FERROELECTRIC PROPERTIES AND FATIGUE OF PBZR0.51TI0.49O3 THIN-FILMS OF VARYING THICKNESS - BLOCKING LAYER MODEL

Ferroelectric capacitors having Pt bottom and top electrodes and a ferroelectric film of composition PbZr0.51Ti0.49O3 (PZT) were fabricated and investigated. The PZT films of thicknesses varying from 0. 12 to 0.69 mum were prepared by organometallic chemical-vapor deposition. Annealed capacitors were investigated by capacitance, hysteresis, and pulse switching measurements. It is found that the thickness dependence of the reciprocal capacitance, the coercive voltage, and the polarization measured by pulse switching can all be explained by a blocking layer model, in which a dielectric layer of thickness d(bl) and relative permittivity epsilon(bl) is situated between the PZT film and an electrode. It is shown that (i) the coercive field is independent of thickness having a value of 2.4 V/mum; (ii) the ratio epsilon(bl)/d(bl) is in the range 20-28 nm-1; (iii) the voltage across the blocking layer is proportional to the polarization, V(bl)-cP, where c=4.1-0.5 V m2/C; and (iv) the polarization depends on the electric field in the PZT layer, independent of thickness. Pulse switching endurance measurements showed that in the saturation range the fatigue for these ferroelectric capacitors is determined by the pulse voltage and is independent of the thickness.