Public Defence: Phillip Alexander Hetland Papatzacos

Phillip Alexander Hetland Papatzacos is defending his dissertation for the degree philosophiae doctor (PhD) at the University of South-Eastern Norway.

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

Thesis: Improved packaging techniques for LWIR microbolometers

Download thesis (USN Open Archive)

You are welcome to follow the trial lecture and the public defence on campus. 

Digital participation (Zoom) 

Summary

We have developed an effective anti-reflective coating capable of surviving higher temperatures than ever before seen in the literature. In addition, microstructures with anti-reflective properties have been designed, produced and tested in collaboration with Stanford University, California. 

We have also experimented with the geometry of the sealing material around the edge of a package before it is sealed. The idea was that less of the melted material would flow to unintended areas. The result, however, that the package withstood higher forces when subjected to durability tests.

The intended application for these techniques is packaging of a new generation of thermal cameras based on microbolometers. These cameras are much cheaper and smaller than their predecessors, but require vacuum to operate. Finding a way to package these camera sensors in a cheap, scalable and efficient way is therefore critical for their implementation and paves the way for underutilized application areas such as self-driving cars and medicine.

A very promising way of encapsulating the sensor, is to use the abundant and widely used material silicon as a cap and seal it. “Solid liquid interdiffusion” using copper and tin was chosen as the sealing technique for the package, because it is air-tight, cheap, and scalable. It is a mature technique, but my work experiments with the pattern in which the copper and tin is placed and the result is a stronger bond with minimal complexity added to the process.

Silicon is transparent in the wavelength region of interest, meaning the infrared light used to measure the heat can readily pass through it. Unfortunately, a lot of the infrared light (∼30%) will reflect off the cap if it is left untreated, which results in lower camera sensitivity. This is the reason we have explored both coatings and microstructures to minimize these reflections. Because the sealing technique of solid liquid interdiffusion with copper and tinn requires heating to ∼270°C, classical anti-reflection techniques were incompatible. The work I performed at USN and Stanford, however, uses state-of-the-art technology to produce and demonstrate effective approaches to lower these reflections.