Investigation of Hybrid Molecular/Silicon Memories With Redox-Active Molecules Acting as Storage Media

In this paper, a physical investigation of hybrid molecular/Si memory capacitor structures is proposed, where redox-active molecules act as storage medium. Fc and $\hbox{ZnAB}_{3}\hbox{P}$ porphyrin were grafted on (1 0 0) Si with both a direct bond and a chemical linker in order to investigate the electron transfer properties of the molecule/Si system. The chemical structures of the molecular layers were analyzed with X-ray photoelectron spectroscopy. Cyclic voltammetry and impedance spectroscopy were also performed on capacitor structures in order to characterize the charge transfer between the redox molecules and the Si and the effect of an organic linker on its rate. To explain our results, an original electrical model of molecule/Si memory structures is proposed. Calculated data are compared to impedance results for the cases of Fc either directly grafted or with linker. The model allows us to give a theoretical confirmation of the influence of the linker over the redox energy and on the time constant of the molecular capacitor. Finally, density functional theory calculations provide an in-depth physical insight of the effect of the linker over the Fc redox energy. The results obtained in this paper show the strong impact of the engineering of the redox molecules and their linker on the electron transfer properties.