Under this condition: University of California, Berkeley.This is a good assumption since the inversion charge is an exponential function of the surface potential.A simple approximation is to assume that once inversion happens, the depletion region stops growing.Apply KCL around loop: Gate (n+ poly) + − − − − − − − University of California, Berkeley.For this condition, the surface potential has to equal the negative of the p-type potential.The threshold voltage is defined as the gate-body voltage that causes the surface to change from p-type to n-type.At this point, the depletion region stops growing and the extra charge is provided by the inversion charge at surface + − + + + + + + + + + + University of California, Berkeley.The surface potential increases to a point where the electron density at the surface equals the background ion density.− − − − − − − − − Body (p-type substrate) − − − − − − − − Inversion Charge has a square-root dependence on applied bias + − + + + + + + + + + + University of California, Berkeley.Potential drop across the oxide and depletion region.Positive charge on gate terminates on negative charges in depletion region.− − − − − − − − − Body (p-type substrate) − − − − − − − − Depletion: VFB Sandwich of conductors separated by an insulator.Gate (n+ poly) Body (p-type substrate) MOS Capacitor I-V Curve University of California, Berkeley.
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