Materials Science Forum, Vol.510-511, 530-533, 2006
Cell sensing margin of lead-free (Bi,La)(4)Ti3O12 thin film deposited on MTP cell structure in high density FeRAM device
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 mu C/cm(2) at the 3 V applied voltage, and the optimized BLT film showed a few fatigue losses about 10% up to 1 X 10(11) cycles. The imprint properties of the BLT film were also characterized at 25 degrees C and 90 degrees C operating temperature after 125 degrees 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.