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

Here, the room temperature piezospectroscopic response of highly-fluorescent, similar to 330nm-thick pulsed laser deposited crystalline ruby (0.05wt.% Cr3+ doped alpha-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 1.9GPa of compressive biaxial stress for the phase-pure (001)-oriented ruby films produced here had the same piezospectroscopic Pi 11 and Pi 22 tensor coefficient values as bulk ruby over its previously calibrated 0-0.9GPa 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.