CRITICAL PARAMETERS IN FABRICATING SOL-GEL DERIVED PZT THIN FILMS

摘要

In the last decade, Lead Zirconate Titanate Oxide (PZT) thin-film actuators have received increasing attention because of their high frequency bandwidth, large actuation strength, fast response, and small size. The thickness of PZT thin films is usually less than several microns as opposed to hundreds of microns for bulk PZT patches that are commercially available. Currently, the most promising technique to fabricate PZT thin films is sol-gel processing. Although recipes to fabricate sol-gel derived PZT films have long been available in the literature, critical parameters affecting the yield have not been identified and reported. In this paper, we present an experimental study to identify critical parameters to improve the yield of sol-gel derived PZT thin films. In our experiments, a typical specimen consists of a 3-in. silicon wafer, a Pt/Ti bottom electrode, 3 coats of PZT films with an overall thickness of 1 μm, and 64 Au/Cr top electrodes uniformly distributed over the PZT film. The resistance at each top/bottom electrode pair is measured and screened. If the resistance measurement indicates an open circuit, the film quality at the measurement spot is considered as "good." In addition, the yield is defined as the percentage of good electrodes on each fabricated wafer. Experimental results show that two parameters can significantly affect the yield. The first parameter is porosity of the Pt/Ti electrode. Experimental results show that porosity in the Pt/Ti electrode enhances the yield of sol-gel derived PZT films. The second parameter is the uniformity of Pt/Ti layer's microstructures. SEM photos and water/Pt contact angle measurements indicate that wafers annealed in the horizontal positions have more uniform microstructures and surface properties. The experimental results show that horizontal wafer positions give better yields than vertical wafer positions (e.g., wafers in a boat). Finally, the water/Pt contact angle at the Pt/Ti bottom electrode does not significantly affect the yield, if the bottom electrode is properly annealed. The contact angle, however, can affect the yield, if the bottom electrode is not properly annealed.