Contact resistance measurements of a MOSFET

The author examines in detail a recent technique for measuring contact resistance of a MOSFET. It is observed that the equations used for determining the contact resistance based on the ´diode´ mode and the ´MOSFET´ mode differ by a constant factor depending on the device geometry in the limit when the sheet resistance dominates. Ideally, the ratio of the probe voltage/drain current (V_m/I) is independent of the drain current and always higher for the MOSFET mode. In the measurement of a conventional MOSFET, a current-dependent V_m/I is observed. This could be explained by the presence of a depletion region near the voltage probe. A word of caution is given with regard to the effects of leakage in the oxide side-wall for a small-geometry MOSFET.