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_x/(100)Si. An NTC film of Mn_1.5CoNi_0.5O₄ with 0.5 μm thickness was deposited on the SiO_x layer (1.2 μm) by PLD (pulsed laser deposition) and annealed at 600-800°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°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 μm. Sensors with a thin sensing membrane show good detection characteristics.