NMOS (N-Cannel Metal Oxide Semiconductor) Transistor e e e oxide insulator e e e NMOS Transistor in Equilibrium oxide insulator Wen te transistor is left alone, some electrons from te wells diffuse into te material to fill oles. Tis creates negative ions in te material and positive ions are left beind in te material.
NMOS Transistor in Cutoff V GS > 0 oxide insulator _ Wen a small, positive V GS is applied, oles move away from te. Electrons from complete atoms elsewere in te material move to fill oles near te instead. NMOS Transistor Cannel V GS > V TH(N) oxide insulator e e _ e e e Wen V GS is larger tan a tresold voltage V TH(N), te attraction to te is so great tat free electrons collect tere. Tus te applied V GS creates an induced cannel under te (an area wit free electrons).
NMOS Transistor rain Current V GS > V TH(N) oxide insulator e e _ e e e V S > 0 Wen a positive V S is applied, te free electrons flow from te to te. (Positive current flows from to ). Te amount of current depends on V S, as well as te number of electrons in te cannel, cannel dimensions, and material. NMOS Transistor V S V GS I G oxide insulator I G I G V GS _ I S - V S
NMOS I-V CHARACTERISTIC G I G V GS _ I S - V S Since te transistor is a 3-terminal device, tere is no single I-V caracteristic. Note tat because of te insulator, I G = 0 A. We typically define te MOS I-V caracteristic as I vs. V S for a fixed V GS. MOES OF OPERATION For small values of V GS, V GS V TH(N), te cannel is not formed. No current flows. Tis is cutoff mode. Wen V GS > V TH(N), current I may flow from to, and te following modes of current flow are possible. Te mode of current flow depends on te propelling voltage, V S, and te cannel-inducing voltage, V GS V TH(N). Wen V S < V GS V TH(N), current is starting to flow. I increases rapidly wit increased V S. Tis is triode mode. Wen V S V GS V TH(N), current is reacing its maximum value. I does not increase muc wit increased V S. Tis is called saturation mode.
NMOS I-V CHARACTERISTIC Cutoff Mode Occurs wen V GS V TH(N) I = 0 Triode Mode Occurs wen V GS > V TH(N) and V S < V GS -V TH(N) I = W µ n C L OX ( V GS V TH(N) ( V S /2)) V S Saturation Mode Occurs wen V GS > V TH(N) and V S V GS -V TH(N) 2 ( V V ) ( 1 λ V ) W 1 I = µ ncox GS TH(N) L 2 n S NMOS I-V CHARACTERISTICS I triode mode saturation mode V GS = 3 V V S = V GS -V TH(N) V GS = 2 V V GS = 1 V V S cutoff mode
PMOS (P-Cannel Metal Oxide Semiconductor) Transistor oxide insulator Same as NMOS, only and switced PMOS Transistor Cannel V GS < V TH(P) < 0 oxide insulator e e e e e e e e e e Wen V GS is more negative tan a tresold voltage V TH(P), te attracts many positive ions and oles (repels electrons) Tus te applied V GS creates an induced cannel under te (an area wit positive ions).
PMOS Transistor rain Current V GS < V TH(P) < 0 V S < 0 oxide insulator e e e e e e e e e e Wen a negative V S is applied, te positive ions flow from te to te. (Positive current flows from to ). Te amount of current depends on V S, as well as te number of ions in te cannel, cannel dimensions, and material. PMOS TRANSISTOR G I G V GS _ I S - V S Symbol as dot at. NMOS does not. I, V GS, V S, and V TH(P) are all negative. Tese values are positive for NMOS. Cannel formed wen V GS < V TH(P). Opposite for NMOS. Saturation occurs wen V S V GS V TH(P). Opposite for NMOS.
PMOS I-V CHARACTERISTIC Cutoff Mode Occurs wen V GS V TH(P) I = 0 Triode Mode Occurs wen V GS < V TH(P) and V S > V GS -V TH(P) I W = µ p C L OX ( V GS V TH(P) ( V S /2)) V S Saturation Mode Occurs wen V GS < V TH(P) and V S V GS -V TH(P) 2 ( V V ) ( 1 λ V ) W 1 I = µ pcox GS TH(P) L 2 p S PMOS I-V CHARACTERISTICS V S cutoff mode V GS = -1 V V GS = -2 V V S = V GS -V TH(P) V GS = -3 V I saturation mode triode mode