Stress and Deformation of Pzt Thin Film on Silicon Wafer Due to Thermal Expansion

Abstract

AbstractStress and deformation of PZT thin films deposited on silicon wafers due to thermal expansion during the annealing process are modeled using a 3-D shell element of ANSYS. Two different designs of PZT thin films on the wafer are modeled. The first design is a PZT/Pt/Ti/silicon dioxide/silicon wafer, which is used for making acoustic emission sensors. The second design is a PZT/Pt/Ti/silicon dioxide/silicon nitride/silicon dioxide/silicon wafer, commonly used in fabrication of cantilever beams. For the design without the silicon nitride layer, the thermal stress of the PZT film is 298MPa, Pt 1280MPa, Ti 647MPa, the silicon dioxide layer is 228MPa, and the silicon wafer is 0.41–1.67MPa. For the design with silicon nitride, the thermal stresses are: PZT 301MPa, Pt 1280MPa, Ti 651MPa, silicon dioxide 226MPa, silicon nitride 416MPa, silicon dioxide 226MPa, and silicon wafer 1.05–4.23MPa. The residual stress of the PZT film is measured at 200–25OMPa for the design without silicon nitride, and 336MPa for the design with silicon nitride. Comparisons of the thermal stress with the tensile or proof stress of material for each layer indicate that thermal stress of the PZT film is slightly greater than its bulk tensile stress, that of Pt film is five times greater than its bulk tensile stress, and that of Ti film is approximately equal to its bulk tensile stress. The thermal stresses of silicon dioxide, silicon nitride, and silicon wafer layers are far smaller than their proof stresses.