Method for manufacturing an ultrasonic transducer, ultrasonic transducer, and distance measuring device

Abstract

A method for manufacturing an ultrasonic transducer (100) comprises the following steps. A first SOI substrate including: a first silicon film (111); a second silicon film (113); and an intermediate silicon oxide film (112) sandwiched between the first silicon film (111) and the second silicon film (113) is prepared. A piezoelectric element (107) is formed on the first silicon film (111) of the first SOI substrate. A diaphragm (103) is formed by etching the second silicon film (113). A silicon substrate is connected to the second silicon film (113). An opening (205) and a gap (101) are formed in an acoustic resonance structure (100a) including the first SOI substrate and the silicon substrate so as to amplify oscillating sound waves of the diaphragm (103), and the resonance frequencies of the diaphragm (103) and the acoustic resonance structure (100a) are matched.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an ultrasonic transducer, an ultrasonic transducer, and a distance measuring device.

Background Art

[0002] As a distance sensor for applications such as peripheral monitoring of automobiles and transport vehicles or non-contact operation of devices, ultrasonic transducers are used. In generally popular ultrasonic transducers, bulk lead zirconate titanate (PZT: Pb(Zr,Ti)O3) is mainly used as an actuator. However, in an ultrasonic transducer using bulk lead zirconate titanate (PZT) as an actuator, there is a limit to miniaturization due to the machining accuracy of machining. For this reason, MEMS (Micro Electro Mechanical Systems) ultrasonic transducers have been developed as ultrasonic transducers that can be miniaturized.

[0003] The most common structure of a MEMS ultrasonic transducer is a structure using a thin-film diaphragm. Silicon is used as the material of the structure of the MEMS ultrasonic transducer including the diaphragm. The MEMS ultrasonic transducer is processed by semiconductor technology such as deep reactive etching (DRIE). By applying semiconductor technology with high dimensional accuracy to the processing, the diaphragm can be miniaturized compared with conventional products manufactured by machining.

[0004] As a method for improving the sound pressure of an ultrasonic transducer, the application of an acoustic resonance structure is known. For example, Japanese Patent Application Publication No. 2010-515335 (Patent Document 1) describes a sound source tracking device including a MEMS microphone, a cavity in which the MEMS microphone is disposed, an opening on the surface of the microphone housing, and a passage extending from the cavity to the opening. In this sound source tracking device, the dimensions of the passage and the cavity are determined so as to form an acoustic amplifier of a frequency.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the sound source tracking device described in the above publication, a microphone housing provided with a cavity, an opening, and a passage forms an acoustic resonance structure. In order to obtain a large amplification effect of the sound pressure of the ultrasonic transducer using the acoustic resonance structure as described in the above publication, it is necessary to make the resonance frequency of the diaphragm as close as possible to the resonance frequency of the acoustic resonance structure. Therefore, with the miniaturization of the diaphragm, high dimensional accuracy is also required for the acoustic resonance structure. In particular, in a miniaturized MEMS ultrasonic transducer, it is necessary to manufacture the dimensions of the acoustic resonance structure with high precision within several tens of micrometers. Therefore, when the MEMS ultrasonic transducer is stored in the acoustic resonance structure, a precise assembly process is required.

[0007] The present disclosure has been made in view of the above problems, and an object thereof is to provide a method for manufacturing an ultrasonic transducer, an ultrasonic transducer, and a distance measuring device that can manufacture a diaphragm and an acoustic resonance structure with high dimensional accuracy and obtain a large amplification effect by matching the resonance frequencies of the diaphragm and the acoustic resonance structure.

Means for Solving the Problems

[0008] The manufacturing method of the ultrasonic transducer of the present disclosure includes the following steps. A first SOI substrate including a first silicon film, a second silicon film, and an intermediate silicon oxide film sandwiched between the first silicon film and the second silicon film is prepared. A piezoelectric element is formed on the first silicon film of the first SOI substrate. An etching process is performed on the second silicon film and the intermediate silicon oxide film of the first SOI substrate to form a diaphragm of the first silicon film. A silicon substrate is connected to the second silicon film. An opening and a gap are formed in an acoustic resonance structure including the first SOI substrate and the silicon substrate so as to amplify the vibration sound wave of the diaphragm, and the resonance frequencies of the diaphragm and the acoustic resonance structure are matched. The step of forming the diaphragm includes the step of forming a first support on the second silicon film. The step of matching the resonance frequency includes forming a groove in the silicon substrate to form a movable plate and a second support connected to the first support, and moving the movable plate relative to the second support to change the volume of the gap, thereby matching the resonance frequencies of the diaphragm and the acoustic resonance structure.

Advantages of the Invention

[0009] According to the manufacturing method of the ultrasonic transducer of the present disclosure, a diaphragm and an acoustic resonance structure can be manufactured with high dimensional accuracy, and a large amplification effect can be obtained by matching the resonance frequencies of the diaphragm and the acoustic resonance structure.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments will be described with reference to the drawings. In the following, the same or corresponding parts are denoted by the same reference numerals, and duplicate explanations will not be repeated.

[0012] Embodiment 1. With reference to FIGS. 1 and 2, the structure of the ultrasonic transducer 100 according to Embodiment 1 will be described. FIG. 1 is a perspective view of the ultrasonic transducer 100 according to Embodiment 1. FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1.

[0013] The ultrasonic transducer 100 according to Embodiment 1 is a MEMS (Micro Electro Mechanical Systems) ultrasonic transducer. That is, the ultrasonic transducer 100 is integrally formed by MEMS.

[0014] The ultrasonic transducer 100 mainly includes a first support 102, a diaphragm 103, a piezoelectric element 107 including a lower electrode 104, a piezoelectric thin film 105, and an upper electrode 106, a second support 203, and a movable plate 204. The piezoelectric element 107 is disposed on the diaphragm 103. An opening 205 is provided in the movable plate 204. The opening 205 is disposed at the center of the movable plate 204 in a plan view. The opening 205 is formed so as to penetrate up to the gap 101. The opening 205 is configured in a columnar shape. The opening 205 communicates with the gap 101. The gap 101 is surrounded by the first support 102, the diaphragm 103, the second support 203, and the movable plate 204. The gap 101 is configured in a substantially columnar shape. The volumes of the opening 205 and the gap 101 are the cavity volume.

[0015] For the materials of the structures of the first support 102, the diaphragm 103, the second support 203, and the movable plate 204, silicon (Si), to which semiconductor manufacturing technology can be easily applied and which has excellent mechanical properties as an elastic material, is desirable. In the present embodiment, the first support 102 and the diaphragm 103 are made of SOI (Silicon On Insulator). The second support 203 and the movable plate 204 are made of a silicon substrate. The acoustic resonance structure 100a includes the first support 102 and the diaphragm 103 made of an SOI substrate, and the second support 203 and the movable plate 204 made of a silicon substrate. The piezoelectric element 107 is attached to the acoustic resonance structure 100a. The diaphragm 103 made of an SOI substrate is connected to the first support 102. The second support 203 made of a silicon substrate is connected to the first support 102 on the side opposite to the diaphragm 103 with respect to the first support 102. The movable plate 204 made of a silicon substrate is connected to the second support 203 so as to face the diaphragm 103. The piezoelectric element 107 is connected to the diaphragm 103 of the acoustic resonance structure 100a. The opening 205 and the gap 101 are formed so as to match the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a. For the materials of the lower electrode 104 and the upper electrode 106, a laminated film of a titanium (Ti) film and a platinum (Pt) film, which are generally used for piezoelectric elements, is desirable. However, other laminated films may be used as long as they have sufficient conductivity as electrodes and can ensure good adhesion to the substrate or the like. Further, an oxide electrode film such as a strontium oxide (SrO) film, which is said to have an effect of reducing polarization fatigue, may be interposed between the upper electrode 106 and the piezoelectric thin film 105. For the piezoelectric thin film 105, materials such as lead zirconate titanate (PZT:Pb(Zr,Ti)O3), aluminum nitride (AlN), or potassium sodium niobate (KNN:(K,Na)NbO3) are used, for example.

[0016] Subsequently, the operation of the ultrasonic transducer 100 according to Embodiment 1 will be described. When a voltage is applied between the lower electrode 104 and the upper electrode 106, the piezoelectric thin film 105 contracts. Due to the contraction of the piezoelectric thin film 105, the diaphragm 103 bends. When a voltage is applied at a frequency close to the resonance frequency of the diaphragm 103, the diaphragm 103 resonates. As a result, the ultrasonic transducer 100 can generate ultrasonic waves.

[0017] Also, when the ultrasonic transducer 100 is used as an ultrasonic sensor, the vibration of the diaphragm 103 vibrated by ultrasonic waves is acquired as a voltage signal by the piezoelectric element 107.

[0018] The dimensions of the gap 101 and the opening 205 are set so that the resonance frequency of the diaphragm 103 and the resonance frequency of the acoustic resonance structure 100a approach each other.

[0019] The resonance frequency f of the acoustic resonance structure 100a h is represented by the following formula (1) using the diameter D of the gap 101, the diameter d of the opening 205, the length l1 of the opening 205, the length l2 of the gap, the opening correction a, the speed of sound c, and the area S of the opening 205. Note that the area S of the opening 205 m and the volume V of the gap 101 c are used. The area S of the opening 205 m is represented by the following formula (2). The volume V of the gap c is represented by the following formula (3).

[0020]

Equation

[0021]

Equation

[0022]

Equation

[0023] In this way, by setting the dimensions of the gap 101 and the opening 205 such that the resonance frequency of the diaphragm 103 and the resonance frequency of the acoustic resonance structure 100a approach each other, the sound pressure of the sound generated by the vibration of the diaphragm 103 can be amplified by acoustic resonance.

[0024] Further, when the ultrasonic transducer 100 is used as an ultrasonic sensor, by amplifying the sound pressure of the received ultrasonic waves by acoustic resonance, the diaphragm 103 can be vibrated more greatly. As a result, since the strain of the piezoelectric element 107 disposed on the diaphragm 103 increases, a larger signal can be obtained.

[0025] Here, in order to match the resonance frequency of the diaphragm 103 and the resonance frequency of the acoustic resonance structure, an adjustment mechanism is necessary. In the ultrasonic transducer 100 according to Embodiment 1, the acoustic resonance frequency can be adjusted by changing the length l2 of the gap by moving the movable plate 204. The position of the movable plate 204 is adjusted while measuring the ultrasonic output generated from the opening 205 by vibrating the diaphragm 103. Then, the maximum amplification structure can be obtained by fixing the movable plate 204 with the adhesive 207 at the position where the optimum value of the ultrasonic output is generated.

[0026] Next, a method for manufacturing the ultrasonic transducer 100 according to Embodiment 1 will be described with reference to FIGS. 3 to 5. FIGS. 3 to 5 are cross-sectional views taken along line II-II of FIG. 1 in each manufacturing process of the ultrasonic transducer 100 according to Embodiment 1. The ultrasonic transducer 100 is manufactured by integral molding using MEMS manufacturing technology.

[0027] FIGS. 3(a) to (c) are schematic cross-sectional views showing the first step of the method for manufacturing the ultrasonic transducer 100 according to Embodiment 1. FIGS. 4(a) to (c) are schematic cross-sectional views showing the second step of the method for manufacturing the ultrasonic transducer 100 according to Embodiment 1. FIGS. 5(a) to (b) are schematic cross-sectional views showing the third step of the method for manufacturing the ultrasonic transducer 100 according to Embodiment 1.

[0028] Referring to FIG. 3(a), a first SOI (Silicon On Insulator) substrate 200 is prepared. FIG. 3(a) shows the initial state of the first SOI substrate 200 before structure processing. The ultrasonic transducer 100 is manufactured by processing the first SOI substrate 200. The first SOI substrate 200 includes a surface silicon oxide film 110, a first silicon film 111, an intermediate silicon oxide film 112, and a second silicon film 113. The first silicon film 111 is disposed on the surface silicon oxide film 110. The intermediate silicon oxide film 112 is disposed on the first silicon film 111. The second silicon film 113 is disposed on the intermediate silicon oxide film 112. The intermediate silicon oxide film 112 is sandwiched between the first silicon film 111 and the second silicon film 113. The thickness of the first silicon film 111 is, for example, 1 μm or more and 100 μm or less. The thickness of the second silicon film 113 is, for example, 100 μm or more and 600 μm or less. There are various methods for forming the surface silicon oxide film 110, but the thermal oxidation method that can make the surface roughness extremely small is suitable.

[0029] Referring to FIG. 3(b), a piezoelectric element 107 is formed on the first silicon film 111 of the first SOI substrate 200. In the present embodiment, through the surface silicon oxide film 110, a piezoelectric element 107 in which a lower electrode 104, a piezoelectric thin film 105, and an upper electrode 106 are laminated in this order is formed on the first silicon film 111. Each of the lower electrode 104, the piezoelectric thin film 105, and the upper electrode 106 is a laminated film laminated with each other. These laminated films are formed by a sputtering method or the like. The thickness of the lower electrode 104 and the upper electrode 106 is, for example, 0.1 μm, and the thickness of the piezoelectric thin film 105 is, for example, several μm.

[0030] Referring to FIG. 3(c), an etching process is performed on the second silicon film 113 and the intermediate silicon oxide film 112 of the first SOI substrate 200. The etching process is preferably deep reactive ion etching (DRIE). The etching process is performed until at least the intermediate silicon oxide film 112 is exposed. The intermediate silicon oxide film 112 serves as an etching stop layer. The intermediate silicon oxide film 112 is removed by performing an etching process such as dry etching. Thereby, the diaphragm 103 of the first silicon film 111 is formed. The diaphragm of the first silicon film 111 constitutes the diaphragm 103. The step of forming the diaphragm 103 includes the step of forming the first support 102 on the second silicon film 113.

[0031] Referring to FIG. 4(a), the silicon substrate 210 has a silicon oxide film 202 on its surface. An adhesive layer 201 is formed at the junction of the silicon oxide film 202 and the second silicon film 113. The adhesive layer 201 is an organic adhesive such as polyimide, a metal such as aluminum or gold that forms a eutectic layer with silicon, or the like. When direct bonding between substrates such as surface activated bonding is used for substrate bonding, the adhesive layer 201 is unnecessary.

[0032] Referring to FIG. 4(b), the silicon substrate 210 is connected to the second silicon film 113. In the present embodiment, the silicon oxide film 202 of the silicon substrate 210 is bonded to the second silicon film 113 via the adhesive layer 201.

[0033] Referring to FIGS. 4(c) to 5(b), an opening 205 and a gap 101 are formed in an acoustic resonance structure 100a including a first SOI substrate 200 and a silicon substrate 210 so as to amplify the vibration sound wave of the diaphragm 103, and the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a are matched. The step of matching the resonance frequencies includes forming a groove 206 in the silicon substrate 210 to form a movable plate 204 and a second support 203 connected to the first support 102, and moving the movable plate 204 relative to the second support 203 to change the volume of the gap 101, thereby matching the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a. The step of matching the resonance frequencies includes a step of fixing the movable plate 204 to the second support 203 in a state where the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a are matched.

[0034] Referring to FIG. 4(c), the silicon substrate 210 is subjected to through-etching by deep reactive ion etching (DRIE). Thereby, the movable plate 204, the opening 205, and the groove 206 are formed. The silicon oxide film 202 serves as an etching stop layer. After the deep reactive ion etching (DRIE), the silicon oxide film 202 in the through portion is removed by dry etching or the like.

[0035] Referring to FIG. 5(a), an adhesive 207 is applied to fill the groove 206. As the adhesive 207, an adhesive that can be fixed after position adjustment, such as a thermosetting resin or a UV (Ultraviolet) curable resin, is used. As a method for forming the adhesive 207 in the groove 206, a method capable of forming a pattern on a high aspect ratio groove, such as screen printing or dispenser drawing, is used.

[0036] With reference to FIG. 5(b), while applying a voltage to the piezoelectric element 107 and observing the sound pressure output from the opening 205, or while inputting a sound wave from the outside into the opening 205 and observing the vibration of the piezoelectric element 107, the position of the movable plate 204 is adjusted. Thereby, the optimum volume of the gap 101 is determined. The adhesive 207 is fixed by heating or UV irradiation or the like. Note that this adjustment may be performed in the wafer state, but may also be performed after the adhesive 207 is applied so as to fill the groove 206 as shown in FIG. 5(a), the chip is separated, and assembled into the package.

[0037] Next, the operation and effect of the first embodiment will be described. In the method for manufacturing the ultrasonic transducer 100 according to the first embodiment, the opening 205 and the gap 101 are formed in the acoustic resonance structure 100a including the first SOI substrate 200 and the silicon substrate 210 so as to amplify the vibration sound wave of the diaphragm 103, and the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a are matched. Therefore, the diaphragm 103 and the acoustic resonance structure 100a can be manufactured using semiconductor technology with high dimensional accuracy. Thereby, the diaphragm 103 and the acoustic resonance structure 100a can be manufactured with high dimensional accuracy. Furthermore, by matching the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a, a large amplification effect can be obtained.

[0038] Also, the ultrasonic transducer 100 is a MEMS ultrasonic transducer. Therefore, the diaphragm 103 and the acoustic resonance structure 100a can be manufactured with high dimensional accuracy by MEMS. For example, the diaphragm 103 and the acoustic resonance structure 100a can be manufactured with dimensional accuracy within an error range of 1 μm or more and 10 μm or less.

[0039] Also, since the ultrasonic transducer 100 is a MEMS ultrasonic transducer, it can be manufactured at low cost by mass production in a wafer process.

[0040] In the manufacturing method of the ultrasonic transducer 100 according to Embodiment 1, the step of matching the resonance frequencies includes forming a groove 206 in the silicon substrate 210 to form the movable plate 204 and the second support 203 connected to the first support 102, and moving the movable plate 204 relative to the second support 203 to change the volume of the gap 101, thereby matching the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a. Therefore, by moving the movable plate 204 relative to the second support 203 to change the volume of the gap 101, the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a can be matched. Thus, the resonance frequency of the acoustic resonance structure 100a can be adjusted.

[0041] In the manufacturing method of the ultrasonic transducer 100 according to Embodiment 1, the step of matching the resonance frequencies includes fixing the movable plate 204 to the second support 203 with the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a being matched. Therefore, the movable plate 204 can be fixed to the second support 203 with the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a being matched. Thus, the adjusted resonance frequency of the acoustic resonance structure 100a can be fixed.

[0042] According to the ultrasonic transducer 100 according to Embodiment 1, the first acoustic resonance structure 100a includes the first support 102 and the diaphragm 103 formed of an SOI substrate, and the second support 203 and the movable plate 204 formed of a silicon substrate. Therefore, the diaphragm 103 and the acoustic resonance structure 100a can be manufactured using semiconductor technology with high dimensional accuracy. Thereby, the diaphragm 103 and the acoustic resonance structure 100a can be manufactured with high dimensional accuracy. Further, the opening 205 and the gap 101 are formed so as to match the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a. Therefore, a large amplification effect can be obtained by matching the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a.

[0043] Embodiment 2. Unless otherwise specified, Embodiment 2 has the same structure, manufacturing method, and effects as Embodiment 1.

[0044] Referring to FIG. 6, the structure and manufacturing method of the ultrasonic transducer 100 according to Embodiment 2 will be described.

[0045] FIGS. 6(a) to 6(c) are schematic cross-sectional views showing the manufacturing method of the ultrasonic transducer 100 according to Embodiment 2. Further, FIG. 6(c) is a schematic cross-sectional view showing the structure of the ultrasonic transducer 100 according to Embodiment 2.

[0046] Referring to FIG. 6(a), in Embodiment 2, instead of the silicon substrate 210 (see FIG. 4(a)) of Embodiment 1, a second SOI substrate 300 is used. That is, the silicon substrate 210 (see FIG. 4(a)) of Embodiment 1 is the second SOI substrate 300. The second SOI substrate 300 is attached to the second silicon film 113 using an adhesive layer 201. The second SOI substrate 300 includes an SOI active layer 301, an SOI support layer 302, an SOI intermediate silicon oxide film 303, and an SOI surface oxide film 304. The SOI intermediate silicon oxide film 303 is sandwiched between the SOI active layer 301 and the SOI support layer 302. The SOI active layer 301 is disposed on the SOI surface oxide film 304.

[0047] In the step of matching the resonance frequency, an etching process is performed on the SOI active layer 301, the SOI support layer 302, and the SOI intermediate silicon oxide film 303 to form the movable plate 204 of the SOI active layer 301. Before the second SOI substrate 300 is attached to the second silicon film 113, openings 205 and grooves 206 are processed by deep reactive ion etching (DRIE) in the active layer 301 of the second SOI substrate 300. The SOI intermediate silicon oxide film 303 serves as an etching stop layer.

[0048] Referring to FIG. 6(b), the SOI support layer 302 is etched by deep reactive ion etching (DRIE). The SOI intermediate silicon oxide film 303 serves as an etching stop layer. After the deep reactive ion etching (DRIE), the SOI intermediate silicon oxide film 303 is removed by dry etching or the like. In this way, the movable plate 204 is formed.

[0049] Referring to FIG. 6(c), the adhesive 207 is applied to fill the groove 206 shown in FIG. 6(b). While applying a voltage to the piezoelectric element 107 and observing the sound pressure output from the opening 205, or while inputting a sound wave from the outside into the opening 205 and observing the vibration of the piezoelectric element 107, the position of the movable plate 204 is adjusted. Thereby, the optimum volume of the gap 101 is determined. The SOI support layer 302 constitutes the second support 203.

[0050] Next, the operation and effect of the second embodiment will be described. In the method for manufacturing the ultrasonic transducer 100 according to the second embodiment, in the step of matching the resonance frequencies, the movable plate 204 of the SOI active layer 301 is formed by subjecting the SOI active layer 301, the SOI support layer 302, and the SOI intermediate silicon oxide film 303 to an etching process. Therefore, since the movable plate 204 is formed of the SOI active layer 301, the thickness of the movable plate 204 is determined by the thickness of the SOI active layer 301. For this reason, it becomes easy to adjust the thickness of the movable plate 204. Particularly when the movable plate 204 is thin, the effect is significant.

[0051] Embodiment 3. Unless otherwise specified, Embodiment 3 has the same structure, manufacturing method, and operation and effect as Embodiment 1 or 2.

[0052] Referring to FIG. 7, the structure and manufacturing method of the ultrasonic transducer 100 according to Embodiment 3 will be described. FIG. 7 is a perspective view of the ultrasonic transducer 100 according to Embodiment 3.

[0053] The step of adjusting the resonance frequency includes the step of forming a beam 401 that connects the movable plate 204 and the second support 203 to the silicon substrate 210. The movable plate 204 having the opening 205 and the second support 203 are connected by the beam 401. The beam 401 has elasticity. The beam 401 is formed by deep reactive ion etching (DRIE) simultaneously with the opening 205 and the movable plate 204. That is, a slit is provided around the beam 401.

[0054] In the ultrasonic transducer 100 according to Embodiment 3 shown in FIG. 7, the movable plate 204 shown in Embodiment 1 is supported by the second support 203 by four beams 401.

[0055] Referring to FIG. 8, the structure and manufacturing method of a modified example of the ultrasonic transducer 100 according to Embodiment 3 will be described. FIG. 8 is a perspective view of a modified example of the ultrasonic transducer 100 according to Embodiment 3.

[0056] In the modified example of the ultrasonic transducer 100 according to Embodiment 3 shown in FIG. 8, the movable plate 204 formed by the SOI active layer 301 of the SOI substrate 300 shown in Embodiment 2 is supported by the SOI active layer 301 by the beam 401. The beam 401 is also formed by the SOI active layer 301.

[0057] Next, the operation and effect of Embodiment 3 will be described. In the manufacturing method of the ultrasonic transducer 100 according to Embodiment 3, the step of adjusting the resonance frequency includes the step of forming a beam 401 that connects the movable plate 204 and the second support 203 to the silicon substrate 210. Therefore, since the movable plate 204 is supported by the beam 401, the movable plate 204 does not separate during manufacturing or during the position adjustment of the movable plate 204, so that the manufacturing can be simplified.

[0058] Embodiment 4. Embodiment 4 has the same structure, manufacturing method, and operation and effect as Embodiment 1 or 2 unless otherwise specified.

[0059] Referring to FIG. 9, an adjustment method for the ultrasonic transducer 100 according to Embodiment 4 will be described. FIG. 9 is a schematic cross-sectional view showing the adjustment method for the ultrasonic transducer 100 according to Embodiment 4.

[0060] The step of adjusting the resonance frequency includes the step of moving the movable plate 204 relative to the second support 203 by the electrostatic attraction of the jig electrode 501. The jig electrode 501 is installed on the movable plate 204. An electrostatic attraction is applied between the jig electrode 501 and the movable plate 204 as shown by the white arrow in the figure. Thereby, the movable plate 204 is adjusted to the optimal position.

[0061] In the adjustment method for the ultrasonic transducer 100 according to Embodiment 4 shown in FIG. 9, the silicon substrate 210 shown in Embodiment 1 is applied to the movable plate 204.

[0062] Referring to FIG. 10, an adjustment method for a modified example of the ultrasonic transducer 100 according to Embodiment 4 will be described. FIG. 10 is a schematic cross-sectional view showing the adjustment method for the modified example of the ultrasonic transducer 100 according to Embodiment 4.

[0063] In the adjustment method for the modified example of the ultrasonic transducer 100 according to Embodiment 4 shown in FIG. 10, the second SOI substrate 300 shown in Embodiment 2 is applied to the movable plate 204. The jig electrode 501 is installed on the SOI support layer 302.

[0064] Next, the effects of Embodiment 4 will be described. In the manufacturing method of the ultrasonic transducer 100 according to Embodiment 4, the step of adjusting the resonance frequency includes the step of moving the movable plate 204 relative to the second support 203 by the electrostatic attraction of the jig electrode 501. Therefore, the position adjustment of the movable plate 204 can be made highly accurate. Also, the position adjustment of the movable plate 204 can be simplified.

[0065] In the manufacturing method of the ultrasonic transducer 100 according to Embodiment 4, the jig electrode 501 is installed on the SOI support layer 302. When the adjustment method of Embodiment 4 is applied to the movable plate 204 supported by the beam 401 shown in Embodiment 3, the position of the movable plate 204 is adjusted by the balance between the electrostatic attraction force and the spring force of the beam 401, so that more accurate position adjustment becomes possible.

[0066] Embodiment 5. Unless otherwise specified, Embodiment 5 has the same structure, manufacturing method, and effects as Embodiment 1.

[0067] Referring to FIG. 11, the adjustment method of the ultrasonic transducer 100 according to Embodiment 5 will be described. FIG. 11 is a cross-sectional view showing the adjustment method of the ultrasonic transducer 100 according to Embodiment 5.

[0068] In the adjustment method of the resonance frequency of the acoustic resonance structure 100a of the ultrasonic transducer 100 shown in Embodiments 1 to 4, the volume of the acoustic resonance structure 100a is adjusted by adjusting the position of the movable plate 204. In this embodiment, an adjustment method different from that of Embodiments 1 to 4 is used.

[0069] In the adjustment method of the ultrasonic transducer 100 according to Embodiment 5 shown in FIG. 11, the resonance frequency is matched by adjusting the length of the opening 205. The step of matching the resonance frequencies includes the step of matching the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a by changing the length of the opening 205. The length of the opening 205 is adjusted by thinning the thickness of the movable plate 204 exposed from the etching mask 601 by dry etching or the like.

[0070] Referring to FIG. 12, the adjustment method of a modified example of the ultrasonic transducer 100 according to Embodiment 5 will be described. FIG. 12 is a cross-sectional view showing the adjustment method of a modified example of the ultrasonic transducer 100 according to Embodiment 5.

[0071] In the adjustment method of the modification of the ultrasonic transducer 100 according to Embodiment 5 shown in FIG. 12, the resonance frequency is adjusted by adjusting the area of the opening 205. The step of adjusting the resonance frequency includes the step of adjusting the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a by changing the area of the opening 205. The area of the opening 205 is adjusted by adjusting the diameter of the opening 205 using a silicon isotropic etching technique such as xenon difluoride (XeF2) with the opening 205 covered with the etching mask 601.

[0072] Next, the operation and effect of Embodiment 5 will be described. In the manufacturing method of the ultrasonic transducer 100 according to Embodiment 5, the step of adjusting the resonance frequency includes the step of adjusting the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a by changing the length of the opening 205. Therefore, the resonance frequency of the acoustic resonance structure 100a can be adjusted by changing the length of the opening 205. Thereby, the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a can be matched.

[0073] Also, in the manufacturing method of the ultrasonic transducer 100 according to Embodiment 5, the step of adjusting the resonance frequency includes the step of adjusting the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a by changing the area of the opening 205. Therefore, the resonance frequency of the acoustic resonance structure 100a can be adjusted by changing the area of the opening 205. Thereby, the resonance frequencies of the diaphragm 103 and the acoustic resonance structure 100a can be matched.

[0074] In the manufacturing method of the ultrasonic transducer 100 according to Embodiment 5, the method of adjusting the resonance frequency of the acoustic resonance structure 100a requires process equipment such as dry etching and thin film formation, but has the advantage of a wide adjustment range. Therefore, by combining the adjustment method according to Embodiment 5 and the position adjustment of the movable plate 204 shown in Embodiments 1 to 4, it is possible to adjust the resonance frequency with a wide adjustment range and high precision.

[0075] Embodiment 6 With reference to FIG. 13, the configuration of the distance measuring device 701 according to Embodiment 6 will be described. The distance measuring device 701 according to Embodiment 6 includes the ultrasonic transducer 100 according to any one of Embodiments 1 to 5.

[0076] The distance measuring device 701 can measure the distance from the distance measuring device 701 to the object 702 using the TOF (Time of Flight) method.

[0077] FIG. 13 is a schematic diagram schematically showing the measurement of the distance to the object 702 by the TOF (Time of Flight) method using the distance measuring device 701. The transmission wave 703 is shown by a solid line. The reflected wave 704 from the object 702 is shown by a broken line. The distance measuring device 701 includes a diaphragm, a piezoelectric element disposed on the diaphragm, and an acoustic resonance structure. When an electrical signal is input to the piezoelectric element and the diaphragm vibrates at the resonance frequency of the diaphragm, ultrasonic waves of that frequency are generated. The ultrasonic waves are amplified by the acoustic resonance structure and transmitted as the transmission wave 703 from the distance measuring device 701. The ultrasonic waves are reflected by the object 702 and reach the distance measuring device 701 as the reflected wave 704. The received ultrasonic waves are amplified by the acoustic resonance structure and resonate the diaphragm. The vibration of the diaphragm is received as an electrical signal by the piezoelectric element disposed on the diaphragm. Using the distance L between the distance measuring device 701 and the object 702, the time t taken from the transmission to the reception of the sound wave, and the speed of sound c, the distance L can be calculated by c×t / 2 (L = c×t / 2).

[0078] Next, the operation and effect of the distance measuring device 701 according to Embodiment 6 will be described. By applying the ultrasonic transducer 100 described in any one of Embodiments 1 to 5 to the distance measuring device 701, the generated sound pressure and sensitivity can be improved. Therefore, the detection distance of the distance measuring device 701 can be improved.

[0079] It is possible to appropriately combine the above-described embodiments. The embodiments disclosed this time should be considered illustrative in all respects and not restrictive. The scope of the present disclosure is indicated by the scope of claims rather than the above description, and it is intended that all modifications within the meaning and scope equivalent to the scope of claims be included.

Explanation of Signs

[0080] 100 Ultrasonic transducer, 100a Acoustic resonance structure, 101 Gap, 102 First support, 103 Diaphragm, 104 Lower electrode, 105 Piezoelectric thin film, 106 Upper electrode, 107 Piezoelectric element, 110 Surface silicon oxide film, 111 First silicon film, 112 Intermediate silicon oxide film, 113 Second silicon film, 200 First SOI substrate, 201 Adhesive layer, 202 Silicon oxide film, 203 Second support, 204 Movable plate, 205 Opening, 206 Groove, 207 Adhesive, 210 Silicon substrate, 300 Second SOI substrate, 301 Active layer, 302 Support layer, 303 SOI intermediate silicon oxide film, 304 Surface oxide film, 401 Beam, 501 Fixture electrode, 701 Distance measuring device.

Claims

1. Preparing a first SOI substrate including a first silicon film, a second silicon film, and an intermediate silicon oxide film sandwiched between the first silicon film and the second silicon film; Forming a piezoelectric element on the first silicon film of the first SOI substrate; Forming a diaphragm of the first silicon film by subjecting the second silicon film and the intermediate silicon oxide film of the first SOI substrate to an etching process; Connecting a silicon substrate to the second silicon film; Forming an opening and a gap in an acoustic resonance structure including the first SOI substrate and the silicon substrate so as to amplify vibration sound waves of the diaphragm, and matching the resonance frequency of the diaphragm and the acoustic resonance structure; and The step of forming the diaphragm includes forming a first support on the second silicon film; The step of matching the resonance frequencies includes forming a groove in the silicon substrate to form a movable plate and a second support connected to the first support, and moving the movable plate relative to the second support to change the volume of the gap, thereby matching the resonance frequencies of the diaphragm and the acoustic resonance structure. A method for manufacturing an ultrasonic transducer.

2. The method for manufacturing an ultrasonic transducer according to claim 1, wherein the step of matching the resonance frequencies includes fixing the movable plate to the second support in a state where the resonance frequencies of the diaphragm and the acoustic resonance structure are matched.

3. The silicon substrate is a second SOI substrate, The second SOI substrate includes an SOI active layer, an SOI support layer, and an SOI intermediate silicon oxide film sandwiched between the SOI active layer and the SOI support layer, The method for manufacturing an ultrasonic transducer according to claim 1 or 2, wherein the step of matching the resonance frequencies includes forming the movable plate of the SOI active layer by subjecting the SOI active layer, the SOI support layer, and the SOI intermediate silicon oxide film to an etching process.

4. The method for manufacturing an ultrasonic transducer according to claim 1, wherein the step of matching the resonance frequencies includes forming a beam connecting the movable plate and the second support on the silicon substrate.

5. The method for manufacturing an ultrasonic transducer according to claim 1, wherein the step of matching the resonance frequencies includes moving the movable plate relative to the second support by electrostatic attraction of a jig electrode.

6. The silicon substrate is a second SOI substrate, The second SOI substrate includes an SOI support layer, The jig electrode is installed on the SOI support layer. The manufacturing method of the ultrasonic transducer according to claim 5.

7. The step of matching the resonance frequencies includes the step of matching the resonance frequencies of the diaphragm and the acoustic resonance structure by changing the length of the opening. The manufacturing method of the ultrasonic transducer according to claim 1.

8. The step of matching the resonance frequencies includes the step of matching the resonance frequencies of the diaphragm and the acoustic resonance structure by changing the area of the opening. The manufacturing method of the ultrasonic transducer according to claim 1.

9. An acoustic resonance structure including a first support and a diaphragm constituted by an SOI substrate, and a second support and a movable plate constituted by a silicon substrate, And a piezoelectric element attached to the acoustic resonance structure, The diaphragm constituted by the SOI substrate is connected to the first support, The second support constituted by the silicon substrate is connected to the first support on the side opposite to the diaphragm with respect to the first support, The movable plate constituted by the silicon substrate is connected to the second support so as to face the diaphragm, The piezoelectric element is connected to the diaphragm of the acoustic resonance structure, An opening is provided in the movable plate, The opening communicates with a void surrounded by the first support, the diaphragm, the second support, and the movable plate, The opening and the void are formed so as to match the resonance frequencies of the diaphragm and the acoustic resonance structure. An ultrasonic transducer.

10. A distance measuring device including the ultrasonic transducer according to claim 9.

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