I. Introduction
Multiple-Gate (MG) MOSFETs such as FinFET [1] or trigate [2]–[4] structures are often considered as the ultimate devices for CMOS scaling to 10-nm gate length and below [5], [6]. At these geometrical dimensions, quantum–mechanical (QM) effects seriously influence the device characteristics. For example, subband formation due to QM confinement causes a threshold voltage shift compared to classical estimations [7], [8]. In contrast to single-gate (SG) silicon-on-insulator (SOI) MOSFETs, in a trigate MOSFET (Fig. 1) not only the body thickness but also the body width contributes to subband formation, and further increases [9]–[11].
(a) Schematic structure of a trigate MOSFET with the definition of the body width and body thickness . Also shown are the three pairs of equivalent conduction band valleys in silicon for the case that each surface has (100) orientation. (b) Schematic cross section of three basic types of MG MOSFETs including the gate-all-around (GAA) architecture.