SAN JOSE, Calif. - Researchers in California said they had created the world's densest memory circuit, one that is about 100 times denser than today's standard circuits, while remaining as small as a human white blood cell.

Scientists from the California Institute of Technology and the University of California, Los Angeles, reported the development in yesterday's issue of the journal Nature.

The circuit has 160,000 bits of capacity, compared with previous generations of molecular circuits that were demonstrated at 64 bits.

But researchers point to the circuit's density as the real breakthrough: 100 billion bits per square centimeter, which the researchers said is about 100 times more tightly packed than current memory circuits.

"As the semiconductor industry moves forward, they're always making things smaller and smaller, and according to their own projections, just a few years from now their manufacturing approach will run out of steam," said Caltech chemistry professor James Heath, who led the research with J. Fraser Stoddart at UCLA. "What we did is leapfrogged that and developed another approach."

Although still at least a decade away from mass production, outside experts say, the circuit would allow manufacturers to build ever-smaller devices.

Martin Reynolds, vice president and research fellow at Gartner Inc., said Hewlett-Packard Co. researchers demonstrated similar technology in 2002, but at 64 bits.

The Caltech and UCLA researchers demonstrated a similar technology the same year, and HP and the university researchers have worked together on developing a manufacturing approach and architecture, but the projects were separate.

The latest development, Reynolds said, shows development progressing from research into something manufacturable.

The researchers described the 160,000 memory bits as being arranged like a large tic-tac-toe board, with 400 silicon wires crossed by 400 titanium wires and a layer of molecular switches in between.