Flexing piezoelectric membranes can be used to convert mechanical energy to electrical energy.The overall deflection of individual membranes is impacted by the residual stress in the system.Membranes comprised of silicon dioxide,Ti/Pt,lead-zirconate-titanate (PZT),and TiW/Au layers deposited on a micromachined boron doped silicon wafer were examined for both morphology and residual stress.By characterizing the membrane residual stress induced during processing with x-ray diffraction,wafer curvature,and bulge testing and identifying methods to reduce stress,the membrane performance and reliability can be optimized.For Zr:Ti ratios of 52:48,the residual stress in the PZT was 350 MPa tensile,with an overall effective stress in the composite membrane of 150MPa.A reduction of stress was accomplished by changing the PZT chemistry to 40:60 Zr:Ti in the PZT to obtain a stress in the PZT of 160 MPa tensile and an overall effective membrane stress of 100 MPa.The crystallization of the 52:48 PZT film at 700 degC causes a 28% reduction in the thickness of the film.
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