An analysis of small-signal substrate resistance effect in deep-submicrometer RF MOSFETs 

[[abstract]]Two different explanations of the S-22 kink phenomenon in deep-submicrometer RF MOSFETs have been reported in the Hjelmgren and Litwin attributed the phenomenon to the substrate resistance, while Lu et al. concluded that it results from the transconductance, or simply speaking, the size of the transistor. In this paper, we extend the dual-feedback circuit methodology for the three-terminal FET model proposed by Lu et al. into a more general four-terminal model in order to account for the influence of the substrate resistance. Our results show that, for a given MOSFET, either substrate resistance or transconductance may cause a kink in S-22. In addition to the single kink, which results from the above two factors, the double kinks, which appear when the substrate resistance of a MOSFET is within a middle range (approximately 10(2) to 10(4) Omega) can also be accounted for by our extended model. Experimental data representative of 0.25-mum-gate MOSFETs are adopted to verify our theory. Excellent agreement between theoretical values and experimental data has been found, which indicates our theory can successfully explain the S-22 kink phenomenon in deep-submicrometer RF MOSFETs.[[note]]SC