From MEMRISTOR to MEMImpedance device

The behavior of the capacitance switching of HfO2 Resistive non-volatile Memories is investigated in view of realizing a MEMImpedance (MEM-Z) device. In such a Metal Insulator Metal structure, the impedance value can be tuned by the adjustment of both resistance and capacitance values. We observe a strong variation of capacitance from positive to negative values in a single layer Metal Insulator Metal device made of HfO2 deposited by Atomic Layer Deposition, but unfortunately no memory effect is observed. However, in the case of a two layer structure, a device has been obtained with a memory effect where both resistance and capacitance values can be tuned simultaneously, with a variation of capacitance down to negative values to get an inductive behavior. Negative capacitance values are observed for voltage values near SET voltage. A schematic model based on shaped oxygen vacancy density is proposed to account for this capacitance variation. The oxygen vacancies can be either isolated or connected in the ...