Development of a Two-Dimensional Micro-SQUID Array for Investigation of Magnetization Spatial Distribution


We developed a two-dimensional array of superconducting quantum interference devices (SQUIDs) for investigation of fine spatial distribution of magnetization in superconducting Sr\(_{2}\)RuO\(_{4}\). Micrometer-sized SQUIDs based on homogeneously formed Al/AlO\(_{x}\)/Al tunnel-type Josephson junctions were fabricated using shadow evaporation technique. Unnecessary electrodes formed by the shadow evaporation were removed by inductively coupled plasma reactive ion etching, in order to realize a dense array of SQUIDs. We measured the magnetic modulation of the maximum Josephson current of each SQUID in the array and evaluated the interaction among the SQUIDs.

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This work was supported by MEXT KAKENHI (Grant Numbers 22103002, 15H05852, and 15H05853), and JSPS KAKENHI (Grant Numbers 20221007, 25390046, and 15K17708). This fabrication was supported by NIMS Nanofabrication Platform in “Nanotechnology Platform Project” sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

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Correspondence to Daisuke Sakuma.


Appendix 1: O\(_{2}\) Plasma Ashing

The Si wafer was cleaned whenever photo- or e-beam resist was applied onto the wafer, using an O\(_{2}\) plasma ashing system, which removes remaining organic substance on the wafer by a burning reaction of the organic substance itself and O\(_{2}\) radical.

Appendix 2: Chemicals Used in the Fabrication

A common surface-activating agent, hexamethyldisilazane (HMDS), was applied before resists below were applied.

The Ti/Au electrodes were fabricated by direct laser lithography, using a photoresist (AZ5214E, Micro Chemicals Corp.) over a highly soluble polymer based on polydimethylglutarimide (LOR5A, Micro-Chem Corp.). These were developed in 2.38 % tetra methyl ammonium hydroxide (TMAH) and rinsed in deionized (DI)–water.

The Al electrodes were fabricated by e-beam lithography, using an e-beam resist (gL2000-14, Micro-Chem Corp.), diluted by thinner (ZEP-A, ZEON CHEMICALS Corp.) at a ratio of 1:2.5 to adjust the viscosity of the resist, over a highly soluble polymer based on polydimethylglutarimide (PMGI SF7, Micro-Chem Corp.). gL2000-14 was developed using developer (ZED-N50, ZEON CHEMICALS Corp.) and rinsed with rinse (ZMD-B, ZEON CHEMICALS Corp.), and PMGI SF7 was developed in 2.38 % TMAH and rinsed in DI- water.

Etching masks for ICP-RIE was patterned by e-beam lithography, using gL2000-14 without dilution.

N-methyl pyrrolidone (NMP) was used to remove all unwanted metal and resist polymers after each process.

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Sakuma, D., Shinozaki, T., Nago, Y. et al. Development of a Two-Dimensional Micro-SQUID Array for Investigation of Magnetization Spatial Distribution. J Low Temp Phys 183, 300–306 (2016).

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  • Magnetization measurement