Pulsed capacitance-voltage measurements on Al2O3-based MOS capacitors

Pulsed capacitance-voltage (C-V) technique was applied to the study of electron trapping in MOS capacitors with amorphous Al₂O₃ as insulating layer. This technique allows to observe fast trapping/detrapping processes as it measures a C-V curve in a few hundred of microseconds. The dependences of the C-V curve with the applied bias and the charging time was investigated. A positive displacement of the voltage value corresponding to a constant capacitance (V_C) was observed as the top level of the pulsed signal is increased and a linear dependence was obtained. Regarding the charging time, the positive V_C-shift showed a logarithmic dependence, evidencing the presence of a tunneling front advancing into the dielectric. Moreover, a fixed V_C-shift was observed after charging with long times (~500 ms), related to traps that can not be discharged between measurements.