Analysis on accuracy of charge-pumping measurement with gate sawtooth pulses [MOSFETs]

Charge-pumping (CP) measurement is performed on MOSFETs with their gates tied to sawtooth pulses. Influence of both rise time (t_r) and fall time (t_f) on the CP current of the devices with different channel lengths is investigated at different pulse frequencies. Results show that the dominant mechanism affecting the measurement accuracy is the energy range of interface-trap distribution D_it(E) swept by the gate signal for frequencies below 500 kHz and carrier emission for frequencies above 500 kHz. For frequencies higher than 600 kHz, incomplete recombination could be an additional mechanism when t_f is too short. Hence, it is suggested that low frequency is more favorable than high frequency, especially for sawtooth pulses with long t_r and short t_f , due to little carrier emission and negligible geometric effects even for devices as long as 50 μm. However, if high frequency (e.g. 1 MHz) is required to obtain a sufficiently large S/N ratio in the CP current, sawtooth pulses with equal t_r and t_f should be chosen for the least carrier emission effect and thus more reliable results on interface-state density, Moreover, for both sawtooth and trapezoidal pulses with a typical amplitude of 5 V, a lower limit of 200 ns for t_r and t_f is necessary to suppress all the undesirable effects in devices shorter than at least 20 μm