Using molecular switches, HP claims nano-technology advance with 64-bit memory IC

A BIT PLEASED: An HP research team surrounds a screen image showing test structures of its nanotechnology breakthrough. The team comprises Stan Williams (seated), Yong Chen (left), and Doug Ohlberg. PHOTO COURTESY OF HEWLETT-PACKARD

Hewlett-Packard (HP) has claimed a major breakthrough in nanotechnology by demonstrating a 64-bit memory using molecular switches. The laboratory device combines both memory and logic functions for the first time ever. The chip fits inside a one-square-micron area and has a bit density more than 10 times greater than silicon-based memory chips, HP says.

HP's use of an advanced manufacturing method makes the breakthrough particularly noteworthy. Employing a method called nanoimprint lithography, the research team was able to quickly print an entire wafer of circuits. Stanley Williams, HP fellow and director of quantum science research at HP Labs, announced the accomplishment in September at a symposium in Stockholm celebrating the 175th anniversary of the Royal Institute of Technology of Sweden.

Williams believes molecular electronics can enable computer technology to transcend the limits of silicon-based manufacturing. "Capacity and performance could be extended enormously by layering molecular-switch devices on conventional silicon without the need for complex and expensive changes to the base technology," he says.

The research team used a three-step process to make the IC, which features a crossbar architecture incorporating molecular switches. Researchers made a master mold of eight parallel lines each measuring 40 nm wide. They pressed the mold into a polymer layer on a wafer to make eight parallel trenches running east-west. The trenches were filled with platinum to form wires.

In the second step, the team deposited a single layer of "electronically switchable molecules" on the surface. In the third step, the researchers rotated the mold 90 degrees to repeat step number one and make an additional eight wires running north-south on top of the molecular layer. The 64 points where the top and bottom wires crossed "sandwiched" approximately 1000 molecules to each become a bit of memory. Applying voltage sets the electrical resistance of the molecules to write the bit. The bit is read by measuring the molecules' resistance at a lower voltage, HP says.

The process combined optical and electron-beam lithography to make the master in approximately one day, Williams says. The master included 625 separate memories connected to wires. Making the imprint required just a few minutes. The memory devices are both rewritable and nonvolatile and thus continue to store information after voltage is turned off. In addition, by configuring molecular-switch junctions, the team placed logic in the same IC to make a demultiplexer. The demultiplexer uses a small number of wires to address memory and give it practical application, HP says.

Hewlett-Packard has received four U.S. patents for the work, and the company has begun submitting scientific papers on the technique to technical journals. Yong Chen, senior scientist, led the research team. The team also comprises Douglas Ohlberg, Xuema Li, Duncan Stewart, Tan Ha, Gun-Young Jun, and Hylke Wiersma.