JP6390428B2 - Ultrasonic transducer cell, ultrasonic probe, and control method of ultrasonic transducer cell - Google Patents

Description

  The present invention relates to an ultrasonic probe used for ultrasonic inspection.

  The ultrasonic probe is attached to the main body of the ultrasonic diagnostic equipment that has the function to send out ultrasonic waves to the inside of the subject, receive ultrasonic signals reflected inside the subject, and acquire information inside the subject. Device.

  Ultrasonic transducers used for ultrasonic probes are mainly composed of piezoelectric ceramics typified by PZT (lead zirconate titanate) arranged in a row, but in recent years, 3D / 4D ultrasonic imaging has become popular. Two-dimensional transducers have been studied for the purpose of realizing a low-cost and compact probe that is possible, and cMUT (Capacitive Micromachined Ultrasonic Transducer) elements have been widely studied as a method suitable for an array structure (for example, Patent Document 1). . This cMUT element is composed of a capacitance type MEMS that drives a vibrating membrane (hereinafter referred to as a membrane) with electrostatic force, and has a structure as shown in FIG. 28, for example. FIG. 28A is a perspective view of the cMUT element, FIG. 28B is an exploded perspective view of the cMUT element, and FIG. 28C is a side sectional view of the cMUT element. As shown in FIG. 28, the cMUT element 50 includes a substrate 51, a lower layer electrode 52 disposed inside the substrate 51, and an insulating film disposed to face the lower layer electrode 52 with a cavity (cavity) 53 interposed therebetween. 55, a membrane 56, and a membrane support 54 are provided. Here, the cavity 53 includes a space surrounded by the membrane 56, the membrane support portion 54, and the lower layer electrode 52, and is configured to be substantially vacuum. The membrane 56 also serves as an electrode, and the lower layer electrode 52 and the membrane 56 are connected to wirings 60a and 60b, respectively.

  In the cMUT element 50 having such a configuration, the membrane 56 is vibrated by the received ultrasonic wave (sound pressure), and the received ultrasonic wave is changed based on the capacitance change between the membrane 56 and the lower layer electrode 52 that occurs at this time. Such an electrical signal can be obtained. The cMUT element 50 can transmit ultrasonic waves by vibrating the membrane 56 by applying DC and AC voltages between the membrane 56 and the lower layer electrode 52.

JP 2009-100459 A JP 2007-229328 A JP 2009-194934 A

  Such a cMUT element has a merit that wiring is easy and suitable for a two-dimensional array of multiple elements, but has a problem that a transmission output is low. In 3D / 4D ultrasonic imaging, it is necessary to further increase the transmission output in the cMUT element in order to acquire a high-quality ultrasonic image in a wide range from a shallow part to a deep part from the subject surface.

  In view of the above problems, an object of the present invention is to increase the output sensitivity of a cMUT and improve the transmission output while maintaining a low supply voltage equivalent to that of an ultrasonic probe using a conventional piezoelectric element.

  In order to solve the above problems, an ultrasonic transducer cell according to an aspect of the present invention includes a substrate, a first electrode disposed on or in the substrate, and a direction perpendicular to the upper surface of the first electrode. A first membrane disposed opposite to the first electrode in a state of being separated from the first membrane; a second membrane disposed opposite to the first membrane in a state of being spaced apart from the upper surface of the first membrane; A first membrane supporting portion disposed in a gap between the substrate and the first membrane and surrounding a space in the gap; and a space in the gap between the first membrane and the second membrane. A second membrane supporting portion surrounding the first membrane, a first wiring portion electrically connected to the first membrane, and a second wiring portion electrically connected to the second membrane, (a) The first membrane is the second A thickness in a direction perpendicular to the top surface of the first membrane is larger than that of the membrane, or (b) a first gap layer surrounded by the first membrane support portion is a second thickness surrounded by the second membrane support portion. The space area in the direction parallel to the upper surface of the first membrane is smaller than the space layer, or (c) the second membrane is perpendicular to the upper surface of the first membrane than the first membrane. Or (d) the second gap layer surrounded by the second membrane support part has a surface above the first membrane than the first gap layer surrounded by the first membrane support part. It has at least one feature that the space area in the parallel direction is small.

  In another aspect, the first membrane includes a lower membrane part facing the first gap layer surrounded by the first membrane support part, and the second membrane support part positioned above the lower membrane part. An upper membrane portion facing the second void layer and a connection portion connecting the lower layer membrane portion and the upper membrane portion are laminated, and the upper membrane portion and the lower membrane portion Are electrically connected by the connecting portion, and a cross-sectional area of the connecting portion in a direction parallel to the top surface of the first membrane is parallel to a top surface of the first membrane of the lower membrane portion and the upper membrane portion. It is smaller than the cross-sectional area.

  The above-described ultrasonic probe according to one aspect of the present invention adopts the above configuration in a structure having an ultrasonic transducer cell in which cMUTs are stacked, thereby reducing the deflection of the upper surface of the first membrane and causing a larger displacement than the second membrane. Can be generated. Therefore, a larger ultrasonic transmission output can be obtained as compared with the case of a single layer, and the transmission output characteristics of the ultrasonic probe can be improved.

1 is a schematic diagram illustrating an overall configuration of an ultrasonic probe 102 according to Embodiment 1. FIG. 3 is a top view showing the arrangement of the ultrasonic transducer array 112 of the ultrasonic probe 102 according to Embodiment 1. FIG. (A) The top view which showed the basic structure of the ultrasonic transducer | vibrator 11 which concerns on Embodiment 1, (b) is sectional drawing of the AA cross section in (a) figure. 2 is a functional block diagram of an ultrasonic diagnostic apparatus 100 using the ultrasonic probe 102 according to Embodiment 1. FIG. 2A is a perspective view of an ultrasonic transducer cell 12 according to Embodiment 1, and FIG. 2B is an exploded perspective view of the ultrasonic transducer cell 12. FIG. FIG. 3 is an explanatory diagram showing the operation of the ultrasonic transducer cell 12 according to the first embodiment, where (a) is a cross-sectional view (b) in a state in which a bias voltage is not applied to the ultrasonic transducer cell 12; It is sectional drawing of the state which applied. 5 is a schematic view showing a method for manufacturing the ultrasonic transducer cell 12 according to Embodiment 1. FIG. 5 is a schematic view showing a method for manufacturing the ultrasonic transducer cell 12 according to Embodiment 1. FIG. FIG. 4 is a diagram illustrating voltages applied to wiring portions 30a, 30b, and 30c and timings in the ultrasonic transducer cell 12. FIG. 6 is a diagram comparing the ultrasonic transmission characteristics of the ultrasonic transducer 11 according to the first embodiment and the ultrasonic transmission characteristics of conventional and comparative capacitive ultrasonic transducers. It is sectional drawing of the ultrasonic transducer | vibrator cell 12 which concerns on the comparative example which laminated | stacked the conventional capacitive ultrasonic transducer structure simply. It is the chart which showed the conditions at the time of investigating the ultrasonic transmission characteristic shown in FIG. 6 is a cross-sectional view of an ultrasonic transducer cell 12 according to a first modification of the first embodiment. FIG. FIG. 6 is a diagram comparing the ultrasonic transmission characteristics of the ultrasonic transducer 11 according to the first modification of the first embodiment and the ultrasonic transmission characteristics of a conventional capacitive ultrasonic transducer. It is the chart which showed the conditions at the time of investigating the ultrasonic transmission characteristic shown in FIG. 6 is a cross-sectional view of an ultrasonic transducer cell 12 according to a second modification of the first embodiment. FIG. 6 is a cross-sectional view of an ultrasonic transducer cell 12 according to a third modification of the first embodiment. FIG. (A) Top view which showed the basic structure of the ultrasonic transducer | vibrator used for the ultrasonic probe 102 which concerns on Embodiment 2, (b) (a) It is sectional drawing of the AA cross section in a figure. (A) A sectional view in a state where a bias voltage is not applied to the ultrasonic transducer cell 12 according to the second embodiment, and (b) is a sectional view in a state where a bias voltage is applied. 6 is a schematic view showing a method for manufacturing the ultrasonic transducer cell 12 according to Embodiment 2. FIG. 6 is a schematic view showing a method for manufacturing the ultrasonic transducer cell 12 according to Embodiment 2. FIG. It is the figure which compared the ultrasonic transmission characteristic of the ultrasonic transducer | vibrator 11 which concerns on Embodiment 2, and the ultrasonic transmission characteristic of the conventional capacitive ultrasonic transducer. 6 is a cross-sectional view of an ultrasonic transducer cell 12 according to a first modification of the second embodiment. FIG. FIG. 10 is a diagram showing ultrasonic transmission characteristics of an ultrasonic transducer 11 according to Modification 1 of Embodiment 2. 6 is a cross-sectional view of an ultrasonic transducer cell 12 according to a second modification of the second embodiment. FIG. FIG. 10 is a diagram comparing the ultrasonic transmission characteristics of the ultrasonic transducer 11 according to the second embodiment and the ultrasonic transmission characteristics of the ultrasonic transducer according to the second modification of the first embodiment. 6 is a cross-sectional view of an ultrasonic transducer cell 12 according to a third modification of the second embodiment. FIG. (A) A perspective view of a conventional capacitive ultrasonic transducer cell, (b) a top view of a conventional capacitive ultrasonic transducer cell, and (c) a conventional capacitive ultrasonic transducer cell. It is sectional drawing. It is the figure which showed the shape of the conventional convex probe.

<< Background to the form for carrying out the present invention >>
The inventors conducted various studies in order to further improve the ultrasonic transmission / reception sensitivity of the ultrasonic transducer cell using the cMUT element. As described above, the conventional cMUT element has the advantage that it is easy to wire and is suitable for a two-dimensional array of multiple elements, while it has a problem that the transmission output is low. Proposals have been made to date.

  As an example, a new operation mode called a collapse mode has been proposed. In the collapse mode, when a DC voltage is applied to the lower electrode, a specific voltage higher than that in the normal mode is applied to attract the membrane with the DC electrostatic force of the lower electrode, and the membrane is in contact with the lower electrode. This is the operating mode to be activated. In this collapse mode, it is said that the sensitivity and drive capability are higher than in the normal mode. For example, an application structure as shown in Patent Document 1 has been proposed.

  However, when utilizing the collapse mode, it is generally necessary to apply a very high DC voltage of about 130-150V, and if such a voltage cannot be provided, this mode should be activated and maintained. I can't go. Further, when used for ultrasonic diagnosis, such a high voltage may adversely affect the human body. On the other hand, the configuration of Patent Document 1 is devised to reduce the necessary DC voltage by fusing the membrane and the substrate in contact with each other, but it can cope with the reliability problem of the collapse mode. Not. That is, in the collapse mode, the membrane and the substrate repeatedly collide around the region where the membrane and the substrate are always in contact with each other, and there is still a problem that the thin insulating film is destroyed.

  Also, a technique for improving output by stacking elements has been studied. For example, a configuration in which a piezoelectric pMUT (piezoelectric Micromachined Ultrasonic Transducer) as shown in Patent Document 2 and a cMUT is combined has been proposed. However, in the configuration described in Patent Document 2, it is necessary to drive pMUT and cMUT with different pulse voltages, and the circuit configuration becomes complicated. Moreover, it is expected that the manufacturing process becomes complicated and the variation becomes large.

  Furthermore, as another method for improving the output by stacking elements, for example, a configuration in which cMUTs as shown in Patent Document 3 are stacked in a pyramid shape has been proposed. However, in the configuration described in Patent Document 3, since the layers are stacked in a pyramid shape, the total area of the electrode becomes smaller as the layer becomes higher, and the effective area that can be used for transmission / reception of ultrasonic waves becomes smaller, which is not efficient. Furthermore, considering a two-stage configuration, for example, the upper membrane is in a form straddling a plurality of lower membranes. Therefore, if a wall is provided between the membrane support parts to seal the upper cavity, There is a problem that the lower layer membrane does not function in the portion provided with.

  In the configuration in which the above-described elements are stacked, both surfaces sandwiching the cavity function as a membrane, and are configured to bend in opposite directions (bend in the direction in which the cavity is contracted) when a bias voltage is applied. As a result of studies aimed at improving transmission / reception sensitivity, the inventors have found that the transmission output characteristics are not improved in a configuration in which both surfaces sandwiching the cavity are bent in opposite directions as a membrane when a bias voltage is applied. In addition, it has also been found that if the deflection of one side is suppressed and the other is largely bent, a high transducer output characteristic can be obtained as a whole large transducer cell. The following embodiment solves the problems of the conventional cMUT based on the above findings based on the inventors' investigation, and maintains the same supply voltage as that of an ultrasonic probe using a piezoelectric element that has been conventionally used. However, it is intended to increase transmission / reception sensitivity by structural improvement of cMUT.

  Hereinafter, an ultrasonic transducer cell according to an embodiment will be described with reference to the drawings.

<< Outline of Embodiment for Implementing the Present Invention >>
The ultrasonic transducer cell according to the present embodiment includes a substrate, a first electrode disposed on or in the substrate, and the first electrode in a state of being vertically separated from the upper surface of the first electrode. A first membrane disposed opposite to the first membrane; a second membrane disposed opposite to the first membrane in a state of being vertically separated from the upper surface of the first membrane; and the substrate and the first membrane A first membrane support portion disposed in the gap and surrounding the space in the gap; and a second membrane support portion disposed in the gap between the first membrane and the second membrane and surrounding the space in the gap. A first wiring portion electrically connected to the first membrane, and a second wiring portion electrically connected to the second membrane; (a) the first membrane is more than the second membrane; Also said 1 men The thickness in the direction perpendicular to the upper surface of the lens is large, or (b) the first gap layer surrounded by the first membrane support part is more than the second gap layer surrounded by the second membrane support part. Or (c) the second membrane has a thickness in a direction perpendicular to the upper surface of the first membrane rather than the first membrane. (D) The second void layer surrounded by the second membrane support portion is larger in spatial area in a direction parallel to the upper surface of the first membrane than the first void layer surrounded by the first membrane support portion. Has at least one of the following characteristics.

  In another aspect, when having the feature (b), the first membrane support portion has a larger cross-sectional area in a direction parallel to the upper surface of the first membrane than the second membrane support portion. May be.

  In another aspect, when having the feature (d), the second membrane support portion has a larger cross-sectional area in a direction parallel to the upper surface of the first membrane than the first membrane support portion. Also good.

  In another aspect, the first membrane support portion may have a configuration in which maximum widths in a direction parallel to the second membrane support portion and the upper surface of the first membrane are substantially equal.

  In another aspect, the substrate, the first electrode disposed on or in the substrate, and the first electrode are arranged opposite to the first electrode in a state of being vertically separated from the upper surface of the first electrode. A first membrane, a second membrane disposed opposite to the first membrane in a state of being vertically separated from an upper surface of the first membrane, and a gap between the substrate and the first membrane. A first membrane support that surrounds the void layer, a second membrane support that is disposed in the gap between the first membrane and the second membrane and surrounds the void layer in the gap, and the first membrane A first wiring part electrically connected to the second membrane and a second wiring part electrically connected to the second membrane, wherein the first membrane is surrounded by the first membrane support part; Lower layer facing the layer Connecting the membrane part, the upper membrane part facing the second gap layer located above the lower membrane part and surrounded by the second membrane support part, the front upper membrane part, and the lower membrane part The upper membrane part and the lower membrane part are electrically connected by the connection part, and the cross-sectional area of the connection part in a direction parallel to the upper surface of the first membrane is The lower layer membrane part and the upper layer membrane part may have a configuration smaller than a cross-sectional area in a direction parallel to the upper surface of the first membrane.

  In another aspect, the upper layer membrane portion may be thicker in the direction perpendicular to the upper surface of the first membrane than the second membrane.

  In another aspect, the lower layer membrane portion may have a greater thickness in a direction perpendicular to the upper surface of the first membrane than the second membrane.

  In another aspect, the lower membrane part may have a smaller width in a direction parallel to the upper surface of the first membrane than the second membrane.

  In another aspect, the lower layer membrane portion, the upper layer membrane portion, and the connection portion may have a configuration in which center positions in a direction parallel to the upper surface of the first membrane coincide with each other.

  In another aspect, the submembrane electrically connected to the second wiring portion, and the submembrane supporting portion that supports the submembrane and electrically connects the submembrane and the wiring inside the substrate. The structure which has these may be sufficient.

  In another aspect, the first membrane and the second membrane may be conductive.

  Moreover, in another aspect, the structure provided with the 1st insulating membrane which consists of an insulating material laminated | stacked above the said 1st membrane may be sufficient.

  Moreover, in another aspect, the structure provided with the 2nd insulating membrane which consists of an insulating material further laminated | stacked above the said 2nd membrane may be sufficient.

  In another aspect, the ultrasonic transducer cell includes a plurality of the ultrasonic transducer cells, and at least one of the second membrane or the second wiring portion of the ultrasonic transducer cells adjacent to each other is connected to the plurality of the ultrasonic transducer cells. It may be an ultrasonic transducer in which the second wiring part of the ultrasonic transducer cell is electrically connected.

  In another aspect, the ultrasonic transducer includes a plurality of ultrasonic transducers, and the plurality of ultrasonic transducers are arranged two-dimensionally in a plane parallel to the upper surface of the second membrane to constitute a transducer array. An ultrasonic probe may be used.

  According to another aspect, there is provided a method for controlling the ultrasonic transducer cell, wherein a bias voltage is applied to the first electrode and the second wiring part, and a pulse voltage is applied to the first wiring part. A method for controlling an ultrasonic transducer cell that transmits ultrasonic waves may be used.

  According to another aspect, there is provided a method for controlling the ultrasonic transducer cell, wherein a bias voltage is applied to the first wiring part, and a pulse voltage is applied to the first electrode and the second wiring part. A method for controlling an ultrasonic transducer cell that transmits ultrasonic waves may be used.

  In another aspect, there may be a method for controlling an ultrasonic transducer cell in which a timing at which a pulse voltage is applied to the first electrode and a timing at which a pulse voltage is applied to the second wiring portion are different.

  In another aspect, a method of controlling an ultrasonic transducer cell in which a pulse width of a pulse voltage applied to the first electrode and a pulse width of a pulse voltage applied to the third electrode are different. .

  Hereinafter, embodiments will be described with reference to the drawings. In addition, the same reference number is attached | subjected to the same component and description is abbreviate | omitted.

<< Embodiment 1 >>
<Configuration of Ultrasonic Probe 102>
FIG. 1 is a schematic diagram showing the overall configuration of the ultrasonic probe 102 according to the first embodiment. As shown in FIG. 1, an ultrasonic probe 102 includes an ultrasonic transducer array 112 (hereinafter referred to as “vibrator array 112”) that transmits and receives ultrasonic waves inside a probe case 111, and an transducer array 112. And a printed circuit board 114 on which a plurality of signal lines for inputting / outputting electric signals independently of the ultrasonic transducer (element) are printed. The ultrasonic probe 102 is connected to the ultrasonic diagnostic apparatus main body 109 via the probe cable 115.

  FIG. 2 is a top view showing the arrangement of the transducer array 112 of the ultrasonic probe 102 according to the first embodiment. FIG. 3A is a top view showing the basic structure of the ultrasonic transducer 11 according to the first embodiment, and FIG. 3B is a cross-sectional view taken along the line AA in FIG.

  As shown in FIG. 2, the transducer array 112 includes an ultrasonic transducer 11 (hereinafter referred to as “vibrator 11”) composed of a plurality of ultrasonic transducer cells 12 (hereinafter referred to as “vibrator cells 12”). Are two-dimensionally arranged. The transducer 11 is a capacitive ultrasonic transducer (cMUT) manufactured using MEMS (Micro Electro Mechanical System) technology, and is configured to transmit and receive ultrasonic waves three-dimensionally within a subject. ing. Each transducer cell 12 mutually converts electrical energy and mechanical energy due to vibration. As shown in FIGS. 2 and 3, in the first embodiment, as an example, the vibrator 11 includes four vibrator cells 12. The diameter of each transducer cell 12 is, for example, 40 to 80 μm. However, the number and size of the transducer cells 12 constituting the transducer 11 can be arbitrarily set and are not limited to the above.

  The transducer cells 12 included in the same transducer 11 are electrically connected and configured to transmit ultrasonic waves in the same phase by applying a pulsed voltage. In addition, by supplying a driving voltage with a predetermined time difference for each transducer 11, it is possible to focus and deflect the generated ultrasonic waves. With this configuration, the ultrasonic probe 102 is configured to perform sector scanning by transmitting ultrasonic waves in a three-dimensional direction.

<Configuration of ultrasonic diagnostic apparatus 100>
FIG. 4 is a functional block diagram of the ultrasonic diagnostic apparatus 100 using the ultrasonic probe 102 according to the first embodiment. The ultrasonic diagnostic apparatus 100 transmits an ultrasonic wave to the subject 101, generates an ultrasonic probe 102 that receives an ultrasonic signal reflected inside the subject 101, and a drive signal for transmitting the ultrasonic wave. And transmitting and receiving the signal detected by the ultrasonic element of the ultrasonic probe 102 and amplifying and digitally converting the signal detected by the ultrasonic element of the ultrasonic probe 102 and the signal output from the transmitter and receiver 103. A signal processing unit 104 that performs digital beam forming, an image processing unit 105 that performs rendering processing of a three-dimensional image based on the three-dimensional data generated by the signal processing unit 104, and processed image data The image display unit 106 that displays an image based on the control, and the control that controls the transmission / reception unit 103 to generate a drive signal at a predetermined timing And a 107.

  The transmission / reception unit 103, the signal processing unit 104, the image processing unit 105, the image display unit 106, and the control unit 107 are stored in the ultrasonic diagnostic apparatus main body 109, and a plurality of signals are exchanged with the ultrasonic probe 102. They are connected by a probe cable that covers the cables of the wires together. Note that some functions of the transmission / reception unit 103 such as detection signal amplification and digital conversion may be realized in the ultrasonic probe 102.

<Configuration of vibrator cell 12>
FIG. 5A is a perspective view of the transducer cell 12 according to Embodiment 1, and FIG. 5B is an exploded perspective view of the transducer cell 12. 6A and 6B are explanatory diagrams showing the operation of the transducer cell 12 according to the first embodiment. FIG. 6A is a cross-sectional view of a state in which a bias voltage is not applied to the transducer cell 12, and FIG. 3 is a cross-sectional view of a state in which a bias voltage is applied to a transducer cell 12. FIG.

  As shown in FIGS. 5A, 5B, and 6A, the vibrator cell 12 includes a substrate 21 made of an electrically insulating material such as a silicon wafer, glass, quartz, and the like, and the inside of the substrate 21. A conductive lower layer electrode 22, a first membrane 25 disposed to face the lower electrode 22 across the first cavity 23 (first gap layer), and a second cavity 27 (second A second membrane 29, a first membrane support portion 31a, and a second membrane support portion 31b are provided so as to be opposed to the first membrane 25 with a gap layer therebetween. Insulating films 24 and 26 are provided below and above the first membrane 25, respectively, and an insulating film 28 is provided below the second membrane 29.

  Here, the thickness of the first membrane 25 in the direction perpendicular to the substrate 12 is configured to be thicker than the thickness of the second membrane 29. For example, the thickness of the first membrane 25 may be 2 to 4 μm, and the thickness of the second membrane 29 may be 1 to 2 μm.

  For example, the lower layer electrode 22 can be made of conductive metal such as aluminum, silver, copper, or chromium. For example, the film thickness can be about 4 μm. The first membrane and the second membrane are made of a conductive material. For example, a metal such as aluminum, silver, copper, or chromium, a conductive resin, or the like can be used. The first membrane 25 and the second membrane 29 also serve as electrodes, and the lower layer electrode 22, the first membrane 25, and the second membrane 29 are connected to the wiring portions 30a, 30b, and 30c, respectively.

For the first membrane support part 31a, the second membrane support part 31b, and the insulating films 24, 26, and 28, an insulating thin film material can be used. For example, SiC, SiO ₂ , SiN, or a mixture thereof is used. May be. The thickness of the first membrane support portion 31a and the second membrane support portion 31b in the plane direction parallel to the upper surface of the substrate 21 in FIG. 6A can be configured to be 2 to 4 μm, for example. Here, the thickness of the one membrane support portion 31a in the planar direction in FIG. 6A is larger than the thickness of the second membrane support portion 31b. For example, the first membrane support 31a can be 3 to 5 μm, and the second membrane support 31b can be 2 to 3 μm.

  The first cavity 23 is a space surrounded by the first membrane 25, the membrane support portion 31 a, and the substrate 21, and the second cavity 27 is surrounded by the first membrane 25, the membrane support portion 31 b, and the second membrane 29. Space. Both the first cavity 23 and the second cavity 27 are configured to be substantially vacuum.

  The first cavity 23 is smaller in width in the direction parallel to the upper surface of the substrate 21 in FIG. 6A than the second cavity 27, that is, the cross-sectional area perpendicular to the stacking direction of the membrane is It is configured to be smaller than the second cavity 27. The width of the first cavity 23 and the second cavity 27 in the direction parallel to the upper surface of the substrate 21 in FIG. 6A can be set to 40 to 80 μm, for example. The height of the first cavity 23 and the second cavity 27 can be set to 200 to 300 nm, for example.

  As described above, the insulating films 24, 26, and 28 are disposed between the first cavity 23 and the second cavity 27 and the first membrane 25 and the second membrane 29, respectively. The thickness of the insulating films 24, 26, and 28 can be set to 200 to 400 nm, for example.

  Hereinafter, the cross-sectional area of the cavity or the membrane support part perpendicular to the stacking direction of the membrane is simply expressed as the cross-sectional area of the cavity or the cross-sectional area of the membrane support part.

  Instead of the first membrane 25 also serving as an electrode, an electrode may be formed on or in the first membrane 25. Similarly, instead of the second membrane 29 also serving as an electrode, an electrode may be formed on or in the second membrane 29. Further, the lower layer electrode 22 may be disposed on the substrate 21 instead of being disposed inside the substrate 21. For example, the first membrane 25 has a first insulating membrane made of an insulating material and upper and lower electrode layers arranged so as to sandwich the first insulating membrane, and the upper and lower electrode layers are electrically connected. It is good also as composition which has. In addition, the second membrane 29 may include a second insulating membrane made of an insulating material and an electrode layer.

  In addition, although the transducer cell 12 in the present embodiment has a hexagonal shape as an example, it is not limited to this and may have other shapes.

<Method for Manufacturing Vibrator Cell 12>
Next, a method for manufacturing the transducer cell 12 will be described. 7 and 8 are schematic views showing a method for manufacturing the transducer cell 12 according to the first embodiment.

  In the first step, an insulating film to be the wiring layer 120 and the substrate 21 is formed on the upper surface of the semiconductor substrate, and a lower layer electrode 22 configured to be connected to the wiring layer 120 is patterned on the upper surface by etching. Further, a thin insulating film 21A is formed thereon (FIG. 7A).

  Next, in the second step, the first sacrificial layer 121 for forming the first cavity 23 and the insulating film 24 are formed on the upper surface of the insulating film 21A. Then, a mask corresponding to a portion where the first cavity 23 is formed is two-dimensionally arranged, and a portion not subjected to the mask is removed by an etching process or the like to form a recess 121A reaching the lower layer electrode 22 (FIG. 7). (B)).

  Next, in the third step, the first membrane 25 and the insulating film 26 are formed so as to fill the recess 121 </ b> A and cover the insulating film 24. Then, a hole 25A that penetrates the first membrane 25 and the insulating film 26 and reaches the first sacrificial layer 121 is formed (FIG. 7C). The hole between the cells may have a groove shape that separates the cells.

  Next, in the fourth step, the first sacrificial layer 121 is removed from the hole by etching using a reactive gas or the like to form the first cavity 23 (FIG. 7D).

  Next, in the fifth step, the third sacrificial layer 123 for forming the second cavity 27 and the insulating film 28 are formed on the upper surface of the insulating film 26 as in the second step. Then, a mask corresponding to a portion where the second cavity 27 is to be formed is two-dimensionally arranged, and the third sacrificial layer 123 and the insulating film 28 are partially removed by etching in a portion where the mask is not applied, so as to be insulated. A recess 123A reaching the film 26 is formed (FIG. 8A). At this time, the lateral opening width of the recess 123A is formed smaller than the lateral opening width of the recess 121A. The insulating film 26 is not removed because the second membrane 29 and the first membrane 25 are insulated.

  Next, in the sixth step, similarly to the third step, a second membrane 29 is formed which is a film that fills the portion of the recess 123A removed in the previous process and covers the insulating film 28. At this time, the film thickness of the second membrane 29 is formed thinner than the film thickness of the first membrane 25. And the hole 29A which penetrates the 2nd membrane 29 and reaches the 3rd sacrificial layer 123 is formed (FIG.8 (b)). The holes between the cells may be groove-shaped, but the cells in the same element are formed so as to be at least partially connected.

  Finally, the third sacrificial layer 123 is removed by etching from the hole 29A formed in the previous step to form the second cavity 27, and the cover layer 124 is formed so that the inside of the second cavity 27 is kept in a vacuum state. The transducer cell 12 is completed by sealing (FIG. 8C).

  By the way, in the above manufacturing method, the first cavity 23 and the second cavity 27 are completely sealed and configured to be almost in a vacuum state. These cavities can be formed using a known MEMS technique, for example, an SM method (Surface Micromachining method; a method of forming a cavity by removing a sacrificial layer).

  At this time, a sacrificial layer removal hole (not shown) is provided between the second cavity 27 and the first cavity 23 so as to pass through the inside of the second membrane 29 and the insulating film 28. Both cavities can be formed. Further, if the sacrificial layer removal hole on the second membrane 29 is closed, both cavities can be sealed.

<Operation of the vibrator cell 12>
Next, the operation of the transducer cell 12 of the first embodiment configured as described above will be described. FIG. 9 is a diagram showing voltages applied to the wiring portions 30a, 30b, and 30c in the transducer cell 12 shown in FIGS. 6A and 6B and timings thereof. Here, 71 indicates a voltage applied to the wiring portions 30a and 30c, and 72 indicates a voltage applied to the wiring portion 30b.

  First, in an initial state (timing of t = t0), a DC bias voltage (for example, −100 V) is applied to the wiring portions 30a and 30c, and the wiring portion 30b is set to 0V.

  Under such a state, as shown in FIG. 6B, electrostatic attraction acts between the first membrane 25 and the second membrane 29, and the second membrane 29 bends downward. In addition, electrostatic attraction acts between the lower layer electrode 22 and the first membrane 25, and the first membrane 25 is slightly bent downward.

  Next, at the timing of t = t1, a pulse voltage about the bias voltage is applied to the wiring portion 30b while the bias voltage is applied to the wiring portions 30a and 30c. Then, the potential difference among the lower layer electrode 22, the first membrane 25, and the second membrane 29 instantaneously becomes almost 0V, and the electrostatic force generated between the electrodes is lost, and the first membrane 25 and the second membrane 29 The state shown in FIG. 6A is restored by the elastic force of the membrane 29. By this reaction, an ultrasonic wave is generated above the second membrane 29.

  At the moment when the pulse voltage is applied to the wiring portion 30b, the first membrane 25 generates a small acceleration but a large acceleration. This acceleration is transmitted to the second membrane 29, and is also synergistic with the elastic force of the second membrane 29. Since a large displacement is generated in the second membrane 29, an output larger than that of the single layer structure can be obtained.

  When an ultrasonic wave (sound pressure) is received with a bias voltage applied, the first membrane 25 and the second membrane 29 vibrate, and the capacitance between the lower layer electrode 22 and the first membrane 25 that occurs at this time is generated. Based on the change and the capacitance change between the first membrane 25 and the second membrane 29, an electrical signal related to the received ultrasonic wave can be acquired.

  6A and 6B, the operation of the transducer cell 12 has been described. However, the transducer 11 configured by the transducer cell 12 and the transducer array 112 configured by the transducer 11 are described. Is the same operation.

<Regarding the ultrasonic transmission characteristics of the transducer cell 12>
Next, the ultrasonic transmission characteristics of the transducer cell 12 will be described. Here, the ultrasonic transmission characteristics of the vibrator according to the first embodiment, the vibrator having the conventional single layer structure, and the vibrator according to the comparative example in which the conventional single layer structure is simply laminated are determined by the finite element method. The analysis results are compared using structural analysis simulation.

  FIG. 10 is a diagram comparing the ultrasonic transmission characteristics of the transducer 11 according to the first embodiment and the ultrasonic transmission characteristics of the conventional and comparative capacitive transducers. FIG. 11 is a cross-sectional view of a transducer cell according to a comparative example in which conventional capacitive transducer structures are simply stacked. FIG. 12 is a chart showing conditions for examining the ultrasonic transmission characteristics shown in FIG.

  Here, in FIG. 10, an ultrasonic transmission characteristic 83 represents a simulation result of the ultrasonic transmission characteristic of the transducer 11 in the first embodiment, and the ultrasonic transmission characteristic 81 has the conventional single-layer structure shown in FIG. It is a simulation result of the ultrasonic transmission characteristic of a vibrator. The ultrasonic transmission characteristic 82 is a simulation result of the ultrasonic transmission characteristic of the vibrator according to the comparative example shown in FIG. 11 in which the membranes are simply laminated without changing the membrane thickness and the cavity cross-sectional area. Here, the membrane thickness and the cross-sectional area of the cavity are as shown in the table of FIG. As an ultrasonic transmission characteristic, the sound pressure at a position separated from the transducer cell 12 by a predetermined distance was obtained by simulation.

  As shown in FIG. 10, when the ultrasonic transmission characteristic 81 according to the conventional example is compared with the ultrasonic transmission characteristic 82 according to the comparative example, the ultrasonic transmission characteristic 81 according to the conventional example having a single-layer structure has a greater membrane thickness. The ultrasonic output was higher than the ultrasonic transmission characteristic 82 according to the comparative example in which the layers were simply laminated without changing the cross-sectional area of the cavity. On the other hand, in the ultrasonic transmission characteristic 83 according to the first embodiment, an output twice (6 dB improvement) was obtained as compared with the ultrasonic transmission characteristic 81 according to the conventional example. That is, in the ultrasonic transmission characteristic 83 according to Embodiment 1, the ultrasonic output was improved by changing the thickness of the membrane and the cross-sectional area (lateral width) of the cavity. Here, it is set as the structure which changes the cross-sectional area of a cavity by changing the cross-sectional area of a membrane support part.

  In the vibrator cell in which the capacitive vibrator structure shown in the first embodiment or the comparative example is laminated, the first membrane 25 generates a small acceleration but a large acceleration at the moment when the pulse voltage is applied to the wiring portion 30b. The acceleration is transmitted to the second membrane 29, and a displacement is generated in the second membrane 29 by a synergistic effect with the elastic force of the second membrane 29. At this time, in Embodiment 1, the frequency of the first membrane 25 is configured to be higher than the frequency of the second membrane 29 by changing the thickness of the membrane and the sectional area (lateral width) of the cavity. Therefore, the phase at the time of displacement of each membrane can be made different between the first membrane 25 and the second membrane 29, and an output larger than that of the single layer structure can be obtained.

  Further, it is desirable that the first membrane 25 does not bend when the second membrane 29 is displaced. In the first embodiment, it is considered that bending can be suppressed by configuring the first membrane 25 to be thicker than the second membrane 29. In the ultrasonic transmission characteristic 83 according to the first embodiment, the bending of the first membrane 25 can be reduced by changing the thickness of the membrane and the cross-sectional area (lateral width) of the cavity. As described above, since the first membrane 25 is made difficult to bend, a large displacement can be generated in the second membrane 29, so that it is considered that an improvement in the ultrasonic output was observed.

  For the sake of simplicity, the shape of the membrane or the like is square in this simulation, but it is thought that the same tendency can be obtained even if simulation is performed with other shapes.

  In the present embodiment, the bias voltage is applied to the wiring portions 30a and 30c and the pulse voltage is applied to the wiring portion 30b. However, the bias voltage is applied to the wiring portion 30b and the wiring portions 30a and 30c are applied. A pulse voltage can also be applied. In this case, since different pulse voltages can be applied to the wiring portions 30a and 30c, it is effective to apply voltages with pulse widths that match the respective resonance frequencies of the first membrane 25 and the second membrane 29. Can be operated automatically. The optimum driving frequency varies depending on the diagnostic purpose of the ultrasonic probe and the location of the subject to be diagnosed. It is preferable to set and drive the resonance frequency of the transducer cell according to the purpose. For example, about 3 Mhz is preferable for a site deep from the skin surface such as the abdomen, and about 10 MHz is preferable for a site shallow from the skin surface such as the carotid artery. Also, about 7 MHz is preferable for the breast. Therefore, the driving frequency is preferably selected from a range including 3 MHz to 10 MHz.

  Further, if the timing of applying a voltage to the second membrane 29 is slightly delayed, the reaction force from the subject is reduced and the second membrane can be greatly deformed toward the subject, so that the output can be further improved.

  In the first embodiment, the same bias voltage is applied to the wiring portions 30a and 30c. However, different bias voltages may be applied. For example, the voltage balance is broken by setting −100V to the wiring portion 30a and −90V to the wiring portion 30c, and the first membrane 25 is attracted to the substrate 21 side. In this case, depending on the configuration, the stroke of the second membrane 29 can be made larger than the interval (vertical width) of the second cavities 27, and the transmission output can be improved.

  As described above, the vibrator 11 according to the first embodiment can greatly improve the transmission output, which has been a problem with the conventional structure. As a result, a two-dimensional array probe capable of transmitting and receiving ultrasonic waves in a wide range from a shallow site to a deep site can be realized, and ultrasonic diagnosis capable of 3D / 4D imaging with a wide range and high image quality is possible.

<Modification 1>
FIG. 13 is a cross-sectional view of the transducer cell 12 according to the first modification of the first embodiment. In the first embodiment, the first membrane 25 is configured to be thicker than the second membrane 29, and the first cavity 23 has a smaller cross-sectional area (lateral width in the drawing) than the second cavity 27. In the first modification, as shown in FIG. 13, the second membrane 29 is configured to be thicker than the first membrane 25, and the second cavity 27 has a smaller width than the first cavity 23. It is configured as follows.

  FIG. 14 is a diagram comparing the ultrasonic transmission characteristics of the vibrator 11 according to the first modification of the first embodiment and the ultrasonic transmission characteristics of a conventional capacitive vibrator. In FIG. 14, the ultrasonic transmission characteristic 81 is the ultrasonic transmission characteristic of the vibrator having the conventional single layer structure shown in FIG. 10, and the ultrasonic transmission characteristic 83 is the ultrasonic wave of the vibrator according to the first embodiment. The transmission characteristic, the ultrasonic transmission characteristic 84, shows the simulation result of the ultrasonic transmission characteristic of the vibrator according to the first modification. Here, the membrane thickness and the cross-sectional area of the cavity are as shown in FIG. Modification 1 and Embodiment 1 are simulation results under conditions in which the membrane thickness and the cavity cross-sectional area are reversed.

  As shown in FIG. 14, the ultrasonic transmission characteristic 84 according to the first modification is higher than about 12 Mhz in comparison with the ultrasonic transmission characteristic 83 according to the first embodiment and the ultrasonic transmission characteristic 81 according to the conventional example. High sound pressure level at frequency. From the simulation results in the first embodiment and the first modification, it can be seen that stacking the membranes with different membrane thicknesses or cavity cross-sectional areas is effective in improving the ultrasonic transmission characteristics.

  Further, as shown in FIG. 14, by comparing the ultrasonic transmission characteristic 84 according to the modification 1 and the ultrasonic transmission characteristic 83 according to the first embodiment, the membrane thickness or the sectional area of the cavity is equal to the resonance frequency of the membrane. You can see that it has an effect.

<Modification 2>
FIG. 16 is a cross-sectional view of the transducer cell 12 according to the second modification of the first embodiment. Although the first embodiment has been described in the form in which the structure of the capacitive vibrator is laminated in two stages, the modification 2 has a structure in which the structure is laminated in three stages as shown in FIG. As shown in FIG. 16, in the second modification, in addition to the configuration of the first embodiment, the third membrane 44 disposed so as to face the second membrane 29, and between the second membrane 29 and the third membrane 44. A membrane supporting portion 31c surrounding the third cavity 42 disposed, and insulating films 41 and 43 inserted between the third cavity 42 and the second membrane 29 and the third membrane 44 are provided.

  The electrode or membrane of each layer is connected to the wiring portions 30a, 30b, 30c, and 30d, and an ultrasonic wave is transmitted by applying a bias voltage to the wiring portions 30a and 30c and a pulse voltage to the wiring portions 30b and 30d.

  Here, the thickness of the third membrane 44 is formed thinner than the thickness of the second membrane 29. Further, the lateral width of the third cavity 42 is configured to be larger than the lateral width of the second cavity 27. Thus, by increasing the number of laminated layers while changing the membrane thickness or the cross-sectional area of the cavity, the ultrasonic transmission output can be further improved with respect to the first embodiment and the first modification.

<Modification 3>
FIG. 17 is a cross-sectional view of the transducer cell 12 according to the third modification of the first embodiment. In the first embodiment, the capacitive vibrator has been described with a symmetric structure. However, in the vibrator cell according to the third modification, the center positions of the first cavity 23 and the second cavity 27 are set as shown in FIG. It has a configuration shifted in the horizontal direction. For example, the widths of the membrane support portions on the left and right sides of the first cavity 23 and the widths of the membrane support portions on the left and right sides of the second cavity 27 are different between the first cavity 23 and the second cavity 27. The center position of each cavity can be shifted in the lateral direction. With this configuration, ultrasonic waves can be transmitted in a direction inclined with respect to the vertical direction of the transducer cell.

  In an ultrasonic probe using a conventional piezoelectric element, a convex probe as shown in FIG. 29 is used in an application that requires a wide scanning angle with a large ultrasonic transmission range. In such a convex probe, a wide scanning angle is realized by arranging the piezoelectric element 45 on a curved surface. On the other hand, by using the transducer cell according to the modified example 3, the piezoelectric element 45 is arranged on a plane. However, strong ultrasonic waves can be transmitted in a direction inclined from the vertical direction, and can be used for applications that require a wide scanning angle.

<< Embodiment 2 >>
Next, the vibrating cell according to the second embodiment will be described with reference to the drawings.

<Configuration of vibrator cell 12>
FIG. 18A is a top view showing the basic structure of the transducer 11 used in the ultrasonic probe 102 according to the second embodiment, and FIG. 18B is a cross-sectional view taken along the line AA in FIG. FIG. 19A is a cross-sectional view in a state where a bias voltage is not applied to the transducer cell 12 according to the second embodiment, and FIG. 19B is a cross-sectional view in a state where a bias voltage is applied.

  As shown in FIGS. 18A, 18B, and 19A, the transducer cell 12 includes a substrate 21 made of an electrically insulating material such as a silicon wafer, glass, quartz, and the like. The conductive lower layer electrode 22, the first cavity 25 disposed so as to face the lower layer electrode 22 across the first cavity 23, and the first membrane 25 opposed across the second cavity 27 The second membrane 29, the first membrane support portion 31a, and the second membrane support portion 31b are arranged. Insulating films 24 and 26 are provided below and above the first membrane 25, respectively, and an insulating film 28 is provided below the second membrane 29.

  The first membrane 25 includes a lower layer membrane portion 25a, a connection portion 25b, and an upper layer membrane portion 25c. The connecting portion 25b is configured such that the width in the horizontal direction in FIG. 19A is smaller than the width in the horizontal direction of the lower layer membrane portion 25a and the upper layer membrane portion 25c. Therefore, the lower layer membrane portion 25a and the upper layer membrane portion 25c can reduce the influence of each displacement on the other. For example, the lateral width of the lower layer membrane portion 25a and the upper layer membrane portion 25c may be 40 to 50 μm, and the lateral width of the connection portion 25b may be 20 to 40 μm. Further, the lower layer membrane portion 25a and the upper layer membrane portion 25c are electrically connected to each other by the connection portion 25b. The first membrane 25 and the second membrane 29 also serve as electrodes, and the lower layer electrode 22, the first membrane 25, and the second membrane 29, which will be described later, are connected to the wiring portions 30a, 30b, and 30c, respectively. The thickness of the lower layer membrane portion 25a and the upper layer membrane portion 25c of the first membrane 25 and the thickness of the second membrane 29 can be configured in the range of 1 to 4 μm. The thickness of the connecting portion 25b can be 2 to 3 μm.

  For example, the lower layer electrode 22 can be made of conductive metal such as aluminum, silver, copper, or chromium. For example, the film thickness can be about 4 μm. The first membrane and the second membrane are made of a conductive material. For example, a metal such as aluminum, silver, copper, or chromium, a conductive resin, or the like can be used.

For the first membrane support part 31a, the second membrane support part 31b, and the insulating films 24, 26, and 28, an insulating thin film material can be used. For example, SiC, SiO ₂ , SiN, or a mixture thereof is used. May be. The thickness of the first membrane support portion 31a and the second membrane support portion 31b in the planar direction in FIG. 19A can be configured to be 2 to 4 μm, for example. Moreover, the thickness of the planar direction in FIG. 19A of the 1st membrane support part 31a and the 2nd membrane support part 31b is substantially the same.

  The first cavity 23 (first gap) is a space surrounded by the first membrane 25, the membrane support 31a and the substrate 21, and the second cavity 27 (second gap) is the first membrane 25 and the membrane support. This is a space surrounded by 31b and the second membrane 29. Both the first cavity 23 and the second cavity 27 are configured to be substantially vacuum.

  The first cavity 23 has substantially the same lateral width in the drawing as the second cavity 27, that is, the cross-sectional area perpendicular to the lamination direction of the membrane is substantially the same in the first cavity 23 and the second cavity 27. It is configured. In other words, the cross-sectional area in the direction perpendicular to the lamination direction of the membrane is the same as that of the membrane support portion 31a and the membrane support portion 31b. The lateral width of the first cavity 23 and the second cavity 27 in FIG. 19A can be set to 40 to 80 μm, for example. The height of the first cavity 23 and the second cavity 27 can be set to 200 to 300 nm, for example.

  Insulating films 24, 26, and 28 are disposed between the first cavity 23 and the second cavity 27 and the first membrane 25 and the second membrane 29, respectively. The thickness of the insulating films 24, 26, and 28 can be set to 200 to 400 nm, for example.

  Instead of the first membrane 25 also serving as an electrode, an electrode may be formed on or in the first membrane 25. Similarly, instead of the second membrane 29 also serving as an electrode, an electrode may be formed on or in the second membrane 29. Further, the lower layer electrode 22 may be disposed on the substrate 21 instead of being disposed inside the substrate 21. Moreover, the 1st membrane 25 can take the structure which has the 1st insulating membrane which has insulation, and the upper and lower electrode layers arrange | positioned so that the 1st insulating membrane may be pinched | interposed. In this case, an electrode layer is inserted between the first insulating membrane and the insulating layers 24 and 26. Similarly, the 2nd membrane 29 can take a structure, if it has the 2nd insulating membrane and electrode layer which have insulation. Also in this case, an electrode layer is inserted between the second insulating membrane and the insulating layer 28.

In addition, although the transducer cell 12 in the present embodiment has a hexagonal shape as an example, it is not limited to this and may have other shapes.
<Method for Manufacturing Vibrator Cell 12>
Next, a method for manufacturing the transducer cell 12 will be described. 20 and 21 are schematic diagrams showing a method for manufacturing the transducer cell 12 according to the second embodiment.

  In the first step, an insulating film to be the wiring layer 120 and the substrate 21 is formed on the upper surface of the semiconductor substrate, and a lower layer electrode 22 configured to be connected to the wiring layer 120 is patterned on the upper surface by etching. Further, a thin insulating film 21A is formed thereon (FIG. 20A).

  Next, in the second step, the first sacrificial layer 121 for forming the first cavity 23 and the insulating film 24 are formed on the upper surface of the insulating film 21A. Then, a mask corresponding to the portion where the first cavity 23 is to be formed is two-dimensionally arranged, and the portion not provided with the mask is removed by etching or the like to form a recess 121A reaching the lower layer electrode 22 (FIG. 20). (B)).

  Next, in a third step, a lower layer membrane portion 25a is formed so as to fill the recess 121A and cover the insulating film 24. And the hole 25B which penetrates the lower layer membrane part 25a and reaches the 1st sacrificial layer 121 is formed (FIG.20 (c)). The hole between the cells may have a groove shape that separates the cells.

  Next, in the fourth step, the first sacrificial layer 121 is removed from the hole by etching using a reactive gas or the like to form the first cavity 23, and patterning is newly performed on the lower layer membrane portion 25a by etching or the like. A second sacrificial layer 122 is formed (FIG. 20D).

  Next, in a fifth step, the connection portion 25b and the upper membrane portion 25a are formed so as to fill the space between the patterned second sacrificial layers 122 and cover the second sacrificial layers 122. Then, a hole 25D that penetrates through the upper membrane portion 25a and reaches the second sacrificial layer 122 is formed (FIG. 21A). Again, the pores between the cells may be in the form of grooves separating the cells.

  Here, the second sacrificial layer 122 is removed using a reactive gas or the like. Thereafter, as in the second step, the third sacrificial layer 123 and the insulating film 28 for forming the second cavity 27 are formed on the upper surface of the insulating film 26, and the third sacrificial layer 123 and the insulating film 28 are partially formed by etching. To remove. Note that the insulating film 26 is not removed in order to insulate the second membrane 29 and the upper layer membrane portion 25a.

  Next, in the sixth step, as in the third step, a second membrane 29 that is a film that fills the portion removed in the previous process and covers the insulating film 28 is formed. And the hole 29A which penetrates the 2nd membrane 29 and reaches the 3rd sacrificial layer 123 is formed (FIG.21 (b)). The holes between the cells may be groove-shaped, but the cells in the same element are formed so as to be at least partially connected.

  Finally, the third sacrificial layer 123 is removed by etching from the hole 29A formed in the previous step to form the second cavity 27, and the cover layer 124 is formed and sealed so that the inside of the second cavity 27 is kept in a vacuum state. Then, the vibrator cell 12 is completed (FIG. 21C).

  By the way, in the above manufacturing method, the first cavity 23 and the second cavity 27 are completely sealed and configured to be almost in a vacuum state. These cavities can be formed using a known MEMS technique, for example, an SM method (Surface Micromachining method; a method of forming a cavity by removing a sacrificial layer).

  At this time, by sacrificing a sacrificial layer removal hole (not shown) between the second cavity 29 and the first cavity 23 so as to pass through the inside of the connection portion 25b with the second membrane 29 and the insulating film 28, Both cavities can be formed with a single sacrificial layer etch. Further, if the sacrificial layer removal hole on the second membrane 29 is closed, both cavities can be sealed. Therefore, the gap 34 can be sealed in a substantially vacuum state by using such a forming method.

<Operation of the vibrator cell 12>
Next, the operation of the transducer cell 12 of the first embodiment configured as described above will be described.
The voltages applied to the wiring portions 30a, 30b, and 30c of the transducer cell 12 of the first embodiment and the timing thereof are the same as in the example of the first embodiment shown in FIG. In FIG. 9, reference numeral 71 denotes a voltage applied to the wiring portions 30a and 30c, and 72 denotes a voltage applied to the wiring portion 30b.

  First, in an initial state (timing of t = t0), a DC bias voltage (for example, −100 V) is applied to the wiring portions 30a and 30c, and the wiring portion 30b is set to 0V.

  Under such a state, as shown in FIG. 19B, electrostatic attraction acts between the lower layer electrode 22 and the first membrane 25, and the lower layer membrane portion 25a of the first membrane 25 bends downward. Further, electrostatic attraction also acts between the upper membrane portion 25c of the first membrane 25 and the second membrane 29, and the second membrane 29 bends downward.

  Next, at the timing of t = t1, a pulse voltage about the bias voltage is applied to the wiring portion 30b while the bias voltage is applied to the wiring portions 30a and 30c. Then, the potential difference among the lower layer electrode 22, the first membrane 25, and the second membrane 29 instantaneously becomes almost 0V, and the electrostatic force generated between the electrodes is lost, and the lower layer membrane portion 25a and the second membrane portion The state shown in FIG. 19A is restored by the elastic force of the membrane 29. By this reaction, an ultrasonic wave is generated above the second membrane 29.

  At the moment when the pulse voltage is applied to the wiring portion 30b, a large acceleration is generated in the lower layer membrane portion 25a, and this acceleration is transmitted to the second membrane 29 via the connection portion 25b and the upper layer membrane portion 25c. Since a large displacement is generated in the second membrane 29 by a synergistic effect with the elastic force, an output larger than that of the single-layer structure can be obtained. Further, at this time, it is considered that a large acceleration can be given to the second membrane 29 because the upper membrane part 25c is not deformed.

  Further, when an ultrasonic wave (sound pressure) is received in a state where a bias voltage is applied, the lower layer membrane portion 25a and the second membrane 29 vibrate, and the capacitance between the lower layer electrode 22 and the lower layer membrane portion 25a that occurs at this time is generated. Based on the change and the capacitance change between the upper layer membrane portion 25c and the second membrane 29, an electrical signal related to the received ultrasonic wave can be acquired.

  19A and 19B, the operation of the transducer cell 12 has been described. However, the transducer 11 configured by the transducer cell 12 and the transducer array 112 configured by the transducer 11 are described. Is the same operation.

<Regarding the ultrasonic transmission characteristics of the transducer cell 12>
Next, the ultrasonic transmission characteristics of the transducer cell 12 will be described. Here, the ultrasonic transmission characteristics of the vibrator according to the second embodiment and the conventional single-layer vibrator are analyzed using a structural analysis simulation by a finite element method, and the results are compared. FIG. 22 is a diagram comparing the ultrasonic transmission characteristics of the transducer 11 according to the second embodiment and the ultrasonic transmission characteristics of a conventional capacitive transducer. In FIG. 22, an ultrasonic transmission characteristic 81 indicates the ultrasonic transmission characteristic in the conventional example, and an ultrasonic transmission characteristic 82 indicates the ultrasonic transmission characteristic in the second embodiment.

  As shown in FIG. 22, in the ultrasonic transmission characteristic 82 according to the second embodiment, an output three times or more (an improvement of 10 dB or more) is obtained as compared with the ultrasonic transmission characteristic 81 according to the conventional example. In the ultrasonic transmission characteristic simulation shown in FIG. 22, the thickness of the lower layer membrane portion 25a and the upper layer membrane portion 25c is 3 μm, the thickness of the second membrane 29 is 1 μm, and the lower layer membrane portion 25a and the upper layer of the first membrane 25 are The membrane portion 25c is configured to be thicker than the second membrane 29. With such a configuration, a result that an output more than twice that of the conventional structure is generated is obtained.

  In the vibrator cell in which the capacitive vibrator structure according to the second embodiment is laminated, at the moment when the pulse voltage is applied to the wiring part 30b, the lower membrane part 25a generates a large acceleration with a small displacement. Is transmitted to the second membrane 29, and the second membrane 29 is displaced due to a synergistic effect with the elastic force of the second membrane 29. At this time, it is desirable that the upper membrane part 25c does not bend, and it is considered that a large displacement can be generated in the second membrane 29 by suppressing the bending of the upper membrane part 25c. In the ultrasonic transmission characteristic 83, the upper layer membrane portion 25c and the lower layer membrane portion 25a are configured to be connected by the narrow connection portion 25b, so that the upper layer membrane portion 25c can reduce bending, and as a result, It is considered that a large displacement can be generated in the second membrane 29 and the ultrasonic output is improved.

  For the sake of simplicity, the shape of the membrane or the like is square in this simulation, but it is thought that the same tendency can be obtained even if simulation is performed with other shapes.

  In the present embodiment, the bias voltage is applied to the wiring portions 30a and 30c and the pulse voltage is applied to the wiring portion 30b. However, the bias voltage is applied to the wiring portion 30b and the wiring portions 30a and 30c are applied. A pulse voltage can also be applied. In this case, since different pulse voltages can be applied to the wiring portions 30a and 30c, it is effective to apply voltages with pulse widths that match the respective resonance frequencies of the lower layer membrane portion 25a and the second membrane 29. Can be operated automatically. The optimum driving frequency varies depending on the diagnostic purpose of the ultrasonic probe and the location of the subject to be diagnosed. It is preferable to set and drive the resonance frequency of the transducer cell according to the purpose. In the ultrasonic probe, the driving frequency is preferably selected from a range including 3 MHz to 10 MHz.

  Furthermore, if the timing of applying a voltage to the second membrane 29 is slightly delayed, the reaction force from the subject is reduced and the second membrane can be greatly deformed toward the subject, so that the output can be improved. .

  In the present embodiment, the same bias voltage is applied to the wiring portions 30a and 30c. However, different bias voltages may be applied. As described above, the vibrator 11 according to the first embodiment can greatly improve the transmission output, which has been a problem with the conventional structure. As a result, a two-dimensional array probe capable of transmitting and receiving ultrasonic waves in a wide range from a shallow site to a deep site can be realized, and ultrasonic diagnosis capable of 3D / 4D imaging with a wide range and high image quality is possible.

<Modification 1>
FIG. 23 is a cross-sectional view of the transducer cell 12 according to the first modification of the second embodiment. Here, the lateral width of the lower layer membrane portion 25 a is made smaller than the lateral width of the second membrane 29. Since other configurations are the same as those in the second embodiment, description thereof is omitted.

  FIG. 24 is a diagram illustrating the ultrasonic transmission characteristics of the transducer 11 according to the first modification of the second embodiment. The ultrasonic transmission characteristic 84 of the vibrator according to the modification 1 is superimposed on the simulation result of FIG.

  24, the ultrasonic transmission characteristic 81 is the ultrasonic transmission characteristic in the conventional example, the ultrasonic transmission characteristic 82 is the ultrasonic transmission characteristic in the second embodiment, and the ultrasonic transmission characteristic 84 is the ultrasonic transmission characteristic in the first modification. Is shown. As shown in FIG. 24, in the ultrasonic transmission characteristic 84 according to the first modification, an output having a higher sound pressure level near the peak was obtained as compared with the ultrasonic transmission characteristic 82 according to the second embodiment. In addition, an output with a sound pressure level that is at least twice as high as the ultrasonic transmission characteristic 81 of the conventional example is obtained.

  Here, in the ultrasonic transmission characteristic simulation shown in FIG. 24, the ultrasonic transmission characteristic 82 according to the second embodiment is the ultrasonic transmission characteristic according to the first modification, in which the lateral width of the first cavity 23 is 28 um. No. 84 was simulated with the lateral width of the first cavity 23 being 24 um. That is, in the transducer cell 12 of the first modification, the lateral width of the lower layer membrane portion 25 a is configured to be smaller than the lateral width of the second membrane 29. At this time, the thicknesses of the lower layer membrane portion 25a and the second membrane 29 are both 1 um.

  Further, as shown in FIG. 24, the comparison between the ultrasonic transmission characteristic 84 according to Modification 1 and the ultrasonic transmission characteristic 82 according to Embodiment 2 shows that the lateral width of the lower layer membrane portion 25 a and the second membrane 29 is It can be seen that this affects the resonance frequency.

  In the modification 1, the simulation is performed by changing the horizontal width of the lower layer membrane portion 25a and the second membrane 29. However, the horizontal width may be changed and the length in the depth direction of the drawing may be changed. Moreover, you may change the cross-sectional area of the lower layer membrane part 25a and a 2nd membrane.

<Modification 2>
FIG. 25 is a cross-sectional view of the transducer cell 12 according to the second modification of the second embodiment. In the second embodiment, since the second membrane 29 also serves as an electrode, adjacent cells in the same element are connected by the second membrane 29. On the other hand, in the second modification, as shown in FIG. 25, a submembrane 32 serving as a path for applying a bias voltage to the second membrane 29 is provided, and the second membrane 29 is pulled out via the submembrane 32. The wiring is configured to be connected to an adjacent cell by wiring in the substrate 21. Except for the point that the sub-membrane 32 is provided, it is the same as the second embodiment, and the description thereof is omitted.

  Here, the submembrane 32 serving as a path for applying a bias voltage to the second membrane 29 may be connected to the first membrane 25 as shown in FIG. In this case, this configuration can be adopted by providing the insulating portion 33 between the upper membrane portion 25c and the portion to which the submembrane 32 is connected.

  FIG. 26 is a diagram comparing the ultrasonic transmission characteristics of the vibrator 11 according to the second modification of the first embodiment and the ultrasonic transmission characteristics of the vibrator according to the comparative example in which the submembrane 32 is removed from the second modification. It is. Here, the simulation is performed assuming that the submembrane 32 is disposed on the first membrane 25. In FIG. 25, the ultrasonic transmission characteristic 83 indicates the ultrasonic transmission characteristic of the vibrator 11 according to the comparative example, and the ultrasonic transmission characteristic 85 indicates the ultrasonic transmission characteristic of the vibrator 11 according to the modification 2.

  As shown in FIG. 25, the ultrasonic transmission characteristic 83 according to the comparative example shows a frequency characteristic having two peaks, but the ultrasonic transmission characteristic 85 according to the modified example 2 has a wide band characteristic. It is considered that this is because the submembrane 32 seals the gap 34 by providing the submembrane 32. Thus, it is considered that excessive vibration in the lateral direction that occurred in the comparative example was suppressed, and a wide band characteristic was obtained.

<Modification 3>
FIG. 27 is a cross-sectional view of the transducer cell 12 according to the third modification of the second embodiment. The second embodiment, the first modification, and the second modification have been described in the form in which the structure of the capacitive vibrator is stacked in two stages. However, as shown in FIG. 27, a three-stage structure may be used.

  In the configuration of FIG. 27, the additional portion 46 has the same structure as the first membrane 25, the insulating film 26, the second cavity 27, and the insulating film 28, and the third membrane 44 is formed thereon. The electrode or membrane of each layer is connected to the wiring portions 30a, 30b, 30c, and 30d, and an ultrasonic wave is transmitted by applying a bias voltage to the wiring portions 30a and 30c and a pulse voltage to the wiring portions 30b and 30d.

  Thus, the transmission output can be further improved by increasing the number of layers.

≪Other variations≫
The ultrasonic probe, ultrasonic transducer, and ultrasonic transducer cell according to each embodiment have been described above. The present invention is not limited to each embodiment. For example, some or all of the processing units included in the ultrasonic diagnostic apparatus in each embodiment may be included in the ultrasonic probe 102.

  Each processing unit included in the ultrasonic diagnostic apparatus according to each embodiment is typically realized as an LSI that is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include a part or all of them.

  Further, the circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.

  Moreover, you may implement | achieve part or all of the function of the ultrasound diagnosing device based on each embodiment, when processors, such as CPU, run a program.

  Furthermore, the present invention may be the above program or a non-transitory computer-readable recording medium on which the above program is recorded. Needless to say, the program can be distributed via a transmission medium such as the Internet.

  In addition, division of functional blocks in the block diagram is an example, and a plurality of functional blocks can be realized as one functional block, a single functional block can be divided into a plurality of functions, or some functions can be transferred to other functional blocks. May be. In addition, functions of a plurality of functional blocks having similar functions may be processed in parallel or time-division by a single hardware or software.

  In addition, the order in which the above steps are executed is for illustration in order to specifically describe the present invention, and may be in an order other than the above. Also, some of the above steps may be executed simultaneously (in parallel) with other steps.

  Moreover, you may combine at least one part among the functions of the ultrasonic transducer | vibrator cell which concerns on each embodiment, and its modification.

  Further, various modifications in which the present embodiment is modified within the scope conceived by those skilled in the art are also included in the present invention without departing from the gist of the present invention.

≪Summary≫
The above-described ultrasonic probe according to one aspect of the present invention adopts the above-described configuration in a structure having an ultrasonic transducer cell in which cMUTs are stacked, thereby reducing the deflection of the upper surface of the first membrane and making the second membrane 29 larger. A displacement can be generated. Thereby, it is possible to obtain a larger ultrasonic transmission output than in the case of a single layer, and to improve the transmission output characteristics of the ultrasonic probe. Thereby, a clear ultrasonic image with less noise can be obtained in 3D / 4D ultrasonic imaging as compared with a conventional cMUT.

<Supplement>
Each of the embodiments described above shows a preferred specific example of the present invention. The numerical values, shapes, materials, constituent elements, arrangement positions and connection forms of the constituent elements, steps, order of steps, and the like shown in the embodiments are merely examples, and are not intended to limit the present invention. In addition, among the constituent elements in the embodiment, steps that are not described in the independent claims indicating the highest concept of the present invention are described as arbitrary constituent elements constituting a more preferable form.

  Further, for easy understanding of the invention, the scales of the components shown in the above-described embodiments may be different from actual ones. The present invention is not limited by the description of each of the above embodiments, and can be appropriately changed without departing from the gist of the present invention.

  Furthermore, in the ultrasonic transducer cell, the ultrasonic transducer, the ultrasonic probe, and the ultrasonic diagnostic apparatus, there are members such as circuit components and lead wires on the substrate. Various aspects can be implemented on the basis of ordinary knowledge, and are not directly related to the description of the present invention, so the description is omitted. Each figure shown above is a schematic diagram, and is not necessarily illustrated strictly.

  As described above, according to the embodiment, it is possible to realize a two-dimensional array probe with high sensitivity up to a deep part. As a result, high-quality 3D / 4D imaging can be realized with a small probe in a wide range from a shallow part to a deep part. In addition, a clear ultrasonic image with little noise can be obtained. Alternatively, the voltage applied to the ultrasonic transducer can be reduced. Thereby, it can contribute to the power saving of an apparatus. For this reason, it has become a technology that extends to the mobile use of ultrasonic diagnostic equipment by extending battery life, and can be widely used for ultrasonic transducer cells, ultrasonic vibrators, ultrasonic probes, and ultrasonic diagnostic equipment. is there.

DESCRIPTION OF SYMBOLS 11 Ultrasonic transducer 12 Ultrasonic transducer cell 21 Substrate 22 Lower layer electrode 23 1st cavity 24, 26, 28 Insulating film 25 1st membrane 25a Lower layer membrane part 25b Connection part 25c Upper layer membrane part 27 2nd cavity 29 2nd membrane 30a, 30b, 30c, 30d Wiring 31a, 31b, 31c Membrane support portion 32 Submembrane 33 Insulating portion 41, 43 Insulating film 42 Third cavity 44 Third membrane 45 Piezoelectric element 46 Additional portion 50 Conventional ultrasonic transducer cell 51 Substrate 52 Lower layer electrode 53 Cavity 54 Membrane support part 55 Insulating film 56 Membrane 60a, 60b Wiring 102 Ultrasonic probe 109 Diagnostic apparatus body 100 Ultrasonic diagnostic apparatus 112 Ultrasonic transducer array

Claims (19)

A substrate,
A first electrode disposed on or within the substrate;
A first membrane disposed facing the first electrode in a state of being vertically separated from the upper surface of the first electrode;
A second membrane disposed facing the first membrane in a state of being vertically separated from the upper surface of the first membrane;
A first membrane support part disposed in a gap between the substrate and the first membrane and surrounding a space in the gap;
A second membrane support portion disposed in a gap between the first membrane and the second membrane and surrounding a space in the gap;
A first wiring portion electrically connected to the first membrane;
A second wiring portion electrically connected to the second membrane;
With
(A) The first membrane is thicker in the direction perpendicular to the top surface of the first membrane than the second membrane, or (b) the first gap layer surrounded by the first membrane support is It has at least one of the characteristics that the space area in the direction parallel to the upper surface of the first membrane is smaller than the second gap layer surrounded by the second membrane support part, or
(C) The second membrane is thicker in the direction perpendicular to the top surface of the first membrane than the first membrane, or (d) the second void layer surrounded by the second membrane support is An ultrasonic transducer cell having at least one of the characteristics that a space area in a direction parallel to the upper surface of the first membrane is smaller than that of the first gap layer surrounded by the first membrane support. The ultrasonic vibration according to claim 1, wherein the first membrane support portion has a larger cross-sectional area in a direction parallel to the upper surface of the first membrane than the second membrane support portion when having the feature (b). Child cell. 2. The ultrasonic transducer according to claim 1, wherein the second membrane support portion has a larger cross-sectional area in a direction parallel to the upper surface of the first membrane than the first membrane support portion when having the feature (d). cell. The first membrane support portion has a substantially equal maximum width in a direction parallel to the second membrane support portion and the top surface of the first membrane;
The ultrasonic transducer cell according to claim 2. A substrate,
A first electrode disposed on or within the substrate;
A first membrane disposed facing the first electrode in a state of being vertically separated from the upper surface of the first electrode;
A second membrane disposed facing the first membrane in a state of being vertically separated from the upper surface of the first membrane;
A first membrane support portion disposed in a gap between the substrate and the first membrane and surrounding a void layer in the gap;
A second membrane support portion disposed in a gap between the first membrane and the second membrane and surrounding a void layer in the gap;
A first wiring portion electrically connected to the first membrane;
A second wiring portion electrically connected to the second membrane;
With
The first membrane includes a lower layer membrane portion facing the first gap layer surrounded by the first membrane support portion, and a second gap located above the lower layer membrane portion and surrounded by the second membrane support portion. The upper membrane part facing the layer and the connection part connecting the lower membrane part and the upper membrane part have a laminated structure,
The upper layer membrane part and the lower layer membrane part are electrically connected by the connection part,
The ultrasonic transducer cell, wherein a cross-sectional area of the connection portion in a direction parallel to the upper surface of the first membrane is smaller than a cross-sectional area of the lower layer membrane portion and the upper layer membrane portion in a direction parallel to the first membrane upper surface. The ultrasonic transducer cell according to claim 5, wherein the upper membrane portion is thicker in the direction perpendicular to the upper surface of the first membrane than the second membrane. The ultrasonic transducer cell according to claim 5, wherein the lower layer membrane portion has a thickness in a direction perpendicular to the upper surface of the first membrane than the second membrane. The ultrasonic transducer cell according to claim 5, wherein the lower layer membrane portion has a smaller width in a direction parallel to the upper surface of the first membrane than the second membrane. The ultrasonic transducer cell according to any one of claims 5 to 8, wherein center positions of the lower layer membrane portion, the upper layer membrane portion, and the connection portion in a direction parallel to the first membrane upper surface coincide with each other. 6. A submembrane electrically connected to the second wiring part, and a submembrane supporting part that supports the submembrane and electrically connects the submembrane and the wiring inside the substrate. The ultrasonic transducer cell according to any one of 9. Ultrasonic transducer cell according to claim 1 or 5, wherein the first membrane and said second membrane is electrically conductive.   The first membrane includes a first insulating membrane made of an insulating material and upper and lower electrode layers arranged so as to sandwich the first insulating membrane, and the upper and lower electrode layers are electrically connected. The ultrasonic transducer cell according to claim 1 or 5. The ultrasonic transducer cell according to claim 1, wherein the second membrane includes a second insulating membrane made of an insulating material and an electrode layer. A plurality of the ultrasonic transducer cells according to any one of claims 1 to 13,
By connecting at least one of the second membrane or the second wiring portion of the ultrasonic transducer cells adjacent to each other, the second wiring portions of the plurality of ultrasonic transducer cells are electrically connected. An ultrasonic transducer. A plurality of ultrasonic transducers according to claim 14,
The ultrasonic probe in which the plurality of ultrasonic transducers are arranged two-dimensionally in a plane parallel to the upper surface of the second membrane to constitute a transducer array. A method for controlling an ultrasonic transducer cell according to any one of claims 1 to 13, comprising:
Applying a bias voltage to the first electrode and the second wiring part;
A method for controlling an ultrasonic transducer cell, wherein a pulse voltage is applied to the first wiring portion to transmit ultrasonic waves. A method for controlling an ultrasonic transducer cell according to any one of claims 1 to 13, comprising:
Applying a bias voltage to the first wiring portion;
An ultrasonic transducer cell control method for transmitting an ultrasonic wave by applying a pulse voltage to the first electrode and the second wiring part. The method of controlling an ultrasonic transducer cell according to claim 17, wherein a timing at which a pulse voltage is applied to the first electrode is different from a timing at which a pulse voltage is applied to the second wiring portion. The method of the ultrasonic transducer cell of the pulse width is different according to claim 18, wherein the pulse voltage the pulse width of the pulse voltage applied to the first electrodes and is applied to the third electrodes.

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