1-D Has a Place Too

Two-dimensional materials are one of highest-interest topics in chemistry. The magical properties of 2-D are being exploited for many applications, including quantum computers (QCs). One breadboard QC image shows several parts mounted in a cylindrical device designed for immersion in a liquid gas dewar.

However, one can anticipate that 2-D devices will be interconnected to others to form circuits enabling specific applications, as is current practice with cell phones and computers. Scientists at NIST report on a process developed to make nanowires, which are one atom deep and electrically conductive, thus a 1-D conductor or “wire” (www.nist.gov/news-events/news/2018/04/blazing-path-buried-bits-quantum-chips).

The fabrication chemistry is interesting. It starts with a wafer substrate of 99.9999 purity 28Si. Natural silica contains about 4.7% 29Si. 29Si provides a route for loss of coherence (state stability) in the electronic state of the qubit. The silicon chip is first treated with hydrogen to create a surface of hydrogen. Next, a scanning electron microscope ablates the hydrogen along a path interconnecting the qubits and other devices such as metal pads for connection to off-chip devices. The chip is exposed to PH3, which deposits the phosphine along the exposed track. Then it is heated to drive off the hydrogens of the adsorbed phosphine, leaving a 1-D track chain of conductive P atoms. A thin cover layer of silicon is bonded to protect the wires. Similar lithographic processes are used in making today’s chips, but with much larger feature sizes.

The authors claim that this X-ray lithographic process is suitable for high-throughput automated processing of chips.

A separate report describes X-ray lithographic technology useful for creating other circuit elements such as qubits in silicon wafers.

Robert L. Stevenson, Ph.D., is Editor Emeritus, American Laboratory/Labcompare; e-mail: [email protected]

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