Design and Fabrication of an Infrared Microspectrometer using Attenuated Total Reflection

This paper presents a concept for a fully integrated spectrometer system based on Attenuated Total Reflection. Operation is in the mid-infrared spectral range (lambda = 1.8 mum-5 mum). The approach allows micromachined integration of all critical components of the system: a thermal IR source, optical filtering, the ATR element, a detector array and a signal processing chip. Two bulk-micromachined silicon dies are used. The wideband light source and detector array for analysing the spectrum are fabricated in the bottom die. Polysilicon heaters on thin oxide- nitride bridges are used as the IR emitter and polysilicon thermocouples on thin membranes as IR detectors. The interaction between the sample and the evanescent field of the internally reflected IR beam takes place at the top die, which contains the bulk silicon ATR element Other optical components, required for defining the path of the IR light beam, like gratings, mirrors, transmission filters, Fresnel lenses and slits, can be fabricated on the top die also.