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 fer roelectric 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. Ann ealed capacitors were investigated by capacitance, hysteresis, and pul se switching measurements. It is found that the thickness dependence o f the reciprocal capacitance, the coercive voltage, and the polarizati on measured by pulse switching can all be explained by a blocking laye r model, in which a dielectric layer of thickness d(bl) and relative p ermittivity epsilon(bl) is situated between the PZT film and an electr ode. It is shown that (i) the coercive field is independent of thickne ss 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; an d (iv) the polarization depends on the electric field in the PZT layer , independent of thickness. Pulse switching endurance measurements sho wed that in the saturation range the fatigue for these ferroelectric c apacitors is determined by the pulse voltage and is independent of the thickness.