Failure Strains in Micromachined Piezoelectric Membranes

The strain at failure was investigated for micromachined lead zirconate titinate (PZT) piezoelectric membranes. The effect of microcracking in the PZT films was overshadowed by the support layers present in the devices. Bare Si membranes achieved the highest strain at failure, 0.49% with the pressure applied to the back side of the membranes compared to Si/SiO(2) and composite PZT membrane structures. Variation in the volume of PZT that was strained and the side length of the composite membranes did not decrease the strain at failure. In addition, the materials utilised in the composite structure for the bottom electrode material and PZT chemistry were investigated and the strain at failure levels was effectively the same for each material system. Composite structures with significantly different levels of effective residual stress failed at applied strains of up to 0.2%. This paper details each of the tests that were performed and the results obtained.