Junichi Karasawa

Sub-100 nm SrBi2Ta2O9 film with ultrathin BiTaO4 capping layer for 3 V or lower-voltage ferroelectric memory operation

This letter proposes an enhanced 700 °C process to improve the dielectric breakdown strength and surface roughness of sub-100 nm SrBi2Ta2O9 (SBT) film with a thin (<20 nm) BiTaO4 (BT) layer for the 3 V or lower voltage ferroelectric memory. The process temperature for rapid thermal annealing and furnace annealing is performed at or below 700 °C. The BT layer is used as a capping layer on top of SBT film. It improves the dielectric breakdown strength (1.2 MV/cm) of SBT film without sacrificing other ferroelectric properties.

Improvement in D-E Hysteresis Curve Squareness of PZT Thin Films—Effect of Oxygen Partial Pressure in High-Pressure Post-Annealing

A high-pressure annealing was applied to a post-annealing process for sol-gel derived PZT thin films. The squareness of D-E hysteresis curves changes depending on both total pressure and oxygen concentration. Moreover, the change follows the product of the total pressure and the oxygen concentration, which correspond to oxygen partial pressure PO2. Where the PO2 is higher than 0.03 MPa, few of the squareness of the hysteresis curve are excellent. The squareness of the hysteresis curves dramatically improve as the PO2 decreases. Where the PO2 is lower than 0.01 MPa, the squareness deteriorates slightly. These changes in the D-E hysteresis curves are thought to be explained by the generation of lead and oxygen vacancies as a function of the PO2.

Fabrication and Characterization of Lead Silicate Doped PZT Thin Films

The crystal structure, surface morphology and electrical properties of PbSiO x (PSO) doped Pb(Zr,Ti)O 3 (PZT) thin films were systematically investigated. The starting solutions of PSO-doped PZT were prepared by mixing sol-gel solutions of PZT and PSO. RTA-calcined thin films were crystallized by means of an oxygen partial pressure controlled post-annealing process. After the calcining process, lightly doped PZT thin films containing an amount of PSO dopant less than 1.0 at.% exhibit (111)-preferred orientation, and fine grains having a diameter of 50 nm and column-like structure. As the amount of PSO dopant is increased to 5.0 at.%, the (111) peaks becomes obscure and the (100) peaks together with the minor (110) peaks becomes dominant. The column-like structure changes into a plate-like structure having coarse grains whose diameter exceeds 500 nm. Further increasing the level of PSO dopant to 20.0 at.% causes the appearance of a pyrochlore phase having an extremely smooth surface without apparent grains. On the other hand, after the post-annealing process, the pyrochlore phase seen in the heavily doped PZT remarkably disappears, replaced by a perovskite phase together with PSO. The remnant polarization (Pr) gradually decreases as the amount of PSO dopant increases. The break down voltage, fatigue, imprint and other reliability parameters are improved within the proper doping range.