JP2014197846A - Electrostatic capacitive type electromechanical conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromechanical conversion device capable of arbitrarily changing a bending amount of a vibrating membrane in units of elements.SOLUTION: An electromechanical conversion device comprises DC voltage applying means where a plurality of elements 108 each having one or more cells comprising a first electrode 102 and a second electrode 105 provided by sandwiching a gap between the first electrode 102 and the second electrode 105 is formed, the first electrode 102 and the second electrode 105 are electrically separated for each element 108 respectively, and the DC voltage applying means independently applies DC voltage to the first electrode 102 for each element 108.

Description

  The present invention relates to a capacitive electromechanical transducer such as a capacitive ultrasonic transducer.

  As an electromechanical transducer that performs at least one of transmission and reception of ultrasonic waves, CMUT (Capacitive Micromachined Ultrasonic Transducer), which is a capacitive ultrasonic transducer, has been proposed (see Patent Document 1). The CMUT is manufactured using a MEMS process to which a semiconductor process is applied.

  FIG. 7 shows a schematic diagram of a cross section of the CMUT. Here, the first electrode 102 and the second electrode 105 that face the vibration film 101 across the gap 104 are referred to as a cell. The vibration film 101 is supported by a support portion 103 formed on the substrate 106. The first electrodes 102 are all electrically connected in the CMUT, and a predetermined DC voltage is applied to the first electrodes 102 so that a desired potential difference occurs between the second electrodes 105. It is applied uniformly. The other second electrode 105 is electrically separated for each element (element which is an assembly of cells). By applying an alternating drive voltage, the second electrode 105 is interposed between the first and second electrodes. An alternating electrostatic attractive force is generated, and the vibration film 101 can be vibrated at a certain frequency to transmit ultrasonic waves. Further, when the vibration film 101 receives ultrasonic waves and vibrates, a minute current is generated in the second electrode 105 due to electrostatic induction, and the received signal can be extracted for each element by measuring the current value. .

  The characteristics when these ultrasonic waves are transmitted and received are determined by the amount of deflection of the vibration film 101 when a DC voltage is applied to the first electrode 102. Usually, the pressure inside the gap 104 of the cell is reduced from the atmospheric pressure, and the vibration film 101 is bent toward the substrate 106 due to the difference between the atmospheric pressure and the internal pressure of the gap 104. The amount of deflection of the vibration film 101 is determined by mechanical characteristics determined by parameters such as the size, shape, thickness, and film quality of the vibration film. Further, when the CMUT is operated, a predetermined potential difference is applied between the two electrodes in order to increase the efficiency of ultrasonic wave transmission / reception, and the vibration film 101 is further moved to the substrate 106 side by electrostatic attraction generated between the electrodes. Will be bent. When transmitting ultrasonic waves, the electrostatic attractive force is inversely proportional to the square of the distance, so that the efficiency is improved by reducing the distance between the electrodes. On the other hand, when receiving ultrasonic waves, the detected small current is inversely proportional to the distance between the electrodes and proportional to the potential difference between the electrodes. It becomes.

Special table 2003-527947

  However, when the potential difference between the two electrodes is increased, the electrostatic force acting between the electrodes and the force generated by the pressure difference exceed the restoring force of the mechanical characteristics of the diaphragm. As a result, the vibration film comes into contact with the electrode on the substrate, and a state called collapse is generated, and the characteristics of the CMUT are greatly changed. For this reason, during the normal CMUT operation (when not driven in a collapsed state), the potential difference between the electrodes is set so that the transmission / reception efficiency is high and the amount of deflection of the vibrating membrane does not cause this collapse.

  Conventionally, all of the first electrodes in the CMUT are electrically connected in the CMUT. Therefore, when operating the CMUT, a voltage is uniformly applied to the first electrode. In CMUT, due to various manufacturing factors, variations occur in the parameters of the diaphragm described above. Therefore, even when there is no potential difference between the electrodes, variation in the amount of deflection of the diaphragm occurs. Furthermore, the amount of deflection of the diaphragm during operation varies.

  As a result, the transmission / reception efficiency deviates from the assumed value, or in some cases, a collapse occurs in some cells, and the transmission / reception characteristics change greatly for each element. In order to solve these problems, an object of the present invention is to provide a capacitance-type electromechanical transducer that can arbitrarily change the amount of deflection of the diaphragm in element units.

  In the electromechanical transducer of the present invention, a plurality of elements each having one or more cells each including a first electrode and a second electrode provided with a gap between the first electrode and the first electrode are formed. The first electrode and the second electrode are electrically separated for each of the elements, and a DC voltage is applied to the first electrode independently for each of the elements. DC voltage applying means is provided.

  By using the electromechanical transducer of the present invention, the amount of deflection of the diaphragm in the electromechanical transducer can be arbitrarily adjusted in units of elements.

It is a figure explaining the electromechanical converter concerning a 1st embodiment. It is a figure explaining the electromechanical converter concerning a 1st embodiment. It is a figure explaining the electromechanical converter which concerns on 2nd Embodiment. It is a figure explaining the electromechanical converter which concerns on 3rd Embodiment. It is a figure explaining the electromechanical converter which concerns on 4th Embodiment. It is a figure explaining the electromechanical converter which concerns on 5th Embodiment. It is a figure explaining the conventional electrostatic capacitance type electromechanical transducer.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a capacitance type electromechanical transducer according to the present invention will be described in detail with reference to the drawings.

(First embodiment)
In FIG. 1, the schematic diagram of the cross section of the electromechanical transducer which concerns on this embodiment is shown. In the present embodiment, the first electrode is described as an upper electrode, and the second electrode is described as a lower electrode. The vibration film 101 on which the upper electrode 102 is formed is supported by a support portion 103 formed on the substrate 106 and vibrates together with the upper electrode 102. A lower electrode 105 is formed on the substrate 106 at a position facing the upper electrode 102 on the vibration film 101 via the gap 104. In the present invention, a configuration including an upper electrode and a lower electrode that are opposed to each other with one gap 104 therebetween is called a cell 107. The element 108 includes one or more cells 107. Specifically, one cell 107 or a plurality (at least two) of cells are electrically connected (connected in parallel). Although one element is formed by two cells in FIG. 1, the present invention is not limited to this, and a plurality of cells may be connected in a two-dimensional array. A plurality of elements (two or more elements) are formed.

  The upper electrode used in the present invention is selected from metals selected from Al, Cr, Ti, Au, Pt, Cu, Ag, W, Mo, Ta, and Ni, AlSi, AlCu, AlTi, MoW, and AlCr. At least one of the alloys can be selected and used. Also, the upper electrode can be provided in at least one of the upper surface, the back surface, and the inside of the vibration film, or when the vibration film is formed of a conductor or semiconductor, the vibration film itself can also serve as the upper electrode. is there. Further, as the lower electrode used in the present invention, the same metal as that of the upper electrode can be used. When the substrate uses a semiconductor substrate such as silicon, the substrate may also serve as the lower electrode.

  FIG. 2 shows a configuration diagram of the electromechanical transducer of this embodiment. The electromechanical transducer of this embodiment is characterized in that not only the lower electrode 105 but also the upper electrode 102 is electrically separated for each element (each element). Within the element, the plurality of upper electrodes 102 and lower electrodes 105 are electrically connected. In this embodiment, the upper electrode in the element (in the element) is individually formed for each cell and is electrically connected by a wiring (not shown) formed on the vibration film. On the other hand, one upper electrode may be formed. Further, the lower electrode may be individually formed for each cell as in the present embodiment, or one lower electrode may be formed for each element.

  A DC voltage applying unit 201 is connected to the upper electrode 102 element by element. The DC voltage applying means 201 applies a desired voltage to the upper electrode independently for each element, and generates a potential difference between the potentials of the lower electrode between the electrodes. This potential difference determines the amount of deflection of the vibration film 101. Further, the drive detection means 202 is connected to the lower electrode 105 element by element. The drive detection unit 202 includes an AC voltage generation unit 203, a current detection unit 205, and a protection switch 204.

  In the configuration of the present embodiment, if the number of elements in the electromechanical transducer is N, the DC voltage applying means 201 also has the same number N. Further, the drive detection means 202 has the same number as the elements.

  Next, the operation of the drive detection unit 202 at the time of ultrasonic transmission and reception will be described. When transmitting ultrasonic waves, an alternating voltage is applied by the alternating voltage generating means 203 connected to the lower electrode 105. As a result, an alternating potential difference is generated between the upper electrode 102 and the lower electrode 105, and an alternating electrostatic attractive force is generated at the vibration film 101. Due to this electrostatic attraction, the vibration film 101 vibrates and transmits ultrasonic waves. At the time of ultrasonic reception, the protective switch 204 connected to the lower electrode 105 is turned off to protect the input portion of the current detection unit 205 from the voltage generated by the AC voltage generation unit 203.

  When receiving the ultrasonic wave, the AC voltage generating means 203 is in a high impedance state and does not affect the potential of the lower electrode 105. On the other hand, the protection switch 204 is turned on, and the lower electrode 105 and the input part of the current detection means 203 are connected. When the vibration film 101 is vibrated by the ultrasonic wave applied from the outside, the capacitance change between the upper and lower electrodes occurs. Since the upper electrode is fixed at a predetermined potential, a minute current flows through the wiring of the lower electrode 105 due to the induced charge generated in the lower electrode 105. By detecting this minute current change by the current detection means 205, it is possible to detect the magnitude of the ultrasonic wave causing the capacitance change. Note that the potential of the lower electrode is fixed to a predetermined potential by the drive detection means 202 except when ultrasonic waves are transmitted.

  According to the configuration of the present embodiment, not only the lower electrode but also the upper electrode is electrically separated in units of elements, and furthermore, the DC voltage applying means is connected to the upper electrode in units of elements, so that each element In addition, a DC voltage can be applied independently. Therefore, different electrostatic attraction can be applied to each element, and the amount of deflection of the diaphragm can be adjusted. Therefore, variation in the characteristics of ultrasonic transmission / reception can be reduced.

  In this embodiment, the DC voltage generating means 203 is connected to the upper electrode 102 and the current detecting means 205 is connected to the lower electrode 105. However, the lower electrode is connected to the DC voltage generating means, and the upper electrode 102 is connected to the upper electrode 102. The electrode may be connected to the current detection means. In addition, the configuration of the drive detection unit is not limited to the configuration of the present specification, and a configuration other than the description, a configuration of only transmission, or a configuration of reception only can be used.

(Second Embodiment)
Next, a second embodiment will be described with reference to FIG. The second embodiment relates to the configuration of wiring from the upper electrode and the lower electrode. The rest is the same as in the first embodiment.

  FIG. 3 is a sectional view of the electromechanical transducer according to this embodiment. The through wiring board 303 includes a lower electrode through wiring 301 (second electrode through wiring) and an upper electrode through wiring 302 (first electrode through wiring) which are two types of wiring penetrating the substrate. Have. All the lower electrodes 105 in one element are connected to one lower electrode through wiring 301. The lower electrode through wiring 301 penetrates from the lower electrode side surface of the through wiring substrate 303 to the printed circuit board side surface, and is connected to the bump electrode 304. The upper electrode 102 is also connected to the upper electrode through wiring 302 in element units, and the upper electrode through wiring 302 is connected to the bump electrode 304.

  Bumps 305 are respectively formed on the bump electrodes 304 formed on the side surface of the printed circuit board of the through wiring board 303. Each wiring is connected to the wiring on the printed circuit board 306 through the bump 305. The electric signal of the lower electrode 105 is input to the drive detection unit 202 via a wiring on a printed circuit board electrically connected to the lower electrode through wiring 302. The electric signal of the upper electrode 102 is input to the DC voltage applying means 201 via a wiring on the printed circuit board 306 electrically connected to the upper electrode through wiring 303.

  The configuration of this embodiment is characterized by having the same number of lower electrode through wires and upper electrode through wires as the number of elements. Thereby, even when a plurality of elements are provided, the wiring of the upper electrode can be taken out on the back surface of the substrate while the wiring of the upper electrode 102 is separated for each element. Therefore, the wiring of the upper electrode can be connected to each of the plurality of DC voltage applying means 201 with almost no reduction in the area of the element for transmitting and receiving ultrasonic waves (with almost no decrease in transmission and reception efficiency).

(Third embodiment)
Next, a third embodiment will be described with reference to FIG. The third embodiment is characterized in that it has control signal generation means for instructing a DC voltage to be applied to the DC voltage application means 201. Other than that, it is the same as any one of the first to second embodiments.

  In FIG. 4, the block diagram of the electromechanical converter which concerns on this embodiment is shown. The diaphragm state detector 401 detects the amount of deflection of the diaphragm 101 (that is, synonymous with detecting the distance between the upper electrode and the lower electrode). The magnitude of the current detected by the lower electrode is inversely proportional to the power of the distance between the upper electrode and the lower electrode (hereinafter simply referred to as interelectrode distance) and proportional to the potential difference between the electrodes. In this case, the current detecting means is connected to the lower electrode 105 to be used as the vibrating membrane state detecting means.

  By using the vibration membrane state detection means 401 of the present embodiment, for example, an ultrasonic wave having a single frequency is transmitted from the outside, and the current generated in the lower electrode is detected for each element, so that the vibration membrane can be detected element by element. Differences in the amount of deflection can be detected. Alternatively, an AC voltage may be superimposed on a DC voltage applied to the upper electrode, and a current generated by the superimposed AC voltage may be detected (described later as a fourth embodiment). Further, as the diaphragm state detecting means, means other than detecting the current may be used, and for example, the amount of deflection of the diaphragm may be directly measured. For example, a method of detecting the deflection of the vibration film using a piezoresistance effect or a method of optically detecting the amount of deflection can be used.

  The signal detected by the vibration film state detection unit is input to the control signal generation unit 402. Based on the detected signal, the control signal generation unit 402 outputs a signal indicating a DC voltage to be applied to the DC voltage application unit 201 so that the bending amount of the CMUT vibration film 101 becomes a desired state. . The DC voltage applying unit 201 generates a DC voltage based on the signal instructed by the control signal generating unit 402 and applies it to the upper electrode 102. The DC voltage applying means 201 that performs such an operation can be easily formed by using a voltage control transmission circuit and a capacitor.

  According to the present embodiment, it is possible to detect the bending amount of each vibration film 101 for each element. Since a DC voltage can be applied to the upper electrode for each element so as to reduce variation in the amount of deflection for each element, the amount of deflection of the vibrating membrane can be made more uniform. Further, even when a parameter that affects the vibration film 101 changes due to a change with time or an environment, the state of the vibration film 101 can be adjusted for each element.

(Fourth embodiment)
Next, a fourth embodiment will be described with reference to FIG. The fourth embodiment is characterized in that it has AC voltage superimposing means 403 that superimposes an AC voltage on a DC voltage applied to the upper electrode. Other than that, it is almost the same as the third embodiment. FIG. 5 shows a configuration diagram of the electromechanical transducer according to the present embodiment.

  The AC voltage superimposing means 403 is connected to the upper electrode 102. The AC voltage is superimposed on the DC voltage applied by the DC voltage applying means 201 to the upper electrode 102 only during the period of detecting the deflection amount of the diaphragm (measurement of deflection amount variation). Even when the vibration film 101 does not vibrate due to the alternating voltage superimposed on the upper electrode 102, charges are induced in the lower electrode 105, and current is generated from the lower electrode 105. This current has a value corresponding to the distance between the upper electrode 102 and the lower electrode 105 when the superimposed alternating voltage is constant. Therefore, by detecting this current with the current detection means 205, the amount of deflection of the vibration film 101 can be detected in the form of the distance between the electrodes.

  As for the frequency of the alternating voltage to be superimposed, it is desirable to avoid the frequency at which the vibrating membrane 101 responds. Thereby, it is possible to detect only the distance between the electrodes without vibrating the vibration film 101 by the superimposed AC voltage.

  A signal switching unit 404 is connected to the output of the current detection unit 205, and an output signal is output to the control signal generation unit 402 during a period in which the deflection amount variation measurement is performed. On the other hand, during a period in which the deflection amount variation measurement is not performed (when ultrasonic waves are measured by vibration of the diaphragm), the output signal is output to the outside of the image processing apparatus or the like as a sensor output. By including the signal switching unit 404, the current detection unit 205 can be used both when measuring deflection amount variation and when measuring ultrasonic waves.

  The control signal generation unit 402 outputs a signal indicating a DC voltage to the DC voltage application unit 201 so as to keep the amount of deflection of the vibration film 101 in a desired state from the input signal.

  With the configuration of the present embodiment, the amount of deflection of the diaphragm for each element can be detected by superimposing an AC voltage and detecting the current generated in the lower electrode by the current detection means. Further, by avoiding the frequency at which the vibrating membrane vibrates as the frequency of the alternating voltage to be superimposed, the deflection amount of the vibrating membrane (distance between the upper and lower electrodes) can be detected without vibrating the vibrating membrane. Therefore, the mechanical vibration characteristics of the vibrating membrane can be eliminated, and measurement can be performed with higher accuracy. Since a DC voltage can be applied to the upper electrode for each element so as to reduce variation in the amount of deflection for each element, the amount of deflection of the vibrating membrane can be made more uniform. Further, even when a parameter that affects the vibration film 101 changes due to a change with time or an environment, the amount of deflection of the vibration film 101 can be adjusted for each element. In addition, since the current detection unit 205 can be used both when measuring the deflection amount variation and when measuring the ultrasonic wave, it can be realized with a simple configuration.

(Fifth embodiment)
Next, a fifth embodiment will be described with reference to FIG. The fifth embodiment is characterized in that the current detection unit 205 is configured to switch between circuit parameters at the time of measuring the deflection amount variation and at the time of measuring the ultrasonic waves. The rest is the same as the fourth embodiment.

  In the present embodiment, description will be made using a transimpedance circuit which is a current-voltage conversion circuit that converts a change in a minute current into a voltage. FIG. 6 shows a configuration diagram of a transimpedance circuit which is the current detection unit 205 according to the present embodiment. Reference numeral 601 denotes an operational amplifier, reference numerals 602, 604, and 606 denote resistors, reference numerals 603, 605, and 607 denote capacitors, and reference numeral 608 denotes circuit element switching means.

  In FIG. 6, the operational amplifier 601 is connected to the positive and negative power supplies VDD and VSS. First, the operation during ultrasonic measurement will be described. The inverting input terminal (−IN) of the operational amplifier 601 is connected to the lower electrode 102 via the protection switch 204. The output terminal (OUT) of the operational amplifier 601 has a configuration in which a resistor 602 and a capacitor 603 connected in parallel are connected to the inverting input terminal (−IN) by the circuit element switching unit 608, and the output signal is fed back. ing. The non-inverting input terminal (+ IN) of the operational amplifier 601 is connected to the ground terminal (GND) by a resistor 604 and a capacitor 605 that are connected in parallel. The voltage of the ground terminal (GND) is an intermediate potential between the positive power supply VDD and the negative power supply VSS. The values of the resistors 602 and 604 and the values of the capacitors 603 and 605 are the same value, and are parameters that meet the specifications at the time of ultrasonic measurement.

  Next, at the time of measuring the deflection amount variation, the circuit element switching means 608 is switched, and the operational amplifier is fed back by the resistor 606 and the capacitor 607 connected in parallel (see the circuit configuration in FIG. 6B). ). The resistor 606 and the capacitor 607 are parameters that meet the specifications when measuring the deflection amount variation.

  According to the present embodiment, it is possible to perform current detection in accordance with specifications such as the frequency and current magnitude used when measuring the deflection amount variation and the specifications such as the ultrasonic frequency and current magnitude when measuring ultrasonic waves. In FIGS. 6A and 6B, the circuit element switching means 608 is used only for the feedback portion of the operational amplifier, but the non-inverting input (+ IN) of the operational amplifier and the ground terminal also have the same configuration and the amount of deflection. The element constant may be switched in accordance with switching at the time of variation measurement or ultrasonic measurement.

  In the present specification, it has been described that the vibration film 101 operates in the conventional mode in which the gap with the lower electrode 105 always exists during the transmission / reception operation of the electromechanical transducer, but the present invention is not limited to this. The present invention can also be used in an operation in other states such as a collapse mode in which the gap between the vibration film 101 and the lower electrode 105 is partially eliminated.

101 Vibration membrane 102 Upper electrode (first electrode)
103 support portion 104 gap 105 lower electrode (second electrode)
DESCRIPTION OF SYMBOLS 106 Board | substrate 201 DC voltage application means 202 Drive detection means 203 AC voltage generation means 204 Protection switch 205 Current detection means 301 Lower electrode through wiring 302 Upper electrode through wiring 303 Through wiring board 401 Vibration film state detection means 402 Control signal generation means 402 403 AC voltage superimposing means 404 Signal switching means 608 Circuit element switching means

The electromechanical conversion device of the present invention includes a plurality of elements, a DC voltage application unit, and a current detection unit. Each of the plurality of elements includes a plurality of cells, and each of the plurality of cells. includes a first electrode, and a second electrode provided across the gap between said first electrode, said first electrodes are electrically isolated from each of the elements and, within the device they are electrically connected, the second electrode is electrically separated for each of the elements, and, within the device are electrically connected, the DC voltage applied The means independently applies a DC voltage to the first electrode for each element , and the current detection means is provided for each element, and outputs a current output from the second electrode for each element. It is characterized by detecting .

Claims (6)

An electromechanical transducer in which a plurality of elements each including one or more cells each including a first electrode and a second electrode provided with a gap between the first electrode and the first electrode are formed,
The first electrode and the second electrode are electrically separated for each element,
An electromechanical conversion device comprising DC voltage applying means for applying a DC voltage independently to each of the elements on the first electrode.   The electromechanical transducer according to claim 1, wherein the number of the first electrode and the second electrode in the element is the same.   3. The electric machine according to claim 1, further comprising: a substrate on which the first electrode through wiring and the second electrode through wiring are formed for each of the elements. Conversion device.   A current detecting means connected to the second electrode for detecting a current generated in the second electrode; and a control for instructing a DC voltage applied to the DC voltage applying means based on the detected current. The electromechanical converter according to claim 3, further comprising a signal generating unit. An AC voltage superimposing unit connected to the first electrode and superimposing an AC voltage on the DC voltage, and detecting a current generated by the AC voltage by the current detecting unit;
5. The electromechanical converter according to claim 4, wherein the DC voltage is instructed to the control signal generating means based on the current generated by the AC voltage.   When detecting the current generated by the AC voltage, the output signal from the current detecting means is connected to the control signal generating means, and is generated by the vibration of the vibrating membrane on which the first electrode or the second electrode is formed. 6. The electromechanical converter according to claim 5, further comprising a signal switching unit that switches an output signal from the current detection unit so as not to be connected to the control signal generation unit when a current to be detected is detected.

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