Lecture 25 - Short Channel MOSFETs

Lecture 25 - Short Channel MOSFETs - Modern MOSFETs...

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1 EE360 – Lecture 25 Modern MOSFETs Questions to be answered: • Why do we want short channels in MOSFETs? • What design criteria do we need to take into account for short channel MOSFETs? EE360 – Lecture 25 Maximizing Cutoff Frequency To maximize cutoff frequency: Improve mobility – good design (minimal surface scattering, low doping) or – higher-mobility materials (not silicon) Reduce channel length – good design (minimize “short channel” effects) and – good fabrication process (high resolution lithography, control of dopant locations) Minimize extrinsic capacitances (neglected in analysis) – Source-drain overlap minimized by high-precision alignment or – Self aligned gate process 2 2 L V f D n m π µ For the linear region
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2 EE360 – Lecture 25 Why do we want short channels? • Higher density integration: we can pack more devices into the same area • Higher speed: cutoff frequency and switching speed depend strongly on channel length • Lower power consumption: smaller V D for a given I D What limits short channel devices? Performance tradeoffs: “Short-channel effects” force us to carefully consider performance gains and penalties for various designs. Fabrication technology:
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Lecture 25 - Short Channel MOSFETs - Modern MOSFETs...

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