Reversible capacitance changes in the MOS capacitor with an ITO/CeO2/p-Si structure

Abstract

A reversible capacitance changes with respect to the polarity of applied voltage is demonstrated in a MOS (metal-oxide-semiconductor) capacitor consisting of a high-k CeO2 and oxygen-reactive indium-tin-oxide (ITO) electrode on p-Si substrate, i.e., an ITO/CeO2/p-Si structure. The capacitance-voltage (C-V), capacitance-time (C-t), and voltage-pulse measurements exhibit consistently that the accumulation capacitance is gradually increased upon repeatedly applying negative voltage to the ITO, while the depletion capacitance is reversibly decreased upon applying positive voltage. Particularly, the capacitance change is observed even at a low voltage of ±0.5 V from the device with 40-nm-thick CeO2 layer. The capacitance change is further enhanced as increasing measurement temperature from 25 to 100 °C, implying that the capacitance change is associated with the thermally activated process under the applied voltage. In addition, the resistance of ITO gate electrode is found to decrease upon applying negative voltage, but it is increased reversibly upon applying positive voltage. The reversible capacitance changes in the MOS capacitor with oxygen-reactive ITO gate electrode are explained with voltage-driven oxygen ion migration between ITO and CeO2 layers that can alter the CeO2 dielectric permittivity and induce the gate depletion in the ITO. These reversible capacitance changes have a potential to be employed to modulate the MOSFET (MOS field-effect-transistor) properties such as on-state current, threshold voltage, and transconductance.