Public defence: Hexin Xia

Hexin Xia will defend her PhD degree in Applied Micro and Nano Technology. The dissertation explores hermetic wafer-level packaging for infrared sensors to ensure long-term reliable performance.

19 Feb

Practical information

  • Date: 19 February 2026
  • Time: 10.15 - 15.00
  • Location: Vestfold, Room A1-36 Horten
  • Download calendar file

    • Link to digital participation.

    Programme

    10:15 Trial lecture: Flexible Low‑Temperature Wafer‑Level Bonding for MEMS

    12:15 Public defence: Hermetic Wafer-level Bonding for Uncooled Microbolometer Focal Plane Arrays

    Assessment committee

    • First opponent: Professor Changqing Liu, Loughborough University
    • Second opponent: Dr. Thi Thuy Luu, engineering manager, GE HealthCare
    • Administrator: Associate Professor Pai Lu, University of South-Eastern Norway

    Supervisors

    • Principal supervisor: Professor Knut Eilif Aasmundtveit, University of South-Eastern Norway
    • Co-supervisor: Professor Per Øhlckers, University of South-Eastern Norway
    • Co-supervisor: Associate Professor Hoang Vu Nguyen, University of South-Eastern Norway
    • Co-supervisor: Associate Professor Avisek Roy, University of South-Eastern Norway

    Host of the public defence: Head of Department of Microsystems, Marius Tannum, University of South-Eastern Norway.

Any questions?

Hexin Xia is defending her thesis for the degree philosophiae doctor (PhD) at the University of South-Eastern Norway.Doktorgradsstudent

The doctoral work has been carried out at the Faculty of Technology, Natural Sciences and Maritime Sciences.

You are invited to follow the trial lecture and the public defence.

Summary

Hexin Xia holds a bachelor’s degree in electronic information engineering from Xi’an University of Technology, China, and a master’s degree in Micro- and Nano Systems Technology from USN. She started her PhD at USN in 2019, focusing on advanced packaging technologies for infrared sensors.

Microbolometers are the core detectors in commercial uncooled infrared cameras and must operate in a high-vacuum environment to function properly. They are typically arranged in focal plane arrays and enclosed within sealed packages. As infrared camera resolution improves, sensor arrays and package sizes increase, creating challenges in reducing packaging cost while maintaining high production volume. At the same time, preserving a stable vacuum in larger packages over long periods has become a major technical challenge.

This doctoral research demonstrates that wafer-level packaging using a copper–tin solid–liquid interdiffusion bonding technique can reduce manufacturing cost, improve scalability, and provide robust vacuum sealing. Packages fabricated using this approach, maintained vacuum under ambient conditions for more than 13 months and showed good resistance to humidity exposure. The results also reveal that for large microbolometer packages, small fabrication defects and sealing-frame non-uniformities can lead to vacuum degradation and reduced sensor performance.

By combining simulation and experimental studies, this work identifies how packaging design, process flow, and bonding conditions influence vacuum stability. The findings provide practical guidelines for improving manufacturing yield and long-term reliability.

In addition, this research explores a simulation-based approach for in-situ vacuum monitoring by adapting the microbolometer structure to function as a miniature vacuum sensor. This concept enables tracking vacuum changes over time and supports better lifetime prediction.

Overall, this work contributes to more reliable and scalable infrared sensor technology for applications requiring long-term vacuum sealing.