KR20100108707A - Sensor using carbon nanotube - Google Patents

Abstract

PURPOSE: A sensor circuit using a carbon nano tube is provided to improve sensitivity by using at least one transistor as a sensor. CONSTITUTION: An inverter(10) is comprised of a first transistor(M11) and a second transistor(M12). A carbon nano tube(CNT) is formed between a drain(D) and a source(S) of the first transistor. A carbon nano tube is formed between a drain and a source of the second transistor. At least one carbon nano tube of the first and second transistors is operated as a sensor. A switching element forms the same voltage in an input terminal and an output terminal before the sensor operates.

Description

Sensor circuit using carbon nanotubes {SENSOR USING CARBON NANOTUBE}

The present invention relates to a sensor circuit using carbon nanotubes applicable to an electrical conductivity sensor, a dielectric constant change sensor, a pH sensor, a humidity sensor, and a biosensor using the properties of carbon nanotubes.

Carbon nanotubes (carbon nanotubes) are nano-sized and have large changes in physical properties due to their surface, and are being studied as sensors using these properties.

Carbon nanotubes have sp ² bonds in which graphite is rolled round, so the surface area per unit area is very wide, so it has excellent adsorption capacity for gas molecules or ions.

The carbon nanotubes have a form such as a single-walled nanotube, a multiwall nanotube, or a nanotube rope structure.

In addition, carbon nanotubes have the characteristics of a conductor or a semiconductor, such as a metal electrically, and has the property that the electrical conductivity changes according to the adsorption of gas molecules or ions.

The degree of ion adsorption varies depending on the state of the material absorbed into the carbon nanotubes having good adsorption properties, and when the carbon nanotubes are used as the sensing bodies, the carbon nanotubes act as molecular units, thereby adsorbing the carbon nanotubes. It indicates that it can be used as an element that can measure changes in electrical properties, pH, humidity, etc. of materials.

However, in the case of a sensor using a carbon nanotube according to the related art, the output and the sensitivity are low due to the use of a single transistor, and thus there is a problem in that measurement reliability cannot be guaranteed when measuring changes in the electrical properties, pH, and humidity.

The present invention is to provide a sensor circuit using carbon nanotubes that can further improve the sensing sensitivity by configuring a transistor to which carbon nanotubes are applied as an inverter and utilizing at least one transistor as a sensor.

Technical means of the present invention for achieving the above object, the first transistor is connected to the current path between the high potential and the output terminal, the first transistor formed carbon nanotube between the drain and the source; And a second transistor having a current path connected between the output terminal and the low potential but having an input terminal connected to a gate and having a carbon nanotube formed between the drain and the source, wherein at least one of the first and second transistors is provided. It is characterized in that the carbon nanotubes are operated as a sensor.

Specifically, the switching device further includes a switching device connected between the input terminal and the output terminal to equalize the voltage of the input terminal and the output terminal before the sensor operation, and is connected between the input terminal and the low potential to charge the voltage of the output terminal when the switching device is turned on. It characterized in that it further comprises a capacitor.

An inverter having the output terminal as an input, the inverter comprising: a third transistor having a current path connected between a high potential and a second output terminal, and a carbon nanotube formed between a drain and a source; A fourth transistor having a current path connected between the second output terminal and the low potential, a gate connected to the output terminal, and a carbon nanotube formed between the drain and the source; And a second switching element connected between the output terminal and the second output terminal and turned on or off according to a predetermined control signal. A capacitor connected between the output terminal and the low potential to charge a voltage at the output terminal; And a coupling capacitor connected between the output terminal and the second switching element.

The first and fourth transistors or the second and third transistors are operated as sensors.

As described above, in the present invention, a transistor in which carbon nanotubes are applied may be configured as an inverter, and at least one transistor may be used as a sensor to further improve sensing sensitivity and to detect a small amount of sensing object. There is a possible advantage.

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

1 is a circuit diagram showing a sensor using a carbon nanotube according to an embodiment of the present invention, Figure 2 is a cross-sectional view showing the circuit of FIG.

The sensor circuit 10 is composed of an inverter. The inverter 10 is composed of a first transistor M11 and a second transistor M12. That is, the output voltage Vout with respect to the input voltage Vin is represented in an inverted form with respect to the input.

The first transistor M11 has a current path connected between the high potential Vdd and the output terminal Vout, the drain D and the gate G are connected to each other, and the second transistor M12 has the output terminal ( The current path is connected between Vout) and the low potential Vss, and the gate G is connected to the input terminal Vin.

As illustrated in FIG. 2, the first transistor M11 and the second transistor M12 have carbon nanotubes (CNTs) formed between the drain D and the source S. A protective film is stacked on the carbon nanotubes CNTs of the two transistors M12, and the first transistor M11 serves as a sensor. Of course, if necessary, the second transistor M12 may be configured as a sensor transistor, and both the first and second transistors M11 and M12 may be configured as sensor transistors.

1 illustrates an inverter configured with an enhancement type transistor, but may also be configured with an inverter configured with a depletion type transistor. In the depletion type, the gate G of the first transistor M11 is connected to the source S rather than the drain D.

The sensor using the properties of the carbon nanotubes (CNT) may be applied to electrical conductivity sensors, dielectric constant change sensors, pH sensors, humidity sensors and biosensors. When used as a sensor it is good to be able to measure even a small amount, in the present invention, the configuration of the inverter increases the sensitivity of the sensor.

Referring to the manufacturing process of the sensor as shown in FIG. 2, first, a gate pattern is formed of metal on various materials such as glass, plastic, or a silicon substrate on which an oxide film is formed, and an insulating film is deposited.

Carbon nanotubes (CNTs) are coated or dispersed with a dispersion solution to form carbon nanotubes (CNTs). Subsequently, carbon nanotubes (CNTs) are formed in a pattern, and metal electrodes for drain and source are deposited and patterned.

Subsequently, a protective film is deposited on the upper ends of the drain and source metal electrodes and the carbon nanotubes (CNTs), and a contact process of etching the protective film of the sensor formation site is performed. At this time, the protective film of a portion to be used as a sensor among the plurality of transistors M11 and M12 is removed.

3 is a circuit diagram illustrating a sensor using carbon nanotubes according to another embodiment of the present invention, wherein the sensor circuit 20 includes a first transistor M21, a second transistor M22, a switching element SW1, and a capacitor ( It consists of inverter including C1). In the above, carbon nanotubes CNTs are formed between the drains D and the sources S of the first and second transistors M21 and M22, respectively.

In the first transistor M21, a current path is connected between the high potential Vdd and the output terminal Vout, and the drain D and the gate G are connected to each other, and the second transistor M22 is connected to the output terminal ( The current path is connected between Vout) and the low potential Vss, but the input node ND_in is connected to the gate G, and the switching element SW1 is connected between the input node ND_in and the output terminal Vout. The capacitor C1 is configured to be turned on or off according to a predetermined control signal, and the capacitor C1 is connected between the input node ND_in and the low potential Vss to charge the voltage at the output terminal Vout.

The switching element SW1 may be configured using a general electrical switch as well as a transistor. In FIG. 3, one of the two transistors M21 and M22 constituting the inverter is covered with a protective film and the other is not covered with a protective film. The transistor not covered with the protective film operates as a sensor.

Here, when the sensing object is adsorbed to the carbon nanotubes (CNT) of the first transistor (M21) acting as a sensor transistor, the electrical resistance changes according to the physical characteristics of the carbon nanotubes (CNTs) as the current path. As a result, a change occurs in the operating voltage of the inverter, thereby changing the output voltage.

At this time, in order to maximize the change of the output voltage, the switching device SW1 is turned on and off before the sensor reaction occurs. When the switching device SW1 is turned on, the input node ND_in and the output terminal Vout of the inverter are electrically connected, and the voltages of the input node ND_in and the output terminal Vout are the same according to the electrical connection. The capacitor C1 is to be charged.

Therefore, the operating point is set in the region where the characteristic change of the inverter is large according to the characteristic curve of the inverter's input / output voltage. As a result, when the resistance of the transistor M21 changes due to the reaction of the sensing object, the change of the output voltage also appears large. Sensitivity is improved.

Meanwhile, in FIG. 3, the capacitor C1 charges a predetermined voltage through the switching element SW1, and the second transistor M22 operates according to the voltage charged in the capacitor C1. C1) may be configured to control the operation of the second transistor M22 by charging a specific operating voltage input arbitrarily from the outside.

3 illustrates an inverter configured with an enhancement type transistor, but may also be configured with an inverter configured with a depletion type transistor. In the depletion type, the gate G of the first transistor M21 is connected to the source S, not the drain D. FIG.

4 is a circuit diagram illustrating a sensor using carbon nanotubes (CNTs) according to another embodiment of the present invention, wherein the sensor circuit 30 includes a first transistor M31, a second transistor M32, and a first switching device. A first inverter including SW1 and a first capacitor C1, and a second inverter including a third transistor M33 and a fourth transistor M34, a second switching element SW2, and a second capacitor C2. Consists of That is, the change in the output signal is further increased by configuring the sensor as a two-stage inverter having a structure in which the output of the first inverter is connected to the input node ND_in of the second inverter.

In the above, carbon nanotubes CNTs are formed between the drains D and the sources S of the transistors M31 to M34, respectively.

In the first transistor M31 of the first inverter, a current path is connected between the high potential Vdd and the first output node ND_out1, but the drain D and the gate G are connected to each other. M32 has a current path connected between the first output node ND_out1 and the low potential Vss, but an input node ND_in is connected to the gate G, and the first switching device SW1 is an input node. It is connected between (ND_in) and the first output node (ND_out1) is configured to turn on, off according to a predetermined control signal, the first capacitor (C1) is connected between the input node (ND_in) and low potential (Vss) And charges the voltage of the first output node ND_out1.

In the third transistor M33 of the second inverter, a current path is connected between the high potential Vdd and the second output terminal Vout, but the drain D and the gate G are connected to each other. M32 is connected to the current path between the second output terminal (Vout) and the low potential (Vss), the first output node (ND_out1) is connected to the gate (G), the second switching device (SW2) is the first It is connected between the output node ND_out1 and the second output terminal Vout and configured to be turned on or off according to a predetermined control signal, and the second capacitor C2 is connected to the first output node ND_out1 and the low potential Vss. ) Is configured to charge the voltage at the second output terminal (Vout).

Meanwhile, the coupling capacitor Cc is further connected between the first output node ND_out1 and the second switching device SW2.

The switching elements SW1 and SW2 may be configured using general electrical switches as well as transistors. In FIG. 4, one of the two transistors M31 and M32 constituting the first inverter or the second inverter, respectively, M33 and M34 is covered with a protective film and the other is not covered with the protective film. Will work as. Herein, when the first transistor M31 is operated as a sensor, the fourth transistor M34 is configured as a sensor, and when the second transistor M32 is operated as a sensor, the third transistor M33 is configured as a sensor. It is preferable to increase the amplification degree of the output signal.

Here, the current path when the sensing object is adsorbed to the carbon nanotube (CNT) of the first transistor (M31) and the fourth transistor (M34) or the second transistor (M32) and the third transistor (M33) acting as a sensor transistor, respectively. According to the physical properties of phosphorus carbon nanotubes (CNT), electrical resistance changes. As a result, a change occurs in the operating voltage of the inverter, thereby changing the output voltage.

At this time, in order to maximize the change in the output voltage, before the sensor reaction occurs, the first and second switching devices SW1 and SW2 are turned on, the first switching device SW1 is turned off, and the second switching device SW2 is sequentially turned on. Turn it off. When the first and second switching devices SW1 and SW2 are turned on, the input node ND_in and the first output node ND_out1 of the first inverter are electrically connected to each other, and the first output node ND_out1 of the second inverter is electrically connected. ) And the second output terminal (Vout) are electrically connected to each other. According to the electrical connection, the voltages of the first output node ND_out1 and the second output terminal Vout are charged to the first and second capacitors C1 and C2, respectively.

Therefore, the operating point is set in the region where the characteristic change of the inverter is large according to the characteristic curve of the inverter's input / output voltage. As a result, when the resistance of the transistor changes due to the reaction of the sensing object, the change of the output voltage also appears to increase the sensitivity. do.

For example, when the sensing object is adsorbed to the carbon nanotubes CNT of the first transistor M31 and the fourth transistor M34 acting as a sensor, the electrical resistance of each of the carbon nanotubes CNT increases. The voltage of the first output node ND_out1 drops. When the voltage of the first output node ND_out1 drops and the electrical resistance of the fourth transistor M34 increases, the rising voltage of the second output terminal Vout increases. That is, by configuring the sensor using the two-stage inverter 30 it is possible to further improve the sensitivity characteristics and the output amplification degree.

In the above, when the sensing object is adsorbed on the carbon nanotubes (CNT), the electrical resistance of the carbon nanotubes may be increased or decreased depending on the type of adsorbent. In the present invention, for convenience of description, the electrical resistance is increased. It is considered, but it is not limited to this. That is, the inverter type sensor of the present invention operates to further improve the output amplification degree even when the sensing object is adsorbed on the carbon nanotubes and the electrical resistance decreases.

4 illustrates an inverter configured with an enhancement type transistor, but may also be configured with an inverter configured with a depletion type transistor. In the depletion type, the gate G of the first transistor M31 is connected to the source S, not the drain D.

In this way, the operating point of the two-stage inverter 30 is determined by using the plurality of switching elements SW1 and SW2, and the characteristic change of the inverter is also large at the determined operating point. Thus, the sensitivity of the sensor can be increased, Detection of the object is also possible.

Preferred embodiments of the present invention are disclosed for purposes of illustration, and those skilled in the art will be able to make various modifications, changes, and additions within the spirit of the present invention. Therefore, such modifications, changes and additions should be determined not only by the claims below, but also by equivalents to those claims.

1 is a circuit diagram showing a sensor using a carbon nanotube according to an embodiment of the present invention.

2 is a cross-sectional view illustrating the sensor circuit of FIG. 1.

3 is a circuit diagram showing a sensor using carbon nanotubes according to another embodiment of the present invention.

4 is a circuit diagram showing a sensor using carbon nanotubes according to another embodiment of the present invention.

Claims (8)

A first transistor having a current path connected between the high potential and the output terminal, and a carbon nanotube formed between the drain and the source; And And a second transistor having a current path connected between the output terminal and the low potential but having an input terminal connected to a gate, and having a carbon nanotube formed between the drain and the source. A sensor circuit using carbon nanotubes in which at least one carbon nanotube of the first and second transistors is operated as a sensor. The method of claim 1, And a switching device connected between the input terminal and the output terminal to equalize the voltages of the input terminal and the output terminal before the sensor operation. The method of claim 2, And a capacitor connected between the input terminal and the low potential to charge a voltage at the output terminal when the switching device is turned on. The method of claim 2, The switching device is a sensor circuit using carbon nanotubes to increase the sensitivity by adjusting the input and output operating point. The method of claim 1, The first transistor is a sensor circuit using a carbon nanotube that is an increased or depleted transistor structure. The method of claim 1, Sensor circuit using a carbon nanotube that is further connected to the inverter to the output terminal. The method of claim 6, The inverter may include: a third transistor having a current path connected between the high potential and the second output terminal, and a carbon nanotube formed between the drain and the source; A fourth transistor having a current path connected between the second output terminal and a low potential, a gate connected to the output terminal, and a carbon nanotube formed between a drain and a source; And a second switching element connected between the output terminal and the second output terminal and turned on or off according to a predetermined control signal. A capacitor connected between the output terminal and the low potential to charge a voltage at the output terminal; And a coupling capacitor connected between the output terminal and the second switching element. The method of claim 7, wherein Sensor circuit using a carbon nanotube formed to operate the first transistor and the fourth transistor or the second transistor and the third transistor as a sensor.

Images