Simulation and design of a germanium L-shaped impact-ionization MOS transistor

Abstract

This paper reports a novel L-shaped impact-ionization MOS (LI-MOS) transistor structure that achieves a subthreshold swing of well below 60 mV/decade at room temperature and operates at a low supply voltage. The device features an L-shaped or an elevated impact-ionization region (I-region), which displaces the hot carrier activity away from the gate dielectric region to improve hot carrier reliability and VT stability problems. Germanium, which has a lower bandgap and impact-ionization threshold energy lower than silicon, is chosen as the material of choice for the LI-MOS transistor structure. Device physics and design principles for the LI-MOS transistor are detailed through extensive two-dimensional device simulations. The LI-MOS transistor exhibits excellent scalability, making it suitable for augmenting the performance of standard CMOS transistors in future technology generations. © 2008 IOP Publishing Ltd.