Low temperature Behavior of Oxygen Vacancies in Memristive Strontium Titanate

Resistance switching (RS) of metal/oxide/metal structures, believed to be based on oxygen vacancy motion, has generated great interest owing to its promise in next generation data storage technologies. In the context of RS, this thesis work examines the behavior of oxygen vacancies in SrTiO3 , a material known to exhibit RS behavior.;Capacitance-voltage measurements of the Pt/SrTiO3-x, diode were made and the results were analyzed to determine the vacancy profile near the Schottky interface. The profile time evolution under typical switching fields (hundreds of kV/cm) were studied at different temperatures to obtain the vacancy mobility (1.5x10-13 cm2/V·s at 300 K) and its activation energy (0.7 eV). The mobility value at each temperature remained constant when over a range of electric (from ∼300 kV/cm to ∼200 kV/cm), indicating a field-independent mobility under typical switching fields.;Fast (<1 micros) resistance switching can occur for vacancies having a 0.7 eV activation energy for diffusion if Joule-heating raises the device temperature to approximately 400 °C. Therefore, the thermo-mechanical effects of Joule heating on SrTiO3-based devices was studied. It was found that local Joule heating leads to extensive plastic deformation of SrTiO3 single crystals, resulting in the formation of [100]-oriented surface steps, identified as slip steps owing to the movement of dislocations on specific planes. A large amount of dislocations were generated during the deformation process. These slip steps are discussed relative to observations made in the RS literature.;To address the effect of dislocations on vacancy mobility, electron beam induced current (EBIC) mapping of the Pt/SrTiO3-x diode was performed. Dislocation arrays in SrTiO3 initially had dark EBIC contrast relative to the crystalline bulk. Annealing the diode in air at 120 °C changed the contrast to bright. Stressing the annealed diode at -20 V caused the contrast to return to dark. The dark contrast was interpreted as region of higher vacancy concentration. The contrast change was interpreted as oxygen vacancy motion occurring faster along dislocations versus the bulk. The contrast differences between the dislocation arrays and the bulk were nevertheless small (∼10%), suggesting the effect of "pipe-diffusion" is minor for oxygen vacancies in SrTiO3, and not capable of accounting for typical RS behavior. All of these results are discussed relative to the prevailing RS theories.;High quality Pt Schottky contacts were fabricated on oxygen vacancy doped SrTiO3 (SrTiO3-x) single crystals to investigate the motion of vacancies. Three factors that could impact vacancy mobility were identified and studied, specifically electric-field dependent mobility, thermal activation owing to Joule-heating, and preferential diffusion of vacancies along dislocations (so-called pipe-diffusion).