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InGaAs `4-D` transistor could be the future for computers

Dec 06, 2012
Indium gallium arsenide is one of the several promising semiconductors being studied to replace silicon
A new type of transistor shaped like a Christmas tree has arrived just in time for the holidays, but the prototype won't be nestled under the tree along with the other gifts.

This image taken with a transmission electron microscope shows the cross section of a new type of transistor shaped like a Christmas tree that was created by researchers at Purdue and Harvard universities. The transistor is made from tiny nanowires of a material called InGaAs, which could replace silicon within a decade. (Purdue University image)

"It's a preview of things to come in the semiconductor industry," says Peide "Peter" Ye, a professor of electrical and computer engineering at Purdue University.

Researchers from the universities of Purdue and Harvard created the transistor, which is made from a material that could replace silicon within a decade.

Each transistor contains three tiny nanowires made not of silicon, but from InGaAs. The three nanowires are progressively smaller, yielding a tapered cross section resembling a Christmas tree.

The research builds on previous work in which the team created a 3-D structure instead of conventional flat transistors. The approach could enable engineers to build faster, more compact and efficient integrated circuits and lighter laptops that generate less heat than today's.

New findings show how to improve the device performance by linking the transistors vertically in parallel.

"A one-story house can hold so many people, but more floors, more people, and it's the same thing with transistors," Ye comments. "Stacking them results in more current and much faster operation for high-speed computing. This adds a whole new dimension, so I call them 4-D."

The findings will be detailed in two papers to be presented during the International Electron Devices Meeting taking place between Dec 8th and 12th in San Francisco. One of the papers has been highlighted by conference organisers as among "the most newsworthy topics and papers to be presented."

The newest generation of silicon computer chips, introduced this year, contain transistors having a vertical 3-D structure instead of a conventional flat design. However, because silicon has a limited "electron mobility" - how fast electrons flow - other materials will likely be needed soon to continue advancing transistors with this 3-D approach, Ye adds.

Transistors contain critical components called gates, which enable the devices to switch on and off and to direct the flow of electrical current. Smaller gates make faster operation possible. In today's 3-D silicon transistors, the length of these gates is about 22 nanometres (nm), or billionths of a metre.

The 3-D design is critical because gate lengths of 22 nm and smaller do not work well in a flat transistor architecture. Engineers are working to develop transistors that use even smaller gate lengths; 14 nm are expected by 2015, and 10 nm by 2018.

However, size reductions beyond 10 nm and additional performance improvements may not be possible using silicon, meaning new materials will be needed to continue progress, Ye says.

Creating smaller transistors also will require finding a new type of insulating, or "dielectric" layer that allows the gate to switch off. As gate lengths shrink smaller than 14 nm, the dielectric used in conventional transistors fails to perform properly and is said to "leak" electrical charge when the transistor is turned off.

"Nanowires in the new transistors are coated with a different type of composite insulator, a 4 nm thick layer of lanthanum aluminate with an ultrathin, half-nanometre layer of aluminium oxide. The new ultrathin dielectric allowed researchers to create transistors made of InGaAs with 20 nm gates, which is a milestone," Ye points out.

The work, based at the Birck Nanotechnology Centre in Purdue's Discovery Park, was funded by the National Science Foundation and the Semiconductor Research Corporation.

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