Measuring Ionic Mobility in Oxide Thin Films by Dynamic I-V Analysis–Impact of Interfaces

Abstract

Ionic transport in solids, e.g. nonstoichiometric oxides, is key to the design and control of non-volatile RAM devices considered for use in neuromorphic hardware. While significant progress has been achieved in the development of neuromorphic devices based on Resistive and ElectroChemical RAM, their performance is limited in part by knowledge of ionic transport phenomena that control conductance changes in filamentary regions and/or at oxide interfaces. We study ionic mobility in oxide materials, e.g. doped ceria, by applying our previously developed Dynamic I-V Analysis technique1 capable of measuring oxygen vacancy mobility dependence on temperature, thermal history and oxygen non-stoichiometry. Here we show that interface resistance, that might arise either at the contact between the oxide under study and its electrodes or between grain boundaries created during pulsed laser deposition, varies significantly. While the interfacial contributions to overall device resistance is sometimes negligibly small, in many cases they become significantly larger than the bulk value. We show that the interface resistance has a direct impact on the effectiveness of the measurement of ionic transport in the oxides of interest. Electrical impedance spectroscopy supported with XRD and electron microscopy are applied to determine the interfacial resistance, and its origins, in oxide thin films, that impacts the oxygen defect transport and impedes characterization. We will present possible ways to mitigate the interfacial resistance, by tuning the PLD parameters and by carefully choosing the electrodes and the supporting substrates materials in the test devices. Finally, we will report near room temperature values for ionic mobility in crossbar devices with optimized ceria layers. [1] D. Kalaev, T. Defferriere, C. Nicollet, T. Kadosh, H. L. Tuller, Dynamic current-voltage analysis of oxygen vacancy mobility in praseodymium doped ceria over wide temperature limits, Adv. Funct. Mater. 30(11), 2020, 1907402.