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WO2009096576A2 - Transducteur à ondes élastiques, réseau de transducteurs à ondes élastiques, sonde à ultrasons et appareil d'imagerie ultrasonore - Google Patents

Transducteur à ondes élastiques, réseau de transducteurs à ondes élastiques, sonde à ultrasons et appareil d'imagerie ultrasonore Download PDF

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Publication number
WO2009096576A2
WO2009096576A2 PCT/JP2009/051678 JP2009051678W WO2009096576A2 WO 2009096576 A2 WO2009096576 A2 WO 2009096576A2 JP 2009051678 W JP2009051678 W JP 2009051678W WO 2009096576 A2 WO2009096576 A2 WO 2009096576A2
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WO
WIPO (PCT)
Prior art keywords
membrane
region
elastic wave
substrate
transducer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/JP2009/051678
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English (en)
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WO2009096576A3 (fr
Inventor
Kenichi Nagae
Osamu Tabata
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Canon Inc
Kyoto University NUC
Original Assignee
Canon Inc
Kyoto University NUC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Canon Inc, Kyoto University NUC filed Critical Canon Inc
Publication of WO2009096576A2 publication Critical patent/WO2009096576A2/fr
Publication of WO2009096576A3 publication Critical patent/WO2009096576A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B3/00—Devices comprising flexible or deformable elements, e.g. comprising elastic tongues or membranes
    • B81B3/0064—Constitution or structural means for improving or controlling the physical properties of a device
    • B81B3/0067—Mechanical properties
    • B81B3/007—For controlling stiffness, e.g. ribs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B2201/00—Specific applications of microelectromechanical systems
    • B81B2201/02—Sensors
    • B81B2201/0271—Resonators; ultrasonic resonators
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B2203/00—Basic microelectromechanical structures
    • B81B2203/01—Suspended structures, i.e. structures allowing a movement
    • B81B2203/0127—Diaphragms, i.e. structures separating two media that can control the passage from one medium to another; Membranes, i.e. diaphragms with filtering function

Definitions

  • the present invention relates to a transducer for performing the transmission and reception of elastic waves, and in particular, it relates to a transducer having a membrane structure.
  • CMUT Capacitive Micromachined Ultrasonic Transducer
  • PMUT Pielectric Micromachined Ultrasonic Transducer
  • These transducers are formed or fabricated by using semiconductor manufacturing techniques, and have benefits and have benefits such as the possibility of an increase of the number of arrays, easiness of integration with circuits, and so on.
  • a CMUT is formed of a substrate having a lower electrode and a membrane structure having an upper electrode arranged in opposition thereto, and hence is of such a construction that a potential difference can be generated between the membrane and the substrate.
  • a direct current potential difference DC bias
  • the membrane is attracted to the substrate by means of an electrostatic attraction force.
  • an alternating current potential difference the membrane is caused to vibrate, whereby an ultrasonic wave can be generated.
  • the ultrasonic wave can be detected by measuring a capacitance change generated between the substrate and the membrane.
  • the receiving sensitivity and “the resonance frequency” as the performance of a CMUT. Because the CMUT is a transducer that detects capacitance, the receiving sensitivity thereof is defined as:
  • the resonance frequency be a value equal to or higher than a certain level, for example a value from 3 MHz to 10 MHz or more.
  • the first method is a method of increasing an electrostatic capacitance formed between the substrate and the membrane by decreasing a distance between the substrate and the membrane (a distance between an electrode formed on the substrate and an electrode formed on the membrane) .
  • the change of capacitance ⁇ C upon displacement of the membrane becomes large by the increased electrostatic capacitance, so it is possible to obtain accordingly larger electric signal.
  • the second method is a method of increasing the change of capacitance ⁇ C by increasing the displacement of the membrane due to the input of an ultrasonic wave (pressure applied to the membrane) .
  • the membrane is a spring mass system having a mass and a restoring force
  • a large displacement of the membrane by a pressure is equivalent to the restoring force or the spring coefficient (or modulus) being small.
  • the membrane is approximately considered to be a spring which is deformed by the deflection w and an external force p ⁇ a 2
  • the spring coefficient k is represented by the following expression 2.
  • the mass m of the membrane is represented by the following expression 3.
  • the resonant frequency f thereof is represented by the following expression 4. [Expression 4]
  • a high sensitivity means that the spring coefficient k is small.
  • expression 4 above it is desirable from expression 4 above that the thickness h of the membrane is thick, and the radius a of the membrane is small. In other words, to hold the resonance frequency equal to or higher than a certain level and to increase the sensitivity demand opposite directionalities or requirements with respect to the thickness h of the membrane and the radius a of the membrane .
  • the present invention provides a technique that can improve receiving sensitivity while holding a resonance frequency in an elastic wave transducer having a membrane structure .
  • the present invention provides a transducer, an elastic wave transducer array, an ultrasonic probe, and an ultrasonic imaging apparatus which have a resonant frequency equal to or higher than a certain level, as well as have high receiving sensitivity and high performance.
  • An elastic wave transducer includes a substrate having a lower electrode, a support member formed on the substrate, and a membrane that is held by the support member and has an upper electrode, wherein the membrane has a first region that is in contact with the support member, and a second region that is out of contact with the support member and is deformed by receiving an elastic wave, and wherein the second region of the membrane has a region in which the bulk density of the second region becomes smaller in accordance with the increasing distance thereof from the first region of the membrane.
  • An elastic wave transducer includes a substrate having a lower electrode, a support member formed on the substrate, and a membrane that is held by the support member and has an upper electrode, wherein the membrane has a first region that is in contact with the support member, and a second region that is out of contact with the support member and is deformed by receiving an elastic wave, and wherein a bulk density ratio of the membrane at least in the second region is larger than or equal to 0.1 and is less than or equal to 0.5.
  • An elastic wave transducer array has a plurality of elastic wave transducers each of the above-mentioned construction that are arranged in an array-like manner.
  • An ultrasonic probe according to a fourth aspect of the present invention is provided with an elastic wave transducer array of the above-mentioned construction.
  • An ultrasonic imaging apparatus is provided with an ultrasonic probe of the above-mentioned construction.
  • an elastic wave transducer having a membrane structure the receiving sensitivity thereof can be improved while holding a resonance frequency thereof.
  • Fig. 1 is a cross sectional view of a transducer of a first embodiment.
  • Fig. 2 is a plan view of the transducer of the first embodiment .
  • Fig. 3A through Fig. 31 are views illustrating a first example of a manufacturing process for the transducer of the first embodiment.
  • Fig. 4A through Fig. 4F are views illustrating a second example of the manufacturing process for the transducer of the first embodiment.
  • Fig. 5 is a cross sectional view of a transducer of a second embodiment.
  • Fig. 6A through Fig. 6F are views illustrating an example of a manufacturing process for the transducer of the second embodiment.
  • Fig. 7 is a cross sectional view of a transducer of a third embodiment.
  • Fig. 8 is a cross sectional view along line B-B 1 of Fig. 7.
  • Fig. 9 is a cross sectional view of a transducer of a fourth embodiment.
  • Fig. 1OA through Fig. 1OC are vertical cross sectional views and a transverse cross-sectional view of regions 803A through 803C of Fig. 9, respectively.
  • Fig. 11 is a cross sectional view of a transducer of a fifth embodiment.
  • an example of an ultrasonic wave transducer will be illustrated as one example of an elastic wave transducer of the present invention.
  • An elastic wave transducer array can be constructed by arranging a plurality of elastic wave transducers according to the present invention in an array- like manner.
  • Such an elastic wave transducer array is preferably applicable, for example, to an ultrasonic detecting element (probe) in an ultrasonic imaging apparatus (ultrasonic diagnostic apparatus) .
  • the present invention can also be applied to transducers of other elastic waves than ultrasonic waves.
  • the inventors have noted the density p of the membrane included in the above-mentioned expression 4.
  • the resonance frequency f thereof can be increased, and hence it becomes possible to accordingly increase the sensitivity by an increased amount of the resonant frequency.
  • the inventors have discovered that a similar effect can also be achieved by decreasing "the bulk density” of the membrane, instead of essentially decreasing the density thereof by changing the material of the membrane.
  • the bulk density is a density calculated from “the volume including voids” and “the mass”, and is a term or expression used for the definition of the density of fine particles, etc. That is, "the bulk density” in this description is a value that is obtained by dividing the mass of the membrane by the entire volume thereof including openings, spaces or the like formed therein even if openings (recesses, concaves) are formed on a surface of the membrane, or if closed spaces (holes and pores) are formed in the interior of the membrane. [0028]
  • Fig. 1 is a cross sectional view of the transducer of this embodiment
  • Fig. 2 is a plan view of the transducer of this embodiment.
  • Fig. 1 illustrates a cross sectional view along line A-A' of Fig. 2.
  • the transducer of this embodiment is composed of a substrate 101, a support member 102 and a membrane 103.
  • the support member 102 is formed into an annular shape on the substrate 101, and serves to support a peripheral portion of the membrane 103 of a substantially disc shape.
  • silicon a part thereof being oxidized by a manufacturing process (see a hatched portion in Fig. 1)
  • silicon oxide is used for the support member 102
  • a silicon thin film or a silicon nitride thin film is used for the membrane 103.
  • the membrane 103 is provided with a first region 105 that is in contact with the support member 102, and a second region 106 that is out of contact with the support member 102 and is deformed into a U-shape by receiving an elastic wave (ultrasonic wave) .
  • the second region 106 is formed in a central portion of the membrane 103, and the first region
  • the 105 is formed around the second region 106 (i.e., in the peripheral portion of the membrane 103) .
  • the second region 106 of the membrane 103 is thicker than the first region 105, and a plurality of openings
  • These openings 104 are a structure for decreasing the bulk density of the membrane 103. With such a structure, it is possible to ensure a sufficient thickness of the second region 106 which is a portion adapted to be caused to vibrate upon reception of an ultrasonic wave, so a desired resonance frequency can be kept. In addition, an improvement in the receiving sensitivity can be expected because the second region 106 is made lighter in weight due to the formation of the openings 104.
  • the bulk density is calculated by defining an upper surface of the membrane 103 as an interface.
  • the second region 106 of the membrane 103 have a stepped portion formed on its substrate side, so that at least part of the second region is thicker than the first region 105.
  • the second region 106 be formed thick in its central portion.
  • the resonance frequency f will be decreased by an amount corresponding to an increased amount of the mass m of the membrane.
  • the bulk density p of the membrane is decreased by the formation of the openings 104 or the like, so that the decrease of the bulk density acts in a direction to increase the resonance frequency.
  • the sensitivity can be improved while keeping the resonance frequency at an appropriate level.
  • the thickness of the membrane is able to keep or hold a constant or fixed rigidity as necessary even if the bulk density p thereof is small, thus making it possible to suppress the decrease of the resonance frequency in an efficient manner.
  • a through hole(s) can be formed through the membrane 103.
  • the membrane itself may be formed of a porous material.
  • the openings 104 are formed so as to change the size and the number per unit area of the openings, as illustrated in Fig. 2, in such a manner that the bulk density decreases toward the center of the membrane 103.
  • the receiving sensitivity can be further improved. This is because an amount of displacement of the membrane upon reception of an ultrasonic wave becomes larger in accordance with the increasing distance from the first region 105 of the membrane 103, i.e., in a direction from the periphery toward the center of the membrane 103.
  • the sensitivity can be more improved in comparison with the case where openings are merely formed in the membrane.
  • the openings are formed, it is preferable from the viewpoint of the strength (rigidity) of the membrane that the area per opening be made greater in a direction toward the central portion of the second region 106, and that the direction of each beam (a wall between adjacent openings) be made in coincidence with a radial direction of the circle of the membrane, as illustrated in Fig. 2.
  • the rigidity of the membrane can be kept at a predetermined level even if the mass of the entire membrane is made light.
  • the distance L from the first region 105" at a certain point P in the second region 106 of the membrane 103 is defined as illustrated in Fig. 2. That is, on the membrane surface when a transducer element is seen from above, the shortest one among rectilinear distances from a boundary 107 between the first region 105 and the second region 106 to the point P is "the distance L from the first region 105". In the case of the membrane where the second region 106 is round, as illustrated in Fig. 2, the distance L can be grasped from a radius that passes through the point P from the center of the circle. [0040]
  • the second region 106 of the membrane 103 the larger the distance from the first region 105, the smaller the bulk density becomes continuously or stepwise.
  • a region need only be included in a part of the second region 106.
  • it may be designed such that the bulk density decreases until halfway in the course of approaching the central portion, but the bulk density becomes unchanged partway and held constant. That is, the second region 106 need only have a region in which the larger the distance from the first region 105 of the membrane, the smaller the bulk density becomes.
  • each opening 104 is parallel to the thickness direction of the membrane in the figures, it may be a rounded side wall or a side wall having irregularities.
  • the bottom surface of each opening 104 need not be in parallel to the membrane surface.
  • the shape of each opening is not limited to such a shape as in this embodiment, but may be polygon.
  • the number and the arrangement of the openings may be set in any manner.
  • the substrate 101 is a low resistance substrate that has an unillustrated lower electrode, and it is electrically grounded.
  • the lower electrode there are employed a silicon substrate itself of which the electric resistance is decreased by doping it with phosphorus, boron, etc., and an electric conductor such as Al, Au, or the like.
  • the membrane 103 is caused to deform to the substrate 101 side under the action of an electrostatic attraction force.
  • the membrane 103 is stopped at a position of balance between the electrostatic attraction force and its own restoring force.
  • the membrane 103 Under such a condition, when an alternating current voltage is applied to the electrodes, the membrane 103 is caused to vibrate about the position of balance so that an ultrasonic wave is thereby generated. On the other hand, when an ultrasonic wave is input to the membrane 103 which is at the position of balance, the membrane 103 ic caused to vibrate, whereby the capacitance between the substrate 101 and the membrane 103 is changed. Thus, the ultrasonic wave can be detected by measuring this change.
  • the upper electrode is formed on a surface of the membrane 103 at the substrate 102 side or a surface thereof at its opposite side. An electric conductor such as Al, Au or the like is used as the upper electrode.
  • the relation between the resonance frequency and the sensitivity will be described by using a dimensional example.
  • silicon nitride is used as a material for the membrane 103, and the size of the second region 106 of the membrane 103 is set to 40 ⁇ m in diameter.
  • the voltage to be applied (hereinafter also referred to as an application voltage) is set to a value of 80 % of a voltage by which the membrane 103 is caused to collide with the substrate 101.
  • An initial gap between the membrane 103 and the substrate 101 is set in such a manner that the gap therebetween when the application voltage is applied thereacross becomes 0.12 ⁇ m.
  • the thickness of the membrane it is set to a value which satisfies a resonance frequency of 5 MHz.
  • the plurality of openings 104 are formed in the second region 106 of the membrane 103 in such a manner that a bulk density ratio of the membrane 103 is adjusted to 0.467.
  • the bulk density ratio of the membrane is a value which is the bulk density of the membrane 103 divided by a theoretical density of the membrane 103.
  • the theoretical density is a value which is the mass of the membrane 103 divided by the true or real volume of the membrane 103 (the volume of the membrane excluding the openings) .
  • the sensitivity for the membrane having the shape of this embodiment is 1.06e-3, and the sensitivity for the membrane of the planar shape is 4.00e-4.
  • the sensitivity is improved by about 2.5 times.
  • Silicon nitride is used as a material for the membrane 103, and the size of the second region 106 is set to 40 ⁇ m in diameter.
  • the application voltage is set to a value of 80 % of a voltage by which the membrane 103 is caused to collide with the substrate 101.
  • An initial gap between the membrane 103 and the substrate 101 is set in such a manner that the gap therebetween when the application voltage is applied thereacross becomes 0.12 ⁇ m.
  • the thickness of the membrane it is set to a value which satisfies a resonance frequency of 5 MHz.
  • the bulk density ratio of the membrane 103 is set to 0.1.
  • the sensitivities of a membrane having the shape of this embodiment is 2.25e-2, and is improved by about 56 times as compared with the sensitivity for the membrane of the planar shape.
  • a preferred range for the bulk density ratio of the membrane is more than or equal to 0.1 and less than or equal to 0.5.
  • the circular membrane has been described, but similar effects will be obtained even in the case of a membrane of a polygonal shape including a square and a rectangle.
  • a low resistance layer 211 is formed on a surface of a silicon substrate 210 by disposing the silicon substrate 210 in a diffusion furnace, introducing a PH 3 gas (10 % hydrogen dilution) into the furnace, and heat-diffusing phosphorus at a temperature of 1,050 degrees C (Fig. 3A).
  • a silicon nitride layer 212 is then formed on the low resistance layer by means of a LPCVD (Fig. 3B) .
  • a mixture gas is used which contains a SiH 4 gas and a NH 3 gas mixed with each other at a mole ratio of 1 to 1.
  • the silicon substrate 210 is disposed in an atmosphere heated to 700 through 800 degrees C, and the mixture gas is then introduced therein, whereby the silicon nitride layer 212 is formed with a thickness of about 50 nm.
  • an amorphous silicon layer 213 is deposited on the silicon nitride layer 212 by means of an RF plasma CVD method (Fig. 3C) .
  • a SiH 4 gas which has been diluted to 10 % with a H 2 gas, is introduced into a plasma CVD apparatus at a substrate temperature of 350 degrees C, whereby the amorphous silicon layer 213 is deposited on the silicon nitride layer 212.
  • a part 214 of the amorphous silicon layer 213 is etched and removed by means of a SF 6 gas.
  • the layer thickness of the amorphous silicon layer is adjusted to 0.12 ⁇ m (Fig. 3D).
  • openings 215 for side walls of the membrane are formed in the amorphous silicon layer 213 by means of etching (Fig. 3E) .
  • a silicon nitride layer 216 which will become the membrane, is formed on the amorphous silicon layer (Fig. 3F) .
  • the silicon nitride layer 216 is formed by the use of an LPCVD method.
  • a mixture gas is used which contains a SiH 4 gas and a NH 3 gas mixed with each other at a mole ratio of 1 to 1.
  • the silicon substrate of Fig. 3E is disposed in an atmosphere heated to 700 through 800 degrees C, and the mixture gas is then introduced therein, whereby the silicon nitride layer 216 is formed with a thickness of about 1.15 ⁇ m.
  • Etching openings 217 for etching the amorphous silicon layer are then formed.
  • the etching openings 217 are formed by etching the silicon nitride layer 216 with a CF 4 gas by the use of a mask of a desired shape (Fig. 3G) .
  • the substrate of Fig. 3G is then soaked into a KOH aqueous solution which has been diluted to 10 %, whereby amorphous silicon layers 218 are removed to form spaces 220. Thereafter, a silicon nitride layer 219 is deposited on the openings 217, whereby the etching openings are closed (Fig. 3H) .
  • a part (a central portion) of the silicon nitride layer 219 is etched by means of a CF 4 gas with the use of a mask pattern as illustrated in Fig. 1 and Fig. 2, whereby the openings 221 are formed (Fig. 31). In this manner, the bulk density ratio of the membrane is controlled so as to become 0.467.
  • An Al electrode is deposited on the membrane to provide an upper electrode.
  • the thickness of the silicon nitride layer 216 is controlled to be about 0.5 ⁇ m in the step of Fig. 3F, a membrane having a bulk density ratio of 0.1 can be prepared.
  • a low resistance substrate 301 is prepared (Fig. 4A) .
  • An opening 302 is formed in the low resistance substrate 301 by means of dry etching (Fig. 4B) .
  • a silicon oxide layer 303 is formed by thermal oxidation (Fig. 4C) .
  • a separately prepared SOI (Silicon On Insulator) substrate 304 is joined or bonded to the silicon oxide layer 303.
  • a convex portion 305 has been beforehand formed on a device layer of the SOI substrate 304 by means of etching (Fig. 4D) .
  • a handling layer and a BOX layer of the SOI substrate 304 are then removed (Fig. 4E) .
  • Openings 306 are formed on a surface of the SOI substrate, and an unillustrated electrode is formed on the surface (Fig. 4F) . In this manner, the transducer of this embodiment can be obtained. [0057]
  • silicon oxide by thermal oxidation is used as an insulating layer
  • other forming techniques such as CVD, sputtering, or the like can be used, and silicon nitride can also be used as a material, and in addition, CVD or other deposition techniques can be adopted as a forming technique therefor.
  • CVD chemical vapor deposition
  • the convex portion 305 is formed, not only etching but also other deposition techniques including epitaxial growth can be used.
  • either of dry etching, wet etching, and mechanical working including grinding can be used, or they can be used in combination.
  • both of dry etching and wet etching can be made use of.
  • a transducer according to a second embodiment of the present invention will be described while referring to Fig. 5.
  • the transducer of the second embodiment has a plurality of openings which are different in depth from each other.
  • the transducer of this embodiment has a cross- sectional structure as illustrated in Fig. 5, and is composed of a substrate 401, a support member 402 and a membrane 403. An unillustrated lower electrode is formed on the substrate 401, and an unillustrated upper electrode is formed on the membrane 403. [0060]
  • a plurality of openings 404 are formed on a vibrating portion (a second region) of the membrane 403.
  • the depths of the openings 404 are large or deep in the center of the membrane 403, and become smaller or shallower in a direction to approach a peripheral portion (a first region) of the membrane 403.
  • the bulk density in the vibrating portion of the membrane 403 can be made smaller in the direction toward the center (i.e., in accordance with the increasing distance from the peripheral portion) .
  • the sensitivity can be increased while keeping or holding the resonance frequency thereof.
  • each opening is not limited to that which is illustrated in this embodiment, but a bottom surface thereof may be or may not be in parallel to the membrane, and in addition, even a rounded bottom surface or side wall may be employed. In addition, the number and the arrangement of the openings can also be altered as necessary.
  • a low resistance substrate 501 is prepared (Fig. 6A) .
  • An opening 502 is formed in the low resistance substrate 501 by means of dry etching (Fig. 6B) .
  • a silicon oxide layer 503 is formed by thermal oxidation (Fig. 6C) .
  • a separately prepared SOI substrate 504 is joined or bonded to the silicon oxide layer 503 (Fig. 6D) .
  • a BOX layer 505 is patterned. On the BOX layer, there is formed a resist layer 506, the thickness of which is varied by changing an amount of exposure (Fig. 6E) .
  • silicon oxide by thermal oxidation is used as an insulating layer
  • other forming techniques such as CVD, sputtering, or the like can be used, and silicon nitride can also be used as a material, and in addition, CVD or other deposition techniques can be adopted as a forming technique therefor.
  • CVD or other deposition techniques can be adopted as a forming technique therefor.
  • to remove the handling layer either of dry etching, wet etching, and mechanical working including grinding can be used, or they can be used in combination.
  • the openings 507 of different depths are formed by varying the thickness of the resist, patterning and etching can be repeated each for openings of the same depth.
  • the depth of each opening can be controlled by varying the size or area of the opening (specifically, by increasing the opening size or area in accordance with the decreasing distance to the center of the membrane) .
  • both of dry etching and wet etching can be made use of.
  • a transducer according to a third embodiment of the present invention will be described while referring to Fig. 7 and Fig. 8.
  • the transducer of the third embodiment has a plurality of closed spaces in the interior of a membrane.
  • the transducer of this embodiment has a cross- sectional structure as illustrated in Fig. 7, and a spatial structure as illustrated in Fig. 8.
  • Fig. 8 illustrates a cross section on line B-B' of Fig. 7, and
  • Fig. 7 illustrates a cross section on line C-C of Fig. 8.
  • the transducer of this embodiment is composed of a substrate 601, a support member 602 and a membrane 603.
  • An unillustrated lower electrode is formed on the substrate 601, and an unillustrated upper electrode is formed on the membrane 603.
  • a plurality of closed spaces 604 of varying or different sizes are formed in the interior of a vibrating portion (a second region) of the membrane 603.
  • the sizes (volumes) of the closed spaces 604 are large in the center of the membrane 603, and become smaller in a direction to approach a peripheral portion (a first region) of the membrane 603.
  • the bulk density in the vibrating portion of the membrane 603 can be made smaller in the direction toward the center (i.e., in accordance with the increasing distance from the peripheral portion) .
  • the sensitivity can be increased while keeping or holding the resonance frequency thereof.
  • the transducer of this embodiment has a flat surface, so the formation of the electrode on the membrane surface can be carried out in an easy manner.
  • each closed space can be spherical or polyhedral including triangular pyramidal, etc.
  • the number and the arrangement of the closed spaces can be set as appropriate.
  • the transducer of this embodiment can also be produced by combining conventional well-known semiconductor manufacturing techniques in an appropriate manner.
  • a transducer according to a fourth embodiment of the present invention will be described while referring to Fig. 9 and Fig. 1OA through Fig. 1OC.
  • the transducer of the fourth embodiment has a plurality of closed spaces in the interior of a membrane.
  • the bulk density is controlled by changing the sizes of the closed spaces, but in the fourth embodiment, the bulk density is controlled by changing the number of closed spaces per unit volume.
  • the transducer of this embodiment has a cross- sectional structure as illustrated in Fig. 9, and is composed of a substrate 801, a support member 802 and a membrane 803. An unillustrated lower electrode is formed on the substrate 801, and an unillustrated upper electrode is formed on- the membrane 803.
  • Fig. 1OA illustrates a vertical cross sectional view (upper row) of a region 803A of the membrane 803, and a transverse cross sectional view (lower row) on line D-D' of the vertical cross sectional view.
  • Fig. 1OB illustrates a vertical cross sectional view and a transverse cross sectional view of a region 803B of the membrane 803, and Fig.
  • 1OC illustrates a vertical cross sectional view and a transverse cross sectional view of a region 803C.
  • region 803A is a central region of the membrane 803
  • region 803B and the region 803C are sequentially and increasingly distant from the center in this order.
  • a plurality of closed spaces 901 of the same size are formed in the interior of a vibrating portion (a second region) of the membrane 803.
  • the number of closed spaces 901 per unit volume is the most in the central region 803A of the membrane 803, and decreases in a direction toward a peripheral portion (a first region) of the membrane 803.
  • the bulk density in the vibrating portion of the membrane 803 can be made smaller in the direction toward the center (i.e., in accordance with the increasing distance from the peripheral portion) .
  • the sensitivity can be increased while keeping or holding the resonance frequency thereof.
  • the membrane is composed of a total of four kinds of regions comprising three kinds of regions containing therein closed spaces and one kind of region containing therein no closed spaces, but the present invention is not limited to this construction.
  • the total number of regions can be three or five or more.
  • the number of closed spaces per unit area can be continuously changed. If doing so, the bulk density of the membrane changes continuously, and hence, it is easy to suppress the anisotropy of the mechanical characteristics of the membrane .
  • a transducer according to a fifth embodiment of the present invention will be described while referring to Fig. 11.
  • the transducer of this embodiment operates in collapse mode where at least part of a vibrating portion (a second region) of a membrane is in contact with a substrate.
  • the collapse mode is a mode in which transmission and reception are carried out with the membrane being in contact with the lower substrate disposed therebelow.
  • the contact between the membrane and the lower substrate will be described.
  • an electrostatic attraction force is increased so that the membrane is thereby attracted to the lower substrate. This attracted position is decided by the balance between the electrostatic attraction force and a restoring force of the membrane.
  • the electrostatic attraction force is increased by making the initial potential difference larger, the electrostatic attraction force exceeds the restoring force of the membrane, whereby the membrane is placed into contact with the lower substrate.
  • the electromechanical transduction (conversion) efficiency of the transducer can be improved by performing the driving in the collapse mode. (Reference: Baris Bayram et al., IEEE UFFC Vol. 50, No. 9, ppll84 -1190, Sep. 2003) [0077]
  • the distance between the membrane and the lower substrate is very small in the vicinity of a region in which the membrane is in contact with the lower substrate, so a change in electrostatic capacitance due to minute vibration of the membrane becomes large.
  • the vicinity of the region in which the membrane and the lower substrate are in contact with each other contributes greatly to the improvement of the electromechanical transduction efficiency.
  • transducers of either structures of the above- mentioned first through fourth embodiments can be driven to operate in the collapse mode.
  • the operation of a transducer in the collapse mode will be described while taking as an example the transducer of the fourth embodiment .
  • Fig. 11 illustrates a cross sectional shape of the transducer when operating in the collapse mode.
  • the membrane 803 is placed in contact with the lower substrate 801.
  • the greatest deflected portion in the membrane is first placed into contact with the lower substrate, so in this embodiment, a part of the region 803A of the membrane 803 comes in contact with the lower substrate 801.
  • the behavior of the membrane in the vicinity of the contacting region contributes greatly to the improvement of the electromechanical transduction efficiency.
  • the bulk density in the vicinity of the contacting region i.e., a peripheral region which is adjacent to the contacting region and functions as the membrane
  • the collapse mode it is possible to further increase the degree of the improvement of the electromechanical transduction efficiency due to the collapse mode, thus making it possible to obtain the further increased effects of the present invention.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Transducers For Ultrasonic Waves (AREA)
  • Ultra Sonic Daignosis Equipment (AREA)

Abstract

L'invention porte sur un transducteur à ondes élastiques qui comprend un substrat (101) ayant une électrode inférieure, un élément de support (102) formé sur le substrat, et une membrane (103) qui est tenue par l'élément de support et a une électrode supérieure. La membrane comprend une première région (105) qui est en contact avec l'élément de support et une seconde région (106) qui est hors de contact avec ledit élément de support et est déformée par réception d'une onde élastique. La seconde région de la membrane comporte une région dans laquelle la densité apparente de la seconde région décroît à mesure que sa distance par rapport à la première région de la membrane croît. De plus, la seconde région a une densité relative apparente qui est supérieure ou égale à 0,1 et est inférieure ou égale à 0,5.
PCT/JP2009/051678 2008-01-31 2009-01-27 Transducteur à ondes élastiques, réseau de transducteurs à ondes élastiques, sonde à ultrasons et appareil d'imagerie ultrasonore Ceased WO2009096576A2 (fr)

Applications Claiming Priority (2)

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JP2008021332A JP2009182838A (ja) 2008-01-31 2008-01-31 弾性波トランスデューサ、弾性波トランスデューサアレイ、超音波探触子、超音波撮像装置
JP2008-021332 2008-01-31

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