New record for quantum chip manufacturing precision

An Australian team has broken the record for precision in manufacturing silicon chips that might one day power quantum computers.

The team from the University of NSW (UNSW) and University of Melbourne managed to implant phosphorous ions into silicon crystal with 99.95% confidence, while simultaneously being precisely located inside the chip. The achievement is detailed in a paper published in the journal Advanced Quantum Technologies.

Manufacturing silicon chips using ion implantation is already used to make the binary bits in ordinary computers. Using the same technique to build quantum chips could offer a flexible and scalable way to fabricate the basic units for quantum computers.

Phosphorous implantation in silicon has already been shown to make exceptionally good qubits.

Other qubit technologies struggle with the quantum “noise.”  But donor spin-based quantum chips support high-fidelity and can retain quantum information for long times.

The issue is in making such technologies.

“The key challenge for donor spin qubits is the development of fabrication methods to place and control individual atoms with sufficient precision, within scalable nanoelectronic structures,” the authors write.

To place a donor ion inside the crystal structure requires high energy. But accelerating the ion to high energy leads to large uncertainties as to the exact location of the atom.

The researchers overcame this issue by implanting the phosphorous ion, not by itself, but as part of the molecular ion phosphorus difluoride (PF2+).

Diagram of two flourine atoms break away from the phosphorous atom after being shot into the silicon crystal blue box green dots pink dot
Two flourine atoms break away from the phosphorous atom after being shot into the silicon crystal. Credit: UNSW Sydney.

Shooting the molecular ion into the chip allows impact detection of 99.95%. But less than half of the energy is passed to the phosphorous atom. The molecule breaks apart at the surface and the phosphorous atom slowly comes to rest in a well-defined position inside the crystal.

According to co-author, UNSW PhD student Benjamin Wilhelm, the researchers are also able show that “the two stray fluorine atoms do not pose any problems to the operation of the phosphorus quantum bits.”

After the implantation, the chip is subjected to a 5-second blast of 1,000°C heat which makes the F atoms diffuse away.

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