Study of Soi Annular Mosfet

Abstract

Annular transistors are enclosed geometry transistors which reduce device leakage by eliminating diffusion edges. Due to the asymmetry of these devices with respect to inner and outer terminals; this study evaluates the behavior of the annular transistor with respect to both the inner and outer drain terminals. Along with this, the effects of geometry of the device on the leakage current and kink effects, related to the NMOS SOS devices at various temperatures are evaluated. Performance of NMOS annular transistor across four different transistor lengths (L= 1.3um, 1.4um 1.5um and 1.6um) are studied along with comparison to a NMOS rectilinear transistors (L=1.4um) at room temperature (RT) and 275C. The experimental results demonstrated a decrease in threshold voltage between the annular transistor with an inner drain compared to the rectilinear transistor by 20% at RT and 33% at 275C. Threshold voltage for an annular transistor with an inner drain is greater than the same transistor with an outer drain by 2% at RT and 3% at 275C. The Ion/Ioff ratio for annular devices with an inner drain compared to a rectangular device shows an improvement of 99% at both RT and 275C. The Ion/Ioff ratio for the same annular transistor with an inner drain verses an outer drain is greater by 75% at RT and 51% at 275C. The kink voltage for an annular transistor with an inner drain is greater than rectangular transistor by 2% at RT while 5% lower at 275C. Kink voltage for annular transistor with an outer drain is greater than the same transistor with an inner drain by 2% at RT and 1% at 275C. Early voltage (VA) for an annular transistor with an inner drain is greater than rectangular transistor by 22% at RT and 21% at 275C. VA for an annular transistor with an inner drain is greater than the same transistor with an outer drain by 22% at RT and 15% at 275C. Output resistance (rds) per unit width of an annular transistor with an inner drain is greater than rectilinear transistor by 77% at RT and 79% at 275C. rds for annular transistor with an inner drain is greater than that with an outer drain of the same device by 4% at RT and is lower by 25% at 275C. In conclusion when it is of the utmost importance to control leakage and device self gain annular transistors provide a significant improvement over the classical rectangular transistor. Some enhanced performance is observed when the inner contact is selected as the drain. It should also be noted that measurement accuracy precludes the taking of any conclusion where changes of less than 2% are observed.