A Model of The Metal-Ferroelectric-Metal Capacitor

AbstractFerroelectric (FE) films, especially PZT films, have received increasing attention for microelectronic applications such as ferroelectric memory and high density DRAM. There has been significant progress in the preparation of high quality PZT films involving wet chemical and physical vapor deposition techniques. Metal-FE-metal structures, typified by Pt-PZT-Pt capacitors, are the basic building blocks for the ferroelectric devices. The leakage currents of the capacitors are known to be non-ohmic and exhibit an exponential dependence on applied voltage.The present paper presents a model based on totally depleted back-to-back Shottky barriers. Predictions based on the model can provide significant new understanding of the FE behavior of thin films. For example, the assumption of total depletion leads to the presence of a built-in field within the film which can explain the ubiquitously higher values of coercive field in FE films than found in bulk ceramics. It will be shown that the agreement between model predictions and actual device I-V characteristics of Pt-PZT-Pt capacitors is very close. Further, the model can also explain the observed hysteresis loop asymmetry and low dielectric constants of films of relaxor FE's, whose dielectric constants are much smaller than those of bulk materials.</jats:p

Characterization of Sol-Gel Derived Tantalum Oxide Films

AbstractWe have studied the densification and dielectric properties of sol-gel derived tantalum oxide thin films as the insulators in MIS capacitors. Hydrolysis of tantalum ethoxide is extremely rapid and goes to completion in ethanol. Condensation is also rapid, and goes to completion in toluene Multiple layers were applied by spin-coating up to thicknesses of 3000 Å before cracking of the coating during drying ensued. Densification occurs from room temperature to 450 C, with the original film thickness decreasing by about half in one hour at 450 C. No additional densification occurs upon heating to 750 C. The dielectric constant decreases from unfired samples to those fired at 450 C, and then increases on firing from 600 to 750 C. The value of the dielectric constant at 1 MHz for samples fired at 750 C for one hour is 20, similar to that of anodically grown Ta2O5. Leakage currents as low as 2 × 10−7 amp cm−2 have been measured for applied fields of 200,000 V cm−1.</jats:p

Piezoelectric Characterization of Bulk and Thin Film Ferroelectric Materials using Fiber Optics

AbstractIn this study, the use of a fiber optic technique for the measurement of the piezoelectric properties of ferroelectric bulk and thin film samples was investigated. The strain and piezoelectric properties (namely the d33 coefficients) were measured using the MTI-2000 Fotonic Sensor, which uses the principle of the optical lever to resolve very small changes in sample displacement (1 Å). Using this technique, we were able to detect the very small strains associated with the converse piezoelectric effect for PVDF films and bulk PZT samples, and correlate the results with data acquired from direct piezoelectric effect measurement. Comparison of the data sets prove that the optical lever would be a useful optical technique for measuring of the d33 values of ceramic thin films, such as BaTiO3, ZnO, and PZT.</jats:p

Sol-Gel Derived Barium Sodium Niobate and Bismuth Titanate Films

AbstractSol-gel derived barium sodium niobate and bismuth titanate films were successfully prepared from precursor solutions of chelated Ba[Nb(OEt)6]2 and NaNb(OEt)6 and from bismuth 2-ethyl hexanoate and Ti(OEt)4 respectively. Single phase Ba2NaNb5O15 was formed at 750C on platinized Si and at 850C on fused SiO2. Monoclinic (pseudo-orthorhombic) Bi4Ti3O12 was formed at temperatures as low as 500C. Both film compositions showed significant second harmonic generation. The dielectric constant of the bismuth titanate film was comparable to that of sputtered films.</jats:p

Sol-Gel Derived PZT Fibers

ABSTRACTSol-gel routes were developed to prepare densified PZT fibers. The effects of the degree of hydrolysis and the addition of an organic polymer to the precursor sol on fiber forming ability were investigated. Results on the crystalline and microstructural development of gels and fibers are presented. The effects of the incorporation of excess PbO and sintering atmosphere are also discussed, particularly in relation to densification.</jats:p

Optimization of Sol-Gel Derived PZT thin Films by the Incorporation of Excess PBO

ABSTRACTA series of PZT precursor solutions was prepared which incorporated excess PbO to give the composition Pb1+xZr0.53Ti0.47O3+x, where 0 &lt; × &lt; 0.3. These solutions were spin coated on platinized Si wafers and fired at elevated temperatures up to 750C for 30 mins. After crystallization into single-phase perovskite, the films were studied using XRD, optical microscopy and electrical characterization techniques (hysteresis loops and dielectric properties). It was found that the presence of excess PbO significantly improved the PZT films in terms of phase assemblage, microstructure and electrical properties. Under optimized conditions, films with dielectric constants of around 3000 can be obtained.</jats:p

Electrical Characterization of Sol-Gel Derived PZT Films

AbstractSol-gel derived PZT films were successfully prepared from precursor solutions based on lead acetate and Zr/Ti alkoxides. A pyrochlore phase was observed in films fired at low temperatures, while single-phase perovskite films were obtained at temperatures above 725C. The dielectric constant increased to above 1000 when there was a higher proportion of perovskite than pyrochlore. The films were essentially fatigue-free up to 108 cycles and exhibited a low aging rate of 5.7% / decade-sec.</jats:p

Characterization Of Sol-Gel Derived Tantalum Oxide Films

ABSTRACTWe have studied the densification and dielectric properties of sol-gel derived tantalum oxide thin films as the insulators in MIS capacitors. Hydrolysis of tantalum ethoxide is extremely rapid and goes to completion in ethanol. Condensation is also rapid, and goes to completion in toluene Multiple layers were applied by spin-coating up to thicknesses of 3000 Å before cracking of the coating during drying ensued. Densification occurs from room temperature to 450 C, with the original film thickness decreasing by about half in one hour at 450 C. No additional densification occurs upon heating to 750 C. The dielectric constant decreases from unfired samples to those fired at 450 C, and then increases on firing from 600 to 750 C. The value of the dielectric constant at 1 MHz for samples fired at 750 C for one hour is 20, similar to that of anodically grown Ta2O5. Leakage currents as low as 2 × 10−7 amp cm−2 have been measured for applied fields of 200,000 V cm−1.</jats:p

Wet Chemical Derived Films For Electrical Applications

ABSTRACTWet chemical methods have been used with success to synthesize films for a variety of electrical applications. After first reviewing the important microstructural features of films, the present paper focuses attention on ferroelectric (FE) films. The present state of and critical issues facing wet chemically derived FE films are considered. The needs for more extensive microstructural characterization and for more systematic exploration of electrical behavior are emphasized.</jats:p