Design Optimization of Extremely Short-Channel Graded Si/Sige Heterojunction Tunnel Field-Effect Transistors for Low Power Applications

Abstract

This study investigates, by a two-dimensional simulation, the design optimization of a proposed 8 nm tunnel field-effect transistor (TFET) for low standby power (LSTP) applications utilizing graded Si/SiGe heterojunction with device parameters based on the ITRS specifications. The source Ge mole fraction should be designed approximately 0.8 because using lower Ge fractions causes severe short-channel effects while with higher values does not significantly improve the device performance but may create big difficulties in fabrication. Based on simultaneously optimizing the subthreshold swing, on-and off-currents, optimum values of source doping, drain doping and length of the proposed device are approximately 10 20 cm -3 , 10 18 cm -3 , and 10 nm, respectively. The 8 nm graded Si/SiGe TFET with optimized device parameters demonstrates high on-current of 360 µA/µm, low off-current of 0.5 pA/µm, low threshold voltage of 85 mV and very steep subthreshold swing of sub-10 mV/decade. The designed TFET with graded Si/SiGe heterojunction exhibits an excellent performance and makes it an attractive candidate for future LSTP technologies because of its reality to be fabricated with existing FET and SiGe growth techniques.