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

我们研究了实现新型MFS-FET型铁电非易失性存储器。利用新材料YMnO_3实现MFS-FET存在漏电流大和剩余极化小两个问题。为了弄清和克服这些问题，我们研究了以下两个问题：(1)生长在镁和铂衬底上的YMnO_3薄膜的剩余极化为0.2muC/cm~2，足以用于器件的工作，而直接生长在Si衬底上的YMnO_3薄膜由于结晶度较弱而没有剩余极化。我们尝试了一些表面修饰，发现Y-Mn-O和Y_2O_3缓冲层提高了YMnO_3的结晶度。我们证实了缓冲层的存在对控制硅表面载流子是有效的。在检查了C-V和脉冲特性等电学特性后，我们确认了基波运动为MFS-FET，但仍然存在较大的泄漏电流。(2)为了弄清泄漏电流的来源，我们对大块样品进行了检查。我们发现，Mn的价态涨落导致了漏电流的产生，Yb取代A位原子和掺入Zr降低了漏电流。掺Yb降低了工艺温度。我们相信，我们的研究对利用RMnO_3实现MFS-FET有很大的贡献。

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.