Quantum computer chips come one step closer to reality

Friday, October 16, 2009

WASHINGTON - Researchers at Ohio State University in the US have discovered a way to make quantum devices using technology common to the chip-making industry today, which might one day enable faster, low-power computer chips.

The research was conducted by Paul Berger, professor of electrical and computer engineering and professor of physics at Ohio State University, and his colleagues.

The team fabricated a device called a tunneling diode using the most common chip-making technique, called chemical vapor deposition.

“We wanted to do this using only the tools found in the typical chip-makers toolbox,” Berger said.

“Here, we have a technique that manufacturers could potentially use to fabricate quantum devices directly on a silicon chip, side-by-side with their regular circuits and switches,” he added.

The quantum device in question is a resonant interband tunneling diode (RITD) - a device that enables large amounts of current to be regulated through a circuit, but at very low voltages.

That means that such devices run on very little power.

RITDs have been difficult to manufacture because they contain dopants - chemical elements - that don’t easily fit within a silicon crystal.

Atoms of the RITD dopants antimony or phosphorus, for example, are large compared to atoms of silicon.

Because they don’t fit into the natural openings inside a silicon crystal, the dopants tend to collect on the surface of a chip.

Berger discovered that RITD dopants could be added during chemical vapor deposition, in which a gas carries the chemical elements to the surface of a wafer many layers at a time.

The key was determining the right reactor conditions to deliver the dopants to the silicon, he found.

“One key is hydrogen. It binds to the silicon surface and keeps the dopants from clumping. So you don’t have to grow chips at 320 degrees Celsius like you do when using molecular beam epitaxy,” Berger said.

“You can actually grow them at a higher temperature like 600 degrees Celsius at a lower cost, and with fewer crystal defects,” he added.

Different ratios are appropriate for different kinds of devices. Logic circuits such as those on a computer chip are best suited by a ratio of about 2.

The RITDs that Berger’s team fabricated had a ratio of 1.85.

“We’re close, and I’m sure we can do better,” he said.

He envisions his RITDs being used for ultra-low-power computer chips operating with small voltages and producing less wasted heat. (ANI)

Filed under: Quantum Computer, Technology

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