High frequency characteristics of dynamic threshold-voltage MOSFET (DTMOS) under ultra-low supply voltage

Dynamic Threshold-Voltage MOSFETs (DTMOS) in which the body is connected to the gate provide extremely high transconductance for supply voltages as low as under 0.7 V. This is because the forward body-source bias lowers the threshold voltage, which results in large gate drive and large drain current. This paper describes the high frequency characteristics of DTMOS for the first time. The DTMOS we analyzed has a small parasitic resistance due to employing optimized Co salicide technology. It also has a small parasitic capacitance due to a reduction in the overlapping region between the gate and drain, which is achieved by employing gate poly-Si oxidation prior to LDD implantation. We obtained an F-t of 78 GHz and an F-max of 37 GHz for a 0.1-mu m-L-eff DTMOS even at a supply voltage of 0.7 V. We also observed an F-max enhancement by 1.5 times for a 0.12-mu m-L-eff DTMOS compared to a conventional SOI MOSFET, which we attributed to high transconductance and large output resistance. The DTMOS can be considered as the most promising device for low-power RF LSIs.