Theoretical modelling of the m.i.s.s structure in one and two dimensions

Abstract

In this thesis, a 1-D computer model of MISS operation is described. This is then used to characterise the qualitative behaviour of the MISS for changes in its structural parameters. The modelled device is assumed to have a four layer MInp structure, commonly used by both theorists and experimentalists. Derived from this 1-D model is a quantitative description of switching in the three layer MIS diode, using a heavily doped (lO(^17)cm(^-3)) n-type substrate. Results are then presented describing its behaviour for changes in fabrication parameters. The computer model of MISS functioning is extended into quasi 2-D by incorporating current spreading in the pn region of the device. Using this, the effect of changes in metal top contact area on device behaviour are explained, with the model providing an accurate quantitative description of these effects for thick oxide (30A) devices. The stability of the MISS as a circuit element is examined in its negative impedance region. A simple equivalent circuit model is produced, and calculated values for negative differential capacitance and negative differential resistances from the quasi 2-D MISS and MIS diode models are used to characterise device behaviour in this region. Within the work a number of accepted terms and ideas are challenged, with their uses being either redefined or discarded. This has been found to be necessary because of the scope of the work presented, which covers such a large range of device parameters.