Characteristics of inorganic and organic ferroelectric thin films for memory applications

Characteristics of inorganic and organic ferroelectric thin films are discussed from viewpoints of ferroelectric random access memory (FeRAM) applications. It has been found in BiFeO₃ films formed by chemical solution deposition that the leakage current at high electric field decreases significantly by substituting Mn atoms for Fe atoms. In these films, well saturated hysteresis loops in P-E (polarization vs. electric field) characteristics have been observed. It has also been found that the fatigue endurance is much improved by substituting Sm atoms for Bi atoms. Next, properties of organic ferroelectric thin films suitable for fabrication of ferroelectric-gate FETs (field effect transistors) are discussed. It has been found in a 60 nm-thick P(VDF-TrFE) (polyvinyliden fluoride-trifluoroethylene) film that the remanent polarization is as large as 11.9 ¿C/cm² and the coercive voltage is as low as 2 V. It has also been found that the data retention characteristics are improved by adding PMMA (poly methyl methacrylate) to P(VDF-TrFE).