Low-temperature mobility behaviour in submicron MOSFETs and related determination of channel length and series resistance

Low temperature behavior of strained-Si n-MOSFETs

“…Typical values for KAPPA(T nom ) were 0.22 (nchannel) while δK values of 4.5e -4 /°K (n-channel) were noted. The fact that MOSFET drain and source lateral depletion widths increase with increasing temperature [5] may help to explain the observed temperature dependences of ETA and KAPPA. The ETA parameter was extracted from the difference between two currents measured at a V GS bias in subthreshold with V ds set to +0.1V and ±2.5V [6].…”

“…The effeccive surface field can be expressed as E eff =(ηQ inv +Q B )/ε Si (5) where best values are η = l / 2 for (100) electrons and η = 1/3 for holes and (111) or (110) electrons [4]. In this equation, ε Si is the permittivity of silicon, Q inv is the inversion layer charge and Q B is the bulk depletion layer charge.…”

“…The inversion layer charge must be accurately known in (5) to obtain an accurate evaluation of mobility. At sufficiently large voltages above the channel threshold voltage the inversion layer charge approaches…”

Analytical modelling of the MOS transistor

“…2 illustrates the influence of 0 both on the values of the extrapolated threshold voltage Utext and the maximum field effect mobility pfemau. When the source-drain series resistance, Rbd, has to be taken into account, which is the case of short gate length derices, one has to replace, in the preceding set of equations, the intrinsic mobility reduction factor 8 by the effective one: 0" = 0 + + WpoC,,K,d/L [13]. So, an increase of the series resistance will result in an accentuated mobility reduction and in a decrease of the extrapolated threshold voltage [14].…”

“…The output conductance gd = cll,/dUd is then deduced from (12) as [17] (13) where GC1 = gd(O) = Wpu,CdM'/(qL) esp (qA( U , -V t ) / k T ) is the ohmic coiiductance.…”