Thermal and mechanical analysis of a microreactor for high temperature catalytic gas phase reactions

The results are described of a study into the thermal and thermo-mech. behavior of a high temp. micro gas reactor for investigation of the intrinsic reaction kinetics of rhodium-catalyzed direct catalytic partial oxidn. (CPO) of methane into synthesis gas. The chip comprises a flow channel etched in silicon, capped with a thin composite membrane of heavily boron-doped silicon (p++-Si) and low stress silicon-rich nitride (SiRN), on which thin film heaters and sensors are located. The results of anal. and numerical models, which are verified with exptl. results, can be used as general guidelines for the design of membrane-based microreactors. A membrane compn. of 850 nm p++-Si and 150 nm SiRN result in time consts. of 1 ms for heating up as well as cooling down, which enables the required fast control of the exothermic reaction. Thermo-mech. analyses demonstrated that this membrane is mech. stable for temps. up to at least 700 Deg. Although the shape of the heaters - meander or sinusoidal - does not affect the mech. stress profiles significantly, a decrease in heater width compared to the membrane width results in a drastically improved thermal efficiency of the microreactor. Furthermore, thermal considerations showed that exact temp. distribution in the composite membrane is mainly detd. by the heater width in combination with the thickness of the heavily boron-doped silicon part of the membrane and its (temp.-dependent) thermal con