Ultrasonic transducer, ultrasonic probe, ultrasonic diagnostic device, and method for manufacturing ultrasonic transducer

Abstract

To improve wide-band characteristics of an ultrasonic transducer.SOLUTION: In an ultrasonic transducer, a periphery of each mobile film 15 where an electromechanical transducing element 13 consisting of a lower electrode layer 13c, an electromechanical transducing layer 13b, and an upper electrode layer 13a is formed on one surface is fixed by a fixing member 11, and an ultrasonic wave is transmitted and / or received on the side of the other surface opposed to the one surface by the displacement of the mobile film. The fixing member fixes the periphery of the mobile film only from the one surface side.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an ultrasonic transducer, an ultrasonic probe, an ultrasonic diagnostic device, and a method for manufacturing an ultrasonic transducer. [Background technology]

[0002] Conventionally, there has been known an ultrasonic transducer in which a movable membrane having an electromechanical transducer element composed of a lower electrode layer, an electromechanical transducer layer, and an upper electrode layer formed on one side is fixed around the periphery by a fixing member, and ultrasonic waves are transmitted and received on the opposite side by displacement of the movable membrane.

[0003] For example, Patent Document 1 discloses a pMUT (Piezoelectric Micro-Machined Ultrasonic Transducer) using a piezoelectric element (electromechanical conversion element) formed by laminating a lower electrode layer, a piezoelectric layer (electromechanical conversion layer), and an upper electrode layer on a base layer. In this pMUT (ultrasonic transducer), a sealing member having a recess for accommodating the piezoelectric element is bonded to one surface (surface on which the piezoelectric element is formed) of a movable membrane on which the piezoelectric element is formed. In addition, a support member (fixing member) that supports (fixes) the periphery of the movable membrane displaced by the piezoelectric element is bonded to the other surface of the movable membrane. In this pMUT, a covering member for forming a sealed space together with the supporting member and the movable membrane is bonded to the supporting member, and this sealed space is filled with an acoustic transmission member made of the same silicone rubber as the covering member. In this pMUT, ultrasonic waves generated by the movable membrane displaced by the piezoelectric element are transmitted through the space surrounded by the supporting member and the covering member bonded to the supporting member. Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional ultrasonic transducers have a problem in that they do not have sufficient broadband characteristics. [Means for solving the problem]

[0005] In order to solve the above problems, the present invention provides a lower electrode layer, an electromechanical transducer layer, and an upper electrode Has layers An ultrasonic transducer in which a movable film having an electromechanical conversion element formed on one surface is fixed by a fixing member, and which transmits or receives, or both, ultrasonic waves on the surface side opposite to the one surface by the displacement of the movable film, the fixing member fixing the periphery of the movable film only from the one surface side. a sealed space forming member that is connected to the fixed member and that forms a sealed space together with the fixed member and the movable membrane; It is characterized by: Effect of the Invention

[0006] According to the present invention, the broadband characteristics of an ultrasonic transducer can be improved. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic configuration diagram showing an example of an ultrasonic diagnostic apparatus according to an embodiment. [Diagram 2] FIG. 2 is a block diagram showing an example of a control unit of the ultrasonic diagnostic apparatus. [Diagram 3] FIG. 2 is a schematic configuration diagram showing another example of an ultrasonic diagnostic apparatus according to an embodiment. [Figure 4] FIG. 2 is an explanatory diagram illustrating an example of an ultrasonic probe according to an embodiment. [Diagram 5] FIG. 2 is a plan view of a portion of the vibration substrate of the pMUT chip, as viewed from the side (back side) where the electromechanical conversion element is formed relative to the base layer (vibration plate). [Figure 6] FIG. 6 is a cross-sectional view taken along the line AA in FIG. 5 . [Figure 7] FIG. 2 is a cross-sectional view showing an example of the configuration of a vibration part substrate of the pMUT chip. [Figure 8] 5A to 5C are explanatory diagrams for explaining a manufacturing process of the vibration part substrate. [Figure 9] 1A is an explanatory diagram for explaining a step of bonding a vibration substrate and an IC substrate, and FIG. 1B is an explanatory diagram showing a state after the vibration substrate and the IC substrate have been bonded. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment in which the present invention is applied to an ultrasonic transducer used in an ultrasonic probe of an ultrasonic diagnostic apparatus will be described. The ultrasonic transducer according to the present invention is not limited to those used in ultrasonic probes of ultrasonic diagnostic devices, but can be applied to various devices. In addition, although the present embodiment is an example in which a human body is used as a measurement object, the measurement object is not limited to a living body such as a human body.

[0009] FIG. 1 is a schematic diagram showing an example of an ultrasonic diagnostic apparatus according to this embodiment. 1, an ultrasound diagnostic device 100 has an ultrasound probe 1 that transmits ultrasound toward a subject 9, which is an object to be measured, and receives ultrasound reflected by the subject 9. The ultrasound diagnostic device 100 also has a display unit 61 that visualizes and displays a signal (echo signal) from the ultrasound probe 1, an operation unit 62 that is operated by an operator, and a control unit 63 that controls the ultrasound probe 1.

[0010] FIG. 2 is a block diagram showing an example of a control unit of the ultrasonic diagnostic apparatus according to this embodiment. 2, the control unit 63 has an ultrasonic pulse generating unit 64 that generates a pulsed electric signal for generating an ultrasonic signal, a converting unit 65 that converts an echo signal received from the ultrasonic probe 1 into a digital signal, and an ultrasonic image forming unit 66 that forms an ultrasonic image such as a two-dimensional image, a three-dimensional image, or various Doppler images corresponding to the echo signal converted by the converting unit 65. Note that the ultrasonic pulse generating unit 64 and the converting unit 65 may be, for example, any ultrasonic transceiver provided separately from the control unit 63.

[0011] The display unit 61 is composed of a monitor device such as an LCD (Liquid Crystal Display), and displays an image formed by the ultrasound image forming unit 66. The operation unit 62 is composed of a push button, a touch panel, etc., and accepts various operations for inputting parameters so that the operator can perform an appropriate diagnosis on the subject 9.

[0012] 1, the ultrasound probe 1 is electrically connected to a control unit 63 via a cable or the like, and under the control of the control unit 63, transmits ultrasound toward a subject 9 and receives ultrasound reflected as an echo from the subject 9. The ultrasound diagnostic device 100 is capable of visualizing and diagnosing the inside of the subject 9 by transmitting and receiving such ultrasound.

[0013] The ultrasonic diagnostic device may be configured, as shown in FIG. 3, to include a display terminal 50 as a display unit, and an ultrasonic probe 1 connected to the display terminal 50 by a cable.

[0014] FIG. 4 is an explanatory diagram that diagrammatically illustrates an example of the ultrasound probe 1 in this embodiment. As shown in Figure 4, the ultrasonic probe 1 is composed of a support part 3 which is a support substrate, a pMUT chip 2 as an ultrasonic converter (ultrasonic transducer) formed on the upper part of the support part 3, a flexible substrate 4, wiring 5, a connector 7, an acoustic lens 8, etc.

[0015] The pMUT chip 2 is connected to a connector 7 via wiring 5 on a flexible substrate 4. The connector 7 is connected to a circuit board described later, and is connected to the above-mentioned control unit 63 via this circuit board. The support unit 3 functions as a backing plate for holding the pMUT chip 2.

[0016] The acoustic lens 8 can be suitably made of, for example, silicone resin. The acoustic lens 8 is for focusing the ultrasonic waves transmitted from the pMUT chip 2 on the measurement position of the subject 9, and has a shape (so-called dome shape) in which the center is thicker than the periphery. The acoustic lens 8 comes into close contact with the subject 9 by deforming when it comes into contact with the subject 9, and exerts a function of refracting and converging the ultrasonic waves in a pseudo manner due to the difference in the propagation speed of the ultrasonic waves caused by the difference in thickness between the center and the periphery. Note that the acoustic lens 8 only needs to have a function of converging the ultrasonic waves in at least one direction, and does not necessarily have to be one that converges the ultrasonic waves to one point.

[0017] The acoustic lens 8 and the pMUT chip 2 are attached to each other by an adhesive 6 serving as an adhesive layer. The adhesive 6 used to bond the acoustic lens and the pMUT chip 2 is preferably a silicone resin adhesive, and is preferably a thin adhesive having a thickness of 20 μm or less.

[0018] FIG. 5 is a plan view of a portion of the vibration portion substrate of the pMUT chip 2, as viewed from the side (hereinafter referred to as the "rear side") on which the electromechanical conversion element is formed with respect to the base layer (vibration plate). FIG. 6 is a cross-sectional view taken along the line AA in FIG. For ease of explanation, FIG. 5 omits an insulating layer 16 and a passivation film 17, which will be described later, as well as an IC substrate bonded to the vibration portion substrate.

[0019] As shown in Fig. 6, the pMUT chip 2 of this embodiment has a structure in which a vibration part substrate 10 and an IC substrate 20 serving as a control substrate are laminated, and the vibration part substrate 10 and the IC substrate 20 are joined at a predetermined interval by metal members 11 and 12. The upper side of this pMUT chip 2 in Fig. 6 is the side that transmits and receives ultrasonic waves (hereinafter referred to as the "transmitting and receiving side"). The IC substrate 20 may be equipped with some of the functions shown in Fig. 2.

[0020] FIG. 7 is a cross-sectional view showing an example of the configuration of the vibration portion substrate 10 of the pMUT chip 2. As shown in FIG. The IC substrate 20 has wirings 21 and 22 electrically connected to the upper electrode 13a and the lower electrode 13c of the piezoelectric vibrator 13, which is an electromechanical conversion element of the vibration substrate 10. Specifically, the wirings 21 and 22 of the IC substrate 20 are electrically connected to the metal members 11 and 12 of the vibration substrate 10, respectively, and are electrically connected to the upper electrode 13a and the lower electrode 13c of the piezoelectric vibrator 13 of the vibration substrate 10 via the metal members 11 and 12. As a result, a drive signal from the IC substrate 20 is sent to the vibration substrate 10 via the first metal member 11 connected to the upper electrode 13a, which is an individual electrode of the piezoelectric vibrator 13. Also, a reception signal of an ultrasonic wave received by the piezoelectric vibrator 13 of the vibration substrate 10 is sent to the IC substrate 20 via the first metal member 11.

[0021] The piezoelectric vibrator 13 of the vibration substrate 10 is composed of an upper electrode 13a, a lower electrode 13c, and a piezoelectric layer 13b interposed between them as an electromechanical conversion layer. The layers constituting the piezoelectric vibrator 13 are laminated on one surface (the surface on the back side of the base layer 14) of a base layer 14 that serves as a vibration plate in the order of the lower electrode 13c layer, the piezoelectric layer 13b, and the upper electrode 13a layer. The vibration substrate 10 of this embodiment is an example in which a plurality of cylindrical piezoelectric vibrators 13 are arranged on the base layer 14, but the shape of the piezoelectric vibrators 13 is not limited to this.

[0022] 5, in the vibration substrate 10 of this embodiment, a first metal member 11 is provided on a base layer 14 so as to surround each of the piezoelectric vibrators 13. The first metal member 11 of this embodiment functions as a fixing member that mechanically supports and fixes the regions of the base layer 14 including each of the piezoelectric vibrators 13 surrounded by the first metal member 11 so as to function as movable films (diaphragms) 15.

[0023] 7, the size of the diaphragm 15 is determined by the diameter (cavity diameter) B of the circular opening of the first metal member 11 surrounding the diaphragm 15. The periphery of the diaphragm 15, which is displaced by the driving of the piezoelectric vibrator 13, is fixed by the rigid first metal member 11, and each diaphragm 15 can vibrate with little interference with each other.

[0024] The size of the diaphragm 15 is important for the resonance characteristics of the vibration structure, and is also an important factor for the frequency characteristics of ultrasonic waves. Therefore, the size of the diaphragm 15 requires high precision. Also, in order to form the diaphragm 15 densely, it is necessary to make the width of the fixing member (first metal member 11) as small as possible. If the diaphragm 15 can be formed densely, the transmitted sound pressure per unit area can be increased, and a large transmission intensity can be obtained.

[0025] The processing accuracy of the first metal member 11 greatly affects the dimensional accuracy of the diaphragm 15. For example, when designing a vibration structure having a resonant frequency at a high frequency with a center frequency of 7 MHz or more, it is possible to set the distance at which the diaphragm 15 and the IC substrate 20 do not come into contact with each other to 3 μm or less, although this depends on the rigidity of the vibration structure. In this case, since the thickness (height) of the first metal member 11 can be made on the order of microns, it is possible to perform highly accurate processing by semiconductor processing using normal photolithography without making the material of the first metal member 11 thicker than necessary. Therefore, it is possible to achieve a pMUT chip 2 having ultrasonic frequency characteristics and large transmission strength.

[0026] Furthermore, in order to form a pMUT chip 2 with a dense diaphragm 15 so that the transmitted sound pressure per unit area can be increased and a large transmission intensity can be obtained, it is preferable to set the width of the first metal member 11 to 50 μm or less. On the other hand, from the viewpoint of the bonding strength between the vibration part substrate 10 and the IC substrate 20 and the airtightness of the sealed space enclosing the piezoelectric vibrator 13, it is preferable to set the width of the first metal member 11 to 3 μm or more. Therefore, in order to ensure the bonding strength and airtightness while increasing the transmitted sound pressure per unit area, it is preferable to set the minimum width of the first metal member 11 in the range of 3 μm to 50 μm.

[0027] In this embodiment, a conductive metal material is used for the first metal member 11, which is a fixing member that fixes the periphery of the diaphragm 15, so that it also functions as a signal transmission member for transmitting electric signals such as drive signals. However, if the fixing member is configured not to function as a signal transmission member, a non-conductive material such as resin having the necessary rigidity may be used for the fixing member.

[0028] In addition, the first metal member 11, together with the second metal member 12, maintains the distance C between the vibration part substrate 10 and the IC substrate 20 at a predetermined distance. This predetermined distance is set to a distance at which the diaphragm 15 and the IC substrate 20 do not come into contact when the diaphragm 15 vibrates. For example, when designing a vibration structure having a resonance frequency of 7 MHz, the distance at which the diaphragm 15 and the IC substrate 20 do not come into contact can be set to 3 μm or less, although this depends on the rigidity of the vibration structure. Of course, this distance C can be set to 3 μm or more, but since the wider the distance C, the thicker the metal film required when forming the metal members 11 and 12, it is preferable to narrow the distance C as much as possible.

[0029] In this embodiment, the IC board 20 is connected to the first metal member 11 and functions as a sealed space forming member, forming a sealed space together with the first metal member 11 and the diaphragm 15 of the vibration part substrate 10. By forming such a sealed space, the piezoelectric transducer 13 of the vibration part substrate 10 can be enclosed in this sealed space. This makes it possible to suppress the transmission of moisture from the subject 9 to the piezoelectric transducer 13 when diagnosing with the ultrasonic diagnostic device 100 of this embodiment, for example. This increases reliability against dielectric breakdown, making it possible to increase the voltage applied to the piezoelectric transducer 13 and obtain a large transmission strength.

[0030] In the piezoelectric vibrator 13 of this embodiment, the lower electrode 13c is a common electrode shared by multiple piezoelectric vibrators 13. The lower electrode 13c, which is the common electrode, is a ground electrode connected to the ground via the second metal member 12. On the other hand, the upper electrode 13a is an individual electrode provided for each piezoelectric vibrator 13, and a drive signal is applied via the first metal member 11. In this embodiment, as shown in FIG. 5, the common first metal member 11 is connected via wiring 11a to the upper electrodes 13a of 3×3=9 piezoelectric vibrators 13. Therefore, the same drive signal is input to these nine piezoelectric vibrators 13, and one cell is formed.

[0031] In the diaphragm 15 in the vibration substrate 10 of this embodiment, the first metal member 11 that fixes the periphery is disposed apart from the piezoelectric layer 13b on the base layer 14 that becomes the vibration plate. Therefore, the layers that constitute the diaphragm 15 between the piezoelectric layer 13b and the first metal member 11 are substantially the base layer 14 and the lower electrode 13c (including the insulating layer 16 and the passivation film 17), and this portion is the thinnest portion of the diaphragm 15. In a region where the driving efficiency of the piezoelectric vibrator 13 disposed in the diaphragm is poor, the upper electrode 13a and the piezoelectric layer 13b are removed to make the diaphragm 15 thinner and lighter, thereby achieving efficient driving.

[0032] For example, silicon, silicon dioxide, silicon nitride, and combinations thereof can be used as the base layer 14. The surface of the back side (the side on which the piezoelectric vibrator 13 is formed) of the base layer 14 is preferably made of an insulating protective film. Silicon dioxide is preferably used as this protective film in terms of insulation properties and adhesion to the lower electrode.

[0033] The lower electrode 13c is formed of platinum (Pt), but is not limited thereto, and may be made of a conductive metal material, a conductive oxide, or a combination thereof, etc. Specifically, the oxide electrode layer may be made of SrRuO3, LaNiO3, etc., and the metal electrode layer may be made of Pt, Ti, Cr, Ta, Rh, Pd, etc.

[0034] In addition, other layers such as an adhesion layer may be provided between the lower electrode 13c and the base layer 14. For example, an adhesion layer made of a titanium layer, a titanium oxide layer, a titanium tungsten layer, an alumina layer, a zirconium oxide layer, or the like may be provided between the lower electrode 13c and the base layer 14. This adhesion layer is generally thin, about several tens of nm, and has a small contribution to the rigidity and a small effect on the function of the diaphragm 15.

[0035] The upper electrode 13a is made of platinum (Pt) like the lower electrode 13c, but is not limited thereto and may be made of conductive metal materials, conductive oxides, or combinations thereof. The material used for the upper electrode 13a may be the same as that for the lower electrode 13c, and may be selected from a wider range of materials than the lower electrode. For the oxide electrode layer, SrRuO3, LaNiO3, IrO2, RuO2, SrO, CaRuO3, etc. may be used, and for the metal electrode layer, Pt, Ir, Ru, Ti, Cr, Ta, Rh, Pd, etc. may be used.

[0036] It is also possible to omit the above-mentioned base layer 14 and use the lower electrode 13c as the base layer. In this case, it is preferable to protect the surface of the lower electrode 13c on the side of the above-mentioned sealed space with an insulating protective film. Silicon dioxide, alumina, etc. can be used as the protective film.

[0037] In this embodiment, the surface of the base layer 14 opposite to the side on which the piezoelectric transducer 13 is formed (the surface of the base layer on the transmitting / receiving side) does not have an uneven structure or a protruding structure, but is a flat surface. The above-mentioned acoustic lens 8 is bonded to this surface of the base layer 14 (the surface of the base layer on the transmitting / receiving side) by an adhesive 6. That is, a fixing member as in the past is not provided on the transmitting / receiving side of the diaphragm 15. This results in a configuration in which there are substantially no other components between the time when the ultrasonic waves generated by the diaphragm 15 are propagated to the acoustic lens 8 or between the time when the ultrasonic waves propagated to the acoustic lens 8 are received by the diaphragm 15. This improves the transmission characteristics of the ultrasonic waves transmitted from the diaphragm 15 or the reception characteristics of the ultrasonic waves received by the diaphragm 15, particularly the wideband characteristics.

[0038] In other words, if the components between the base layer 14 and the acoustic lens 8 are considered to constitute the diaphragm 15, this embodiment can realize a thinner diaphragm 15. Therefore, the transmission characteristics of the ultrasonic waves transmitted from the diaphragm 15 or the reception characteristics of the ultrasonic waves received by the diaphragm 15, particularly the wideband characteristics, are improved.

[0039] In this embodiment, an adhesive 6 is interposed between the surface of the base material layer 14 (the surface of the base material layer on the transmitting and receiving sides) and the acoustic lens 8 to bond them together. However, since the diaphragm 15 in this embodiment is formed thin as described above, even if warping occurs on the surface of the base material layer 14 (the surface of the base material layer on the transmitting and receiving sides) due to film stress or residual stress in the manufacturing process before the acoustic lens 8 is bonded, it is only slight. Therefore, even with a thin adhesive 6 of, for example, 20 μm or less, the base material layer 14 and the acoustic lens 8 can be bonded with a good yield. Therefore, the adhesive 6 present on the surface of the base material layer 14 (the surface of the base material layer on the transmitting and receiving sides) can also be made thin, and since its contribution to rigidity is small, its effect on the function of the diaphragm 15 is small.

[0040] The piezoelectric layer 13b of this embodiment is formed of a lead zirconate titanate (PZT)-based piezoelectric material. Of course, other elements may be included in the PZT-based composite oxide. The piezoelectric layer 13b is mechanically deformed by applying a drive signal (drive voltage) between the upper electrode 13a and the lower electrode 13c, and the periodic fluctuation of the drive signal causes the diaphragm 15 to vibrate at a predetermined frequency, thereby transmitting ultrasonic waves from the diaphragm 15. When an external ultrasonic wave vibrates the piezoelectric layer 13b, the piezoelectric layer 13b is polarized, causing a potential difference between the upper electrode 13a and the lower electrode 13c, generating an electric signal (received signal) according to the vibration.

[0041] The insulating layer 16 is an insulating film for preventing a short circuit between the wiring 11a connected to the first metal member 11, the upper electrode 13a, and the lower electrode 13c. The wiring 11a is made of aluminum or the like, and a passivation film 17 is formed on the wiring 11a as a protective layer. A silicon nitride film that is suitable for mass production and functions as a high-quality protective film is preferably used as the passivation film 17. The passivation film 17 functions as a protective film that protects the piezoelectric vibrator 13 from impurities, moisture, scratches, and the like.

[0042] However, in this embodiment, as described above, the piezoelectric vibrator 13 is enclosed in a sealed space formed by the first metal member 11 and the IC substrate 20. This suppresses contact of impurities and moisture with the piezoelectric vibrator 13, so if scratches and the like during the manufacturing process can be prevented, the above-mentioned passivation film 17 does not necessarily need to be provided. Even if the passivation film 17 is provided to prevent scratches and the like during the manufacturing process, all or a part of the passivation film 17 may be removed in the end. In any case, not providing the passivation film 17 allows the diaphragm 15 to be made thinner, which contributes to improving the wideband characteristics.

[0043] Furthermore, the shape of the diaphragm 15 is determined by the shape of the opening (cavity) of the first metal member 11, and in this embodiment, it is circular as shown in FIG. 5, but is not limited to this, and the shape can be freely set, for example, to a square, ellipse, polygon, etc.

[0044] In addition, in this embodiment, as described above, one cell to which the first metal members 11 are connected is composed of nine diaphragms 15, but there is no limit to the number, and it may be composed of one diaphragm 15, or three or more diaphragms 15. The arrangement of the diaphragms 15 constituting one cell can also be freely set. In addition, in this embodiment, one piezoelectric vibrator 13 is provided for one diaphragm 15, but two or more piezoelectric vibrators 13 may be provided for one diaphragm 15.

[0045] 5, the second metal member 12 connected to the lower electrode 13c of each piezoelectric vibrator 13, which is a common electrode, is disposed at one location on the vibration substrate 10, but there is no restriction on the position, number, or size of the second metal member 12, and they can be freely set. In this embodiment, the second metal member 12 is a member common to a plurality of cells, but, for example, an individual second metal member 12 may be disposed for each cell. In this way, increasing the number of second metal members 12 connected to ground contributes to noise reduction, etc.

[0046] Also, for example, the second metal member 12 may be disposed so as to surround one or more cells on the vibration substrate 10. In this case, not only does it contribute to noise reduction, but it also increases the bonding surface between the vibration substrate 10 and the IC substrate 20, thereby enhancing the bonding strength. In addition, since an airtight space can be formed by the second metal member 12, the vibration substrate 10, and the IC substrate 20, contact of impurities and moisture with the piezoelectric vibrator 13 is further suppressed.

[0047] Next, a method for manufacturing the pMUT chip 2 in this embodiment will be described. FIG. 8 is an explanatory diagram for explaining the manufacturing process of the vibration portion substrate 10. As shown in FIG. For the sake of simplicity, only two piezoelectric vibrators 13 are shown in FIG.

[0048] In the manufacturing process of the vibration part substrate 10, a silicon substrate made of silicon (Si) material is used as the support substrate 30. As described later, this support substrate 30 is finally removed or extremely thinned, and when extremely thinned, it functions as a vibration plate together with the base layer 14.

[0049] In manufacturing the vibration part substrate 10, first, the surface of the support substrate 30 is thermally oxidized to form an insulating film of SiO2 on the support substrate 30. This insulating film of SiO2 becomes the base layer 14 and constitutes the diaphragm. The thickness of the base layer 14 (the insulating film of SiO2) at this time is set to, for example, 0.3 μm.

[0050] Next, the lower electrode 13c is formed. At this time, in this embodiment, a titanium oxide (TiO2) layer (not shown) is formed as an adhesive layer between the lower electrode 13c and the base material layer 14 (SiO2 insulating film) by sputtering. Then, the titanium film is thermally oxidized in an O2 atmosphere at 650 to 800°C for 1 to 10 minutes using an RTA (Rapid Thermal Annealing) device to convert the titanium film into a titanium oxide film. As a result, an adhesive layer of a titanium oxide film is formed on the base material layer 14. At this time, the thickness of the adhesive layer (titanium oxide film) is preferably 10 nm or more and 50 nm or less. To form the adhesive layer (titanium oxide film), reactive sputtering may be used, but a thermal oxidation method using a high temperature of the titanium film is preferable. The lower electrode 13c formed on the adhesive layer is formed by, for example, forming a platinum (Pt) film with a thickness of 50 to 300 nm by sputtering.

[0051] Next, the piezoelectric layer 13b is formed on the lower electrode 13c. Specifically, as an example, a solution is prepared with a composition ratio of Pb:Zr:Ti=110:52:48. This solution can use lead acetate trihydrate, titanium isopropoxide, and zirconium isopropoxide as starting materials. The crystal water of lead acetate is dissolved in methoxyethanol and then dehydrated. It is preferable to have an excess amount of lead relative to the stoichiometric composition. This is to prevent a decrease in crystallinity due to so-called lead loss during heat treatment.

[0052] Titanium isopropoxide and zirconium isopropoxide are dissolved in methoxyethanol, and an alcohol exchange reaction and an esterification reaction are carried out. The PZT precursor solution is synthesized by mixing with the methoxyethanol solution in which the lead acetate is dissolved. The PZT concentration at this time is set to 0.5 mol / l. The precursor solution is used to form a PZT precursor film on the lower electrode 13c by spin coating, and after the film formation, it is dried at 120°C and subjected to a thermal decomposition treatment at 400°C. After the thermal decomposition treatment of the third layer, the PZT precursor is subjected to a crystallization heat treatment (temperature 700°C) by RTA treatment (rapid thermal processing). It should be noted that if the film thickness formed by one application of the precursor solution is increased, there is a concern that cracks may easily occur, so in this embodiment, the film thickness after crystallization is adjusted to be within about 100 nm.

[0053] After the crystallization heat treatment is completed, the treatment is repeated until a piezoelectric layer 13b having a desired thickness is obtained. In this embodiment, the coating process of the precursor solution is repeated 5 to 40 times to form the piezoelectric layer 13b having a thickness of 0.5 μm to 4 μm.

[0054] In this embodiment, PZT is used for the piezoelectric layer 13b, but the material is not limited to AlN, ScAlN, KNN, etc. Also, although the film formation method is CSD, various film formation methods such as sputtering, MOCVD, and PLD can be appropriately selected.

[0055] Next, the upper electrode 13a is formed on the piezoelectric layer 13b. Specifically, first, a conductive oxide film, SrRuO3 film (thickness 40 nm), is sputter-deposited on the piezoelectric layer 13b. The substrate temperature during sputter-deposition is 300°C. Then, post-annealing is performed in an O2 atmosphere at 550°C / 300s by RTA processing. Then, a metal film, platinum film (thickness 60 nm), is sputter-deposited to form the upper electrode 13a.

[0056] In order to obtain the piezoelectric vibrator 13 having a predetermined shape, for example, after the upper electrode 13a is formed, a photosensitive resist is patterned on the upper electrode 13a as a mask layer, and then dry etching or wet etching is performed. The patterning of the photosensitive resist can be performed by a known photolithography technique.

[0057] Specifically, photosensitive resist is applied onto the upper electrode 13a by a spin coater or roll coater, and then exposed to ultraviolet light using a glass photomask on which a desired pattern has been formed in advance. The photosensitive resist mask layer is then developed, washed with water, and dried to form a mask layer. The end inclination of the pattern of the mask layer affects the inclined cross section during etching, so the mask layer may be selected in accordance with the desired inclination angle, taking into consideration the resist selection ratio (etching rate between the material to be etched and the mask material). After etching, the photosensitive resist remaining on the upper electrode 13a can be removed with a dedicated stripping solution or by oxygen plasma ashing.

[0058] Dry etching using reactive gas is often selected for the sake of shape stability, but etching gas can be a halogen-based gas such as a chlorine-based or fluorine-based gas, or a gas in which a halogen-based gas is mixed with Ar or oxygen. By changing the etching gas or etching conditions, the upper electrode 13a and the piezoelectric layer 13b can be etched continuously, or a resist pattern can be re-formed and etching can be performed in several steps.

[0059] Alternatively, instead of the above-mentioned method, the piezoelectric layer 13b may be processed (etched) into a predetermined shape before the upper electrode 13a is formed, and then the upper electrode 13a may be formed only on the piezoelectric layer 13b of the predetermined shape.

[0060] As described above, the piezoelectric vibrator 13 can be formed through a relatively simple manufacturing process, has the same performance as bulk ceramics, and can be subsequently bonded to the IC substrate 20 to manufacture the pMUT 2.

[0061] After the upper electrode 13a is formed, an insulating layer 16 is formed on the upper electrode 13a by photolithography and etching to have a predetermined pattern. The insulating layer 16 in this embodiment is a silicon oxide film formed by depositing a film having a thickness of 0.4 μm to 1.0 μm using a plasma CVD method with monosilane (SiH4) and nitrous oxide (N2O) gas as raw materials.

[0062] By the above-mentioned patterning, a contact hole is opened at the portion of the upper electrode 13a in the insulating layer 16. In this contact hole, a wiring material of Al-Cu (1 μm) / Ti (50 nm) is formed by sputtering, and then patterned by photolithography and etching to form the wiring 11a.

[0063] Furthermore, a silicon nitride film (Si3N4) is formed as a protective layer, and a passivation film 17 is formed with an opening only at the electrode terminal portion connected to the wiring 11a (the portion where the first metal member 11 is formed). The passivation film 17 in this embodiment can be a silicon nitride film (Si3N4) of about 0.5 μm to 1.5 μm formed by plasma CVD using monosilane (SiH4), nitrous oxide (N2O), and ammonia (NH3) gas as raw materials. The opening at the electrode terminal portion can be formed by photolithography and etching.

[0064] Next, aluminum, which is the material of the first metal member 11, is deposited by sputtering to a thickness of about 3 μm, and then patterned into a predetermined pattern to form an aluminum member 11A that will become the first metal member 11 on the electrode terminal in the opening of the passivation film 17. In this embodiment, as shown in Fig. 9(a), an aluminum member 11B that will become the first metal member 11 is also formed on the IC substrate 20 side. In this embodiment, the first metal member 11 is formed by metal-bonding these aluminum members 11A and 11B.

[0065] The material of the first metal member 11 is not limited to Al, and may be any material suitable for metal bonding, such as Au, Cu, Ge, etc. In addition, the material of the first metal member 11 is preferably one that maintains good electrical conductivity even after bonding.

[0066] Once the vibration substrate 10 and the IC substrate 20 are prepared in this manner, as shown in Fig. 9(a), the vibration substrate 10 and the IC substrate 20 are bonded to each other while applying heat and pressure using a wafer bonding device. The method for bonding the vibration substrate 10 and the IC substrate 20 can be selected from direct bonding, diffusion bonding, eutectic bonding, and the like. Before bonding, CMP may be performed to flatten the bonding surface of the first metal member 11, and then bonding may be performed.

[0067] 9(b), the gap C between the diaphragm 15 on the vibration portion substrate 10 and the IC substrate 20 is set to 1 μm. This gap C is preferably 3 μm or less.

[0068] When the vibration substrate 10 and the IC substrate 20 are bonded, the support substrate 30 is present on the vibration substrate 10, but this support substrate 30 is finally removed. Specifically, the silicon support substrate 30 is thinned to a thickness of about 10 μm to 200 μm by back grinding and polishing, and then the remaining support substrate 30 is removed by dry etching. The support substrate 30 can also be left without being completely removed to a thickness of about 10 μm or less so that it functions as a vibration plate. The etching process of the support substrate 30 can be easily performed by etching with SF6 plasma using a silicon etcher.

[0069] Finally, dicing and the like are performed to complete the wafer production process of the pMUT chip 2. In this embodiment, bonding at the wafer level has been described, but the pMUT chip 2 can also be completed by performing chip bonding or chip-wafer (C2W) bonding instead of wafer bonding.

[0070] As described above, the pMUT chip 2 in this embodiment is used as an ultrasonic transducer that transmits and receives ultrasonic waves by vibrating the diaphragm 15, and can be applied to medical diagnosis, industrial, automotive, and marine inspection and measurement devices. In particular, when used in a medical diagnostic device such as this embodiment, it is widely used because it does not damage the living body of the subject 9 and allows easy real-time observation of internal tissues.

[0071] The above description is merely an example, and each of the following aspects provides unique effects. [First aspect] The first aspect is an ultrasonic transducer (e.g., pMUT chip 2) in which a movable membrane (e.g., diaphragm 15) having an electromechanical conversion element (e.g., piezoelectric vibrator 13) consisting of a lower electrode layer (e.g., lower electrode 13c), an electromechanical conversion layer (e.g., piezoelectric layer 13b) and an upper electrode layer (e.g., upper electrode 13a) formed on one side (e.g., the rear side) is fixed around its periphery by a fixing member (e.g., first metal member 11), and which transmits or receives ultrasonic waves, or both, on the side opposite to the one side (the transmitting / receiving side) by displacement of the movable membrane, characterized in that the fixing member fixes the periphery of the movable membrane only from the one side. Conventional ultrasonic transducers were realized by dicing ceramic PZT (lead zirconate titanate), known as bulk, into individual pieces. In recent years, pMUT (Piezoelectric Micro-machined Ultrasonic Transducers) and cMUT (Capacitive Micro-machined Ultrasonic Transducers) are used as ultrasonic transducers using semiconductor elements. These can achieve high resolution and high frequency through microfabrication using semiconductor technology, and may become mainstream in the future. In particular, high-performance ultrasonic probes for medical diagnostic equipment have been put to practical use using cMUT. cMUT can achieve acoustic characteristics close to those of living organisms by making the diaphragm thin, soft, and light. Therefore, it is easy to realize short pulse waveforms and wide bandwidth without using an acoustic matching layer. On the other hand, in the case of an ultrasonic probe using a pMUT, it has been difficult to provide an ultrasonic probe and an ultrasonic diagnostic apparatus using the same that prevent electrical leakage to the subject 9 by providing a suitable insulating structure and improve electrical safety while also providing a short pulse waveform and wideband characteristics. However, in the ultrasonic probe using a pMUT described in Patent Document 1, a common electrode (ground electrode) that is the lower electrode 13c of the piezoelectric transducer 13 is arranged on the ultrasonic transmission / reception side, so that the electrode on the subject 9 side becomes a ground electrode, and electrical safety can be improved by reducing the current flowing from the electrode to the subject 9 side. However, the short pulse waveform and wideband characteristics are still insufficient. In the ultrasonic transducer disclosed in Patent Document 1, ultrasonic waves generated by the displacement of the movable membrane are transmitted from a covering member (a member forming a sealed space together with the fixed member and the movable membrane) via an acoustic transmission member in a sealed space surrounded by a fixed member. Also, in the ultrasonic transducer disclosed in Patent Document 1, ultrasonic waves from the outside transmitted to the covering member are propagated to the movable membrane via an acoustic transmission member in a sealed space surrounded by a fixed member and received. In such a conventional ultrasonic transducer, ultrasonic waves generated by the movable membrane must propagate within the sealed space surrounded by the fixed member before being transmitted to the outside of the ultrasonic transducer, or ultrasonic waves from the outside must propagate within the sealed space surrounded by the fixed member before being received by the movable membrane. When a configuration for propagating within a sealed space is interposed in this way, acoustic characteristics (especially wideband characteristics) are limited, making it difficult to obtain sufficient wideband characteristics. In this embodiment, the fixing member that fixes the periphery of the movable membrane is provided only on the one surface side of the movable membrane, that is, only on the side opposite to the side (the other surface side of the movable membrane) where ultrasonic waves are transmitted or received, or both. Therefore, no fixing member is provided on the ultrasonic transmission side or reception side of the movable membrane. This makes it possible to omit a sealed space surrounded by the fixing member (or an acoustic transmission member therein), which is interposed in the conventional configuration between the ultrasonic waves generated by the movable membrane and transmitted to the outside, or between the ultrasonic waves from the outside and received by the movable membrane. As a result, it is possible to make the movable membrane thin, soft, and light, and it is possible to improve acoustic characteristics such as a short pulse waveform and wide band, especially wide band characteristics, compared to the conventional configuration.

[0072] [Second aspect] The second aspect is characterized in that the first aspect further comprises a sealed space forming member (eg, IC substrate 20) that is connected to the fixed member and forms a sealed space together with the fixed member and the movable film. When the electromechanical transducer is exposed to moisture, insulation breakdown is likely to occur, so the voltage of the drive signal applied to the electromechanical transducer cannot be increased, making it difficult to increase the transmission strength of the ultrasonic waves. According to this embodiment, the electromechanical transducer is enclosed within the sealed space formed by the fixed member, the movable film, and the sealed space forming member, so that the electromechanical transducer is prevented from being exposed to moisture. Therefore, it is possible to increase the voltage of the drive signal and increase the transmission strength of the ultrasonic waves. In addition, it is possible to omit a protective film (e.g., passivation film 17) that protects the electromechanical transducer from moisture, so that the movable film can be made thinner, softer, and lighter, enabling further improvement in the wideband characteristics.

[0073] [Third aspect] A third aspect is the first or second aspect, characterized in that the fixing member is a signal transmission member that transmits an electrical signal between the lower electrode layer and the upper electrode layer. This eliminates the need to provide a signal transmission member separately from the fixed member, making it possible to simplify the configuration.

[0074] [Fourth aspect] A fourth aspect is any one of the first to third aspects, characterized in that the fixing member is spaced apart from the electromechanical transducer layer and fixes the periphery of the movable film. According to this embodiment, the layer constituting the movable film between the electromechanical transducer layer and the fixed member does not have an electromechanical transducer layer, and this portion is the thinnest portion of the movable film. In the region where the driving efficiency of the electromechanical transducer element arranged in the movable film is poor, the upper electrode and the electromechanical transducer layer are removed to make the movable film thin and light, and efficient driving can be achieved. In particular, since the material of the electromechanical transducer layer is generally dense and heavy, the absence of the electromechanical transducer layer in the thinnest portion (between the electromechanical transducer layer and the fixed member), which is important for realizing efficient driving of the movable film, can realize a lighter movable film and further improve the wideband characteristics.

[0075] [Fifth aspect] The fifth aspect is characterized in that, in any of the first to fourth aspects, a plurality of electromechanical conversion elements (e.g., piezoelectric vibrators 13) are formed on one surface (the rear surface) of the movable film, and the lower electrode layer is a ground electrode common to the plurality of electromechanical conversion elements. In this embodiment, since the lower electrode layer, which is the electrode that transmits and receives ultrasonic waves, is a ground electrode, it is possible to reduce the current flowing from the electrode of the electromechanical conversion element to the object to be measured, thereby improving the electrical safety of the ultrasonic converter.

[0076] [Sixth aspect] A sixth aspect is characterized in that, in any of the first to fifth aspects, a plurality of electromechanical conversion elements are formed in an array on one surface of the movable film, and the fixing member fixes the periphery of a movable film including one electromechanical conversion element or a movable film including two or more electromechanical conversion elements. This makes it easier to achieve higher transmission strength.

[0077] [Seventh aspect] The seventh aspect is an ultrasonic probe 1 that transmits ultrasonic waves from an ultrasonic transducer (e.g., a pMUT chip 2) to a measurement object (e.g., a subject 9) and receives the ultrasonic waves reflected by the measurement object, characterized in that the ultrasonic transducer is an ultrasonic transducer of any of the first to sixth aspects, and a control board (e.g., an IC board 20) that transmits and receives electrical signals between the lower electrode layer and the upper electrode layer in the ultrasonic transducer via a signal transmission member of the ultrasonic transducer is provided on one side (e.g., the back side) of the movable membrane. This makes it possible to realize an ultrasonic probe having improved acoustic characteristics, such as a short pulse waveform and broadband, particularly improved broadband characteristics, compared to conventional configurations.

[0078] [Eighth aspect] An eighth aspect is the seventh aspect, characterized in that the control board is connected to the fixed member of the ultrasonic converter and forms an enclosed space together with the fixed member and the movable membrane. When the electromechanical conversion element is exposed to moisture, insulation breakdown is likely to occur, so the voltage of the drive signal applied to the electromechanical conversion element cannot be increased, making it difficult to increase the transmission strength of the ultrasonic waves. According to this embodiment, the electromechanical conversion element is enclosed within an enclosed space formed by the fixed member, the movable film, and the control board, so that the electromechanical conversion element is prevented from being exposed to moisture. This makes it possible to increase the voltage of the drive signal and increase the transmission strength of the ultrasonic waves. In addition, it is possible to omit a protective film (e.g., passivation film 17) that protects the electromechanical conversion element from moisture, so that the movable film can be made thinner, softer, and lighter, enabling further improvement in the wideband characteristics.

[0079] [Ninth aspect] A ninth aspect is the eighth aspect, characterized in that the minimum width of the fixing member is 3 μm or more and 50 μm or less. This makes it possible to increase the transmitted sound pressure per unit area while ensuring sufficient bonding strength and airtightness.

[0080] [Tenth aspect] A tenth aspect is the liquid crystal display device according to any one of the seventh to ninth aspects, characterized in that a distance C between the movable film and the control substrate is 3 μm or less. According to this, the thickness of the member (for example, first metal member 11) that joins the ultrasonic transducer and the control board with a predetermined gap therebetween can be reduced, and the manufacturing process can be simplified.

[0081] [Eleventh aspect] An eleventh aspect is characterized in that, in any one of the seventh to tenth aspects, a covering member is bonded onto the opposite surface (e.g., the transmitting / receiving surface) of the movable membrane in the ultrasonic transducer. According to this aspect, no acoustic matching layer is provided on the side of the ultrasonic transducer that transmits and receives ultrasonic waves, and a covering member such as an acoustic lens is directly bonded thereto, thereby improving the wideband characteristics.

[0082] [12th aspect] The twelfth aspect is an ultrasound diagnostic device 100, characterized in that it has an ultrasound probe of any of the seventh to eleventh aspects and a display unit (e.g., display unit 61, display terminal 50) for displaying the shape of the object to be measured. According to this embodiment, an ultrasound probe with improved acoustic characteristics, such as a short pulse waveform and wideband, particularly improved wideband characteristics, is used, so that an ultrasound diagnostic device 100 that enables more appropriate diagnosis can be provided.

[0083] [13th aspect] The 13th aspect is a manufacturing method for an ultrasonic converter in which a movable membrane having an electromechanical conversion element consisting of a lower electrode layer, an electromechanical conversion layer, and an upper electrode layer formed on one side is fixed by a fixing member, and ultrasonic waves are transmitted or received, or both, on the side opposite to the one side by displacement of the movable membrane, characterized in that the fixing member is formed only on the one side. According to this aspect, it is possible to provide an ultrasonic transducer having improved acoustic characteristics, such as a short pulse waveform and a wide band, in particular improved wide band characteristics. [Explanation of symbols]

[0084] 1:Ultrasonic probe 2: pMUT chip 3: Support part 4: Flexible board 5: Wiring 6: Adhesive 7: Connector 8: Acoustic lens 9: Subject 10: Vibration board 11: First metal member 11a: Wiring 12: Second metal member 13: Piezoelectric transducer 13a: Upper electrode 13b: Piezoelectric layer 13c: Lower electrode 14: Base material layer 15: Diaphragm 16: Insulating layer 17: Passivation film 20: IC board 21, 22: Wiring 30: Support substrate 50: Display terminal 61:Display section 62:Operation unit 63: Control section 64: Ultrasonic pulse generator 65: Conversion section 66: Ultrasound imaging unit 100: Ultrasound diagnostic equipment [Prior art documents] [Patent documents]

[0085] [Patent Document 1] Patent No. 5560928

Claims

1. An ultrasonic transducer, comprising: a movable film having an electromechanical transducer element having a lower electrode layer, an electromechanical transducer layer, and an upper electrode layer formed on one surface thereof, the periphery of the movable film being fixed by a fixing member; and the ultrasonic transducer transmits or receives, or both, ultrasonic waves on a surface opposite to the one surface in response to the displacement of the movable film, the fixing member fixes the periphery of the movable film only from the one surface side, an ultrasonic transducer comprising: a sealed space forming member connected to the fixed member and forming a sealed space together with the fixed member and the movable membrane;

2. The ultrasonic transducer according to claim 1, The ultrasonic transducer according to claim 1, wherein the fixing member is a signal transmission member that transmits an electrical signal between the lower electrode layer and the upper electrode layer.

3. 3. The ultrasonic transducer according to claim 1, The ultrasonic transducer according to claim 1, wherein the fixing member is spaced apart from the electromechanical conversion layer and fixes the periphery of the movable film.

4. 4. An ultrasonic transducer according to claim 1, a plurality of electromechanical transducers are formed on the one surface of the movable film; The ultrasonic transducer according to claim 1, wherein the lower electrode layer is a ground electrode common to the plurality of electromechanical conversion elements.

5. 5. An ultrasonic transducer according to claim 1, a plurality of electromechanical transducers are formed in an array on the one surface of the movable film; An ultrasonic transducer, characterized in that the fixing member fixes the periphery of a movable film including one electromechanical conversion element or a movable film including two or more electromechanical conversion elements.

6. An ultrasonic probe that transmits ultrasonic waves from an ultrasonic transducer to a measurement object and receives the ultrasonic waves reflected by the measurement object, The ultrasonic transducer according to any one of claims 1 to 5 is used as the ultrasonic transducer, An ultrasonic probe characterized in that a control board that transmits and receives electrical signals between the lower electrode layer and the upper electrode layer in the ultrasonic transducer via a signal transmission member of the ultrasonic transducer is provided on one surface side of the movable membrane.

7. 7. The ultrasonic probe according to claim 6, The ultrasonic probe, wherein the sealed space forming member is the control board.

8. 8. The ultrasonic probe according to claim 7, The ultrasonic probe according to claim 1, wherein the minimum width of the fixing member is 3 μm or more and 50 μm or less.

9. 9. The ultrasonic probe according to claim 6, An ultrasonic probe, characterized in that the distance between the movable film and the control substrate is 3 μm or less.

10. 10. The ultrasonic probe according to claim 6, An ultrasonic probe, characterized in that a covering member is bonded to a surface of the ultrasonic transducer opposite to the movable membrane.

11. An ultrasonic probe according to any one of claims 6 to 10, and a display unit for displaying the shape of the object to be measured.

12. A method for manufacturing an ultrasonic transducer, comprising the steps of: fixing a periphery of a movable film, on one side of which an electromechanical transducer element having a lower electrode layer, an electromechanical transducer layer, and an upper electrode layer is formed; and transmitting or receiving, or both, ultrasonic waves on a surface side opposite to the one surface by displacement of the movable film, comprising: forming the fixing member only on the one surface side; and connecting, to the fixed member, an enclosed space forming member which forms an enclosed space together with the fixed member and the movable membrane.

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