Answer Happy

A large area n-channel MOSFET transistor has been characterised by means of la(Vas) curves at various values of the gate bias Vgs. Using the graphical data shown on Figure 4, and assuming that the width of the gate is Z = 1000 um, its length is L = 10 um, the thickness of the channel, at full enhancement, is d = 40 nm, the effective permittivity of the oxide is Eox = 10, and the longitudinal effective mass is m = 0.1 me, estimate the following: (a) the electron mobility within the device's channel region; [10 marks] (b) the threshold voltage Vth and the effective doping level within the channel Na, neglecting any edge effects close to pinch-off; [3 marks] (c) the top of the frequency band over which the device can provide useful gain (the highest frequency for over-unity gain) at gate bias of Vgs = 5 V, assuming that the transit cyclic (or unity gain) frequency of the device can be approximated as wt = gsd/Cgs, where gsd is the source-drain conductance;