Chapter 3 - Status of Metal-Ferroelectric- Semiconductor Field Effect Transistors (MFSFETs) and Related Devices

Abstract

A metal-ferroelectric-semiconductor field effect transistor (MFSFET) is a field effect transistor whose gate insulator is composed of a ferroelectric material. In FET, the surface state of the semiconductor substrate is changed from accumulation to inversion by altering the polarization direction of the ferroelectric film. The nondestructive readout characteristic, one of the most important features of the FET-type ferroelectric memory, is superior to the capacitor-type memory. This type of FET can also be used as an analog memory if applying pulse signals that are shorter than the polarization reversal time continuously controls the polarization of the ferroelectric film. Although MFSFETs have many important application fields, fabrication of actual devices is rather difficult due to poor interfaces between ferroelectrics and semiconductors. To avoid this interface problem, related devices with metal-ferroelectric-insulator-semiconductor (MFIS) gate structures are also proposed and fabricated. In this chapter, the history of MFSFET and related devices is reviewed. Proposals on novel MFSFET arrays for digital and analog memories are introduced and the status of the experimental studies on MFS capacitors and FET are discussed. Based on the various kinds of materials discussed in the chapter, the author emphasizes that the best ferroelectric material for the gate insulator has not been determined yet.