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454Lec05_MOSFET2-1

454Lec05_MOSFET2-1 - ECEN 454 Digital Integrated Circuit...

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ECEN 454 Lecture 5 1 ECEN 454 Digital Integrated Circuit Design Lecture 5 MOS Transistor II
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ECEN 454 Lecture 5 2 MOS Transistors N-channel MOS transistor Enhancement mode vs. depletion mode transistors Enhancement: no conducting channel exists at zero gate bias Depletion: a conducting channel exists at zero gate bias Symbols for enhancement-mode MOSFETs
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ECEN 454 Lecture 5 3 Switch Model of NMOS
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ECEN 454 Lecture 5 4 Threshold Voltage (1) Band diagram when the inversion layer is formed Four factors that determine the threshold voltage Work function difference between the gate and the channel Change the surface potential at the silicon surface Offset the depletion region charge Offset the nonideal charge at the interface between the gate oxide and silicon
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ECEN 454 Lecture 5 5 Threshold Voltage -- NMOS (1) Work function difference (built-in potential) or Change the surface potential by Offset the depletion region charge Depletion charge density: no body effect (V SB =0) Depletion charge density: w/ body effect ) ) ( metal substrate M F GC φ φ = Φ ) )( ) ( poly gate substrate F F GC φ φ = Φ F φ 2 SB F Si A B V N q Q + = φ ε 2 2 F Si A B N q Q φ ε 2 2 0 =
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