Optimization of PZT (52/48) through Improved Platinum Metallization, Use of a PbTiO3 Seed Layer, and Fine Tuning of Annealing Conditions for Applications in Multilayer Actuator MEMS Technology

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Using a systematic approach, the processing of PZT (52/48) was optimized to achieve both a high degree of {001} texture and high piezoelectric properties. Initial experiments examined the influence of Ti/Pt and TiO2/Pt thins films used as the base-electrode for chemical solution deposition PZT thin film growth. The second objective was to achieve highly {001}-textured PZT using a seed layer of PbTiO3 (PTO). A comparative study was performed between Ti/Pt and TiO2/Pt bottom electrodes. The results indicate that the use of a highly oriented TiO2 led to highly {111}-textured Pt, which in turn improved both the PTO and PZT orientations. A third objective was to determine the effects of lead excess in the starting PTO and PZT solution on the films orientations and piezoelectric properties. During the annealing of PZT (52/48), lead (Pb) is volatilized from the films leading to a non stoichiometric state which ultimately reduces the electrical properties. To remedy this issue, a percentage of Pb-excess is added to the PZT solution prior to deposition to compensate for the Pb that is lost during the thermal treatment. This study thoroughly examines the effects of the Pb-excess in the PTO seed layer with percentages between 0% and 30% and PZT (52/48) with Pb-excesses between 0% and 10%. The final objective, leveraged the texture optimization on single 500nm thick PZT thin films, to deposit high quality PZT films in multiple Pt/PZT/Pt layers for use in multilayer actuators (MLA). Efforts have been focused on developing actuators using a four 250 nm layer stack of PZT using 10% lead excess in solution. By performing x-ray diffraction (XRD) measurements between each layer, the texture within the films could be monitored during the growth process. To electrically measure the quality of the PZT multilayer stack, a series of six-sided capacitors were fabricated. In addition to capacitors, cantilever actuators were fabricated so as to measure the piezoelectric induced deformation. These measurements on MLA PZT films demonstrate high piezoelectric coefficients that are suitable for tactile radio and mm-scale robotic devices.