An Accurate Technique For Calculating Multiplication Currents, Including Non-localised Impact Ionisation

The substrate current in MOSFET´s is conventionally calculated by integrating the ionisation rate a(E) along the path of the channel current. As supply voltages are scaled down the total energy available from the field is comparable to the ionisation threshold energy and this method becomes inaccurate and physically invalid. This paper describes a new technique for calculating multiplication currents in MOSFET´s based on a modification of the lucky drift theory developed by B K Ridley. It is shown that the theory properly includes the non-localised nature of impact ionisation and agrees well with experimental results.