Molecular Computer Takes a Major Stride


Scientists at UCLA and Hewlett-Packard Laboratories have created the first crude components of a computer based not on silicon, but on exotic molecules that could lead to microprocessors billions of times more powerful and compact than today's most advanced devices.

The scientists, led by UCLA chemistry professor James Heath, used a class of complex organic chemicals known as rotaxanes to construct simple logic gates--the building blocks of all digital computers--the group reported in a paper published today in the journal Science.

"We can potentially get the computational power of 100 workstations on the size of a grain of sand," Heath said. "I'm hopeful we can do it in about a decade."

By sandwiching a thin film of rotaxanes between a grid of etched wires, the scientists were able to configure the molecules at each junction point to perform basic logical functions.

It marks one of the first demonstrations of how molecular components can be linked and configured to create a computing device.

Dan Herr, director of material and process science at the North Carolina-based Semiconductor Research Corp., a nonprofit research consortium, said the work by UCLA and Hewlett-Packard is one of the few designs in the field of molecular computing that seems to be buildable.

"Their approach is a significant step," he said. "It's still definitely in the research domain, but this is the closest thing I've seen to a molecular computer."

The development of molecular computing components comes at a time when the traditional method of etching circuits on silicon is facing the physical limitations of miniaturization.

Silicon chips are made through a process known as photolithography, in which light is used to etch circuits onto photosensitive chips.

Packing more components onto a chip means etching thinner lines on the chip, which requires ever more exotic light sources. Packing millions of components onto a chip has sent the cost of chip plants into the billions of dollars.

Molecular devices have been an attractive possibility, for they are the tiniest possible devices that could be built.

But the idea has always been on the fringe of computer science, largely because of the difficulty of dealing with chemical components and controlling interactions at the molecular level.

Heath's solution, developed with the help of postdoctoral students Pat Collier and Eric Wong, revolves around the distinctive characteristics of rotaxanes--a group of molecules that resemble a barbell with a ring around it.

The molecules are easy to manipulate and align into a tightly packed, uniform array.

The group created logic gates out of the sandwich of etched wires and rotaxanes by either leaving a junction point untouched or by applying high voltage, essentially breaking the link between the two ends of the barbell, thus altering the electrical characteristics of the molecule.

Heath said the next step is to group several of the logic gates together to form a logic circuit capable of performing basic computing functions such as addition.

"Once you have [that], you can do everything," he said.

"We should be able to configure these wires and switches to do what a very complicated silicon-based circuit does, including performing logic operations, providing memory, and routing signals through the machine and to the outside world."

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