Semiconductor Device Modeling & Characterization Lecture 23 Professor Ronald L. Carter ronc@uta.edu Spring 2001 L23 April 10

MOSFET equivalent circuit elements Fig 10.51* L23 April 10

MOS small-signal equivalent circuit Fig 10.52* L23 April 10

MOS channel- length modulation Fig 11.5* L23 April 10

Analysis of channel length modulation L23 April 10

Channel length mod- ulated drain char Fig 11.6* L23 April 10

Fully biased n- channel VT calc L23 April 10

Q’d,max and xd,max for biased MOS capacitor Fig 8.11** |Q’d,max|/q (cm-2) xd,max (microns) L23 April 10

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Values for fms with silicon gate L23 April 10

I-V relation for n-MOS ohmic ID non-physical ID,sat saturated VDS,sat L23 April 10

Analysis of channel length modulation L23 April 10

Associating the output conductance ID ID,sat VDS,sat VDS L23 April 10

n-channel enhancement MOSFET in ohmic region 0< VT< VG e- channel ele + implant ion Channel VS = 0 0< VD< VDS,sat EOx,x> 0 n+ e-e- e- e- e- + + + + + + + + + + + + n+ Depl Reg p-substrate Acceptors VB < 0 L23 April 10

Ion implantation L23 April 10

“Dotted box” approx L23 April 10

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Mobilities L23 April 10

Fully biased n- channel VT calc L23 April 10

Subthreshold conduction Below O.S.I., when the total band-bending < 2|fp|, the weakly inverted channel conducts by diffusion like a BJT. Since VGS>VDS, and below OSI, then Na>nS >nD, and electr diffuse S --> D Electron concentration at Source Concentration gradient driving diffusion L23 April 10

Subthreshold current data Figure 10.1** Figure 11.4* L23 April 10

Mobility variation due to Edepl Figures 11.7,8,9* L23 April 10

Velocity saturation effects Figure 11.10* L23 April 10

References *Semiconductor Physics and Devices, by Donald A. Neamen, Irwin, Chicago, 1997. **Device Electronics for Integrated Circuits, 2nd ed., by Richard S. Muller and Theodore I. Kamins, John Wiley and Sons, New York, 1986 L23 April 10