KR20110076293A - Acoustic sensor using nanotube and method for manufacturing thereof - Google Patents

Abstract

PURPOSE: An acoustic sensor using a nanotube and a manufacturing method thereof are provided to miniaturize the sensor compared to an acoustic element which uses a piezoelectric body. CONSTITUTION: An acoustic sensor(100) using a nanotube comprises a substrate(10), a vibration plate(20), an electrode pattern(30), a nanotube(40), a cavity(50), and a vent hole(70). The vibration plate is formed on the substrate. The electrode pattern is formed on the vibration plate and comprises first and second electrodes. The nanotube is spread on a gap between the first and second electrodes. The cavity is formed in the substrate. The vent hole is coupled to the bottom of the substrate and uniformly maintains the pressure of the cavity.

Description

Acoustic sensor using nanotube and method for manufacturing

The present invention relates to an acoustic sensor, to a high-sensitivity and miniaturized acoustic sensor using nanotubes and to a method of manufacturing the same.

1 is a perspective view illustrating an acoustic sensor using a conventional piezoelectric ceramic. The acoustic sensor forms electrodes on both sides of the piezoelectric body and has a natural frequency of the acoustic band so that ultrasonic waves are detected by reading a charge proportional to the stress applied to the piezoelectric body from mechanical deformation of the structure when ultrasonic waves are applied. In the case of using a piezoelectric processed product, there is a disadvantage in that the size is large and it is difficult to integrate with a signal processing circuit.

2A is a cross-sectional view illustrating a capacitive acoustic sensor using a conventional MEMS process, and FIGS. 2B to 2G are process diagrams illustrating a process of manufacturing the acoustic sensor.

Recently, a sound sensor is manufactured as shown in FIG. 2 with a structure similar to that of a capacitive MEMS microphone. The acoustic sensor 10 includes a diaphragm 1 and a bipolar plate 2, and ultrasonic waves may be applied by applying a high voltage thereto. When the capacitance between the diaphragm and the bipolar plate changes due to the vibration of the diaphragm, and when a constant voltage is applied therefrom, a method of detecting ultrasonic waves by using a point where the charge changes is used. In the case of the capacitive acoustic sensor, there is a problem in that the production cost is high because a step-up circuit for applying a high voltage is required and a complicated multi-step micromachining process as shown in FIGS. 2b to 2g is required to form a diaphragm and a bipolar plate.

The present invention is to solve the problems of the prior art as described above, to provide an acoustic sensor and a manufacturing method thereof having a high sensitivity using a nanotube, which can be miniaturized in a simple process.

The present invention to achieve the above object,

Board; A diaphragm formed on the substrate and manufactured according to a natural frequency of a sound to be sensed; An electrode pattern formed on the diaphragm and including a first electrode and a second electrode; A nanotube applied between the first electrode and the second electrode to allow an electrical signal to be connected between both electrodes; A cavity formed in the substrate under the diaphragm and serving as a reference value for an external pressure change; And a plate coupled to a lower portion of the substrate and including a plate having a vent hole formed to maintain a constant pressure of the cavity.

In the acoustic sensor according to the present invention, the nanotubes are preferably carbon nanotubes having a high gauge constant, and the nanotubes are formed by dropping ink on an electrode already formed by using an inkjet printing process and drying the electrode pattern. To be connected. In addition, the resistance pattern of the nanotubes is formed to be dispersed in various places across the boundary surface of the diaphragm, the nanotube resistance pattern may be formed in a position where the stress is reversed to be able to output a signal in a differential type.

In addition, in another embodiment according to the present invention, the acoustic sensor is formed as a reference resistance by forming a nanotube pattern of the same size separate from the nanotube pattern formed on the diaphragm, and further forms a third electrode It can also manufacture by the method of making. In addition, the diaphragm used in the acoustic sensor of the present invention is preferably formed of a silicon nitride film or a polycrystalline silicon film.

In addition, the present invention comprises a first step of forming a diaphragm having a natural frequency of the sound band on the substrate; A second step of forming an electrode pattern including the first electrode and the second electrode on the diaphragm; A third step of forming a nanotube applied between the first electrode and the second electrode to allow an electrical signal to be connected between both electrodes; A fourth step of forming a cavity in the substrate below the diaphragm serving as a reference value for an external pressure change; And a fifth step of coupling the plate having the vent hole to the substrate so that the cavity maintains a constant pressure.

A first step of forming a diaphragm having a natural frequency of an acoustic band on a substrate different from the above method; Forming a nanotube on the diaphragm; A third step of forming an electrode pattern including a first electrode and a second electrode on the nanotube through a shadow mask process or a photolithography process; A fourth step of forming a cavity in the substrate below the diaphragm serving as a reference value for an external pressure change; And a fifth step of coupling the plate having the vent hole to the substrate so that the cavity maintains a constant pressure.

In addition, in addition to the method of manufacturing the acoustic sensor, forming a nanotube pattern having the same size as the nanotube pattern formed on the diaphragm and used as a reference resistance, and further comprising the step of further forming a third electrode Acoustic sensors can be manufactured.

In the method of manufacturing an acoustic sensor according to the present invention, the nanotubes are preferably carbon nanotubes having a high gauge constant, and the nanotubes are formed by dropping ink on an electrode already formed by using an inkjet printing process and drying the electrode pattern. It is formed to be connected by nanotubes. In addition, the resistance pattern of the nanotubes is formed to be dispersed in several places across the boundary surface of the diaphragm, the nanotube resistance pattern may be formed in a position where the stress is reversed to be able to output a signal in a differential type.

The acoustic sensor according to the present invention can be further miniaturized compared to an acoustic device using a piezoelectric material by using nanotubes, and since the diameter of the nanotubes is very small, a very thin diaphragm can be used in consideration of relative stiffness. It is effective to obtain high sensitivity even in the diaphragm.

In addition, there is an effect that can produce a miniaturized acoustic sensor in a much simpler process than the device manufactured by the conventional MEMS process.

The present invention relates to a substrate; A diaphragm formed on the substrate and manufactured according to a natural frequency of a sound to be sensed; An electrode pattern formed on the diaphragm and including a first electrode and a second electrode; A nanotube applied between the first electrode and the second electrode to allow an electrical signal to be connected between both electrodes; A cavity formed in the substrate under the diaphragm and serving as a reference value for an external pressure change; And a plate coupled to a lower portion of the substrate and including a plate having a vent hole formed to maintain a constant pressure of the cavity.

In the acoustic sensor according to the present invention, the nanotubes are preferably carbon nanotubes having a high gauge constant, and the nanotubes are formed by dropping ink on an electrode already formed by using an inkjet printing process and drying the electrode pattern. To be connected. In addition, the resistance pattern of the nanotubes is formed to be dispersed in several places across the boundary surface of the diaphragm, the nanotube resistance pattern may be formed in a position where the stress is reversed to be able to output a signal in a differential type.

The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention, and do not represent all of the technical idea of the present invention, which can be replaced at the time of the present application It should be understood that there may be various equivalents and variations.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3A to 3D are cross-sectional views illustrating an acoustic sensor using nanotubes according to an embodiment of the present invention. The acoustic sensor 100 includes a substrate 10, a diaphragm 20, an electrode pattern 30, a nanotube 40, a cavity 50, and a plate 60.

The nanotubes 40 used in the acoustic sensor according to the present invention may use various nanotubes having piezoresistive properties. In particular, carbon nanotubes may be used as the piezoresistor of the present invention because of the large gauge constant indicating piezoresistive performance. desirable.

Carbon nanotubes, which have recently been spotlighted as new material devices, have the advantage of being capable of operating at room temperature, having good sensitivity and fast reaction speed. This advantage is due to the physical properties of carbon nanotubes. Carbon nanotubes are a tube-shaped molecule formed by rounding a graphite plate (sp2) made of carbons connected by hexagonal rings, ranging in diameter from several tens of nm. Carbon nanotubes are strong and well bent and do not damage or wear out even after repeated use, and the electrical properties vary according to the dried form, structure and diameter.

In the method of forming the nanotubes, ink is dropped on a pre-formed electrode by using an inkjet printing process and dried to connect the electrodes to the nanotubes, and thus, the production cost is reduced because the process is very simple. On the other hand, unlike the above method, an electrode can be formed by forming a nanotube first on a diaphragm and using a method for forming a general electronic circuit such as a shadow mask method or a photolithography process. Since the contact resistance is reduced and more stable circuit configuration is possible, it is suitable for high-precision sensors, so it can be appropriately selected and manufactured.

In addition, the nanotube resistance pattern applied to the acoustic sensor according to the present invention may be placed as shown in the figure or may be dispersed in various places over the boundary surface A of the diaphragm 20. In addition, the nanotube resistance pattern may be formed at the center portion B of the diaphragm, that is, at a position where stress is reversed, to output a signal in a differential type.

4A and 4B are cross-sectional views illustrating nanotubes in which tensile stress is generated according to an embodiment of the present invention.

Referring to the drawings, when the sound is incident on the diaphragm 20, when the displacement occurs downward tensile stress (tensile stress) occurs in the nanotube 40 near the edge of the diaphragm. On the other hand, the compressive stress occurs in the nanotube 40 in the center portion B of the diaphragm. Therefore, since the resistance increases on one side and decreases on one side, connecting two nanotube resistors increases the signal in the center twice as much as using only one nanotube resistor as shown in the figure.

Alternatively, instead of separately configuring the reference resistor, a nanotube pattern (C) of the same size can be formed separately from the nanotube pattern that spans the diaphragm on a single device and used as a reference resistor. Is provided. (See Figure 4b)

Since the diaphragm has excellent mechanical properties, such as a silicon nitride film or a polycrystalline silicon film, which are frequently used in a micromachining process, it is preferable to manufacture the diaphragm using this.

The operation principle of the acoustic sensor according to the present invention with reference to Figures 3a and 3b in more detail as follows.

First, an acoustic sensor using nanotubes forms a diaphragm having a natural frequency of an acoustic band, and forms an electrode pattern thereon, and then applies nanotubes of a material having piezoresistive properties, such as carbon nanotubes, between the electrodes. Allow electrical signals to be connected between the two electrodes.

3c is a plan view of the structure in which the nanotubes are applied between electrodes according to the present invention, and FIG. 3d is a circuit diagram showing an operation principle of an acoustic sensor.

The cavity 50 of a suitable volume is formed below the diaphragm 20 to act as a reference value for the external pressure change, and one electrode A is applied with an applied voltage, and the other electrode B is connected to the reference resistor to The other side C is grounded. (See FIG. 3D) In forming the cavity 50, a plate 60 is attached, and a vent hole 70 is formed in the plate 60 to function as a connection passage with external air.

When ultrasonic waves are applied, the diaphragm 20 vibrates, and mechanical deformation occurs in the carbon nanotubes 40 formed on the diaphragm 20, which is caused by the piezoelectric resistance of the carbon nanotubes. This will change. Then, since the voltage ratio with the reference resistance is changed, a voltage waveform proportional to the acoustic signal applied to the electrode B is displayed with an offset voltage. Therefore, if a capacitor is connected to the rear of the electrode, only the AC signal from which the offset is removed is detected to detect ultrasonic waves. . The position of the two electrodes A and B is appropriately the edge of the diaphragm in which the maximum stress at the time of diaphragm deformation. (Part A of FIG. 3A)

In order for the stress to appear only in one direction throughout the nanotube, the stiffness of the nanotubes must be sufficiently small compared to the stiffness of the diaphragm, otherwise the compressive and tensile stresses will appear simultaneously within the nanotubes. However, nanotubes have a very small diameter, so even if the diaphragm is as thin as 1 um, only one direction of stress appears. In addition, if the thickness of the diaphragm is thin, the sensitivity is improved, so that a thin diaphragm can be used by the use of nanotubes, and the diameter of the diaphragm must be small to maintain the same natural frequency in the thin diaphragm, thereby miniaturizing the chip.

In addition, the present invention comprises a first step of forming a diaphragm having a natural frequency of the sound band on the substrate; A second step of forming an electrode pattern including the first electrode and the second electrode on the diaphragm; A third step of forming a nanotube applied between the first electrode and the second electrode to allow an electrical signal to be connected between both electrodes; A fourth step of forming a cavity in the substrate below the diaphragm serving as a reference value for an external pressure change; And a fifth step of coupling the plate having the vent hole to the substrate so that the cavity maintains a constant pressure.

Unlike the above method, a second step of forming a nanotube on the diaphragm; It is also possible to perform the third step of forming an electrode pattern including the first electrode and the second electrode on the nanotube through a shadow mask process or a photolithography process.

When manufacturing the acoustic sensor, the nanotube resistance pattern may be placed in one or distributed in several places across the boundary surface of the diaphragm. In addition, a nanotube resistance pattern may be formed at the center of the diaphragm, that is, at a position where stress is reversed, to output a signal in a differential type.

Alternatively, instead of configuring the reference resistor separately, a nanotube pattern of the same size can be formed separately from the nanotube pattern across the diaphragm on a single device and used as a reference resistor. Use the method of formation.

Although the present invention has been described with reference to one embodiment shown in the accompanying drawings, this is merely exemplary, and various modifications and equivalent other embodiments are possible to those skilled in the art. I can understand. Accordingly, the true scope of protection of the present invention should be determined only by the appended claims.

1 is a perspective view illustrating an acoustic sensor using a conventional piezoelectric ceramic.

2A is a cross-sectional view illustrating a capacitive acoustic sensor using a conventional MEMS process, and FIGS. 2B to 2G are process diagrams illustrating a process of manufacturing the acoustic sensor.

3A to 3D are cross-sectional views illustrating an acoustic sensor using nanotubes according to an embodiment of the present invention.

4A and 4B are cross-sectional views illustrating nanotubes in which tensile stress is generated according to an embodiment of the present invention.

Claims (25)

Board; A diaphragm formed on the substrate and manufactured according to a natural frequency of a sound to be sensed; An electrode pattern formed on the diaphragm and including a first electrode and a second electrode; A nanotube applied between the first electrode and the second electrode to allow an electrical signal to be connected between both electrodes; A cavity formed in the substrate under the diaphragm and serving as a reference value for an external pressure change; And The sensor coupled to the lower substrate, the acoustic sensor using a nanotube comprising a plate formed with a vent hole so that the cavity maintains a constant pressure. The method according to claim 1, The nanotubes are acoustic sensors using nanotubes, characterized in that the high carbon constant carbon nanotubes. The method according to claim 1, The nanotube is an acoustic sensor using a nanotube, characterized in that the electrode pattern is connected to the nanotube by dropping and drying the ink on the electrode already formed by using an inkjet printing process. The method according to claim 1, The resistance pattern of the nanotubes is an acoustic sensor using nanotubes, characterized in that formed in a number of places distributed over the boundary surface of the diaphragm. The method according to claim 4, The nanotube resistance pattern is formed in a position where the stress is reversed by the acoustic sensor using a nanotube, characterized in that to output a signal in a differential type. The method according to claim 1, The nanotube pattern formed on the diaphragm is formed as a separate nanotube pattern of the same size and used as a reference resistor, and further formed a third electrode, the acoustic sensor using nanotubes. The method according to claim 1, The diaphragm is an acoustic sensor using nanotubes, characterized in that formed of a silicon nitride film or a polycrystalline silicon film. A first step of forming a diaphragm having a natural frequency of an acoustic band on a substrate; A second step of forming an electrode pattern including the first electrode and the second electrode on the diaphragm; A third step of forming a nanotube applied between the first electrode and the second electrode to allow an electrical signal to be connected between both electrodes; A fourth step of forming a cavity in the substrate below the diaphragm serving as a reference value for an external pressure change; And And a fifth step of coupling the plate having the vent hole to the substrate so that the cavity maintains a constant pressure. The method according to claim 8, The nanotube is a sound sensor manufacturing method using a nanotube, characterized in that the high carbon constant carbon nanotubes. The method according to claim 8, The nanotube is an acoustic sensor manufacturing method using a nanotube, characterized in that formed by the method of dropping and drying the ink using an inkjet printing process. The method according to claim 8, The resistance pattern of the nanotubes is a sound sensor manufacturing method using nanotubes, characterized in that formed to be dispersed in several places across the boundary surface of the diaphragm. The method according to claim 8, The nanotube resistance pattern is formed in a position where the stress is opposite to the acoustic sensor manufacturing method using a nanotube, characterized in that formed to output a signal in a differential type. The method according to claim 8, The diaphragm is an acoustic sensor manufacturing method using a nanotube, characterized in that formed of a silicon nitride film or a polycrystalline silicon film. A first step of forming a diaphragm having a natural frequency of an acoustic band on a substrate; Forming a nanotube on the diaphragm; A third step of forming an electrode pattern including a first electrode and a second electrode on the nanotube through a shadow mask process or a photolithography process; A fourth step of forming a cavity in the substrate below the diaphragm serving as a reference value for an external pressure change; And And a fifth step of coupling the plate having the vent hole to the substrate so that the cavity maintains a constant pressure. The method according to claim 14, The nanotube is a sound sensor manufacturing method using a nanotube, characterized in that the carbon nanotubes with a high gauge constant. The method according to claim 14, The nanotube is an acoustic sensor manufacturing method using a nanotube, characterized in that formed by the method of dropping and drying the ink using an inkjet printing process. The method according to claim 14, The resistance pattern of the nanotubes is a sound sensor manufacturing method using nanotubes, characterized in that formed to be dispersed in several places across the boundary surface of the diaphragm. The method according to claim 14, The nanotube resistance pattern is formed in a position where the stress is opposite to the acoustic sensor manufacturing method using a nanotube, characterized in that formed to output a signal in a differential type. The method according to claim 14, The diaphragm is an acoustic sensor manufacturing method using a nanotube, characterized in that formed of a silicon nitride film or a polycrystalline silicon film. A first step of forming a diaphragm having a natural frequency of an acoustic band on a substrate; A second step of forming an electrode pattern including the first electrode and the second electrode on the diaphragm; A third step of forming a nanotube applied between the first electrode and the second electrode to allow an electrical signal to be connected between both electrodes; A fourth step of forming a cavity in the substrate below the diaphragm serving as a reference value for an external pressure change; Coupling a plate having a vent hole to the substrate such that the cavity maintains a constant pressure; And Forming a nanotube pattern of the same size separate from the nanotube pattern formed on the diaphragm to use as a reference resistor, and further comprising a sixth step of further forming a third electrode acoustic sensor manufacturing method using a nanotube. The method of claim 20, The nanotube is a sound sensor manufacturing method using a nanotube, characterized in that the carbon nanotubes with a high gauge constant. The method of claim 20, The nanotube is an acoustic sensor manufacturing method using a nanotube, characterized in that formed by the method of dropping and drying the ink using an inkjet printing process. The method of claim 20, The resistance pattern of the nanotubes is a sound sensor manufacturing method using nanotubes, characterized in that formed to be dispersed in several places across the boundary surface of the diaphragm. The method of claim 20, The nanotube resistance pattern is formed in a position where the stress is opposite to the acoustic sensor manufacturing method using a nanotube, characterized in that formed to output a signal in a differential type. The method of claim 20, The diaphragm is an acoustic sensor manufacturing method using a nanotube, characterized in that formed of a silicon nitride film or a polycrystalline silicon film.

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