Lecture 4_0916

18 leakage what about current in cutoff simulated

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Unformatted text preview: n which Vt decreases with L 4: Nonideal Transistor Theory CMOS CMOS VLSI Design 4th Ed. 18 Leakage What about current in cutoff? Simulated results What differs? – Current doesn’t go to 0 in cutoff 4: Nonideal Transistor Theory CMOS CMOS VLSI Design 4th Ed. 19 Leakage Sources Subthreshold conduction – Transistors can’t abruptly turn ON or OFF – Dominant source in contemporary transistors Gate leakage – Tunneling through ultrathin gate dielectric Junction leakage – Reverse-biased PN junction diode current 4: Nonideal Transistor Theory CMOS CMOS VLSI Design 4th Ed. 20 Subthreshold Leakage Subthreshold leakage exponential with Vgs n is process dependent – typically 1.3-1.7 Rewrite relative to Ioff on log scale S 100 mV/decade @ room temperature 4: Nonideal Transistor Theory CMOS CMOS VLSI Design 4th Ed. 21 Gate Leakage Carriers tunnel thorough very thin gate oxides Exponentially sensitive to tox and VDD – A and B are tech constants – Greater for electrons • So nMOS gates leak more Negligible for older processes (tox > 20 Å...
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This note was uploaded on 01/22/2014 for the course ECE 261 taught by Professor Morizio,j during the Winter '08 term at Duke.

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