Generation lifetime in fully depleted, enhancement mode SOI MOSFETs

A new technique for determining the generation lifetime in fully-depleted, enhancement-mode SOI (silicon-on-insulator) MOSFETs is described. Island isolated, fully depleted n-channel MOSFETs of various widths and lengths fabricated in different thicknesses of SIMOX (separation by implantation of oxygen) SOI films were used in this experiment. The nature of the charge generation and the charge accumulation processes at the interface between the Si film and the SIMOX buried oxide is complicated and unknown. Hence it is difficult to model analytically the first transient. The problem can be simplified by studying the second, smaller transient which is observed when the back side of the Si film is further accumulated by increasing the negative substrate bias. Both the first and the second transient were studied as functions of the bias conditions and device geometry