Comprehensive model for the electronic transport in Pt/SrTiO3 analog memristive devices

Abstract

The presented study considers the electronic conduction across a $\mathrm{SrTi}{\mathrm{O}}_{3}\text{/}\mathrm{Pt}$ Schottky electrode in a resistive switching cell. It is generally accepted that the resistive switching effect is based on the migration of oxygen vacancies, which can be understood as mobile donors. In the experimental approach, a $\mathrm{Nb}:\mathrm{SrTi}{\mathrm{O}}_{3}\text{/}\mathrm{SrTi}{\mathrm{O}}_{3}\text{/}\mathrm{Pt}$ resistive switching cell is fabricated and tested for its electronic and resistive switching characteristics. Using different voltage stimuli, several analog resistance states are realized. Afterwards, the electrical transport properties under different applied voltages and temperatures are measured for each analog resistive state. To gain physical insight into the analog resistive switching a numerical simulation model is developed. The electronic conduction is calculated based on the single band transport theory and a phonon scattering theory accounting for polar material systems. The simulation model allows testing of the conduction in these resistive switching cells by using different doping (oxygen vacancy) concentrations. Combining the simulation model and the experiment, it delivers a comprehensive physical description for the conduction. By means of simulation, the energy resolved current transport across the Schottky barrier is analyzed. It forms a peaklike distribution, originating from the limited thermal excitation and tunneling probability across the $\mathrm{SrTi}{\mathrm{O}}_{3}\text{/}\mathrm{Pt}$ Schottky barrier. Thus, the conduction processes in all states are identified as a balance between a thermally assisted tunneling effect and a phonon dominated bulk transport. Applying this understanding, the resistive switching effect is reduced to a modification of the Schottky tunnel barrier, based on the rearrangement of oxygen vacancies. Thus a low vacancy concentration leads to a high and wide tunneling barrier, which is reduced and shortened for higher concentrations. All resistance states in between are understood as an adjustment of intermediate tunneling barriers. The physical insights leading to the realization of analog resistance states is mandatory to realize new types of neuromorphic computing circuits based on resistive switching devices. Furthermore, the obtained results could be easily transferred to other systems where a static doping concentration applies. This makes the results highly interesting to other applications in the field of electronic oxides and Schottky barrier dominated systems.