Effect of probe coupling on MOSFET series resistance extraction up to 110 GHz

Abstract

The measurement of series extrinsic resistances of MOSFETs is not straightforward and the gate resistance (Rg) in particular is very sensitive to noise measurement and measurement inaccuracies. They are critical elements that need an accurate estimation for proper FET modeling and RF figures of merit assessment, as they limit the extrinsic cutoff and maximum oscillation frequencies (ft, fmax) in deeply scaled CMOS technologies. This work compares the extrinsic resistances extraction with different off-wafer and on-wafer calibration and de-embedding methods to provide an insight on the appropriate procedure for accurate correction. Then, measurements obtained with three different probe technologies are compared. A resonance-like signature specific to each probe technology is observed, caused by unwanted coupling between the probe and the on-chip neighbor environment of the test structures. This coupling is not well corrected by the calibration and de-embedding procedure and is reflected back on the corrected measurements, mainly on the fmax and Rg curves. Overall, the best probe technology for DC-110 GHz measurements among the probes tested in this work is identified to be Picoprobe, featuring a gate resistance extraction with less than ±3% variation from 10 to 60 GHz.