Anomalous Transconductance in Long Channel Halo Implanted MOSFETs: Analysis and Modeling

In this paper, we report anomalous behavior of transconductance (
${g}_{m}$
) in halo implanted MOSFET for linear and saturation regions across both gate and body biases. The
${g}_{m}$
characteristics undergo sharp change of slope in saturation which cannot be modeled by conventional compact models. The cause of such behavior is identified and explained using the TCAD simulations of source side halo, drain side halo (DH), both side halos, and uniformly doped transistors. An analytical model, based on the equivalent conductance of the halo device, is developed to understand the
${g}_{m}$
behavior. It is shown that the commonly used approach where only the DH region is considered in saturation, is insufficient to model the atypical
${g}_{m}$
behavior. The effect of oxide thickness (
${T}_{\text {ox}}$
) variation on
${g}_{m}$
is also studied, which demonstrates a deviation from the conventional
$g_{m}$
behavior for halo implanted devices with thicker
${T}_{\text {ox}}$
. A computationally efficient SPICE model is proposed to model
${g}_{m}$
characteristics which shows excellent matching with the measured data.