New three dimensional doping profile for devices in subthreshold circuit

One of the important aspects of integrated circuit design is the doping profile of a transistor along its length, width and depth. Devices for super-threshold circuit usually employ halo and retrograde doping profiles in the channel to eliminate many unwanted effects. Devices for subthreshold circuits do not require halo and retrograde doping profiles due to lower operating voltage. This will reduce the number of steps in the fabrication process, parasitic capacitance and substrate noise dramatically. This paper introduces a new doping profile for devices to be used in subthreshold circuits. The proposed scheme addresses doping variations along all the dimensions of the device. This new doping scheme proposes to employ Gaussian distribution of doping concentration along the length of the channel with highest concentration at the middle of the channel. The doping concentration across the depth of the device is exponentially decreasing with channel surface at the highest concentration. The proposed doping scheme keeps the doping concentration along the width of the device uniform. Results show that the optimized device with the proposed doping profile offers higher ON current in the subthreshold device.