Nanorods Versus Nanoparticles: A Comparison Study of Au/ZnO-PMMA/Au Non-Volatile Memory Devices Showing the Importance of Nanostructure Geometry on Conduction Mechanisms and Switching Properties

摘要

Hybrid organic-inorganic devices offer a simple and low cost route to the fabrication of resistive memory devices. However the switching and conduction mechanisms are not well established. This work compares ZnO-based devices made in the same manner but having two different nanostructure geometries, vertically aligned ZnO nanorods and randomly dispersed ZnO nanoparticles, both embedded within a PMMA host material and sandwiched between two gold electrodes in a crossbar device configuration. Both device types do not require a forming step to initiate switching and exhibit bipolar switching at relatively low operating voltages. In the low field regime both device types exhibit Ohmic behavior, however in the high field regime their switching and conduction mechanisms are distinctly different. ZnO nanorod-based devices exhibit smooth I-V curves and smooth switching behavior and a conduction mechanism that changes from Poole-Frenkel to Schottky emission when switching from the ON state to the OFF state. In contrast, ZnO nanoparticle devices exhibit sharp switching properties with SCLC behavior in the OFF state and Ohmic conduction in the ON state. These differences in the conduction and switching properties of devices containing the same materials clearly demonstrates the importance of the nanostructure geometry and device architecture on the switching and conduction properties of memristor devices. For each device type we discuss the results and propose plausible mechanisms to account for their different behavior.