Design and Fabrication of Indium Tin Oxide Based Thin Film Piezoresistive Pressure Sensor

The design and development of Indium Tin Oxide (ITO) thin film based piezoresistive pressure sensor is presented in this paper. ITO (90:10) nanoparticles were synthesized by green combustion method using indium and tin as precursors and, carica papaya seed extract as fuel. ITO (90:10) thin film piezoresistors were deposited using synthesized nanoparticles on AlN coated circular steel (SS 304) diaphragm using E-beam evaporation technique. Diaphragm models of different thickness (0.75, 1 and 1.25 mm) were created using ANSYS finite element analysis in order to determine the maximum stress and deflection region for applied pressure of 1 to 10 bar. ANSYS results exhibited that maximum stress and deflection occurred at the center and circumference of diaphragm. ITO thin film piezoresistors were deposited at these regions using mechanical mask. TiW metal contact was established to these ITO thin film piezoresistors using DC sputtering method. ITO thin film piezoresistive pressure sensor with TiW contact connected in Wheatstone full bridge configuration was calibrated and tested for 50 pressure cycles by applying 2 V DC supply. Sensitivity (S) of the developed ITO thin film pressure sensor was obtained as 0.686, 0.566 and 0.495 mV/bar for diaphragm thickness of 0.75, 1, and 1.25 mm pressure sensors respectively. The non-linearity (NLi) in the output response of the pressure sensors was found to be 9.14, 9.82 and 11.27% for diaphragm thickness of 0.75, 1, and 1.25 mm respectively. Hysteresis errors were found to be 0.0344, 0.0525 and 0.054 for diaphragm thickness of 0.75, 1, and 1.25 mm respectively.