/Characterization of magnetic flux trapping for superconducting circuits

Characterization of magnetic flux trapping for superconducting circuits

PhD - Leuven | More than two weeks ago

Theoretical and experimental study of flux pinning in thin-film superconductors with different materials and engineered defects relevant to a multilayer IC fabrication stack.

​Unsustainable demand for computing power and unsustainable production hardware costs open the door to new technologies in the post-Moore era. Superconducting digital logic devices have the potential to be a VLSI digital technology [MVB1] positioned between state-of-art CMOS and quantum computing. The differentiating strengths of superconducting digital technology are energy efficiency, high computational density, and high interconnect bandwidth [1]. Imec is approaching the scaling of superconducting technology holistically by co-developing fabrication process, logic, memory, and interconnects driven by system architecture studies. 

In superconducting devices, parasitic magnetic flux failures often result in unwanted variability among different cooldowns of the same device. Such flux failures can be either trapping of the persistent current in the circuit, or flux trapping in the ground plane surrounding the circuit [2-3]. This has historically been a serious limiting issue. While understandings have improved as circuit scale and complexity have increased, the best methods of parasitic flux mitigation have not yet been fully implemented due to limitations imposed by materials and fabrication processes.

In this PhD research, you will investigate effective flux-trap engineering techniques for superconducting circuits as a function of material uniformity and stability against fabrication processing[MVB2] , and patterning. A systematic approach is needed for characterization of material parameters such as London penetration depth, pinning constant, viscosity, and coherence length [MVB3] using electrical transport techniques, magnetic imaging of the flux in the devices [4], and design of functional-circuit test vehicles. The experimental work needs to be complemented by developing a simulation package based on Ginzburg-Landau potentials [5]. You will interact closely with top researchers in superconductivity at imec and KU Leuven, in magnetic imaging at Cornell University, and materials research at Jefferson Lab.  

[1] Q. P. Herr, A. Y. Herr, O. T. Oberg, and A. G. Ioannidis, “Ultra-low-power superconductor logic,” Journal of applied physics, vol. 109, no. 10, p. 103903, 2011.

[2] V. Shmidt and G. Mkrtchyan, “Vortices in type-II superconductors,” Soviet Physics Uspekhi, vol. 17, no. 2, p. 170, 1974.

[3] G. Stan, S. B. Field, and J. M. Martinis, “Critical field for complete vortex expulsion from narrow superconducting strips,” Physical review letters, vol. 92, no. 9, p. 097003, 2004.

[4] J. Kirtley, “Fundamental studies of superconductors using scanning magnetic imaging,” Reports on Progress in Physics, vol. 73, no. 12, p. 126501, 2010.

[5] I. Sadovskyy, A. Koshelev, C. L. Phillips, D. A. Karpeyev, and A. Glatz, “Stable large-scale solver for Ginzburg–Landau equations for superconductors,” Journal of Computational Physics, vol. 294, pp. 639–654, 2015.

Required background: Physics

Type of work: 50% Modelling/simulation, 50% experimental

Supervisor: Margriet Van Bael

Daily advisor: Anna Herr

The reference code for this position is 2022-119. Mention this reference code on your application form.