Infineon builds nanotube-based power transistor using standard processes

A SIMPLE PROCESS: Simulation of carbon nanotube power transistor, which employs about 300 nanotube structures. SOURCE: INFINEON TECHNOLOGIES

A team of reseachers from Infineon has built what's being touted as the world's first carbon nanotube (CNT) power transistor. The single-walled CNTs were produced using a regular CVD process in a few minutes, then built into a test chip on a silicon substrate. Other parameters, such as materials and temperature, are suitable for use in conjunction with standard chip manufacturing processes, according to the company.

One lithographic step is needed to make the whole transistor with the drain, source, and gate contacts. The drain and source contacts were made of palladium, while the gate dielectric material was high-k aluminum dioxide. The CNTs are distributed randomly in what the company calls a simple process, although enough of them are arranged in parallel to connect the drain and source.

Infineon says that the device made in its labs employs about 300 nanotube structures, each about 1 nm in diameter and capable of delivering about 24 μA. They work in parallel to switch enough current (2 mA at about 2.5 V) to run a light-emitting diode or small motor. The prototype can be scaled for higher power ratings.

The high conductance and current-carrying capacity that CNTs provide can increase switching resistances and current densities considerably. The Infineon group showed that the typical switching resistance for power transistors made with CNTs is 20 times less than for conventional transistors, resulting in a much lower loss of power. Also, the nanotubes can withstand current densities 200 times higher than the levels found in conventional silicon devices, such as power MOSFETs.

"One important characteristic of nanotubes is that they can be metallic or semiconducting," explains Franz Kreupl, Infineon's project manager in the CNT research section. "This makes it possible to build active switching elements, such as field-effect transistors for controlling electronic loads, and we are the first to successfully demonstrate this." The company's carbon-nanotube-related research work is underwritten by the German Federal Ministry of Education and Research.