Berkeley ELENG 241B - MOS Models, Technology Scaling (16 pages)

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MOS Models, Technology Scaling



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MOS Models, Technology Scaling

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Lecture Notes


Pages:
16
School:
University of California, Berkeley
Course:
Eleng 241b - Advanced Digital Integrated Circuits

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EE241 EE241 Spring 2002 Advanced Digital Integrated Circuits Lecture 2 MOS Models Technology Scaling UC Berkeley EE241 B Nikolic Digital Gate Basic Properties Functionality Robustness Swing Noise margins Delay tPLH t PHL Power energy consumption Power Delay Product Area Density UC Berkeley EE241 B Nikolic 1 EE241 Basic CMOS Gate Properties Output levels determined by supply Large noise margins Performance loss at low voltages UC Berkeley EE241 B Nikolic The MOS Transistor S VGS VDS G n V x ID D n L x p substrate B MOS transistor and its bias conditions UC Berkeley EE241 B Nikolic 2 EE241 MOS Current Vertical field set by VGS induces channel charge l Gradual charge assumption l Fixed charge is completely cancelled at VGS VTh l Charge in the channel is Qn Cox VGS VTh VC x l By Ohm s law IDS WQn x v WCox VGS VTh VC x E l Also E dVC x dx l Key assumption is that v E and mobility is constant l UC Berkeley EE241 B Nikolic MOS Current IDS WCox VGS VTh VC x E IDS WCox VGS VTh VC x VC x dx l When integrated I DS l W V Cox VGS VTh DS VDS L 2 Transistor saturates when VGD VTh the channel pinches off at drain s side I DS UC Berkeley EE241 W 2 Cox VGS VTh 2L B Nikolic 3 EE241 MOS Current VGS VDS VGS VT G D S n VGS VT n Pinch off UC Berkeley EE241 B Nikolic MOS Transistor Models Long channel Short channel Rabaey UC Berkeley EE241 B Nikolic 4 EE241 n m s Velocity Saturation sat 105 Constant velocity Constant mobility slope c 1 5 V m UC Berkeley EE241 B Nikolic Velocity Saturation l l Velocity is not always proportional to field Modeled through variable mobility mobility degrades at high fields v l l eff E E 1 E0 n 1 n E0 2v sat eff NMOS n 2 PMOS n 1 Hard to solve for n 2 Assume n 1 close enough Sodini84 UC Berkeley EE241 B Nikolic 5 EE241 Velocity Saturation l Piecewise linear approximation eff E E E EC v 1 EC v sat E EC EC 2v sat eff Toh Ko Meyer JSSC 8 88 EC is a function of doping and vertical field controled by VGS EC is around 5V m in 0 25 m technology UC Berkeley EE241 B



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