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HP fellow talks of triple achievement in molecular electronics

STOCKHOLM, Sweden -- Speaking at a symposium celebrating the 175th anniversary of the Royal Institute of Technology of Sweden, Stanley Williams, a Hewlett Packard fellow and director of quantum science research at HP Labs, said his group had scored three important achievements in molecular electronics.

Williams said that his group had created the highest density electronically addressable memory, had combined memory with logic based on molecular switching, and also built the assembly using a candidate technology for volume manufacturing.

"This is the first demonstration that molecular logic and memory can work together on the same nano-scale circuits," Williams said in a statement.

The group's laboratory demonstration circuit, a 64-bit memory using molecular switches as active devices, easily fits inside a square micron and uses platinum wires 40 nanometers in width. The bit density of the device is more than 10 times greater than today's silicon memory chip, the company claimed..

The circuits were made using a method called nano-imprint lithography, essentially a printing method that allows an entire wafer of circuits to be stamped out from a master. The method should prove quick and inexpensive, the company claimed.

"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." said Williams.

The researchers made a master mold of eight parallel lines, each only 40 nanometers wide. Then, in a three-step process, researchers made a cross matrix separated by switchable molecular material.

Firstly they pressed the mold into a polymer layer on a silicon wafer to make eight parallel "east-west" trenches, which they then filled with platinum metal to form wires. Secondly they deposited a single layer of electronically switchable molecular material on the surface; and thirdly repeated the first step, after rotating the mold 90 degrees to make another eight wires, running "north-south," on top of the molecular layer.

At each of the 64 points where the top and bottom wires crossed, the roughly 1,000 molecules sandwiched between them became a bit of memory. A bit can be written by applying a voltage pulse to set the molecules' electrical resistance and read by measuring their resistance at a lower voltage.

"Using a combination of optical and electron beam lithography, it took about a day to create the master, which included 625 separate memories connected to conventional wires so that we can communicate with them," said Williams in his statement. "After that, it took just a few minutes to make an imprint."

The memories have proved to be both rewritable and non-volatile, the company said.

The researchers also put logic in the same circuit by configuring molecular-switch junctions to make a demultiplexer -- a logic circuit that uses a small number of wires to address memory. A demultiplexer is essential to make practical memory devices.

The HP Labs research team that fabricated and tested the memory was led by senior scientist Yong Chen and included Douglas Ohlberg, Xuema Li, Duncan Stewart, Tan Ha, Gun-Young Jung and Hylke Wiersma. Four U.S. patents have been awarded in connection with this work and scientific papers are being submitted to reviewed technical journals for publication.

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