US20070097791A1 - Capacitive ultrasonic transducer and method of fabricating the same - Google Patents

Capacitive ultrasonic transducer and method of fabricating the same Download PDF

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Publication number
US20070097791A1
US20070097791A1 US11/324,408 US32440806A US2007097791A1 US 20070097791 A1 US20070097791 A1 US 20070097791A1 US 32440806 A US32440806 A US 32440806A US 2007097791 A1 US2007097791 A1 US 2007097791A1
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United States
Prior art keywords
layer
metal
ultrasonic transducer
capacitive ultrasonic
metal layer
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US11/324,408
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English (en)
Inventor
Ming-Wei Chang
Tsung-Ju Gwo
Tse-Min Deng
Zhen-Yuan Chung
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Industrial Technology Research Institute ITRI
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Industrial Technology Research Institute ITRI
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Assigned to INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE reassignment INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: CHANG, MING-WEI, CHUNG, ZHEN-YUAN, DENG, TSE-MIN, GWO, TSUNG-JU
Assigned to INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE reassignment INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: CHANG, MING-WEI, CHUNG, ZHEN-YUAN, DENG, TSE-MIN, GWO, TSUNG-JU
Priority to US11/427,194 priority Critical patent/US7626891B2/en
Publication of US20070097791A1 publication Critical patent/US20070097791A1/en
Priority to US12/049,224 priority patent/US7937834B2/en
Abandoned legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/0292—Electrostatic transducers, e.g. electret-type
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/005—Electrostatic transducers using semiconductor materials
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R31/00—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor
    • H04R31/006—Interconnection of transducer parts
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/43—Electric condenser making
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49005—Acoustic transducer
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49117—Conductor or circuit manufacturing
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49117—Conductor or circuit manufacturing
    • Y10T29/49124—On flat or curved insulated base, e.g., printed circuit, etc.
    • Y10T29/49128—Assembling formed circuit to base
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49117—Conductor or circuit manufacturing
    • Y10T29/49124—On flat or curved insulated base, e.g., printed circuit, etc.
    • Y10T29/49155—Manufacturing circuit on or in base
    • Y10T29/49156—Manufacturing circuit on or in base with selective destruction of conductive paths

Definitions

  • the present invention relates to a capacitive ultrasonic transducer and method of fabricating the same, and more particularly, to a capacitive ultrasonic transducer, which is substantially a stacking of multiple metal layers having structures and cavities of excitation being formed therein by electrochemical depositing/etching and lithographing, and thus the method for fabricating the aforesaid transducer can waive the steps of electrode forming and annealing.
  • Ultrasonic imaging has found widespread use in industrial and medical applications. Flaw detection, thickness measurement, and diagnostic imaging are just a few of the tools utilizing this technology. All information acquired by the ultrasound system passes through the transducer before being processed and presented to the operator. Therefore, the performance characteristics of the transducer can significantly influence system performance, especially when the miniaturization of ultrasonic transducer is the trend of future development. It possesses several advantages over other techniques, like x-rays or magnetic resonance imaging (MRI), including being noninvasive, relatively inexpensive, portable, and capable of producing a tomographical image—an image of a two-dimensional slice of the body. Another very important advantage is that ultrasound produces images fast enough to monitor the motion of structures within the body, such as a fetus or a beating heart. Close attention should be paid to the design and fabrication of a proper transducer for the application, taking into consideration the performance of the imaging system as a whole.
  • MRI magnetic resonance imaging
  • CMUTs capacitive micromachined ultrasonic transducers
  • CMUTs provide the following advantages over piezoelectric transducers: (1) CMUTs can be batch produced with a standard IC process and thus integrated with IC devices, which is difficult with piezoelectric transducers since they require to be processed by a high-temperature process; (2) The frequency generated by a CMUT is in a frequency range of 200 KHz ⁇ 5 MHz while a piezoelectric transducer is operating at a frequency range of 50 KHx ⁇ 200 KHz, that has restricted the application of the piezoelectric transducers to a smaller area than that of the CMUTs.
  • FIG. 1A is schematic view of a conventional capacitive ultrasonic transducer.
  • the configuration of the conventional capacitive ultrasonic transducer 10 is similarly to a parallel plane capacitor, by which a thin film is enabled to vibrate ultrasonically as alternating voltage signals are being applied on a fixed electrode 101 and another electrode 102 arranged on the thin film 103 .
  • FIGS. 2 A ⁇ 2 H are diagrams depicting the successive steps of fabricating a conventional ultrasonic transducer.
  • the fabrication method shown in FIGS. 2 A ⁇ 2 H is first developed by Jin, et al. at 1998, and is adapted for making an ultrasonic transducer suitable for operating in a gaseous or liquid ambient by the use of a technique of surface micromachining.
  • the processing flow of the aforesaid method starts at the step shown in FIG. 2A , where a highly silicon wafer 11 with high conductivity is provided and being used as a substrate; and then the flow proceeds to the step shown in FIG. 2B .
  • FIG. 2A where a highly silicon wafer 11 with high conductivity is provided and being used as a substrate; and then the flow proceeds to the step shown in FIG. 2B .
  • a layer of nitrides 12 referred as first nitride layer, is formed on the substrate 11 at 800° C. ambient by a means of low-pressure chemical vapor deposition (LPCVC), and then the flow proceeds to the step shown in FIG. 2C .
  • LPCVC low-pressure chemical vapor deposition
  • a sacrificial layer 13 made of an amorphous silicon material is formed on the first nitride layer 12 , and then the flow proceeds to the step shown in FIG. 2D .
  • the sacrificial layer 13 is etched to form a plurality of hexagon islands by a means of dry etching, and then the flow proceeds to the step shown in FIG. 2E .
  • FIG. 2E In FIG.
  • second nitride layer 14 another layer of nitrides, referred as second nitride layer 14 , is deposited to cover the hexagon islands of the sacrificial layer 13 whereas a portion of the second nitride layer 14 is going to be used to form a plurality of thin films while another portion of the second nitride layer 14 is going to be used as frames for supporting the thin films, and then the flow proceeds to the step shown in FIG. 2F .
  • FIG. 2E another layer of nitrides
  • the second nitride layer 14 is etched to form a plurality of apertures 15 channeling to the corresponding hexagon islands of the sacrificial layer 13 and then the plural hexagon islands are removed by feeding a potassium hydroxide solution into the plural apertures 15 to form a plurality of excitation cavities 17 accordingly, and then the flow proceeds to the step shown in FIG. 2G .
  • the apertures are sealed by depositing silicon dioxide therein, and then the flow proceeds to the step shown in FIG. 2H .
  • a layer of aluminum 18 is coated on top of the structure of FIG. 2G whereas the aluminum is being patterned to form top electrodes by a means of wet etching.
  • the ultrasonic transducer made by the aforesaid method can have a dynamic range in excess of 110 dB is observed in air at 2.3 MHz, and a dynamic range in excess of 600 dB is observed in air at 3.5 MHz.
  • Cianci, et al. had developed a low-temperature process cooperating with a thermal annealing step for fabricating a capacitive ultrasonic transducer whereas the annealing is perform in a 510° C. ambient for 10 hours.
  • the pressure stress of the thin film of the capacitive ultrasonic transducer is eliminated while obtaining an ideal condition of preserving a slight tension stress exerting on the thin film.
  • a further fabrication method of capacitive ultrasonic transducer is disclosed in U.S. Pat. No.
  • ultrasonic transducers there are a variety of ultrasonic transducers currently available and also corresponding methods of fabricating the same. Most of which are made of silicon-based material that are being processed by either a means of surface micromachining or a means of bulk micromachining so as to enable the resulting ultrasonic transducer to have thinner oscillation film and smaller excitation cavity and thus enable the same to have high vibration frequency, enhanced sensitivity and high resolution. It is also because of that, all those prior-art processes of fabricating capacitive ultrasonic transducer are commonly troubled by the problems of high processing temperature, high residual stress, complicated process that is hard to controlled, and high cost. Especially the problem of high residual stress will cause the oscillation film to deform. Therefore, an additional thermal annealing procedure is required to reduce the residual stress and thus alleviate the deformation of oscillation film caused by the same. Nevertheless, the additional annealing step will inevitably cause the time and cost of the fabrication process to increase.
  • the oscillation film of a prior-art capacitive ultrasonic transducer is substantially a layer of silicon nitride deposited by a means of low-pressure chemical vapor deposition (LPCVC)
  • LPCVC low-pressure chemical vapor deposition
  • the high residual stress caused by the high temperature ambient required for enabling the LPCVC deposition of silicon nitride not only will adversely affect the quality of the resulting capacitive ultrasonic transducer, but also the geometric size of the oscillation film is restricted by the same.
  • the aforesaid prior-art ultrasonic transducers can be sealed and protected by a microcap 19 as shown in FIG. 1B .
  • the additional microcap is going to cause some technical problems, such as the positioning and alignment during packaging, the status of surface adhesion including roughness, phase variation, etc.
  • the primary object of the present invention is to provide an improved capacitive ultrasonic transducer and method of fabricating the same, whereas the capacitive ultrasonic transducer is substantially a stacking of multiple metal layers so that the manufacturing cost of the same can be reduced since an additional step of electrode formation can be saved from the method of fabricating the same.
  • Another object of the invention is to provide a capacitive ultrasonic transducer and method of fabricating the same, wherein the capacitive ultrasonic transducer is comprised of a protective bulk, being used for protecting the oscillation film and the main body of the capacitive ultrasonic transducer.
  • the present invention provide a capacitive ultrasonic transducer, comprising: an assembly of supporting frames, being formed on a substrate; and a metal layer, being formed on top of the assembly; wherein at least a cavity is formed by the enclosure of the metal layer, the assembly of supporting frames and the substrate.
  • At least a bulk which is preferably being made of nickel, is being formed on the metal layer at a position corresponding to each supporting frame.
  • each supporting frame is made of a metal, preferably being nickel.
  • the present invention provides a method for fabricating a capacitive ultrasonic transducer, comprising the steps of:
  • the step (b) of forming the first structure in the above fabrication method further comprises the steps of: (b1) forming a layer of photo resist on the insulating layer; (b2) removing a portion of the photo resist layer to form at least a cavity thereby; (b3) forming a sacrificial layer on the partially removed photo resist layer while enabling each cavity to be filled by the sacrificial layer; (b4) polishing the surface of the sacrificial layer for enabling the remaining photo resist layer and the sacrificial layer to coplanar; (b5) removing the remaining photo resist layer so as to form hollows in the sacrificial layer; and (b6) depositing a layer of a second metal on the sacrificial layer by a means of electrochemical deposition while filling the hollows with the second metal to form the assembly of supporting frames.
  • the step (b) of forming the first structure in the above fabrication method further comprises the steps of:
  • the above fabrication method further comprises the steps of:
  • each supporting frame is made of a metal, preferably being nickel.
  • the sacrificial layer of made of copper.
  • step (f) of removing the sacrificial layer in the above fabrication method further comprises the steps of:
  • the plural apertures are going to be filled by a posterior process, wherein the etching of the sacrificial layer is performed by a means of wet etching.
  • FIG. 1A is a schematic view of a conventional capacitive ultrasonic transducer.
  • FIG. 1B is a schematic view of a conventional capacitive ultrasonic transducer with protective microcap.
  • FIG. 2A to FIG. 2H are schematic diagrams depicting a flow chart of a method for fabricating capacitive ultrasonic transducers according to prior art.
  • FIG. 3 is schematic view of a capacitive ultrasonic transducer according to a preferred embodiment of the invention.
  • FIG. 4A to FIG. 4N are schematic diagrams depicting a flow chart of a method for fabricating capacitive ultrasonic transducers according to a preferred embodiment of the invention.
  • FIG. 5A to FIG. 5N are schematic diagrams depicting a flow chart of a method for fabricating capacitive ultrasonic transducers according to another preferred embodiment of the invention.
  • FIG. 3 is schematic view of a capacitive ultrasonic transducer according to a preferred embodiment of the invention.
  • the capacitive ultrasonic transducer 2 of FIG. 3 comprises: an assembly of supporting frames 23 , being formed on a substrate 20 ; a metal layer 24 , being formed on top of the assembly 23 ; and a plurality of protective bulks 25 , each being formed on the metal layer 24 at a position corresponding to a supporting frame corresponding thereto; wherein at least a cavity 26 is formed by the enclosure of the metal layer 24 , the assembly of supporting frames 23 and the substrate 20 .
  • an insulating layer 21 and a seed layer 22 are successively formed and sandwiched between the assembly of supporting frames 23 and the substrate 20 .
  • each supporting frame of the assembly 23 is made of a metal, preferably to be nickel, and the substrate 20 can be made of a silicon-based material, which can be adapted to be the electrode for driving the capacitive ultrasonic transducer 2 .
  • the metal layer 24 is used to act as the oscillation film and the driving electrode of the resulting capacitive ultrasonic transducer 2 , that it can be made of nickel in this preferred embodiment. Since the vibration of ultrasonic waves is generated by the oscillation of the metal layer 24 , it is importance to prevent the metal layer from being damaged by foreign objects during operating. Hence, a plurality of protective bulks 25 are formed on the metal layer 24 , each at a position corresponding to a supporting frame of the assembly 23 corresponding thereto, so that the metal layer 24 can be protected thereby.
  • the protective bulk 25 is made of a metal, preferably to be nickel.
  • FIG. 4A to FIG. 4N are schematic diagrams depicting a flow chart of a method for fabricating capacitive ultrasonic transducers according to a preferred embodiment of the invention.
  • the flow starts at the step shown in FIG. 4A .
  • a substrate 30 is provided, which has an insulating layer 31 deposited thereon, and then the flow proceeds to the step shown in FIG. 4B .
  • a seed layer 32 is being deposited on the insulating layer 31 , and then the flow proceeds to the step shown in FIG. 4C .
  • FIG. 4C a layer of photo resist 33 is formed on the seed layer 32 , and then the flow proceeds to the step shown in FIG. 4D .
  • FIG. 4A a substrate 30 is provided, which has an insulating layer 31 deposited thereon, and then the flow proceeds to the step shown in FIG. 4B .
  • a seed layer 32 is being deposited on the insulating layer 31 , and then the flow proceeds to the step shown in FIG. 4C .
  • an optic mask is employed to define a pattern of cavities 331 on the photo resist layer 33 by lithography, and then the patterned photo resist layer 33 is being etched to form a plurality of cavities 331 thereon, and then the flow proceeds to the step shown in FIG. 4E .
  • a sacrificial layer 34 is being formed by a means of electrochemical deposition while enabling each cavity 331 to be filled therewith, preferably the sacrificial layer 34 is made of a metal that can be cooper, and then the flow proceeds to the step shown in FIG. 4F .
  • the resulting structure of FIG. 4E is being polished for enabling the sacrificial layer 34 and the photo resist layer 33 to coplanar, and then the flow proceeds to the step shown in FIG. 4G .
  • FIG. 4G the remaining photo resist layer 33 is removed so as to form hollows 332 in the sacrificial layer 34 , and then the flow proceeds to the step shown in FIG. 4H .
  • a second metal layer 35 is deposited on the sacrificial layer 34 by a means of electrochemical deposition while enabling the hollows 332 to be filled therewith, preferably the second metal is nickel, and then the flow proceeds to the step shown in FIG. 41 .
  • FIG. 41 the resulting structure of FIG. 4H is polished for enabling the second metal layer 35 and the sacrificial layer 34 to coplanar, and then the flow proceeds to the step shown in FIG. 4J .
  • FIG. 41 the resulting structure of FIG. 4H is polished for enabling the second metal layer 35 and the sacrificial layer 34 to coplanar, and then the flow proceeds to the step shown in FIG. 4J .
  • a first metal layer 36 is formed on the coplanar structure of FIG. 41 by a means of electrochemical deposition and then the formed first metal layer 36 is being polished until a specific thickness of the same is achieved, preferably the first metal is nickel, and then the flow proceeds to the step shown in FIG. 4K .
  • a third metal layer is formed on the first metal layer 36 by a means of electrochemical deposition and then the third metal layer is first being polished to a specific thickness, and then a portion of the polished third metal layer is removed so as to form a plurality of protective bulks 37 , each at a position corresponding to the remaining second metal layer 35 corresponding thereto, preferably the third metal is nickel, and then the flow proceeds to the step shown in FIG. 4L .
  • a plurality of apertures 361 are formed on the first metal layer 36 and are channeled to the corresponding sacrificial layer 34 , and then the flow proceeds to the step shown in FIG. 4M .
  • a plurality of cavities 38 are formed by wet-etching the remaining sacrificial layer 34 while etchant is fed to the sacrificial layer 34 through the plural apertures 361 , and then the flow proceeds to the step shown in FIG. 4N .
  • the plural apertures 361 are filled so as to seal the plural cavities 38 , preferably the apertures are filled by an isotropic material of good coverage that further has the same electrochemical characteristic as that of the first metal layer.
  • FIG. 5A to FIG. 5N are schematic diagrams depicting a flow chart of a method for fabricating capacitive ultrasonic transducers according to another preferred embodiment of the invention.
  • the flow starts at the step shown in FIG. 5A .
  • a substrate 40 is provided, which has an insulating layer 41 deposited thereon, and then the flow proceeds to the step shown in FIG. 5B .
  • a seed layer 42 is being deposited on the insulating layer 41 , and then the flow proceeds to the step shown in FIG. 5C .
  • FIG. 5C a layer of photo resist 43 is formed on the seed layer 42 , and then the flow proceeds to the step shown in FIG. 5D .
  • FIG. 5A a substrate 40 is provided, which has an insulating layer 41 deposited thereon, and then the flow proceeds to the step shown in FIG. 5B .
  • a seed layer 42 is being deposited on the insulating layer 41 , and then the flow proceeds to the step shown in FIG. 5C .
  • an optic mask is employed to define a pattern of an assembly of supporting frames on the photo resist layer 43 by lithography, and then the patterned photo resist layer 43 is being etched to create hollows 431 for forming the assembly of supporting frames therein in a later step, and then the flow proceeds to the step shown in FIG. 5E .
  • a second metal layer 44 is being formed by a means of electrochemical deposition while enabling the hollows 431 to be filled therewith, preferably the second metal layer 44 is made of nickel, and then the flow proceeds to the step shown in FIG. 5F .
  • the resulting structure of FIG. 5E is being polished for enabling the second metal layer 44 and the photo resist layer 43 to coplanar, and then the flow proceeds to the step shown in FIG. 5G .
  • FIG. 5G the remaining photo resist layer 43 is removed so as to form cavities 432 in the second metal layer 44 , and then the flow proceeds to the step shown in FIG. 5H .
  • a sacrificial layer 45 is deposited on the second metal layer 34 by a means of electrochemical deposition while enabling the cavities 432 to be filled therewith, preferably the sacrificial layer 45 is made of copper, and then the flow proceeds to the step shown in FIG. 5I .
  • FIG. 5I the resulting structure of FIG. 5H is polished for enabling the second metal layer 44 and the sacrificial layer 45 to coplanar, and then the flow proceeds to the step shown in FIG. 5J .
  • FIG. 5J the sacrificial layer 45
  • a first metal layer 46 is formed on the coplanar structure of FIG. 5I by a means of electrochemical deposition and then the formed first metal layer 46 is being polished until a specific thickness of the same is achieved, preferably the first metal is nickel, and then the flow proceeds to the step shown in FIG. 5K .
  • a third metal layer is formed on the first metal layer 46 by a means of electrochemical deposition and then the third metal layer is first being polished to a specific thickness, and then a portion of the polished third metal layer is removed so as to form a plurality of protective bulks 37 , each at a position corresponding to the remaining second metal layer 35 corresponding thereto, preferably the third metal is nickel, and then the flow proceeds to the step shown in FIG. 5L .
  • a plurality of apertures 461 are formed on the first metal layer 46 and are channeled to the corresponding sacrificial layer 45 , and then the flow proceeds to the step shown in FIG. 5M .
  • a plurality of cavities 48 are formed by wet-etching the remaining sacrificial layer 45 while etchant is fed to the sacrificial layer 45 through the plural apertures 461 , and then the flow proceeds to the step shown in FIG. 5N .
  • the plural apertures 461 are filled so as to seal the plural cavities 48 , preferably the apertures are filled by an isotropic material of good coverage that further has the same electrochemical characteristic as that of the first metal layer.
  • the capacitive ultrasonic transducer is made by an improved fabrication method combining the techniques of electrochemical deposition and super fine polishing, whereas the oscillation film and the electrodes of the resulting capacitive ultrasonic transducer is formed by the use of lithography, electroplating, evaporation deposition, sputtering deposition and technology of sacrificial layer.
  • the cavity of the capacitive ultrasonic transducer of the invention is formed by etching a metal sacrificial layer, the cavity can be formed in any shape at will, which is further has structure characteristics of low stress and high density.
  • the removal of the sacrificial layer in the fabrication method of the invention is achieved by wet etching that is implemented by channeling apertures to the corresponding sacrificial layer for filling etchant thereto, not only the efficiency of the removal of sacrificial layer is enhanced, but also the formation of cavity is improved.
  • the protective bulks can protect the capacitive ultrasonic transducer effectively, such that the problems caused by the microcap used in the conventional transducer can be avoided.
  • the fabrication method of the invention use an electrochemical means for fabricating the oscillation film of the capacitive ultrasonic transducer, the resulting oscillation film will have better mechanical properties that it is easier to control the stress, density and thickness thereof.
  • the deposited film is further processed by a mean of super fine polishing.
  • the capacitive ultrasonic transducer of the invention is characterized by two features, which are (1) the oscillation film is made of a metal; and (2) the capacitive ultrasonic transducer is configured with protective bulks.
  • the fabrication method of the invention uses a means of electrochemical deposition for forming the main structure of a capacitive ultrasonic transducer that can be achieved without the steps of electrode formation, high temperature processing and annealing, not only the manufacturing cost is reduced and the manufacturing process is simplified, but also the packaging problem troubling the conventional capacitive ultrasonic transducer is solved,

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  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Manufacturing & Machinery (AREA)
  • Transducers For Ultrasonic Waves (AREA)
  • Ultra Sonic Daignosis Equipment (AREA)
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US12/049,224 US7937834B2 (en) 2005-10-28 2008-03-14 Method of fabricating capacitive ultrasonic transducers

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070258332A1 (en) * 2006-05-03 2007-11-08 Esaote S.P.A. Multi-level capacitive ultrasonic transducer
US20130071964A1 (en) * 2011-09-20 2013-03-21 Canon Kabushiki Kaisha Method of manufacturing an electromechanical transducer
CN110510573A (zh) * 2019-08-30 2019-11-29 中国科学院深圳先进技术研究院 一种电容式微机械超声换能器及其制备方法和应用

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