breakthrough semiconducting nanowires
Experts in the industry have predicted that within the next five to ten years the dimension of silicon transistors may have been pushed to their limits and it will be impossible to make them any smaller, therefore without a miracle breakthrough on some level Moores Law will cease to exist.
A group of engineers however from IBM, Purdue University and the University of California have managed to create nanowires coated in materials which make for efficient transistors. Nanowires are nanostructures with the diameter of the order of a nanometer and by using nanotechnology such components could be created out of chemical compounds. Nanowires have many interesting properties that are not seen in bulk or 3-D materials … this is because electrons in nanowires are quantum confined laterally and occupy energy levels that are different from the traditional progression of energy levels or bands found in bulk materials.
“Having sharply defined layers of materials enables you to improve and control the flow of electrons and to switch this flow on and off.” said Eric Stach, associate professor of materials Engineering from Purdue.
The research team have said that electronic devices are often created of heterostructures – a terminology that means the structure contains sharply defined layers of different semiconducting materials such as germanium and silicon. The issues in the past have revolved around producing nanowires with the necessary defined layer structures.
In the November 27th edition of ‘Science‘ the team have said that their transistors are not made on flat pieces of silicon but the nanowires have been created vertically making them have a much finer footprint which means that many more nanowires can be placed in the same area of silicon compound.
The nanowires were formed by heating tiny particles of a gold aluminium alloy inside a vacuum chamber and after this alloy was melted down, they then injected silicon gas and the alloy head absorbed the gas becoming supersaturated with silicon. This in effect causes the silicon wire to increase in mass from the alloy bead and produce a final product of silicon wire with a mushroom shaped gold-aluminum alloy bead. Then the researchers reduced the temperature of the chamber by a specific factor to allow the alloy bead at the head of the wire tip to solidify, thereby allowing germanium to be deposited on the silicon precisely creating the required heterostructure needed to create a transistor. The heterostructure allows the formation of a germanium gate in each transistor allowing devices to switch on and off.
Stach said that the the cycle could be repeated, switching the gases from germanium to silicon as desired to make specific types of heterostructures.