Dethroning the Transistor
A new molecular logic switch

Context: The terms “semiconductor” and “computer” have become entwined; better semiconductor manufacturing has enabled the release of chips with smaller and faster circuits every year. But in a decade, the miniaturization of silicon transistors may reach physical limits that prevent further improvements. So engineers from Hewlett-Packard have created a molecular device that could be the heart of the computer of the future.

Methods and Results: The circuits proposed by Phil Kuekes and his HP colleagues rely on a “crossbar”: an array of crossed metal wires separated by a single layer of molecules. Like a transistor, a crossbar can be switched between a high and low conducting state, allowing it to store information. Kuekes shows how to link crossbars so that they can not only store data but also restore noisy data and apply a logic operation called inversion, which swaps binary 0s for 1s and 1s for 0s. The crossbars can be linked with other components to generate the entire family of logic needed for computing. The researchers have yet to combine all these capabilities into a stand-alone computing device, and they have not yet found a way to make molecular junctions that switch states quickly and reliably enough to compete with silicon transistors. Nonetheless, they have provided the first demonstration that crossbars can perform all the functions transistors can perform.

Why it Matters: The HP researchers have cleared a path toward a computer chip without conventional transistors. The process used to create their crossbars is inexpensive and in principle could lead to logic elements even smaller than those constructed from the most advanced silicon transistors, which would enable faster and more efficient computer chips. But even if the performance and reliability of crossbars surpass those of transistors, they may still lack the muscle to compete with the entrenched semiconductor industry. Crossbars may instead find their first applications elsewhere, in flexible logic devices, for example, or displays.

Source: Kuekes, P. J., D. R. Stewart, and R. S. Williams. 2005. The crossbar latch: logic value storage, restoration, and inversion in crossbar circuits. Journal of Applied Physics 97:034301.