A new AC technique for accurate determination of channel charge and mobility in very thin gate MOSFET´s

A new method is described for determining the channel charge and mobility of a MOS transistor as a function of gate bias from the ac admittance measurements. The admittance of the conduction channel of the MOSFET is derived from a transmission line model. The peaks of the versus ω curves are used to deduce gate-channel capacitance and mobility. The mobile carrier density and mobility in very thin-oxide MOSFET\´s can be measured more accurately using this ac method, since a zero lateral field and a uniform mobile charge distribution along the channel is maintained with zero drain-source voltage and interface trap effects are reduced by using high test frequencies. Measured data on the electron mobility versus gate voltage are presented for 90-A gate dielectric MOS transistors.