KR100692916B1 - Carbon nanotube transistor with SU-8 resist coated in electrode - Google Patents

Abstract

The present invention relates to a carbon nanotube transistor having a deformation electrode, and more particularly, a stable p-dope is applied to a carbon nanotube transistor by coating SU-8, a easily patternable negative photoresist, on the electrode portion of the carbon nanotube transistor. The invention relates to a carbon nanotube transistor having a strained electrode capable of inducing and insulating the electrode for use as a biosensor.

To this end, the present invention is a carbon nanotube transistor comprising a source electrode and a drain electrode in electrical contact with each end of the carbon nanotube, respectively,

Provided is a carbon nanotube transistor having a modified electrode, characterized in that the electrode is coated with any one of a photoresist, a low molecular self-assembled film and other polymers.

SU-8 negative photoresist, carbon nanotube, transistor, low molecular self-assembled film, polymer

Description

Carbon nanotube transistor with strain electrode {Carbon nanotube transistor with SU-8 resist coated in electrode}

1A is a schematic view showing a carbon nanotube transistor coated with an SU-8 resist on an electrode according to the present invention.

Figure 1b is a structural diagram showing the chemical structure of the SU-8 resist coated on the electrode of the carbon nanotube transistor according to the present invention.

2 is a block diagram showing a mask pattern for selectively coating a SU-8 resist on the electrode of the carbon nanotube transistor according to the present invention.

Figure 3 is a schematic diagram showing the manufacturing process of the carbon nanotube transistor coated with the SU-8 resist on the electrode according to the present invention.

4 is an enlarged photograph of a portion of a carbon nanotube transistor coated with an SU-8 resist on an electrode according to the present invention with an optical microscope.

5 is an enlarged photograph of a portion of a carbon nanotube transistor coated with an SU-8 resist on an electrode according to the present invention by an atomic force microscope.

6 is a graph showing the electrical properties before and after the SU-8 resist is coated on the electrode in the carbon nanotube transistor according to the present invention.

7 is a graph showing the insulating properties of the carbon nanotube transistor coated with the SU-8 resist on the electrode according to the present invention.

8 is a state diagram showing a change in the size of the Schtky barrier according to the change in the work function of the metal generated by the SU-8 resist is adsorbed on the electrode.

Figure 9 is a graph showing the electrical changes generated by the adsorption of aminoethanthiol (aminoethanthiol) to the electrode.

10 is a graph showing the electrical properties of a device treated with aminoethanethiol on one electrode.

Fig. 11 is a schematic diagram showing the change in work function and band diagram due to adsorption of aminoethanethiol on the electrode;

<Description of Symbols for Main Parts of Drawings>

10 substrate 12 electrode

14 carbon nanotube 16: SU-8 negative photoresist

The present invention relates to a carbon nanotube transistor having a deformation electrode, and more particularly, a stable p-dope is applied to a carbon nanotube transistor by coating SU-8, a easily patternable negative photoresist, on the electrode portion of the carbon nanotube transistor. The invention relates to a carbon nanotube transistor having a strained electrode capable of inducing and insulating the electrode for use as a biosensor.

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 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.

Meanwhile, carbon nanotubes are recognized as representative materials of next-generation nanodevices due to their unique physical and chemical properties and excellent electrical conductivity, and are sensitive to the adsorption of specific gas particles, biomolecules or organic molecules as a representative application field of the nanodevices. Nanosensors that detect

It is well known that carbon nanotube transistors generally act as p-type semiconductors by oxygen doping of the channel, but the negative gate voltage is mainly due to the threshold voltage at which the current turns turn on towards the negative gate voltage. There is a problem that can operate as a sensor only after.

Therefore, the development of a new technology capable of stable p-doped carbon nanotubes is an essential element in the application of carbon nanotubes.

P-doped carbon nanotube transistors can be chemically doped to the channel or reduced by the Schottky barrier by employing a metal with a large work function as the electrode material of the transistor. Doping is possible.

In the former case, a doping method of carbon nanotubes capable of stably and continuously doping has not been developed, and has a disadvantage of being inadequate due to the possibility of changing the sensor characteristics of the doped carbon nanotubes.

In the latter case, Pd is already well-received as a metal that can minimize the Schottky barrier size, and there is a research showing that the coating of PMMA (polymethylmetaacrylate) on the whole nanotube increases the p-doping effect.

The present invention has been made in view of the above, and by coating the SU-8 negative photoresist on the electrode of the carbon nanotube transistor, the effective hole doping to the carbon nanotube by increasing the threshold voltage to a positive gate voltage At the same time, an object of the present invention is to provide a carbon nanotube transistor having a strained electrode in which the SU-8 negative photoresist layer forms an excellent insulating film so that the SU-8 negative photoresist layer can be used as an electric biosensor.

The present invention for achieving the above object is a carbon nanotube transistor comprising a source electrode and a drain electrode in electrical contact with both ends of the carbon nanotube, respectively,

The electrode is coated with any one of a photoresist, a low molecular self-assembled film and other polymers.

In a preferred embodiment, the carbon nanotubes are any one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanotube bundles.

In a more preferred embodiment, the material coated on the electrode is characterized in that any one of all the adsorbates that can exhibit insulating properties.

In addition, the electrode coating film is characterized in that formed by any one method of lithography, spin coating, inkjet printing or self-assembled film.

In addition, the electrode coating film is characterized by using a polymer that can effectively modify the work function of the electrode, a self-assembled film of organic molecules, a photoresist, an electron beam resist.

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

FIG. 1A is a schematic view showing a carbon nanotube transistor coated with an SU-8 resist on an electrode according to the present invention, and FIG. 1B is a chemistry of a SU-8 resist coated on an electrode of a carbon nanotube transistor according to the present invention. It is a structural diagram which shows a structural formula.

According to the present invention, the SU-8 negative photoresist 16 is coated on the electrode 12 of the carbon nanotube transistor to be adsorbed on the metal surface to effectively increase the work function of the metal, and to serve as an insulating film. There is a point.

The carbon nanotube transistor of the present invention is composed of a carbon nanotube 14 located between two electrodes 12 and a SU-8 negative photoresist 16 coated on the electrode 12.

The SU-8 negative photoresist 16 coated on the electrode 12 of the carbon nanotube transistor protects the electrode 12 from various organic molecules and other adsorbates and serves as an insulating film. Induce hole doping in 14) to increase the threshold voltage.

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

3 is a schematic diagram showing a manufacturing process of a carbon nanotube transistor coated with an SU-8 resist on an electrode 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) A transistor is fabricated by attaching the electrode 12 to the carbon nanotubes 14, and the SU-8 negative photoresist 16 is coated to form an insulating film.

At this time, the mask for forming the SU-8 negative photoresist 16 insulating film is shown in Figure 2 the contact pad for the SU-8 negative photoresist (16) layer wiring with the outside (contact pad) You can see that it takes the form of wrapping the rest except for).

4 is an enlarged optical micrograph of a portion of the carbon nanotube transistor manufactured as described above. As shown in FIG. 4, it can be seen that only the channel portion between the electrodes is exposed and the remaining portion is coated with the SU-8 negative photoresist.

FIG. 5 is an enlarged photograph of a portion of the carbon nanotube transistor manufactured by such a process by an atomic force microscope, in which one single wall nanotube is caught between electrodes. Can be.

When the SU-8 negative photoresist 16 is coated and heat treated on the source (drain) electrode 12 of the carbon nanotube transistor by the fabrication process as described above, the SU-8 negative photoresist 16 is formed of various organic solvents. And an insulating film which is stable against the penetration of water and stable even at a high temperature.

Therefore, the application of the biosensor using the carbon nanotubes 14 without the need for a separate insulating film is possible.

In addition, as shown in FIG. 1B, when the SU-8 negative photoresist 16 is coated on the metal surface, oxygen atoms at the SU-8 end make it difficult for the electrons to stick out of the metal, resulting in a work function of the metal. It will have a synergistic effect.

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. The sample is then immersed in acetone solution to remove metal from unwanted areas to complete the carbon nanotube transistors.

After spin coating SU-8 negative photoresist 16 on the nanotube transistor again, baking at 90 ° C. for 2 minutes to remove the organic solvent. When the photoresist 16 coated in this manner is exposed to UV, the polymer of the UV-irradiated portion remains solid and serves as an insulating film.

In addition, it is also possible to use an organic molecular film having a thiol (SH) attached to the electrode by using a self-assembly method. The electrode pattern manufactured by this method is as shown in FIG.

Experimental Example

In order to evaluate the electrical characteristics of the carbon nanotube transistor manufactured according to the above embodiment, the current change was measured while changing the voltage at regular intervals. While varying the voltage in the range of -1 V to +1 V, the current change characteristic curve according to the voltage change was obtained, and the result is as shown in FIG.

At this time, in Fig. 6 (a), the black line shows the voltage-current curve after coating the electrode with the SU-8 resist, the red line after coating the SU-8 resist.

After coating the SU-8 negative photoresist 16 on the electrode 12, it can be seen that the electrical conductivity of the transistor increases by about 90%.

6 (b) corresponds to a curve (I-Vg) in which the current of the transistor is measured while changing the gate voltage at a specific bias voltage (−1, 0, 1 V). At this time, the portion shown in black is the electrical characteristics before the coating of the SU-8 negative photoresist 16 on the electrode 12, the red is the electrical characteristics after the SU-8 negative photoresist 16 is coated on the electrode 12 Indicates.

It was clearly observed that when the SU-8 negative photoresist 16 was coated on the electrode 12, the threshold voltage Vth of the device changed toward the positive gate voltage, and at the same time, the electrical conductivity (current value) increased.

In order to examine the insulation characteristics of the transistor manufactured in the present invention, a buffer solution was dropped on the carbon nanotubes 14 and used as a gate.

As shown in FIG. 7, when the voltage between -200 mV and 200 mV is applied to the buffer solution used as the gate, the leakage current value is less than several pA, so that the insulating property of the SU-8 negative photoresist 16 is excellent. It can be seen.

In addition, as shown in FIG. 8, when a metal having a relatively large work function is attached to the carbon nanotube 14, which is a p-type semiconductor, the height of the Schottky barrier generated at the metal-semiconductor interface is reduced. The result is an increase in electrical conductivity and an increase in hole carriers.

8 (b) shows such an effect. As the work function of the electrode 12 is increased, it can be seen that the charge depletion region between the metal and the carbon nanotube is reduced, thereby increasing the electrical conductivity.

Carbon nanotubes 14 according to the present invention may be selected from single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon nanotube bundles, etc. In addition, semiconductor nanostructures (nanowires, nanoribbons, nanorods, It can also be applied to transistors using nano-oring.

Here, the semiconductor nanowires include GaP, GaN, Si, InP, InAs, GaAs, ZnO, TiO ₂ , SnO _2, and the like.

Common methods for forming a protective film on the electrode 12 include spin coating and photolithography, but other pattern forming methods such as e-beam lithography or inkjet printing and a self-assembled film may be used.

The layer of SU-8 photoresist 16 coated on the carbon nanotube transistor can be replaced with a self-assembled monolayer of other polymers or organic molecules, and limited to the SU-8 negative photoresist 16 only. It doesn't work.

In other words, the self-assembled film is formed to expose the source or drain electrode 12 of the carbon nanotube transistor to increase or decrease the work function.

As described above, the work function of the metal may be changed to affect the electrical conductivity and the doping state of the carbon nanotube transistor.

FIG. 9 is a graph showing electrical changes generated by adsorption of aminoethanthiol to an electrode.

As shown in FIG. 9, the adsorption of aminoenthanthiol to the source electrode 12 of the carbon nanotube transistor effectively lowers the work function of the electrode, so that the electrical characteristics of the carbon nanotube 14 are bipolar ( It is ambipolar and shows the same characteristics as a diode.

FIG. 10 shows the electrical characteristics of the device treated with the amino ethanol at one electrode 12 as described above. A typical diode curve was observed, and this nonlinear electrical characteristic was commonly observed for the samples with one electrode 12 deformed.

FIG. 11 shows the change in work function and band diagram due to adsorption of aminoethanethiol on the electrode.

As described above, according to the carbon nanotube transistor having the modified electrode according to the present invention, when the self-assembled film of SU-8 negative photoresist or organic molecules is coated and adsorbed on the electrode of the carbon nanotube transistor, The relatively high function has the advantage of inducing effective hole doping in carbon nanotubes.

In addition, by forming an excellent insulating film of the SU-8 negative photoresist, it is possible to apply the biosensor application of the carbon nanotube transistor without additional fluid tube or insulating film treatment.

In addition, the carbon nanotube transistor of the present invention has a meaning that it can be easily doped with a simple and inexpensive photoresist process, and can be used as an excellent insulating film, and a transistor sensor and a gas sensor using various nanostructures. And biosensors.

Claims (5)

In a carbon nanotube transistor comprising a source electrode and a drain electrode in electrical contact with both ends of the carbon nanotubes, The carbon nanotube transistor having a strained electrode, characterized in that the electrode is coated with any one of a photoresist, a low molecular self-assembled film and other polymers. The carbon nanotube transistor of claim 1, wherein the carbon nanotubes are any one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanotube bundles. The carbon nanotube transistor of claim 1, wherein the material coated on the electrode is any one of all adsorbates capable of exhibiting insulating properties. The carbon nanotube transistor of claim 1, wherein the electrode coating layer is formed by any one of lithography, spin coating, inkjet printing, and self-assembly. The carbon nanotube transistor according to claim 1 or 4, wherein the electrode coating layer uses a polymer capable of effectively modifying the work function of the electrode, a self-assembled film of organic molecules, a photoresist, and an electron beam resist. .

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