Clarification of floating-body effects on drive current and short channel effect in deep sub-0.25-micron partially depleted SOI MOSFETs

We point out for the first time that floating-body effects cause the reduction of the saturation drive current in partially depleted (PD) SOI MOSFETs. It is demonstrated that when the channel concentration of the SOI MOSFETs is set higher in order to suppress the increase of the off current caused by floating-body effects, the drive current decreases due to the large body effect. In the conventional SOI structure where the source-drain junction is in contact with the buried oxide, the 0.18-micron floating PD SOI MOSFET suffers around 17 percent decrease in the drive current under the same threshold voltage (V(th)) in comparison with the body-fixed one. However, floating PD SOI MOSFETs show smaller V(th)-roll-off. Further considering the short channel effect down to the minimum gate length of 0.16 micron, the current decrease becomes 6 percent. Also, we propose a floating PD SOI MOSFET with shallow source-drain junction (SSD) structure to suppress the floating-body effects. By using the SSD structure, we confirmed an increase in the drive current. (Author)