Molecular electronic memories.

摘要

The feasibility of building large memories using molecular electronic devices with bistable conductance-state memory has been investigated. A novel fabrication method for two-terminal molecular memory devices that is integratable into large-scale arrays while avoiding top-contact evaporation on a molecular monolayer has been developed. A sacrificial layer underneath the top contact metal is wet-etched to create free-standing cantilevers in aqueous solution and a self-assembled monolayer is formed on the underside of the cantilever. Subsequent atmospheric drying causes the freestanding structure to become permanently adhered to the substrate, resulting in a two-terminal molecular structure. This device has been investigated with alkanethiol monolayers as a proof-of-concept, and the expected decrease in current with increasing chain length is observed. The measured current density in control devices without molecules is also consistent with models of loaded cantilevers. Previously characterized molecules exhibiting memory behavior were also investigated and demonstrated bistable memory effects similar to earlier observations.;The scalability of such bistable molecular memory devices was analyzed from a circuits perspective, and the impact of different system parameters was quantified. It is necessary to build large arrays with at least several hundred molecular memory cells along each dimension, in order to prevent peripheral circuitry from dominating the area. It is quantitatively shown how this requirement constrains the minimum allowable forward/reverse-bias rectification ratio of the molecular devices, as well as the minimal on/off ratio of the two molecular conductance states. The parasitic wiring impedance is negligible in the case of metallic interconnect, but the impedance of currently available molecular wires makes large-scale all-molecular arrays infeasible.