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Research targets HBT device running at 500GHz

Posted: 23 Nov 2011 ?? ?Print Version ?Bookmark and Share

Keywords:heterojunction bipolar transistor? SiGe:C? radar application?

Imec has revealed a SiGe:C heterojunction bipolar transistor (HBT) device that according to the research center is a driver for future high-volume millimeter-wave low-power circuits for automotive radar application. It added that the device will open opportunities for better imaging systems for security, scientific and medical functions.

The research institutes said the extremely high-speed devices have a fully self-aligned architecture by self-alignment of the emitter, base and collector region, and implement an optimized collector doping profile. Compared to III-V HBT devices, SiGe:C HBTs combine high-density and low-cost integration, making them suitable for consumer applications, added Imec. The devices can open up new application areas, working at very high frequencies with lower power dissipation, or applications that require a reduced impact of process, voltage and temperature variations at lower frequencies for better circuit reliability, continued Imec.

HBT device

The SiGe:C heterojunction bipolar transistors combine high-density and low-cost integration.

To achieve the ultra-high-speed requirements, modern SiGe:C HBTs need further up-scaling of the device performance. Thin sub-collector doping profiles are generally believed to be mandatory for this up-scaling. Usually, the collector dopants are introduced in the beginning of the processing and thus, exposed to the complete thermal budget of the process flow. This complicates the accurate positioning of the buried collector. By in-situ arsenic doping during the simultaneous growth of the sub-collector pedestal and the SiGe:C base, Imec introduced a thin, well-controlled, lowly-doped collector region close to the base and a sharp transition to the highly doped collector without further complicating the process.

This resulted in a considerable increase of the overall HBT device performance: 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. Despite the aggressive scaling of the sub-collector doping profile, the collector-base capacitance values did not increase much. Moreover, the current gain is well defined, with an average around 400 and the emitter-base tunnel current, visible at low VBE values, is limited as well.

These outstanding results were realized within the framework of the European joint research project DOTFIVE that aims at developing SiGe:C HBT devices that operate at 500GHz at room temperature.

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