FMN Laboratory team participated in MNE 2018

21 september 2018

Quantum information processing has emerged as promising field due to both its potential applications in cryptography and computational speedup and its role in designing quantum systems that can be used to study fundamental physics in previously inaccessible regimes of parameter space. Therefore, in last 5 years leading companies pays attention quantum informatics and in particular quantum schemes on the superconductor qubits. Superconductive qubits fabrication have high requirements to their key elements, called Josephson Junctions.

Josephson junctions fabrication include cleaning wafer, e-beam lithography, shadow evaporation trough Dolan bridge and liftoff. There are many fabrication problems at each over technology process, but we consider fabrication of submicron suspended Dolan bridges affecting to reproduction Josephson Junctions. Exact reproduction is the main characteristic of Josephson Junctions as elements of qubit schemes. Therefore, it is necessary to pay attention to exact corresponding dimension and small resist mask deformation. We expect to reach small deformation by increase hardness bridge. Firm bridge can be obtained by hard mask or enlargement resist height. In fact, that fabrication hard inorganic mask requires several steps of e-beam evaporation or PVD with RIE this technic seems too complicated. Fabrication of resist mask is a more simple and used technology. In this experiments we are using thick resist mask.

According to calculation, widening bridge is possible by increase evaporation angle or increase copolymer thickness. However last option accord negative influence to Josephson Junction evaporation. So, we increase angle evaporation and change mask size to save constant area junction. It should be noted that it is necessary control undercut exactly by addition area exposure.

Another way is approach T-construction to increase area junction reproduction. To check it were fabricated T-construction Josephson Junctions equality the previous junction square. This technic let leave out electrode junction deformation. Thus, bridge deformation should not significant influence to Josephson Junctions area. Experiments done for different length electrodes and different squares correspondingly. The topology for large areas corrected.

It was measured geometric and electric reproduction of Josephson Junctions massive. It was fabricate flux qubits with parallel and SQUIDs with T-construction Josephson Junctions. 

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