Hui-Qing Ling

Metalorganic Chemical Vapor Deposition of Lanthanum Aluminate Thin Films for Gate Dielectrics

Amorphous lanthanum aluminate (LAO) gate dielectric has been grown on silicon substrates by low-pressure metalorganic chemical vapor deposition. The structure, morphology, thermal stability, bandgap, and electrical properties have been characterized by various techniques. The LAO films exhibit excellent thermal stability and keep noncrystalline structure even after 900°C rapid thermal anneal. The smooth surface and larger bandgap are also confirmed. By optimizing the processing, the minimume value of equivalent oxide thickness around 0.9 nm of LAO/Si has been achieved.

Top electrode postanneal effect on ferroelectric properties of Pt/SrBi2Ta2O9/Pt capacitors

Abstract The effect of top electrode postanneal on ferroelectric properties of Pt/SrBi2Ta2O9 (SBT)/Pt capacitors is studied. Pt top electrodes on metalorganic derived SBT films were deposited by sputtering with a shadow mask. Well-saturated hysteresis loops of Pt/SBT/Pt capacitors could be achieved after 750 °C postanneal, while the as deposited capacitors exhibit large leakage current. This is ascribed to morphology change of the Pt/SBT interface during postanneal. Interfacial diffusion increases with increasing postanneal time. XPS quantitative analysis shows that 7% of atoms in 50nm-thick Pt top electrodes are Bi atoms after postanneal at 750 °C for 600 s. Remanent polarization decreases with postanneal time from 11.3 μC/cm2 to 7.5 μC/cm2, accompanied with the increase of apparent coercive voltage. The voltage drop across the interfacial layer is found to increase from 0.21 V to 0.36 V.

Effects of anneal atmosphere on the structural and ferroelectric properties of SrBi2Ta2O9 thin films

Abstract SrBi2Ta2O9 (SBT) films were prepared on Pt/TiO2/SiO2/Si substrates at 750°C in oxygen by metalorganic decomposition method. SBT film capacitors were re-annealed in Ar (N2) at 350-750°C and then followed the O2 recovery at 750°C. Effects of anneal atmosphere on the structure, morphology and ferroelectric properties have been investigated deeply. After above 550°C 100% Ar or N2 reanneal, the remnant polarization decreases and coercive field increases significantly. The subsequent O2 recovery can hardly rejuvenated them. The result is different from that from forming gas processing (annealing in hydrogen atmosphere). The possible origin and mechanism is discussed and proposed.