Effect of substrate contact shape and placement on RF characteristics of 45 nm low power CMOS devices

The substrate resistance of 45 nm CMOS devices shows a strong dependence on the distance between the device edge and the substrate ring; as well as on the number of sides that the device is surrounded by the contact ring. We find that the unilateral gain is impacted by the substrate resistance (R_sx) through the gate-body capacitance feedback path at low to medium frequencies (< 20 GHz). At mm wave frequencies, the unilateral gain is affected by the R_sx through the drain-body capacitance pole, and deviates from the ideal -20 dB/dec slope. The impact of substrate resistance on f_T, maximum available gain, high frequency noise and power characteristics of the devices is minimal.