A field-effect transistor (FET) is commonly used for amplification of weak-signal such as wireless signals. FET can amplify analog or digital signals and can also switch DC or function as an oscillator. The field-effect transistors are used in wireless communications because they can function at temperatures as low as 4.3 K and operate at radio frequencies.

Field-effect transistors exist in two major classifications known as the junction FET and the metal-oxide- semiconductor FET. Field-effect transistors are fabricated onto silicon integrated circuit (IC) chips. A single IC can contain many thousands of FETs, along with other components such as resistors, capacitors, and diodes.

Graphene is a flat sheet of carbon just one atom thick that conducts electrons at extremely high speeds. The fact that the electrons behave like relativistic particles with no rest mass and have other unusual physical properties makes graphene to replace silicon to make faster transistors than any that exist today. Transistors made from graphene could be used in radio-frequency microelectronic devices for wireless communications.

Scattering of charge carriers

These devices can be made by transferring high-quality graphene sheets, produced by chemical vapour deposition (CVD), onto a suitable, insulating substrate such as silicon dioxide. However, the problem is that the substrate can severely degrade the electronic properties of graphene because of scattering of charge carriers in graphene. This scattering, which drastically limits the speed of the charge carriers, comes about due to interactions between graphene and the dielectric substrate material.

Researchers at IBM Thomas J. Watson Research Center, New York have come up with an answer to this problem. The researchers used diamond-like carbon as the top layer of the substrate, with the carbon atop a standard silicon wafer. Diamond-like carbon is already widely used in the semiconductor industry and is created by chemical vapour deposition (CVD). At IBM and many other laboratories around the world, scientists are now perfecting the CVD process and steadily increasing its performance. Diamond-like carbon is a non-polar dielectric material and hence it does not trap charges nor does it scatter charge as much as silicon dioxide does. It is also cheap to make in large areas; does not absorb much water; and has excellent thermal conductivity. Also the cut-off frequency is the highest so far for transistors made from CVD-graphene.

High-frequency transistors are widely used primarily in communications for mobile phones, the internet and radar, medical imaging, security, sensors and in space as the new transistors can work well at extremely low temperatures. Diamond-like carbon could be an ideal substrate for graphene transistors. So say researchers in the US who have made advanced devices with a record-high cut-off frequency of 155 GHz and the shortest gate length ever of just 40 nm.