Numerical analysis of island-edge effects in SOS MOSFETs

Degradation of electric characteristics of SOS MOSFETs occurs due to a parasitic transistor in the islands edge. When SOS devices are fabricated with a wet etch process, the island-edge effects are caused by high interface-state densities in the ⟨111⟩ sloping edge and field concentrations near the edge. However, although a nearly vertical island-edge can be obtained by a dry etch process, there still remains field concentration and some damage at the Si-SiO₂ interface. Numerical simulation results on the parasitic transistors in the ⟨111⟩ sloping island edge and in the vertical island edge are reported. The effective width and threshold voltage of the parasitic edge transistors were obtained by two-dimensional simulation, and edge-effects on subthreshold characteristics in SOS MOSFETs were studied. The simulation results showed good agreement with experiment