Piezoelectric element and ultrasonic transducer

Abstract

Provided are a piezoelectric element and an ultrasonic transducer with which it is possible to increase the operation frequency of a piezoelectric element. A piezoelectric element (1) comprises a metal substrate (2), a lower electrode (4), a piezoelectric body layer (5), and an upper electrode (6). The metal substrate (2) contains at least iron and chromium. The lower electrode (4) is provided on the metal substrate (2). The piezoelectric body layer (5) is provided on the lower electrode (4). The upper electrode (6) is provided on the piezoelectric body layer (5). In a plan view, a first outer edge of the lower electrode (4) is positioned on the inside of a second outer edge of the metal substrate (2). In the plan view, a third outer edge of the piezoelectric body layer (5) is positioned on the inside of the first outer edge of the lower electrode (4). In the plan view, a fourth outer edge of the upper electrode (6) is positioned on the inside of the third outer edge of the piezoelectric body layer (5).

Description

Piezoelectric elements and ultrasonic transducers

[0001] The present disclosure relates to a piezoelectric element and an ultrasonic transducer, and more particularly to a piezoelectric element having a lower electrode and an upper electrode, and an ultrasonic transducer including the piezoelectric element.

[0002] Patent Document 1 discloses an ultrasonic transmitter / receiver (ultrasonic transducer) for use in the air that uses a piezoelectric element, and that includes a piezoelectric ceramic, silver electrodes formed by sintering a conductive paste provided on both sides of the piezoelectric ceramic, and a cylindrical case with a bottom.

[0003] In some cases, it is desirable to increase the operating frequency (resonant frequency) of a piezoelectric element.

[0004] JP 2014-82655 A

[0005] An object of the present disclosure is to provide a piezoelectric element and an ultrasonic transducer that can increase the operating frequency of the piezoelectric element.

[0006] A piezoelectric element according to one aspect of the present disclosure includes a metal substrate, a lower electrode, a piezoelectric layer, and an upper electrode. The metal substrate contains at least iron and chromium. The lower electrode is provided on the metal substrate. The piezoelectric layer is provided on the lower electrode. The upper electrode is provided on the piezoelectric layer. In a plan view, a first outer edge of the lower electrode is located inside a second outer edge of the metal substrate. In the plan view, a third outer edge of the piezoelectric layer is located inside the first outer edge of the lower electrode. In the plan view, a fourth outer edge of the upper electrode is located inside the third outer edge of the piezoelectric layer.

[0007] An ultrasonic transducer according to one aspect of the present disclosure includes the piezoelectric element, a vibration plate portion, a first conductive member, a second conductive member, a first conductive joint portion, and a second conductive joint portion. The vibration plate portion is joined to the metal substrate of the piezoelectric element. The first conductive member is connected to the lower electrode of the piezoelectric element. The second conductive member is connected to the upper electrode of the piezoelectric element. The first conductive joint portion joins the lower electrode and the first conductive member. The second conductive joint portion joins the upper electrode and the second conductive member.

[0008] FIG. 1 is a plan view of a piezoelectric element according to a first embodiment. FIG. 2 is a cross-sectional view of the piezoelectric element taken along line A1-A1 in FIG. 1 . FIG. 3 is an explanatory diagram of a manufacturing method of the piezoelectric element. FIG. 4 is a plan view of an ultrasonic transducer including the piezoelectric element. FIG. 5 is a cross-sectional view of the ultrasonic transducer including the piezoelectric element taken along line A2-A2 in FIG. 4 . FIG. 6 is a plan view of a piezoelectric element according to a second embodiment. FIG. 7 is a cross-sectional view of the piezoelectric element taken along line A3-A3 in FIG. 6 . FIG. 8 is a plan view of an ultrasonic transducer including the piezoelectric element. FIG. 9 is a cross-sectional view of the ultrasonic transducer including the piezoelectric element taken along line A4-A4 in FIG. 8 . FIG. 10 is a plan view of a piezoelectric element according to a third embodiment. FIG. 11 is a cross-sectional view of the piezoelectric element taken along line A5-A5 in FIG. 10 . FIG. 12 is a cross-sectional view of an ultrasonic transducer according to a fourth embodiment.

[0009] The drawings referred to in the following embodiments 1 to 4 are all schematic drawings, and the ratios of the sizes and thicknesses of the components in the drawings do not necessarily reflect the actual dimensional ratios.

[0010] First Embodiment A piezoelectric element 1 will be described below with reference to FIGS. 1 to 3, and then an ultrasonic transducer 100 including the piezoelectric element 1 will be described with reference to FIGS.

[0011] (1) Overview of Piezoelectric Element and Ultrasonic Transducer As shown in Figures 1 and 2, the piezoelectric element 1 comprises a metal substrate 2, an alumina layer 3, a lower electrode 4, a piezoelectric layer 5, and an upper electrode 6. The metal substrate 2 contains at least iron and chromium. The lower electrode 4 is provided on the metal substrate 2. The piezoelectric layer 5 is provided on the lower electrode 4. The upper electrode 6 is provided on the piezoelectric layer 5. In a plan view, the outer edge of the piezoelectric element 1 is, for example, rectangular. "In a plan view" has the same meaning as "when viewed from above the metal substrate 2 in a direction along the thickness direction of the metal substrate 2." In other words, "in a plan view" has the same meaning as "when viewed from above the metal substrate 2 in the thickness direction of the metal substrate 2."

[0012] As shown in Figures 4 and 5, the ultrasonic transducer 100 includes a piezoelectric element 1, a diaphragm portion 120, a first lead wire 141, a second lead wire 142, a first conductive joint portion 131, and a second conductive joint portion 132. In the ultrasonic transducer 100, the first lead wire 141 constitutes a first conductive member, and the second lead wire 142 constitutes a second conductive member. The diaphragm portion 120 is joined to the metal substrate 2 of the piezoelectric element 1. More specifically, the diaphragm portion 120 is joined to the metal substrate 2 of the piezoelectric element 1 by a joint portion 105. The first lead wire 141 is connected to the lower electrode 4 of the piezoelectric element 1. The second lead wire 142 is connected to the upper electrode 6 of the piezoelectric element 1. The first conductive joint portion 131 joins the lower electrode 4 and the first lead wire 141. The second conductive joint 132 joins the upper electrode 6 and the second lead wire 142 .

[0013] The ultrasonic transducer 100 transmits an ultrasonic wave by converting a first electrical signal (an AC voltage with a predetermined drive frequency) into a first mechanical vibration in the piezoelectric element 1. In the ultrasonic transducer 100, when the first electrical signal is applied to the piezoelectric element 1, the piezoelectric element 1 vibrates in the thickness direction of the diaphragm portion 120 in response to vertical vibration of the piezoelectric element 1 due to horizontal expansion and contraction motion of the piezoelectric element 1, and an ultrasonic wave is transmitted. Furthermore, the ultrasonic transducer 100 converts, for example, into a second electrical signal in the piezoelectric element 1, a second mechanical vibration of the piezoelectric element 1 that is caused by vibration in the thickness direction of the diaphragm portion 120 when a reflected wave of an ultrasonic wave transmitted from the ultrasonic transducer 100 is incident on the diaphragm portion 120.

[0014] In the ultrasonic transducer 100, the vibration plate portion 120 is flat. The ultrasonic transducer 100 further includes a case 101 that houses the piezoelectric element 1. The case 101 has a bottom plate portion 102 and a tubular portion 103. The bottom plate portion 102 is flat. The tubular portion 103 protrudes from the periphery of one surface of the bottom plate portion 102 in the thickness direction of the bottom plate portion 102 and surrounds the piezoelectric element 1. The portion of the bottom plate portion 102 that is surrounded by the tubular portion 103 also serves as the vibration plate portion 120.

[0015] 5, the ultrasonic transducer 100 further includes a sound absorbing member 150 disposed above the piezoelectric element 1 within the case 101, and a sealing portion 160 disposed on the sound absorbing member 150 within the case 101. Note that the sound absorbing member 150 and the sealing portion 160 are not shown in FIG.

[0016] (2) Details (2.1) Piezoelectric Element Hereinafter, the piezoelectric element 1 according to the first embodiment will be described in more detail with reference to FIGS.

[0017] (2.1.1) Metal Substrate The metal substrate 2 is flat. As shown in Fig. 2, the metal substrate 2 has an upper surface (first main surface) 21 and a lower surface (second main surface) 22. As shown in Fig. 1, the outer edge 20 of the metal substrate 2 is, for example, quadrangular (e.g., rectangular) in plan view. The thickness of the metal substrate 2 is, for example, 0.1 mm, but is not limited to this.

[0018] The metal substrate 2 contains iron, chromium, and aluminum. The metal substrate 2 is a stainless steel substrate containing iron as a main component, and also contains chromium and aluminum in addition to iron. The stainless steel substrate constituting the metal substrate 2 is, for example, an aluminum-containing ferritic stainless steel substrate. The aluminum-containing ferritic stainless steel substrate has, for example, a chromium content of 18 wt% and an aluminum content of 3 wt%. The chromium content is not limited to 18 wt%. Furthermore, the aluminum content is not limited to 3 wt%. The metal substrate 2 may further contain elements other than iron, chromium, and aluminum.

[0019] (2.1.2) Alumina Layer The alumina layer 3 is provided on the upper surface 21 (see FIG. 2) of the metal substrate 2. As shown in FIG. 1, the outer edge 30 of the alumina layer 3 has a quadrangular (e.g., rectangular) shape in plan view. The thickness of the alumina layer 3 is, for example, 1 μm, but is not limited to this.

[0020] The main phase of the alumina forming the alumina layer 3 is the γ-alumina phase. That is, the alumina layer 3 is mainly composed of γ-alumina phase particles. "Mainly composed of γ-alumina phase particles" means that more than 50 wt % of the alumina layer 3 is composed of γ-alumina phase particles. The crystalline phase of the material (particles) forming the alumina layer 3 can be identified by measuring the X-ray diffraction pattern of an exposed portion of the alumina layer 3 using an X-ray diffractometer. The upper surface of the alumina layer 3 includes part of the surfaces of the multiple scale-like particles of the alumina layer 3. Considering the SEM (Scanning Electron Microscope) image of the upper surface of the alumina layer 3 and the measurement results of the X-ray diffraction pattern together, it is estimated that the scale-like particles are γ-alumina particles.

[0021] (2.1.3) Lower Electrode The lower electrode 4 is provided on the upper surface 31 (see FIG. 2) of the alumina layer 3. As shown in FIG. 1, the outer edge 40 of the lower electrode 4 is, for example, rectangular in plan view, but is not limited to this. The thickness of the lower electrode 4 is, for example, 3 μm, but is not limited to this.

[0022] The material of the lower electrode 4 includes, for example, silver (Ag) and palladium (Pd), and more specifically, the material of the lower electrode 4 includes, for example, an Ag—Pd alloy.

[0023] (2.1.4) Piezoelectric Layer The piezoelectric layer 5 is provided on the upper surface 41 (see FIG. 2 ) of the lower electrode 4. As shown in FIG. 1 , the outer edge 50 of the piezoelectric layer 5 is, for example, rectangular in plan view, but is not limited to this. The thickness of the piezoelectric layer 5 is, for example, 5 μm to 40 μm, and preferably 10 μm to 30 μm. The thickness of the piezoelectric layer 5 is, for example, 11 μm, but is not limited to this.

[0024] The material of the piezoelectric layer 5 includes, but is not limited to, for example, Pb, Zr, Zn, Nb, and O. More specifically, the material of the piezoelectric layer 5 includes, for example, Pb １．０１５ Zr ０．４４ (Zn １／３ Nb ２／３ ) ０．１０ O ３．０１５ However, the composition ratio of the material of the piezoelectric layer 5 is not limited to this.

[0025] (2.1.5) Upper Electrode The upper electrode 6 is provided on the upper surface 51 (see FIG. 2) of the piezoelectric layer 5. As shown in FIG. 1, the outer edge 60 of the upper electrode 6 has, for example, a rectangular shape in plan view, but is not limited to this. The thickness of the upper electrode 6 is, for example, 3 μm, but is not limited to this.

[0026] The material of the upper electrode 6 includes, for example, Ag and Pd, and more specifically, the material of the upper electrode 6 includes, for example, an Ag—Pd alloy.

[0027] (2.1.6) Layout of the Lower Electrode, Piezoelectric Layer, and Upper Electrode in the Piezoelectric Element In the piezoelectric element 1, as shown in FIG. 1 , in a plan view, the outer edge 40 (first outer edge) of the lower electrode 4 is located inside the outer edge 20 (second outer edge) of the metal substrate 2. In a plan view, the outer edge 50 (third outer edge) of the piezoelectric layer 5 is located inside the outer edge 40 of the lower electrode 4. In a plan view, the outer edge 60 (fourth outer edge) of the upper electrode 6 is located inside the outer edge 50 of the piezoelectric layer 5. In the piezoelectric element 1, the area of ​​the upper surface 41 (see FIG. 2 ) of the lower electrode 4 is smaller than the area of ​​the upper surface 21 (see FIG. 2 ) of the metal substrate 2, the area of ​​the upper surface 51 (see FIG. 2 ) of the piezoelectric layer 5 is smaller than the area of ​​the upper surface 41 of the lower electrode 4, and the area of ​​the upper surface 61 (see FIG. 2 ) of the upper electrode 6 is smaller than the area of ​​the upper surface 51 of the piezoelectric layer 5.

[0028] 1, an orthogonal coordinate system having three mutually orthogonal axes, namely, an X-axis, a Y-axis, and a Z-axis, will be defined, and in particular, the axis along the thickness direction of the metal substrate 2 will be referred to as the "Z-axis," the axis along the longitudinal direction of the metal substrate 2 as the "X-axis," and the axis along the lateral direction of the metal substrate 2 as the "Y-axis." The X-axis, Y-axis, and Z-axis are all imaginary axes, and the arrows indicating "X," "Y," and "Z" in the drawings are merely shown for the purpose of explanation and do not have any physical substance.

[0029] In the piezoelectric element 1, a portion 411 of the upper surface 41 of the lower electrode 4 that is not covered by the piezoelectric layer 5 also serves as a terminal portion for external connection. In the piezoelectric element 1, as shown in FIG. 1 , the distance between the outer edge 40 of the lower electrode 4 and the outer edge 50 of the piezoelectric layer 5 is not uniform in plan view, and the first width W1 is wider than the second width W2. The first width W1 is the width between the outer edge 40 of the lower electrode 4 and the outer edge 50 of the piezoelectric layer 5 at a first end of the piezoelectric element 1 in the direction along the X-axis. The second width W2 is the width between the outer edge 40 of the lower electrode 4 and the outer edge 50 of the piezoelectric layer 5 at a second end of the piezoelectric element 1 in the direction along the X-axis.

[0030] (2.1.7) Method for Manufacturing Piezoelectric Element A method for manufacturing the piezoelectric element 1 according to the first embodiment will be briefly described with reference to FIG.

[0031] In the manufacturing method of the piezoelectric element 1 according to the first embodiment, first, a metal substrate 2A (see FIG. 3) capable of producing multiple metal substrates 2 is prepared, and then the first, second, third, fourth, fifth and sixth steps are carried out in sequence.

[0032] In the first step, a metal substrate 2A containing iron, chromium, and aluminum is heat-treated in the atmosphere to form an alumina layer 3A (see FIG. 3 ) covering the entire upper surface 21A of the metal substrate 2A. Regarding the conditions for the heat treatment, the heat treatment temperature is, for example, 850° C. or higher and 900° C. or lower, and the heat treatment time is, for example, 2 hours. In the first step, in addition to the first alumina layer 3A, a second alumina layer may be formed that covers the entire lower surface 22A of the metal substrate 2A.

[0033] In the second step, a paste containing the material of the lower electrode 4 (for example, an Ag-Pd alloy paste) is screen-printed to form a first pattern portion including a plurality of lower electrode material portions on the alumina layer 3A.

[0034] In the third step, a second pattern portion including a plurality of piezoelectric material portions is formed on the first pattern portion by printing a paste including the material of the piezoelectric layer 5 using a metal mask. １．０１５ Zr ０．４４ (Zn １／３ Nb ２／３ ) ０．１０ O ３．０１５ is.

[0035] In the fourth step, a paste containing the material of the upper electrode 6 (for example, an Ag—Pd alloy paste) is screen-printed to form a third pattern portion including a plurality of upper electrode material portions on the second pattern portion.

[0036] In the fifth step, the first pattern portion, the second pattern portion, and the third pattern portion are fired at a predetermined firing temperature (e.g., 875°C) to form a lower electrode pattern portion 4A including a plurality of lower electrodes 4, a piezoelectric layer pattern portion 5A including a plurality of piezoelectric layers 5, and an upper electrode pattern portion 6A including a plurality of upper electrodes 6 (see FIG. 3). This forms a structure 1A including a plurality of piezoelectric elements 1 (see FIG. 3).

[0037] In the sixth step, the structure 1A is diced with a dicing blade 200 (see FIG. 3 ) to separate the structure 1A into individual piezoelectric elements 1. In the structure 1A, the metal substrate 2A and the alumina layer 3A are present in the dicing lane, but the lower electrode pattern portion 4A, the piezoelectric layer pattern portion 5A, and the upper electrode pattern portion 6A are not present. The thickness H2 of the dicing blade 200 is smaller than the first distance L1 between two adjacent lower electrodes 4 sandwiching the dicing lane in the structure 1A. The thickness H2 of the dicing blade 200 is also smaller than the second distance L2 between two adjacent piezoelectric layers 5 sandwiching the dicing lane in the structure 1A. The thickness H2 of the dicing blade 200 is also smaller than the third distance L3 between two adjacent upper electrodes 6 sandwiching the dicing lane in the structure 1A. As a result, in the sixth step, the relationship of thickness H2 of dicing blade 200<first distance L1<second distance L2<third distance L3 is satisfied.

[0038] According to the manufacturing method of the piezoelectric element 1, cracking and chipping of the lower electrode 4, the piezoelectric layer 5, and the upper electrode 6 are unlikely to occur in the sixth step. Therefore, the manufacturing method of the piezoelectric element 1 can improve the manufacturing yield. Furthermore, with the piezoelectric element 1, since it is possible to prevent a handling tool from coming into contact with the lower electrode 4, the piezoelectric layer 5, and the upper electrode 6 during handling, it is possible to prevent damage to the lower electrode 4, the piezoelectric layer 5, and the upper electrode 6. Therefore, the piezoelectric element 1 allows the piezoelectric layer 5 to be made thinner than a bulk-type piezoelectric element.

[0039] In the sixth step, the structure 1A is diced with a dicing blade 200, but the method is not limited to using the dicing blade 200. Laser dicing may also be performed, in which laser light is irradiated along the dicing lanes of the structure 1A to dice it. In either the method using the dicing blade 200 or laser dicing, the first screen printing mask used in the second step, the metal mask used in the third step, and the second screen printing mask used in the fourth step are designed so that the width dimension of the dicing lane is wider than the cutting width (maximum width) due to dicing.

[0040] (2.2) Ultrasonic Transducer The ultrasonic transducer 100 according to the first embodiment will be described in more detail below with reference to FIGS.

[0041] The ultrasonic transducer 100 is configured to be capable of both transmitting (transmitting) and receiving (receiving) ultrasonic waves. The ultrasonic transducer 100 is used, for example, as an ultrasonic sensor mounted on a vehicle such as an automobile to detect objects (such as obstacles) around the vehicle. The ultrasonic sensor includes, for example, the ultrasonic transducer 100, a driving circuit, and a signal processing circuit. The ultrasonic sensor is, for example, a time-of-flight (TOF) ultrasonic sensor. The driving circuit applies an electrical signal to the piezoelectric element 1 of the ultrasonic transducer 100 to drive the piezoelectric element 1 to transmit ultrasonic waves from the ultrasonic transducer 100. The signal processing circuit processes the electrical signal output from the piezoelectric element 1 when the ultrasonic transducer 100 receives reflected ultrasonic waves. The signal processing circuit detects, for example, at least one of the presence or absence of an object within the detection area of ​​the ultrasonic sensor and the distance from the ultrasonic transducer 100 to the object. The ultrasonic transducer 100 of the ultrasonic sensor is attached, for example, to the bumper of the automobile. When the ultrasonic transducer 100 is used as an ultrasonic sensor for an automobile, the ultrasonic transducer 100 is installed so that, for example, the X-axis direction (left-right direction in FIG. 4 ) is the vertical direction, the Y-axis direction (up-down direction in FIG. 4 ) is the horizontal direction, and the Z-axis direction (direction perpendicular to the paper surface in FIG. 4 ) is the detection direction (direction of transmitting and receiving ultrasonic waves). Note that the mounting orientation of the ultrasonic transducer 100 can be changed as appropriate depending on, for example, the application of the ultrasonic transducer 100. Note that the ultrasonic transducer 100 may include at least one of a drive circuit and a signal processing circuit.

[0042] (2.2.1) Case In the case 101, the bottom plate portion 102 and the tube portion 103 are integrally formed. The case 101 has a cylindrical shape with a bottom. In a plan view, the outer edge of the case 101 is circular. As shown in FIG. 5 , the diaphragm portion 120 has an upper surface 121 and a lower surface 122. The thickness of the diaphragm portion 120 is, for example, 0.3 mm to 1.0 mm, for example, 0.9 mm. In a plan view, the outer diameter of the case 101 is, for example, 14 mm, but is not limited to this, and may be, for example, 15.5 mm. Furthermore, the length of the case 101 in the Z-axis direction is, for example, 9 mm, but is not limited to this. In the case 101, the lower surface 122 of the diaphragm portion 120 forms the ultrasonic wave transmitting and receiving surface.

[0043] The material of the case 101 is, for example, an aluminum alloy, but is not limited to this and may be, for example, a magnesium alloy, stainless steel, a titanium alloy, or an engineering plastic.

[0044] 4, in a plan view, the diaphragm portion 120 has a shape in which a first maximum length R1 in a first direction (X-axis direction) is longer than a second maximum length R2 in a second direction (Y-axis direction). This allows the ultrasonic transducer 100 to have a narrower directivity angle in the X-axis direction than in the Y-axis direction. Note that the first maximum length R1 is 12.6 mm and the second maximum length R2 is 8 mm, but these values ​​are not limited to these.

[0045] (2.2.2) Bonding Section As shown in Fig. 5, the bonding section 105 is interposed between the lower surface 22 of the metal substrate 2 of the piezoelectric element 1 and the upper surface 121 of the diaphragm section 120. The material of the bonding section 105 is, for example, a resin-based adhesive, a conductive bonding material, or a DAF (Die Attach Film). The resin-based adhesive includes, for example, an epoxy adhesive. The conductive bonding material includes, for example, a conductive paste (silver paste, etc.).

[0046] (2.2.3) First lead wire, second lead wire, first conductive joint, second conductive joint In the ultrasonic transducer 100, the first lead wire 141 constitutes a first conductive member connected to the lower electrode 4 of the piezoelectric element 1, and the second lead wire 142 constitutes a second conductive member connected to the upper electrode 6 of the piezoelectric element 1. A first end of the first lead wire 141 is joined to the lower electrode 4 by a first conductive joint 131 and is electrically connected to the lower electrode 4. A first end of the second lead wire 142 is joined to the upper electrode 6 by a second conductive joint 132 and is electrically connected to the upper electrode 6.

[0047] The first lead wire 141 and the second lead wire 142 are flexible electric wires. A portion of the first lead wire 141 and a portion of the second lead wire 142 are led out of the case 101. The second ends of the first lead wire 141 and the second lead wire 142 are connected to, for example, a drive circuit and a signal processing circuit included in the ultrasonic sensor.

[0048] The material of the first conductive joint 131 and the second conductive joint 132 includes, for example, solder.

[0049] In the ultrasonic sensor, when the ultrasonic transducer 100 is used to transmit (transmit) ultrasonic waves, the ultrasonic transducer 100 is connected to a drive circuit. In the ultrasonic sensor, when the ultrasonic transducer 100 is used to receive (receive) ultrasonic waves, the ultrasonic transducer 100 is connected to a signal processing circuit.

[0050] (2.2.4) Sound-Absorbing Member The sound-absorbing member 150 is disposed above the piezoelectric element 1 inside the case 101. The material of the sound-absorbing member 150 includes, for example, a foam. The foam includes, for example, a urethane-based foam and a silicone foam.

[0051] (2.2.5) Sealing Part The sealing part 160 is disposed on the sound absorbing member 150 inside the case 101. The material of the sealing part 160 includes, for example, silicone resin.

[0052] (3) Effects (3.1) Piezoelectric Element The piezoelectric element 1 according to the first embodiment includes a metal substrate 2 containing iron, chromium, and aluminum. In the piezoelectric element 1 according to the first embodiment, in a plan view, the outer edge 40 (first outer edge) of the lower electrode 4 is located inside the outer edge 20 (second outer edge) of the metal substrate 2, the outer edge 50 (third outer edge) of the piezoelectric layer 5 is located inside the outer edge 40 of the lower electrode 4, and the outer edge 60 (fourth outer edge) of the upper electrode 6 is located inside the outer edge 50 (third outer edge) of the piezoelectric layer 5. This allows the piezoelectric element 1 according to the first embodiment to achieve a higher operating frequency (resonance frequency). More specifically, the piezoelectric element 1 according to the first embodiment allows the piezoelectric layer 5 to be made thinner, thereby enabling the resonant frequency of the piezoelectric element 1 to be increased and the drive frequency to be increased.

[0053] Furthermore, the piezoelectric element 1 according to embodiment 1 includes an alumina layer 3 interposed between the lower electrode 4 and the metal substrate 2, and the upper surface 31 of the alumina layer 3 includes a portion of the surface of the multiple scale-like particles of the alumina layer 3, thereby making it possible to suppress peeling of the lower electrode 4.

[0054] In the piezoelectric element 1 according to the first embodiment, the alumina layer 3 covers the entire upper surface 21 of the metal substrate 2, which enables improved piezoelectric characteristics. More specifically, in the piezoelectric element 1 according to the first embodiment, thermal diffusion between the metal substrate 2 and the piezoelectric layer 5 during manufacturing can be suppressed, enabling improved piezoelectric characteristics.

[0055] (3.2) Ultrasonic Transducer The ultrasonic transducer 100 according to the first embodiment includes a piezoelectric element 1 and a diaphragm portion 120 bonded to the metal substrate 2 of the piezoelectric element 1, thereby enabling the operating frequency (resonance frequency) of the piezoelectric element 1 to be increased. This allows the ultrasonic transducer 100 to have a higher driving frequency for the piezoelectric element 1, thereby enabling the ultrasonic beam angle to be narrower. Therefore, for example, when an ultrasonic sensor including the ultrasonic transducer 100 is installed and used in an automobile, it is possible to prevent ultrasonic waves transmitted from the ultrasonic transducer 100 from being incident on the road surface, curbstones, etc., and to prevent reflected waves from the road surface, curbstones, etc. from being received by the ultrasonic transducer 100. This improves the S / N ratio of the ultrasonic sensor, thereby enabling the distance at which an object can be detected to be longer.

[0056] (Embodiment 2) A piezoelectric element 1a according to embodiment 2 will be described with reference to Figures 6 and 7, and then an ultrasonic transducer 100a including the piezoelectric element 1a will be described with reference to Figures 8 and 9. With regard to the piezoelectric element 1a according to embodiment 2, components similar to those of the piezoelectric element 1 according to embodiment 1 (see Figures 1 and 2) will be assigned the same reference numerals and descriptions thereof will be omitted. Furthermore, with regard to the ultrasonic transducer 100a according to embodiment 2, components similar to those of the ultrasonic transducer 100 according to embodiment 1 (see Figures 4 and 5) will be assigned the same reference numerals and descriptions thereof will be omitted as appropriate.

[0057] (1) Configuration (1.1) Piezoelectric Element The piezoelectric element 1a according to the second embodiment differs from the piezoelectric element 1 according to the first embodiment (see FIGS. 1 and 2) in that it further includes a terminal electrode 7 and a wiring portion 8, as shown in FIGS. 6 and 7 .

[0058] The terminal electrode 7 is provided on the piezoelectric layer 5 and is spaced apart from the upper electrode 6. More specifically, the terminal electrode 7 is provided on the upper surface 51 of the piezoelectric layer 5 and is spaced apart from the upper electrode 6 in the X-axis direction. A gap 9 is formed between the terminal electrode 7 and the upper electrode 6. The portion of the terminal electrode 7 connected to the wiring portion 8 is not surrounded by the upper electrode 6 in the X-axis direction, for example. In the piezoelectric element 1a, the terminal electrode 7 is disposed on the upper surface 51 of the piezoelectric layer 5 at a first end in the direction along the X-axis. Here, in a planar view, the terminal electrode 7 is located inside the outer edge 50 of the piezoelectric layer 5. In a planar view, the terminal electrode 7 has, for example, a rectangular shape, but is not limited thereto and may have a circular shape.

[0059] The thickness of the terminal electrode 7 is the same as the thickness of the upper electrode 6. Here, "the thickness of the terminal electrode 7 is the same as the thickness of the upper electrode 6" is not limited to the case where they are exactly the same, but also includes the case where the thickness of the terminal electrode 7 is within a range of 95% to 105% of the thickness of the upper electrode 6.

[0060] Furthermore, in the piezoelectric element 1a, the terminal electrode 7 and the upper electrode 6 have the same thickness, so that the first height from the upper surface 21 of the metal substrate 2 to the upper surface 71 of the terminal electrode 7 is the same as the second height from the upper surface 21 of the metal substrate 2 to the upper surface 61 of the upper electrode 6. Here, the phrase "the first height is the same as the second height" is not limited to being strictly the same, but also includes cases where the first height is within a range of 95% to 105% of the second height.

[0061] The material of the terminal electrode 7 is the same as the material of the upper electrode 6, and contains, for example, Ag and Pd.

[0062] The wiring portion 8 is provided across the upper surface 41 of the lower electrode 4, the side surface 53 of the piezoelectric layer 5, and the upper surface 51 of the piezoelectric layer 5, and connects the lower electrode 4 and the terminal electrode 7. Therefore, the wiring portion 8 includes a portion 81 formed on the upper surface 51 of the piezoelectric layer 5. The wiring portion 8 is not formed on the lower surface 52 of the piezoelectric layer 5.

[0063] The material of the wiring portion 8 is the same as the material of the upper electrode 6 and the material of the terminal electrode 7, and contains, for example, Ag and Pd.

[0064] 6, in a plan view, the wiring portion 8 is located inside the outer edge 20 of the metal substrate 2. In a plan view, the width of the wiring portion 8 in the Y-axis direction is narrower than the width of the terminal electrode 7 in the Y-axis direction. As shown in Fig. 7, in a side view from the Y-axis direction, the wiring portion 8 is inverted L-shaped.

[0065] In the piezoelectric element 1a, the terminal electrodes 7 and the wiring portion 8 are formed by screen printing in the same process as the upper electrode 6.

[0066] The manufacturing method of piezoelectric element 1a is substantially the same as the manufacturing method of piezoelectric element 1, except that a screen mask having openings for forming upper electrode 6, openings for forming terminal electrodes 7, and openings for forming wiring portion 8 is used instead of the screen mask used in the fourth step of the manufacturing method of piezoelectric element 1. In the fourth step of the manufacturing method of piezoelectric element 1a, an upper electrode material portion, a terminal electrode material portion, and a wiring material portion, which are the basis of upper electrode 6, terminal electrode 7, and wiring portion 8, respectively, are formed by moving a squeegee in the direction of arrow B1 in Figures 6 and 7. Therefore, in the manufacturing method of piezoelectric element 1a, the third pattern portion includes a plurality of terminal electrode material portions and a plurality of wiring material portions in addition to a plurality of upper electrode material portions.

[0067] In the method for manufacturing the piezoelectric element 1a, the first pattern portion, the second pattern portion, and the third pattern portion are fired at a predetermined firing temperature (e.g., 875°C) to form a lower electrode pattern portion 4A (see FIG. 3) including a plurality of lower electrodes 4, a piezoelectric layer pattern portion 5A (see FIG. 3) including a plurality of piezoelectric layers 5, an upper electrode pattern portion 6A (see FIG. 3) including a plurality of upper electrodes 6, a terminal electrode pattern portion including a plurality of terminal electrodes 7, and a wiring pattern portion including a plurality of wiring portions 8. This forms a structure including a plurality of piezoelectric elements 1a.

[0068] (1.2) Ultrasonic Transducer The ultrasonic transducer 100a according to the second embodiment differs from the ultrasonic transducer 100 according to the first embodiment (see FIGS. 4 and 5) in that the first conductive joint 131a is disposed on the terminal electrode 7, as shown in FIGS. 8 and 9.

[0069] In the ultrasonic transducer 100a according to the second embodiment, the first lead wire 141 and the terminal electrode 7 are joined by a first conductive joint 131a. The material of the first conductive joint 131a includes, for example, solder.

[0070] (2) Effects (2.1) Piezoelectric Element The piezoelectric element 1a according to the second embodiment includes a metal substrate 2 containing iron, chromium, and aluminum. In the piezoelectric element 1a according to the second embodiment, in a plan view, the outer edge 40 of the lower electrode 4 is located inside the outer edge 20 of the metal substrate 2, the outer edge 50 of the piezoelectric layer 5 is located inside the outer edge 40 of the lower electrode 4, the outer edge 60 of the upper electrode 6 is located inside the outer edge 50 of the piezoelectric layer 5, and the terminal electrode 7 and the wiring portion 8 are located inside the outer edge 20 of the metal substrate 2. As a result, the piezoelectric element 1a according to the second embodiment can achieve a higher operating frequency (resonance frequency). More specifically, like the piezoelectric element 1 according to the first embodiment, the piezoelectric element 1a according to the second embodiment can achieve a thinner piezoelectric layer 5, thereby enabling a higher resonant frequency of the piezoelectric element 1a and a higher drive frequency.

[0071] Furthermore, the piezoelectric element 1a is provided with terminal electrodes 7 and wiring portions 8, and since the terminal electrodes 7 and wiring portions 8 are located inside the outer edge 20 of the metal substrate 2, there is no need to form folded electrodes, which makes manufacturing easier and makes it possible to prevent damage to the terminal electrodes 7 and wiring portions 8 when handling the piezoelectric element 1a.

[0072] Furthermore, in the piezoelectric element 1a, the first height from the upper surface 21 of the metal substrate 2 to the upper surface 71 of the terminal electrode 7 is the same as the second height from the upper surface 21 of the metal substrate 2 to the upper surface 61 of the upper electrode 6, which makes it easy to mount the piezoelectric element 1a on, for example, a flexible printed wiring board including a first lead electrode (first conductor portion) and a second lead electrode (second conductor portion), and also makes it possible to improve connection reliability. When mounting the piezoelectric element 1a on a flexible printed wiring board, the first lead electrode (first conductor portion) and the second lead electrode (second conductor portion) included in the flexible printed wiring board are joined to the terminal electrode 7 and the upper electrode 6 of the piezoelectric element 1a by first conductive joint portions 131a and second conductive joint portions 132, instead of the first lead wire 141 and the second lead wire 142.

[0073] Furthermore, in the piezoelectric element 1a according to the second embodiment, the terminal electrodes 7 are located inside the outer edge 50 of the piezoelectric layer 5 in a plan view. The wiring portion 8 includes a portion 81 provided on the upper surface 51 of the piezoelectric layer 5. This allows the piezoelectric element 1a according to the second embodiment to have an improved uniformity in the thickness of the terminal electrodes 7.

[0074] Furthermore, the piezoelectric element 1a according to embodiment 2 can realize a configuration in which the terminal electrode 7 connected to the lower electrode 4 is arranged on the upper surface 51 of the piezoelectric layer 5 without adopting the folded electrode structure disclosed in Patent Document 1.

[0075] (2.2) Ultrasonic Transducer The ultrasonic transducer 100a according to the second embodiment includes a piezoelectric element 1a and a diaphragm portion 120 bonded to the metal substrate 2 of the piezoelectric element 1a, thereby enabling the operating frequency (resonance frequency) of the piezoelectric element 1a to be increased. This allows the ultrasonic transducer 100a to achieve a higher drive frequency for the piezoelectric element 1a, thereby narrowing the beam angle of the ultrasonic waves. Therefore, for example, when an ultrasonic sensor including the ultrasonic transducer 100a is installed in an automobile, the ultrasonic waves transmitted from the ultrasonic transducer 100a can be prevented from being reflected by the road surface. This improves the S / N ratio of the ultrasonic sensor, thereby enabling the distance at which an object can be detected to be increased.

[0076] Furthermore, in the ultrasonic transducer 100a according to the second embodiment, a first height from the upper surface 21 of the metal substrate 2 to the upper surface 71 of the terminal electrode 7 in the piezoelectric element 1a is the same as a second height from the upper surface 21 of the metal substrate 2 to the upper surface 61 of the upper electrode 6. As a result, in the ultrasonic transducer 100a according to the second embodiment, when, for example, a first lead electrode (first conductor portion) and a second lead electrode (second conductor portion) of a flexible printed wiring board are adopted as the first and second conductive members instead of the first lead wire 141 and the second lead wire 142, mounting on the flexible printed wiring board becomes easier and connection reliability can be improved.

[0077] (Embodiment 3) A piezoelectric element 1b according to embodiment 3 will be described with reference to Fig. 10. With regard to the piezoelectric element 1b according to embodiment 3, components similar to those of the piezoelectric element 1 according to embodiment 1 (see Figs. 1 and 2) are denoted by the same reference numerals, and descriptions thereof will be omitted as appropriate.

[0078] (1) Configuration The piezoelectric element 1b according to the third embodiment differs from the piezoelectric element 1 according to the first embodiment in that the piezoelectric layer 5 has an opening 54 that exposes a portion of the upper surface 41 of the lower electrode 4.

[0079] The opening 54 in the piezoelectric layer 5 is formed along the thickness direction of the piezoelectric layer 5. In a plan view, the opening shape of the opening 54 is rectangular, but is not limited to this and may be circular, for example. In the piezoelectric element 1b, a part (portion 411b) of the lower electrode 4 exposed by the opening 54 in the piezoelectric layer 5 constitutes a terminal portion.

[0080] The manufacturing method of the piezoelectric element 1b is substantially the same as the manufacturing method of the piezoelectric element 1, and the opening 54 in the piezoelectric layer 5 can be formed by changing the pattern of the screen mask used in the third step in the manufacturing method of the piezoelectric element 1.

[0081] (2) Effects The piezoelectric element 1b according to the third embodiment includes a metal substrate 2 containing iron, chromium, and aluminum. In the piezoelectric element 1b according to the third embodiment, in a plan view, the outer edge 40 of the lower electrode 4 is located inside the outer edge 20 of the metal substrate 2, the outer edge 50 of the piezoelectric layer 5 is located inside the outer edge 40 of the lower electrode 4, and the outer edge 60 of the upper electrode 6 is located inside the outer edge 50 of the piezoelectric layer 5. This allows the piezoelectric element 1b according to the third embodiment to achieve a higher operating frequency (resonance frequency). More specifically, like the piezoelectric element 1 according to the first embodiment, the piezoelectric element 1b according to the third embodiment can achieve a thinner piezoelectric layer 5, thereby enabling the resonant frequency of the piezoelectric element 1b to be increased, thereby enabling a higher drive frequency.

[0082] Furthermore, in the piezoelectric element 1b according to the third embodiment, the piezoelectric layer 5 has an opening 54 that exposes a portion of the upper surface 41 of the lower electrode 4, so that the portion of the upper surface 41 of the lower electrode 4 can also be used as a terminal portion. This makes it possible to narrow the area that functions as a terminal portion in the piezoelectric element 1b according to the third embodiment compared to the piezoelectric element 1 according to the first embodiment, and makes it possible to suppress variations in characteristics during use.

[0083] (Embodiment 4) An ultrasonic transducer 100c according to embodiment 4 will be described below with reference to Fig. 12. Note that, with respect to the ultrasonic transducer 100c according to embodiment 4, components similar to those of the ultrasonic transducer 100 according to embodiment 1 are denoted by the same reference numerals, and descriptions thereof will be omitted as appropriate.

[0084] The ultrasonic transducer 100c according to the fourth embodiment includes a conical diaphragm portion 120c with an open bottom, instead of the diaphragm portion 120 in the ultrasonic transducer 100 according to the first embodiment.

[0085] Moreover, the ultrasonic transducer 100c according to the fourth embodiment includes a case 101c instead of the case 101 in the ultrasonic transducer 100 according to the first embodiment.

[0086] In the ultrasonic transducer 100c, a piezoelectric element 1 and a diaphragm portion 120c are housed in a case 101c. The diaphragm portion 120c is bonded to the lower surface 22 of the metal substrate 2 of the piezoelectric element 1. The diaphragm portion 120c is a separate member from the case 101c and is separated from the case 101c.

[0087] The case 101c includes a base 170, a cap 106, and a mesh member 165. The ultrasonic transducer 100c also includes a support portion 180 that protrudes from the base 170 and supports the piezoelectric element 1. The ultrasonic transducer 100c also includes a first conductive joint portion 131 and a second conductive joint portion 132, a first lead wire 141 and a second lead wire 142, and a first lead terminal 191 and a second lead terminal 192.

[0088] The base 170 is disk-shaped and may be made of, for example, an aluminum alloy, but is not limited to this and may be made of, for example, a magnesium alloy, stainless steel, a titanium alloy, or an engineering plastic.

[0089] The cap 106 is cylindrical with a bottom, having a bottom wall 161 and a cylindrical peripheral wall 162, and is fixed to the base 170 so as to cover the piezoelectric element 1 and the vibration plate portion 120c. The material of the cap 106 is, for example, an aluminum alloy, but is not limited to this and may be, for example, a magnesium alloy, stainless steel, a titanium alloy, or engineering plastic.

[0090] The mesh member 165 is disposed in a window hole 163 formed in the bottom wall 161 of the cap 106, and is located in front of the diaphragm portion 120c. The mesh member 165 has a plurality of openings 166 that allow ultrasonic waves to pass through.

[0091] The first lead wire 141 and the second lead wire 142 are flexible electric wires. In the ultrasonic transducer 100c, a first end of the first lead wire 141 is joined and electrically connected to the lower electrode 4 of the piezoelectric element 1 by a first conductive joint 131, and a second end of the first lead wire 141 is joined and electrically connected to a first lead terminal 191. In the ultrasonic transducer 100c, a first end of the second lead wire 142 is joined and electrically connected to the upper electrode 6 of the piezoelectric element 1 by a second conductive joint 132, and a second end of the second lead wire 142 is joined and electrically connected to a second lead terminal 192.

[0092] Each of the first lead terminal 191 and the second lead terminal 192 is pin-shaped. The first lead terminal 191 and the second lead terminal 192 penetrate the base 170 in the thickness direction of the base 170. The first lead terminal 191 and the second lead terminal 192 are electrically insulated from the base 170 by a first insulating portion and a second insulating portion interposed between the first lead terminal 191 and the base 170 and the second lead terminal 192, but this is not limiting. For example, one of the first lead terminal 191 and the second lead terminal 192 may be electrically connected to the base 170.

[0093] The ultrasonic transducer 100c according to the fourth embodiment includes a piezoelectric element 1 and a vibration plate portion 120c bonded to the metal substrate 2 of the piezoelectric element 1, and therefore it is possible to increase the operating frequency (resonance frequency) of the piezoelectric element 1. This makes it possible to increase the drive frequency of the piezoelectric element 1 in the ultrasonic transducer 100c, and to narrow the directivity angle of the ultrasonic waves.

[0094] (Modifications) Embodiments 1 to 4 are merely examples of various embodiments of the present disclosure. Various modifications of Embodiments 1 to 4 can be made depending on the design and the like as long as the object of the present disclosure can be achieved.

[0095] For example, the outer edge 20 of the metal substrate 2 in plan view is not limited to a rectangular shape, but may be, for example, a square shape, a circle shape, an ellipse shape, or an oval shape.

[0096] The metal substrate 2 does not necessarily need to contain aluminum, but may contain at least iron and chromium.

[0097] Furthermore, it is not essential that the piezoelectric elements 1, 1a, and 1b include the alumina layer 3. In other words, the piezoelectric elements 1, 1a, and 1b may not include the alumina layer 3, and the lower electrode 4 may be provided directly on the metal substrate 2.

[0098] The material of the piezoelectric layer 5 is a material containing Pb, Zr, Zn, Nb, and O, for example, Pb １．０１５ Zr ０．４４ (Zn １／３ Nb ２／３ ) ０．１０ O ３．０１５ including, but not limited to, lead zirconate titanate (PZT), barium titanate, lead magnesium niobate (PMN), KNbO ３ , NaNbO ３ or K ０．５ Na ０．５ NbO ３ may be.

[0099] In addition, in the piezoelectric elements 1, 1a, and 1b, the piezoelectric layer 5 is provided directly on the lower electrode 4, but this is not limiting, and the piezoelectric layer 5 may be provided on the lower electrode 4 via a buffer layer. The buffer layer includes, for example, at least a part of the material of the lower electrode 4 and at least a part of the material of the piezoelectric layer 5.

[0100] Furthermore, in the piezoelectric element 1a, the wiring portion 8 is not limited to a configuration in which it is provided across the upper surface 41 of the lower electrode 4, the side surface 53 of the piezoelectric layer 5, and the upper surface 51 of the piezoelectric layer 5. For example, the wiring portion 8 only needs to connect the lower electrode 4 and the terminal electrode 7 and not be provided on the lower surface 52 of the piezoelectric layer 5, and only needs to be provided across at least the upper surface 41 of the lower electrode 4 and the side surface 53 of the piezoelectric layer 5.

[0101] Furthermore, it is not essential that the piezoelectric element 1b have a narrow portion between the portion of the outer edge 50 of the piezoelectric layer 5 that is close to the opening 54 and the opening 54 of the piezoelectric layer 5, and the opening 54 may be open upward and to the sides.

[0102] In the ultrasonic transducers 100, 100a, the first conductive member and the second conductive member are not limited to the first lead wire 141 and the second lead wire 142, but may be, for example, a first lead electrode (first conductor portion) and a second lead electrode (second conductor portion) included in the conductor pattern portion of a flexible printed wiring board.

[0103] Furthermore, in the ultrasonic transducer 100c, the first and second conductive members are not limited to the first lead wire 141 and the second lead wire 142, but may be, for example, a first conductive wire and a second conductive wire.

[0104] Moreover, the ultrasonic transducer 100c may include a piezoelectric element 1a or a piezoelectric element 1b instead of the piezoelectric element 1.

[0105] (Aspects) Based on the above-described first to fourth embodiments, the present specification discloses the following aspects.

[0106] A piezoelectric element (1; 1a; 1b) according to a first aspect includes a metal substrate (2), a lower electrode (4), a piezoelectric layer (5), and an upper electrode (6). The metal substrate (2) contains at least iron and chromium. The lower electrode (4) is provided on the metal substrate (2). The piezoelectric layer (5) is provided on the lower electrode (4). The upper electrode (6) is provided on the piezoelectric layer (5). In a planar view, a first outer edge (outer edge 40) of the lower electrode (4) is located inside a second outer edge (outer edge 20) of the metal substrate (2). In a planar view, a third outer edge (outer edge 50) of the piezoelectric layer (5) is located inside a first outer edge (outer edge 40) of the lower electrode (4). In a planar view, a fourth outer edge (outer edge 60) of the upper electrode (6) is located inside a third outer edge (outer edge 50) of the piezoelectric layer (5).

[0107] According to the piezoelectric element (1; 1a; 1b) of the first aspect, it is possible to increase the operating frequency of the piezoelectric element (1; 1a; 1b).

[0108] The piezoelectric element (1; 1a; 1b) according to the second aspect is the first aspect, and further includes an alumina layer (3). The alumina layer (3) is interposed between the metal substrate (2) and the lower electrode (4). The metal substrate (2) further includes aluminum. The upper surface (31) of the alumina layer (3) includes a portion of the surface of the multiple scale-like particles of the alumina layer (3).

[0109] The piezoelectric element (1; 1a; 1b) according to the second aspect can suppress peeling of the lower electrode (4).

[0110] In the piezoelectric element (1; 1a; 1b) according to the third embodiment, the alumina layer (3) covers the entire upper surface (21) of the metal substrate (2) in the second embodiment.

[0111] In the piezoelectric element (1; 1a; 1b) according to the third aspect, it is possible to improve the piezoelectric characteristics.

[0112] A piezoelectric element (1a) according to a fourth aspect is any one of the first to third aspects, further comprising a terminal electrode (7) and a wiring portion (8). The terminal electrode (7) is provided on the piezoelectric layer (5) and is spaced apart from the upper electrode (6). The wiring portion (8) is provided across the upper surface (41) of the lower electrode (4) and the side surface (53) of the piezoelectric layer (5), connecting the lower electrode (4) and the terminal electrode (7). In a plan view, the wiring portion (8) is located inside a second outer edge (outer edge 20) of the metal substrate (2).

[0113] The piezoelectric element (1a) according to the fourth aspect can be easily mounted on a flexible printed wiring board and can improve connection reliability.

[0114] In the piezoelectric element (1a) according to the fifth aspect, in the fourth aspect, the terminal electrode (7) is located inside the third outer edge (outer edge 50) of the piezoelectric layer (5) in a plan view. The wiring portion (8) includes a portion (81) provided on the upper surface (51) of the piezoelectric layer (5).

[0115] In the piezoelectric element (1a) according to the fifth aspect, it is possible to improve the uniformity of the thickness of the terminal electrodes (7).

[0116] In the piezoelectric element (1b) according to the sixth aspect, in any one of the first to third aspects, the piezoelectric layer (5) has an opening (54) that exposes a part of the upper surface (41) of the lower electrode (4).

[0117] In the piezoelectric element (1b) according to the sixth aspect, a part of the upper surface (41) of the lower electrode (4) constitutes the terminal portion, so that it is possible to narrow the area that functions as the terminal portion, and it is possible to suppress the variation in characteristics during use.

[0118] An ultrasonic transducer (100; 100a; 100c) according to a seventh aspect includes a piezoelectric element (1; 1a; 1b) according to any one of the first to sixth aspects, a vibration plate portion (120; 120c), a first conductive member (first lead wire 141), a second conductive member (second lead wire 142), a first conductive joint portion (131), and a second conductive joint portion (132). The vibration plate portion (120; 120c) is joined to the metal substrate (2) of the piezoelectric element (1; 1a; 1b). The first conductive member (first lead wire 141) is connected to the lower electrode (4) of the piezoelectric element (1; 1a; 1b). The second conductive member (second lead wire 142) is connected to the upper electrode (6) of the piezoelectric element (1; 1a; 1b). The first conductive joint (131) joins the lower electrode (4) and the first conductive member (first lead wire 141). The second conductive joint (132) joins the upper electrode (6) and the second conductive member (second lead wire 142).

[0119] The ultrasonic transducer (100; 100a; 100c) according to the seventh aspect makes it possible to increase the operating frequency of the piezoelectric element (1; 1a; 1b).

[0120] An ultrasonic transducer (100; 100a) according to an eighth aspect is the seventh aspect, further comprising a case (101) that houses the piezoelectric element (1; 1a; 1b). The case (101) has a bottom plate portion (102) and a tubular portion (103). The bottom plate portion (102) is flat. The tubular portion (103) protrudes from the periphery of one surface of the bottom plate portion (102) in the thickness direction of the bottom plate portion (102) and surrounds the piezoelectric element (1; 1a; 1b). The portion of the bottom plate portion (102) surrounded by the tubular portion (103) also serves as a vibration plate portion (120).

[0121] The ultrasonic transducer (100; 100a) according to the eighth aspect can be used, for example, as an ultrasonic sensor that is attached to a vehicle and detects an object outside the vehicle.

[0122] DESCRIPTION OF SYMBOLS 1, 1a, 1b Piezoelectric element 2 Metal substrate 20 Outer edge (second outer edge) 3 Alumina layer 30 Outer edge 31 Upper surface 4 Lower electrode 40 Outer edge (first outer edge) 41 Upper surface 411 Part 5 Piezoelectric layer 50 Outer edge (third outer edge) 51 Upper surface 53 Side surface 54 Opening 6 Upper electrode 60 Outer edge (fourth outer edge) 61 Upper surface 7 Terminal electrode 71 Upper surface 8 Wiring portion 81 Part 9 Gap 100, 100a, 100c Ultrasonic transducer 101, 101c Case 102 Bottom plate portion 103 Cylinder portion 120, 120c Vibration plate portion 131 First conductive joint portion 132 Second conductive joint portion 141 First lead wire (first conductive member) 142 Second lead wire (second conductive member)

Claims

1. A metal substrate containing at least iron and chromium; a lower electrode provided on the metal substrate; a piezoelectric layer provided on the lower electrode; an upper electrode provided on the piezoelectric layer; a first outer edge of the lower electrode is located inside a second outer edge of the metal substrate in a plan view; a third outer edge of the piezoelectric layer is located inside the first outer edge of the lower electrode in the plan view, In the plan view, a fourth outer edge of the upper electrode is located inside the third outer edge of the piezoelectric layer. Piezoelectric element.

2. further comprising an alumina layer interposed between the metal substrate and the lower electrode; The metal substrate further comprises aluminum; the upper surface of the alumina layer includes a portion of the surfaces of the plurality of scale-like particles of the alumina layer; The piezoelectric element according to claim 1 .

3. The alumina layer covers the entire upper surface of the metal substrate. The piezoelectric element according to claim 2 .

4. a terminal electrode provided on the piezoelectric layer and spaced apart from the upper electrode; a wiring portion provided across an upper surface of the lower electrode and a side surface of the piezoelectric layer, connecting the lower electrode and the terminal electrode; In the plan view, the wiring portion is located inside the second outer edge of the metal substrate. The piezoelectric element according to any one of claims 1 to 3.

5. the terminal electrode is located inside the third outer edge of the piezoelectric layer in the plan view, the wiring portion includes a portion provided on an upper surface of the piezoelectric layer, The piezoelectric element according to claim 4.

6. the piezoelectric layer has an opening exposing a portion of an upper surface of the lower electrode; The piezoelectric element according to any one of claims 1 to 3.

7. A piezoelectric element according to any one of claims 1 to 3, a vibration plate portion of the piezoelectric element bonded to the metal substrate; a first conductive member connected to the lower electrode of the piezoelectric element; a second conductive member connected to the upper electrode of the piezoelectric element; a first conductive joint that joins the lower electrode and the first conductive member; a second conductive joint portion joining the upper electrode and the second conductive member, Ultrasonic transducer.

8. The piezoelectric element further includes a case that accommodates the piezoelectric element. The case is A flat bottom plate portion, a cylindrical portion that protrudes from a peripheral portion of one surface of the bottom plate portion in a thickness direction of the bottom plate portion and surrounds the piezoelectric element; A portion of the bottom plate portion surrounded by the cylindrical portion also serves as the diaphragm portion.

8. The ultrasonic transducer of claim 7.