Two-dimensional modeling of locally damaged short-channel MOSFET's operating in the linear region

The effect of localized damage (interface states and/or trapped charges) on the ohmic region characteristics of electrically stressed MOSFET's is analyzed using the two-dimensional (2-D) solution of Poisson's equation. The device aging induced by hot-electron injection is summarized in the formation of a narrow defective interface region whose nature, extension, and position in the channel are the parameters of our investigation. Fundamental differences are observed between the effect of interface states and that of fixed oxide charges. In addition, the channel conductance
G
is shown to be greatly influenced by the extension and position of the zone of defects. The correlation between the degradation of the maximum transconductance and that of the threshold voltage is modeled and demonstrated to be an important tool in the diagnosis of device degradation. The interaction between the damaged and undamaged channel regions is found to produce a transconductance overshoot that attenuates the aging effects. A negative transconductance degradation (i.e., transconductance increase) in the case of positively charged defects and an apparent amelioration of the mobility degradation factor θ in the case of localized acceptor states are two direct consequences of this effect. The errors arising from the modeling of aged devices with 1-D homogeneous analytical models are outlined.