Fast transient temperature operating micromachined emitter for mid-infrared for optical gas sensing systems

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 spider type hotplate concepts were studied in order to find a design with excellent mechanical stability and high thermal decoupling. The thermal emitters are fabricated using silicon on insulator (SOI) technology and KOH-etching. The emitters are heated with Pt-meanders. For temperature determination an additional Pt-structure is deposited onto the hotplates. 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.