The investigation of key processing parameters in fabrication of Pb(Zr _x Ti_1-x )O₃ thick films for MEMS applications

It has always been a big challenge to deposit dense and crack-free Pb(Zr _x Ti_1-x )O₃ (PZT) thick films through Chemical Solution Deposition (CSD). In this study, a sol with higher concentration (0.6 M) was spun onto a platinised silicon substrate. The single layer thickness of a dense, crack-free film with several tenths of nanometres up to 350 nm could be obtained. It was found that the key factor in obtaining thick crack-free films was to choose an appropriate heating profile. In this study, the deflection of a single layer at various stages of heating was analysed through the measurement of the wafer curvature using the Dektak profilometer. As a result three characteristic changes of deflection were found, happening at 300, 450 and 500 °C. These obvious changes in wafer deflection closely relate to the transformations of sol-to-gel, gel-to-amorphous solid and amorphous solid-to-solid crystals. Furthermore, using these temperatures to thermally treat each single layer, it was possible to obtain thick crack-free films by repeatedly spin coating. The dielectric and piezoelectric properties, such as d_33,f and e_31,f, of the films with different thicknesses and orientations were measured and compared.