Electrooptic and piezoelectric properties of (Pb,La)(Zr,Ti)O₃ films with various Zr/Ti ratios

A systematic investigation of the electrooptic properties of (Pb,La)(Zr,Ti)O₃ (PLZT) films was carried out. 700-nm-thick polycrystalline PLZT films with 2mol% La and various Zr/Ti ratios were formed on Pt/Ti/SiO₂/Si substrates, and their reflectance spectra were measured. Zr/Ti ratio significantly affected the surface morphology of the films, and PLZT films with what Ti/(Zr + Ti) ratios ranging from 40 to 70% showed less reflectance light loss that because of their smooth surface. The maximum resonant wavelength shift was attained at a Ti/(Zr + Ti) ratio of 40%. These results suggest that the PLZT film with a Ti/(Zr + Ti) ratio of 40% is optimum for application in optical devices such as a spatial light modulator (SLM). The piezoelectric properties of the PLZT films were also evaluated because their resonant wavelength shift was caused by changes in not only refractive index but also film thickness. The piezoelectric displacement showed a maximum Ti/(Zr + Ti) ratio of 10% and monotonically decreased with increasing Ti/(Zr + Ti) ratio in our PLZT films. The exact Pockels coefficient of the PLZT(2/60/40) film was estimated to be 104 pm/V at 600 nm by subtracting the effect of the change in film thickness from the resonant wavelength shift.