Giulia Casula, Yan Busby, Alexis Franquet, Valentina Spampinato, Laurent Houssiau, Annalisa Bonfiglio, Piero Cosseddu
Organic Electronics, Volume 64, January 2019, Pages 209-215
Flexible electronics is one of the main challenges for future hi-tech electronics. Since information storage elements are essential in any electronic system, the development of high-performance and flexible organic memories is a key requirement. Organic resistive switching memories represent a viable and promising technology ensuring scalability, flexibility, low cost and easy processing. However, despite of the remarkable progress, organic memory reliability, long term stability, ambient operation and large-area processing still need to be improved. Moreover, the rational device implementation lacks of a clear understanding of resistive switching mechanisms. In this work, high-performance cross-bar resistive memories based on a Parylene-C resistive layer sandwiched between silver electrodes are fabricated by means of large-area and high-throughput procedure. Parylene-C is a biocompatible, thermoplastic polymer, which can be deposited at room temperature. Memory elements show a reliable and reproducible switching behavior with low operating voltages, high ION/IOFF current ratio and record retention time in ambient conditions as well as high mechanical stability under bending conditions. The 3D molecular distribution of pristine and programmed devices is determined by state-of-the-art time-of-flight secondary ion mass spectrometer combined with an in-situ scanning probe microscopy (TOF-SIMS/SPM). The depth profile analysis indicates that resistive switching is driven by the formation of few localized nanometer scale conductive filaments formed by the diffusion of silver and oxygen across the organic layer which are activated, locally interrupted and re-activated during the memory cycling. The SPM images allow separating surface morphology related effects from the 3D molecular analysis and to identify some typical artefacts in TOF-SIMS image reconstructions due to preferential sputtering.