A wafer-level characterization method of thin film transverse piezoelectric coefficient evaluation

Accurate measurement of the piezoelectric property of thin films is critical for thin film process development and device design optimization. In this paper, we proposed a wafer-level thin film characterization method that provides a non-destructive, single-side measurement solution for evaluating and in-process monitoring the transverse piezoelectric coefficient (e31,f). The e31,f of piezoelectric films was determined by measuring the deflection of circular electrode induced by the converse piezoelectric effect, with the electrodes fabricated on top of piezoelectric thin film on a silicon substrate. The constitutive equation of the unimorph plate reveals a quadratic dependence of top electrode deflection (δ) on the radius (r), which was subsequently utilized to calculate the e31,f while considering the electrode edge effect. Determined by non-constant variations of |δ/r2| from finite element method (FEM) simulation results, the electrode edge effect leads to the specification of electrode size and substrate thickness for evaluating piezoelectric coefficient. A comprehensive FEM simulation analysis of the influence of wafer size and electrode location on the accuracy of the proposed method demonstrated its reliability for wafer-level characterization. The e31,f measurement results of single-crystal (s-PZT) and polycrystalline PZT (p-PZT) exhibit good agreement between the proposed wafer-level method and the die-level cantilever method. These results demonstrated that the proposed single-side wafer-level method provides a reliable measurement technique for e31,f characterization of piezoelectric thin film. [Display omitted] •This paper proposed a wafer-level thin film characterization method that provides a non-destructive, single-side measurement solution for evaluating and in-process monitoring the transverse piezoelectric coefficient (e31,f).•Based on the analysis of edge effect with FEM method, the specification of electrode size and substrate thickness for evaluating e31,f was provided.•A comprehensive FEM simulation analysis of the influence of wafer size and electrode location on the accuracy of the proposed method demonstrated its reliability for wafer-level characterization.•The e31,f measurement results of s-PZT and p-PZT exhibit good agreement between the proposed method and the cantilever method. The proposed wafer-level method would be a practical technique for the actual piezoelectric MEMS engineers to evaluating and monitoring e31,f of piezoelect