The drive strength of a FET, ldasr is given, in the ideal case, by: l dasr = Z m

Question

The drive strength of a FET, ldasr is given, in the ideal case, by: l dasr = Z mu R (VG - V1)2 / 2dl which is the same as Eq. 6.52 and 5.63 with the oxide capacitance Ci explicitly written out as 0 R / d (as usual 0 = dielectric permittivity of free space; R = relative dielectric constant -- this time of SiO2 not Si; d = oxide thickness; L = channel length; Z = width; mu = effective mobility) Explain the physical reasons for the scaling of Idzar:. linearly with width inversely with oxide thickness inversely with channel length & linearly with mobility quadratically with VG- VT(Hint: express the current in the channel in terms of microscopic parameters like mobility, charge density, and electric field. Relate those microscopic quantities to the device parameters and applied voltages.)

Explanation / Answer

by observing the expression of Idsat 1) Width is directly proportional to Idsat so it has to be scaled linearly with width 2)oxide thickness (d) is inversely proportional to Idsat. 3) Length is inversely proportional to Idsat so it has to be scaled inversely with length 4) mobility (mew) is directly proportional to Idsat so it has to be scaled linearly with mobility 5) (Vgs-Vt) is quardratically proportional to Idsat so it has to be scaled linearly with (Vgs-Vt)^2

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