TWI622104B - Producing method of semiconducting single walled carbon nanotube transistor - Google Patents

Abstract

The invention relates to a method for manufacturing a single-walled carbon nanotube transistor, which is mainly characterized by dissolving a semiconducting carbon nanotube coated with a polymer rr-P3DDT in a solvent of toluene and precipitating a metallic carbon nanotube through a centrifugal process. After that, the supernatant is extracted and filtered by a syringe filter, dissolved in toluene, and the substrate is immersed in toluene to attach the semiconducting carbon nanotube to the substrate to complete the active after removing the polymer rr-P3DDT and toluene. The layer is formed on the active layer of the substrate to complete the carbon nanotube transistor; by the above manufacturing method, the concentration of the semiconducting carbon nanotube can be increased to avoid the phenomenon that the leakage current of the transistor is too high.

Description

Single wall type carbon nanotube transistor manufacturing method

The invention relates to a method for manufacturing a carbon nanotube transistor, in particular to a method for manufacturing a single-walled carbon nanotube transistor, which can increase the concentration of a semiconducting carbon nanotube.

The transistor is the basic component in the logic gate. Under the trend of miniaturization of the current integrated circuit process, the process technology of the conventional silicon wafer has gradually faced the technical bottleneck of optics and physics. Therefore, various attempts have been made to various kinds of nanometers. The grade material is made of nano-crystal, in which the technology of carbon nanotube as the active layer develops most rapidly, and it is predicted that it will replace the existing transistor into the mainstream technology of the transistor material, and the single-walled carbon nanotube is regarded as the mainstream technology. One of the most ideal materials for making carbon nanotube transistors.

Single-walled carbon nanotubes can be classified into metallic carbon nanotubes (m-SWNT) and semiconducting carbon nanotubes (s-SWNT) according to their palmarity, both of which are produced simultaneously, but electricity The active layer of the crystal requires a high concentration of semiconducting carbon nanotubes (s-SWNT). If it is doped with a high concentration of metallic carbon nanotubes (m-SWNT), the leakage current of the transistor will be too high. Therefore, there is still a need to find a technique for separating two characteristic carbon nanotubes at low cost and high efficiency in the process.

In view of the technical defects that the conventional carbon nanotube transistor manufacturing method fails to effectively separate the semiconducting carbon nanotubes and the metallic carbon nanotubes, and the leakage current of the transistor is too high, the present invention proposes a single-walled nanometer. The carbon tube transistor manufacturing method can increase the concentration of the active layer semiconducting carbon nanotubes and avoid the generation of leakage current.

The technical means for achieving the above purpose is to make the single-walled carbon nanotube transistor manufacturing method include:

Providing a substrate, and sequentially forming at least one gate and a dielectric layer on the substrate;

Providing a carbon nanotube mixed solution comprising a carbon nanotube, a polymer rr-P3DDT (poly 3-dodecylthiophene, poly 3-dodecylthiophene-2,5-diyl), and Toluene

Aspirating the above carbon nanotube mixed solution for centrifugation to precipitate a metallic carbon nanotube;

Aspirating the supernatant of the carbon nanotube mixed solution after centrifugation, filtering with a sterile syringe filter, and injecting into a toluene solvent;

Soaking the substrate in the toluene solvent to adhere the carbon nanotubes to the substrate;

Cleaning the toluene solvent on the substrate;

Removing the polymer rr-P3DDT on the substrate;

A source and a drain are formed on the carbon nanotube of the substrate.

The above single-walled carbon nanotube transistor manufacturing method utilizes a polymer rr-P3DDT to coat a semiconducting carbon nanotube, leaving a metal carbon nanotube insoluble in toluene, and after a centrifugal separation step, the metallic nephew The carbon nanotubes are precipitated at the bottom, and the high-concentration semiconducting carbon nanotubes can be extracted from the supernatant and filtered, and the invention can greatly improve the semiconductor by immersing the substrate in a toluene solvent for the attachment of the carbon nanotubes. The concentration of the carbon nanotubes, experimentally tested, Raman spectroscopy shows that the above-mentioned single-walled carbon nanotube transistor manufacturing method can almost completely remove the metallic carbon nanotubes to avoid leakage current.

Referring to FIG. 1 and FIG. 2( a ) to FIG. 2( e ), the method for manufacturing the single-walled carbon nanotube transistor of the present invention comprises:

A substrate 10 is provided, and at least one gate 11 and a dielectric layer 12 are sequentially formed on the substrate 10. In this embodiment, the substrate 10 is first subjected to an RCA cleaning process, and then on the surface of the substrate 10 Electron beam evaporation, depositing chromium (Cr) metal on the substrate 10 to form the gate 11, and then chemical vapor deposition of cerium oxide (SiO ₂ ) as the dielectric layer 12, as shown in Fig. 2(b) In order to improve the adhesion of the carbon nanotubes, the substrate 10 can be further immersed in 3-aminopropylmethyltriethoxysilane (APTS) for 50 to 70 minutes, as shown in Fig. 2(c). Show

Providing a carbon nanotube mixed solution comprising a carbon nanotube (including a semiconducting carbon nanotube s-SMNTs and a metallic carbon nanotube m-SMNTs), a polymer rr-P3DDT and Toluene

The above-mentioned carbon nanotube mixed solution is taken up and centrifuged, and since the polymer rr-P3DDT has high selectivity to the semiconducting carbon nanotube, it is coated on the semiconducting carbon nanotube and dissolved in toluene, and after centrifugation step, The metallic carbon nanotubes m-SMNTs will be precipitated at the bottom of the test tube, and the semiconducting carbon nanotubes s-SMNTs and the polymer rr-P3DDT are retained in the supernatant;

The supernatant of the carbon nanotube mixed solution after centrifugation is aspirated and filtered by a sterile syringe filter and injected into a solvent of toluene. In this embodiment, it is filtered by a syringe filter having a pore diameter of 0.45 μm. The supernatant after the aspiration is injected into the toluene solvent. At this time, only a high concentration of the semiconducting carbon nanotubes s-SMNTs and the polymer rr-P3DDT are present in the toluene solvent.

The substrate 10 is immersed in the toluene solvent, and a carbon nanotube is attached to the substrate 10 to increase the density of the carbon nanotubes on the substrate 10. In the present embodiment, the substrate 10 is immersed in a toluene solvent. After 24 hours, and placed at room temperature, the active layer 20 of the semiconductor carbon nanotubes was formed on the substrate 10 by dip coating, as shown in Fig. 2(d).

The toluene solvent on the substrate 10 is further washed and dried at room temperature; the polymer rr-P3DDT on the substrate is removed, and in the present embodiment, the substrate is placed in a flowing argon of 760 Torr for heating 500. °C for at least 60 minutes.

The source 31 and the drain 32 are formed on the carbon nanotube of the substrate 10. In the embodiment, the source 31 and the drain are formed on the active layer of the semiconductor carbon nanotube of the substrate by a yellow light developing process. 32. A carbon nanotube semiconductor as shown in Fig. 2(e) was produced, and the length of the semiconductor channel formed in this experiment was 5 μm.

In addition to rr-P3DDT, the above polymer may also use rr-P3DT (Poly(3-decyl-thiophene-2,5-diyl)) or rr-P3OT (Poly(3-octyl-thiophene-2,5- Diyl), selective coating of semiconducting carbon nanotubes s-SMNTs.

The above-described separated metal carbon nanotubes and semiconducting carbon nanotubes are characterized by using toluene as a separation solvent and utilizing a difference in dielectric constant between the metallic carbon nanotubes and the semiconducting carbon nanotubes. Since the carbon nanotubes are insoluble in the toluene solvent, and the dielectric constant of the semiconducting carbon nanotubes is less than 5, which is much smaller than the dielectric constant of the metallic carbon nanotubes of 1000, the toluene-soluble polymer rr-P3DDT The semiconducting carbon nanotubes are selectively coated. After high-speed centrifugation, the uncoated metal carbon nanotubes will precipitate to the bottom, and the supernatant will retain a high concentration of semiconducting carbon nanotubes. After filtration through a syringe filter, the supernatant injected into the toluene solvent has largely removed the metallic carbon nanotubes.

In the above manufacturing method, the ratio of the carbon nanotubes, the polymer rr-P3DDT and the toluene affects the concentration of the semiconductor carbon nanotubes in the finished product. In the present embodiment, the carbon nanotubes and the polymer rr-P3DDT are The ratio of 1:2 is dissolved in toluene solvent, and placed in a 40-60 ° C environment for 60 minutes, and then centrifuged at high speed (25000 g) for more than 120 minutes to precipitate the metallic carbon nanotubes. In actual experiments, the system will 10 mg of polymer rr-P3DDT, 5 mg of carbon nanotubes were mixed with 37 ml of toluene, and centrifuged at high speed (25,000 g) for 120 minutes.

In order to confirm that the supernatant contained in the toluene solvent in the above step has been removed from the metallic carbon nanotubes, the experiment is conducted by Rayleigh spectroscopy with lasers at 633 nm and 785 nm.

Please refer to Figure 3(a). In the figure, the RBM peak in the Lehmann spectrum shows that the peak of 200 cm ^-1 is a metallic carbon nanotube, and the peak of 173 cm ^-1 and 153 cm ^-1 is a semiconducting nanometer. The carbon tube, from which it can be seen that the metallic carbon nanotubes have been almost completely removed. Referring further to Fig. 3(b), the resonance of the metallic carbon nanotubes and the semiconducting carbon nanotubes is detected, and the metallic carbon nanotubes are also almost removed. Referring further to Figure 3(c), it is known by spectral detection that the polymer rr-P3DDT has been removed after heating.

Please refer to FIG. 4( a ) and FIG. 4( b ) for further description of the transistor prepared by removing the metallic carbon nanotube and the I _D -V _{D of the} transistor made by the manufacturing method of the present invention _. Characteristic curve, the test sample has a channel length of 5 μm and a channel width of 30 μm. It can be seen that the I _D -V _{D is} almost linear between the gate voltage of 0~5V, and it can be confirmed that the metal is in contact with the carbon nanotubes as ohmic contacts, and the invention is made of ohmic contacts. The carbon nanotube transistor has a lower saturation current operating in the saturation region.

Please refer to Fig. 5(a) and Fig. 5(b) for further cooperation. As can be seen from Fig. 5(a), the finished product of the metallic carbon nanotube is not removed, and the current switching ratio is 10 ³ , and Fig. 5(b) It can be seen that the finished product after removal of the metallic carbon nanotubes has an on/off ratio of 10 ⁷ . Metallic carbon nanotubes are considered to be the main obstacles to carbon nanotube semiconductors. Because metallic carbon nanotubes have little or no bandgap, they will cause conductive paths in the carbon nanotube network. Increase leakage current. Figure 5(b) shows that under the operating voltage of 4V, the transistor after removal of the metallic carbon nanotubes has a gate leakage current reduced to less than 10 fA. By the characteristics of the above ohmic contact and high current switching ratio, it can be known that the manufacturing method of the present invention has an efficient selectivity for a semiconducting carbon nanotube, and the electron mobility μ (mobility) is calculated by the following standard formula: ……(1)

Where C: ……(2)

Substituting A ₀ ^-1 of the semiconductor carbon nanotube for 20/μm ² and substituting it into the formula (1), the electron mobility μ is 2.3 cm ² when V _DS is -1 V. V ^-1 . S ^-1 , further can find the sub-threshold swing SS (subthreshold slop): ...(3)

From the above measurement, when the semiconductor carbon nanotube is not separated to form a semiconductor, the sub-critical slope is calculated to be 1.27 V/dec, and the metal carbon nanotube is separated by the manufacturing method of the present invention, and then the semiconductor is fabricated. The critical swing is 154mV/dec.

The results confirmed that the semiconductor fabricated after the separation of the metallic carbon nanotubes has a higher on/off ratio and a smaller subthreshold slop, and the less the metality is mixed. The carbon nanotubes can increase the current switching ratio and reduce the electron mobility, thereby reducing the saturation current Ion of the transistor operating in the saturation region. According to the above description, the single-walled carbon nanotube transistor manufacturing method of the present invention can be almost The removal of the metallic carbon nanotubes into a carbon nanotube semiconductor having a channel length of 5 μm has almost no characteristics of a metallic semiconductor, and the leakage current is greatly reduced.

10‧‧‧Substrate
11‧‧‧ gate
12‧‧‧Dielectric layer
20‧‧‧ active layer
31‧‧‧ source
32‧‧‧汲polar

Figure 1: Schematic diagram of the process of the present invention. 2(a) to 2(e) are schematic diagrams showing the state of one of the steps in the flow of Fig. 1. Figure 3 (a) ~ 3 (c): is a Raman spectrum of the carbon nanotubes in RBM mode. 4(a) and 4(b) are graphs showing I _D -V _D characteristics of a carbon nanotube transistor and a conventional carbon nanotube transistor of the present invention. 5(a) and 5(b) are graphs showing I _D -V _G characteristics of a carbon nanotube transistor and a conventional carbon nanotube transistor of the present invention.

Claims (1)

A method for manufacturing a single-walled carbon nanotube transistor, comprising: providing a substrate, and forming, by electron beam evaporation on the substrate, chrome metal to form at least one gate, and then depositing cerium oxide by chemical vapor deposition; a dielectric layer, and immersing the substrate in 3-aminopropylmethyltriethoxysilane for 50 to 70 minutes; providing a carbon nanotube mixed solution, which is a 5 mg carbon nanotube with 10 mg of polymer rr-P3DDT is dissolved in 37 ml of toluene solvent in a ratio of 1:2, and placed in a 40-60 ° C environment for 60 minutes; the above-mentioned carbon nanotube mixed solution is centrifuged at 25000 g to precipitate a metallic carbon nanotube; After centrifugation, the supernatant of the carbon nanotube mixed solution was filtered through a sterile syringe filter having a pore size of 0.45 μm and injected into a solvent of toluene; the substrate was immersed in the solvent of toluene for 24 hours to make a nanometer. a carbon tube is attached to the substrate; the toluene solvent on the substrate is cleaned; the substrate is placed in a flowing argon of 760 torr at 500 ° C for at least 60 minutes to remove the polymer rr-P3DDT on the substrate; Yellow light developing process on the carbon nanotube of the substrate For at least one source and at least one drain.