The excellent quality of the Si/SiO2 interface is one of the main reasons for the success of modern VLSI MOS technology. Therefore, it is very important to characterize the quality of this interface as precisely as possible.
The charge-pumping method has proved to be a very reliable and precise method, allowing an in-depth analysis of the interface directly in the MOSFET device. Additionally it requires only basic equipment and is relatively easy to set up. The effect was first reported by Brugler and Jespers in 1969. They reported a net DC substrate current when periodic pulses were applied to the gate of a MOS transistor, while the source and drain were kept grounded. The current was found to be proportional to the gate area and the frequency of the applied gate pulses. It was flowing in the opposite direction of the leakage current of the source and drain to substrate diodes. They showed that the current originates from the recombination of minority and majority carriers at traps at the Si/SiO2 interface. Therefore, the method can be used to measure the interface trap density in MOSFETs for the evaluation of MOSFET degradation. The major breakthrough for the charge-pumping method was the thorough investigation and correct explanation of the method, applied directly to MOSFET structures, by Groeseneken et al. in 1984.
The device simulator Minimos-NT is used for numerical analysis of the charge-pumping effect. For each base voltage (Vbase) of interest, a transient simulation of the gate pulse is performed. The resulting currents can then be plotted versus the base voltage to obtain the typical charge-pumping current ICP versus Vbase plot.