Strontium Barium Niobate Thin Films for Dielectric and Electro-Optic Applications

Abstract

The existence of strontium barium niobate crystals (SrxBa1-xNb2O6, noted SBN:100x) was first reported in 1960 (Francombe, 1960) and first large SBN single crystals were grown by Ballman and Brown over the range 0.25<x<0.75 (Ballman & Brown, 1966). In 1970, the Bell Telephone Laboratories had published successive thorough investigations of the optical, electrical, and structural properties of SBN crystals. The high values of the electro-optic and pyroelectric coefficients oriented further work mainly towards holographic and pyroelectric applications. The development of SBN films started at the USSR Academy of Science in Novosibirsk (Baginsky et al., 1978) using a RF sputtering technique. Different deposition techniques have been then investigated: mainly sol-gel process, metal-organic chemical vapor deposition (MOCVD), and pulsed laser deposition (PLD). Thin SBN films are particularly attractive for their potential use as low voltage electro-optic (e-o) waveguides. Electro-optic light modulation is a key function in light-wave technologies, mostly realized by exploiting the linear e-o Pockels effect in ferroelectric bulk crystals like lithium niobate (LN) for primary example. Optimizing the performance of an eo modulator involves minimizing the half-wave voltage-length product (Vπ L) and the drive power (P). A considerable decrease in the required Vπ L and P values, by three orders of magnitude, is expected from the replacement of bulk crystals by thin film waveguides about 1μm thick. Beside LN and SBN, the ferroelectric materials which have been considered in the literature in view of preparing electro-optic thin films are mainly BaTiO3 (BT), (Ba,Sr)TiO3 (BST), and (Pb,La)(Zr,Ti)O3 (PLZT). The implementation of Pockels e-o effect in thin film waveguides also opens up the path to the realization of electrically-tunable photonic crystal (PC) devices. Through the engineering of photonic band gaps, PC structures enable developing the functionality and reducing radically the size of optical devices. Theoretically position and shape of a photonic band gap can be electro-optically controlled. This e-o control considerably broadens the scope of PC structures potential functionality. The future deployment of photonic technology largely rests on the tunability of PC characteristics. The Pockels electro-optic effect is the expression of the dielectric non linear properties in the range of optical frequencies where ionic displacement is negligible and relative dielectric permittivity is reduced to its electronic component. The interest for dielectric non linear