Army

Carbon nanotube transistor

A field effect array utilizing single-wall carbon nanotubes as the channel with a simple way for processing

Electronics

Dr. Govind Mallick, a research chemist with the U.S. Army Research Laboratory, is one of the inventors.

Carbon nanotubes (CNTs) are perhaps the best available material for realizing nano and molecular scale electronics and sensor devices.

Experiments demonstrating the use of single-wall nanotubes (SWNTs) as the active channel in a semiconductor (MOS) field effect transistor (FET) have opened the possibility for a wide range of integrated carbon nano-tube nanoelectronics.

One roadblock to a broader use of CNTs in electronics and other devices lies in the several tedious steps to produce even a single or a few functional devices. Furthermore, existing assembly and fabrication methods do not lend themselves to high-yield microcircuit production.

Army scientists are breaking through this roadblock and have developed a FET array utilizing SWNTs as the channel for the transistor, as well as a method for fabricating the FET which overcomes the scalability issues above. The research team has simplified the fabrication process down to three steps.

In this invention, available to businesses for commercialization, a metal oxide layer is formed on a highly N-doped silicon substrate using conventional semiconductor fabrication techniques. Then, an iron-containing catalyst precursor polymer film is spun on the substrate, forming a thin layer. Thereafter, SWNTs are grown in the polymer film by chemical vapor deposition such that long strands are formed on the MOS layer. The SWNTs may be either single tubes or thin, uniform bundles of tubes. After formation of the carbon nanotubes on the MOS, titanium and gold alloy electrodes are deposited over the nano-tubes in a parallel configuration.

The carbon nanotubes formed on the substrate include both metallic carbon nanotubes and semiconductor carbon nanotubes. The metallic carbon nanotubes, which do not exhibit the semiconductor characteristics desired for a field effect transistor, are then destroyed by applying a relatively high voltage (1-2 volts) between each successive pair of electrodes, leaving only the semiconductor-carbon nanotubes between adjacent electrodes. Following the destruction of the metallic carbon nanotubes, separate FETs remain with adjacent electrodes forming the source and drain.

This technology may have direct application in massively parallel switches and chemical-biological sensors.

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