Ferroelectric random access memory (FRAM) has been commercialized for about 20 years and its reliability has been well proven all over the world. In the recent Internet of Things (IoT) era, it also plays important roles to particularly in edge computing because of its high writing speed, high rewriting endurance, and low writing energy consumption. We review the history of semiconductor memories using ferroelectrics and overview the progresses of the new ferroelectrics and promising ferroelectric applications in the future.

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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%.

we have developed ferroelectric capacitor fabrication technique and a new sensing amplifier circuit to realize lowvoltage and high-density FRAM. Improvement of IrO x top electrode near the ferroelectric interface successively lowers operation voltage. And our developed "Dual Reference Sensing Amplifier" enables to commercialize highly-reliable FRAM with memory density of 4Mb or larger. FRAM, Feroelectric, PZT, IrO, Dual SensingI.