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We have proposed ReMnO3 (Re:rare earth) thin films as a new candidate for nonvolatile memory devices. In this letter, we report on fabrication of (0001) YMnO3 films on (111)MgO, (0001)ZnO:Al/(0001) sapphire, and (111)Pt/(111)MgO using rf magnetron sputtering. We succeeded in obtaining (0001) epitaxial YMnO3 films on (111) MgO and (0001)ZnO:Al/(0001) sapphire substrate, and polycrystalline films on (111)Pt/(111)MgO. The dielectric properties of the epitaxial and polycrystalline YMnO3 films are almost the same. The dielectric permittivities of both films are smaller than those reported for YMnO3 single crystal.

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Ferroelectric properties of YMnO3 epitaxial films were studied. The ferroelectric properties of epitaxially grown (0001) YMnO3 films on (111)Pt/(0001)sapphire (epi-YMO/Pt) with an excellent crystallinity were compared to (0001)-oriented poly crystalline films on (111)Pt/ZrO2/SiO2/Si. The epi-YMO/Pt had saturated polarization–electric-field (P–E) hysteresis loops, with a remanent polarization (Pr) of 1.7 μC/cm2 and a coercive field (Ec) of 80 kV/cm. The fatigue property showed no degradation up to 1010 measured cycles. These results suggested that the YMnO3 epitaxial films were suitable ferroelectric material for the ferroelectric-gate field-effect transistors. Consequently, epitaxially grown (0001)YMnO3 films on epitaxial Y2O3/Si (epi-YMO/Si) were fabricated. The epi-YMO/Si capacitor had almost equivalent crystallinity compared to epi-YMO/Pt. It was recognized that the epi-YMO/Si capacitor exhibited the ferroelectric type C–V hysteresis loop with the width of the memory window of 4.8 V, which was almost identical to the value of twice coercive voltage of the P–E hysteresis loops of the epi-YMO/Pt. A retention time exceeding 104 s was obtained in the epi-YMO/Si capacitor.

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