Conduction mechanisms in thin-film accumulation-mode SOI p-channel MOSFETs

A model developed to explain conduction mechanisms in thin-film accumulation-mode SOI p-channel MOSFETs is discussed. It is found that, unlike that which occurs in thin-film fully depleted n-channel devices, there is little or no coupling between the front and back gates, unless the surface-state density is so high that the film remains depleted even when an accumulation channel is formed. The apparent front threshold shift is explained by back-gate modulation of a body current, flowing from the source to the drain. Indeed, the body of the device presents a p⁺-p^--p⁺ structure whose conductivity is controlled by the depth of the depletion zones arising from the top and the bottom of the silicon film. The model is used to calculate drain current as a function of front- and back-gate bias as well as output characteristics