GROWTH AND PROPERTIES OF EPITAXIAL FILMS OF FERROELECTRIC BISMUTH TITANATE

摘要

Earlier phases of this study demonstrated the feasibility of growing epitaxial films of Bi4Ti3O12 by rf sputtering from ceramic targets containing excess Bi2O3. They were unsuitable for device exploitation of the unusual electro-optic display properties of this material because of their twinned, multidomain character. During the present phase, clamping effects exerted by the MgO substrate were shown to prevent electrical conversion to the single domain state. Other substrates were investigated, TiO2 and sapphire giving the (001) orientation desired for the differential retardation display mode, and MgAl2O4 giving the (010) orientation required for the extinction mode. The latter is obtained untwinned, a result attributed to the thermal expansion properties of the system, which, however, also lead to cracking and peeling due to stresses along the c axis. The peeling problem was alleviated by a novel stress compensation growth technique. The films on MgAl2O4, showing minimal substrate clamping effects, were converted by electrical poling to the single domain state. The electro-optic switching properties were measured and found to be superior to those of any other film thus far produced (including detached flakes). A bar display structure incorporating and interdigitated electrode configuration was fabricated, tested, and shown to exhibit contrast ratios better than 7 to 1. (Author)