Residual stress development in Pb(Zr,Ti)O3/ZrO2/SiO2 stacks for piezoelectric microactuators

The residual stress of multilayers in piezoelectric microelectromechanical systems structures influences their electromechanical properties and performance. This paper describes the development of residual stress in 1.6 D*mm Pb(Zr0.52,Ti0.48)O3 (PZT)/0.3 D*mm ZrO2/0.5 D*mm SiO2 stacks for microactuator applications. The residual stresses were characterized by wafer curvature or load-deflection measurements. PZT and zirconia films were deposited on 4-in. (100) silicon wafers with 0.5 D*mm thick thermally grown SiO2 by sol-gel processes. After the final film deposition, the obtained residual stress of PZT, ZrO2, and SiO2 were 100-150, 230-270, and -147 MPa, respectively. The average stress in the stack was ~80 MPa. These residual stresses are explained in terms of the thermal expansion mismatch between the layers and the substrate. Load-deflection measurements were conducted to evaluate localized residual stresses using released circular diaphragms. The load-deflection results were consistent with the average stress value from the wafer curvature measurements. It was found that more reasonable estimates of the stack stresses could be obtained when mid-point vertical deflection data below 6 D*mm were used, for diaphragms 0.8-1.375 mm in diameter.