(Invited) Resistive States in Strontium Titanate Thin Films

Tuesday, 3 October 2017: 16:00
Camellia 4 (Gaylord National Resort and Convention Center)
M. Kubicek (TU Wien)
Recently, resistive switching devices have attracted a lot of attention, especially for use as non-volatile memories being an alternative to classic transistor technology. Hysteretic I-V characteristics allow modulations between high and low resistive states with potential for fast switching speed, high scalability and low switching energies. Perovskite oxides are an interesting class of active switching materials: Their interplay of band structure, electronic and ionic defects, and interface effects control the switching process. The processes on the atomic scale (e.g. reordering of anions or cations) to accomplish the changes between resistive states require attention. Here, local high electric fields and/or locally elevated temperatures are enabling resistive switching. Studies on strontium titanate (SrTiO3) thin films deposited by pulsed laser deposition (PLD) are presented, focusing on understanding defect chemical and mechanistic implications and requirements of the switching process.

Defect chemical differences between the changes of resistive states at room temperature and at elevated temperatures were investigated. Here we use the temperature change to switch between two regimes in which oxygen vacancies are either mobile or immobile. By using combined electric DC and Electrical Impedance Spectroscopy (EIS) techniques we were able to develop and test a model which can explain different hysteretic I-V responses or pseudo-inductive loops found in impedance spectra as a consequence of the change of resistive states.

Also the influence of PLD parameters on the conductivity of SrTiO3 thin films as well as on their resistive switching behavior was studied in detail. By using microelectrodes, it was investigated how certain areas of a SrTiO3 thin film either required a forming process for reversible resistive switching or not. We propose critical defects distributed in the thin films to explain experiments with differently sized microelectrodes.

Additionally, the influence of the PLD process itself is critically discussed. For this purpose, we use a newly developed in-situ technique combining pulsed laser deposition and electrical DC or electrochemical impedance measurements. Recent results show that interactions with the plasma plume and/or the UV light has a strong impact on the electrical properties of oxide thin films. Interestingly, PLD interactions were even found to affect strontium titanate substrates used for deposition.