Abstract
The limited sensitivity of existing analysis techniques at the nanometer scale makes it challenging to systematically examine the complex interactions in redox-based resistive random access memory (ReRAM) devices. To test models of oxygen movement in ReRAM devices beyond what has previously been possible, we present a new nanoscale analysis method. Harnessing the power of secondary ion mass spectrometry, the most sensitive surface analysis technique, for the first time, we observe the movement of 16O across electrically biased SiOx ReRAM stacks. We can therefore measure bulk concentration changes in a continuous profile with unprecedented sensitivity. This reveals the nanoscale details of the reversible field-driven exchange of oxygen across the ReRAM stack. Both the reservoir-like behavior of a Mo electrode and the injection of oxygen into the surface of SiOx from the ambient are observed within one profile. The injection of oxygen is controllable through changing the porosity of the SiOx layer. Modeling of the electric fields in the ReRAM stacks is carried out which, for the first time, uses real measurements of both the interface roughness and electrode porosity. This supports our findings helping to explain how and where oxygen from ambient moisture enters devices during operation.
Highlights
Redox-based resistive random access memory (ReRAM) has been extensively studied over the last decade for the generation of non-volatile memories and novel neuromorphic, braininspired, electronic technologies
We have developed a powerful new Secondary Ion Mass Spectrometry (SIMS) analysis method for measuring chemical changes across switching layers and electrodes
Our results indicate that tuning the energetics and microstructure of the electrodes can improve this exchange and produce more reliable devices with longer lifetimes
Summary
Redox-based resistive random access memory (ReRAM) has been extensively studied over the last decade for the generation of non-volatile memories and novel neuromorphic, braininspired, electronic technologies. Using Resistance Switching (RS) (or ReRAM) devices as “synapses” is a promising route to neuromorphic systems due to their two-terminal structure, stability (>10 years retention), high endurance (>1012 cycles), and multi-level analog states.. Intrinsic switching relies on changing the properties of the pure oxide without any indiffusion of conductive species from the electrodes. As the oxide is only nanometers thick, a small voltage applied between the electrodes generates large enough electric fields to drive oxygen diffusion. This initially lowers the resistance of the device—an effect currently attributed to conductive oxygen vacancy filaments forming between the electrodes. Subsequent voltage pulses sequentially break and reform these filaments through redox processes, allowing information to be stored in the changing device resistance
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