Tetrahertz ICs coming closer

Europeans continue to rise to the challenge of advancing communications, imaging and radar integrated circuits to work at high frequencies.

A team at Interuniveritair Micro-Electronica Centrum Vzw (imec) in Belgium recently introduced the device fT.fMAX 245/450 GHz SiGe:C heterojunction bipolar transistor.

This device will help facilitate future high-volume millimetre-wave low-power circuits to be used in motor vehicle radar applications.

The study was funded in part by the DOTFIVE (Towards 0.5 terahertz silicon/germanium hetero-junction bipolar technology) project, which received EUR9.7 million under the ‘Information and communication technologies’ theme of the EU’s Seventh Framework Programme (FP7).

HBT devices are instrumental in helping silicon-based millimetre-wave circuits penetrate the terahertz gap. They enable enhanced imaging systems for security, medical and scientific applications, according to researchers.

The team says the HBT devices are very fast and have a fully self-aligned architecture: self-alignment of the emitter, base and collector region. They can implement an optimised collector doping profile, they add.

To secure the ultra-high speed requirements, SiGe:C HBTs require additional upscaling of the device performance. For the most part, thin sub-collector doping profiles are considered a must for this upscaling.

The collector dopants are typically introduced at the start of the processing and are exposed to the complete thermal budget of the process flow.

Because of this, the accurate positioning of the buried collector is harder to obtain.