Achieving accuracy in modeling the temperature coefficient of threshold voltage in MOS transistors with uniform and horizontally nonuniform channel doping

Abstract

A thorough investigation on the threshold voltage temperature coefficient (TVTC) in MOS transistors is carried out. The TVTC behavior is analyzed in both conventional MOSFETs with uniformly-doped channel (UDC) and double-diffused devices (DMOS). First, a survey of analytical TVTC models proposed in literature for UDC MOSFETs is presented. Due to the need of simple TVTC expressions also for power devices, the listed UDC models are extended to the DMOS case via the straightforward “maximum doping” approach, which is commonly believed to correctly describe the turn-on mechanism in nonuniformly doped channels (NUDC). The accuracy degree of all TVTC expressions and the adequacy of the above method are—for the first time—deeply analyzed through ATLAS 2-D simulations of both DMOS and ideal UDC structures. As a main result, the “maximum doping” approach is demonstrated too coarse for suitably modeling the underlying DMOS physics. Nevertheless, it is shown that the TVTC in DMOSTs characterized by proper technological parameters is described with reasonable agreement by the Klaassen–Hes UDC model. Conversely, more compact formulations are proved to suffer from an unacceptable inaccuracy regardless of the MOS typology.