Designing Strained Interface Heterostructures for Memristive Devices

The question of how to design material heterostructures and integrate them into strained ionic memristive devices is explored for the first time for the property of memristance. We fabricate biaxially strained heterostructure oxide microdots to study the influence of strain on oxygen anionic switching and the memristive behavior. The microdots are fabricated using pulsed laser deposition (PLD), ablating thin films onto single crystalline sapphire substrates. Now to rationally access the strained interfaces down to nanoscale, it is necessary to develop a unique device design with sideways attached electrodes contacting the free-etched heterostructure dots on a chip. The switching mechanism for ceria-based memristive devices is based on oxygen vacancy conduction in the ion conductor balanced by electronic carriers which we will now actively tune by imposing the strain field in various degrees with the insulating erbia layer and monolayer thickness variations in the heterostructure dot device. High-resolution transmission electron microscopy (HRTEM) imaging and diffraction techniques have been successfully employed to investigate oxide heterolayers, such as Fourier analysis of high-resolution images to investigate crystallographic orientation relationships at heterolayer interfaces. In cross-sectional annular dark field STEM images, we observe well-defined layers of Gd_0.1Ce_0.9O_2-Σ and Er₂O₃ stacked consecutively with monolayer thicknesses down to 3 nm. While keeping the total device thickness constant, the number of interfaces is being increased. This results in an increase of the strain-affected volume over the total device.