the piezoelectric layer  122  is disposed over the entire or substantially the entire width direction orthogonal or substantially orthogonal to the extending direction of the beam portion  120 . 
     The piezoelectric layer  122  may preferably be made of, for example, a polycrystalline material, or may preferably be made of, for example, a single crystal material. The piezoelectric layer  122  is preferably made of lead zirconate titanate (PZT) based ceramics, aluminum nitride (AlN), lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), or the like, for example. 
     In the present preferred embodiment, the upper electrode layer  123  is disposed on an upper side of the piezoelectric layer  122 . The upper electrode layer  123  is disposed from a portion closer to the tip portion side than the end portion  121  of the beam portion  120  to the tip portion in the extending direction of the beam portion  120 . Further, the upper electrode layer  123  is disposed over the entire or substantially the entire width direction perpendicular or substantially perpendicular to the extending direction of the beam portion  120  when the piezoelectric transducer  100  is viewed from above. 
     The upper electrode layer  123  is preferably made of a conductive material, such as Pt, for example. An adhesion layer made of Ti or the like, for example, may be disposed between the upper electrode layer  123  and the piezoelectric layer  122 . 
     The lower electrode layer  124  faces at least a portion of the upper electrode layer  123  with the piezoelectric layer  122  interposed therebetween. In the present preferred embodiment, the lower electrode layer  124  is disposed over the entire or substantially the entire length from the end portion  121  side to the tip portion side of the beam portion  120  in the extending direction of the beam portion  120 . Further, the lower electrode layer  124  is located over the entire or substantially the entire width direction orthogonal or substantially orthogonal to the extending direction of the beam portion  120 . 
     The lower electrode layer  124  is preferably made of a conductive material, such as Pt, for example. An adhesion layer made of Ti or the like, for example, may be disposed between the lower electrode layer  124  and the base portion  110 . 
     In the present preferred embodiment, each of the plurality of beam portions  120  further includes an active layer  125  on a lower side of the lower electrode layer  124 . The active layer  125  is disposed over the entire or substantially the entire length from the end portion  121  side to the tip portion side of the beam portion  120  in the extending direction of the beam portion  120 . Further, the active layer  125  is located over the entire or substantially the entire width direction perpendicular or substantially perpendicular to the extending direction of the beam portion  120 . 
     In the present preferred embodiment, the active layer  125  is preferably made of Si, for example. The active layer  125  may be made of a material having an electrical insulation property. An adhesion layer made of Ti or the like, for example, may be disposed between the lower electrode layer  124  and the active layer  125 . 
     As illustrated in  FIG. 1  and  FIG. 2 , the fixing portion  130  is disposed on the beam portion  120  so as to sandwich the end portion  121  of each of the plurality of beam portions  120  between the fixing portion  130  and the base portion  110 . The fixing portion  130  overlaps at least a portion of the base portion  110  in the up-down direction, and extends so as to protrude from the base portion  110  in the extending direction of the beam portion  120 . The plurality of fixing portions  130  are spaced away from each other with the gap  101  interposed therebetween, and extends on an imaginary ring as viewed from the up-down direction. 
     In the present preferred embodiment, when the piezoelectric transducer  100  is viewed from above, an end surface of the fixing portion  130  located on the opposite side to the tip portion side of the beam portion  120  is preferably located closer to the tip portion side of the beam portion  120  than the end surface of the beam portion  120  located on the opposite side of the tip portion side of the beam portion  120 , but may overlap the end surface of the beam portion  120 . 
     In the present preferred embodiment, when the piezoelectric transducer  100  is viewed from above, a region in the beam portion  120  from a portion in which the end surface of the fixing portion  130  on the tip portion side of the beam portion  120  is located to the tip portion of the beam portion  120  is a movable portion  126 . 
     In addition, in the present preferred embodiment, the fixing portion  130  is disposed on the piezoelectric layer  122 . Further, when the piezoelectric transducer  100  is viewed from above, the fixing portion  130  does not overlap the upper electrode layer  123 . The end surface of the fixing portion  130  on the tip portion side of the beam portion  120  and an end surface of the upper electrode layer  123  on the base portion  110  side are in contact with each other. 
     Note that the fixing portion  130  may be disposed on the upper electrode layer  123 . In this case, it is possible to eliminate the need for alignment of the end surface of the fixing portion  130  on the tip portion side of the beam portion  120  and the end surface of the upper electrode layer  123  on the base portion  110  side. 
     In the present preferred embodiment, the fixing portion  130  is made of a material different from the material forming the upper electrode layer  123 . The fixing portion  130  can be patterned without changing the shape of the upper electrode layer  123  by etching the fixing portion  130  using an etchant that does not react with the material forming the upper electrode layer  123 . 
     Further, the material of the fixing portion  130  is harder than the material of the plurality of beam portions  120 , and in the present preferred embodiment, the material of the fixing portion  130  has a higher Young&#39;s modulus than each of the material of the piezoelectric layer  122  and the material of the upper electrode layer  123 . Specifically, the Young&#39;s modulus of the material of the fixing portion  130  is preferably equal to or greater than about 200 GPa, for example. The fixing portion  130  may be made of a metal material, or may be made of a non-metal material. However, in a case where the fixing portion  130  is in contact with the upper electrode layer  123  or the lower electrode layer  124 , the fixing portion  130  is preferably made of a non-metal material. 
     As illustrated in  FIG. 2 , in the piezoelectric transducer  100  according to the present preferred embodiment, the base portion  110  and the beam portion  120  are formed by providing a recessed portion  102  from the lower surface side with respect to a multilayer body described later. Hereinafter, a non-limiting example of a method for manufacturing the piezoelectric transducer  100  according to Preferred Embodiment 1 of the present invention will be described. 
       FIG. 3  is a sectional view illustrating a state in which a lower electrode layer is provided on an upper surface of an active layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. As illustrated in  FIG. 3 , the lower electrode layer  124  is provided on the upper surface of the active layer  125  by a lift-off method, a plating method, an etching method, or the like, for example. 
     Note that in the present preferred embodiment, the multilayer body including the lower base portion  111 , the upper base portion  112 , and the active layer  125  is prepared in advance as a silicon on insulator (SOI) substrate, for example. 
       FIG. 4  is a sectional view illustrating a state in which a piezoelectric layer is provided on an upper surface of the lower electrode layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. As illustrated in  FIG. 4 , the piezoelectric layer  122  is provided on the upper surface of the lower electrode layer  124  by a chemical vapor deposition (CVD) method, a physical vapor deposition (PVD) method, or the like, for example. 
       FIG. 5  is a sectional view illustrating a state in which an upper electrode layer is provided on an upper surface of the piezoelectric layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention.  FIG. 6  is a diagram illustrating a state in which the upper electrode layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. 
     As illustrated in  FIG. 5  and  FIG. 6 , the upper electrode layer  123  is provided on the upper surface of the piezoelectric layer  122  by a lift-off method, a plating method, an etching method, or the like, for example, and the upper electrode layer  123  is patterned. Thus, the gap  101  is formed in the upper electrode layer  123 . 
       FIG. 7  is a diagram illustrating a state in which the piezoelectric layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. As illustrated in  FIG. 7 , the piezoelectric layer  122  is patterned by a lift-off method, an etching method, or the like, for example. Thus, the gap  101  is formed in the piezoelectric layer  122 . 
       FIG. 8  is a diagram illustrating a state in which a lower electrode layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. As illustrated in  FIG. 8 , the lower electrode layer  124  is patterned by a lift-off method, an etching method, or the like, for example. Thus, the gap  101  is formed in the lower electrode layer  124 . 
       FIG. 9  is a diagram illustrating a state in which the active layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. As illustrated in  FIG. 9 , the active layer  125  is patterned by a lift-off method, an etching method, or the like, for example. Thus, the gap  101  is formed in the active layer  125 . 
       FIG. 10  is a diagram illustrating a state in which a fixing portion is provided on the upper surface of the piezoelectric layer in the manufacturing method for the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. As illustrated in  FIG. 10 , the fixing portion  130  is provided on the upper surface of the piezoelectric layer  122  by a lift-off method, a plating method, an etching method, or the like, for example. 
       FIG. 11  is a diagram illustrating a state in which a recessed portion is formed in a lower base portion in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 1 of the present invention. As illustrated in  FIG. 11 , by performing deep reactive ion etching, wet etching, or the like, for example, on the lower base portion  111  from a lower surface side of the lower base portion  111 , the recessed portion  102  is formed in the lower base portion  111 . 
     Further, by performing deep reactive ion etching, wet etching, or the like, for example, on the upper base portion  112  from the lower surface side of the upper base portion  112 , the recessed portion  102  is formed in the upper base portion  112 . By these steps, the piezoelectric transducer  100  according to Preferred Embodiment 1 of the present invention as illustrated in  FIG. 2  is manufactured. 
       FIG. 2  illustrates a state in which an alignment error between the processing to form the gap  101  and the processing to form the recessed portion  102  does not occur. As such, in  FIG. 2 , when viewed from the up-down direction of the piezoelectric transducer  100 , extension lengths La of the plurality of beam portions  120  from an upper side of the base portion  110  are equal or substantially equal to each other, and lengths Lb of movable portions of the plurality of beam portions  120  are equal or substantially equal to each other. 
     In the piezoelectric transducer  100  according to the present preferred embodiment, it is possible to reduce or prevent the occurrence of a difference in the lengths of the movable portions of the plurality of beam portions  120  even in a case where a difference occurs in the extension lengths of the plurality of beam portions  120  from the upper side of the base portion  110  due to an alignment error between the processing for forming the gap  101  and the processing for forming the recessed portion  102 . 
     Hereinafter, a description will be provided of a difference in effect of the above-described alignment error between the piezoelectric transducer according to Preferred Embodiment 1 of the present invention and a piezoelectric transducer according to a comparative example, which is different from the piezoelectric transducer according to Preferred Embodiment 1 of the present invention only in that the fixing portion  130  is not provided. 
       FIG. 12  is a sectional view of a piezoelectric transducer according to an example of a preferred embodiment of the present invention. The sectional view of a piezoelectric transducer  100   x  in  FIG. 12  illustrates the same sectional view as the sectional view of the piezoelectric transducer  100  illustrated in  FIG. 2 . 
     As illustrated in  FIG. 12 , in the piezoelectric transducer  100   x  according to the example, since an alignment error occurs between the processing for forming the gap  101  and the processing for forming the recessed portion  102   x,  the extension lengths of the plurality of beam portions  120   x  from upper side of the base portion  110   x  are different from each other. For example, among the plurality of beam portions  120   x,  an extension length of one beam portion  120   x  from the upper side of the base portion  110   x  is Lc, an extension length of another one of the beam portions  120   x  from the upper side of the base portion  110   x  is Ld, and Lc&lt;Ld. 
     The piezoelectric transducer  100   x  according to the example includes a fixing portion  130   x.  The fixing portion  130   x  overlaps at least a portion of the base portion  110   x  in the up-down direction, and extends so as to protrude from the base portion  110   x  in an extending direction of the beam portion  120   x.  As illustrated in  FIG. 12 , since a portion in which the fixing portion  130   x  is provided in each of the plurality of beam portions  120   x  is fixed by the fixing portion  130   x,  a position of an end surface of the fixing portion  130   x  on a tip portion side of the beam portion  120   x  is a fixed end of a movable portion  126   x.    
     In the processing for forming the fixing portion  130   x,  since the alignment is performed, similarly to the processing for forming the gap  101 , from a front surface side of the piezoelectric transducer  100   x,  the alignment error is less likely to occur as compared to a case of using a double-sided aligner in the processing for forming the recessed portion  102   x.  As such, it is possible to reduce or prevent variation in the formation position of the fixing portion  130   x  due to the alignment error. As a result, even in a case where the extension lengths of the plurality of beam portions  120   x  from the upper side of the base portion  110   x  are different from each other, the lengths Lb of movable portions of the plurality of beam portions  120   x  can be maintained equal or substantially equal to each other. 
     Accordingly, as illustrated in  FIG. 12 , when the piezoelectric transducer  100   x  according to the example is driven, it is possible to uniformly or substantially uniformly deform the movable portions  126   x  of the plurality of beam portions  120   x,  as indicated by a region surrounded by a dotted line. 
       FIG. 13  is a sectional view of a piezoelectric transducer according to a comparative example. The sectional view of a piezoelectric transducer  900  in  FIG. 13  illustrates the same sectional view as the sectional view of the piezoelectric transducer  100  illustrated in  FIG. 2 . 
     As illustrated in  FIG. 13 , in the piezoelectric transducer  900  according to the comparative example, since an alignment error occurs between the processing for forming the gap  101  and the processing for forming a recessed portion  902 , extension lengths of a plurality of beam portions  920  from upper side of base portion  910  are different from each other. For example, among the plurality of beam portions  920 , an extension length of one beam portion  920  from the upper side of the base portion  910  is Le, an extension length of another one of the beam portions  920  from the upper side of the base portion  910  is Lf, and Le&lt;Lf. 
     In the piezoelectric transducer  900  according to the comparative example, the entire portion of each of the beam portions  920  that extend from the upper side of the base portion  910  is a movable portion  926 . Thus, a position of an end surface of the base portion  910  on a tip portion side of the beam portion  920  is a fixed end of the movable portion  926 . As a result, lengths of the plurality of movable portions  926  are different from each other. Therefore, the length of the movable portion  926  of the above-described one beam portion  920  is Le, the length of the movable portion  926  of another one of the beam portions  920  is Lf, and Le&lt;Lf. 
     Accordingly, as illustrated in  FIG. 13 , when the piezoelectric transducer  900  according to the comparative example is driven, as indicated by a region surrounded by a dotted line, the movable portions  926  of the plurality of beam portions  920  are not uniformly deformed. 
     As described above, in the piezoelectric transducer  100  according to Preferred Embodiment 1 of the present invention, the fixing portion  130  is disposed on the beam portion  120  so as to sandwich the end portion  121  of each of the plurality of beam portions  120  between the fixing portion  130  and the base portion  110 . The fixing portion  130  overlaps at least a portion of the base portion  110  in the up-down direction, and extends so as to protrude from the base portion  110  in the extending direction of the beam portion  120 . 
     By equalizing the lengths of the movable portions  126  of the plurality of beam portions  120 , mechanical characteristics, such as a resonant frequency and a deformation amount of the plurality of beam portions  120 , are made uniform or substantially uniform, and it is possible to improve input/output characteristics of the piezoelectric transducer  100 . 
     In the piezoelectric transducer  100  according to the present preferred embodiment, the fixing portion  130  is disposed on the piezoelectric layer  122 . 
     Accordingly, since the piezoelectric layer  122  sandwiched between the upper electrode layer  123  and the lower electrode layer  124  is not located under the fixing portion  130 , the end portion  121  of each of the plurality of beam portions  120  can be stably fixed by the fixing portion  130 . As a result, it is possible to stably improve the input/output characteristics of the piezoelectric transducer  100 . 
     In the piezoelectric transducer  100  according to the present preferred embodiment, the material of the fixing portion  130  has a higher Young&#39;s modulus than each of the material of the piezoelectric layer  122  and the material of the upper electrode layer  123 . 
     Accordingly, at the time of driving the piezoelectric transducer  100 , when the movable portion  126  of the beam portion  120  is displaced, the end portion  121  of the beam portion  120  can be more firmly fixed by the fixing portion  130 . 
     Next, a piezoelectric transducer according to a modified example of Preferred Embodiment 1 of the present invention will be described with reference to the drawings. Note that the piezoelectric transducer according to the modified example of Preferred Embodiment 1 of the present invention differs from the piezoelectric transducer  100  according to Preferred Embodiment 1 of the present invention mainly in that a plate-shaped portion is included, and each of the plurality of beam portions has a rectangular or substantially rectangular shape and does not extend toward the imaginary center point C. Therefore, a description will not be repeated for the same or corresponding configuration as that of the piezoelectric transducer  100  according to Preferred Embodiment 1 of the present invention. 
       FIG. 14  is a plan view illustrating the configuration of the piezoelectric transducer according to the modified example of Preferred Embodiment 1 of the present invention.  FIG. 15  is a sectional view of the piezoelectric transducer illustrated in  FIG. 14  taken along line XV-XV and viewed from a direction indicated by arrow.  FIG. 16  is a sectional view of the piezoelectric transducer illustrated in  FIG. 14  taken long line XVI-XVI and viewed from a direction indicated by arrow. 
     As illustrated in  FIG. 14  to  FIG. 16 , a piezoelectric transducer  100   a  according to the modified example of Preferred Embodiment 1 of the present invention includes a base portion  110   a,  a plurality of beam portions  120   a,  a fixing portion  130   a,  and a plate-shaped portion  140   a.    
     As illustrated in  FIG. 14 , each of the plurality of beam portions  120   a  has an outer shape in which a width in the extending direction is constant or substantially constant when the piezoelectric transducer  100   a  is viewed from above. Specifically, each of the plurality of beam portions  120   a  has a rectangular or substantially rectangular outer shape when the piezoelectric transducer  100   a  is viewed from above. 
     The piezoelectric transducer  100   a  according to the modified example of Preferred Embodiment 1 includes four beam portions  120   a.  As illustrated in  FIG. 14  and  FIG. 16 , when the piezoelectric transducer  100   a  is viewed from above, on an inner side of the base portion  110   a  having a rectangular or substantially rectangular annular outer shape, each of the four beam portions  120   a  extends along a corresponding side of a plurality of sides of the rectangular or substantially rectangular annular shape. Each of the plurality of beam portions  120   a  extends while being spaced from the base portion  110   a  by a gap  101   a  having a constant or substantially constant width. Each of the plurality of beam portions  120   a  is located such that a tip portion of the beam portion  120   a  is spaced apart from an adjacent beam portion  120   a  by the gap  101   a  having a constant or substantially constant width. 
     As illustrated in  FIG. 14 , in the piezoelectric transducer  100   a  according to the modified example of Preferred Embodiment 1, the tip portion on the side opposite to the base portion  110   a  side of each of the plurality of beam portions  120   a  is connected to the plate-shaped portion  140   a.    
     In the modified example of Preferred Embodiment 1, when the piezoelectric transducer  100   a  is viewed from above, the plate-shaped portion  140   a  is located on an inner side of the plurality of beam portions  120   a.  The plate-shaped portion  140   a  has a rectangular or substantially rectangular outer shape. The plate-shaped portion  140   a  is connected to the beam portion  120   a  at an apex of the rectangular or substantially rectangular shape. 
     As illustrated in  FIG. 15 , in the modified example of Preferred Embodiment 1, the plate-shaped portion  140   a  includes a piezoelectric layer  122   a,  a lower electrode layer  124   a,  and an active layer  125   a,  similar to an end portion  121   a  of the beam portion  120   a.  The lower electrode layer  124   a  is disposed on a lower side of the piezoelectric layer  122   a.  The active layer  125   a  is disposed on a lower side of the lower electrode layer  124   a.    
     In the modified example of Preferred Embodiment 1, the piezoelectric layer  122   a  included in the plate-shaped portion  140   a  is continuous with the piezoelectric layer  122   a  included in each of the plurality of beam portions  120   a.  The lower electrode layer  124   a  included in the plate-shaped portion  140   a  is continuous with the lower electrode layer  124   a  included in each of the plurality of beam portions  120   a.  The active layer  125   a  included in the plate-shaped portion  140   a  is continuous with the active layer  125   a  included in each of the plurality of beam portions  120   a.  As described above, the plate-shaped portion  140   a  is continuous with each of the plurality of beam portions  120   a.    
     The plate-shaped portion  140   a  vibrates up and down together with the movable portion  126  of the beam portion  120   a  that displaces up and down when the piezoelectric transducer  100   a  is driven. Note that, as illustrated in  FIG. 16 , also in the piezoelectric transducer  100   a  according to the modified example of Preferred Embodiment 1, the fixing portion  130   a  is disposed on the beam portion  120   a  so as to sandwich the end portion  121   a  of each of the plurality of beam portions  120   a  between the fixing portion  130   a  and the base portion  110   a.  The fixing portion  130   a  overlaps at least a portion of the base portion  110   a  in the up-down direction, and extends so as to protrude from the base portion  110   a  in an extending direction of the beam portion  120   a.    
     An extension length of each of the plurality of beam portions  120   a  from the upper side of the base portion  110   a  is Lg, and the length of the movable portion  126  of each of the plurality of beam portions  120   a  is Lh. 
     Also in the piezoelectric transducer  100   a  according to the modified example of Preferred Embodiment 1, even in a case where a difference occurs in the extension lengths Lg of the plurality of beam portions  120   a  from the upper side of the base portion  110   a  due to an alignment error between the processing for forming the gap  101   a  and the processing for forming the recessed portion  102 , it is possible to reduce or prevent the occurrence of a difference in the lengths Lh of the movable portions  126  of the plurality of beam portions  120   a.    
     By equalizing the lengths Lh of the movable portions  126  of the plurality of beam portions  120   a,  mechanical characteristics, such as a resonant frequency and a deformation amount of the plurality of beam portions  120   a,  are made uniform or substantially uniform, and it is possible to improve input/output characteristics of the piezoelectric transducer  100   a.    
     Preferred Embodiment 2 
     Hereinafter, a piezoelectric transducer according to Preferred Embodiment 2 of the present invention will be described. The piezoelectric transducer according to Preferred Embodiment 2 of the present invention differs from the piezoelectric transducer  100  according to Preferred Embodiment 1 in the configuration of the fixing portion. Therefore, the description of the same or similar configuration as that of the piezoelectric transducer  100  according to Preferred Embodiment 1 of the present invention will not be repeated. 
       FIG. 17  is a plan view illustrating the configuration of the piezoelectric transducer according to Preferred Embodiment 2 of the present invention. As illustrated in  FIG. 17 , a fixing portion  230  on each of a plurality of beam portions  220  is defined by a single member so as to be continuous, and has an annular shape when viewed from the up-down direction. Accordingly, the end portion  121  of each of the plurality of beam portions  220  can stably and more firmly be fixed by the fixing portion  230 . As a result, it is possible to stably improve the input/output characteristics of a piezoelectric transducer  200 . 
     Preferred Embodiment 3 
     Hereinafter, a piezoelectric transducer according to Preferred Embodiment 3 of the present invention will be described. The piezoelectric transducer according to Preferred Embodiment 3 of the present invention differs from the piezoelectric transducer  100  according to Preferred Embodiment 1 of the present invention in the position at which the fixing portion is disposed. Therefore, the description of the same or similar configuration as that of the piezoelectric transducer  100  according to Preferred Embodiment 1 of the present invention will not be repeated. 
       FIG. 18  is a sectional view illustrating the configuration of the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. The sectional view of a piezoelectric transducer  300  in  FIG. 18  illustrates the same sectional view as the sectional view of the piezoelectric transducer  100  illustrated in  FIG. 2 . 
     As illustrated in  FIG. 18 , in the piezoelectric transducer  300  according to Preferred Embodiment 3 of the present invention, a piezoelectric layer  322  is located from a position closer to a tip portion side of a beam portion  320  than an end portion  321  to the tip portion of the beam portion  320  in an extending direction of the beam portion  320 . That is, the piezoelectric layer  322  is not disposed above a base portion  310 . 
     Further, in the piezoelectric transducer  300  according to the present preferred embodiment, a fixing portion  330  is disposed on a lower electrode layer  324 . An end surface of the fixing portion  330  on a tip portion side of the beam portion  320  and an end surface of the piezoelectric layer  322  on the end portion  321  side are in contact with each other. 
     Hereinafter, a non-limiting example of a method for manufacturing the piezoelectric transducer  300  according to Preferred Embodiment 3 of the present invention will be described. 
       FIG. 19  is a sectional view illustrating a state in which a lower electrode layer is provided on an upper surface of an active layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. As illustrated in  FIG. 19 , the lower electrode layer  324  is provided on an upper surface of an active layer  325  by a lift-off method, a plating method, an etching method, or the like, for example. Note that in the present preferred embodiment, a multilayer body including a lower base portion  311 , an upper base portion  312 , and the active layer  325  is prepared in advance as a SOI substrate. 
       FIG. 20  is a sectional view illustrating a state in which a fixing portion is provided on an upper surface of the lower electrode layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. As illustrated in  FIG. 20 , the fixing portion  330  is provided on an upper surface of the lower electrode layer  324  by a lift-off method, a plating method, an etching method, or the like, for example. 
       FIG. 21  is a sectional view illustrating a state in which a piezoelectric layer is provided on the upper surface of the lower electrode layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. As illustrated in  FIG. 21 , the piezoelectric layer  322  is provided on the upper surface of the lower electrode layer  324  by a CVD method, a PVD method, or the like, for example. 
       FIG. 22  is a sectional view illustrating a state in which an upper electrode layer is provided on an upper surface of the piezoelectric layer in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention.  FIG. 23  is a diagram illustrating a state in which the upper electrode layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. 
     As illustrated in  FIG. 22  and  FIG. 23 , an upper electrode layer  323  is provided on an upper surface of the piezoelectric layer  322  by a lift-off method, a plating method, an etching method, or the like, for example, and a gap  301  is formed in the upper electrode layer  323 . 
       FIG. 24  is a diagram illustrating a state in which the piezoelectric layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. As illustrated in  FIG. 24 , the piezoelectric layer  322  is patterned by a lift-off method, an etching method, or the like, for example. Thus, the gap  301  is formed in the piezoelectric layer  322 . 
       FIG. 25  is a diagram illustrating a state in which the lower electrode layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. As illustrated in  FIG. 25 , the lower electrode layer  324  is patterned by a lift-off method, an etching method, or the like, for example. Thus, the gap  301  is formed in the lower electrode layer  324 . 
       FIG. 26  is a diagram illustrating a state in which the active layer is patterned in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. As illustrated in  FIG. 26 , the active layer  325  is patterned by a lift-off method, an etching method, or the like, for example. Thus, the gap  301  is formed in the active layer  325 . 
       FIG. 27  is a diagram illustrating a state in which a recessed portion is formed in a lower base portion in the method for manufacturing the piezoelectric transducer according to Preferred Embodiment 3 of the present invention. As illustrated in  FIG. 27 , by performing deep reactive ion etching, wet etching, or the like, for example, on the lower base portion  311  from a lower surface side of the lower base portion  311 , a recessed portion  302  is formed in the lower base portion  311 . 
     Further, by performing the deep reactive ion etching, the wet etching, or the like, for example, on the upper base portion  312  from a lower surface side of the upper base portion  312 , the recessed portion  302  is formed in the upper base portion  312 . By these steps, the piezoelectric transducer  300  according to Preferred Embodiment 3 of the present invention as illustrated in  FIG. 18  is manufactured. 
     As described above, in the piezoelectric transducer  300  according to the present preferred embodiment, the fixing portion  330  is disposed on the lower electrode layer  324 . Thus, since the piezoelectric layer  322  is not located below the fixing portion  330 , the end portion  321  of each of the plurality of beam portions  320  can stably be fixed by the fixing portion  330 . As a result, it is possible to stably improve the input/output characteristics of the piezoelectric transducer  300 . 
     Also in the piezoelectric transducer  300  according to the present preferred embodiment, even in a case where a difference occurs in extension lengths Li of the plurality of beam portions  320  from an upper side of the base portion  310  due to an alignment error between the processing for forming the gap  301  and the processing for forming the recessed portion  302 , it is possible to reduce or prevent the occurrence of a difference in lengths Lj of the movable portions  126  of the plurality of beam portions  320 . 
     By equalizing the lengths Lj of the movable portions  126  of the plurality of beam portions  320 , mechanical characteristics, such as a resonant frequency and a deformation amount of the plurality of beam portions  320 , are made uniform or substantially uniform, and the input/output characteristics of the piezoelectric transducer  300  can be improved. 
     Preferred Embodiment 4 
     Hereinafter, a piezoelectric transducer according to Preferred Embodiment 4 of the present invention will be described. The piezoelectric transducer according to Preferred Embodiment 4 of the present invention differs from the piezoelectric transducer  100  according to Preferred Embodiment 1 in the shape of the movable portion in each of the plurality of beam portions. Therefore, the description of the same or similar configuration as that of the piezoelectric transducer  100  according to Preferred Embodiment 1 of the present invention will not be repeated. 
       FIG. 28  is a plan view illustrating the configuration of the piezoelectric transducer according to Preferred Embodiment 4 of the present invention.  FIG. 29  is a sectional view of the piezoelectric transducer illustrated in  FIG. 28  taken along line XXIX-XXIX and viewed from a direction indicated by arrow. 
     As illustrated in  FIG. 28  and  FIG. 29 , in a piezoelectric transducer  400  according to Preferred Embodiment 4 of the present invention, a plurality of through-holes  427  penetrating through a beam portion  420  in an up-down direction are provided in each of the plurality of beam portions  420 . Each of the plurality of through-holes  427  is located closer to a tip portion side of the beam portion  420  than a fixing portion  430  in an extending direction of the beam portion  420 . 
     That is, each of the plurality of through-holes  427  is located in a movable portion  426  of the beam portion  420 . Accordingly, in each of the plurality of beam portions  420 , the rigidity of the movable portion  426  is reduced, and an end portion  421  of each of the plurality of beam portions  420  can be stably fixed by the fixing portion  430 . As a result, it is possible to stably improve the input/output characteristics of the piezoelectric transducer  400 . 
     The plurality of through-holes  427  are disposed so as to be symmetric with respect to the extending direction of the beam portion  420  in each of the plurality of beam portions  420 . The plurality of through-holes  427  in each of the plurality of beam portions  420  are disposed such that shapes of the plurality of beam portions  420  are point-symmetric to each other with respect to the imaginary center point C of the piezoelectric transducer  400 . 
     In the present preferred embodiment, the plurality of through-holes  427  are formed in processing for patterning a gap  401 , for example. However, the method for forming the plurality of through-holes  427  is not limited to the above-described method, and the plurality of through-holes  427  may be formed by processing, such as perforating, for example, different from the processing for patterning the gap  401 . 
     Also in the piezoelectric transducer  400  according to the present preferred embodiment, even in a case where a difference occurs in extension lengths Lk of the plurality of beam portions  420  from an upper side of a base portion  410  due to an alignment error between the processing for forming the gap  401  and the processing for forming the recessed portion  102 , it is possible to reduce or prevent the occurrence of a difference in lengths Lm of the movable portions  426  of the plurality of beam portions  420 . 
     By equalizing the lengths Lm of the movable portions  426  of the plurality of beam portions  420 , mechanical characteristics, such as a resonant frequency and a deformation amount of the plurality of beam portions  420 , are made uniform or substantially uniform, and it is possible to improve input/output characteristics of the piezoelectric transducer  400 . 
     In the description of the above-described preferred embodiments, configurations able to be combined may be combined with each other. 
     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.