Imec extends silicon transistors to 450 GHz

EDN Europe, 11 Oct 2011

To build mass-market and cost-effective products that operate at frequencies in the millimetre-wave region, the industry needs transistors that can be produced on volume manufacturing processes and that operate in the hundreds-of-GHz domain. Prospective users include automotive radar, medical and other imaging systems, security, and communications including short-range, ultra-high-bandwidth data services. A European joint research project called DOTFIVE (meaning, 0.5 THz, or 500 GHz) seeks to achieve these transistor parameters. Under the auspices of that programme, Belgium-based Imec has announced that it has built a SiGe:C (silicon germanium carbide) device that exhibits an fT (transition frequency) of 245 GHz and an fMAX of 450 GHz. The HBT (heterojunction bipolar transistor) has a fully self-aligned architecture that Imec researchers achieved by self-alignment of the emitter, base and collector region, with an optimised collector doping profile. Compared to III-V HBT devices, Imec says, SiGe:C HBTs combine high-density and low-cost integration.

Peak fMAX values above 450GHz are obtained on devices with a high early voltage, a BVCEO of 1.7V and a sharp transition from the saturation to the active region in the IC-VCE output curve. Current gain is well defined, with an average around 400 and the emitter-base tunnel current, visible at low VBE values, is limited.