Transistor doping profile optimization for low power subthreshold circuits

Conventional device uses the halo and retrograde doping profiles to minimize short channel effect, body punch through, drain induced barrier lowering (DIBL) and variation of the threshold voltage. Also scaled non-uniform doping profile is required for super-threshold circuit to provide better control of the electrical characteristics of the device. Devices for subthreshold circuits do not require halo and retrograde doping profiles. This will reduce the number of steps in the fabrication process, parasitic capacitance and substrate noise dramatically. This paper introduces a new three-dimensional doping scheme for the transistors in subthreshold circuits. It is characterized by the absence of halos at the source and drain region. Under the proposed scheme there can be four different doping profiles for subthreshold device. In this paper we concentrate on Gaussian doping distributions both along the channel and across the depth of the transistor. Results show that the optimized device with the proposed doping profile improves the ON current. The analysis is done by varying the doping profile and gate-source voltage (V_gs), and the observations are compared with the super-threshold device.