Wafer mapping of the transverse piezoelectric coefficient, e _31,f, using the wafer flexure technique with sputter deposited Pt strain gauges

Measurement of the transverse piezoelectric coefficient (e _31,f) in thin films is crucial for the development of microfabricated sensors, actuators, and transducers. Here, a method is described such that lithographically defined strain gauges enable non-destructive, position-dependent characterization of e _31,f in conjunction with the wafer flexure technique. Measurements of 100 nm thick Pt gauges deposited on 1 μm thick PbZr _0.52Ti _0.48O ₃ thin films yield gauge factors of 6.24, with a gauge-to-gauge variation that is 5% of this value. The system allows for simultaneous measurement of the charge and strain, improving the overall accuracy of measurement. The small footprint of the combined strain gauge array/electrode pattern used for determining e _31,f, allows for a non-destructive mapping of the transverse piezoelectric coefficient across large-area wafers. Due to the clamping configuration used in wafer flexure experiments, e _31,f values can accurately be obtained within the central ∼2/3 of a full wafer. Measurements performed on a 1.3 μm thick randomly oriented polycrystalline PbZr _0.52Ti _0.48O ₃ film made deposited on a 4 in. platinized silicon wafer by the sol-gel process show a high degree of uniformity, with e _31,f of -6.37 ± 0.60 C/m ² for points measured within r = 3 cm.