Ferroelectric Properties of BaZrO₃ Doped Sr_0.8Bi_2.2Ta₂O₉ Thin Films

Abstract

Novel sol–gel derived Sr0.8Bi2.2Ta2O9 (SBT) doped with 5 and 7% molar ratio BaZrO3 (BZ) thin films were fabricated, characterized, and electrical properties were evaluated with Pt electrodes. X-ray diffraction (XRD) analysis showed all the characteristic peaks of the layered perovskite structure with (115) orientation and slight peak broadening by BZ doping. X-ray photoelectron spectra (XPS) showed a small shift in the Sr 3d peak with BZ substitution. Scanning electron microscopy (SEM) cross-sectional photographs of the films show smaller grain size and greater porosity with BZ addition. The remanent polarization (2Pr) was significantly reduced from ∼16.4 µC/cm2 for SBT to ∼2.3 µC/cm2 for SBT with 7% BZ. Capacitance–voltage measurements performed at a frequency of 1 MHz showed butterfly type hysteresis loops, which is further evidence of ferroelectricity of the modified SBT, and dielectric constant of 135 for SBT with 7% BZ. Leakage current measurements showed one order of magnitude higher leakage current for SBT with 5% BZ compared to SBT. Lower film dielectric constant leads to higher leakage current in BZ doped SBT. Although leakage mechanisms predict this general trend, it runs counter to the objective of preparing ferroelectric films with low leakage and low dielectric constants for ferroelectric gate field-effect transistor (FeFET) type memory.

Electrical and memory window properties of Sr0.8-xBaxBi2.2Ta2-yZryO9 ferroelectric gate in metal-ferroelectric-insulator-semiconductor structure

“…Furthermore, it is also attributed to electron trapping/detrapping. Further discussion about the leakage current was previously reported in [13][14][15].…”

“…It is noted that, for higher doping, (115) peak becomes slightly broader and less intense. This is due to a degradation of crystallinity which affects ferroelectricity by means of both lowering remanent polarization and dielectric constant [13][14][15]. Surface microstructure of SBT examined by SEM [15] showed that a dense structure.…”

“…Moreover, increasing grain boundary regions and oxygen vacancies also degrade the insulating character as well as ferroelectric properties. It is implied that leakage current at M-F interface is enhanced [14]. Although an interface material was probably formed due to the change of chemical composition of interface, it was not determined in XRD analysis because of the low detection limit.…”

Investigating structural features of Ba and Zr co-substituted strontium bismuth tantalate thin films

“…Each of Sr 3d spin-orbit-split pairs constitutes two overlapping peaks. While the pairs of lower binding energy are associated with Sr ions in the perovskite structure, those of higher binding energy are assigned to Sr in oxide or carbonate [20]. Broadening of Sr 3d 3/2 and 3d 5/2 evidenced Sr ions in the perovskite structure by Ba substitution.…”

“…Moreover, enhancement of defect concentrations causes a decrease in remanent polarization. Hence, such mobile charges have ability to affect ferroelectric and electrical properties seriously [20]. The impact of co-substitution on ferroelectric properties was studied by measuring polarization vs. switchable component of polarization were decreased by increasing the substitution ratio.…”