KR20110001713A - Carbon-nano-tube gas sensor for detecting ethanol, and manufacturing method thereof - Google Patents

Abstract

PURPOSE: A carbon nano-tube gas sensor for sensing ethanol and a manufacturing method thereof are provided to enhance the reactivity and sensitivity for sensing ethanol using high efficiency of ethanol gas sensor. CONSTITUTION: A carbon nano-tube gas sensor for sensing ethanol comprises a substrate(10), an insulating layer(20), electrodes(30), a carbon nano-tube(40) and a conductive polymer(50). The insulating layer is formed on the substrate. The electrodes are formed on both sides on the insulating layer and are formed from a metallic material. The carbon nano-tube is located between the electrodes. The conductive polymer is coated on the carbon nano-tube. The carbon nano-tube is arranged by the voltage application across the electrodes. The conductive polymer is formed of PEDOT:PSS.

Description

Carbon-nano-tube gas sensor for detecting ethanol, and manufacturing method

The present invention relates to a carbon nanotube gas sensor, and more particularly to a carbon nanotube gas sensor and a manufacturing method for detecting ethanol having high sensitivity to ethanol.

With the recent reports of new physical phenomena and improved material properties in nanometer-sized microspheres, a new field of nanotechnology has emerged, and these nanoscience technologies can lead the 21st century. It is emerging as a future technology in the fields of electronic information communication, medicine, materials, manufacturing process, environment and energy.

Among these nanotechnology fields, carbon nanotubes, in particular, are able to realize new material properties, and thus, the importance of basic research and industrial applicability are receiving great attention at the same time. In general, a carbon nanotube is a carbon allotrope composed of carbon present in a large amount on the earth, and one carbon is combined with another carbon atom in a hexagonal honeycomb pattern to form a tube, and the diameter of the tube is nanometer (nm = 10 billion

It is an extremely small area of matter, on the order of one meter.

Carbon nanotubes have excellent mechanical properties, electrical selectivity, excellent field emission characteristics, high-efficiency hydrogen storage media, and are known to be perfect new materials with few defects in existing materials.

The carbon nanotubes have a graphite sheet rounded to a nano-sized diameter and have a sp2 bonding structure. Depending on the angle and shape of the graphite surface is curled, it is electrically conductive characteristics of the conductor or semiconductor. In addition, carbon nanotubes are classified into single walled nanotubes or multiwalled nanotubes according to the number of bonds forming walls, and bundles of multiple single-walled nanotubes are bundled together. It is called Rope NanoTube.

Therefore, carbon nanotubes are used in electron emitters, vacuum fluorescent displays (VFDs), white light sources, field emission displays (FEDs), lithium ion secondary battery electrodes, hydrogen storage fuel cells, nanowires, and nanocapsules of various devices. , Nano-tweezers, AFM / STM tips, single-electron devices, gas sensors, medical / engineering microcomponents, and high-performance composites.

Carbon nanotubes have excellent mechanical robustness and chemical stability, can exhibit both semiconductor and conductor properties, and have a small diameter and relatively long lengths, making them excellent materials for flat panel displays, transistors, and energy storage. It shows properties, and its applicability as nano-sized various electronic devices is very large.

On the other hand, the term 'nanostructure' material, C 60 fullerene, nanoparticles such as fullerene concentric graphite particles, nanowires / nanorods such as Si, Ge, SiO x, GeO x, or carbon, Bx Ny , Materials including nanotubes consisting of single or multiple elements such as Cx By Nz, MoS2 and WS2.

One of the common features of nanostructured materials is the basic building blocks. One nanoparticle or carbon nanotube is less than 500 nm in size in at least one direction. These types of materials are known to exhibit certain properties that are of interest in many fields and processes. Carbon nanotubes and semiconductor nanowires are recognized as representative materials of next-generation nanodevices due to their unique physical and chemical properties and excellent electrical conductivity.

Nanostructures such as nanotubes and nanowires have a characteristic that the relative surface area / volume ratio is very high so that the influence of surface adsorption can be sensitively reflected in their electrical properties. However, semiconductor nanowires, which have a relatively low surface area ratio compared to carbon nanotubes, have a disadvantage that they are relatively insensitive to molecular adsorption such as adsorption of chemicals. Therefore, sensitivity is only maintained when the temperature of the sensor is high. .

In addition, in the case of strong volatile gas such as ethanol, there is a problem that requires a more sensitive reactivity, and a device having a high surface cross-sectional area as a sensor tip and a high reactivity to the gas such as ethanol.

An object of the present invention for solving the above problems is to provide a high-efficiency gas sensor having a high reactivity, sensitivity and reactivity for detecting ethanol, manufacturing a gas sensor having a high efficiency with a simple and easy manufacturing method To provide a way to do it.

A first aspect of the present invention for solving the above problems is a substrate; An insulating layer formed on the substrate; Electrodes formed on both sides of the insulating layer and made of metal; Carbon nanotubes disposed on the insulating layer between the electrodes; And a conductive polymer coated on the carbon nanotubes.

Here, the carbon nanotubes are preferably arranged by applying a voltage across the electrode, and the conductive polymer is preferably PEDOT: PSS.

And, a carbon nanotube gas sensor manufacturing method, the second aspect of the present invention comprises the steps of forming an insulating layer on the substrate; Forming bar electrodes on both sides of the insulating layer; Arranging carbon nanotubes on the insulating layer between the electrodes by electrophoresis; And spin coating a conductive polymer on the carbon nanotubes.

Here, the step of arranging the carbon nanotubes, (a) preparing a carbon nanotube dispersion; (b) injecting a substrate on which the electrode is formed into the carbon nanotube dispersion; (c) applying an alternating voltage to both electrodes to form a carbon nanotube bridge; (d) It is preferred to include the step of removing the device from the dispersion, washing and drying.

In addition, preferably the dispersion of step (a) is preferably prepared by a method of sonicating carbon nanotubes in dichloroethane (Dichloroethane), repeating steps (c) and (d) In this case, it is preferable to form the resistance measured at both electrodes at 100 kPa to 500 kPa, and it is preferable to spin coat using the conductive polymer as PEDOT: PSS.

According to the present invention, it is possible to provide a high-efficiency entanol gas sensor with a structure that increases surface area much more than nanotips having the same size as nanowires and simultaneously uses high reactivity with respect to ethanol of a conductive polymer.

In addition, a high-efficiency gas sensor can be easily manufactured by using a carbon nanotube tip arranged at a high density and a conductive polymer that increases reactivity to ethanone.

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

1 is a perspective view and a photograph showing the configuration of a carbon nanotube sensor for detecting ethanol according to the present invention. As shown in FIG. 1, the sensor of the present invention includes a substrate 10, an insulating layer 20 formed on an upper surface of the substrate 10, a rod-shaped electrode 30 formed on both sides of the insulating layer 20, and the electrode ( Between 30) is made of a structure in which the carbon nanotubes 40 coated with the conductive polymer 50 is arranged.

Increasingly, many kinds of gas are monitored and monitored daily. In particular, ethanol gas containing alcohol as a volatile substance is often measured. For example, small amounts of ethylene, ethanol, and aldehydes are generated in vegetables and fruits from the beginning, mercaptans are generated from the time of vegetable and fruit decay, and amines such as ammonia are produced from the time of fruit decay. I know that.

As a result, gas or ethylene, ethanol, or aldehyde is effective for detecting freshness of vegetables and fruits, and amines such as mercaptans and ammonia are effective for detecting corruption of vegetables and fruits.

Accordingly, the present invention proposes a carbon nanotube 40 gas sensor for ethanol measurement, and as illustrated in FIG. 1, the tip size for measurement is nanoscale and uses a carbon nanotube 40 having a large surface area. When the carbon nanotube 40 is coated with a conductive polymer 50 such as PEDOT: PSS and formed on a semiconductor device, it becomes a gas sensor exhibiting a sensitive reaction to ethanol.

Here, PEDOT: PSS is a high-tech material used for various display electronic devices such as LEDs, OLEDs, and LCDs as a conductive polymer, and is a high-tech material device having both advantages of being easy to handle due to the flexibility and flexibility of the polymer 50 and having advantages of conductivity.

As shown in FIG. 1A, an insulating layer 20 is formed on a substrate 10, rod-shaped electrodes 30 are formed on both sides of the insulating layer 20, and between the electrodes 30. Carbon nanotubes 40 coated with the conductive polymer 50 form a structure arranged. Such a structure has a much higher surface area than nanotips of the same size, such as nanowires of carbon nanotubes 40, and provides a highly efficient ethanol gas sensor with a structure that simultaneously uses high reactivity with respect to ethanol of the conductive polymer 50. It becomes possible.

FIG. 1B is a SEM photograph showing the gas sensor element corresponding to FIG. 1A. The carbon nanotubes 40 arranged in the center are more highly aligned than the carbon nanotubes 40 arranged by the conventional spin coating method, and are hardly shown where they are clustered. It can be seen that the sensor.

2 is a view illustrating a manufacturing process of the carbon nanotube 40 gas sensor according to the present invention. As shown in FIG. 2, the manufacturing method according to the present invention includes the steps of forming an insulating layer 20 on a substrate 10; Forming rod-shaped electrodes (30) on both sides of the insulating layer (20); Arranging carbon nanotubes 40 on the insulating layer 20 between the electrodes 30 by electrophoresis; And spin coating the conductive polymer 50 on the carbon nanotubes 40.

Herein, the substrate 10 uses the silicon substrate 10 as the semiconductor substrate 10, uses silicon dioxide (SiO ₂ ) as the insulating layer 20, and as the electrode 30, such as gold (Au). The material is made of high conductive material. In the structure of the semiconductor device, the field effect transistors having both electrodes 30 serving as drain and source electrodes 30 and the gate electrode 30 of the substrate 10 positioned under the insulating layer 20 ( FINFET).

That is, when the tip of the carbon nanotube 40 located above the active region reacts with the gas to be measured (ethanol gas), a sudden change in device resistance occurs, and a change in current flow of the semiconductor device occurs due to the change in resistance. It is a structure which detects gas.

As shown in FIG. 2, first, an insulating layer 20 such as silicon dioxide is deposited on the substrate 10 ((a) and (b) of FIG. 2), and rod-shaped electrodes on both sides of the insulating layer 20 are provided. 30 is formed by a general photolithography method (FIG. 2C). Then, the carbon nanotubes 40 are arranged on the insulating layer 20 between the rod-shaped electrodes 30 by an electrophoretic method. 2 (d), the conductive polymer 50 (PEDOT: PSS) is spin-coated on the carbon nanotubes 40 to complete the final device.

Here, the arrangement method of the carbon nanotubes 40 by the electrophoresis method (a) preparing a dispersion of carbon nanotubes (40); (b) injecting the substrate 10 on which the electrode 30 is formed into the carbon nanotube 40 dispersion; (c) applying an alternating voltage to both electrodes 30 to form a carbon nanotube 40 bridge; And (d) removing the device from the dispersion, and washing and drying the device.

The carbon nanotube 40 dispersion is prepared by putting the carbon nanotube 40 in dichloroethane (CH ₂ ClCH ₂ Cl) and performing ultrasonic treatment for about 20 hours. After dipping the substrate 10 on which the electrode 30 is formed in the carbon nanotube 40 dispersion prepared as described above, the carbon nanotube 40 is applied to both electrodes 30 by applying an alternating voltage as shown in FIG. Form a bridge.

Then, the device is taken out of the dispersion, washed in ethanol and dried, and the baking is carried out at 80 degrees for about 30 minutes to remove the dispersion on the device. This process is repeated several times so that the resistance of the device can be expressed as a value between 100 kW and 500 kW. The resistance can be adjusted by adjusting the time for applying the alternating voltage to both electrodes 30, but the longer the time, the more the carbon nanotubes 40 are arranged and the resistance decreases. Therefore, it is a matter of course that various conditions of the process can be changed to make an element of a necessary resistance.

3 is a photograph comparing the case where the carbon nanotubes 40 are arranged by the spin coating method (FIG. 3A) and the case where the carbon nanotubes 40 are arranged by the electrophoresis method (FIG. 3B). As shown in (a) of FIG. 3, when the carbon nanotubes 40 are raised by the conventional spin coating method, the carbon nanotubes 40 agglomerated in the dispersion phase act largely on the resistance of the device to detect external environmental changes. Contact cross-sectional area of the polymer 50 to the carbon nanotubes 40 which form a resistance when coated for the polymers 50 due to the inefficient surface and the state of the carbon nanotubes 40 overlapping and entangled with each other. This has the disadvantage of being smaller.

On the other hand, as shown in Figure 3 (b), the electrophoresis method applied to the present invention because only the well-dispersed carbon nanotubes 40 are arranged regularly between the electrodes 30 without entanglement, the contact area is increased, It is more sensitive to the external environment than the spin coating method, and makes the carbon nanotube 40 arrangement more effective for coating the polymer 50.

 4 is a comparative graph illustrating a change in resistance to ethanol of a sensor coated with a conductive polymer 50 only on a substrate 10 and a gas sensor according to the present invention. Figure 4 (a) is a graph showing a resistance change in response to ethanol for a sensor formed by spin coating PEDOT: PSS at 3000rpm for 60 seconds on a conventional substrate 10, Figure 4 (b) the present invention The carbon nanotube 40 according to the gas sensor is a graph showing the resistance change appeared by reacting with ethanol.

As shown in FIG. 4A, the reaction of ethanol to the conductive polymer 50 layer shows that the error is very large and the resistance is very large, as shown in FIG. 4B. It can be seen that the reactivity is reduced, the error is reduced, and the reaction result is much more stable.

While the invention has been shown and described with respect to the specific embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Anyone with it will know easily.

1 is a perspective view and a photograph showing the configuration of a carbon nanotube sensor for detecting ethanol according to the present invention;

2 is a view illustrating a manufacturing process of a carbon nanotube 40 gas sensor according to the present invention;

3 is a photograph comparing the case where the carbon nanotubes 40 are arranged by the spin coating method (FIG. 3A) and the case where the carbon nanotubes 40 are arranged by the electrophoresis method (FIG. 3B).

4 is a comparative graph illustrating a change in resistance to ethanol of a sensor coated with a conductive polymer 50 only on a substrate 10 and a gas sensor according to the present invention.

Claims (8)

Board; An insulating layer formed on the substrate; Electrodes formed on both sides of the insulating layer and made of metal; Carbon nanotubes disposed on the insulating layer between the electrodes; And Carbon nanotube gas sensor, characterized in that it comprises a conductive polymer coated on the carbon nanotubes. The method of claim 1, The carbon nanotube gas sensor, characterized in that arranged by applying a voltage across the electrode. The method of claim 1, The conductive polymer is a carbon nanotube gas sensor, characterized in that the PEDOT: PSS. Forming an insulating layer on the substrate; Forming bar electrodes on both sides of the insulating layer; Arranging carbon nanotubes on the insulating layer between the electrodes by electrophoresis; Carbon nanotube gas sensor manufacturing method comprising the step of spin coating a conductive polymer on the carbon nanotubes. The method of claim 4, wherein Arranging the carbon nanotubes, (a) preparing a carbon nanotube dispersion; (b) injecting a substrate on which the electrode is formed into the carbon nanotube dispersion; (c) applying an alternating voltage to both electrodes to form a carbon nanotube bridge; (d) removing the device from the dispersion, and washing and drying the carbon nanotube gas sensor. The method of claim 5, The dispersion of step (a), Carbon nanotube gas sensor manufacturing method characterized in that the carbon nanotubes are prepared by a method of ultrasonication by putting in dichloroethane. The method of claim 5, Repeating steps (c) and (d) to form a resistance measured at both electrodes to form a carbon nanotube gas sensor. The method according to any one of claims 4 to 7, Carbon nanotube gas sensor manufacturing method characterized in that the spin coating using the conductive polymer as PEDOT: PSS.

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