MOS Transistors - Faculty

1 1 MOS Transistors Silicon substrate doped with impurities Adding or cutting away insulating glass (SiO2) Adding wires made of polycrystalline silicon (polysilicon, poly) or metal, insulated from the substrate by SiO2 Drain Source Gate n n Drain Source Gate SiO2 (insulator) p-type (doped) substrate Drain Source Gate nMOS transistor pMOS transistor channel Width W Length L Conductor (poly) 2 MOS transistor Switches N a b s N-switch a b s S = 0 S = 1 Good 0, Poor 1 0 1 0 1 (degraded) 2 3 MOS transistor Switches P-switch a b s P a b s S = 1 S = 0 Good 1, Poor 0 1 0 1 0 (degraded) a b s s CMOS switch a b s C S = 0 S = 1 a Good 0 Good 1 (Transmission gate) b s s 4 Signal Strength Strength of signal How close it approximates ideal voltage source VDD and GND rails are strongest 1 and 0 nMOS pass strong 0 But degraded or weak 1 pMOS pass strong 1 But degraded or weak 0 Thus nMOS are best for pull-down network 3 5 Pass Transistors Transistors can be used as switches 6 Transmission Gates Pass Transistors produce degraded outputs Transmission gates pass both 0 and 1 well 4 7 Complementary CMOS Complement

1 1 MOS Transistors • Silicon substrate doped with impurities • Adding or cutting away insulating glass (SiO 2) • Adding wires made of polycrystalline silicon (polysilicon, poly) or metal, insulated from the substrate by SiO 2

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