Novel 3D PZT thin film structure for micromechanics

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In this work, fabrication and properties of 3-dimensional structures coated with piezoelectric Pb(Zr,Ti)O3 (PZT) thin films have been studied in order to improve the piezoelectric coupling into the third dimension. Calotte layers have been chosen as demonstration devices. The base diameters range from 40 to 120 μm, the height varies between 10 to 40 μm. A dynamic, in-situ co-sputtering process allowing for in-situ growth was applied. Micromoulds were formed by wet etching in silicon. The etchant was a HNA solution (HF, HNO3, CH3COOH) on a silicon dioxide mask. Calottes were obtained with the desired geometry and smooth surface state after few minutes etching time, and the use of chemical mechanical polishing (CMP). After deposition of the PZT membrane, deep silicon dry etching was then used to liberate the calotte layer. The dielectric constant and loss tangent of the calotte capacitors amounted to 830 and 5%, respectively (10 kHz). The fundamental resonance frequencies varied between 2.5 and 16.5 MHz, and were found to be inversely proportional to the base area of the calotte, the proportionality factor being 0.08 Hz m2.