Novel Methods of Fabrication and Metrology of Superconducting NanoStructures

Líu, Hao; Macfarlane, J.C.; Gallop, John; Cox, D. C.; Joseph-Franks, Patrick; Hutson, David; Chen, Jie; Lam, Siu Shu Eddie

doi:10.1109/tim.2007.890593

Cited by 13 publications

(13 citation statements)

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“…22) or Nb are suitable candidates); (4) ultralow dissipation (∼1...100 fW), which makes it ideal for nanoscale applications; (5) ease of implementation in a series or parallel array (depending on the biasing mode) for enhanced output; and (6) ease of integration with superconducting refrigerators 23 to actively tune the device working temperature. Finally, as far as specific applications 24 are concerned, measurements of small magnetic systems 25 (for instance, the magnetic flux induced by atomic spins as well as singlemolecule nanomagnets), single-photon detection 26 , scanning microscopy as well as quantum metrology 27 and nanoelectromechanical measurements 28 with SQUIPT devices could be predicted. Our approach opens the way to magnetic-field detection based on 'hybrid' interferometers that take advantage of the flexibility intrinsic to proximity metals.…”

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confidence: 99%

Superconducting quantum interference proximity transistor

et al. 2010

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When a superconductor is placed close to a non-superconducting metal, it can induce superconducting correlations in the metal [1][2][3][4][5][6][7][8][9][10] , known as the 'proximity effect' 11. Such behaviour modifies the density of states (DOS) in the normal metal [12][13][14][15] and opens a minigap 12,13,16 with an amplitude that can be controlled by changing the phase of the superconducting order parameter 12,15 . Here, we exploit such behaviour to realize a new type of interferometer, the superconducting quantum interference proximity transistor (SQUIPT), for which the operation relies on the modulation with the magnetic field of the DOS of a proximized metal embedded in a superconducting loop. Even without optimizing its design, this device shows extremely low flux noise, down to ∼10 −5 Φ 0 HzWb is the flux quantum) and dissipation several orders of magnitude smaller than in conventional superconducting interferometers [17][18][19] . With optimization, the SQUIPT could significantly increase the sensitivity with which small magnetic moments are detected.One typical SQUIPT fabricated with electron-beam lithography is shown in Fig. 1a. It consists of an aluminium (Al) superconducting loop interrupted by a copper (Cu) normal-metal wire in good electric contact with it. Furthermore, two Al electrodes are tunnel-coupled to the normal region to enable the device operation. A detailed view of the sample core (see Fig. 1b) shows the Cu region of length L 1.5 µm and width 240 nm coupled to the tunnel probes and the superconducting loop. The SQUIPTs were implemented into two different designs (see Fig. 1c), namely, the A-type configuration, where the loop extends into an extra third lead, and the B-type configuration, which contains only two tunnel probes. The ring geometry enables us to change the phase difference across the normal-metal/superconductor boundaries through the application of an external magnetic field, which gives rise to a total flux Φ through the loop area. This modifies the DOS in the normal metal, and hence the transport through the tunnel junctions.Insight into the interferometric nature of the SQUIPT can be gained by first analysing the theoretical prediction of its behaviour. Figure 2a shows the simplest implementation of the device in the A-type configuration, that is, that with just one junction tunnelcoupled to the normal metal. For simplicity, we suppose the tunnel probe (with resistance R T ) to be placed in the middle of the wire, and to feed a constant electric current I through the circuit while the voltage drop V is recorded as a function of Φ. In the limit that the kinetic inductance of the superconducting loop is negligible, the magnetic flux fixes a phase difference φ = 2πΦ/Φ 0 across the normal metal, where Φ 0 = πh/e is the flux quantum,h is the reduced Planck's constant and e is the electron charge. Figure 2b shows the low-temperature quasiparticle current-voltage (I -V ) characteristic of the SQUIPT calculated at a few selected values of Φ. The calculations were carried out f...

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Superconducting quantum interference proximity transistor

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“…The device is then etched using electron cyclotron resonance system with CF 4 plasma. The nanobridges are fabricated using FEI Strata 400 Focus Ion Beam (FIB) system [18,19,20,21,22] at accelerating voltage of 30 kV and Ga ions current of 9.7 pA. The outer dimensions of the bridges are about 150 × 50 nm .…”

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confidence: 99%

Intermode dephasing in a superconducting stripline resonator

et al. 2010

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We study superconducting stripline resonator (SSR) made of Niobium, which is integrated with a superconducting interference device (SQUID). The large nonlinear inductance of the SQUID gives rise to strong Kerr nonlinearity in the response of the SSR, which in turn results in strong coupling between different modes of the SSR. We experimentally demonstrate that such intermode coupling gives rise to dephasing of microwave photons. The dephasing rate depends periodically on the external magnetic flux applied to the SQUID, where the largest rate is obtained at half integer values (in units of the flux quantum). To account for our result we compare our findings with theory and find good agreement.

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“…This was then patterned into the overall geometry of a SQUID loop using conventional photolithography. Then two nanobridge Josephson junctions were etched into the loop using Focused Ion Beam (FIB) milling, producing constrictions down to a width of 80 nm [6]. To provide good mechanical/magnetic coupling between the NEMS resonator and the SQUID readout, we fabricated a mechanical resonator on the same substrate, directly above the SQUID loop.…”

Section: Prototype Device Fabrication and Modelingmentioning

confidence: 99%

“…Devices) developed at NPL [5], [6] as readouts. This will require operation at cryogenic temperatures but this is already necessary to satisfy inequality (1).…”

Section: Squid Readout Our Proposed Technique Involves the Use Of mentioning

confidence: 99%

“…Here the conducting NEMS cantilever carries an ac current orthogonal to this field and vibrational excitation occurs along the third axis. We will present calculations which show that a sufficiently sensitive form of readout can be provided by our on-going development of nanoSQUIDs [5], [6]. Here a SQUID structure is fabricated, using focused ion beam etching, on the same chip as the NEMS resonator.…”

Section: Introductionmentioning

confidence: 99%

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Focused Ion Beam NanoSQUIDs as Novel NEMS Resonator Readouts

Líu

Gallop

Cox

et al. 2009

IEEE Trans. Appl. Supercond.

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Abstract-Nano electromechanical systems (NEMS) represent an important new class of device with wide ranging applications. In this paper we report proposals and calculations for novel methods for excitation and readout of cantilever-style NEMS resonators which are applicable over a wide temperature range. We suggest a Lorentz force-based excitation method and discuss an ultrasensitive readout provided by a nanoSQUID, where the cantilever vibration modulates the inductance of the nanoSQUID loop, allowing potentially sub-picometer amplitude sensitivity to be achieved.

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Novel Methods of Fabrication and Metrology of Superconducting NanoStructures

Cited by 13 publications

References 10 publications

Superconducting quantum interference proximity transistor

Superconducting quantum interference proximity transistor

Intermode dephasing in a superconducting stripline resonator

Focused Ion Beam NanoSQUIDs as Novel NEMS Resonator Readouts

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