KR20070002111A - Semiconductor nano-element - Google Patents

Abstract

A semiconductor nano device is provided to improve sensitivity of a gas sensor and to reduce sensor size by coating metal nano particles on a surface of a carbon nanotube transistor. An alignment marker is formed on a SiO2/Si substrate(10). A pattern of liquid catalyst is manufactured using a PMMA(polymethylmethacrylate) layer on the SiO2/Si substrate that is insulated by a SiO2 layer. The PMMA layer is removed by an acetone solution. A single walled carbon nanotube(14) is grown at CH4 and H2 atmosphere during 10 minutes in a furnace of 900 ‹C. An electrode(12) is formed by performing photolithography and thermal evaporation on the carbon nanotube, thereby configuring a carbon nanotube transistor. A metal nano particle(16) is coated on a surface of the carbon nanotube transistor.

Description

Semiconductor nano-element

1 is a schematic view showing a carbon nanotube transistor sensor coated with metal nanoparticles according to the present invention.

2 is a schematic view showing a carbon nanotube transistor fabrication process and a metal nanoparticle coating process according to the present invention.

Figure 3a is an enlarged photograph of a portion of the carbon nanotube transistor according to the present invention with an optical microscope.

3b is an enlarged photograph of a portion of a carbon nanotube transistor according to the present invention by an atomic force microscope.

Figure 4 is a graph showing the change in electrical properties according to different metal nanoparticles coated on the carbon nanotube transistor according to the present invention.

5 is a graph showing a gas reaction of a Pd-coated carbon nanotube transistor.

6 is a graph showing the electrical characteristics and gas reaction characteristics of Al-coated carbon nanotube transistors.

Figure 7 is a graph showing the coating effect of the metal nanoparticles in the semiconductor nanowires GaP nanowires.

8 is a graph showing a gas reaction of a sensor coated with Pd nanoparticles on a GaP nanowire transistor.

9 is a graph and a schematic diagram showing the principle that the gate effect is lost when the Pd nanoparticles coated on the carbon nanotube transistor.

10 is a schematic diagram showing the effect of adsorption of metal nanoparticles on the electrical properties of carbon nanotubes or semiconductor nanowires.

<Description of the symbols for the main parts of the drawings>

10 silicon substrate 12 electrode

14 carbon nanotube 16 metal nanoparticle

The present invention relates to a semiconductor nanodevice, and more particularly, in the fabrication of an electrical sensor manufactured using nanostructures such as carbon nanotubes and semiconductor nanowires, the sensitivity of the semiconductor nanodevices is obtained by using a simple metal nanoparticle coating process. It relates to a semiconductor nanodevice that can be increased.

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 =). One billionth of a meter) is an extremely small area of matter.

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 sp ² bond 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 a wall, 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, MoS ₂ and WS ₂ .

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. .

Recently, Kolmakov et al. Have researched to improve the sensitivity of the sensor by coating Pd metal nanoparticles on SnO ₂ nanowires and nanobelts. I couldn't.

The present invention has been made in view of the above, and by coating the surface of the nanostructure transistor with metal nanoparticles having different work functions according to the major carrier (charge transporter) type of the nanostructure to change the electrical properties of the nanostructure Or, to provide a semiconductor nano-device that can be coated on the surface of the nano-structure transistor metal nanoparticles that act as a catalyst to improve the molecular adsorption, that is, the sensitivity to gases such as NO ₂ , NH _3, etc. .

The present invention for achieving the above object is a semiconductor device in which a nanostructure is formed in a channel,

The channel is coated with metal nanoparticles having different work functions.

In a preferred embodiment, it is characterized in that the metal nanoparticles are coated on the channel as a catalyst.

In a more preferred embodiment, the nanostructure is any one of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanotube bundles and semiconductor nanostructures (nanoribbons, nanorods, nanotubes, nanowires, nano-orings, etc.) Is selected.

In addition, the coating of the nanoparticles is characterized by consisting of any one of the methods of deposition, chemical / physical adsorption, spin coating, adsorption using an electrochemical reaction and immobilization using self-assembly.

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

1 is a schematic view showing a carbon nanotube transistor sensor coated with metal nanoparticles according to the present invention.

According to the present invention, the surface of a nanostructure transistor is coated with metal nanoparticles 16 having a high (or low) work function according to the properties of the nanostructure, thereby reducing the number of charge transporters in the nanostructure, thereby reducing the sensitivity of the transistor sensor using the nanostructure. The main point is to increase the sensitivity of the sensor by increasing the or by using the catalytic role of the metal nanoparticles.

As shown in FIG. 1, the present invention relates to carbon nanotubes 14 grown directly on a silicon substrate 10, source and drain electrodes 12 connected to both ends of the carbon nanotubes 14, and sensitivity. It is composed of coated metal nanoparticles 16 to improve.

The present invention may use nanostructures such as semiconductor nanowires, nanobelts, and nanorods in addition to the carbon nanotubes 14, and the metal nanoparticles 16 are coated on the channel portion of the transistor using the same.

First, in the case of a sensor using a carbon nanotube transistor that operates as a p-type semiconductor at room temperature, carbon nanoparticles (Al) having low work function may be carbon so that adsorption of the metal nanoparticles 16 attracts and depletes surrounding holes. The channel of the nanotubes 14 is coated.

In the case of GaP nanowire transistors operating as n-type semiconductors, metal nanoparticles (Pd) having a large work function are added to the channel portion of the nanowire transistor so that adsorption of the metal nanoparticles 16 attracts and depletes surrounding electrons. Coating.

As described above, due to the depletion of the charge transporter due to the adsorption of the metal nanoparticles 16, the electrical conductivity of each of the nanostructure transistors tends to decrease, and accordingly, the response to external stimuli such as molecular adsorption is also large.

The sensitivity enhancement technology of the semiconductor nanodevice of the present invention first plays a key role in improving the back gate and sensitivity using the carbon nanotube 14 or the semiconductor nanostructure, the source and drain electrodes 12 and the silicon substrate 10 connected thereto. It consists of metal nanoparticles (16) coated on the surface of the nanostructure to be performed.

Referring to the manufacturing process of the carbon nanotube transistor according to the present invention.

2 is a schematic view showing a carbon nanotube transistor fabrication process and a metal nanoparticle coating process according to the present invention.

① Alignment markers are formed on the SiO ₂ / Si substrate 10.

② A pattern in which a liquid catalyst remains on the silicon substrate 10 insulated with SiO ₂ layer using PMMA.

③ The silicon substrate 10 reacted with the liquid catalyst is immersed in acetone solution to remove the PMMA layer.

④ Grow single-walled carbon nanotubes (14) for 10 minutes in a CH ₄ , H ₂ atmosphere in a 900 ° C furnace.

⑤ The electrode 12 is formed on the grown carbon nanotubes 14 by photolithography and thermal evaporation to manufacture a one-step transistor.

⑥ The metal nanoparticles are coated on the surface of the carbon nanotube transistor thus manufactured by thermal evaporation or chemical reaction.

FIG. 3A is an enlarged photograph of a portion of a carbon nanotube transistor according to the present invention by an optical microscope, and FIG. 3B is an enlarged photograph of a portion of the carbon nanotube transistor according to the present invention by an atomic force microscope. .

Hereinafter, the present invention will be described in more detail with reference to Examples. It will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples.

Example

First, the Fe / Mo catalyst solution was sprayed and lifted off on the PM ₂ patterned SiO ₂ / Si substrate (10), followed by a single wall for 10 minutes in a CH ₄ , H ₂ atmosphere at a 900 ° C furnace. The carbon nanotubes 14 are grown.

After forming an electrode pattern on the substrate 10 on which the carbon nanotubes 14 were grown by photolithography, 5 nm of Ti and 30 nm of Au were continuously deposited without breaking a vacuum by thermal evaporation. Subsequently, the sample is immersed in acetone solution to remove metal from unwanted portions to complete the carbon nanotube transistor.

In the case of a semiconductor nanowire (GaP) transistor, nanowires dispersed in an organic solvent are placed on a substrate having a coordinate system, and then the positions of the respective nanowires are confirmed, and the electrodes 12 are formed using e-beam lithography, or the magnetic The transistor is fabricated by placing the nanowire at a desired position using an assembly membrane or a microfluidic tube and then forming an upper electrode.

The metal nanoparticles 16 are coated on the carbon nanotube transistors or semiconductor nanowire transistors fabricated as described above using simple deposition or chemical reduction.

When the metal nanoparticles 16 were coated by the deposition method, a metal film having an average thickness of 0.2 to 0.5 nm was deposited at a high vacuum of 10 ⁻⁶ or less. In the case of the chemical reduction method, a solution containing metal ions was coated on the transistor sample. The metal nanoparticles 16 were coated by heat treatment at about 400 ° C.

Experimental Example

In order to evaluate the electrical characteristics of the carbon nanotube transistor and the semiconductor nanowire manufactured according to the above embodiment, the change of the current according to the change of the gate voltage at a constant bias voltage (1V) was measured.

Figure 4 is a graph showing the change in electrical properties according to different metal nanoparticles coated on the carbon nanotube transistor according to the present invention.

4 (a) shows the electrical properties of the carbon nanotube transistor coated with Pd nanoparticles, Figure 4 (b) shows the electrical properties of the carbon nanotube transistor coated with Al nanoparticles.

As shown in (a) of FIG. 4, first, the Pd-coated carbon nanotube transistor completely loses the change due to the gate voltage after the Pd coating in the (black line) sample, which exhibits obvious semiconductor characteristics (red line). Was observed. That is, when the Pd nanoparticles are coated, the semiconductor carbon nanotubes no longer react to the gate.

In addition, it can be seen that the current value when the gate voltage is not applied, that is, when the gate voltage is 0, is significantly increased compared to before the Pd coating.

9 is a graph and a schematic diagram showing the principle that the gate effect is lost when the Pd nanoparticles coated on the carbon nanotube transistor, Figure 10 is the effect of the adsorption of metal nanoparticles on the electrical properties of carbon nanotubes or semiconductor nanowires It is a schematic diagram showing.

As shown in FIG. 9, the carbon nanotube transistors surface-modified with Pd nanoparticles by the metal nanoparticles 16 screening the electric field of the gates do not respond to changes in the gate voltage.

In addition, as shown in FIG. 10, when the metal nanoparticles (Pd) 16 having a high work function are adsorbed onto the surface of the carbon nanotubes or the semiconductor nanowires, the metal nanoparticles having a high work function are emitted from the carbon nanotubes 14. As the electrons transition towards the particles 16, the electrical conductivity increases for the carbon nanotubes 14 operating as the p-type semiconductor, and for the n-type nanowire transistors.

On the contrary, when the metal (Al) having a low work function is immobilized on the surface of the carbon nanotube 14 or the semiconductor nanowire, electrons move from the metal nanoparticle 16 toward the carbon nanotube 14 or the semiconductor nanowire. In the case of the p-type carbon nanotubes 14, the electrical conductivity decreases, and in the case of the n-type nanowires, the electrical conductivity increases.

Unlike completely losing the change in gate voltage when the Pd nanoparticles are coated, as shown in FIG. 4 (b), the gate effect is maintained in the carbon nanotube transistors coated with Al nanoparticles, and the Al nanoparticles are maintained. After coating of the particles (red curve) it can be seen that the electrical conductivity values of the carbon nanotube transistors decrease.

4A and 4B show AFM images of carbon nanotubes coated with Pd and Al nanoparticles, respectively. It can be seen that the metal nanoparticles 16 are adsorbed in small lumps on the surface of the carbon nanotubes 14.

Next, the gas sensor characteristics of the carbon nanotube transistor coated with the metal nanoparticles 16 were investigated.

5 is a graph showing gas reaction characteristics of Pd-coated carbon nanotube transistors.

The carbon nanotubes 14 are known to exhibit a sensitive reaction to NO ₂ and NH ₃ by themselves, and after the coating of Pd nanoparticles, they still react with similar sensitivity to NO ₂ and NH ₃ gases. (Red curve).

However, Pd-coated carbon nanotubes 14 have a sensitive reaction to hydrogen gas, while general carbon nanotube transistors do not react at all with hydrogen gas.

Figure 5 (b) is a graph showing the reaction of the Pd-coated carbon nanotube transistor to the hydrogen gas of 100ppm concentration.

As shown in (b) of FIG. 5, as soon as the hydrogen gas flows into the gas chamber, the electrical conductivity decreases. On the contrary, when the hydrogen gas inflow is cut off, the electrical conductivity value is restored.

This reaction can be explained by the fact that Pd nanoparticles lower their work function while dissociating hydrogen molecules into hydrogen atoms.

That is, since the Pd nanoparticles adsorbed on the carbon nanotubes 14 and giving the hole doping effect react with hydrogen molecules to lower the work function, the hole doping effect is lowered, thereby reducing the electrical conductivity of the carbon nanotubes 14.

However, the effect of dissociated hydrogen atoms adsorbed on the surface of the carbon nanotubes 14 to transfer electrons to the carbon nanotubes 14 cannot be completely excluded. Therefore, it can be seen that the Pd nanoparticles here acted as a catalyst to enhance the reaction to hydrogen.

Next, the gas sensor response was measured when the Al nanoparticles were immobilized on the carbon nanotube transistor.

6 is a graph showing the electrical characteristics and gas sensor response of Al-coated carbon nanotube transistors.

As shown in FIG. 6 (a), it was observed that a large number of samples showed diode-like properties after Al nanoparticle coating.

In addition, it can be seen that as time passes, the gate threshold voltage gradually shifts toward the positive gate voltage, which is due to the effect of relatively increasing the work function as the oxidation of Al nanoparticles progresses with time.

The gas sensor reaction of the Al nanoparticle-coated carbon nanotube transistor is shown in FIG. 6 (b). As shown in FIG. 6 (b), it can be seen that a sample that exhibited about 2.5 times the sensitivity before coating the Al nanoparticles (black line) reacted with a sensitivity of 100 times or more (red line) after Al nanoparticle coating.

In addition, the coating of the metal nanoparticles 16 above was applied to the semiconductor nanowire transistor sensor.

Figure 7 shows the electrical properties of the GaP nanowires used in the experiment.

As shown in Fig. 7A, the GaP nanowires operate as n-type semiconductors having high current values at positive gate voltages. In this case, in order to increase the sensitivity of the GaP nanowire sensor, which is an n-type transistor, Pd nanoparticles, which are metal having a high work function, were used.

Figure 7 (b) is a graph showing the electrical properties of the GaP nanowires before and after the Pd nanoparticles are coated.

As shown in FIG. 7 (b), it can be seen that coating the Pd nanoparticles having a high work function brings about a depletion effect of charge, thereby significantly reducing the electrical conductivity (blue line).

Next, the gas sensor operation of the GaP transistor sensor surface-modified with Pd nanoparticles was tested.

Prior to surface modification with Pd nanoparticles, GaP nanowires showed little response to NO ₂ , NH ₃ and H ₂ gases.

8 shows the gas reaction of GaP nanowire sensors surface-modified with Pd nanoparticles.

As shown in FIG. 8 (a), the GaP nanowire sensor surface-modified with Pd nanoparticles shows that the electrical conductivity decreases when 100 ppm NO ₂ gas is introduced, and the electrical conductivity increases for NH ₃ .

In addition, as shown in FIG. 8 (b), it can be seen that the electrical conductivity increases with respect to 100 ppm hydrogen gas. This phenomenon can be explained by the increase in the electrical conductivity when reacted with the NH ₃ gas of reducing gas in the GaP nanowire of the n-type semiconductor, and the reduction in electrical conductivity when reacting with NO ₂ of the oxidizing gas.

In addition, since Pd nanoparticles react with hydrogen to lower the work function, the electron depletion region of GaP nanowires may be reduced when reacting with hydrogen gas, thereby increasing electrical conductivity.

Carbon nanotubes 14 that can be used in the present invention may be selected from single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon nanotube bundles, etc. In addition, transistors using semiconductor nanostructures and metal oxide nanostructures Nanostructures (nanoribbons, nanorods, nanotubes, nanowires, nano-orings, etc.) used here include GaP, GaN, Si, InP, InAs, GaAs, ZnO, TiO ₂ , SnO _2, etc. .

The material coated on the channel is not only metal nanoparticles having different work functions, but also metal nanoparticles which perform a catalytic role, an oil which can deplete or accumulate charge carriers of a nanostructure transistor by charge transport phenomenon or oxidation and reduction. Inorganic compounds, biomolecules, DNA, RNA and recombinant proteins may also be applicable.

As described above, according to the semiconductor nano device according to the present invention, by coating the metal nanoparticles on the surface of the carbon nanotube transistor or semiconductor nanowire transistor sensor to improve the sensitivity of the gas sensor, a high sensitivity sensor without a separate heating wire It can be used as a military purpose sensor that requires not only reduction of power consumption but also small size of sensor itself and rapid detection of trace amount of gas.

In addition, the process is very simple and inexpensive and excellent in effect, it can be applied to transistor sensors, gas sensors and biosensors using various nanostructures.

Claims (4)

In a semiconductor device in which a nanostructure is formed in a channel, A semiconductor device, characterized in that the metal nanoparticles with different work functions are coated on the channel. The semiconductor device according to claim 1, wherein metal nanoparticles serving as catalysts are coated on the channel. The method of claim 1, wherein the nanostructure is any one of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanotube bundles and semiconductor nanostructures (nanoribon, nanorods, nanotubes, nanowires, nano-oring, etc.) A semiconductor device, characterized in that selected. The semiconductor according to claim 1 or 2, wherein the coating of the nanoparticles is performed by any one of deposition, chemical / physical adsorption, spin coating, adsorption using an electrochemical reaction, and a high purification method using self-assembly. Nano device.

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