A Self-Flux-Biased NanoSQUID with Four NbN-TiN-NbN Nanobridge Josephson Junctions

Abstract

We report the development of a planar 4-Josephson-junction nanoscale superconducting quantum interference device (nanoSQUID) that is self-biased for optimal sensitivity without the application of a magnetic flux of Φ0/4. The nanoSQUID contains novel NbN-TiN-NbN nanobridge Josephson junctions (nJJs) with NbN current leads and electrodes of the nanoSQUID body connected by TiN nanobridges. The optimal superconducting transition temperature of ~4.8 K, superconducting coherence length of ~100 nm, and corrosion resistance of the TiN films ensure the hysteresis-free, reproducible, and long-term stability of nJJ and nanoSQUID operation at 4.2 K, while the corrosion-resistant NbN has a relatively high superconducting transition temperature of ~15 K and a correspondingly large energy gap. FIB patterning of the TiN films and nanoscale sculpturing of the tip area of the nanoSQUID’s cantilevers are performed using amorphous Al films as sacrificial layers due to their high chemical reactivity to alkalis. A cantilever is realized with a distance between the nanoSQUID and the substrate corner of ~300 nm. The nJJs and nanoSQUID are characterized using Quantum Design measurement systems at 4.2 K. The technology is expected to be of interest for the fabrication of durable nanoSQUID sensors for low temperature magnetic microscopy, as well as for the realization of more complex circuits for superconducting nanobridge electronics.

Contribution of Processes in SN Electrodes to the Transport Properties of SN-N-NS Josephson Junctions

“…The approach we have demonstrated in this paper allows calculation of the parameters of the equivalent scheme of SN-N-NS, BVT, and DB structures. Their representation in the form of a serial connection of the Josephson contact having and the linear inductance of conductive electrodes is useful for the interpretation of experimental data in bridges [ 13 , 86 ], analysis of processes in nano-SQUIDs [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ], experimental determination of inductance in various low-current superconducting devices [ 3 , 9 ], and in the design of digital circuits [ 12 , 13 , 14 ].…”

“…The first consists of calculating the distribution of the supercurrent (15) along the normal film, that is, in solving the boundary value problem (2), ( 4), ( 7)- (10) for a given phase distribution χ(x, 0). The second task is to use the finite element method to find the dependencies of χ(x, y) and J s (x, y) by solving the Laplace Equation ( 6) with the boundary conditions (10), (13), (14). The solution of the Laplace equation χ(x, y) is determined up to a constant.…”

“…These structures are now widely used in the fabrication of nano-SQUIDs [1][2][3][4][5][6][7][8][9][10][11] as well as in the design and implementation of digital circuits [12][13][14]. The ordinary metals Nb, NbN [3][4][5]12,15], TiN [8,9,9], Al [2,16,17], Pb [18], Au [19][20][21], and Cu [22] as well as two-dimensional electron gas [23,24] and topological insulators have been used as the weak coupling material of the Josephson elements in these devices.…”

“…These structures are now widely used in the fabrication of nano-SQUIDs [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ] as well as in the design and implementation of digital circuits [ 12 , 13 , 14 ]. The ordinary metals Nb, NbN [ 3 , 4 , 5 , 12 , 15 ], TiN [ 8 , 9 , 9 ], Al [ 2 , 16 , 17 ], Pb [ 18 ], Au [ 19 , 20 , 21 ], and Cu [ 22 ] as well as two-dimensional electron gas [ 23 , 24 ] and topological insulators [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , …”

TiN-NbN-TiN and Permalloy Nanostructures for Applications in Transmission Electron Microscopy

“…[18] and ref. [19], TiN and NbN thin films exhibit good superconducting properties when they are deposited onto an LPCVD SiN buffer layer and grown epitaxially on top of each other. The lattice constants of TiN and NbN are 0.424 nm and 0.439 nm, respectively.…”