Fast transient temperature operating micromachined emitter for mid-infrared optical gas sensing systems: design, fabrication, characterization and optimization

Abstract

A novel micromachined thermal emitter for fast transient temperature operation is presented. Compared to most commercial available thermal emitters, the one here presented is able to operate in a pulsed mode. This allows the use of lock-in techniques or pyrodetectors in the data acquisition without the use of an optical chopper for light modulation. Therefore, these types of thermal emitters are very important for small filter photometers. Several hot-plate suspension concepts were studied in order to find a design with excellent mechanical stability and high thermal decoupling. In contrary to the classical spider suspension design, a novel approach based on a non-axis-symmetric design is presented. The thermal emitters are fabricated using silicon on insulator technology and KOH-etching. The emitters are heated with Pt-meanders. For temperature determination an additional Pt-structure is deposited onto the hot-plates. The emitters are mounted in TO-5 housings using a ceramic adhesive and gold wire bonding. The used operation temperature is 750°C. In pulsed operation it’s important to have a large modulation depth in terms of thermal radiation intensity in the needed spectral range. The maximal reachable modulation depth ranges from ambient temperature to steady state temperature. A modulation frequency of 5 Hz still allows using nearly the maximum modulation depth. A parameterized finite element model was realized and adapted to the measured data. This was the basis for the numerical optimization procedure for a new improved design.