Development of lead-based electro-optic monolayer and multilayer systems for optical applications
Date of Issue2013
School of Materials Science and Engineering
Lead-based ferroelectric films exhibit a combination of dielectric, piezoelectric, pyroelectric and electro-optic (EO) properties that make them attractive for a variety of optoelectronic and electro-optic applications. Among these materials, Pb(Zr1-x,Tix)O3 (PZT), (Pb1-x,Lax)(Zry,Tiz)O3 (PLZT), and (1-x) Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), are gaining increasing importance in the development of integrated optic and EO devices due to their high transparency and excellent linear or quadratic EO effects. In the present work, three different EO multilayer systems based on PZT, PLZT, and PMN-PT have been designed. Enhancements on dielectric and EO properties in these systems were observed and compared with the corresponding monolayer films. Modified surface charge method was employed to optimize the electrode parameter in the transverse modulators. EO devices based on these materials were also introduced. Using (Pb0.86,La0.14)TiO3 (PLT) as the seeding layer was found to be able to significantly increase the critical thickness of a single PZT layer and promote the crystallization of perovskite phase. The influence of crystal phase, transparent substrates, and lead defect on the microstructure, optical, and EO properties in PZT films have been systematically discussed. PZT films were observed to linear EO behavior and a maximum EO coefficient of 219.6 pm/V was obtained in PZT(52), a composition near morphotropic phase boundary (MPB). The EO coefficient of lead-deficient PZT film annealed by rapid thermal processing (RTP) is also measured. Furthermore, the largest linear EO coefficient of 250.2 pm/V was obtained by stacking up 20 periods in PZT(52)/PZT(65) multilayer system. This is attributed to thickness-dependent tetragonality introduced by lattice distortion in multilayer structure, thereby leading to high strains. In addition, the crystallization, dielectric, optical and EO properties of PLZT(9/65/35) monolayer film were studied. Quadratic EO coefficient of the film was found to be 1.61x10-16 (m/V)2. The effect of multilayer stacking period on the microstructure, transparency, dielectric and EO properties of other material system, such as PZT(52)/PLZT(9/65/35) multilayer systems, were also studied. PZT/PLZT multilayer was noted to exhibit linear EO behaviors, and the largest linear electro-optic (EO) coefficient of 227.5 pm/V was observed again at the stacking periods of 20. The earlier work has shown that multilayer systems enhance EO properties, however, it is noted that the EO coefficient behaves linearly in both PZT and PZT/PLZT multilayer systems. As a result, we turned into the growth of quadratic PLZT/PMN-PT multilayer systems. The as-deposited PMN-PT monolayer grown on PLT-coated glass shown characterization of typical relaxor and normal ferroelectrics, and possessed a high transparency of 75% and quadratic EO coefficient of 3.76x10-17 (m/v)2. The pure-perovskite PLZT/PMN-PT multilayer films with various stacking periods were also deposited using PLT as the seeding layer. It is noted that multi-layered film exhibited quadratic EO effect, and a large quadratic EO coefficient of 2.47 x 10-16 (m/V)2 was obtained at 25 stacking periods. Based on the study above, two EO devices such as optical modulator and beam deflector, were discussed. Surface charge method was used to optimize the electrode parameters, and to study the relationship between the electrode parameters, driving voltage, and response time. The enhancement mechanism of both linear and quadratic EO effects in the multilayer systems was also discussed. The present study has shed light on the understanding of multilayer EO materials and their potential to be used in advanced optical applications.