DOTSEVEN is a very ambitious 3.5 year R&D project targeting the development of Silicon Germanium (SiGe) Heterojunction Bipolar Transistor (HBT) technologies with cut-off frequencies (fmax) of around 700 GHz. The project is publically funded within the European Union's Seventh Framework Program for Research (FP7). It started in October 2012 and is now at the beginning of its second year. 10 out of the 12 DOTSEVEN participants were already partnering in the predecessor FP7 project DOTFIVE which succeeded for the first time to push fmax of SiGe HBTs (at room temperature) into the 500 GHz region thus setting a new world-wide benchmark.
For a given lithography node, SiGe HBTs provide much higher cut-off frequencies compared to CMOS transistors while offering higher power density and better analog performance. Although ITRS roadmaps predict ever increasing cut-off frequencies for CMOS transistors up to the THz region, there are indications that at least fmax will saturate around the 28 nm node at 300-400 GHz (depending on the extraction methodology) and will even drop beyond that node due to parasitic gate resistance. Thus SiGe HBT technology and SiGe HBT enhanced CMOS (SiGe BiCMOS) will be key enablers for demanding mm-wave systems requiring more than a few µWatts of RF output power (which limits the applicability of even very advanced CMOS) and also offer high integration levels at low cost which precludes expensive and less integrated III-V solutions.
Within the project the capabilities and benefits of >500 GHz SiGe HBT technology will be demonstrated by benchmark circuits and advanced system applications in the 0.1 to 1 THz range like THz imaging and sensing, wireless Gb/s communications and millimeter-wave radar. Process development will be strongly supported by TCAD and physics-based modeling including 3D, nanoscale and thermal effects where as "first-time-right" circuit design will be enabled by accurate compact device modeling including electro-thermal, substrate and other parasitic effects. Of course these models have to be based on accurately extracted parameter sets for which in turn accurate and reliable characterization and extraction methodologies are mandatory. High current densities, excessive self-heating and operation at collector-emitter voltages above the open-base VCE breakdown limit might impose considerable reliability risks in downscaled HBTs and limit their practical application. Therefore in-depth reliability modeling and investigations will be undertaken in the project too.