Researchers have grown a nanoscale layer of a superconducting material that can integrate quantum qubits into existing microelectronics.
Scientists from Japan have discovered how a superconducting material, niobium nitride, can be added as a flat, crystalline layer to a nitride-semiconductor substrate. This technique will make it easier to make quantum qubits usable in conventional computing devices. Discovering a technique to integrate quantum and conventional logic units on a single chip, or even to add quantum capabilities to existing fabrication lines, could accelerate the adoption of these new systems.
A group of scientists from The University of Tokyo’s Institute of Industrial Science has shown how thin films of niobium nitride (NbNx) can be grown directly on top of an aluminum nitride (AlN) layer. Niobium nitride becomes superconducting at temperatures colder than 16 degrees Celsius above absolute zero. Because of this, it can be used to create a superconducting qubit when arranged in a structure called a Josephson junction.
“We found that due to the small lattice mismatch between aluminum nitride and niobium nitride, a highly crystalline layer can grow at the interface, the structural similarity between the two materials facilitates the integration of superconductors into semiconductor optoelectronics that tools,” said the first and corresponding author. Atsushi Kobayashi.
The scientists investigated the effect of temperature on the crystal structures and electrical properties of NbNx thin films grown on AlN template substrates. They showed that the spacing of the atoms in the two materials was close enough to form flat layers.
The crystalline nature of NbNx was characterized by X-ray diffraction, and the surface topology was obtained using atomic force microscopy. The team also showed how the arrangement of atoms, nitrogen content, and electrical conductivity all depend on growth conditions, especially temperature.
This interface between the AlN substrate, which has a wide bandgap, and NbNx is essential for future quantum devices, such as Josephson junctions. Superconducting layers that are only a few nanometers thick and have high crystallinity can be used as detectors of a photon or an electron.
Reference: “Crystal-Phase Controlled Epitaxial Growth of NbNx Superconductors on Wide-Bandgap AlN Semiconductors” by Atsushi Kobayashi, Shunya Kihira, Takahito Takeda, Masaki Kobayashi, Takayuki Harada, Kohei Ueno and Hiroshi Fujioka, 21 September 2022, Advanced Materials Interface.