Analysis of thick film thermistor geometries

A new NTC thick film paste called 3K3-95/2 was composed of submicron powder (a mixture of Mn, Co and Fe oxides), 4% Bi/sub 2/O/sub 3/ and an organic vehicle. The paste was screen printed on an alumina substrata and sintered in a thick film conveyor furnace at temperatures in the range 650 to 1000 /spl deg/C. Thick film thermistor layers were characterized by X-ray data, optical microscopy and SEM. Electrical measurements were performed on the samples after printing Ag epoxy electrodes on the top of the NTC layers. Then, new test NTC thick film matrices with different planar thermistor geometries were constructed and realized: "sandwich", "multilayer", "segmented" and "interdigitated" geometries. Their resistivity varied as a function of layer thickness, electrode size and shape in the range of 10 /spl Omega/ to 100 M/spl Omega/. The electrical resistivity of planar thermistors was measured in the climate chamber in the range -30/spl deg/C to 120/spl deg/C, when the thermistor temperature parameters B and Tc were obtained (B=4200 K, Tmax=130/spl deg/C). The main advantages of planar thick film thermistor geometries over bulk types are faster temperature response and custom design possibility for sensor applications.