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ng .c om Design and Implementation of VLSI Systems Lecture04 cu u du on g th an co MOSFET om MOS transistor theory ng cu u du on g th an co Ideal (Shockley) Model Non-ideal model Inverter DC characteristics SPICE .c Schedule for 4 lectures gate-oxide-body sandwich = capacitor om p-type body ng .c + polysilicon gate silicon dioxide insulator (a) co Operating modes Accumulation Depletion Inversion Vg < 0 th an 0 < V g < Vt depletion region du on g + (b) cu u The charge accumulated V >V is proportional to the + excess gate-channel voltage (Vgc-Vt) g t inversion region depletion region (c) du on g th an co ng .c om Gate capacitance as a function of Vgs cu u QuickTime™ and a decompressor are needed to see this picture. The MOS transistor has three regions of operation om co ng .c Cut off Vgs < Vt du on g th an Linear (resistor): Vgs > Vt & Vds < VSAT=Vgs-Vt Current prop to Vds cu u NMOS transistor, 0.25um, Ld = 10um, W/L = 1.5, VDD = 2.5V, VT = 0.4V Saturation: Vgs > Vt and Vds ≥ VSAT=Vgs-Vt Current is independent of Vds How to calculate the current value? .c om MOS structure looks like parallel plate capacitor while operating in inversion ng Gate – oxide – channel du on g th an co Qchannel = CV C = εoxWL/tox = CoxWL (where Cox=εox/tox) V = Vgc – Vt = (Vgs – Vds/2) – Vt gate Vg cu u + + Cg Vgd drain source Vgs Vs Vd channel + n+ n+ Vds p-type body CuuDuongThan

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