서강대학교

초록/요약

Traditional memory technologies are rapidly approaching the miniaturization limits which are based on charge storage and become increasingly difficult to reliably retain sufficient electrons in these shrinking cells. The artificial molecular devices can be realized by mimicking the electron transport function of biological materials and the organization of functional molecules in the biological system. In this study a nanoscale biomemory device composed of recombinant azurin is investigated based on the electron transport mechanism between the protein and solid electrode surface. Ferredoxin is used as charge storage element which possesses a memory effect via a charge transfer mechanism is proposed. Cysteine modified ferredoxin was directly coordinated with the gold (Au) surface without use of any additional linkers. The thin film formation of ferredoxin molecules on Au electrode is confirmed with analytical instruments. Using electrochemical methods the memory switching characteristics of the fabricated device was examined. The charge transfer between ferredoxin protein molecules and Au electrode enables a bi-stable electrical conductivity allowing the system to be used as a digital memory device. Data storage is achieved by applying redox voltages which are within the range of −500 mV. The proposed device has a function of memory and can be used for construction of future nano-scale bioelectronic device. Further, experiments for temperature effect and multiple reading of the stored charge in ferredoxin based memory were examined. The electric switching measurements on the device exhibited tri-stable switching for charge ？write？ ？read？ and ？erase？ functions. The conductance-temperature dependent switching experiments allowed the device operation up to 320 K. The key performance of the present device is it enables multiple times reading of the stored charge. Finally, the device showed good retention time and can be switched without degradation in performance. A multiple bit storage device is of great demand for high density storage purpose, hence a multi-bit biomemory composed of cysteine modified azurin has been developed. The recombinant azurin was directly immobilized on four different gold (Au) electrodes patterned on a single silicon substrate. Multi-electrode chip was fabricated by conventional fabrication methods. Using analytical measurements the morphology of azurin on electrodes were confirmed. Using electrochemical methods, the redox property and the memory function of the fabricated biodevice was validated. The charge transfer occurs between protein molecules and Au electrode enables a bi-stable electrical conductivity. Applying oxidation potentials in different combinations to each Au electrodes, multi-bit information was stored in to the azurin molecules. Finally, the switching robustness and reliability of the proposed device has been examined. Further a nanoscale biomemory is of great importance to overcome the limitations of conventional memory devices. Hence using Anodic alumina mask and Nanosphere lithography, highly dense and uniform Au-nanodots with size controllable method were fabricated on indium tin oxide (ITO) substrate. Cysteine modified azurin was directly immobilized on the fabricated Au-nanodots. Scanning electron microscopy, Atomic force microscopy and Electrochemical scanning tunneling microscopy (ECSTM) revealed the monolayer formation with an in-situ cyclic voltammetry to observe redox behavior of both bare Au-dots and protein immobilized Au-dots. Memory function characteristics and I-V characteristics were obtained on protein immobilized Au-dots patterned on ITO conductive electrodes towards the development of nanoscale biomemory device. A nanobiomemory device composed of quantum-dot/azurin hybrid layer was developed. Azurin was linked CdSe-ZnS quantum dots by covalent linking chemistry and was applied towards nanoscale memory device. Electrical measurements (I-V) were conducted by STM on both the individual and its hybrid structures. It is observed that the hybrid material displays an electrical bistability and memory phenomena. Further, the device ON/OFF currents was fitted to the mathematical models to examine the device switching behavior. Hence, this bio-nano hybrid molecule enables the formation of switchable memory device and it could be used for nanoscale memory device. The proposed nanobiomemory device by mimicking the electron transfer mechanism of azurin protein as a key element can be applied as model system for the development of next generation biomemory devices.