WO2011008043A2

WO2011008043A2 - Gas sensor

Info

Publication number: WO2011008043A2
Application number: PCT/KR2010/004635
Authority: WO
Inventors: 이상훈; 황하룡
Original assignee: (주)와이즈산전
Priority date: 2009-07-17
Filing date: 2010-07-16
Publication date: 2011-01-20
Also published as: KR20110007676A; WO2011008043A9; WO2011008043A3

Abstract

Disclosed is a gas sensor. A gas sensor according to one example of the present invention comprises: a first electrode and a second electrode which are formed on a base plate, which have an alternating power source applied to them, and which are positioned apart from each other; and a carbon nanotube powder or nanowire powder coated in regions formed between the first electrode and the second electrode, and the impedance of the nanotube powder changes depending on the concentration of a gas.

Description

Gas sensor

TECHNICAL FIELD The present invention relates to a gas sensor, and more particularly, to a gas sensor that can easily and accurately sense gas while increasing reaction rate and recovery rate by using carbon nanotube powder dispersed between electrodes.

In general, the gas sensor operates on a principle of measuring the amount of harmful gas by using a characteristic that the electrical conductivity or electrical resistance changes depending on the degree of adsorption of gas molecules.

Recently, carbon nanotubes, which are in the spotlight as new material devices, can operate at room temperature and have excellent sensitivity, and gas sensors for measuring changes in electrical resistance using carbon nanotubes have been widely developed. .

However, gas sensors using carbon nanotubes take a long time to return to their original electrical conductivity after sensing. In addition, gas sensors using carbon nanotubes must be heated to return to the original conductivity, which requires additional elements such as heaters and the like. When the heater or the like is mounted on the gas sensor, the power consumption is high, so that it cannot be used in a portable device, and the manufacturing process is complicated.

The technical problem to be achieved by the present invention is to provide a gas sensor that can operate easily and accurately while increasing the response speed and recovery speed.

According to an aspect of the present invention, there is provided a gas sensor comprising: a first electrode and a second electrode formed on a substrate, to which an AC power is applied, and spaced apart from each other; And carbon nanotube powder or nanowires dispersed in a region formed between the first electrode and the second electrode, and the impedance of the carbon nanotube powder is changed according to the concentration of the gas.

Preferably, the substrate may be a flexible printed circuit board implemented with a polyimide film.

Preferably, the first electrode is formed integrally with the first electrode and has first sub electrodes whose ends are directed toward the second electrode, and the second electrode is integrally formed with the second electrode. An end is provided with second sub-electrodes facing the first electrode, and the first sub-electrodes and the second sub-electrodes are comb-shaped with the second sub-electrodes positioned between each other and the first sub-electrodes. It may be provided in the inter-digitated (inter-digitated) shape.

Preferably, the first sub-electrode and the second sub-electrode may be spaced apart from each other by 10 micrometers or less.

Preferably, the carbon nanotube powder or nanowire powder may be dispersed in a solvent by a surfactant and applied between the first electrode and the second electrode.

In this case, the solution in which the carbon nanotube powder or the nanowire powder is dispersed may be applied between the first electrode and the second electrode by a spray method. Alternatively, the carbon nanotube powder or the nanowire powder may be dispersed in a stamping method by imposing a solution in which the carbon nanotube powder or the nanowire powder is dispersed in a region formed between the first electrode and the second electrode.

Preferably, the heater may be further provided below the first electrode and the second electrode to maintain the temperature of the gas sensor. In this case, a via penetrating the first electrode or the second electrode and the heater may be further provided, and a bias voltage having a voltage level according to the type of gas to be sensed may be applied to the via.

Preferably, the AC power may be applied at a frequency according to the type of gas to be sensed.

The gas sensor according to the present invention has an advantage of improving sensitivity and reaction speed. In addition, by varying the bias voltage to improve the selectivity for a particular gas, or by varying the frequency of the AC power source can be variously designed according to the needs of the user, such as adjusting the selectivity or recovery rate for a particular gas.

BRIEF DESCRIPTION OF THE DRAWINGS In order to better understand the drawings cited in the detailed description of the invention, a brief description of each drawing is provided.

1 is a view showing a gas sensor according to an embodiment of the present invention.

FIG. 2 is a view for explaining a difference between dropping and spraying a solution in which carbon nanotube powder is dissolved in the gas sensor of FIG. 1.

3 is a view showing that the sensitivity of the gas sensor of FIG. 1 is improved when the carbon nanotube powder is dispersed in the gas sensor of FIG.

4 is a view for explaining a case in which carbon nanotube powder is dispersed in a stamping method in the gas sensor of FIG.

5 is a diagram illustrating an experimental example of a correlation between a gap between a first electrode and a second electrode of the gas sensor of FIG. 1 and a sensitivity of the gas sensor.

6 is a diagram illustrating a relationship between a frequency of an AC power source applied to the gas sensor of FIG. 1 and a sensitivity of the gas sensor of FIG. 1 to nitrogen.

FIG. 7 is a diagram illustrating a correlation between a bias voltage applied to the gas sensor of FIG. 1 and an impedance of carbon nanotube powder.

FIG. 8 is a diagram for describing a chip including the gas sensor of FIG. 1.

9 is a view illustrating a result of performing heat treatment or washing on the chip of FIG. 8.

FIG. 10 is a diagram illustrating a result of increasing sensitivity and recovery speed of a gas sensor when the chip of FIG. 8 is heat-treated at a high temperature.

DETAILED DESCRIPTION In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings which illustrate preferred embodiments of the present invention and the contents described in the drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

Referring to FIG. 1A, which is a cross-sectional view of a gas sensor 100 according to an embodiment of the present invention, the gas sensor 100 according to the embodiment of the present invention includes a substrate 110, an insulating layer 120, The first electrode 130 and the second electrode 140 are provided.

The substrate 110 may be a flexible printed circuit board implemented with a film such as polyimide.

The first electrode 130 and the second electrode 140 are formed on the substrate 110 and spaced apart from each other. An insulating layer 120 may be formed between the first electrode 130, the second electrode 140, and the substrate 110. The first electrode 130 and the second electrode 140 may be made of various materials such as Au, Ti, or an alloy thereof. Since the first electrode 130 and the second electrode 140 are formed on one substrate 110, the manufacturing process may be simplified.

AC power AC may be applied to the first electrode 130 and the second electrode 140.

Referring to FIG. 1A, which is a cross-sectional view of a gas sensor 100 according to an embodiment of the present invention, the first electrode 130 and the second electrode 140 are each inter-digitated with each other. It may include a plurality of first sub-electrodes 132 and the second sub-electrodes 142 formed in a digitated form. That is, the plurality of first sub-electrodes 132 and the second sub-electrodes 142 face each other and are spaced apart from each other, such that the second sub-electrodes 142 are positioned between the first sub-electrodes 132. The first sub electrodes 132 are positioned between the second sub electrodes 142.

In addition, as shown in FIG. 1, the first sub-electrodes 132 may be formed in a comb-like shape integrally formed with the first electrode 130 and extending toward the second electrode 140. Similarly, the second sub-electrodes 142 may be formed integrally with the second electrode 140 and may have a comb-shaped shape extending toward the first electrode 130.

Carbon nanotube powder (CNT) may be distributed between the first electrode 130 and the second electrode 140, that is, between the first sub-electrodes 132 and the second sub-electrodes 142. However, the present invention is not limited thereto, and nanowire powder may be used instead of carbon nanotube powder (CNT). The nanowire is a wire structure having a size in nanometers, and may be applied between the first electrode 130 and the second electrode 140 in the same manner as the carbon nanotube powder (CNT) described below. The impedance can be changed accordingly. Therefore, for convenience of description, hereinafter, only carbon nanotube powder (CNT) will be described. However, those of ordinary skill in the art to which the present invention pertains may easily perform the gas sensor of the present invention using the nanowire powder from the description of the following carbon nanotube powder (CNT).

As described above, when the carbon nanotube is used in a gas sensor, the carbon nanotube can be operated at room temperature, and the impedance change is large even when reacting with harmful gases such as NH ₃ , NO _2, or volatile organic compounds (VOCs). Sensitivity is very good. In addition, there is an advantage that the reaction rate and response rate is fast.

Carbon nanotubes originally have hydrophobic properties because of the structure of carbon nanotubes. However, surface defects of carbon nanotubes have a strong bonding force and thus easily bond with other molecules. Therefore, hydrophobic or hydrophilic properties of the carbon nanotubes can be controlled by surface defects of the carbon nanotubes.

By adjusting the hydrophobic or hydrophilic properties of the carbon nanotubes as described above, the gas sensor using the carbon nanotubes can give a selectivity to a specific gas, it is possible to accurately measure the concentration of various gases.

However, as described above, the gas sensor using the carbon nanotube according to the prior art has a problem that it takes a long time to initialize the sensor after the sensing operation is finished or the sensing sensitivity is lowered.

On the other hand, the gas sensor 100 according to the embodiment of the present invention can reduce the recovery speed (time required for initialization) while increasing the sensitivity. This is described in more detail.

Subsequently, referring to FIG. 1, the carbon nanotube powder CNT dispersed between the first electrode 130 and the second electrode 140 may be applied to the type of gas when AC power is applied. As a result, impedance changes. The impedance change amount of the carbon nanotube powder (CNT) dispersed between the first electrode 130 and the second electrode 140 is measured by a measuring device (not shown) such as an LCR (inductance, capacitance and resistance) meter. Since dispersed carbon nanotubes are in the form of very small tubes with diameters of several tens of nanometers, a strong electric field is applied to the ends. As a result, adsorption of gas molecules on the ends and surfaces of the carbon nanotubes causes large changes in capacitance. Will appear. Thus, by measuring the impedance to be changed, the concentration of the gas can be measured.

Preferably, the carbon nanotube powder (CNT) is DCE (1,2-dichloroethane, [ClCH 2 CH 2 Cl]), SDS (Sodium Dodecyl Sulfate, [CH 3 (CH 2) 11 OSO 3 Na +]) and NaDDBS (Sodium Dodecylbenzene Sulfonate, [CH 3 (CH 2) 11C6H4SO3Na +]), and the like, may be dispersed in a solvent and applied to the first electrode 130 and the second electrode 140. When the carbon nanotube powder (CNT) is dispersed in the solvent by the surfactant, the carbon nanotube powder (CNT) may be evenly applied between the first electrode 130 and the second electrode 140. Therefore, the sensing sensitivity can be improved.

The gas sensor 100 according to the exemplary embodiment of the present invention may apply carbon nanotube powder (CNT) dispersed in a solvent by a surfactant in a spray method. When carbon nanotube powder (CNT) is applied using a spray, it is as shown in (b) of FIG. 2 rather than dropping a solution in which the carbon nanotube powder is dissolved ((a) of FIG. 2). Likewise, carbon nanotube powder (CNT) may be uniformly applied.

Therefore, when the carbon nanotube powder (CNT) is dispersed in a spray method, as shown in FIG. 3 (a), the sensitivity may increase, and as shown in FIG. 3 (b), a recovery time (t) can be reduced. In addition, the spray method has an advantage that the carbon nanotube formation conditions can be precisely adjusted than when the solution in which the carbon nanotube powder is dispersed is dropped.

In addition to dispersing the carbon nanotube powder (CNT) in a spray method, the gas sensor 100 according to an embodiment of the present invention shows the carbon nanotube powder (CNT) dispersed by a surfactant in FIG. As described above, the solution is formed in the shape of hemisphere by the surface tension of the solution in which the carbon nanotube powder is dispersed at the end of the tube by using a tube having an inner diameter similar to that of the electrode, and the solution is formed in the first electrode 130 It can be dispersed in a stamping (stamping) method in the space between the second electrode 140. Carbon nanotube powder (CNT) dispersed in a stamping method, as shown in Figure 4 (a), can be applied quickly, simply and uniformly. This, when dropping the solution drops as shown in Figure 4 (b), by the surface tension (arrow) during the drying process, the carbon nanotube powder (CNT) can solve the problem of dense to the edge of the drop of the solution have. That is, in the case of the stamping method, the carbon nanotube powder (CNT) is evenly distributed, so that the sensitivity of the gas sensor may be improved.

Thus, the gas sensor 100 according to the embodiment of the present invention may improve the sensitivity of the dispersion of the solution in which the carbon nanotube powder (CNT) is dissolved by spraying or stamping.

Referring back to FIG. 1, as the distance between the first electrode 130 and the second electrode, that is, the first sub-electrode 132 and the second sub-electrode 142 is narrower, sensitivity may increase. Referring to FIG. 5, which shows an experimental example of the correlation between the interval between the first electrode 130 and the second electrode 140 and the sensitivity, it can be seen that the sensitivity is increased at about 5 micrometers or less.

In addition, as shown in FIG. 6 showing the relationship between the frequency of the AC power applied to the gas sensor of FIG. 1 and the sensitivity of the gas sensor of FIG. 1 with respect to nitrogen, the specific gas may be improved in sensitivity at a specific frequency. . Gas sensor according to an embodiment of the present invention, by using a characteristic that the specific gas has a good sensitivity and recovery rate at a specific frequency, by checking the sensitivity to the gas at three or more different frequencies, respectively, selectivity to the gas Can have

As such, by differently setting the frequency of the AC power applied to the gas sensor according to the embodiment of the present invention, the sensitivity or the recovery speed for the specific gas can be set.

Referring back to FIG. 1, the gas sensor 100 according to the embodiment of the present invention may further include a heater 150. The heater 150 may be located between the substrate 110 and the electrodes 130 and 140. A current is supplied to the heater 150 to maintain the temperature of the gas sensor 100, thereby improving the sensitivity and reliability of the sensor. The heater mainly uses platinum, which is stable at high temperatures, and may be implemented as a material having a moderate thermal expansion coefficient between the substrate and the heater material, such as titanium (Ti), to solve the problem of peeling off due to the difference in thermal expansion coefficient with the substrate. have.

Preferably, the gas sensor 100 according to the embodiment of the present invention may further include vias 160 connecting the first electrode 130 or the second electrode 140. The gas sensor 100 according to the exemplary embodiment of the present invention may set the gas to be sensed by applying the bias voltage DC to the via 160.

Referring to FIG. 7 showing the correlation between the bias voltage DC and the impedance of the carbon nanotube powder CNT, it can be seen that the type of gas sensed varies according to the magnitude of the bias voltage DC. That is, the sensitivity of a particular gas at a specific bias voltage can be improved. For example, in a section in which the bias voltage is about −2V to 0V, sensitivity to nitrogen dioxide may be improved.

Therefore, the gas sensor 100 according to the exemplary embodiment of the present invention may set the type of gas to be sensed by differently setting the bias voltage DC.

FIG. 8A illustrates an operating power supply (AC, AC) for supplying a voltage to the gas sensor 100 of FIG. 1 and the first electrode 130 and the second electrode 140 of the gas sensor 100 of FIG. 1. ) Shows a chip CIP provided with voltage pads VPAD for supplying the CPAD and heater pads HPAD for supplying the heater operating power or the bias voltage DC to the heater 150 and the bias electrode. The gas sensor 100 may be positioned in the middle of the voltage pads VPAD and the heater pads HPAD. A, b, c, and d of FIG. 1B may be connected to a ', b', c ', and d' of FIG. 8A, respectively. The heater is mainly composed of a platinum resistor that is stable at high temperature and generates heat when a current flows. When the current is supplied to the heater, the heater is heated to generate heat, and when the heater power is controlled, the temperature of the heater can be controlled. In addition, when the heater does not need to be used, the sensor may have a selectivity to gas by applying a bias voltage between the heater pattern and the electrode using the same pad.

The chip CIP of FIG. 8A or the wafer of FIG. 8B may be heated or cleaned. When the chip CIP of FIG. 8A or the wafer of FIG. 8B is heated, as shown in FIG. 9A, the surfactant is removed to increase the reaction and recovery rate of the gas sensor. Faster. Similarly, when the chip CIP of FIG. 8A or the wafer of FIG. 9B is washed with alcohol or water and then thermally treated, as shown in FIG. 9B, the surfactant is removed to form a gas. The response and recovery rate of the sensor is faster.

As described above, the uniformity of the carbon nanotube powder (CNT) applied to the region between the first electrode 130 and the second electrode 140 can have a significant effect on the sensitivity of the sensor.

The chip CIP of FIG. 8A or the wafer of FIG. 8B can also be heat treated using a halogen lamp or the like. By the heat treatment at a high temperature, the sensitivity and reaction speed of the gas sensor as shown in FIG. 10 (a) can be improved as shown in FIG. 10 (b).

The gas sensor according to the present invention has an advantage of improving sensitivity and reaction speed. In addition, by varying the bias voltage to improve the sensitivity to a specific gas, or by varying the frequency of the AC power source can be variously designed according to the needs of the user, such as adjusting the sensitivity or recovery rate.

As described above, optimal embodiments have been disclosed in the drawings and the specification. Although specific terms have been used herein, these terms are only used for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the meaning or claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

The present invention can be used in the field of manufacturing gas sensors.

Claims

A first electrode and a second electrode formed on the substrate, the AC power being applied, and spaced apart from each other; And

And a carbon nanotube powder or nanowire dispersed in a region formed between the first electrode and the second electrode, wherein the impedance of the carbon nanotube powder is changed according to the concentration of the gas.
The method of claim 1, wherein the substrate,

Gas sensor, characterized in that the flexible printed circuit board implemented by a polyimide film (Polyimide film).
According to claim 1,

The first electrode has first sub-electrodes formed integrally with the first electrode and whose ends face the second electrode,

The second electrode has second sub electrodes formed integrally with the second electrode and whose ends face the first electrode.

The first sub electrodes and the second sub electrodes are each other,

And the second sub-electrodes are positioned between the first sub-electrodes to have a comb-shaped inter-digitated shape.
The method of claim 3, wherein the first sub-electrode and the second sub-electrode are each other,

A gas sensor, characterized in that it is spaced apart by less than 10 micrometers.
The method of claim 1, wherein the carbon nanotube powder or nanowire powder,

A gas sensor, which is dispersed in a solvent by a surfactant and applied between the first electrode and the second electrode.
The method of claim 5,

The carbon nanotube powder or the solution in which the nanowire powder is dispersed, the gas sensor, characterized in that the spray is applied between the first electrode and the second electrode (Spray) method.
The method of claim 5,

The gas sensor, characterized in that the dispersion of the carbon nanotube powder or nanowire powder is dispersed in a stamping (stamping) method to the area formed between the first electrode and the second electrode by using a fine tube.
According to claim 1,

And a heater positioned below the first electrode and the second electrode to maintain a temperature of the gas sensor.
The method of claim 8,

And a via penetrating the first electrode or the second electrode and the heater,

And a bias voltage having a voltage level corresponding to a type of gas to be sensed.
The method of claim 1, wherein the AC power source,

Gas sensor, characterized in that applied to the frequency according to the type of gas to be sensed.