MOSFET Characteristics

[urn]

Hi,

I would to know the effect of (W/L) on the transistor characteristics.

i.e., even though if we keep the ratio same, how would different (W/L)s effect the shape of the transfer curves of the MOSFET.

Ex: (6/2) , (12/4), (24/8) etc. In all these examples the ratio is 3 but the characteristics are different.

Thanks in advance,

 

[erikl]

Due to several physical effects (VS = velocity saturation, VFMR = vertical field mobility reduction, CLM = channel length modulation, DIBL = drain induced barrier lowering) these effects exert varying impacts on the transistor characteristics. The first 3 mentioned effects are important mostly in strong inversion operation (VS acting mainly on short channel FETs to decrease drain current with shorter L, whereas VFMR and CLM tend to decrease Id at longer L ).
DIBL acts with increasing Id at shorter L, also in weak and moderate inversion operation.

For more info see the books on Analog Circuit Design, mentioned in this forum in various topics. I'd recommend especially D. Binkley's book Tradeoffs and Optimization in Analog CMOS Design, where these effects are exhaustively described and presented with characteristics, s. fig. 3.11 & 3.18 for VS & VFMR effects, fig. 3.35 for CLM impact, and 3.40 for DIBL influence.