Molecular memory chips boggle the mind

Scientists have built a memory chip the size of a white blood cell about one-2,000th of an inch on a side with wires as thin as proteins. It holds 160,000 bits and is 40 times as dense as today’s memory chips — very impressive.

The chips don’t quite work yet, and may never be sold commercially, but if they were, the possibilities for gadgets and computers could be endless: from smarter robots to keychains that hold hundreds of video games. And Google would have no problem finding storage space for detailed images of the entire solar system.

Although the chip is modest in capacity — with 160,000 bits of information — the bits are crammed together so tightly that it is the densest ever made. The achievement points to a possible path toward continuing the exponential growth of computing power even after current silicon chip-making technology hits fundamental limits in 10 to 20 years.

The scientists, led by James R. Heath of the California Institute of Technology and J. Fraser Stoddart of the University of California, Los Angeles reported on aspects of their work , which included specially designed molecular switches and a novel technique for making ultrathin wires as far back as 1999. The new work pulls the components into an integrated circuit.

The density of bits on the chip — about 100 billion per square centimeter — is about 40 times as much as current memory chips, Dr. Heath said. Improvements to the technique could increase the density by a factor of 10.

Dr. Heath though says that he did not know if this technique would be commercially useful. “I don’t know if the world needs memory like this,” he said. “I do know if you can manufacture at these dimensions, it’s a fundamentally enabling capability.”

For example, the wires used in the chip are about the same width as proteins, and that could make possible tiny circuits that could detect cancer or other diseases. The researchers are making transistors and simple logic circuits using similar techniques.

A crucial component of the chip is its molecular switch, designed by Dr. Stoddart. The switch, which belongs to a class of molecules known as rotaxanes, looks like a dumbbell with a ring that can slide along the central bar. Voltage pulses push the ring between two positions on the bar, which represent the zeros and ones used by computers to store data. The dumbbell shape keeps the ring from sliding off.

To build the chip, the researchers etched 400 parallel wires, each less than a millionth of an inch wide and separated by about one-750,000th of an inch from its neighbors. On top of the wires, they deposited a layer of the molecular switches, the dumbbells standing vertically, and then a second set of 400 wires turned 90 degrees to the first set.

Each crossing point between two perpendicular wires, with about 100 of the molecular switches wedged in between, is the storage location of one bit of information.

Not everything about the chip works yet. When the researchers tested a small part of it, they found that only 30 percent of the bits actually worked. But it is possible to use only the working parts of the chip, and the researchers successfully wrote and read information to those parts, though even there the success was temporary. The switches routinely broke after being flipped about 10 times.

The researchers readily concede that the chip is merely a demonstration and is not refined enough for any applications.