In cooperation with SenseAir AB the research group in Detector and Photonics have been investigating possibilities to develop a thermal detector, which could be produced at a low cost and with a maintained functionality. In this process we have investigating the use of both bolometer and thermopiles. Both types have been based on a closed polymer membrane.
This membrane has low thermal conductivity, which is an advantage for the sensitivity. Additionally the membrane material is applied using rather simple processing methods. A key feature for the detector sensitivity is the infrared absorber, which is added to the detector in order to increase the membrane heating. The absorber should have high absorption efficiency and should contribute to the total thermal conductance as little as possible.
Investigation of the absorber layer
By integrating the IR absorber in the membrane of the detector would contribute to the total thermal conductance minimally. Using an absorption layer with high absorption in the wavelength region of interest would be an advantage. The use of an absorption layer based on destructive interference has been simulated and measured. This structure uses the membrane itself as a part of the absorption structure. The work of integrating such structure in the detector membrane has started and will continue during the continuation of the project.
Fabricated polymer membrane based thermopile (no absorber).
Measurement and Simulation of IR absorption in interference based absorber.
A second part of the project looks into the possibility of developing a bolometer using Lead Selenide (PbSe)as resistance material. PbSe is a semiconductor material which has sensitivity in the Mid IR region. Using a material which is direct sensitive would eliminate the need for both membrane and infrared absorber. A pre-study on deposition of Lead Selenide has started and will be continued.