Full Authority Digital Electronic Control (FADEC) systems as used for the majority of engines and gas turbines require temperature and pressure sensors in high temperature environment.

Further engine control incorporating torque, speed, oil & fuel monitoring as well as, diagnostics and monitoring, are achieved using physical measurement sensors such as: tachometer, position, proximity, angular, level switch, force and flow torque, a number of which can be based on micro-magnetometers (exploiting GMR or Hall effect). It is indeed well-known and documented that the engine control application will be the main area to benefit most from MNT/MEMS. In addition to pressure sensors (see next section), two other important study cases have attracted our attention.

1. Flame detection and spectroscopy: A typical long-documented application concerns the control of combustion in engines by either simple flame indicators [Cusack94, Palmour94, Brown96] or more complex light spectrum sensors [Sims96]. A number of implementations with diverse photodiodes (SiC, GaP) and opamps (SiC, SOI, bulk Si) issued from various technologies have been presented over the years and maximum temperatures in excess of 200°C have been demonstrated. A major difficulty is to maintain the opamp performance over the temperature range, major limitations deriving from the hybrid implementation of external resistors [Cusack94] or the cooling of bulk Si opamps [Brown96]. SOI opamps thus appear as the best candidates for their high performances, while maintaining much lower power supply and input offset especially when compared to wide bandgap implementations.

2. Gas sensing: Applications of interest for gas sensing in aerospace systems include fuel leak, fire detection and emission monitoring. Sensors to measure hydrogen, oxygen, nitrogen oxides, carbon oxides and hydrocarbons should be combined in adequate miniaturized arrays. The transducing layers are based on metals or metal oxides which must be heated to precise and uniform temperatures to absorb specific gas species. Isolation of the sensing area from the nearby electronics located over the bulk substrate then allows, firstly, to limit the electrical power required for heating, and secondly to maintain the read-out circuitry at a lower temperature than that required by the sensor optimal operation. Temperatures of 400°C are commonly reported for the sensors while engine ambient temperature can be up to 300-340°C.