The Interfacial Layer between Pt/PCMO and the Bi-stable Resistive States

Nobel metals in contact with perovskite metal oxides, Pr1−xCaxMnO3 (PCMO) for example, have shown switching resistance values, with a couple of orders of magnitude difference, upon the stimulation of electrical pulses. In this paper, the Pt/PCMO/Pt structures were made through e-beam evaporation (Pt electrodes) and RF sputtering (PCMO films) for the switching mechanism study. Specially designed experiments along with extensive electrical characterizations were performed on the Pt/PCMO/Pt structure. The existence of a contact resistance, or an interfacial layer, between Pt electrodes and PCMO was evident by simply measuring initial resistance (R0) of the stack against PMCO film thickness. Temperature dependence of the R0 and the time-bias tests were used to study the transport mechanism in the bulk of PCMO and the interfacial layer. Above a threshold voltage, the transport changes from mainly electronic to ionic conduction especially at the interfaces, causing electrode polarization. The transient characteristics of Pt/PCMO/Pt stack, i.e. the response to the pulsing in the time domain, were characterized in the frequency domain instead through the admittance spectroscopy measurements. The temperature dependence of Cole-Cole plots were used to study the polarized interfacial layer or interface dipole polarization (IDP). This IDP layer is the origin of contact resistance and also responsible for the uni-polar long-short switching because the calculated relaxation time constants of the IDP corresponding to low resistive state (LRS) and high resistive state (HRS) were similar to the experimental values. Therefore, the so-called bi-stable resistive states are just two different IDP states: one is much leakier than the other.