Highly Flexible and Transparent Memristive Devices Using Cross-Stacked Oxide/Metal/Oxide Electrode Layers.

Flexible and transparent memristive (FT memristors) devices are considered to be among the promising candidates for future nonvolatile memories. To realize these devices, it is essential to achieve flexible and transparent conductive electrodes (TCEs). However, conventionally used TCEs such as indium tin oxide, gallium zinc oxide, and indium zinc oxide are not so flexible and even necessitate thermal annealing for high conductivity and optical transmittance. Here, we introduce Ag/ZnO/Ag- and Ag/Al2O3/Ag-based FT memristors using cross-stacked oxide/metal/oxide electrode layers (i.e., ZnO/Ag/ZnO + ZnO/Ag/ZnO and Al2O3/Ag/Al2O3 + Al2O3/Ag/Al2O3) without using any annealing process on poly(ethylene terephthalate) substrates (PETs). Both Ag/ZnO/Ag- and Ag/Al2O3/Ag-based FT memristors on PETs exhibited excellent properties, including high transmittance (>86% in the visible region), high on/off current ratios (>103), and long retention times (>105 s). In addition, they showed very stable and flexible characteristics on PETs even after 2500 bending cycles with a bending radius of 8.1 mm. Finally, we analyzed transmission electron microscopy images and time-of-flight secondary ion mass spectroscopy profiles to identify switching mechanisms in these devices.