JP2014068674A - Ultrasonic element and ultrasonic endoscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic element having wide bandwidth and high transmission/reception efficiency.SOLUTION: An ultrasonic element 20 includes: a plurality of first transducer cells 10A1 in which lower electrodes and upper electrodes are facingly disposed via first cavities 14A1 that are isotropic in planar view; and a plurality of second transducer cells 10A2 in which lower electrodes and upper electrodes are facingly disposed via second cavities 14A2 that are anisotropic in planar view.

Description

  The present invention relates to an ultrasonic element having a plurality of capacitive transducer cells and an ultrasonic endoscope including the ultrasonic element.

  US Pat. No. 6,854,338 discloses a capacitive ultrasonic element 120. As shown in FIG. 1, the ultrasonic element 120 has 25 transducer cells 110 that are the basic structure of a cMUT (capacitive Micro-machined Ultrasonic Transducer). As shown in FIG. 2, in the transducer cell 110, the lower electrode 112 and the upper electrode 116 are arranged to face each other through a cavity 114 that is a space surrounded by a partition wall 113 made of an insulating material. The cavity 114 has a cylindrical shape, and its plan view shape is circular.

  When a voltage is applied between the lower electrode 112 and the upper electrode 116, the upper electrode 116 is attracted toward the lower electrode 112 (downward) by an electrostatic force and deformed. When no voltage is applied, the upper electrode 116 returns upward due to elastic force. Ultrasonic waves are emitted by the deformation of the upper electrode 116. When the reflected wave (echo) of the emitted ultrasonic wave is incident on the transducer cell 110, the upper electrode 116 is deformed by the sound pressure of the ultrasonic wave, and the thickness of the cavity 114, that is, the lower electrode 112 and the upper electrode 116 is changed. The distance changes. For this reason, the incident ultrasonic wave is detected from the capacitance value change between the counter electrodes.

  Here, the “Q value” of the transducer cell will be described. As shown in FIG. 3, the intensity (power) P of the emitted ultrasonic wave becomes maximum when the frequency of the drive signal is the resonance frequency FC of the transducer cell, and decreases when the drive frequency deviates from the resonance frequency FC. A value defined by a difference between two frequencies FL and FH before and after the resonance frequency FC at which the intensity P is 50% with respect to the peak intensity PC at the resonance frequency FC is referred to as a bandwidth (BW). A value obtained by dividing the resonance frequency FC by the bandwidth (BW) is a “Q value”.

  Q = F1 / BW = F1 / (FH-FL)

  The Q value indicates the sharpness of resonance vibration. When the Q value is large, the intensity P is strong when the drive frequency is the resonance frequency FC, but when the drive frequency deviates from the resonance frequency FC, the intensity P decreases rapidly. To do. On the other hand, when the Q value is small, the strength P does not rapidly decrease even if the drive frequency deviates from the resonance frequency FC. Similarly, when receiving ultrasonic waves, a transducer cell having a large Q value exhibits high detection sensitivity for ultrasonic waves having a resonance frequency FC, but detection sensitivity for ultrasonic waves having a frequency deviating from the resonance frequency FC is abrupt. To drop.

  The cMUT has a high Q value. For example, when the resonance frequency FC = 9.8 MHz and the Q value = 98, BW = 0.1 MHz, FL = 9.75 MHz, and FH = 9.85 MHz. That is, the ultrasonic intensity P at f = 9.75 MHz or f = 9.85 MHz is half of the ultrasonic intensity P at f = 9.8 MHz.

  In the medical field such as an ultrasonic endoscope, changing the frequency (wavelength) of an ultrasonic wave or acquiring information on the direction and flow velocity of a blood flow as a test object using the Doppler effect, In some cases, ultrasonic waves having a frequency deviating from the resonance frequency FC may be received.

  However, it can be said that the transducer cell 110 whose cavity 114 has a circular shape in plan view has a relatively high Q value and a narrow bandwidth BW, and therefore has high reception efficiency of ultrasonic waves having a frequency deviated from the resonance frequency FC. There wasn't.

US Pat. No. 6,854,338

  Embodiments of the present invention are intended to provide an ultrasonic endoscope having a wide bandwidth and high transmission / reception efficiency, and an ultrasonic endoscope having a wide bandwidth and high transmission / reception efficiency. .

  An ultrasonic element according to an embodiment of the present invention includes a plurality of first transducer cells in which a lower electrode and an upper electrode are opposed to each other via a first cavity having an isotropic shape in plan view, and in plan view And a plurality of second transducer cells in which a lower electrode and an upper electrode are arranged to face each other through a second cavity having an anisotropic shape.

  An ultrasonic endoscope according to another embodiment includes a plurality of first transducer cells in which a lower electrode and an upper electrode are disposed to face each other through a first cavity having an isotropic shape in plan view. An ultrasonic element having a plurality of second transducer cells in which a lower electrode and an upper electrode are opposed to each other through a second cavity having an anisotropic shape in plan view is disposed at a distal end portion. An insertion portion, an operation portion disposed on the proximal end side of the insertion portion, and a universal cord extending from the operation portion.

  According to the embodiment of the present invention, it is possible to provide an ultrasonic element having a wide bandwidth and an ultrasonic element having good transmission / reception efficiency and an ultrasonic element having a wide bandwidth and high transmission / reception efficiency.

It is a top view of the conventional ultrasonic element. It is sectional drawing of the transducer cell of the conventional ultrasonic element. It is a figure for demonstrating "Q value" of a vibrator cell. It is a block diagram for demonstrating the ultrasonic endoscope system containing the ultrasonic endoscope of 1st Embodiment. It is a perspective view of the front-end | tip part of the ultrasonic endoscope of 1st Embodiment. It is a perspective view of the ultrasonic element of a 1st embodiment. It is sectional drawing of the transducer cell of the ultrasonic element of 1st Embodiment. FIG. 3 is a layout diagram of a plurality of cavities of the transducer cell of the ultrasonic element according to the first embodiment. It is a top view of the 2nd cavity of the ultrasonic element of a 1st embodiment. FIG. 10 is a layout diagram of a plurality of cavities of transducer cells of an ultrasonic element according to a modification of the second embodiment. FIG. 10 is a layout diagram of a plurality of cavities of transducer cells of an ultrasonic element according to a modification of the third embodiment. FIG. 10 is a layout diagram of a plurality of cavities of transducer cells of an ultrasonic element according to a modification of the fourth embodiment.

<First Embodiment>
Hereinafter, the ultrasonic endoscope 20 having the ultrasonic element 20 and the ultrasonic element 20 according to the first embodiment will be described with reference to the drawings. Each figure is a schematic diagram for explanation, and the number of components, size, ratio of size, and the like are different from actual ones.

<Configuration of ultrasonic endoscope>
As shown in FIG. 4, the ultrasonic endoscope 2 constitutes an ultrasonic endoscope system 1 together with the ultrasonic observation device 3 and the monitor 4. The ultrasonic endoscope 2 includes an elongated insertion portion 41 to be inserted into the body, an operation portion 42 disposed at the proximal end of the insertion portion 41, and a universal cord 43 extending from a side portion of the operation portion 42. It has.

  A connector 44 </ b> A connected to a light source device (not shown) is disposed at the base end of the universal cord 43. From the connector 44A, there are a cable 45 that is detachably connected to a camera control unit (not shown) via a connector 45A, and a cable 46 that is detachably connected to the ultrasonic observation apparatus 3 via a connector 46A. It is extended. The ultrasonic observation apparatus 3 to which the monitor 4 is connected includes a drive signal generator 3A that generates a drive signal for ultrasonic transmission, a capacitance signal detector 3B that receives the ultrasonic wave, and a ground potential line 3C. And having.

  The insertion portion 41 is operated in order from the distal end side, the distal end rigid portion (hereinafter referred to as “the distal end portion”) 47, the bending portion 48 positioned at the rear end of the distal end portion 47, and the rear end of the bending portion 48. A flexible tube portion 49 having a small diameter, a long length, and flexibility reaching the portion 42 is continuously provided.

  As shown in FIG. 5, an ultrasonic unit 30 in which a plurality of ultrasonic elements 20 (hereinafter also simply referred to as “elements”) is arranged in a radial shape is disposed at the distal end portion 47 of the insertion portion 41. Has been. The ultrasonic unit may be a convex scanning type in which a plurality of elements 20 are arranged in a convex shape, or a linear scanning type in which a plurality of elements 20 are arranged on a plane.

  As shown in FIG. 6, the element 20 that is a basic unit for transmitting and receiving ultrasonic waves has a first main surface 20SA and a second main surface 20SB facing the first main surface 20SA, for example, silicon. The substrate 11 is a base. A transmitter / receiver 21 for transmitting and receiving ultrasonic waves is formed at a substantially central portion of the first main surface 20SA of the ultrasonic element 20, and external electrodes 22A1, 22A2, 22B is disposed.

  The external electrode 22A1 is a drive external electrode connected to the drive signal generating unit 3A for ultrasonic transmission, and the external electrode 22A2 is a detection external electrode connected to the capacitive signal detection unit 3B for receiving ultrasonic waves. The external electrode 22B is a ground potential external electrode connected to the ground potential line 3C.

  In the transmission / reception unit 21, a plurality of capacitive type two transducer cells 10 (10A1, 10A2) (hereinafter also simply referred to as “cells”) are arranged. In FIG. 6, the cavities 14 of some of the transducer cells are indicated by broken lines.

As shown in FIG. 7, in the transducer cell 10, the upper electrode 16 constituting the membrane is disposed so as to face the lower electrode 12 through a cavity (gap portion) 14. As will be described later, the cavity 14 is formed by etching the sacrificial layer. An upper insulating layer / protective film made of SiN, SiO ₂ , polyimide, or the like is further formed on the upper electrode 16, but is not shown. That is, the membrane is composed of the upper electrode 16, the upper insulating layer, and the protective film.

  The lower electrode 12 is a single layer film or a multilayer film made of a refractory metal such as tungsten, molybdenum, or titanium or an alloy containing the metal. The lower insulating layer 13 and the upper insulating layer 15 located above and below the cavity 14 are made of an insulating material such as silicon nitride, silicon oxide, tantalum oxide, or hafnium oxide. The upper electrode 16 is a single layer film or a multilayer film made of a metal such as aluminum, tungsten, molybdenum, or titanium or an alloy containing the metal.

  In forming the cavity 14, a material having a high etching selectivity with respect to the material of the adjacent lower insulating layer 13 and upper insulating layer 15 is disposed on the lower insulating layer 13 as a sacrificial layer. As the sacrificial layer, typically, an insulating material such as phosphorus glass, a semiconductor material such as polycrystalline silicon, a metal thin film material such as tungsten, or the like is used. After forming the upper insulating layer 15 on the sacrificial layer, the cavity 14 is formed by selectively etching the sacrificial layer.

  As shown in FIG. 8, the element 20 includes a plurality of first transducer cells in which a lower electrode and an upper electrode are arranged to face each other via a first cavity 14A1 having an isotropic circular shape in plan view. 10A1 and a plurality of second transducer cells 10A2 in which the lower electrode and the upper electrode are arranged to face each other via the second cavity 14A2 having a flat-shaped ellipse having an anisotropic shape in plan view. Have. That is, the first cavity 14A1 has a cylindrical shape, and the second cavity 14A2 has an elliptic cylinder shape.

  The external electrode 22A1 of the ultrasonic element 20 is a common electrode for the lower electrodes of the plurality of first transducer cells 10A1, and the external electrode 22A2 is a common electrode for the lower electrodes of the plurality of second transducer cells 10A2. The electrode 22B is a common electrode for the upper electrodes of the plurality of first transducer cells 10A1 and the plurality of second transducer cells 10A2.

  That is, the first transducer cell 10A1 is an ultrasonic transmission cell, and the second transducer cell 10A2 is an ultrasonic reception cell.

  Next, the operation principle of the ultrasonic element 20 (cell 10) will be described. At the time of ultrasonic transmission, a drive signal is applied from the drive signal generator 3A between the lower electrode 12 and the upper electrode 16 of the plurality of first transducer cells 10A1. In particular, with a drive signal in which the applied voltage is repeatedly turned ON / OFF at a resonance frequency FC determined by the constituent materials and structure parameters of the membrane, the membrane vibrates efficiently, and ultrasonic waves having a frequency equal to the resonance frequency FC are emitted. .

  On the other hand, when receiving ultrasonic waves, the membranes of the plurality of second transducer cells 10A2 vibrate at the frequency of the incident ultrasonic wave due to the sound pressure of the ultrasonic waves, and the thickness of the cavity 14A2, that is, the upper electrode 16 is corresponding to the vibration. And the distance between the lower electrode 12 changes. Since the electric capacitance value between the electrodes changes according to the distance between the electrodes, the intensity and frequency of the incident ultrasonic wave are detected by detecting the time change of the capacitance value between the two electrodes.

  As already described, the first vibrator cell 10A1 having a circular shape in the plan view of the cavity 14A1 has a high Q value because the radius in the radial direction, which is the maximum fixed end distance when the membrane vibrates, is constant. For this reason, an ultrasonic wave having a predetermined resonance frequency FC is efficiently generated.

  On the other hand, the second transducer cell 10A2 has an elliptical shape in which the shape of the cavity 14A2 in plan view is anisotropic. Here, the shape “isotropic” means a flat shape in which the vertical direction or the horizontal direction is crushed with respect to an “isotropic” shape such as a circle or a regular hexagon.

  For this reason, in the second transducer cell 10A2, the radius in the radial direction, which is the maximum fixed end distance when the membrane vibrates, continuously varies depending on the location. For this reason, the vibration state of the membrane is the addition (superposition) of vibrations of circular membranes having different diameters.

  For example, when the plan view shape of the cavity 14A1 of the first transducer cell 10A1 is a circle having a diameter of 26.5 μm, the resonance frequency FC = 22.8 MHz, Q = 55.0, and BW = 0.415 MHz.

  On the other hand, when the plan view shape of the cavity 14A2 of the second transducer cell 10A2 is an ellipse having a major axis (DL) of 30 μm and a minor axis (DS) of 23 μm as shown in FIG. The same resonance frequency FC = 22.8 MHz as that of the transducer cell 10A1, but Q = 29.3 and BW = 0.778 MHz.

  As described above, the ultrasonic element 20 of the embodiment efficiently transmits ultrasonic waves by the first transducer cell 10A1 having a high Q value at the time of transmission and the second transducer having a wide band at the time of reception. An ultrasonic wave can be efficiently received by the cell 10A2.

  That is, the ultrasonic element 20 has a wide bandwidth and good transmission / reception efficiency. In particular, if the resonance frequency of the first transducer cell 10A1 and the resonance frequency of the second transducer cell 10A2 are the same, it is possible to efficiently convert the ultrasonic wave in a wide band with the transmission frequency as the center main wave number into the ultrasonic wave. Can be received. For example, based on the detection of the frequency shift of reflected ultrasound due to the Doppler effect accompanying the movement of the test object (for example, blood flow in the blood vessel), the movement information (movement direction and speed) of the test object is calculated. Easy to do.

  The plan view shape of the cavity 14A2 of the second transducer cell 10A2 is not limited to an ellipse as long as it is anisotropic, and a flat polygon, a racetrack shape, an oval shape, or a corner is curved. It may be a polygon.

  In addition, as a shape with few locations where stress locally increases when the membrane is deformed, it is most preferable that the outer periphery of an ellipse or an oval shape is configured by a curve. This is because there is no fear of deterioration of long-term characteristics such as reliability and durability.

  However, as shown in FIG. 9, it is preferable that the length (DL) in the major axis direction of the cavity 14A2 in a plan view is 130% or more and 200% or less of the length (DS) in the minor axis direction. If it is above the above range, the bandwidth spread is remarkable as in the ultrasonic element 20, and if it is below the above range, the Q value falls within the allowable range.

<Second Embodiment to Fourth Embodiment>
Next, the ultrasonic elements 20B to 20D of the second embodiment to the fourth embodiment will be described. Since these embodiments differ only in the arrangement form of the plurality of transducer cells 10 as compared with the ultrasonic element 20 of the first embodiment, other description is omitted.

  As shown in FIG. 10, in the ultrasonic element 20B of the second embodiment, an elliptical second cavity 14B2 (cell 10B2) is arranged so as to surround the circular first cavity 14B1 (cell 10B1). Yes.

  The ultrasonic element 20 shown in FIG. 6 has anisotropic directivity reflecting the reception directivity of the cell 10A2 having the elliptical cavity 14A2. That is, there was in-plane anisotropy in ultrasonic reception sensitivity.

  On the other hand, in the ultrasonic element 20B, since the ultrasonic directivity of each cell 10B2 is offset, the directivity of the entire element 20B is uniform and excellent in diffusibility.

  In the ultrasonic element 20C according to the third embodiment shown in FIG. 11, a plurality of elliptical second cavities 14C2 (cells 10C2) are arranged in an in-plane isotropic manner. Further, a plurality of circular first cavities 14C1 (cells 10C1) are arranged so as to surround the plurality of second cavities 14C2 (cells 10C2).

  The beam width d at the focal point of the ultrasonic wave is expressed by the following (formula 1), where λ is the wavelength of the ultrasonic wave, F is the focal length, and D is the aperture of the sound source.

    d = 1.2 × λ × F / D (Formula 1)

  The focal length F is the focal length when an acoustic lens is used, and corresponds to the radius of curvature when the element 20) is bent concavely without using the acoustic lens.

  In the ultrasonic element 20C, since the first cell 10C1 having the circular first cavity 14C1 is disposed around the second cell 10C2, the aperture D of the sound source is large. For this reason, the beam width d at the focal point of the ultrasonic wave is narrow, and a high-resolution ultrasonic image can be acquired.

  The ultrasonic element 20D of the fourth embodiment shown in FIG. 12 includes two types of circular cavities 14D1 (cell 10D1) and 14D2 (cell 10D2) having different sizes, and two types of elliptical shapes having different sizes and shapes. And cavities 14D3 (cell 10D3) and 14D4 (cell 10D4).

  Cells with different cavity sizes or shapes have different resonant frequencies. That is, the transmission / reception sensitivity of the ultrasonic element 20D is obtained by superimposing peaks at a plurality of resonance frequencies.

  For this reason, the ultrasonic element 20D can transmit and receive ultrasonic waves with a wider band.

  Note that the ultrasonic endoscopes 2B to 2D in which the ultrasonic elements 20B to 20D described above are disposed at the distal end portion 47 have the effect of the ultrasonic endoscope 2, and are particularly preferable as a medical endoscope. Needless to say, it can be used.

  The present invention is not limited to the above-described embodiments and modifications, and various changes and modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Ultrasound endoscope system 2, 2B-2D ... Ultrasound endoscope, 3 ... Ultrasonic observation apparatus, 3A ... Drive signal generation part, 3B ... Capacitance signal detection part, 3C ... Ground potential line, 4 ... Monitor 10, vibrator cell 11, silicon substrate, 12 lower electrode, 13 lower insulating layer, 14 cavity, 15 upper insulating layer, 16 upper electrode, 20, 20B to 20D ultrasonic element, 22A1 , 22A2, 22B ... external electrodes

Claims (9)

A plurality of first transducer cells in which a lower electrode and an upper electrode are arranged to face each other through a first cavity having an isotropic shape in plan view;
An ultrasonic element comprising: a plurality of second transducer cells in which a lower electrode and an upper electrode are arranged to face each other through a second cavity having an anisotropic shape in plan view. A ground potential external electrode that connects the upper electrode of the plurality of first transducer cells and the upper electrode of the plurality of second transducer cells to a ground potential line;
An external electrode for driving connected to the driving signal generator for transmitting ultrasonic waves, the lower electrode of the plurality of first transducer cells;
2. The ultrasonic element according to claim 1, wherein the lower electrode of the plurality of second transducer cells includes a detection external electrode connected to a capacitive signal detection unit for receiving ultrasonic waves. .   The ultrasonic element according to claim 2, wherein the first transducer cell and the second transducer cell have the same resonance frequency.   4. The ultrasonic element according to claim 3, wherein a length of the second cavity in the major axis direction of the plan view shape is 130% or more and 200% or less of a length in the minor axis direction.   The ultrasonic element according to claim 4, wherein an outer periphery of the planar view shape is configured by a curve. The plan view shape of the first cavity is a circle;
The ultrasonic element according to claim 5, wherein the shape of the second cavity in plan view is an ellipse.   The ultrasonic element according to claim 6, wherein the plurality of first transducer cells and the plurality of second transducer cells are evenly arranged.   The ultrasonic element according to claim 6, wherein the plurality of first transducer cells are arranged so as to surround the second transducer cell. An insertion portion in which the ultrasonic element according to any one of claims 1 to 8 is disposed at a tip portion;
An operation portion disposed on a proximal end side of the insertion portion;
An ultrasonic endoscope comprising: a universal cord extending from the operation unit.

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