Charge Trapping Control in MOS Capacitors

This paper presents an active control of capacitance-voltage (C-V) characteristic for MOS capacitors based on sliding-mode control and sigma-delta modulation. The capacitance of the device at a certain voltage is measured periodically and adequate voltage excitations are generated by a feedback loop to place the C-V curve at the desired target position. Experimental results are presented for an n-type c-Si MOS capacitor made with silicon dioxide. It is shown that with this approach, it is possible to shift the C-V curve horizontally to the desired operation point. A physical analysis is also presented to explain how the C-V horizontal displacements can be linked to charge trapping in the bulk of the oxide and/or in the silicon-oxide interface. Finally, design criteria are provided for tuning the main parameters of the sliding-mode controller.