JP6071286B2 - Capacitive transducer and manufacturing method thereof - Google Patents

Description

The present invention relates to a capacitive transducer used as an ultrasonic transducer, a manufacturing method thereof, and the like.

Conventionally, micromechanical members manufactured by micromachining technology can be processed on the micrometer order, and various micro functional elements are realized using these. A capacitive transducer using such a technique has been studied as an alternative to a piezoelectric element. According to such a capacitive transducer, it is possible to transmit and receive acoustic waves such as ultrasonic waves, sound waves, and photoacoustic waves (hereinafter sometimes represented by ultrasonic waves) using vibrations of the vibrating membrane. . In particular, it is possible to easily obtain excellent broadband characteristics (characteristics having a relatively high electromechanical conversion coefficient in a wide frequency range) in a liquid.

As a technique described above, there has been proposed a capacitive transducer that realizes broadband characteristics using a cell having a vibration film having a high spring constant and a cell having a vibration film having a low spring constant (see Patent Document 1). In addition, a capacitive transducer that has a cell group composed of a plurality of cells having a high spring constant and a cell group composed of a plurality of cells having a low spring constant has been proposed to realize broadband characteristics ( Patent Document 2).

US Pat. No. 5,870,351 US Patent Publication 20070059858

In the capacitive transducer as described above, transmission and reception driving can be performed by applying a common voltage to the common electrode. However, in that case, an electromechanical conversion coefficient that converts vibrations of the vibration film at the time of reception into an electric signal in a plurality of types of cells including a cell having a vibration film having a high spring constant and a cell having a vibration film having a low spring constant. Alternatively, the electromechanical conversion coefficient for converting the electrical signal at the time of transmission into the vibration of the diaphragm may be different. Accordingly, wideband characteristics can be realized, but the electromechanical conversion coefficients of the plurality of types of cells may be different, and transmission sensitivity or reception sensitivity may be reduced.

In order to solve the above-described problems, a capacitive transducer according to the present invention supports a vibrating membrane including a vibrating membrane including a second electrode facing the first electrode with a gap therebetween, and the gap is formed. A cell including the diaphragm supporting portion; and a voltage applying means for applying a voltage between the first electrode and the second electrode. The cell includes a first cell including a vibration film having a first spring constant, and a second cell including a vibration film having a second spring constant lower than the first spring constant. At least one of the one cell and the second cell is provided with an insulating portion that is at least partially charged, and the first and second electrodes of the first cell and the second cell by the voltage application means By applying a common voltage between the first cell and the second cell, the first cell and the second cell are driven in a state where the potential difference between the first electrode and the second electrode is different .

Since the capacitive transducer of the present invention has a plurality of types of cells having vibration films having different spring constants, the frequency band at the time of reception or the frequency band at the time of transmission can be widened. Furthermore, the difference between the pull-in voltage of the first cell and the pull-in voltage of the second cell can be reduced or the same. Alternatively, the difference between the ratio of the applied voltage to the pull-in voltage of the first cell and the ratio of the applied voltage to the pull-in voltage of the second cell can be reduced or made the same. Thereby, the transmission sensitivity or the reception sensitivity of each cell can be improved. Therefore, in the capacitive transducer of the present invention, the frequency band at the time of reception or the frequency band at the time of transmission can be widened, and the transmission sensitivity or the reception sensitivity can be improved. In the present specification, the pull-in voltage is a voltage at which the electrostatic attractive force is larger than the restoring force of the vibrating membrane when a voltage is applied between the first electrode and the second electrode. When a voltage higher than the pull-in voltage is applied, the vibrating membrane comes into contact with the lower surface of the cavity. The pull-in voltage increases as the spring constant of the diaphragm increases and the distance between the first electrode and the second electrode increases. Therefore, the pull-in voltage of a cell having a high vibration constant of the diaphragm is higher than the pull-in voltage of a cell having a low spring constant of the diaphragm.

BRIEF DESCRIPTION OF THE DRAWINGS The figure explaining the electrostatic capacity type transducer of Example 1 of this invention. The figure explaining the electrostatic capacity type transducer of Example 2 of this invention. The figure explaining the electrostatic capacity type transducer of Example 3 of this invention. Sectional drawing explaining the example of the manufacturing method of the electrostatic capacitance type transducer of this invention. Explanatory drawing of the corona discharge process in preparation of the capacitive transducer of this invention. The figure explaining operation | movement of the capacitive transducer of this invention. The figure explaining the electrostatic capacity type transducer of Example 4 of this invention. Sectional drawing explaining the example of the manufacturing method of the electrostatic capacitance type transducer of this invention. Sectional drawing explaining the example of the manufacturing method of the electrostatic capacitance type transducer of this invention. The figure which shows the example of the subject information acquisition apparatus using the capacitive transducer of this invention.

A feature of the capacitive transducer of the present invention is that it has a plurality of types of cells having vibrating membranes having different spring constants, and at least one of the plurality of types of cells is provided with an insulating portion at least partially charged. It is. With such a configuration, an electrostatic attractive force applied to the vibrating membrane of the first cell having a large spring constant is applied to the vibrating membrane of the second cell having a small spring constant while a common voltage is applied by the voltage applying means. It can be larger than the electrostatic attractive force. Thereby, the frequency band at the time of reception or the frequency band at the time of transmission can be widened, and the transmission sensitivity or the reception sensitivity can be improved.

Since the pull-in voltages of the plurality of types of cells with different spring constants are different, when a common voltage is applied to the common electrode of the plurality of types of cells in this state, the electromechanical conversion coefficient of the first cell is Therefore, it becomes lower than the electromechanical conversion coefficient of the second cell, and the transmission sensitivity or the reception sensitivity is lowered. The higher the ratio of the applied voltage to the pull-in voltage, the higher the electromechanical conversion coefficient for converting the vibration of the vibrating membrane during reception into an electric signal, or the electromechanical conversion coefficient for converting the electric signal into vibration of the vibrating membrane during transmission. Therefore, in the present invention, a potential difference corresponding to the difference between the pull-in voltages is provided to at least one type of cell by providing a charging insulating portion so that a plurality of types of cells are pulled in with the same applied voltage. Thereby, for example, the ratio of the applied voltage to the compensated pull-in voltage can be made substantially the same in each cell, or the difference can be reduced. In addition, the difference between the pull-in voltage of the first cell and the pull-in voltage of the second cell can be reduced or made the same. Thus, transmission sensitivity or reception sensitivity of each cell can be improved. Therefore, in the capacitive transducer of the present invention, the frequency band at the time of reception or the frequency band at the time of transmission can be widened, and the transmission sensitivity or the reception sensitivity can be improved.

As a specific configuration example, the thickness of the vibration film of the first cell having a large spring constant is made larger than the thickness of the vibration film of the second cell having a small spring constant, and the vibration film of the first cell The area can be made substantially the same as the area of the diaphragm of the second cell. In this case, the radiation impedance of each cell can be made substantially the same. Such an example is shown in FIG. In this specification, the radiation impedance is the ratio between the vibration speed of the diaphragm and the force (pressure) acting on the outside (air, liquid medium, etc.) from the diaphragm. Dependent. Further, the area of the diaphragm of the first cell having a large spring constant is made smaller than the area of the diaphragm of the second cell having a small spring constant, and the thickness of the diaphragm of the first cell is set to a second value. The thickness of the diaphragm of the cell can be almost the same. In this case, production can be facilitated. Such an example is shown in FIG. 1, FIG. 2 and FIG.

On the other hand, a first voltage applying means for applying a voltage between the electrodes of the first cell and a second voltage applying means for applying a voltage between the electrodes of the second cell may be provided. In this case, even if the pull-in voltage of the first cell and the pull-in voltage of the second cell are not sufficiently adjusted and are slightly different, by appropriately adjusting the magnitude of the voltage applied to each of the plurality of types of cells. Transmission sensitivity or reception sensitivity can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1A is a top view of an embodiment of the capacitive transducer of the present invention, and FIG. 1B is a cross-sectional view taken along line AB of FIG. The present embodiment has a plurality of capacitive transducers 1 each having a plurality of first cells 12 and second cells 19. In FIG. 1, only two capacitive transducers 1 are shown, but any number of transducers may be used. The capacitive transducer 1 is composed of 22 first cells 12 and 8 second cells 19, but the number of each may be any number. Further, any arrangement of cells may be used.

The first cell 12 includes a substrate 2, an insulating film 3 formed on the substrate 2, a first electrode 4 formed on the insulating film 3, and an insulating film 5 on the first electrode 4. Furthermore, it has a vibration film 8 including a second electrode 6 and a membrane 7 facing the first electrode 4, a vibration film support portion 10 that supports the vibration film 8, and a cavity (gap) 9. When the substrate 2 is an insulating substrate such as a glass substrate, the insulating film 3 is not necessary. The second cell 19 has substantially the same configuration as the first cell 12. In the second cell 19, the second spring constant of the vibration film 16 is lower than the first spring constant of the vibration film 8 of the first cell 12. In FIG. 1B, the vibrating membrane 16 is made of the same material and thickness as the vibrating membrane 8, and the second spring constant is set by making the diameter 22 of the vibrating membrane 16 larger than the diameter 21 of the vibrating membrane 8. It is small. Here, the vibration film has a circular shape, but may have a square shape, a rectangular shape, or the like.

Further, voltage application means 11 for applying a voltage between the first electrode and the second electrode of the first cell 12 and the second cell 16 is provided. In the present embodiment, the membranes 7 and 14 of the vibration films 8 and 16 are insulating films. In particular, since the silicon nitride film can be formed with a low tensile stress, for example, a tensile stress of 300 MPa or less, it is preferable that a large deformation of the vibration film due to the residual stress of the silicon nitride film can be prevented. However, the membranes 7 and 14 of the vibration films 8 and 16 may not be insulating films. For example, a low resistance silicon single crystal of 1 Ωcm or less can be used as the membranes 7 and 14. In that case, the membrane can also be used as the second electrode.

With the above configuration, when a common voltage is applied to the first electrode 4, 13 or the second electrode 6, 14, an electromechanical conversion coefficient that converts vibration of the vibrating membrane during reception into an electric signal, or transmission Sometimes the electromechanical conversion coefficient for converting the electrical signal into the vibration of the diaphragm is lower in the first cell 12 than in the second cell 16. This is because the spring constant of the diaphragm 16 of the second cell is lower than the spring constant of the first cell 12, and the pull-in voltage of the cell having a high spring constant of the diaphragm is low. This is because it is higher than the pull-in voltage of the cell. Therefore, in this configuration, the electrostatic attractive force applied to the vibrating membrane of the first cell in a state where no voltage is applied is different from the electrostatic attractive force applied to the vibrating membrane of the second cell. In this configuration, when a common voltage is applied to the common electrode by the voltage applying means 11, a different potential difference occurs between the first cell and the second cell, and the electrostatic attractive force applied to the vibrating membrane of the first cell is reduced. , Larger than the electrostatic attractive force applied to the vibrating membrane of the second cell. If this potential difference is set to a value that cancels out the difference in the pull-in voltage due to the difference in the spring constant, both cells are pulled in with substantially the same applied voltage. Further, the ratio of the applied voltage to the pull-in voltage of the first cell and the second cell can be made substantially the same. For this purpose, the difference between the ratio of the applied voltage to the pull-in voltage of the first cell and the ratio of the applied voltage to the pull-in voltage of the second cell in the configuration in which the pull-in voltage difference due to the difference in the spring constant exists exists. A potential difference may be given to one cell, for example.

Any method may be used for such a configuration. For example, it is assumed that the difference in pull-in voltage between the first cell and the second cell is 20 V due to the difference in the spring constant. At this time, the membrane 14 of the second cell is charged by 20 V (see FIG. 1B). In this state, when a positive sign voltage that pulls in the first cell is applied to the first electrode 4, a potential difference is generated in the first cell by the voltage applied to the first electrode 4. On the other hand, in the second cell, a potential difference is generated by the difference between the voltage applied to the first electrode 13 and the potential of 20 V due to the charging. Thereby, the cells 12 and 19 having different spring constants can be simultaneously pulled in with the common voltage applied to the first electrodes 4 and 13 which are common electrodes. Moreover, you may apply a common voltage to the 2nd electrodes 6 and 15 which are another common electrode. What is necessary is just to apply the voltage of the negative sign which the 1st cell 12 pulls in to the 2nd electrodes 6 and 15. Further, the membrane 14 of the second cell 19 may be charged at −20V. In that case, the sign of the common voltage applied to the first electrodes 4 and 13 which are common electrodes may be applied with a negative sign. In addition, when a common voltage is applied to the second electrodes 6 and 15 that are common electrodes, it may be applied with a positive sign. The common voltage may be applied to the common electrode so that the difference between the pull-in voltage of the first cell and the voltage due to the charging becomes the pull-in voltage of the second cell.

Further, the first cell 12 may be charged. In this case, for example, the membrane 7 of the first cell is charged by −20V. In this state, when a positive voltage at which the second cell 19 is pulled in is applied to the first electrodes 4 and 13, a potential difference is generated in the second cell by the voltage applied to the first electrodes 4 and 13. On the other hand, in the first cell 12, a potential difference is generated by the difference between the voltage applied to the first electrode 4 and the potential due to the charging. Thereby, the cells 12 and 19 having different spring constants can be simultaneously pulled in with the common voltage applied to the first electrodes 4 and 13 which are common electrodes. Moreover, you may apply a common voltage to the 2nd electrodes 6 and 15 which are another common electrode. A negative sign voltage that pulls in the second cell 19 may be applied to the second electrodes 6 and 15. Further, the membrane 7 of the first cell 12 may be charged by 20V. In that case, the sign of the common voltage applied to the first electrodes 4 and 13 that are common electrodes may be applied with a negative sign. In addition, when a common voltage is applied to the second electrodes 6 and 15 that are common electrodes, it may be applied with a positive sign. The common voltage may be applied to the common electrode so that the difference between the pull-in voltage of the second cell and the voltage due to the charging becomes the pull-in voltage of the first cell.

The charging location of this configuration may be not only the membranes 7 and 14 but also the insulating films 5 and 13. That is, at least one of the first cell and the second cell may be provided with an insulating portion that is at least partially charged. In the above configuration, a part of one of the cells is charged by the difference in the pull-in voltage between the first cell and the second cell due to the difference in the spring constant. Next, the common voltage may be applied to the common electrode so that the potential difference between the pull-in voltage of the uncharged cell and the voltage due to the charging becomes the pull-in voltage of the charged cell. With this configuration, the difference between the pull-in voltage of the first cell and the pull-in voltage of the second cell can be reduced or made the same, so that the transmission sensitivity or the reception sensitivity can be improved. In the above description, the difference in the pull-in voltage has been described, but the same can be said for the difference in the ratio of the applied voltage to the pull-in voltage. As described above, in the capacitive transducer of this embodiment, the frequency band at the time of reception or the frequency band at the time of transmission can be widened, and the transmission sensitivity or the reception sensitivity can be improved.

Furthermore, the area of the diaphragm of the first cell 12 is smaller than the area of the diaphragm of the second cell 19, and the diaphragm thickness of the first cell is the same as the diaphragm thickness of the second cell. It can also be. By adopting this configuration, a cell having a high vibration constant of the diaphragm and a cell having a low spring constant of the diaphragm can be manufactured by the same manufacturing process. Therefore, a capacitive transducer can be manufactured at low cost. In addition, with this configuration, the vibration film of the first cell and the vibration film of the second cell can be manufactured by the same manufacturing process. If the vibration thickness of the first cell and the vibration thickness of the second cell are not the same, if one of the vibration membranes is etched or formed in a different process, The ratio between the spring constant of the vibration membrane and the spring constant of the vibration membrane of the second cell tends to vary. In such a case, the transmission or reception sensitivity and frequency band of the capacitive transducer may not be desired. Therefore, with the above configuration, variations in transmission sensitivity, reception sensitivity, and frequency band can be reduced.

Further, as shown in FIG. 3B, the vibration film thickness of the first cell is larger than the vibration film thickness of the second cell, and the vibration film area of the first cell is the second cell. It can also be set as the structure which is the same as the vibration membrane area. By adopting this configuration, as shown in FIG. 3A, the shape of each cell viewed from above can be made the same, and the radiation impedances of all the cells can be made uniform. Therefore, since the radiation impedance of each cell is the same, the vibrating membranes of each cell vibrate in the same manner, so that unnecessary vibration that reduces the electromechanical conversion coefficient can be prevented.

The above configuration can also be applied when there are three or more types of cells having different spring constants. For example, as shown in FIG. 2B, a part of the insulating layer may be charged in a different manner or uncharged for each cell having a different spring constant. A reference cell is determined, and a part of each cell is charged or uncharged by the difference in the pull-in voltage due to the difference in spring constant. In the portion to be charged, the membrane may be charged in each cell, or the insulating films 5 and 23 may be charged in each cell. The common voltage may be applied to the common electrode so that the potential difference between the pull-in voltage of the reference cell and the voltage due to the charging becomes the pull-in voltage of the charged cell.

In the above configuration, each cell having a different spring constant is driven by a separate voltage without applying a common voltage to the common electrode by charging or uncharging a part of the cell in a different manner. Is also possible. With the above configuration, the difference in pull-in voltage between cells having different spring constants can be reduced or the same. Further, since the difference in the ratio of the applied voltage to the pull-in voltage of each cell having a different spring constant can be reduced or made the same, the transmission sensitivity or the reception sensitivity can be improved.

In the above configuration, any method may be used for charging the cell. For example, the electrostatic capacity transducer can be charged during the manufacturing process, or the cell can be charged after the manufacturing process, before the use, or even during the use. In the case of charging during the production of the capacitance type transducer, it is only necessary to charge the portion (membrane or insulating film) to be charged of the cell by performing corona discharge treatment. In addition, when charging is performed after manufacturing or during use, a cell or an insulating film may be charged by pulling in a cell to be charged.

In the above configuration, the charged portion may be a portion of any material as long as it is made of a material that is easily charged. For example, a silicon oxide film, a silicon nitride film, barium titanate, strontium titanate, barium / strontium titanate, tantalum pentoxide, niobium oxide stabilized tantalum pentoxide, aluminum oxide, titanium oxide, and the like can be given. Further, not only a single type of film such as a vibrating membrane may be a single layer, but a plurality of types of films may be combined to form a plurality of layers. For example, as shown in FIG. 3, the cell membrane may have a two-layer structure, and may be composed of a silicon nitride film and a silicon oxide film. The charge amount can be adjusted by these materials and composition ratios.

Here, an embodiment of the manufacturing method of the present invention will be described with reference to FIGS. FIG. 4 is a cross-sectional view of the capacitive transducer, and has substantially the same configuration as FIG. FIG. 4 is a cross-sectional view corresponding to the line AB in FIG. First, as shown in FIG. 4A, the insulating film 72 is formed on the substrate 71. The substrate 71 is a silicon substrate, and the insulating film 72 is for forming insulation from the first electrode. When the substrate 71 is an insulating substrate such as a glass substrate, the insulating film 72 may not be formed. The substrate 71 is preferably a substrate having a small surface roughness. When the surface roughness is large, the surface roughness is transferred even in the film forming process in the subsequent step of this process, and the distance between the first electrode and the second electrode depends on the surface roughness between the cells. It will vary. Since this variation is a variation in electromechanical conversion coefficient, it is a variation in sensitivity and bandwidth. Therefore, the substrate 71 is preferably a substrate having a small surface roughness.

Further, the first electrode 73 is formed. The first electrode 73 is preferably a conductive material having a small surface roughness, such as titanium or aluminum. Similar to the substrate, when the surface roughness of the first electrode is large, the distance between the first electrode and the second electrode varies between the cells and between the elements having a plurality of cells due to the surface roughness. Therefore, a conductive material having a small surface roughness is desirable.

Next, insulating films 74 and 75 are formed. The insulating films 74 and 75 are preferably made of an insulating material having a small surface roughness, and an electrical connection between the first electrode and the second electrode when a voltage is applied between the first electrode and the second electrode. It is formed to prevent short circuit or dielectric breakdown. In the case of driving at a low voltage, since the membrane is an insulator, the insulating films 74 and 75 need not be formed. Such an insulating film is further formed in order to prevent the first electrode from being etched when the sacrificial layer is removed in a subsequent process of this process. In the case where the first electrode is not etched by the etching solution or the etching gas used when removing the sacrificial layer, the insulating films 74 and 75 may not be formed. Similarly to the substrate, when the surface roughness of the insulating films 74 and 75 is large, the distance between the first electrode and the second electrode varies depending on the surface roughness. A membrane is desirable. For example, a silicon nitride film, a silicon oxide film, or the like.

Next, as shown in FIG. 4B, sacrificial layers 76 and 77 are formed. The width of the sacrificial layer 76 is formed to be smaller than the width of the sacrificial layer 77. With this configuration, the diameter of the cavity of the first cell can be made smaller than the diameter of the cavity of the second cell. The sacrificial layers 76 and 77 are preferably made of a material having a small surface roughness. Similar to the substrate, when the surface roughness of the sacrificial layer is large, the distance between the first electrode and the second electrode varies between the cells due to the surface roughness, so a sacrificial layer with a small surface roughness is desirable. . In addition, in order to shorten the etching time for removing the sacrificial layer, a material having a high etching rate is desirable. In addition, a sacrificial layer material that does not substantially etch the insulating film or the membrane is required for an etching solution or etching gas for removing the sacrificial layer. When the insulating film or membrane is etched against the etching solution or etching gas that removes the sacrificial layer, the thickness of the vibration film varies and the distance between the first electrode and the second electrode varies. There are things to do. Variations in the thickness of the vibrating membrane and variations in the distance between the first electrode and the second electrode are variations in sensitivity and bandwidth between cells. In the case where the insulating film or the membrane is a silicon nitride film or a silicon oxide film, a sacrificial layer material that can use an etchant or an etching gas that has a small surface roughness and is difficult to etch the insulating film or the membrane is desirable. For example, amorphous silicon, polyimide, chrome, etc. In particular, since the chromium etching solution does not substantially etch the silicon nitride film or the silicon oxide film, it is desirable that the insulating film or the membrane is a silicon nitride film or a silicon oxide film.

Next, membranes 78 and 79 are formed as shown in FIG. The membranes 78 and 79 desirably have low tensile stress. For example, a tensile stress of 300 MPa or less is good. The silicon nitride film can be stress-controlled and can have a low tensile stress of 300 MPa or less. When the membrane has compressive stress, the membrane may cause sticking or buckling, and may be greatly deformed. In addition, in the case of a large tensile stress, the first membrane may be broken. Therefore, the membranes 78 and 79 are desirably low tensile stress. For example, it is desirable to use a silicon nitride film capable of controlling the stress and capable of producing a low tensile stress.

Further, an etching hole (not shown) is formed, the sacrificial layers 76 and 77 are removed through the etching hole, and the etching hole is sealed. Thereby, gaps 76 and 77 are formed. For example, it can be sealed with a silicon nitride film or a silicon oxide film. The sacrificial layer removal step or the sealing step can also be performed after the second electrode is formed.

Next, as shown in FIG. 4D, second electrodes 81 and 82 are formed. The second electrodes 81 and 82 are preferably made of a material having a small residual stress, such as aluminum. When the sacrificial layer removing step or the sealing step is performed after the second electrode is formed, the second electrode is preferably made of a material having etching resistance and heat resistance against sacrificial layer etching. For example, titanium. In FIG. 4D, the second electrodes 81 and 82 are electrically separated, but may be electrically connected. Thereby, the vibration films 83 and 84 supported by the vibration film support portion 80 are formed.

Next, as shown in FIG. 4E, the membrane 79 of the second cell 86 is charged. In the state of FIG. 4D, since the second cell is not charged yet, when a common voltage is applied to the common electrode, the two types of cells cannot be pulled in with the same voltage. Further, the two types of cells cannot be driven with a common voltage at the same ratio of applied voltage to each pull-in voltage. Therefore, when a voltage for pulling in the second cell 86 is applied between the first electrode and the second electrode by the external voltage applying means 87, the spring constant of the first cell 85 is higher than that of the second cell 86. Because it is expensive, only the second cell pulls in. Using this fact, only the second cell is pulled in. When the second cell is pulled in, charges are injected into the insulating film, and the insulating film is charged. In the case of the cell shown in FIG. 4E, charges 88 are accumulated in the silicon nitride film forming the membrane 79. The direction of the sign to be charged is such that when the common voltage is applied to the common electrode later, the strength of the electric field applied to the second cell 86 is equal to the strength of the electric field applied to the first cell 85. Charge. This charge amount can be controlled by the voltage application time for pull-in.

In FIG. 4E, the insulating film 74 and the like can be charged by changing the type and film configuration of the insulating film. In addition, after the process shown in FIG. 4A, the process shown in FIG. 5 can be performed to charge the cell. In FIG. 5, the insulating film 74 is charged by corona discharge. For example, the wire-like electrode 91 is disposed on the upper part of the portion to be charged. The electrode 91 is connected to a grounded power source 92 (indicated by 93) to which a high voltage can be applied. The first electrode 73 is grounded (indicated by 94), a high voltage of several kV is applied to the electrode 91, and a corona discharge is generated at a location to be charged. In this way, since negative charges are discharged from the electrode 91, negative charges 95 are charged on the surface side of the silicon oxide film, and positive charges are charged on the surface on the first electrode 73 side. In FIG. 5, if the direction of the potential of the power source 92 is reversed, the surface side of the silicon oxide film can be charged with a positive charge. By moving the electrode 91 to a location to be charged and performing corona discharge, a desired charge can be charged at a desired location. The charge amount can be controlled by the magnitude of the applied voltage for corona discharge.

As shown in FIG. 6, when the first cell 85 having a high spring constant is charged, the sign direction of charging is such that when the common voltage is applied to the common electrode later, the strength of the electric field applied to the second cell is the first. The cell is charged in a direction equivalent to the electric field strength applied to the cell. In order to stabilize the charged electric charge 88, heat treatment may be performed. For example, when the treatment is performed at 150 ° C. for about 1 hour in the atmosphere, the charged charge is stabilized.

As described above, when a common voltage is applied to the common electrode, the cells are charged so that pull-ins of cells having different spring constants are generated simultaneously. In addition, the cells can be charged so that the ratio of the applied voltage to the pull-in voltage of cells having different spring constants is the same in each cell. By charging each cell so that the ratio of the applied voltage to the pull-in voltage is the same in each cell when a common voltage is applied to the common electrode, the electromechanical conversion coefficient of each cell can be increased.

By producing a capacitive transducer by the above production method, it is possible to widen the frequency band at the time of reception or the frequency band at the time of transmission, and to produce a capacitive transducer that can improve transmission sensitivity or reception sensitivity. I can do it.

Hereinafter, the present invention will be described in detail with reference to more specific examples.
Example 1
A first embodiment of the present invention will be described with reference to FIG. The basic structure of this example is the same as that of the above embodiment. The first cell 12 includes a silicon substrate 2 having a thickness of 300 μm, an insulating film 3 on the silicon substrate 2, a first electrode 4 on the insulating film 3, and an insulating film 5 on the first electrode 4. Furthermore, a vibration film 8 including the second electrode 6 and the membrane 7, a vibration film support portion 10 that supports the vibration film 8, and a cavity (gap) 9 are provided. The height of the cavity 9 is 100 nm. Furthermore, voltage application means 11 for applying a voltage between the first electrode and the second electrode is provided.

The insulating film 3 is a 1 μm thick silicon oxide film formed by thermal oxidation. The insulating film 5 is a 100 nm silicon oxide film formed by Plasma-Enhanced-Chemical-Vapor Deposition (PE-CVD). The first electrode 4 is titanium having a thickness of 50 nm, and the second electrode 6 is aluminum having a thickness of 100 nm. The membrane 7 is a silicon nitride film produced by PE-CVD, is formed with a tensile stress of 200 MPa or less, and has a thickness of 1400 nm.

The capacitive transducer according to the present embodiment can extract an electrical signal from the second electrodes 6 and 15 by using a lead wiring (not shown). When receiving ultrasonic waves with a capacitive transducer, a DC voltage is applied to the first electrodes 4 and 13 in advance. When the ultrasonic waves are received, the vibrating membranes 8 and 16 having the second electrodes 6 and 15 and the membranes 7 and 14 are deformed, and therefore, between the second electrodes 6 and 15 and the first electrodes 4 and 13. The distance between the cavities 9 and 17 changes, and the capacitance changes. This capacitance change causes a current to flow through the lead-out wiring. This current can be received as a voltage by a current-voltage conversion element (not shown) to receive ultrasonic waves. Further, the vibrating membranes 8 and 16 can be vibrated by electrostatic force by applying a DC voltage to the first electrode and applying an AC voltage to the second electrode. Thereby, an ultrasonic wave can be transmitted.

The second cell 19 has substantially the same configuration as the first cell 12. In the first cell 12, the diameter 21 of the vibration film 8 is 36 μm, while in the second cell 19, the diameter 22 of the vibration film 16 is 44 μm. Therefore, the spring constant of the vibration film 16 is lower than that of the cell 12. The height of the cavity 17 of the second cell 19 is also 100 nm. In FIG. 1B, the vibration film 16 is made of the same material and thickness as the vibration film 8, and the spring constant is reduced by making the diameter of the vibration film 16 larger than that of the vibration film 8. The spring constant of the first cell is 82 kN / m and the spring constant of the second cell is 55 kN / m. Here, the spring constant is a value obtained by dividing the load applied to the diaphragm by the average displacement of the diaphragm at that time. Since the first cell having the vibration film having a high spring constant and the second cell having the vibration film having a low spring constant, the frequency band at the time of reception or the frequency band at the time of transmission can be widened. I can do it.

Further, in this embodiment, the vibration film 16 is made of the same material and thickness as the vibration film 8, and the process of forming the vibration film can be the same in the first cell and the second cell. . Accordingly, since the variation in the ratio between the spring constant of the diaphragm of the first cell and the spring constant of the diaphragm of the second cell can be reduced, the variation in transmission sensitivity, reception sensitivity, and frequency band can be reduced.

Further, in this configuration, the vibration film 16 is made of the same material and thickness as the vibration film 8, and the thicknesses of the insulating films 5 and 23 are almost the same 100 nm. Therefore, the first electrode and the second electrode The distance is almost the same. Further, as described above, the spring constant of the vibration film 16 of the second cell 19 is lower than the spring constant of the vibration film 8 of the first cell 12. Since the voltage at which the electrostatic attractive force is larger than the restoring force of the vibrating membrane is the pull-in voltage, the pull-in voltage of the first cell due to the difference in the spring constant is higher than the pull-in voltage of the second cell. Here, the pull-in voltage of the first cell 12 is 155V, and the pull-in voltage of the second cell 19 is 100V.

In this embodiment, the common voltage applied to the common electrode is 125V. That is, the voltage is 80% of the pull-in voltage of the first cell. If 125 V is applied to the common electrode in this state, a potential difference of 125 V is also generated in the second cell, so that the second cell is pulled in. When the cell is pulled in, the vibrating membrane is difficult to vibrate, and the electromechanical conversion coefficient is greatly reduced. Therefore, the voltage applied to the cell is preferably lower than the pull-in voltage and as close to the pull-in voltage as possible. In this embodiment, the first cell and the second cell can be driven at 80% of the pull-in voltage of each cell. In that case, with the above configuration, the potential difference generated in the first cell is 125V, and the potential difference generated in the second cell is 80V. Here, since the potential difference generated between the first cell and the second cell has a difference of 45V, the second cell is charged by 45V. In this embodiment, only the second cell is pulled in, and the membrane 14 of the second cell is charged by 45V. A voltage of 150 V is applied from the external voltage application means 11 to the second electrodes 6 and 15 which are common electrodes, and only the second cell 19 is pulled in. When the common voltage is returned to 0 V after holding this state for 1 hour, the negative charge of about 45 V is charged on the membrane 14 of the second cell.

In this state, when −125 V is applied to the first electrodes 4 and 13 that are common electrodes, a potential difference of 125 V is generated in the first cell, and a potential difference of 80 V is generated in the second cell. Thereby, even when a common voltage is applied to the common electrode of cells having different spring constants, it can be driven at the same applied voltage ratio to the pull-in voltage. The electromechanical conversion coefficient depending on the ratio of the applied voltage to the pull-in voltage can be the same in the first cell and the second cell.

Also in this embodiment, the frequency band at the time of reception or the frequency band at the time of transmission can be widened, and the transmission sensitivity or the reception sensitivity can be improved. Furthermore, it can be used while being repeatedly charged as appropriate, for example, by pulling in again during use and performing a charging treatment.

(Example 2)
The configuration of the capacitive transducer according to the second embodiment will be described with reference to FIG. FIG. 2A is a top view of the capacitive transducer of this embodiment, and FIG. 2B is a cross-sectional view taken along the line AB of FIG. The configuration of the capacitive transducer 31 of the second embodiment is almost the same as that of the first embodiment. The difference is that the insulating film on the first electrode 36 has a two-layer structure, and there are three types of cells having different spring constants, and the respective charged states are different. They are called the first cell 32, the second cell 33, and the third cell 54 in descending order of the spring constant.

The diameter of the diaphragm 49 of the first cell 32 is 32 μm, the diameter of the diaphragm 50 of the second cell 33 is 40 μm, and the diameter of the diaphragm 51 of the third cell 54 is 50 μm. The vibration films 49, 50 and 51 all have the same thickness of 1400 nm. The heights of the cavities (gap) 39, 40, 41 are all the same 100 nm. The insulating films 35, 37, and 55 are silicon nitride films and have a thickness of 70 nm. The insulating film 38 is a silicon oxide film and has a thickness of 60 nm. The insulating films 37, 53, and 55 can be formed of a silicon nitride film by a method similar to the method described in FIG. The insulating film 38 can also be formed of a silicon oxide film after forming the insulating films 35, 37, and 55 by a method similar to the method described in FIG.

With this configuration, the spring constant of the first cell is 103 kN / m, the spring constant of the second cell is 66 kN / m, and the spring constant of the third cell is 42 kN / m. Further, the pull-in voltage of each cell in the configuration as it is is 200V for the first cell, 125V for the second cell, and 75V for the third cell. The driving voltage of the electrostatic transducer in this embodiment is an applied voltage of 80% with respect to the pull-in voltage of each cell. In this case, the driving voltage of each cell is 160V for the first cell, 100V for the second cell, and 60V for the third cell. Assuming that the common voltage applied to the common electrode is 100V, the difference from the drive voltage of each cell is 60V for the first cell, 0V for the second cell, and -40V for the third cell. The difference from the common voltage is charged in each cell.

The charging method in this embodiment is performed by corona discharge treatment. First, insulating films 35, 37, and 55 are formed on the first electrode 36 formed on the insulating film 57 on the substrate 34 by the same method as in FIG. Then, in the same manner as in FIG. 5, the insulating film in the portion inside the cavity of each cell is charged. The insulating film inside the cavity of the first cell is charged to −60V. The insulating film inside the cavity of the third cell is charged to 40V. After the insulating films of the first cell and the third cell are charged (indicated by 52 and 53) and then heated in the atmosphere at 150 ° C. for about 1 hour, the charged state is stabilized. Thereafter, a second insulating film 38 is formed. After the film formation, the electrostatic transducer shown in FIG. 2 can be produced by performing the same steps as in FIGS. 4B to 4D. In FIG. 2, reference numerals 42 and 43 to 45 denote a vibrating membrane support portion and a membrane, respectively.

In this state, when 100 V is applied to the second electrodes 46, 47, and 48, which are common electrodes, by the voltage application means 56, a potential difference of 160 V is generated in the first cell, and a potential difference of 100 V is generated in the second cell. In the third cell, a potential difference of 60 V is generated. Thereby, even when a common voltage is applied to the common electrode of cells having different spring constants, it can be driven with an applied voltage having the same ratio as the pull-in voltage. The electromechanical conversion coefficient depending on the ratio of the applied voltage to the pull-in voltage can be the same in the first cell, the second cell, and the third cell. Therefore, the capacitive transducer of the present embodiment can widen the frequency band at the time of reception or the frequency band at the time of transmission, and can improve the transmission sensitivity or the reception sensitivity.

(Example 3)
The configuration of the capacitive transducer according to the third embodiment will be described with reference to FIG. The configuration of the capacitive transducer 61 of the third embodiment is substantially the same as that of the first embodiment, and FIG. 3B is a cross-sectional view taken along the line AB of FIG. In this example, the vibration film thickness of the cell having a high vibration film spring constant is larger than the vibration film thickness of the cell having a low vibration film spring constant, and the vibration film area of the cell having a high vibration film spring constant is The area of the diaphragm of the cell having the low spring constant of the diaphragm is the same.

The diameter of the vibration film 77 of the first cell 62 and the diameter of the vibration film 78 of the second cell 63 are both 36 μm, and the vibration film thicknesses are 1400 nm and 1200 nm, respectively. With this configuration, the spring constant of the first cell is 82 kN / m, and the spring constant of the second cell is 55 kN / m. The height of the cavities 70 and 71 is 100 nm. The insulating films 68 and 69 are silicon nitride films and have a thickness of 175 nm. The insulating films 68 and 69 can be made of a silicon nitride film by the same method as described in FIG. The capacitive transducer according to the present embodiment includes the first cell 62 having a vibration film having a high spring constant and the second cell 63 having a vibration film having a low spring constant. The frequency band or the frequency band at the time of transmission can be widened.

In this configuration, the spring constant of the vibration film 78 of the second cell 63 is lower than the spring constant of the vibration film 77 of the first cell 62. Since the voltage at which the electrostatic attractive force is larger than the restoring force of the vibrating membrane is the pull-in voltage, the pull-in voltage of the first cell in the configuration as it is is higher than the pull-in voltage of the second cell. The pull-in voltage of the first cell 62 is 155V, and the pull-in voltage of the second cell 63 is 90V. Consider a case where the drive voltage of the electrostatic transducer in this embodiment is 80% of the pull-in voltage of each cell. In this case, the drive voltage of each cell in the configuration as it is is 125V for the first cell and 72V for the second cell. If the common voltage applied to the common electrode is 125V, the difference from the drive voltage of each cell is ± 53V. The difference from the common voltage is compensated by charging the second cell 63.

The charging method in this embodiment is also subjected to corona discharge treatment. First, insulating films 68 and 69 are formed on the first electrode 66 formed on the insulating film 65 on the substrate 64 by the same method as in FIG. Then, in the same manner as in FIG. 5, the insulating film 69 in the portion inside the cavity 71 of the second cell is charged by −53 V (indicated by 67). Next, heating at 150 ° C. for about 1 hour in the atmosphere stabilizes the charged state. Thereafter, the same processes as those shown in FIGS. 4B to 4D are performed.

After forming the second electrode 74 of the first cell 62 and the second electrode 75 of the second cell 63 in order to produce this configuration, the thickness of the vibration film 77 of the first cell 62 is increased. For this purpose, the membrane 72 is formed by depositing silicon nitride, which is the same material as the membrane under the second electrode 74. Thereafter, the silicon nitride layered also on the second electrode 75 of the second cell 63 is removed by etching. At this time, since the second electrode 75 of the second cell 63 serves as an etching stop layer, the distance between the second electrode 74 of the first cell 62 and the first electrode 66 is set to the first electrode 66 as in this configuration. The distance between the second electrode 75 and the first electrode 66 of the second cell 63 can be easily made the same.

In this state, when 125 V is applied to the second electrodes 74 and 75, which are common electrodes that are electrically conducting at a location not shown, by the voltage applying means 79, a potential difference of 125 V is generated in the first cell, In the two cells, a potential difference of 72V occurs. Thereby, even when a common voltage is applied to the common electrode of cells having different spring constants, it can be driven at the same applied voltage ratio to the pull-in voltage. Thus, the electromechanical conversion coefficient depending on the ratio of the applied voltage to the pull-in voltage can be the same in the first cell and the second cell. Further, in this embodiment, when the charge amount of the second cell changes, 150 V is applied to the first electrode 66 that is the common electrode, and only the second cell 63 is pulled in, so that the second cell The insulating film 69 can be further charged. In FIG. 3, reference numerals 73 and 76 denote a membrane and a diaphragm supporting portion of the second cell 63, respectively.

As described above, the capacitive transducer according to the present embodiment can widen the frequency band at the time of reception or the frequency band at the time of transmission, and can improve the transmission sensitivity or the reception sensitivity. Further, with the above configuration, as shown in FIG. 3A, the cells 62 and 63 have the same shape as viewed from above, so that the radiation impedances of all the cells can be made uniform. Further, since the radiation impedance of each cell is the same, the vibrating membranes of each cell vibrate in the same manner, so that unnecessary vibrations that reduce the electromechanical conversion coefficient can be prevented.

Example 4
The configuration of the capacitive transducer of Example 4 will be described with reference to FIG. In addition, a manufacturing method of the capacitive transducer of Example 4 will be described with reference to FIGS. FIG. 7A is a top view of the capacitive transducer 101 of the present invention, and FIG. 7B is a cross-sectional view taken along line AB of FIG. 7A. The cell arrangement of this embodiment is the same as that shown in FIG. 1A, but the manufacturing method of the capacitive transducer is different.

The first cell 102 has a 300 μm thick silicon substrate 119, an insulating film 115 formed on the silicon substrate 119, and a second insulating film 116 formed on the insulating film 115. The silicon substrate 119 will later become the first electrode. Further, the vibration film 131 including the second electrode 130 and the membrane 129, the vibration film support portion 120 that supports the vibration film 131, and the cavity (gap) 124 are provided. The height of the cavity 124 is 100 nm. Furthermore, voltage application means 132 for applying a voltage between the first electrode and the second electrode is provided.

The insulating film 115 is a 40 nm thick silicon oxide film formed by thermal oxidation. The second insulating film 116 is a 105 nm silicon nitride oxide film formed by PE-CVD. The vibration film support 120 is a 700 nm thick silicon oxide film formed by thermal oxidation. The first electrode is a silicon substrate 119, and the second electrode 127 is aluminum having a thickness of 100 nm. The membrane 129 is silicon having a thickness of 2000 nm. The membrane 129 of this example is a single crystal silicon film. The single crystal silicon film has almost no residual stress and small variation in thickness as compared with a vibration film (for example, a silicon nitride film) formed by lamination. In addition, since the variation in the spring constant of the vibration film 131 can be reduced, the performance variation between elements of the capacitive transducer and between cells can be reduced.

The capacitive transducer of this embodiment can extract an electrical signal from the second electrode 130 by using a lead wiring (not shown). When receiving ultrasonic waves with a capacitive transducer, a DC voltage is applied to the first electrode 119 in advance. When the ultrasonic wave is received, the vibrating membrane 131 having the second electrode 130 is deformed, so that the distance of the cavity 124 between the second electrode 130 and the first electrode 119 changes, and the capacitance changes. This capacitance change causes a current to flow through the lead-out wiring. This current can be received as a voltage by a current-voltage conversion element (not shown) to receive ultrasonic waves. Further, the vibrating membrane 131 can be vibrated by electrostatic force by applying a DC voltage to the first electrode and applying an AC voltage to the second electrode. Thereby, an ultrasonic wave can be transmitted.

The second cell 103 has substantially the same configuration as the first cell 102. In the first cell 102, the diameter of the vibrating membrane is 36 μm, whereas in the second cell, the diameter of the vibrating membrane 128 including the second electrode 127 and the membrane 126 is 44 μm, so the spring constant of the vibrating membrane is The spring constant of the first cell 102 is lower. The height of the cavity 125 of the second cell 103 is 100 nm. As shown in FIG. 7B, the vibrating membrane 128 is made of the same material and thickness as the vibrating membrane 131. By making the diameter of the vibrating membrane 128 larger than the diameter of the vibrating membrane 131, the spring constant is reduced. ing. The spring constant of the first cell 102 is 82 kN / m, and the spring constant of the second cell 103 is 55 kN / m. The spring constant here is also a value obtained by dividing the load applied to the diaphragm by the average displacement of the diaphragm at that time.

In this embodiment, the vibration films 131 and 128 are made of the same material and thickness, and the process of forming the vibration film can be the same in the first cell and the second cell. Accordingly, since the variation in the ratio between the spring constant of the diaphragm of the first cell and the spring constant of the diaphragm of the second cell can be reduced, the variation in transmission sensitivity, reception sensitivity, and frequency band can be reduced. Further, in the first cell and the second cell, the thicknesses of the insulating films 115 and 117 and the second insulating films 116 and 118 are almost the same 100 nm, so the distance between the first electrode and the second electrode is It will be almost the same.

Further, the spring constant of the vibration film 128 of the second cell 103 is lower than the spring constant of the vibration film 131 of the first cell 102. Since the voltage at which the electrostatic attractive force is larger than the restoring force of the vibrating membrane is the pull-in voltage, in this state, the pull-in voltage of the first cell is higher than the pull-in voltage of the second cell. The pull-in voltage of the first cell 102 is 155V, and the pull-in voltage of the second cell 103 is 100V.

In the electrostatic transducer of this embodiment, the common voltage applied to the common electrode is 125V. That is, the voltage is 80% of the pull-in voltage of the first cell. When 125 V is applied to the common electrode in this state, a potential difference of 125 V is generated in the second cell 103, so that the second cell is pulled in. When the cell is pulled in, the vibrating membrane is difficult to vibrate, and the electromechanical conversion coefficient is greatly reduced. Therefore, the voltage applied to the cell is preferably lower than the pull-in voltage and as close to the pull-in voltage as possible. In the present embodiment, it is assumed that the first cell and the second cell are driven at 80% of a compensated pull-in voltage of each cell described later. In that case, the potential difference generated in the first cell is 125V, and the potential difference generated in the second cell is 80V. Here, since there is a difference of 45V in the potential difference generated between the first cell and the second cell, compensation processing for charging the second cell by 45V (indicated by 133) is performed.

Next, a manufacturing method of the capacitive transducer of Example 4 will be described with reference to FIGS. As shown in FIG. 8A, insulating films 111 and 112 are formed on the silicon substrate 119. The insulating films 111 and 112 are silicon oxide films formed by patterning and etching after thermally oxidizing the silicon substrate 119 to a thickness of about 2 μm. Next, as shown in FIG. 8B, the second thermal oxidation is performed to form the insulating film 113. The insulating film 113 is a silicon oxide film. Next, as shown in FIG. 8-1 (c), all of the formed insulating film is removed by etching. Then, as shown in FIG. 8-1 (d), insulating films 115 and 117 are formed.

The silicon substrate 119 is thermally oxidized to form a 40 nm thick silicon oxide film. Next, a silicon nitride film with a thickness of 105 nm is formed. After that, by patterning and etching, insulating films 115 and 116 that become the cavity bottom face of the first cell and insulating films 117 and 118 that become the cavity bottom face of the second cell are formed. Next, as shown in FIG. 8-1 (e), the diaphragm support 120 is formed by thermal oxidation. The thickness is about 700 nm.

Next, as shown in FIG. 8-2 (f), the SOI substrate is bonded. The SOI substrate is a substrate having a structure in which a silicon oxide layer 122 (BOX layer) is inserted between a silicon substrate 123 (handle layer) and a surface silicon layer 121 (active layer). Next, the handle layer 123 of the SOI substrate is thinned to expose the active layer 121. The handle layer can be removed by grinding, CMP, or etching. The BOX layer can be removed by etching the oxide film (dry etching, wet etching such as hydrofluoric acid). Wet etching such as hydrofluoric acid is more preferable because it can prevent silicon from being etched, and thus can reduce variation in thickness of the single crystal silicon film due to etching. Since the thickness variation of the active layer 121 of the SOI substrate is small, the thickness variation of the single crystal silicon film can be reduced, and the spring constant variation of the single crystal silicon film can be reduced. It can be reduced.

Next, as shown in FIG. 8-2 (g), second electrodes 130 and 127 are formed on the single crystal silicon films 129 and 126. The second electrodes 130 and 127 are aluminum having a thickness of 100 nm. Next, as shown in FIG. 8B, the insulating film 118 included in the second cell 103 is charged. In this embodiment, only the second cell 103 is pulled in, and the insulating film 118 of the second cell is charged by −45V. A voltage of 150 V is applied from the external voltage application means 132 to the first electrode 119, which is a common electrode, and only the second cell is pulled in. When the common voltage is returned to 0 V after holding this state for 1 hour, the negative charge 133 of about 45 V is charged in the insulating film 118 included in the second cell.

In this state, when −125 V is applied to the second electrodes 130 and 127 that are common electrodes, a potential difference of 125 V is generated in the first cell 102, and a potential difference of 80 V is generated in the second cell 103. Thereby, even when a common voltage is applied to a common electrode of cells having different spring constants, the cell can be driven with an applied voltage having the same ratio with respect to the pull-in voltages of a plurality of types of cells having a configuration in which charging is performed. . Thus, the electromechanical conversion coefficient depending on the ratio of the applied voltage to the pull-in voltage can be the same in the first cell and the second cell.

As described above, in the capacitive transducer of this embodiment, the frequency band at the time of reception or the frequency band at the time of transmission can be widened, and the transmission sensitivity or the reception sensitivity can be improved. Furthermore, it can be used while being repeatedly charged, such as performing a charging process by pulling in again during use.

(Example 5)
The probe including the capacitive transducer described in the above embodiments and examples can be applied to a subject information acquisition apparatus using acoustic waves. The acoustic wave from the subject is received by the capacitive transducer, and the outputted electrical signal can be used to obtain subject information reflecting the subject's optical characteristic values such as a light absorption coefficient.

FIG. 9 shows an object information acquiring apparatus according to the present embodiment using the photoacoustic effect. The pulsed light 152 generated from the light source 151 that generates light in a pulsed form is irradiated onto the subject 153 via an optical member 154 such as a lens, a mirror, or an optical fiber. The light absorber 155 inside the subject 153 absorbs the energy of the pulsed light and generates a photoacoustic wave 156 that is an acoustic wave. A probe (probe) 157 having a housing that houses a capacitive transducer of the present invention having a wide-band characteristic and a good electromechanical conversion coefficient receives the photoacoustic wave 156, converts it into an electrical signal, and performs signal processing. Output to the unit 159. The signal processing unit 159 performs signal processing such as A / D conversion and amplification on the input electric signal and outputs the signal to the data processing unit 150. The data processing unit 150 acquires subject information (subject information reflecting an optical characteristic value of the subject such as a light absorption coefficient) as image data using the input signal. The display unit 158 displays an image based on the image data input from the data processing unit 150. Note that the probe may be mechanically scanned, or may be a probe (handheld type) that a user such as a doctor or engineer moves with respect to the subject. Of course, the capacitive transducer that is the electromechanical transducer of the present invention can also be used in a subject diagnostic apparatus that detects acoustic waves from a subject to which acoustic waves are applied. Also here, the acoustic wave from the subject is detected by the capacitive transducer, and the converted signal is processed by the signal processing unit to acquire the information inside the subject. Here, the acoustic wave transmitted toward the subject can be transmitted from the capacitive transducer of the present invention.

The capacitive transducer of the present invention can be applied to an optical imaging apparatus that obtains information in a measurement target such as a living body, a conventional ultrasonic diagnostic apparatus, and the like. Furthermore, it can be used for other applications such as an ultrasonic flaw detector.

1 .. Capacitance type transducer 3, 3, 5 .. Insulating film (insulating part) 4, 13,... First electrode, 6, 15 .. Second electrode, 7, 14 .. Membrane (insulating part) ), 8, 16 .. Vibration membrane, 9, 17 .. Cavity (gap), 10 .. Supporting part, 11 .. Voltage applying means, 12 .. First cell, 19.

Claims (2)

A vibration film including a first electrode, a second electrode facing the first electrode across a gap, and a vibration film support portion that supports the vibration film so that the gap is formed Cell
Voltage applying means for applying a voltage between the first electrode and the second electrode;
A capacitive transducer comprising:
The cell includes a first cell including the vibration film having a first spring constant, and a second cell including the vibration film having a second spring constant lower than the first spring constant. And
At least one of the first cell and the second cell is provided with an insulating portion that is at least partially charged ,
By applying a common voltage between the first electrode and the second electrode of the first cell and the second cell by the voltage application means, the first electrode and the second cell A capacitive transducer , wherein each of the first cell and the second cell is driven in a state in which a potential difference between the first electrode and the second electrode is different . The capacitive transducer according to claim 1 ;
A light source that generates light;
A signal processing unit for processing a signal output from the capacitive transducer;
Have
A photoacoustic wave generated by the light emitted from the light source and applied to the subject is received by the capacitive transducer, and a signal converted into an electric signal is processed by the signal processing unit, thereby A subject information acquisition apparatus characterized by acquiring information.

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