Accumulation Mode, Saturation Regime

Saturation turns on when the charge at drain vanishes, that is when g(L) = 0. The saturation current can be estimated by following a method introduced by Brown and coworkers [16] and developed further by Horowitz et al. [17], We assume that the accumulation layer extends from the source up to a point where V(x) = K (see Fig. 14-10), beyond which it turns to a depletion layer. The drain current is hence given by the sum of two integrals. 

The second term is integrated up to the saturation voltage where Q L) — 0. As in the previous section, we change the integration variable from V to W, which is done via Eq. (14.48), and integrate from VT(Vg) = 0 to W(Vj,sa ) = ds. 

The result can be simplified by making use of the above-defined pinch-off voltage [Eq. (14.54)] and dielectric capacitance of the semiconducting layer. Further simplifications result from the assumptions that Cj C, (Eq. (14.57)), and that the dopant and carrier concentrations are equal (Eq. (14.58)). 

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