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UNSW researcher creates four-atom silicon wires

Quantum-scale lifeline for Moore's Law and Ohm's Law

Researchers at the University of New South Wales have created what the uni thinks is the narrowest-ever silicon conducting wire.

At just four atoms wide and one atom tall, the wire has demonstrated a surprising property: Ohm’s law (current equals voltage divided by resistance) holds true even at such a tiny scale, the resistivity of the wire unaffected by its width.

"It is extraordinary to show that such a basic law still holds even when constructing a wire from the fundamental building blocks of nature – atoms," says lead author of the study, Bent Weber, a student at the university’s ARC Centre of Excellence for Quantum Computing.

This result gets around what’s been seen as an approaching limit to shrinking the feature size of microelectronics: previous researchers have found that as wires shrink below 10 nanometers, quantum effects take over from Ohm’s law, and resistivity rises exponentially.

According to Nature, the tiny conductors were fabricated by covering a silicon crystal with hydrogen atoms, using the tip of a scanning electron microscope to carve out a channel in the hydrogen, and “doped” the exposed silicon with phosphorus atoms to create a conductive wire, which is finally coated with another layer of silicon.

A co-author of the paper, ARC director Michelle Simmons, explained to Nature that there are two reasons these wires obey Ohm’s law: the high density of phosphorus in the wires creates a strong overlap of electron waveforms; and since the doped silicon wires are completely encapsulated in silicon, there are no external surfaces to inhibit the mobility and availability of electrons.

She notes that the technique Weber’s research used would not be suitable for mass-produced chips. However, by demonstrating that quantum-scale wires can be made to demonstrate classical behaviours, the research holds out the prospect Moore’s Law can be kept intact for many years to come.

Scientists at the University of Melbourne and Purdue University in America also took part in the research. ®

University of NSW animation of the tiny wire.

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