Since the emergence of the concept, molecular logic gates have evolved to one of most active areas in molecular devices. Small size is the main advantage of molecular devices. In addition, the range of response times for molecular devices is in the order of femtoseconds while the fastest present devices operate in the nanosecond regime resulting in a 106 increase in speed. (Tour 2000). Also molecular-based systems offer distinct advantages in uniformity and potential fabrication costs. However, challenges still remain.
• Molecules are easier to synthesise but are difficult to arrange on a surface or a 3-D array and cannot be ensured that they would stay in a place.
• Due to higher density, heat dissipation has a million-fold increase in circuit density and an enormous cooling fan would be needed to prevent the ensuing meltdown or decomposition of the molecules. As part of the new design scenarios molecular devices could function by electrostatic interactions produced by small reshapes of the electron density due to the input signals. Electrostatic potential interactions between molecules would transport the information throughout the CPU and there is no need for electron current or electron transfer as in the present devices.
• Another challenge is the switching frequency of the molecular devices. It is normally smaller than 1000 Hz, which is substantially smaller than that of MOSFET of 1011 Hz or 1012 of superconductor device.
These concerns provide a real challenge for molecular electronic computing research. Although a few architectural constructions of molecular wires and devices have been achieved, extensive R&D work still need to be done to tackle these challenges satisfactorily.
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