Characteristic of thin-film NTC thermal sensors

The characteristics of thin-film negative temperature coefficient of resistance (NTC) thermal sensors fabricated by micromachining technology were studied as a function of the thickness of the membrane. The overall structure of the thermal sensor has the form of Au/Ti/NTC/SiO/sub x//(100)Si. An NTC film of Mn/sub 1.5/CoNi/sub 0.5/O/sub 4/ with 0.5 /spl mu/m thickness was deposited on the SiO/sub x/ layer (1.2 /spl mu/m) by PLD (pulsed laser deposition) and annealed at 600-800/spl deg/C in air for 1 hr. Au (200 nm)/Ti (100 nm) electrode was coated on the NTC film by DC sputtering. From the results of microstructure, X-ray and NTC analysis, post-annealed NTC films at 700/spl deg/C for 1 hr showed the best characteristics as an NTC thermal sensing film. In order to reduce the thermal mass and thermal time constant of sensor, the sensing element was built-up on a thin membrane with the thickness of 20-65 /spl mu/m. Sensors with a thin sensing membrane show good detection characteristics.