Accuracy of the charge pumping technique for small geometry MOSFETs

The channel-length dependence of the charge-pumping current for MOSFETs is investigated using a two-dimensional simulation technique. The dependence of charge-pumping current on signal offset voltage for various MOSFET channel lengths is studied using energy-dependent interface trap distributions. Simulation results are compared to experimental charge-pumping measurements on irradiated MOSFETs with different gate lengths with good agreement for the shape of the curves. It is found that as the effective channel length decreases the accepted charge pumping model has decreasing accuracy that results in an underestimation of the mean interface trap density. The loss in accuracy is due to the nonuniformity of surface potential across the channel caused by source/drain proximity. Using the charge-pumping technique to measure interface trap densities on advanced devices with an effective channel length less than 1 μm may result in unacceptable errors