Physical limits on binary logic switch scaling

We examine the scaling limits of energy dissipation in a specific and concrete physical model - that of clocked quantum-dot cellular automata (QCA). Prototype QCA devices exist and have demonstrated true power gain, an essential feature for any general-purpose computational technology. Though present devices operate at cryogenic temperatures, much work has been done on molecular implementations which can operate at room temperature and are notably smaller than 1.5 nm. QCA represents a radical departure from CMOS, but is still a charge-based binary approach. We solve the equations of motion for the system in the presence of a thermal environment with no a priori assumptions about energy flow. We show directly the effect of the logical structure of the calculation on the heat generated by a circuit. These calculations point to the real nature of the thermodynamic limitations of scaling binary logic devices and suggest strategies for achieving the ultimate limits of device scaling.