3 In either case, molecular electronics will play an ever increasing role in the development of computer devices. The second scenario is that semiconductor evolution will “hit a wall” for economic reasons, and computer technologists will redirect their efforts toward the exploration of new architectures rather than smaller feature sizes. The first is that Moore's law will remain valid until 2030 and that lithographic techniques will evolve to create nanoscale devices with properties much like those currently envisioned for molecular devices. However, extrapolation of Moore's law 1 predicts that semiconductor feature sizes will approach the molecular domain around 2030. A molecular computer could, in principle, be 2−3 orders of magnitude smaller and faster than a present day semiconductor computer composed of a comparable number of logic gates. Two commonly stated rationales for exploring molecular electronics are the potential of significant decreases in both device feature sizes and gate propagation delays. It is unlikely that lithography will ever provide the level of control available through organic synthesis or genetic engineering. A key advantage of the molecular approach is the ability to design and fabricate devices from the “bottom-up”, on an atom-by-atom or residue-by-residue basis. This approach contrasts with current techniques, in which these functions are accomplished via lithographic manipulation of bulk materials to generate integrated circuits. Molecular electronics is broadly defined as the encoding, manipulation, and retrieval of information at a molecular or macromolecular level. We also examine current efforts to optimize the protein memory medium by using chemical and genetic methods. The methods and procedures of prototyping these bioelectronic devices are discussed. By using a sequential multiphoton process, parallel write, read, and erase processes can be carried out without disturbing data outside of the doubly irradiated volume elements. The three-dimensional memory utilizes an unusual branching reaction that creates a long-lived photoproduct. The associative memory is based on a Fourier transform optical loop and utilizes the real-time holographic properties of the protein thin films. ![]() We examine here the use of this protein as the active component in holographic associative memories as well as branched-photocycle three-dimensional optical memories. The light-transducing protein bacteriorhodopsin provides not only an efficient photonic material, but also a versatile template for device creation and optimization via both chemical modification and genetic engineering. Bioelectronics offers valuable near-term potential, because evolution and natural selection have optimized many biological molecules to perform tasks that are required for device applications. The promise of new architectures and more cost-effective miniaturization has prompted interest in molecular and biomolecular electronics.
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