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 5-nm fin width and 3-nm PZT-5H thickness, SS values down to 40 mV/decade are achievable after design optimizations. A figure of merit, E
_cr
d
_z3
/S
_pie,33
, is proposed for the piezo-materials in terms of the critical electric field (E
_cr
), the piezoelectric strain constant (d
_z3
), and the elastic compliance constant (S
_pie,33
), to guide the Piezo-FinFET designs.