Current status of ferroelectric-gate Si transistors and challenge to ferroelectric-gate CNT transistors

Current status of ferroelectric-gate FETs (field effect transistors) is reviewed. First, characteristics of Si FETs with MFIS (metal–ferroelectric–insulator–semiconductor) gate structures are discussed. It has been shown that the data retention characteristics of ferroelectric-gate FETs are much improved by use of HfO2-based buffer layers which are inserted between the ferroelectric-gate film and Si substrate for preventing inter-diffusion of constituent elements. Then, usefulness of organic ferroelectrics such as copolymers of vinyliden fluoride and trifluoroethylene (P(VDF–TrFE)) in fabrication of MFIS devices is demonstrated. In an Au/P(VDF–TrFE)/Ta2O5/Si MFIS diode, a memory window as wide as 2.9 V has been obtained with a voltage sweep of ±4 V. Finally, operation mechanisms in ferroelectric-gate CNT (carbon nano-tube) transistors are discussed, assuming Schottky barrier conduction at the source and drain contacts.