TO REALIZE FERROELECTRIC NON-VOLATILE MEMORIES (MFS) BY USING YMNO_3 AND SURFACE MODIFICATION

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We have studied to realize new MFS-FET type ferroelectric non-volatile memories. There were two problems, large leak currents and small remanent polarizations to realize MFS-FET using the new material, YMnO_3.To make clear and overcome these problems, we have examined as follows.(1) YMnO_3 films grown on MgO and Pt substrates have remanent polarization of 0.2muC/cm^2, which is sufficient to operate devices, but those directly on Si substrates do not have remanent polarization because of weak crystallinity. We have tried some surface modification, and found that Y-Mn-O and Y_2O_3 buffer layr improve the crystallinity of YMnO_3. We have confirmed that existence of buffer layr is effective to control the carrier on the Si surface. After examining electric properties, such as C-V and pulse characteristics, we have confirmed fundamental movements as MFS-FET.However, there is still large leak current.(2) To make clear the origin of leak current, we have examined on bulk samples. We have found that valence fluctuation of Mn leads to the leak current, and substitution of A-site atom by Yb and doping of Zr decrease the leak current. Substitution by Yb decreases the prosess temperature. We do believe that our study is much contributing to realize MFS-FET using RMnO_3.