Capacitive ultrasonic transducer, production method thereof, and capacitive ultrasonic probe

Abstract

It becomes possible to obtain high sound pressure in a high frequency domain by a capacitive ultrasonic transducer which comprises a membrane on which one electrode is formed, a cavity constructed in its backface, and a substrate on which these are mounted and supported and on whose surface an electrode is provided, on a surface in an ultrasonic transmission and reception side, characterized in that the membrane comprises two or more layers, and at least one layer of them comprises a high dielectric constant film.

1 . A capacitive ultrasonic transducer, comprising: 
 a first electrode;    a second electrode which faces the first electrode, and is arranged with keeping a predetermined gap; and    a high dielectric constant film which is formed on a surface of at least one electrode of the electrodes, that is, the surface which faces another one of the electrodes.    
   
   
       2 . The capacitive ultrasonic transducer according to  claim 1 , wherein the high dielectric constant film includes at least any one among barium titanate, strontium titanate, a solid solution of barium and titanate strontium, and niobium oxide stabilized tantalum pentoxide.  
   
   
       3 . The capacitive ultrasonic transducer according to  claim 1 , wherein the high dielectric constant film includes at least any one among tantalum oxide, aluminum oxide, and titanium oxide.  
   
   
       4 . The capacitive ultrasonic transducer according to  claim 1 , wherein the capacitive ultrasonic transducer is constructed using a substrate made of silicon single crystal or glass.  
   
   
       5 . A production method of a capacitive ultrasonic transducer which comprises a first electrode, a second electrode which faces the first electrode and is arranged with keeping a predetermined gap, and a high dielectric constant film which is given on a surface of at least one electrode of the electrodes, that is, the surface which faces another one of the electrodes, comprising: 
 a stacked layer forming step of performs stacked layer formation of one or more layers including the first electrode and high dielectric constant film on a first substrate;    a cavity forming step of forming cavities in a second substrate for forming the cavities which are spaces between the first electrode and the second electrode;    an electrode forming step of forming a second electrode in bottom sections of the cavities;    a bonding step of bonding a surface in a stacked layer formation side of the first substrate, on which the stacked layer formation is performed, with a convex section surface of the second substrate; and    a substrate removing step of removing the first substrate from the first substrate on which the stacked layer formation is performed.    
   
   
       6 . The production method of a capacitive ultrasonic transducer according to  claim 5 , wherein an anode bonding method is used at the bonding step.  
   
   
       7 . The production method of a capacitive ultrasonic transducer according to  claim 5 , wherein the high dielectric constant film is formed on the first electrode by performing hydrolytic cleavage and oxidation after making a metal alkoxide compound solution of tantalum, titanium, and barium coated and performing a sol-gel spin coat method.  
   
   
       8 . A production method of a capacitive ultrasonic transducer which comprises a first electrode, a second electrode which faces the first electrode and is arranged with keeping a predetermined gap, and a high dielectric constant film which is given on a surface of at least one electrode of the electrodes, that is, the surface which faces another one of the electrodes, comprising: 
 a substrate forming step of not only forming cavities in a second substrate for forming the cavities which are spaces between the first electrode and the second electrode, but also forming the second electrode in the bottom sections of the cavities;    a sacrifice layer forming step of forming a sacrifice layer by making the cavities of the second substrate filled with a resist agent;    a high dielectric constant film forming step of forming one or more films, including the high dielectric constant film, on a surface of a side of the second substrate where is filled with the resist agent;    an electrode forming step of forming the first electrode on the film; and    a sacrifice layer removing step of making holes penetrate the first electrode and the film, and removing the sacrifice layer from the holes.    
   
   
       9 . The production method of a capacitive ultrasonic transducer according to  claim 8 , wherein the second substrate comprises two substrates of a glass substrate and a silicon substrate, one or more holes for forming cavities in one substrate between the two substrates are provided, the second electrodes are provided only in positions corresponding to positions of the holes in another substrate, and the two substrates are bonded by anode bonding.  
   
   
       10 . An ultrasonic endoscope apparatus, comprising the capacitive ultrasonic transducer according to  claim 1 .  
   
   
       11 . An ultrasonic endoscope apparatus, comprising the capacitive ultrasonic transducer produced by the production method according to  claim 5 .  
   
   
       12 . An ultrasonic endoscope apparatus, comprising the capacitive ultrasonic transducer produced by the production method according to  claim 8 .  
   
   
       13 . A capacitive ultrasonic transducer, having structure of not only arraying capacitive ultrasonic transducer cells, which comprise a substrate, electrodes formed on the substrate, a membrane constructed at a distance from an air-gap layer, membrane support members for constructing the membrane on the substrate at a distance from an air-gap layer, and electrodes formed on the membrane, two-dimensionally along with an in-plane of the substrate, but also stacking and building them vertically to the substrate.  
   
   
       14 . The capacitive ultrasonic transducer according to  claim 13 , wherein the membrane support members of the capacitive ultrasonic transducer cells have layered structure of being positioned in an almost center portion of a lower layer of membrane.  
   
   
       15 . The capacitive ultrasonic transducer according to  claim 13 , wherein a leg base of the membrane support member has structure of being bonded only near a center portion of a lower layer of membrane.  
   
   
       16 . The capacitive ultrasonic transducer according to  claim 13 , wherein the membrane becomes thicker as a layer number becomes smaller.  
   
   
       17 . The capacitive ultrasonic transducer according to  claim 13 , having structure of making a capacitive ultrasonic transducer cell group, arranged two-dimensionally along with an in-plane of the substrate, one drive element, and bonding a leg base of a capacitive ultrasonic transducer cell arranged in a peripheral section of the drive element with a lower layer linearly.  
   
   
       18 . The capacitive ultrasonic transducer according to  claim 13 , wherein electrodes formed on respective layers of membranes are connected so as to become an equal potential every other layer, and terminals to which a drive voltage in which an RF signal for drive and a DC bias signal are superimposed is applied between a pair of terminals formed hereby are formed.  
   
   
       19 . The capacitive ultrasonic transducer according to  claim 13 , wherein a lower electrode formed on each layer of membrane serves as an upper electrode of a lower layer of capacitive ultrasonic transducer cell, or an upper electrode formed on a membrane serves as a lower electrode of an upper layer of capacitive ultrasonic transducer cell.  
   
   
       20 . A production method of a stacked capacitive ultrasonic transducer, not only comprising: 
 a first step of forming an insulating layer on an upper face of a semiconductor substrate and forming a first electrode layer on its upper face;    a second step of forming a temporary layer for cavity formation on an upper face of this first electrode layer;    a third step of forming masks corresponding to portions, where cavities are formed, on the temporary layer so as to make them arranged two-dimensionally;    a fourth step of forming concavities reaching the first electrode layer by removing portions, to which the masks are not given, by etching and the like;    a fourth step of removing the masks and exposing the temporary layer;    a fifth step of forming a film covering the temporary layer while filling the concavities;    a sixth step of forming holes which penetrate the film and reach the temporary layer;    a seventh step of removing the temporary layer by etching or the like using the holes;    an eighth step of forming a membrane layer on an upper face of the film;    a ninth step of forming a second electrode layer on an upper face of the membrane layer; and    a tenth step of repeating the second step to ninth step once or more on the second electrode layer,    but also forming upper side masks with shifting them so as to become positions between two just lower layers of masks when forming them at that time.    
   
   
       21 . The capacitive ultrasonic transducer according to  claim 13 , not only arranging the stacked capacitive ultrasonic transducer cells two-dimensionally along with an in-plane of the substrate, but also arranging what are respective drive units in which electrodes which are stacked and arranged also vertically to the substrate two-dimensionally to the substrate.  
   
   
       22 . The capacitive ultrasonic transducer according to  claim 13 , wherein the membrane support member becomes thicker as a layer number becomes smaller.  
   
   
       23 . The capacitive ultrasonic transducer according to  claim 20 , forming masks with shifting them so as to become positions between two masks of a just lower layer when forming them at the tenth step.  
   
   
       24 . A capacitive ultrasonic probe for medical diagnoses, having acoustic matching means of performing acoustic matching of both acoustic impedances between an acoustic impedance of a tissue, and an acoustic impedance of ultrasonic transducer cells which construct the capacitive ultrasonic probe.  
   
   
       25 . The capacitive ultrasonic probe according to  claim 24 , wherein the capacitive ultrasonic probe has a capacitive ultrasonic transducer, and a sheath which includes this capacitive ultrasonic transducer, and the acoustic matching means is arranged inside of a sheath.  
   
   
       26 . The capacitive ultrasonic probe according to  claim 25 , wherein an air layer intervenes between a surface of the capacitive ultrasonic transducer, and inside surface of the sheath.  
   
   
       27 . The capacitive ultrasonic probe according to  claim 24 , wherein the acoustic matching means is formed in a cavity which is a component of a capacitive ultrasonic transducer cell.  
   
   
       28 . The capacitive ultrasonic probe according to  claim 27 , wherein the acoustic matching means is a multi-fine elastic pillar.  
   
   
       29 . The capacitive ultrasonic probe according to  claim 28 , wherein conductive films are uniformly formed on surfaces of the multi-fine elastic pillar.  
   
   
       30 . The capacitive ultrasonic probe according to  claim 24 , wherein the acoustic matching means has a distribution characteristic in an acoustic impedance within a surface of an ultrasonic transducer cell.  
   
   
       31 . The capacitive ultrasonic probe according to  claim 24 , wherein the acoustic matching means comprises a concavoconvex protective film horn.  
   
   
       32 . The capacitive ultrasonic probe according to  claim 31 , wherein the concavoconvex protective film horn is a sheet with folding lines which spread in a whole ultrasonic transducer element.  
   
   
       33 . The capacitive ultrasonic probe according to  claim 31 , wherein a lower crown portion of the concavoconvex protective film horn is arranged and connected so as to contact to a center portion of an ultrasonic transducer cell.  
   
   
       34 . The capacitive ultrasonic probe according to  claim 24 , wherein the acoustic matching means is arranged with intervening between a membrane, which is a component of a capacitive ultrasonic transducer cell, and an object.  
   
   
       35 . The capacitive ultrasonic probe according to  claim 34 , wherein the acoustic matching means comprises at least one layer of acoustic matching layer which performs impedance matching between an apparent acoustic impedance at the time of seeing a membrane, and an acoustic impedance of a tissue.  
   
   
       36 . The capacitive ultrasonic probe according to  claim 35 , wherein the acoustic matching means comprises two layers, their first layer is made of a porous resin, and their second layer is made of a homogeneous resin material which is the same material as that of the first layer, but does not include holes.  
   
   
       37 . The capacitive ultrasonic probe according to  claim 36 , wherein the resin material is any one or a composite resin of a silicone resin, an urethane resin, an epoxy resin, a Teflon® resin, and a polyimide resin.  
   
   
       38 . The capacitive ultrasonic probe according to  claim 37 , having structure of an air layer intervening between the acoustic matching means and a membrane.  
   
   
       39 . The capacitive ultrasonic probe according to  claim 38 , wherein Helmholtz resonator structure intervenes between the acoustic matching means and a membrane.  
   
   
       40 . The capacitive ultrasonic probe according to  claim 24 , wherein the acoustic matching means is means of changing an apparent acoustic impedance at the time of seeing a membrane.  
   
   
       41 . The capacitive ultrasonic probe according to  claim 40 , wherein the means of changing an apparent acoustic impedance is a sound medium arranged between an upper electrode and a lower electrode.  
   
   
       42 . The capacitive ultrasonic probe according to  claim 41 , wherein the sound medium arranged between an upper electrode and a lower electrode has an acoustic impedance having a value of 0.5 to 3.0 Mrayl.  
   
   
       43 . A capacitive ultrasonic probe which embeds a capacitive ultrasonic transducer which transmits and receives an ultrasonic wave by vibration of a membrane section, forming focusing means of focusing ultrasonic beams structurally by a curvature membrane section made by making the membrane section, which constructs the capacitive ultrasonic transducer, a curvature.  
   
   
       44 . The capacitive ultrasonic probe according to  claim 43 , wherein the focusing means is formed by a spherical membrane section which is formed by making a membrane section, arranged in a cavity constructed by a first substrate in which a concavity is formed, and a second substrate arranged so as to plug an opening portion of the concavity, a spherical surface.  
   
   
       45 . The capacitive ultrasonic probe according to  claim 44 , wherein circular electrodes are formed concentrically on a surface of the spherical membrane section.  
   
   
       46 . The capacitive ultrasonic probe according to  claim 44 , wherein a spiral electrode is formed on a surface of the spherical membrane section.  
   
   
       47 . The capacitive ultrasonic probe according to  claim 45 , wherein the circular electrodes are made to be driven in different timing, respectively.  
   
   
       48 . The capacitive ultrasonic probe according to  claim 44 , having at least one layer of acoustic matching layer in an ultrasonic transmitting surface side.  
   
   
       49 . The capacitive ultrasonic probe according to  claim 44 , wherein two or more vent holes are provided in the spherical membrane section.  
   
   
       50 . The capacitive ultrasonic probe according to  claim 44 , enabling to form a focal point obtained by synthesizing a fixed focal point by making the membrane section into a curvature, and a variable focal point obtained by controlling timing of applying a drive voltage to each capacitive ultrasonic transducer element which constructs the capacitive ultrasonic transducer.  
   
   
       51 . A capacitive ultrasonic transducer which transmits and receives an ultrasonic wave by vibration of a membrane section, comprising: 
 focusing means of focusing an ultrasonic beam structurally.    
   
   
       52 . The capacitive ultrasonic transducer according to  claim 51 , being arranged at an end portion of the ultrasonic probe which has an insertion section which can be inserted into a body cavity or the like.  
   
   
       53 . The capacitive ultrasonic transducer according to  claim 51 , wherein the focusing means is formed by a spherical membrane section which is formed by making a membrane section, arranged between a first substrate in which a concavity is formed, and a second substrate arranged so as to plug an opening portion of the concavity, a spherical surface.  
   
   
       54 . The capacitive ultrasonic transducer according to  claim 53 , wherein the first substrate in which the concavity is formed is made of a flexible material.  
   
   
       55 . The capacitive ultrasonic transducer according to  claim 54 , wherein the second substrate is made of a flexible material.  
   
   
       56 . The capacitive ultrasonic transducer according to  claim 55 , having an acoustic matching layer, wherein the acoustic matching layer is made of a flexible material.  
   
   
       57 . The capacitive ultrasonic transducer according to  claim 54 , giving means of facilitating deformation to either or both of a first substrate which is made of a flexible material, and a second substrate which is made of a flexible material.  
   
   
       58 . The capacitive ultrasonic transducer according to  claim 55 , giving means of facilitating deformation to either or both of a first substrate which is made of a flexible material, and a second substrate which is made of a flexible material.  
   
   
       59 . The capacitive ultrasonic transducer according to  claim 57 , wherein a structure given the means of facilitating deformation is deformed into a spherical surface, and is fixed in the state.  
   
   
       60 . The capacitive ultrasonic transducer according to  claim 58 , wherein a structure given the means of facilitating deformation is deformed into a spherical surface, and is fixed in the state.  
   
   
       61 . The capacitive ultrasonic transducer according to  claim 57 , wherein a structure given the means of facilitating deformation is deformed into an aspherical surface, and is fixed in the state.  
   
   
       62 . The capacitive ultrasonic transducer according to  claim 58 , wherein a structure given the means of facilitating deformation is deformed into an aspherical surface, and is fixed in the state.  
   
   
       63 . A capacitive ultrasonic probe, having structure that two or more capacitive ultrasonic transducer cells are arranged in a length direction of a spiral substrate, and are fixed to holding means with keeping a state of being given deformation that all the positions in a longitudinal direction of the spiral substrate contact a spherical surface.  
   
   
       64 . The capacitive ultrasonic transducer according to  claim 53 , wherein the focusing means has structure that an inner surface of the concavity has a spherical surface or an aspherical surface near a spherical surface, a further finer concave work surface is formed with leaving a part of a region of the spherical surface or the aspherical surface near a spherical surface, and a flexible sheet having an electrode in one side is bonded over after forming a lower electrode in a surface which is not the further finer concave work surface.  
   
   
       65 . A production method of a capacitive ultrasonic transducer, produced by: 
 a first step of forming a spherical surface or an aspherical surface near a spherical surface in one surface of a substrate;    a second step of forming a further finer concave work surface with leaving a part of a region of the spherical surface or the aspherical surface near a spherical surface;    a third step of forming a lower electrode in a surface which is not the further finer concave work surface, after the second step; and    a fourth step of bonding a flexible sheet, which is given an upper electrode on the lower electrode and can be vibrated, after the third step.    
   
   
       66 . A capacitive ultrasonic transducer driven by a driving signal, a shape of the driving signal applied to the capacitive ultrasonic transducer being composed of superimposed waves of a rf pulse and a dc pulse whose period is longer than the period of the rf pulse.  
   
   
       67 . The dc pulse according to  claim 66 , the dc pulse has a gradual slope in a down edge of the dc pulse.  
   
   
       68 . Driving method is that the polarity of the dc pulse according to  claim 66  changes every other dc pulse in driving pulse train.