In the realm of energy and electronics, a team of researchers from Northrop Grumman Corporation, including Sergey K. Tolpygo, Ravi Rastogi, David Kim, Terence J. Weir, Neel Parmar, and Evan B. Golden, have been making strides in the development of superconducting electronics. Their recent work focuses on the fabrication and properties of Josephson junctions, which are crucial components in superconducting circuits.
Superconducting electronics (SCE) are of great interest to the energy sector due to their potential for high-speed, low-power computing and efficient power transmission. As the integration scale of SCE increases, there is a need for miniaturizing key components such as inductors and Josephson junctions (JJs). The researchers have been developing a ten-superconductor-layer planarized fabrication process with NbN kinetic inductors and exploring suitable self-shunted JJs to potentially replace high Josephson critical current density, Jc, Nb/Al-AlOx/Nb junctions.
The team reported on the fabrication and electrical properties of NbN/NbNx/NbN junctions produced by reactive sputtering on 200-mm wafers at 200 degrees Celsius. These junctions were incorporated into a planarized process with two Nb ground planes and Nb wiring layer. NbN is a stoichiometric nitride with a superconducting critical temperature of 15 K, while NbNx is a high resistivity, nonsuperconducting nitride deposited using a higher nitrogen partial pressure than for the NbN electrodes. For comparison, the researchers also fabricated Nb/NbNx/Nb JJs using the same NbNx barriers deposited at 20 degrees Celsius.
By varying the NbNx barrier thickness from 5 nm to 20 nm, the researchers achieved a range of Jc from about 1 mA/um^2 down to approximately 10 uA/um^2. They extracted coherence lengths of 3 nm and 4 nm in NbNx deposited, respectively, at 20 degrees Celsius and 200 degrees Celsius. Both types of JJs were well described by the resistively and capacitively shunted junction model without any excess current. The researchers found that the Jc of NbN/NbNx/NbN JJs was somewhat lower than that of Nb/NbNx/Nb JJs with the same barrier thickness, despite a much higher Tc and energy gap of NbN than of Nb electrodes. IcRn products up to approximately 0.5 mV were obtained for JJs with Jc around 0.6 mA/um^2. The researchers also measured Jc(T) dependences.
The practical applications of this research for the energy sector include the potential for more efficient and compact superconducting electronics. These advancements could lead to improved power transmission, high-speed computing, and other energy-related technologies. The research was published in the Journal of Applied Physics.
This article is based on research available at arXiv.