Papers by Keyword: (Bi,La)₄Ti₃O₁₂

Abstract: A 16Mb 1T1C FeRAM device was successfully fabricated with the lead-free BLT capacitors. The average value of the switchable polarization obtained in the 32k-array (unit capacitor size: 0.68 μm2) BLT capacitors was about 16 μC/cm2 at the applied voltage of 3V and the uniformity within an 8-inch wafer was about 2.8%. But random bit failures were detected during the measuring the bit-line signal of each cell. It was revealed that the grain size and orientation of the BLT thin film were severely non-uniform. Therefore, the grain size and orientation was optimized by varying the process conditions of nucleation step. The random bit failure issue was solved by adopting the optimized BLT film. The cell signal margin of the optimized FeRAM device was about 340 mV.

Abstract: 1mm-thick BLT ceramics were sintered in accordance with a bulk ceramic fabrication process. All XRD peaks detected in the sintered ceramics were indexed as the Bi-layered perovskite structure without secondary phases. Density was increased with increasing the sintering temperature up to 1050°C and the maximum value was about 98% of the theoretical density. The remanent polarization (2Pr) value of BLT ceramic sintered at 1050°C was approximately 6.5 μC/cm2 at the applied voltage of 4.5kV. The calculated electromechanical couping factor (kt) of it was about 5% and the mechanical quality factor (Qm) was about 2200. From these results, a BLT ceramic target for plused laser deposition (PLD) system was successfully fabricated.

Abstract: A 16Mb 1-transistor /1-capacitor (1T1C) FeRAM device was fabricated with lead-free Bi3.25La0.75Ti3.0O12 (BLT) capacitors. The key integration processes contain a scalable MTP (Merged Top-electrode and Plate-line) cell structure and reliable BLT ferroelectric capacitors. Ferroelectric properties of BLT films were optimized on the newly developed MTP cell structure. BLT films were coated on Pt/IrOx/Ir bottom electrode using sol-gel solutions. The composition of the optimized BLT film was about Bi3.25La0.75Ti3.0O12. The switchable polarization obtained in a 100nm-thick BLT film was about 20 µC/cm2 at the 3 V applied voltage, and the optimized BLT film showed a few fatigue losses about 10% up to 1 × 1011 cycles. The imprint properties of the BLT film were also characterized at 25°C and 90°C operating temperature after 125°C data storage. The average cell signal sensing margin between data "1" and data "0" was measured to be about 900 mV, which is a sufficiently large margin for device operation.

Abstract: Ferroelectric properties of Pb-free (Bi,La)4Ti3O12 (BLT) films were optimized on a newly developed MTP cell structure. BLT films were coated on Pt/IrOx/Ir bottom electrode using sol-gel solutions. The composition of the optimized BLT film was about Bi3.25La0.75Ti3.0O12, which was analyzed by ICP-MS method. The switchable polarization obtained in a 100nm-thick BLT film was about 20 uC/cm2 at the 3 V applied voltage, and the optimized BLT film showed little fatigue loss about 10% up to 1×1011 cycles. The imprint properties of the BLT film were also characterized at 25 °C and 90 °C operating temperature after 125 °C data storage. Regardless of operating temperature, switchable polarization of BLT had a sufficiently large margin for device operation up to 10 years.