Correlation between the wafer curvature and fluorescence of pulsed laser deposited ruby thin films stressed to ∼2 GPa

Here, the room temperature piezospectroscopic response of highly-fluorescent, ∼330 nm-thick pulsed laser deposited crystalline ruby (0.05 wt. % Cr3+ doped α-Al2O3) thin films on either (001)-oriented sapphire or (001)-oriented yttria-stabilized zirconia wafers was investigated and calibrated against biaxial film stress measurements obtained from a multibeam optical stress sensor or profilometry-determined wafer curvature measurements. The piezospectroscopic frequency shift from 0 to 1.9 GPa of compressive biaxial stress for the phase-pure (001)-oriented ruby films produced here had the same piezospectroscopic Π11 and Π22 tensor coefficient values as bulk ruby over its previously calibrated 0–0.9 GPa range. This extended calibration may be useful when using ruby to measure the amount of biaxial stress in a variety of multilayer devices and coatings.