Design and Fabrication of on-chip Midinfrared Emitter and LVOF

Abstract

In this thesis,two essential parts of microspectrometer are designed, fabricated and measured. They are a hot wire of polysilicon with constant temperature profile that used as the IR light source, and the LVOF which is aimed at IR spectral range. In order to have the desired IR source, the hot wire should have temperature distribution as uniform as possible based on black-body emission. Thus, the thermal mechanics inside the hot wire is fully studied including heat generation, conduction, convection and radiation. The thermal energy is electrically generated by voltage and current source. While the heat loss causing non-uniformity on temperature is mainly induced by heat conduction between the hot wire body and substrate, and to surrounding air. For the first one, the geometry including the length, width and thickness, the resistivity profile of hot wire and the meander bridge at the end of hot wire body are designed. The meander bridge works as the connection and interface to substrate which to some extent determines the heat conduction through it. Moreover, it can bear tensile force induced by thermal expansion. Besides, the meander middle bridge is added to hot wire as well in some design plans for stronger mechanical stability. On the other hand, since the temperature on hot wire is significant related to air pressure due to heat conduction to surrounding air, all hot wires are designed to operate in vacuum environment. Finally, a bunch of hot wires with different geometry, resistivity and TCR are designed and fabricated. To design the LVOF aimed at IR band, the working schematics and properties of LVOF are firstly studied in depth. All factors such as reflectance, incident angle, cone angle and so on that might affect its performance which includes the most important transmittance are researched. The LVOF is also designed in different length and tilt angle. The case that the LVOF with the hot wire as IR source is paid special attention to. Eventually, the electrical property and optical performance of hot wire is measured in vacuum chamber by FLIR IR camera. So far, the hot wire that has best performance is the one comprised of array of short hot wires. The result is fully discussed and divergence between actual performance and design plan is analyzed from many aspects.