Physical mechanisms involved in the formation and operation of memory devices based on a monolayer of gold nanoparticle-polythiophene hybrid materials

Understanding the physical and chemical mechanisms occurring during the forming process and operation of an organic resistive memory device is a major issue for better performances. Various mechanisms were suggested in vertically stacked memory structures, but the analysis remains indirect and needs destructive characterization (e.g. cross-section to access the organic layers sandwiched between electrodes). Here, we report a study on a planar, monolayer thick, hybrid nanoparticle/molecule device (10 nm gold nanoparticles embedded in an electro-generated poly(2-thienyl-3,4-(ethylenedioxy)thiophene) layer), combining, in situ, on the same device, physical (scanning electron microscope, physico-chemical (thermogravimetry and mass spectroscopy, Raman spectroscopy) and electrical (temperature dependent current-voltage) characterizations. We demonstrate that the forming process causes an increase in the gold particle size, almost 4 times larger than the starting nanoparticles, and that the organic layer undergoes a significant chemical rearrangement from a sp3 to sp2 amorphous carbon material. Temperature dependent electrical characterizations of this nonvolatile memory confirm that the charge transport mechanism in the device is consistent with a trap-filled space charge limited current in the off state, the sp2 amorphous carbon material containing many electrically active defects.