Lecture 4_0916

14 body effect body is a fourth transistor terminal

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Unformatted text preview: gth: Short Channel Effect 4: Nonideal Transistor Theory CMOS CMOS VLSI Design 4th Ed. 14 Body Effect Body is a fourth transistor terminal Vsb affects the charge required to invert the channel – Increasing Vs or decreasing Vb increases Vt s = surface potential at threshold – Depends on doping level NA – And intrinsic carrier concentration ni = body effect coefficient 4: Nonideal Transistor Theory CMOS CMOS VLSI Design 4th Ed. 15 Body Effect Cont. For small source-to-body voltage, treat as linear 4: Nonideal Transistor Theory CMOS CMOS VLSI Design 4th Ed. 16 DIBL Electric field from drain affects channel More pronounced in small transistors where the drain is closer to the channel Drain-Induced Barrier Lowering – Drain voltage also affect Vt High drain voltage causes current to increase. 4: Nonideal Transistor Theory CMOS CMOS VLSI Design 4th Ed. 17 Short Channel Effect In small transistors, source/drain depletion regions extend into the channel – Impacts the amount of charge required to invert the channel – And thus makes Vt a function of channel length Short channel effect: Vt increases with L – Some processes exhibit a reverse short channel effect i...
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