Layer-by-layer assembled enzyme multilayers with adjustable memory performance and low power consumption via molecular-level control

Electrochemical properties of enzymes are of fundamental and practical importance in bio-electrochemical applications. These redox properties, which can cause the reversible changes in the current according to their redox reactions in solution, often depend on the chemical activity of transition metal ions as cofactors within the active sites of enzymes. Here, we demonstrate that the reversible resistance changes in enzyme-based multilayer films can be caused by the externally applied voltage as a result of charge trap/release of haem Fe-III/Fe-II redox couples in dry form. It is also demonstrated that the electrically bistable switching properties of redox enzymes can be applied to nonvolatile memory devices requiring low power consumption. For this study, cationic poly(allylamine hydrochloride) (PAH) was alternately layer-by-layer assembled with anionic catalase enzyme onto Pt-coated substrates until the desired number of layers was deposited. A top electrode was deposited onto (PAH/catalase)(n) multilayer films to complete device fabrication. When an external bias was applied to the devices, a switching phenomenon depending on the voltage polarity (i.e., bipolar switching) was observed at low operating voltages (RESET at 1.8 V and SET voltage at -1.5 V), fast switching speed at the nanosecond level, and an ON/OFF current ratio of similar to 10(2). In the case of inserting insulating layers of about 2 nm thickness between adjacent catalase (CAT) layers, these devices exhibited the higher memory performance (ON/OFF current ratio of similar to 10(6)) and the lower power consumption than those of (PAH/CAT)(15) multilayer devices.