Ferroelectric Properties and Fatigue Characteristics of Bi₄Ti₃O₁₂ Thin Films by Sol-Gel Processing

Abstract

Stoichiometric Bi 4 Ti 3 O 12 thin films were prepared by sol-gel processing. This paper discusses the synthesis of polymerizable solutions containing Bi and Ti, ferroelectric properties and fatigue characteristics of the resulting Bi 4 Ti 3 O 12 thin films. The complex alkoxide was prepared by allowing Bi acetate to react with Ti alkoxides. Bismuth acetate and titanium methoxyethoxide, the solvents 2-methoxyethanol and glacial acetic acid were selected based on their successful use in a number of related systems. Thin films of Bi 4 Ti 3 O 12 were obtained onto platinized Si substrates by spin casting, followed by heat treated at 700° C. The value of the dielectric constant and loss at 400 Hz, 100 mVrms, 25° C of this virgin films were 132 and 0.8%, respectively. This thin films with single phase layerd perovskite-like structure had very good D-E hysteresis characteristics. The remnant polarization, P r , and coercive field, E c , of this virgin films were 5.5 µ C/cm 2 and 6.2 kV/cm, respectively. The remnant polarization of this thin films, P r + , P r - , and 2 P r , were nearly constant up to 10 8 cycles. At 4×10 8 cycles, the decay in remnant polarization, P r + , P r - , and 2 P r , was observed to be about 35% of the initial values, respectively. The coercive field was drastically increased after 10 8 cycles. The D-E hysteresis loop after 10 8 cycles was not completely saturated. After 10 8 cycles, leakage current was typically increased. We considered that the fatigue characteristics observed in our study are resulted from increasing of leakage current.