British Claim World's Fastest Transistor

A group at the Defense Evaluation and Research Agency (DERA, Malvern, Worcestershire, England) claimed to have fabricated the fastest transistor yet produced with an fT of 74 GHz. This enhancement mode device (Fig. 1) has a gate length of 0.7 µm (70 nm), but the  workers predict 185 GHz operation when the gate length is scaled down to 0.25 µm (250 nm).

The transistor employs indium antimonide as the basic semiconductor material. This has a high electron mobility, while its high saturation electron velocity (the greatest speed electrons can achieve in its lattice) is at least five times that of gallium arsenide. These factors enable high speed of operation to be achieved even with fairly low internal electric fields. However, the small energy gap of indium antimonide of about 0.7 eV results in a high leakage current because of thermal carrier generation. The main advance made by DERA is the reduction of this leakage by the use of minority carrier exclusion and extraction. The researchers have proposed the fabrication of a depletion mode device (Fig. 2) that will not require such accurate alignment of the gate electrode. This will not only simplify the fabrication process, but enable the gate width and hence the gate capacitance to be reduced to improve performance for a given feature size.

1. Shown is a cross section of the DERA enhancement mode device.

2. The p type semiconductor material used in this proposed depletion mode device is about equally balanced with respect to n- and p-type dopants. 1. This Temic SiGe amplifier chip is designed for sensor technology and information processing.