JP2014236841A - Capacitive transducer, and driving method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device capable of reducing noise without reducing an arrangement density of electric elements in a capacitive transducer.SOLUTION: In a capacitive transducer, a pair of or more elements in electric elements 104a, 104b, 105a and 105b apply bias voltages 102 and 103 of which the polarities are inverse to each other with a reference potential 101 interposed therebetween, between electrodes of one and the other of paired elements. Signals from elements caused by acoustic waves are obtained by calculating a differential between an output signal of one of paired electric elements and an output signal of the other of paired electric elements.

Description

The present invention relates to a capacitive transducer such as an ultrasonic transducer used in an ultrasonic diagnostic apparatus, a driving method thereof, and the like.

One ultrasonic diagnostic apparatus uses photoacoustic vibration. The photoacoustic vibration is, for example, ultrasonic vibration or acoustic wave vibration generated when a pulse laser irradiated from outside the body is absorbed by a tissue in the body. In addition, in this specification, an acoustic wave includes what is called a sound wave, an ultrasonic wave, and a photoacoustic wave. For example, it includes photoacoustic waves generated inside the subject by irradiating the subject with light (electromagnetic waves) such as visible light and infrared rays. In the following, in many cases, an acoustic wave is represented by an ultrasonic wave. Since photoacoustic vibration is generated in a specific tissue in the body, it is possible to image the body tissue using this information. An ultrasonic probe is used to detect ultrasonic vibration generated in the body. An ultrasonic transducer is disposed in the ultrasonic probe, and converts ultrasonic vibration into an electrical signal.

Conventionally, ultrasonic transducers using the piezoelectric effect have been used, but in recent years, electrostatic capacitance type research and development has also been active. The capacitive ultrasonic transducer includes, for example, a space called a cavity maintained in a substantially vacuum and two electrodes provided so as to sandwich the space. One of the two electrodes is fixed to the membrane and held so as to be able to vibrate. When the membrane vibrates due to ultrasonic vibration and the distance between the two electrodes changes, the capacitance changes. If a voltage is applied between the two electrodes, a change in capacitance can be taken out as a current signal (ultrasonic reception operation). Further, the voltage applied between the two electrodes generates an electrostatic attractive force between the two electrodes. The membrane can be vibrated by changing the magnitude of the applied voltage over time (ultrasonic transmission operation).

A structural unit of a capacitive transducer composed of one cavity and two electrodes is called a cell. The plurality of cells are electrically connected in parallel every certain number. The plurality of connected cells serve as one conversion element. This electrical unit is called an electrical element. A capacitive ultrasonic transducer manufactured by applying a semiconductor microfabrication technique is called a CMUT (CMUT: Capacitive-Micromachined-Ultrasonic-Transducer). The CMUT can arrange a plurality of elements at high density. This structural feature is suitable as a means for improving the image quality of imaging, which is a need for an ultrasonic diagnostic apparatus.

In order to improve the image quality of the ultrasonic diagnostic apparatus, it is also important that the ultrasonic detection signal has low noise. In the imaging of a body tissue using ultrasonic waves, for example, a signal intensity (amplitude) for each time of an ultrasonic detection signal is converted into image luminance to form an image. In such a case, an image unrelated to biological information may be formed due to noise generated in the ultrasonic detection signal. One type of noise that causes problems when constructing an image of an ultrasonic diagnostic apparatus is one that propagates on the chip of a capacitive transducer. This type of noise is particularly affected because it is amplified by a subsequent amplifier circuit. As a prior art for removing this noise, Patent Document 1 can be cited. Patent Document 1 discloses a technique of providing a capacitive component for detecting noise on an acoustic sensor and obtaining a difference between a signal from the acoustic sensor and a signal from the capacitive component.

JP 2007-208549 A

When the transducer driving method disclosed in Patent Document 1 is applied to a capacitive ultrasonic transducer, a noise detection capacitor is arranged on the transducer, and thereby the arrangement density of the electric elements is increased. There is a fear that will decrease.

In view of the above problems, a capacitive transducer according to the present invention includes a cell having a vibration film including a first electrode and a second electrode provided to face the first electrode through a cavity. A plurality of electrical elements each having one or more are provided. In one or more electric elements of the plurality of electric elements, the polarity of the bias voltage applied between the first electrode and the second electrode of one electric element forming the pair is the other electric element forming the pair The polarity of the bias voltage applied between the first electrode and the second electrode is opposite to the reference potential. Then, a difference between the output signal of the one electric element forming the pair and the output signal of the other electric element forming the pair is taken to obtain a signal from the electric element by an acoustic wave.

In addition, in view of the above problems, the capacitive transducer driving method of the present invention includes a first electrode and a second electrode of a pair of electric elements in a pair of electric elements of a plurality of electric elements. A bias voltage having opposite polarities across the reference potential is applied between the first electrode and the first electrode and the second electrode of the other electric element of the pair,
A difference between the output signal of the one electric element forming the pair and the output signal of the other electric element forming the pair is taken to obtain a signal from the element by an acoustic wave.

In the present invention, the capacitive transducer utilizes the feature that ultrasonic waves can be detected regardless of the polarity of the bias voltage. By utilizing this feature, noise can be suppressed and S / N can be improved without providing a noise detection capacitor on the sensor surface. In the present invention, since the bias between the electrodes of the paired elements has a reverse polarity with respect to the reference potential, the ultrasonic detection signal has a reverse polarity. Therefore, the ultrasonic detection signal can be strengthened by differentially processing each signal.

It is a figure explaining the transducer of Example 1, and its drive method. It is a figure explaining the drive principle of Example 1. FIG. It is a figure explaining the effect of Example 1. FIG. It is a top view explaining the device which can apply the drive method of Example 1. FIG. It is sectional drawing explaining the device which can apply the drive method of Example 1. FIG. It is sectional drawing explaining the device which can apply the drive method of Example 1. FIG. It is a figure explaining the transducer of Example 2, and its drive method. It is a top view explaining the device which can apply the drive method of Example 2. It is sectional drawing explaining the device which can apply the drive method of Example 2. FIG. It is sectional drawing explaining the device which can apply the drive method of Example 2. FIG. It is a figure explaining the information acquisition apparatus using the transducer of this invention.

In the present invention, in one or more elements of a plurality of elements, the polarity of the bias voltage applied between the electrodes of one element forming a pair is set to the bias voltage applied between the electrodes of the other element forming a pair. The polarity is reversed with respect to the reference potential. By doing so, the ultrasonic detection signal has a reverse polarity. Therefore, the ultrasonic detection signal can be strengthened by differentially processing each signal. On the other hand, since the noise propagating on the chip propagates from the noise source to the electrode, the polarity of the noise signal does not depend on the polarity of the bias potential. Therefore, the noise signal can be weakened by the difference processing of the signal. Therefore, the noise of the detection signal can be reduced. Further, since it is not necessary to arrange a noise detection capacitor on the transducer, it is possible to suppress a reduction in the arrangement density of the electric elements.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Example 1
FIG. 1 illustrates an electrical coupling structure according to a first embodiment of the present invention. The ground potential 101 is a reference potential for electrical operation. The bias power source 102 and the bias power source 103 generate a potential difference with respect to the ground potential 101. The electric element 104a, the electric element 104b, the electric element 105a, and the electric element 105b are capacitive ultrasonic transducers. For the purpose of explanation, the symbol p1 is attached to one terminal of the element 104a, and the symbol p2 is attached to the other terminal. Similarly, the symbols p3 to p8 are attached to the electric elements 104b, 105a, and 105b. One terminal p1 of the electric element 104a is connected to the bias power source 102 and is supplied with a positive bias potential Vp. The other terminal p2 is connected to an IV (current / voltage) converter 106a. The IV converter 106a converts the current signal generated by the electric element 104a into a voltage signal corresponding to the direction and magnitude of the current (generates a voltage proportional to the magnitude of the current, and generates a voltage according to the direction of the current. The terminal p2 is fixed to the ground potential 101. The IV converter 106a can be easily realized by using, for example, a transimpedance circuit (known technology).

One terminal p3 of the electric element 104b is connected to the bias power supply 103 and is given a negative bias potential Vm. The other terminal p4 is connected to the IV converter 106b. Similarly to the IV converter 106a, the IV converter 106b converts the current signal generated by the electric element 104b into a voltage circuit and fixes the terminal p4 to the ground potential 101. A ground potential 101 is connected to each of the IV converter 106a and the IV converter 106b. The output voltages of the IV converter 106a and the IV converter 106b are input to the positive input (+) and the negative input (−) of the differential amplifier 108, respectively. A differential voltage between the output voltage of the IV converter 106a and the output voltage of the IV converter 106b is output to the output terminal 110 of the differential amplifier 108.

In this embodiment, the electric element 104 a and the electric element 104 b make a pair, and a signal is generated at one output terminal 110. In the configuration of FIG. 1, similarly, a signal is generated at the output terminal 111 by the electric element 105 a and the electric element 105 b, the IV converter 107 a, the IV converter 107 b, and the differential amplifier 109. The terminals p1 and p5 of the electric element 104a and the electric element 105a are connected in parallel to the bias power source 102. The terminals p3 and p7 of the electric element 104b and the electric element 105b are connected in parallel to the bias power source 103. If the same method is used thereafter, it is possible to arbitrarily increase the number of electric elements and output terminals with respect to a pair of bias power supply 102 and bias power supply 103.

The operation principle of this embodiment will be described with reference to FIGS. FIG. 2 is a diagram showing extracted elements related to the output terminal 110 described in FIG. 2, the corresponding components in FIG. 1 are given the same numbers or will be described. In FIG. 2, the electric element 104a and the electric element 104b are illustrated in a cross-sectional schematic diagram of a capacitive transducer. Each cell in the electric element 104a includes a lower electrode (one of the first electrode and the second electrode) 113, a vibrating membrane 114, and an upper electrode (the other of the first electrode and the second electrode) 115. , The gap 116. The lower electrode 113 corresponds to the terminal p1 in FIG. The lower electrode 113 is applied with a positive bias potential Vp by the bias power source 102. The vibration film 114 is a thin film capable of ultrasonic vibration. An upper electrode 115 is provided on the upper surface of the vibration film 114. The upper electrode 115 corresponds to the terminal p2 in FIG. The upper electrode 115 is connected to the IV converter 106 a and is held at the ground potential 101.

Each cell in the electric element 104 b is composed of a lower electrode 118, a vibrating membrane 119, an upper electrode 120, and a gap 121. The lower electrode 118 and the upper electrode 120 correspond to the terminals p3 and p4 in FIG. In the configuration of FIG. 2, it is assumed that the vibration film 114 of the electric element 104a receives a force F in the direction of the arrow in response to ultrasonic vibration from the outside. Since there is a gap 116 between the vibrating membrane 114 and the lower electrode 113, the deflection of the vibrating membrane 114 increases in the arrow direction. Since the distance between the lower electrode 116 and the upper electrode 115 approaches as the deflection increases, the capacitance of the element 104a increases. Similarly, when the electric element 104b receives the force F, the capacitance of the element 104b increases.

As described above, the upper electrode 115 of the electric element 104a holds the ground potential, and the lower electrode 113 holds the positive bias potential Vp. Therefore, when the capacitance of the electric element 104a increases, the negative charge of the upper electrode 115 increases, and thus a current flows through the IV converter 106a in the direction i1. Further, the ground potential 101 is held on the upper electrode 120 of the electric element 104b, and the negative bias potential Vm is held on the lower electrode 118. Therefore, when the capacitance of the electric element 104b increases, a current flows through the IV converter 106b in the direction i2. That is, since the positive charge to the upper electrode 120 flows in the i2 direction, the current flows in the i2 direction as a result. When the direction of the force F acts in the direction opposite to the arrow, the deflection of the vibration film 114 and the vibration film 119 increases in the direction opposite to the arrow, so the capacitance of the electric element 104a and the electric element 104b is Decrease. At this time, the directions of the currents i1 and i2 are opposite to the arrows shown in FIG. As described above, since the polarities of the output voltages of the IV converter 106a and the IV converter 106b are determined by the direction of the current, the output voltages of the IV converter 106a and the IV converter 106b due to ultrasonic vibration have opposite polarities. .

Next, a case where electromagnetic noise 123 from the outside acts on the ultrasonic transducer in the configuration of FIG. 2 will be described. The electromagnetic noise 123 tends to act on the upper electrode 115 and the upper electrode 120 having a high electrical impedance with respect to the ground potential 101. That is, the fluctuation (effect level) of the electrode potential due to electromagnetic noise is determined by the magnitude of the impedance with respect to the bias potential, and the smaller the impedance, the higher the ability to fix the electrode to the bias potential, so the voltage fluctuation due to electromagnetic noise is small. . The lower electrode is connected to the bias potential via the conductor, whereas the upper electrode is connected to the bias potential via the capacitor. Therefore, the upper electrode has higher impedance than the lower electrode, and electromagnetic noise is generated. Easy to act. When subjected to the action of the electromagnetic noise 123, the potentials of the upper electrode 115 and the upper electrode 120 change.

Assume that the potential of the upper electrode 115 fluctuates in the positive direction due to the electromagnetic noise 123. Since the lower electrode 113 facing the upper electrode 115 has a positive bias polarity, the potential difference between the lower electrode and the upper electrode decreases. At this time, the negative charge amount accumulated in the electric element 104a decreases. Due to the decrease in the charge amount, a current i3 flows through the IV converter 106a in the direction of the arrow (the direction opposite to the negative charge flow direction). Similarly, it is assumed that the potential of the upper electrode 120 fluctuates in the positive direction due to the electromagnetic noise 123. Since the lower electrode 118 facing the upper electrode 120 has a negative bias polarity, the potential difference between the lower electrode and the upper electrode increases. At this time, the positive charge amount accumulated in the electric element 104b increases. As the charge amount increases, a current i4 flows through the IV converter 106b in the direction of the arrow (the direction of positive charge flow). As described above, since the polarities of the output voltages of the IV converter 106a and the IV converter 106b are determined by the direction of the current, the output voltage of the IV converter 106a and the output voltage of the IV converter 106b due to the electromagnetic noise 123 are the same polarity. It becomes.

FIG. 3 is a diagram for explaining the relationship between the current i 1 to the current i 4 and the output voltage of the output terminal 110 together with the operation of the differential amplifier 108. FIG. 3A is an example of a time change of the output terminal voltage of the IV converter 106a. It is assumed that the voltage change between time t1 and time t2 is due to vibration of the vibration film 114 due to ultrasonic vibration. The voltage change between time t3 and time t4 is caused by the change in the potential of the upper electrode 115 due to electromagnetic noise. FIG. 3B is an example of the time change of the output terminal voltage of the IV converter 106b. The output voltage of the IV converter 106b is opposite in phase from time t1 to time t2 and in phase from time t3 to time t4, compared to the output voltage of the IV converter 106a. FIG. 3C shows the voltage change at the output terminal 110. The voltage at the output terminal 110 is the output of the differential amplifier 108. The output of the differential amplifier 108 is obtained by subtracting the output terminal voltage of the IV converter 106b from the output terminal voltage of the IV converter 106a. Accordingly, since the ultrasonic signals between time t1 and time t2 have opposite polarities, they are added and the amplitude is amplified. On the other hand, since the voltage changes due to electromagnetic noise between time t3 and time t4 are in phase with each other, the amplitude is reduced by subtraction. From the above principle, in this embodiment, the electromagnetic noise of ultrasonic waves can be reduced.

For the sake of explanation, the output signal and electromagnetic noise in FIG. 3 are shown as being temporally separated, but the present invention is not limited to this. Even when the output signal and the electromagnetic noise are not separated in time and are mixed, the same effect can be obtained according to the driving method of the present invention including this embodiment. Since this effect is obtained by obtaining an ultrasonic signal of opposite phase and removing the in-phase electromagnetic noise signal by subtraction, it can be obtained similarly even if the roles of the upper electrode and the lower electrode are reversed. . The reference potential may not be the ground potential. In addition, the potential difference (absolute value) from the reference potential is not necessarily equal between the bias potential Vp and the bias potential Vm (that is, the potential is symmetric with respect to the reference potential). 2 is equal to the current i3 and i4. Therefore, the effects of canceling each other out and greatly reducing electromagnetic noise to the outside can be obtained.

4 to 6 are diagrams illustrating the structure of an ultrasonic transducer suitable for the first embodiment. 4 is a top view (partially expressed in a perspective view), FIG. 5 is a cross-sectional view taken along the line A-A ′ of FIG. 4, and FIG. 6 is a cross-sectional view taken along the line B-B ′ of FIG. Constituent elements corresponding to the elements in FIGS. 1 and 2 are given the same numbers or will be described. The transducer of this embodiment is formed on the substrate 131. Of the insulating materials, the substrate 131 is particularly preferably glass. However, it may be single crystal silicon which is a conductive material. When using a conductive material, it is necessary to form an insulating material on the surface. In the case of single crystal silicon, the insulating layer is particularly preferably silicon oxide or silicon nitride. 4 to 6 illustrate the case where the substrate 131 is made of an insulating material.

As illustrated in FIG. 5, the lower electrode 132 and the lower electrode 133 are formed on the substrate 131. The material of the lower electrode may be a conductive material, but for example, a single layer of Al, Ti, Au, Cr, Cu, Ni or a multilayer made of a plurality of materials is particularly suitable. The lower electrode 132 and the lower electrode 133 correspond to the lower electrode 113 and the lower electrode 118 in FIG. A plurality of cavities 134 are formed above the lower electrode 132 and the lower electrode 133. The cavity 134 corresponds to the gap 116 and the gap 121 in FIG. FIG. 5 illustrates a state in which the cavity 134 is formed on the lower electrode 132. The cavity 134 above the lower electrode 133 has the same structure. A vibration film 135 is formed on the cavity 134. The vibration film 135 corresponds to the vibration film 114 and the vibration film 119 in FIG. As the vibration film 135, for example, silicon oxide or silicon nitride by CVD (chemical vapor deposition) is particularly suitable. An upper electrode 136 and an upper electrode 137 are formed on the vibration film 135. The upper electrode 136 and the upper electrode 137 correspond to the upper electrode 115 and the upper electrode 120 in FIG. The material of the upper electrode may be any conductive material, but for example, a single layer of Al, Ti, Au, Cr, Cu, Ni or a multilayer made of a plurality of materials is particularly suitable.

As shown in FIG. 4, a plurality of cavities 134 are two-dimensionally arranged on the substrate 131. In FIG. 4, the cavities 134 are circular, but may be triangular or square. Among the plurality of cells each including the cavity 134, those sharing the lower electrode and sharing the upper electrode constitute one electrical element. For example, the element 104 a in FIG. 4 shares the lower electrode 132 and the upper electrode 136. Comparing the electrode structure of FIG. 4 with the circuit of FIG. 1, it can be seen that the element 104a of FIG. 4 corresponds to the element 104a of FIG. The lower electrode 132 and the upper electrode 136 correspond to the terminal p1 and the terminal p2 in FIG.

The element 104b in FIG. 4 shares the lower electrode 133 and the upper electrode 138. Element 104b in FIG. 4 corresponds to element 104b in FIG. The lower electrode 133 and the upper electrode 138 correspond to the terminal p3 and the terminal p4 in FIG. The terminal p1, the terminal p2, the terminal p3, and the terminal p4 correspond to the electric pad 144, the electric pad 140, the electric pad 145, and the electric pad 141 on the device of FIG. Each electric pad is connected to a bias power source and an IV conversion circuit in accordance with the circuit of FIG. The opening 146 is an opening of the vibration film 135. FIG. 6 shows a cross-sectional view thereof. The opening 146 is provided to draw out the pad 144 and the pad 145 formed under the vibration film 135 to the surface of the ultrasonic transducer.

FIG. 4 also shows an element 105a sharing the lower electrode 132 and the upper electrode 137, and an element 105b sharing the lower electrode 133 and the upper electrode 139. Comparing the electrode structure of FIG. 4 with the circuit of FIG. 1, it can be seen that the elements 105a and 105b in FIG. 4 correspond to the elements 105a and 105b in FIG. 1, respectively. The elements 104a and 104b and the elements 105a and 105b can be arranged in the left-right direction in FIG. Examples are shown in the elements 105a 'and 105b'. If the above method is used, an arbitrary number of electrical elements can be two-dimensionally arranged on the ultrasonic transducer. From the viewpoint of simplifying the circuit wiring, the paired electric elements are preferably electric elements adjacent to each other in a two-dimensional arrangement.

(Example 2)
FIG. 7 illustrates an electrical coupling structure according to the second embodiment of the present invention. A technical description similar to that of the first embodiment is omitted. The second embodiment is particularly suitable for a capacitive ultrasonic transducer in which one of the upper electrode and the lower electrode cannot be electrically divided. The ground potential 201 is a reference potential for electrical operation. The bias power source 202 and the bias power source 203 generate a potential difference with respect to the ground potential 201. In this embodiment, a reference potential is connected to each of at least a pair of electrical elements among the pair of electrical elements.

The electric element 204a, the electric element 204b, the electric element 205a, and the electric element 205b are capacitive ultrasonic transducers. For the sake of explanation, the symbol p9 is attached to one terminal of the element 204a, and the symbol p10 is attached to the other terminal. Similarly, symbols p11 to p16 are attached to the electric elements 204b, 205a, and 205b. One terminal p9 of the electric element 204a is connected to the ground potential 201. The other terminal p10 of the electrical element 204a is connected to the IV converter 206a via the coupling capacitor 212a and to the bias power source 202 via the coil 214. The IV converter 206a converts the current signal generated by the electric element 204a into a voltage signal corresponding to the direction and magnitude of the current. The IV converter 206a can be easily realized by a transimpedance circuit or the like.

One terminal p11 of the electric element 204b is connected to the ground potential 201. The other terminal p12 of the electrical element 204b is connected to the IV converter 206b via the coupling capacitor 212b and to the bias power source 203 via the coil 215. Similar to the IV converter 206a, the IV converter 206b converts the current signal generated by the electric element 204b into a voltage circuit. A ground potential 201 is connected to each of the IV converter 206a and the IV converter 206b. The output voltages of the IV converter 206a and the IV converter 206b are input to the positive input (+) and the negative input (−) of the differential amplifier 208, respectively. A differential voltage between the output voltage of the IV converter 206a and the output voltage of the IV converter 206b is output to the output terminal 210 of the differential amplifier 208.

In this embodiment, the electric element 204 a and the electric element 204 b make a pair, and a signal is generated at one output terminal 210. Similarly, in FIG. 7, a signal is generated at the output terminal 211 by the electric element 205 a, the electric element 205 b, the IV converter 207 a, the IV converter 207 b, and the differential amplifier 209. Differences from the operation of FIG. 1 will be described using the ground potential 201, the bias power source 202, the coil 214, the terminal p10 of the electric element 204a, the coupling capacitor 212a, the IV converter 206a, and the like.

The bias power source 202 applies a positive bias potential Vp to the terminal p10 of the electric element 204a with the ground potential 201 as a reference. However, since there is a coil 214 between the bias power source 202 and the terminal p10 of the electric element 204a, the DC impedance of the bias power source 202 is low and the AC impedance is high. The bias power source 202 determines only the DC potential of the terminal p10 of the electric element 204a. Since there is a coupling capacitor 212a between the terminal p10 of the electric element 204a and the IV converter 206a, the DC impedance between the terminal p10 of the electric element 204a and the IV converter 206a is high and the AC impedance is low. Only the ultrasonic signal of the electric element 204a is transmitted to the IV converter 206a as the positive bias potential Vp of the bias power source 202. Therefore, when the electric element 204a receives ultrasonic vibration, the current flowing through the IV converter 206a corresponds to the current i1 of the first embodiment. With respect to the bias power source 203, the same effect as that of the bias power source 202 can be obtained by connecting to the terminal p12 of the electric element 204b via the coil 215. When the electric element 204b receives ultrasonic vibration, the current flowing through the IV converter 206b corresponds to the current i2 of the first embodiment.

The terminal p10 of the electric element 204a and the terminal p14 of the electric element 205a are connected in parallel to the bias power source 202 via the coil 214 and the coil 216. The terminal p12 of the electric element 204b and the terminal p16 of the electric element 205b are connected in parallel to the bias power source 203 via the coil 215 and the coil 217. If the same method is used thereafter, the number of electrical elements and output terminals can be arbitrarily increased.

Hereinafter, the IV converter 206a, the IV converter 206b, the differential amplifier 208, and the output terminal 210 perform the same operations as the IV converter 106a, the IV converter 106b, the differential amplifier 108, and the output terminal 110 of the first embodiment. . Electromagnetic noise can be reduced by the same principle as in the first embodiment.

8 to 10 are diagrams for explaining the structure of an ultrasonic transducer suitable for the second embodiment. 8 is a top view (only the outline of the member is shown as a perspective view), FIG. 9 is a cross-sectional view taken along the line C-C ′ of FIG. 8, and FIG. 10 is a cross-sectional view taken along the line D-D ′ of FIG. Constituent elements corresponding to the elements in FIG. 7 are given the same numbers or will be described. The transducer of this embodiment is formed on the substrate 231. The substrate 231 is particularly preferably a single crystal silicon substrate. Since the substrate 231 also functions as a lower electrode, a material with low resistivity is desirable. For example, a P-type silicon substrate having a resistivity of 0.02 Ω · cm or less is preferable.

As shown in FIG. 9, an insulating layer 232 is formed on the substrate 231. As a material for the insulating layer 232, silicon oxide is suitable. An insulating layer can be formed by thermally oxidizing the surface of single crystal silicon. A part of the upper surface of the insulating layer 232 has a plurality of recesses with respect to the periphery. Such a structure can be obtained by removing a part of the thermal oxide film of single crystal silicon by etching to form a recess and then performing additional thermal oxidation. A vibration film 235 is formed on the insulating layer 232. A cavity 234 is formed by the concave portion on the insulating layer 232 and the vibration film 235. The cavity 234 corresponds to the cavity 134 of FIG.

The vibration film 235 is preferably a silicon single crystal thin film. For example, after the surface of the device layer of the SOI substrate and the surface of the insulating layer 232 are bonded by direct bonding, the handle layer and the box layer of the SOI substrate are removed to form the vibration film 235 of a silicon single crystal thin film. be able to. On the vibration film 235, an upper electrode 236, an upper electrode 237, an upper electrode 238, and an upper electrode 239 are formed. The material of each upper electrode may be a conductive material, but for example, a single layer of Al, Ti, Au, Cr, Cu, Ni, or a multilayer made of a plurality of materials is particularly suitable.

As shown in FIG. 8, a plurality of cavities 234 are two-dimensionally arranged on the substrate 231. In FIG. 8, the cavity 234 is circular, but could be a triangle or a quadrangle. Among the plurality of cavities 234, one that shares the upper electrode is one electrical element. For example, the element 204a in FIG. 8 shares the upper electrode 236. Comparing the electrode structure of FIG. 8 with the circuit of FIG. 7, it can be seen that the element 204a of FIG. 8 corresponds to the element 204a of FIG. The substrate 231 and the upper electrode 236 correspond to the terminal p9 and the terminal p10 in FIG.

The element 204 b in FIG. 8 shares the upper electrode 238. The element 204b in FIG. 8 corresponds to the element 204b in FIG. The substrate 231 and the upper electrode 238 correspond to the terminal p11 and the terminal p12 in FIG. The terminals corresponding to the terminals p9 and p11 in FIG. 7 are the electric pads 244 in FIG. Further, terminals corresponding to the terminal p10 and the terminal p12 in FIG. 7 are the electric pad 240 and the electric pad 241 in FIG. Each electric pad is connected to a bias power source and an IV conversion circuit in accordance with the circuit of FIG. Note that the opening 245 is an opening of the insulating layer 232. FIG. 10 shows a cross-sectional view thereof. The opening 245 is provided for extracting the substrate 231 under the insulating layer 232, that is, the lower electrode, to the surface of the ultrasonic transducer. An electrical pad 244 is provided in the opening 245.

FIG. 8 also shows an element 205 a sharing the upper electrode 237 and an element 205 b sharing the upper electrode 239. Comparing the electrode structure in FIG. 8 with the circuit in FIG. 7, it can be seen that the elements 205a and 205b in FIG. 8 correspond to the elements 205a and 205b in FIG. 7, respectively. The elements 204a and 204b and the elements 205a and 205b can be arranged in the left-right direction in FIG. Examples are shown in elements 205a 'and 205b'. If the above method is used, an arbitrary number of electrical elements can be two-dimensionally arranged on the ultrasonic transducer.

An application example of an information acquisition apparatus such as an ultrasonic diagnostic apparatus having the transducer of the above embodiment will be described. Using the electrical signal that is received by the transducer and receiving the acoustic wave from the subject, subject information that reflects the subject's optical characteristic values such as the light absorption coefficient, subject information that reflects the difference in acoustic impedance, etc. Can be acquired. More specifically, one embodiment of the subject information acquiring apparatus irradiates the subject with light (electromagnetic waves including visible light and infrared rays). Thus, photoacoustic waves generated at a plurality of positions (parts) in the subject are received, and characteristic distributions indicating distributions of characteristic information respectively corresponding to the plurality of positions in the subject are acquired. Characteristic information acquired by photoacoustic waves indicates characteristic information related to light absorption. The initial sound pressure of photoacoustic waves generated by light irradiation, or the optical energy absorption density derived from the initial sound pressure, the absorption coefficient And characteristic information reflecting the concentration of substances constituting the tissue. The substance concentration is, for example, oxygen saturation, total hemoglobin concentration, oxyhemoglobin or deoxyhemoglobin concentration. The object information acquisition apparatus can also be used for diagnosis of malignant tumors, vascular diseases, etc. of humans and animals and follow-up of chemical treatment. Therefore, the subject is assumed to be a living body, specifically, a diagnosis target such as a breast, neck or abdomen of a human or animal. The light absorber inside the subject indicates a tissue having a relatively high absorption coefficient inside the subject. For example, if a part of the human body is a subject, there are oxyhemoglobin or deoxyhemoglobin, blood vessels containing many of them, tumors containing many new blood vessels, and plaques on the carotid artery wall. Furthermore, molecular probes that specifically bind to malignant tumors using gold particles or graphite, capsules that transmit drugs, and the like are also light absorbers.

In addition to the reception of photoacoustic waves, the distribution of the acoustic characteristics in the subject is obtained by receiving the reflected waves from the ultrasonic echoes reflected by the ultrasound transmitted from the probe including the transducer in the subject. You can also The distribution relating to the acoustic characteristics includes a distribution reflecting the difference in acoustic impedance of the tissue inside the subject. However, it is not essential to acquire distributions related to transmission / reception of ultrasonic waves and acoustic characteristics.

FIG. 11A shows an object information acquisition apparatus using a photoacoustic effect. Pulse light oscillated from the light source 2010 is irradiated onto the subject 2014 via an optical member 2012 such as a lens, a mirror, or an optical fiber. The light absorber 2016 inside the subject 2014 absorbs the energy of the pulsed light and generates a photoacoustic wave 2018 that is an acoustic wave. The capacitive transducer 2020 of the present invention in the probe 2022 receives the photoacoustic wave 2018, converts it into an electrical signal, and outputs it to the signal processing unit 2024. The signal processing unit 2024 performs signal processing such as A / D conversion and amplification on the input electrical signal and outputs the signal to the data processing unit 2026. The data processing unit 2026 acquires object information (characteristic information reflecting the optical characteristic value of the object such as a light absorption coefficient) as image data using the input signal. Here, the signal processing unit 2024 and the data processing unit 2026 are collectively referred to as a processing unit. The display unit 2028 displays an image based on the image data input from the data processing unit 2026. As described above, the subject information acquisition apparatus of the present example includes the capacitance-type transducer of the present invention and a processing unit that acquires subject information using an electrical signal output from the transducer. The transducer receives an acoustic wave from the subject and outputs an electrical signal.

FIG. 11B shows a subject information acquiring apparatus such as an ultrasonic echo diagnostic apparatus that uses reflection of acoustic waves. The acoustic wave transmitted from the capacitive transducer 2120 of the present invention in the probe (probe) 2122 to the subject 2114 is reflected by the reflector 2116. The transducer 2120 receives the reflected acoustic wave (reflected wave) 2118, converts it into an electrical signal, and outputs it to the signal processing unit 2124. The signal processing unit 2124 performs signal processing such as A / D conversion and amplification on the input electrical signal, and outputs the signal to the data processing unit 2126. The data processing unit 2126 acquires object information (characteristic information reflecting a difference in acoustic impedance) as image data using the input signal. Here, the signal processing unit 2124 and the data processing unit 2126 are also referred to as a processing unit. The display unit 2128 displays an image based on the image data input from the data processing unit 2126. As described above, the subject information acquisition apparatus of this example includes the capacitive transducer, the light source, and the data processing apparatus of the present invention. The transducer receives a photoacoustic wave generated by irradiating the subject with light oscillated from the light source and converts the photoacoustic wave into an electrical signal, and the data processing apparatus acquires the subject information using the electrical signal. To do.

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. In the case of an apparatus using a reflected wave as shown in FIG. 11B, a probe that transmits an acoustic wave may be provided separately from a probe that receives the acoustic wave. Further, the apparatus has both the functions of the apparatus of FIG. 11A and FIG. 11B, and the object information reflecting the optical characteristic value of the object and the object information reflecting the difference in acoustic impedance are provided. Both of them may be acquired. In this case, the transducer 2020 in FIG. 11A may transmit not only the photoacoustic wave but also the acoustic wave and the reflected wave.

101..Ground potential (reference potential), 102, 103..Bias power supply, 104a, 104b, 105a, 105b..Electric element, 108, 109..Differential amplifier, 110, 111..Output terminal, 106a, 106b 107a, 107b, IV converter

Claims (8)

An electrostatic capacitance type comprising a plurality of electric elements each having one or more cells each having a vibration film including a first electrode and a second electrode provided to face the first electrode through a cavity A transducer,
In one or more electric elements of the plurality of electric elements, the polarity of the bias voltage applied between the first electrode and the second electrode of one electric element forming the pair is the other forming the pair The polarity of the bias voltage applied between the first electrode and the second electrode of the electrical element is opposite to the reference potential,
A transducer characterized by taking a difference between an output signal of one electric element forming the pair and an output signal of the other electric element forming the pair and obtaining a signal from the electric element by an acoustic wave. 2. The transducer according to claim 1, wherein the bias potentials of the one electric element and the other electric element forming the pair are symmetrical with respect to the reference potential. The transducer according to claim 1, wherein the plurality of electric elements are arranged in a two-dimensional manner, and the paired electric elements are electric elements adjacent to each other in the two-dimensional arrangement. 4. The transducer according to claim 1, wherein the reference potential is connected to each of at least a pair of electrical elements among the pair of electrical elements. 5. An electrostatic capacitance type comprising a plurality of electric elements each having one or more cells each having a vibration film including a first electrode and a second electrode provided to face the first electrode through a cavity A transducer driving method comprising:
In the one or more electric elements of the plurality of electric elements, between the first electrode and the second electrode of one electric element making a pair, and the first electric electrode of the other electric element making a pair A bias voltage having opposite polarities across a reference potential is applied between the electrode and the second electrode,
A driving method comprising: obtaining a signal from the element by an acoustic wave by taking a difference between an output signal of the one electric element forming the pair and an output signal of the other electric element forming the pair. 6. The driving method according to claim 5, wherein the bias potentials of the one electric element and the other electric element forming the pair are symmetrical with respect to the reference potential. The capacitive transducer according to any one of claims 1 to 4, and a processing unit that acquires information on a subject using an electrical signal output from the transducer,
2. The object information acquiring apparatus according to claim 1, wherein the transducer receives an acoustic wave from an object and outputs the electric signal. The capacitive transducer according to any one of claims 1 to 4, a light source, and a data processing device,
The transducer receives a photoacoustic wave generated by irradiating the subject with light oscillated from the light source, converts the photoacoustic wave into an electrical signal,
2. The object information acquiring apparatus according to claim 1, wherein the data processing apparatus acquires object information using the electrical signal.

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