PZT thin film pressure sensor for on-line monitoring injection molding

In this paper, a new fabrication process for lead zirconate titanate (PbZrTiO₃, PZT) micro pressure sensor is presented. The PZT pressure sensor can be applied to on-line monitoring of the pressure in the mold´s core and cavity during the injection process. This PZT piezoelectric thin film sensor is deposited on the surface of steel wafer at 300°C by RF sputtering process and is micro fabricated directly. The composition of the steel wafer is similar to the injection mold used in most injection machines. After the sputter deposition, rapid or slow thermal annealing treatment is proceeded at 650°C. Rapid thermal annealing will attain better ferroelectric property and better perovskite crystal structure of PZT thin films. However, rapid thermal annealing can cause film cracks. This research developed multilayer PZT thin film techniques, which can reduce the effect of film cracks. The properties of the proposed PZT thin film pressure sensor are: the remnant polarization (P_r), coercive field (E_c), and relative dielectric constant (ε_s ) of the PZT films are 10.41 C/cm², 79.2 kV/cm and 1535, respectively; the piezoelectric constant d₃₃ and d₃₁ are estimated to be 129.9 pc/N and -48.03 pc/N, respectively