High quality Nb-based tunnel junctions for high frequency and digital applications

Abstract

A number of new fabrication techniques are developed and optimized in order to fit the requirements of contemporary superconducting electronics. To achieve ultimate performance of integrated submm receivers with operational frequency of 1 THz, tunnel junctions with AlN tunnel barrier having a value as low as 1 m 2 have been developed. High quality characteristics of Nb/AlN/Nb tunnel junctions with = 16 and = 10 m 2 have been demonstrated. Electron Beam Lithography (EBL) in combination with Chemical Mechanical Polishing (CMP) has been incorporated to produce Nb/AlN/Nb junctions with 0.03 m 2 area. A new approach to get overdamped Nb/AlO /Nb tunnel junction has been proposed and realized. The dependencies of the main parameters of novel junctions on the currents density and circuits geometry have been studied. These junctions may have a good potential in Josephson Junction Arrays and Single-Flux-Quantum applications (RSFQ).

Fabrication of $\hbox{Nb/Al}_{2}\hbox{O}_{3}/\hbox{Nb}$ Josephson Junctions Using In Situ Magnetron Sputtering and Atomic Layer Deposition

“…The quasiparticle branch of the IVC has a very low sub-gap leakage current and the much higher specific resistance of ~ 3.57 kΩµm 2 shows that the tunnel barrier layer is dominated by ALD-grown Al 2 O 3 instead of the thermal oxidation of the Al wetting layer. The sub-gap resistance R sg ~ 4.5 kΩ was measured at V=π∆/2e ~ 1.8 mV, and the sub-gap/normal-state resistance ratio R sg /R N ≈ 20.5 is comparable to previous reports using AlN tunneling barriers [19,20]. However, I c R N product of the junctions made from the reference trilayer and the ALD trilayer are only about 0.3 mV to 0.5 mV which is a factor of three to five less than that expected from the Ambegaokar-Baratoff formula and/or empirical results compiled from junctions made from Nb/AlAlO x /Nb trilayers with controlled thermal oxidation.…”

Development of Nb/Al-AlN/NbTiN SIS Junctions With ICP Nitridation

“…Using this new pentalevel process, well defined junction diameters as small as 0. 6 can be achieved using optical lithography. Fig.…”

Analysis of the fabrication process of Nb/Al-AlN/sub x//Nb tunnel junctions with low R/sub n/A values for SIS mixers

“…In order to evaluate the limits of this technology, it is necessary to make junctions of sub-micron area. Dmitriev et al have shown good quality junctions with m [19]. …”