USA EE 534 - Lecture 05: MOS Resistance and Static CMOS inverter (16 pages)

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Lecture 05: MOS Resistance and Static CMOS inverter



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Lecture 05: MOS Resistance and Static CMOS inverter

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Lecture Notes


Pages:
16
School:
University of South Alabama
Course:
Ee 534 - VLSI Design Systems

Unformatted text preview:

CMOS Inverter Dynamic EE534 VLSI Design System Summer 2004 Transient or dynamic response determines the maximum speed at which a device can be operated VDD Last lecture s focus Lecture 05 MOS Resistance and Static CMOS inverter Vout 0 CL Rn tpHL f Rn CL Vin V DD Review Sources of Capacitance Sources of Resistance Vout Vin Today s focus Vout2 CL Top view Poly Gate Drain n M2 Vin CGD12 W M4 CDB2 CDB1 M1 Source n CG4 Vout L Vout2 Cw M3 CG3 intrinsic MOS transistor capacitances extrinsic MOS transistor fanout capacitances wiring interconnect capacitance MOS structure resistance Ron Source and drain resistance Contact via resistance Wiring resistance Equivalent MOS Structure Resistance The simplest model assumes the transistor is a switch with an infinite off resistance and a finite on resistance Ron VGS VT S Ron D However Ron is nonlinear so use instead the average value of the resistances Req at the end points of the transition VDD and VDD 2 Req Ron t1 Ron t2 The on resistance is inversely proportional to W L Doubling W halves Req For VDD VT VDSAT 2 Req is independent of VDD see plot Only a minor improvement in Req occurs when VDD is increased due to channel length modulation Once the supply voltage approaches VT Req increases dramatically 7 x105 for VGS VDD VDS VDD VDD 2 6 Req Ohm MOS Structure Resistance 5 4 3 2 1 0 0 5 1 1 5 2 2 5 VDD V VDD V NMOS k PMOS k 1 35 115 1 5 19 55 2 15 38 2 5 13 31 Req for W L 1 for larger devices divide Req by W L Source and Drain Resistance Contact Resistance G D S RS RD RS D LS D W R RC where LS D is the length of the source or drain diffusion R is the sheet resistance per square of the source or drain diffusion 20 to 100 Rc is contact resistance More pronounced with scaling since junctions are shallower Wire Resistance L A Sheet Resistance R R H R1 L HW R2 W Material Silver Ag m 1 6 x 10 8 Copper Cu Gold Au Aluminum Al Tungsten W 1 7 x 10 8 2 2 x 10 8 2 7 x 10 8 5 5 x 10 8 Material n p well diffusion n p diffusion n p diffusion with



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