Here we create a model experiment to investigate the asymmetries due to the environment and different electrodes on a 50 nm thick nominally undoped SrTiO3 thin films. For this, we fabricated two model resistive switches between metallic electrodes (LaNiO3 and Pt) differing in their work functions and implication on defects formed at the interfaces. We grow the switching oxide either on top of LaNiO3 or on platinum that form the bottom electrode and fabricate the top electrode from the other material respectively.
The I-V curves of the model resistive devices are in general asymmetric in the positive and negative bias direction due to the above-mentioned asymmetries.
Firstly, we observe independently on the choice of the bottom electrode resistive switching behavior with the same counter-clockwise switching polarity. We link the switching polarity to the microstructural defect density at the interface of SrTiO3 and the top electrode, which we investigate by transmission electron microscopy.
Secondly, we observe a highly rectifying asymmetric I-V behavior with high current levels in the positive bias direction for both model samples. The similar asymmetry in the I-V characteristics we link to the environmental influence. To investigate the humidity influence on the two model devices further, we perform I-V measurements at 40% and 5% relative humidity. We report, that the transport characteristics are consistent with hydrogen forming a shallow donor level in the switching material in accordance to Ref. . This leads to a lower conduction, higher switching voltage and a larger hysteresis opening of the I-V switching curve under lower humidity levels.
Through the model experiment we contribute to an understanding on the role of defects at interfaces and how to explain humidity influence for SrTiO3 resistive switching units. These findings have large implications for the fabrication of 3D staked multi-bit memories to increase the computer memory storage density.
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