OctEval: Tunnel Junction Circuit Fabrication Technology

Planarized fabrication technology integration for superconducting electronics and magnetic memory applications

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• Microelectronic test structures
• Embedded sensors
• Tunnel junction circuit fabrication
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Contact: mbhushan@octeval.com

 Limit fabrication and yield woes by

• Integrating a planarized process using chemical-mechanical polishing for sub-micron tunnel junctions and multilayer interconnects
• Setting up a robust Nb/AlOx/Nb trilayer deposition process for superconducting circuits
• Designing compact test structures for superconducting process monitoring

Setting up a robust and repeatable fabrication process in a research or university laboratory environment, often with shared equipment and materials across several projects, is challenging. Appropriate monitors, test structures and a touch of discipline can alleviate these difficulties.

Dr. Manjul Bhushan led the first university based team that successfully demonstrated planarization using chemical-mechanical polishing (CMP) for microelectronic fabrication. She combined high quality Nb/AlOx/Nb trilayers with CMP and electron-beam lithography to fabricate low parasitic capacitance, deep-submicron Josephson junctions. These processes were subsequently used to fabricate high-speed digital devices and low noise analog detectors. She set up robust Nb/AlOx/Nb triayer processes in several laboratories in research and industrial establishments (Unisys, MIT Lincoln Laboratory, AT&T Bell Labs and SUNY at Stony Brook) in the mid 1980's through the mid 1990's. She continues to advise in this area today as these remain state-of-the-art processes.

In 2013-15, she consulted with a start-up company and helped in enabling a CMP based process for magnetic memories (MRAM). She continues to advise in the area of fabrication of tunnel junctions as these remain state-of-the-art processes.

Selected Publications:

1. Nb/AlOx/Nb trilayer process for the fabrication of submicron Josephson junctions and low noise SQUIDs
Bhushan M, Macedo EM (1991). Appl Phys Lett 58:1323-1325
2. Fabrication of high quality deep sub-micron Nb/AlOx/Nb Josephson junctions using chemical mechanical polishing
Bao Z, Bhushan M, Hans S, Lukens JE (1995). IEEE Trans Appl Supercond 5:2731-2734
3. Sub-um planarized Nb-AlOx-Nb Josephson junction process for 125 mmm wafers developed in partnership with Si technology
Ketchen MB, Pearson DJ, Kleinsasser AW, Hu C-K, Smyth M, Logan J, Stawiasz K, Baran E, Jaso M, Ross T, Petrillo K, Manny M, Basavaiah S, Brodsky S, Kaplan SB, Gallagher WJ, Bhushan M (1991). Appl Phys Lett 59:2609-2611