Yukihisa Okada

Role of excess Bi in SrBi2Ta2O9 thin film prepared using chemical liquid deposition and sol-gel method

We studied the role of excess Bi, added to improve ferroelectirc properties of SrBi 2 Ta 2 O 9 (SBT) thin film whose Bi-layered structure is fatigue-free characteristics for Nonvolatile memory. The lost of Bi by annealing process was not observed even after annealing at 850°C in chemical liquid deposition (mixed alkoxide solution system). In SBT films composed of fluorite and Bi-layered structure grains, Bi-layered structure grains had a higher Bi content than that in fluorite grains. Excess Bi was added to promote crystallization of fluorite to the Bi-layered structure easy. SBT film close to stoichimometric composition formed by a hydrolyzed, condensed solution (sol-gel method) had superior ferroelectric properties despite its closely stoichiometric Sr 0.9 Bi 2.1 Ta 2 O 9 composition. Closely stoichiometric Sr 0.9 Bi 2.1 Ta 2 O 9 SBT film shows no fatigue even after 3 x 10 12 switching cycles. The improved SBT formation solution that is hydrolyzed, condensed solution makes excess Bi unnecessary.

THERMO-REVERSIBLE RECORDING MEDIA

We have developed a medium using the thermosensitive recording layer, which consists of polyvinyl acetal and higher fatty acid. It has distinctive thermo-reversible characteristics, and is able to take two states, a transparent state and an opaque state, reversibly at room temperature through the difference in cooling rates after heating. Thermo-reversible mechanism of the media is responsible for miscibility and immiscibility for this blend system. After 100 cycles of printing by a thermal head and erasing by a heat roller, no deterioration of either transparent states or opaque states is observed.