Extraction of eleven model parameters for consistent reproduction of lateral bipolar snapback high-current I-V characteristics in NMOS devices

Abstract

A series of literature models originally devoted to the second breakdown trigger current I-t2 in a grounded-gate nMOS transistor can further find promising potential in handling high-current I-V due to lateral bipolar snapback. This is achieved primarily by building significant linkage between bipolar current-gain beta -related parameters: 1) the collector-to-base junction voltage dependencies A(1) and A(2) of the medium-level injection beta roll-off factor; 2) the high-level beta roll-off factor A(3); and 3) the collector-to-base junction voltage dependencies A(4) and A(5) Of the collector corner current at the onset of high-level beta roll-off. The new parameters A(1) to A(5) enable a consistent I-V solution along with other existing six model parameters such as the substrate resistance R-sub and its conductivity modulation factor A(r), the impact ionization coefficients K-1 and K-2, and the emitter series resistance R-e and collector series resistance R-c. Parameter extraction except Rc is thoroughly performed using only the parametric analyzer, and opposed to the traditional procedure, impact ionization coefficients and current gains are all assessed without entering the snapback regime. Remarkably, not only excellent agreements are gotten, but also bipolar snapback I-V measured under the current pulsing condition can be separated into two distinct parts: medium- and high-level injection region. This is quite effective under R-e = R-c. Series resistance, although having very low value, is not to be absent under the high-level injection conditions. Experimental evidences from test structures with different epitaxial layer thicknesses strongly confirm the validity of the assumptions such as R-e = R-c. In light of the epitaxial layer thickness dependencies of the model parameters, the epitaxial layer thickness effect is addressed as well.