Processing of sol-gel derived PZT coatings on non-planar substrates

Sol-gel derived lead zirconate titanate (PZT) coatings were prepared on flat substrates and substrates with elevated surface features similar to those found in some microelectromechanical devices. Crystalline PZT coatings with thicknesses ranging from 0.058 to 0.34 μm were fabricated on substrates with features of height 0.13-1 μm (45° rise). Coatings were prepared by spin coating alkoxide solution, drying at 200°C, and then heating at 400°C and 700°C. Thermogravimetric analysis, Fourier transform infrared spectroscopy and x-ray diffraction were used to characterize structural evolution of PZT coatings on flat substrates. For substrates with surface features, the distribution of PZT after spin coating depended on feature height and spinning rate. The thickness of the coating on top of the step was less than that on the surrounding substrate surface; distribution was particularly non-uniform for features with smaller lateral dimensions and for coatings that were thin with respect to the feature height. Coatings on substrates with surface features had a greater tendency to crack and delaminate, particularly after the high temperature (700°C) heating. Cracking was more severe when the ratio of coating thickness to step height was low (<0.35). To best accommodate surface features, multilayer deposition was used to build up the coating thickness prior to the higher temperature processing steps.