Igniters and temperature sensors for a micro-scale combustion system

This paper presents the development of micro-fabricated “on-chip” polysilicon igniters and temperature sensors for the combustion system of a micro-gas turbine engine. We have reported the design and fabrication results of a novel through-wafer interconnect scheme that could greatly facilitate electrical contacts in multi-level MEMS devices by allowing direct electrical access to the backside of a wafer. This paper presents the results of a further effort that uses these interconnects to make electrical contacts to a thin-film polysilicon resistor so as to evaluate its ignition capability and its use as a wall temperature sensor for the micro-gas turbine engine. An application of the through-wafer interconnects to a concept demonstration of thin-film polysilicon resistive igniters for the micro-engine showed that it was possible to initiate combustion and locally raise the temperature of the igniter to 900 °C so long as the chip is thermally isolated. The results were found to be in good agreement with the predictions of an FEM thermal model. The possibility of using the resistors as temperature sensors is also examined. The non-linear variation of polysilicon resistivity with annealing temperatures due to complex effects resulting from dopant atom segregation, secondary grain growth and crystallographic relaxation reduced the operating range of the sensors to 450 °C.