Thermal and mechanical design optimisation of a micro machined mid-infrared emitter for optical gas sensing systems

The numerical pre-design of a novel micro-machined thermal infrared emitter, using a spider type hotplate concept is presented. The spider concept introduced allows the fast transient operation of the emitter and thus a direct modulation of the radiation without additional mechanical tools like choppers. The thermal radiation source is excited by a pulsed electrical voltage and is thermally separated from the carrier substrate. Miniaturisation, cost reduction and economy of scale can be realized by applying the silicon on insulator (SOI) technology in combination with KOH-etching. In order to reach the maximum performance in the operation-relevant wavelength range over 8 mum, a coupled field simulation of the electro-thermal heating and the transient thermal behaviour considering thermal conduction, convection and radiation was performed. With respect to the required long term reliability of the emitter, the mechanical stability of the component was investigated and improved by additional structure-mechanical modelling and calculations of the electric current density of the heating structure to avoid electro migration effects. The advantageous reliability properties of the new designs were validated by experimental tests performed on prototype samples.