Measurement of electro-optic properties of ferroelectric thin films using the ultimate ellipsometer

Ferroelectric(FE) films constitute an important component of electro-optic devices; such films have been used for second harmonic generation, spatial light modulators and optical switches. FE films typically yield large values of linear and quadratic electro-optic coefficients. Most electric field induced birefringence measurements have been made with transverse electrodes, i.e. with light beam between poled electrodes. In the present study, an Ultimate Ellipsometer was used ; a HeNe laser was directed perpendicularly through FE capacitors with applied voltages and the phase change monitored. The layout of this device is discussed in details. Sol-gel derived PZT 53/47 and PLZT 28/0/100 films were prepared on conductive glass substrates. 0.5M precursor solutions based on the stoichiometric amounts of Pb acetate, La nitrate and Ti/Zr alkoxides were refluxed for 1 hour and spincoated on the substrates under clean room conditions. The films were then fired to 550C to crystallize them to single phase perovskite. Top AuPd electrodes were deposited to form an array of monolithic PZT and PLZT capacitors. The refractive indices and extinction coefficients of the films were also obtained using multiangle ellipsometry. With applied voltages, the induced birefiingences were measured, resulting in typical birefringence-voltage butterfly loops. The linear electro-optic coefficients of the films were then calculated. The linear electrooptic coefficients of PLZT 28/0/100 and PZT 53/47 were measured to be 59 and 3 15 pdV, respectively The latter value represents the highest reported for any ferroelectric film.