Print Email Facebook Twitter Wafer-level direct bonding of optimized superconducting NbN for 3D chip integration Title Wafer-level direct bonding of optimized superconducting NbN for 3D chip integration Author Li, Ye (Student TU Delft) Mirza Gheytaghi, Amir (TU Delft Electronic Components, Technology and Materials) Trifunovic, M. (TU Delft QID/Ishihara Lab) Xu, Yuanxing (Student TU Delft) Zhang, Kouchi (TU Delft Electronic Components, Technology and Materials) Ishihara, R. (TU Delft QID/Ishihara Lab; TU Delft Quantum Circuit Architectures and Technology; Kavli institute of nanoscience Delft) Date 2021 Abstract 3D integration has well-developed for traditional CMOS technology operating at room temperature, but few studies have been performed for cryogenic applications such as quantum computers. In this paper, a wafer-to-wafer bonding of superconductive joints based on niobium nitride (NbN) is performed to demonstrate the possibility of 3D integration of superconducting chips. The NbN thin films are deposited by magnetron sputtering. Its high critical temperature (15.2 K) is achieved by optimizing the sputtering recipe in terms of N2 flow rate and discharge voltage. Wafer-level bumping is bonded by the thermo-compression method. The sheet resistance of the thin film and the contact resistance of the joints are measured by the Greek-cross (4-point Kelvin method) and daisy chain structures at cryogenic temperature, respectively. Direct-bonding wafers with NbN superconductive joints avoid using adhesive layers and the bonding interface could still present superconducting electrical connections in a cryogenic environment above 4 K, which will allow us to use a smaller and high-cooling power cryostat. The contribution of this work could lead to the fabrication of multi-layered superconducting chip that operates beneficially in cryogenic temperature, which is essential in building scalable quantum processors. Subject NbNSputteringSuperconductivityThermo-compressionWafer bonding To reference this document use: http://resolver.tudelft.nl/uuid:8148382c-86a9-43b3-88bd-2c2355915778 DOI https://doi.org/10.1016/j.physc.2021.1353823 ISSN 0921-4534 Source Physica C: Superconductivity and its Applications, 582 Part of collection Institutional Repository Document type journal article Rights © 2021 Ye Li, Amir Mirza Gheytaghi, M. Trifunovic, Yuanxing Xu, Kouchi Zhang, R. Ishihara Files PDF 1_s2.0_S092145342100006X_main.pdf 5.48 MB Close viewer /islandora/object/uuid:8148382c-86a9-43b3-88bd-2c2355915778/datastream/OBJ/view