Revised Analysis of Design Options and Minimum Subthreshold Swing in Piezoelectric FinFETs

The theoretical limit of sub-threshold swing (SS) in the n-type piezoelectric FinFET (Piezo-FinFET) is thoroughly investigated. Gate voltage modulated strain, conduction band edge shift and the SS are evaluated utilizing physics-based modeling and numerical simulation, indicating a strong dependence of SS on the fin width, crystalline orientation and physical properties of the piezo-material used in the gate stack. For [001] Si and [111] Ge Piezo-FinFETs with 5nm fin width and 3nm PZT-5H thickness, SS values down to 40mV/decade are achievable after design optimizations. A figure of merit, Ecrdz3/Spie,33, is proposed for the piezo-materials in terms of the critical electric field (Ecr), the piezoelectric strain constant (dz3) and the elastic compliance constant (Spie,33), to guide the Piezo-FinFET designs. Index Terms—Piezoelectric, Silicon, Germanium, MOSFET, FinFET, Strain, Sub-threshold Swing (SS), Steep Slope