Hybrid organic-inorganic materials for molecular proton memory devices

Molecular storage elements consisting of a stack of a proton conducting layer (PCL) and a proton trapping layer (PTL) are investigated in view of their perspective application to non-volatile proton memories. Experimental studies are conducted on PCL and PTL materials made of poly(methyl methacrylate) (PMMA) with embedded molecules of 12-tungstophosphoric acid (HPW) and 2-aminoanthracene (AA), respectively. Particular emphasis is placed on the thermal processing parameters (temperature and duration) used in material preparation and their optimization for circumventing undesirable phenomena, for the device stability and performance, like reactions between HPW and PMMA and inter-mixing of the PCL and PTL. Transient current measurements performed on metal-insulator-semiconductor devices containing an HPW/PMMA layer allowed the determination of both the concentration and mobility of the protons within this layer. Comparison of the extracted proton concentration (ca. 3.8 × 1017 protons/cm3) under full polarization conditions with the HPW concentration determined by UV spectroscopy indicates that only 2 protons per ∼1000 HPW molecules are mobile and contribute to the current. Finally, the material features of a generic PCL/PTL stacked structure affecting the operation of a molecular proton memory device are examined from a theoretical point of view. Results indicate that the write characteristics of this type of memory such as the magnitude of the memory window and the write speed depend on the thickness, the proton mobility and the proton concentration of the PCL, while the write voltage is mainly determined by the thickness of the PTL. In light of these analyses, it appears that memory windows as large as 2.8 V might be obtained for a 1 ms/3 V write operation regime even in the case of PCL and PTL thicknesses as high as 175 nm. These observations suggest that a PTL/PCL storage element may be well suited in future low-cost, low-power, and non-volatile single-organic transistor memory applications.