High-k shallow traps observed by charge pumping with varying discharging times

Abstract

In this paper, we investigate the influence of falling time and base level time on high-k bulk shallow traps measured by charge pumping technique in n-channel metal-oxide-semiconductor field-effect transistors with HfO2/metal gate stacks. N-T-V-high level characteristic curves with different duty ratios indicate that the electron detrapping time dominates the value of N-T for extra contribution of I-cp traps. N-T is the number of traps, and I-cp is charge pumping current. By fitting discharge formula at different temperatures, the results show that extra contribution of I-cp traps at high voltage are in fact high-k bulk shallow traps. This is also verified through a comparison of different interlayer thicknesses and different TixN1-x metal gate concentrations. Next, N-T-V-high level characteristic curves with different falling times (t(falling time)) and base level times (t(base level)) show that extra contribution of I-cp traps decrease with an increase in t(falling time). By fitting discharge formula for different t(falling time), the results show that electrons trapped in high-k bulk shallow traps first discharge to the channel and then to source and drain during t(falling time). This current cannot be measured by the charge pumping technique. Subsequent measurements of N-T by charge pumping technique at t(base level) reveal a remainder of electrons trapped in high-k bulk shallow traps. (c) 2013 AIP Publishing LLC.