Experimental Observation of Negative Susceptance in HfO2-Based RRAM Devices

Negative susceptance is experimentally measured in the low resistance state of TiN/Ti/HfO₂/W resistive RAM memories. A meminductive-like behavior appears along with the memristive effects. A detailed study of small-signal parameters measured at 0 V after applying positive and negative voltage pulses is presented. A simple model for the conductive filaments consisting in a resistance in series with an inductance is used. In the equivalent circuit, both elements are in parallel with the geometrical capacitance of the structure. Both resistance and inductance show two clearly differentiate states. Positive voltages switch the device to the ON state, in which the resistance value is low and the inductance value is high. By applying appropriate negative voltages, the device switches to the OFF state, in which resistance value is high and inductance becomes negligible. The negative susceptance could be related to lags between current and electric field due to transport mechanisms occurring in the ON state.