Buried Silicon Germanium pMOSFETs: Experimental Analysis in VLSI Logic Circuits under Aggressive Voltage Scaling

In this paper, the potential of Silicon Germanium (SiGe) technology for VLSI logic applications is investigated from a circuit perspective for the first time. The study is based on experimental measurements on 45-nm SiGe pMOSFETs with a high-/metal gate stack, as well as on 45-nm Si pMOSFETs with identical gate stack for comparison. In the reference SiGe technology, an innovative technological solution is adopted that limits the SiGe material only to the channel region. The resulting SiGe device merges the higher speed of the Ge technology with the lower leakage of the Si technology. Appropriate circuit- and system-level metrics are introduced to identify the advantages offered by SiGe technology in VLSI circuits. Analysis is performed in the context of next-generation VLSI circuits that fully exploit circuit- and system-level techniques to improve the energy efficiency through aggressive voltage scaling, other than low-leakage techniques. Analysis shows that the SiGe technology has more efficient leakage-delay and dynamic energy-delay trade-offs at nominal supply, compared to Si technology. Moreover, it is shown that the traditional analysis performed at nominal supply actually underestimates the benefits of SiGe pMOSFETs, since the speed advantage of SiGe VLSI circuits is further emphasized at low voltages. This demonstrates that SiGe VLSI circuits benefit from aggressive voltage scaling significantly more than Si circuits, thereby making SiGe devices a very promising alternative to Si transistors in next-generation VLSI systems.