Channel length-dependent series resistance?

A recently developed series resistance (R_SD) extraction procedure from a single nanoscale device is shown to be highly robust. Despite these virtues, the technique unexpectedly results in a channel length-dependent R_SD which is observed across a wide range of channel lengths and across many different technologies (SiO₂, SiON, and high-k) (see Figs. 1a-f). This observation obviously raises some concerning issues and implications as R_SD is universally accepted as channel length-independent. However, careful examination of the R_SD extraction procedure as well as comparison between R_SD-corrected field effect mobility (u_FE) and geometric magnetoresistance mobility (u_MR) suggests that this unexpected observation may be valid.