Molecular Switches

The world of molecular computing, with its ultrafast speeds, low power needs and inexpensive materials, is one step closer to reality. Using chemical processes rather than silicon based photolithography, researchers at Rice University and Yale University in the US have created a molecular computer switch with the ability to be turned on and off repeatedly.

Such a switch, or logic gate, is a necessary computing component, used to represent ones and zeros, the binary language of digital computing.

As far as building the basic components of molecular computing is concerned, 50 percent of the job is done, the other 50 percent is memory. Rice and Yale researchers plan to announce a molecular memory device soon.

The cost of the molecular switches would be at least several thousand times less expensive than traditional solid state devices. They also promise continued miniaturisation and increased computing power, leapfrogging the limits of silicon.

The switch works by applying a voltage to a 30 nanometer wide self assembled array of the molecules, allowing current to flow in only one direction within the device. The current only flows at a particular voltage, and if that voltage is increased or decreased it turns off again making the switch reversible. In other previous demonstrations of a molecular logic gate there was no reversibility.

In addition the difference in the amount of current that flows in the on/off state, known as the peak to valley ratio is 1000 to 1. The typical silicon device response is at best, 50 to 1. The dramatic response from off to on when the voltage is applied indicates the increased reliability of the signal.

The active electronic compound, 2'-amino-4-ethynylphenyl-4'-ethynylphenyl-5'-nitro-1-benzenethiol, was designed and synthesised at Rice. The molecules are one million times smaller in area than typical silicon-based transistors.

Not only is it much smaller than any switch that you could build in the solid state, it has complementary properties, which in this case if you want a large on/off ratio it blows silicon away.

The measurements of the amount of current passing through a single molecule occurred at a temperature of approximately 60 Kelvin, or about -350 degrees Fahrenheit.

In addition to logic gates, potential applications include a variety of other computing components, such as high frequency oscillators, mixers and multipliers.

It really looks like it will be possible to have hybrid molecular and silicon based computers within five to 10 years.