Effect of Annealing on the Sol-Gel Derived SrBi4Ti4O15 Thin Films for Piezoelectric Pressure Sensors

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This paper reports the effect of annealing on fabrication of Strontium Bismuth Titanate SrBi4Ti4O15 (SBT) thin films for piezoelectric pressure sensors. The SBT films and capacitance devices with structure of Al/TiO2/SBT/TiO2/SiO2/Si were fabricated using sol-gel technique. The microstructure of SBT thin films have been systematically studied in as-prepared (un- annealed) condition as well as after annealing at 400, 500, 600 and 700 degC. The general trend seems to indicate that annealed temperature show better piezoelectric properties. X-ray diffraction patterns reveal changes of crystalline structure after annealing at 600 degC temperature. Another important parameter is dielectric constant, which is found toward higher value within annealing temperature. For the sensor device measurement, the SBT thin film pressure sensors were tested by pneumatic loading method at pressure range between 0 to 450 kPa. It found that the sensors sensitive to the applied pressure and the response recovered back when the pressure were removed. The 600 degC annealed pressure sensor demonstrates better repeatability compared to the others. The results indicated that the sensor performance was affected by the structure of the film. A crystalline structure gives an optimum response towards pneumatic pressure. However, the too high of annealing temperature may cause a catastrophic failure of the pressure sensor response, hence the existing of crack and inter diffusion between top and bottom electrode. The correlation between annealing process with structure of SBT pressure sensors and the piezoelectric properties will be discussed.