The pressure sensing properties of SnO₂, TiO₂, and TiO₂/ZnO thick film sensors are investigated.

To form the dielectric layers, the metal oxides powders were respectively mixed with isopropanol and wet ball milled for 24 hours. The mixtures were dried at 120 °C to evaporate the alcohol. The powders were then placed under 2 tons of pressure to form pellets, which were fired at 1250 °C (rate of 5 °C per min) in a vacuum of 6 x 10^-3 mbar for five hours, followed by cooling (rate of 3 °C per min). After firing, the powders were mixed with 7 wt.% of polyvinyl butyral (binder) and suitable amount of Ethylenglycolmonobutylether (solvent) to form the pastes. These were screen-printed over the Ag electrodes on alumina substrates to form SnO₂, TiO₂, and TiO₂/ZnO capacitor pressure sensors accordingly.

The capacitance of the sensors with interdigitated electrodes is largely dependant on the number of fingers (N), their length (L) and width (W), in addition to the gap between electrodes (G), spatial wavelength (λ =2(W+G)) and the metallization ratio (η = 2W/λ) [1]. Any changes in capacitance are due to deformation of the dielectric layer, deposited over the electrodes. The overall capacitance of the device is generally determined by using a conformal mapping technique [2].

The evaluation of pressure sensing properties of these sensors was performed using a HP 4192A Impedance Analyser, which recorded the changes in the values of the capacitances under different mechanical stresses. At the applied load of 5 kPa, the response times of 2.5 s, 5.6 s and 4 s were recorded for SnO₂, TiO₂, and TiO₂/ZnO sensors respectively.

In addition to instant response times, these pressure sensors have the advantage of being reusable, as their electrical properties were restored to the original value after annealing for 2 hours at 80 °C.

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