Investigation of Reactively Sputtered Titanium Oxide Memristors

Over the previous decade, flash memory has made massive gains in storage density and market share. However, due to fundamental scaling limits being reached, a replacement memory device must be found. Resistive random access memory (RRAM) is a leading candidate to replace flash memory as a storage-class memory. RRAM is a broad classification of devices, all of which share the commonality that their information is stored in the resistance of a material. These devices are often described as being memristive. The objective of the study performed was to develop a process for fabricating microelectronic structures to investigate the memristive behavior of materials. The first approach taken was to explore a self-aligned fabrication process that relies on angular deposition of electrodes to create crossbar structures. These structures consist of a bottom electrode, the material being characterized, and a top electrode. Issues related to access to contacts were encountered while using the self-aligned process, and it was refined into an improved process. This process used conventional lithography and patterning techniques to replace the angular self-aligned deposition. The improved process successfully demonstrated memristive switching of a titanium oxide film, with on/off ratios of 4.25E5 at 1 V observed. Set voltages of 3 V were used to switch the memristors into a low-resistance state. Large variations in resistances between devices were observed, and are commonly encountered in memristors at microscales due to stochastic nature of filament formation. Further work using shaped electrodes to improve characteristics has been proposed, and a shaping etch which could be applied towards this goal was demonstrated