New Properties and New Challenges in MOS Compact Modeling

Conventional (four-terminal) bulk-MOS models are based on unipolar conduction in a doped body with body contact and ideal symmetric PN-junction source/drain (S/D) contacts. As bulk-MOS technology is approaching its fundamental limit, non-classical devices such as ultra-thin body (UTB) SOI as well as multiple-gate (MG) and gate-all-around/Si-nanowire (GAA/SiNW) MOSFETs emerge as promising candidates for futuregeneration device building blocks. This trend poses new challenges to developing a compact model suitable for these new device structures and requires a paradigm shift in the core model structure. In MG/NW (including non-body-contacted UTB-SOI) MOSFETs, however, the (three-terminal) device has a nearly undoped body and without a body contact, and S/D contacts (PN-junction or Schottky) also become an integral part of intrinsic channel. Carrier transport may become bipolar and may change from drift-diffusion dominant to tunneling dominant, depending on the S/D contacts. Source–drain asymmetry, either intentional or unintentional, in a theoretically symmetric MOSFET also becomes important to be captured in a compact model, which is nontrivial in a model that depends on terminal S/D swapping at the circuit level. This paper discusses these new challenges and demonstrates solution methods based on the unified regional modeling (URM) approach to the ultimate goal of unification of MOS compact models.