Soichiro Ozawa

Control of La-doped Pb(Zr,Ti)O3 crystalline orientation and its influence on the properties of ferroelectric random access memory

We investigated the crystallization mechanisms of sputter-deposited La-doped Pb(Zr,Ti)O3 (PLZT) on a Pt/Ti metal stack in the postdeposition annealing (PDA) at 600 °C in O2-mixed Ar ambient. As-deposited amorphous PLZT generally transforms to a perovskite phase over 550 °C through a metastable pyrochlore phase during the PDA. We found that the O2 content of the PDA ambient crucially affects the pyrochlore-perovskite transformation (PPT) speed. While an O2 content much higher than 2% of the PDA ambient suppresses PPT, an O2 content much lower than 2% enhances PPT. An O2 content around of 2% of the PDA suppresses PPT near the surface of PLZT and simultaneously keeps PPT fast in the inner regions of PLZT in the pyrochlore phase because of the O2 diffusion limit from the PLZT surface, eventually resulting in almost only the growth of highly {111} oriented columnar PLZT on Pt, which reveals better electric properties than those obtained by the PDA with the ambient of O2 contents much higher or lower than 2%.

A Triple-Protection Structured COB FRAM with 1.2-V Operation and 1017-Cycle Endurance

We have developed a ferroelectric RAM (FRAM) with a low operation voltage of 1.2 V and a high switching endurance up to 1017 cycles. Our newly developed triple-protection structured cell array, has constructed without an additional mask step, effectively protects 0.4-μm2 ferroelectric capacitors from hydrogen and moisture degradation. We have designed our capacitor-over-bit-line (COB) structure to have a small cell size of 0.5 μm2.