Processing of PZT piezoelectric thick films on silicon for microelectromechancial systems

Thick-film printed lead zirconate titanate (PZT) structures can be combined with micromachined silicon structures and offer relatively large actuation forces compared to alternative techniques. This paper describes the initia l investigation into the compatibility issues of micromachining silicon waf ers with PZT layers printed on the surface. In assesses the effect of many standard photolithography and micromachining upon the printed PZT layer. In particular the adhesion of the printed layer to the substrate and its inte rnal structure have been studied after exposure to each process. Standard p hotolithography using positive resists has been found to destroy the adhesi on of the platinum electrode and an alternative masking technique using a t hick-film printed dielectric polymer has been developed. Aluminium top elec trodes have been fabricated using this masking technique combined with ion beam milling. Finally many standard micromachining etching processes have b een carried out on a range of silicon substrates incorporating platinum ele ctrode/thick film PZT structures. Wet silicon and silicon dioxide etches we re found to be unsuitable since they also attacked the adhesion of the bott om electrode. Plasma etching processes appear to be well suited for the com bination of materials since there is a wide range of etches available that do not affect the PZT. These can therefore be used for the micromachining o f the silicon substrate after thick-film processing greatly expanding the r ange of applications suited to this combination of technologies.