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。用新材料YMnO_3实现MFS-FET存在漏电流大和反射极化小两个问题。(1)在MgO和Pt衬底上生长的YMnO_3薄膜具有0.2 μ C/cm ^2的反射极化，这足以使器件工作，而直接在Si衬底上生长的YMnO_3薄膜由于结晶性差而没有反射极化。我们对YMnO_3进行了表面改性，发现Y-Mn-O和Y_2O_3缓冲层的加入提高了YMnO_3的结晶度。证实了缓冲层的存在对控制硅表面载流子是有效的。通过C-V特性、脉冲特性等电气特性的检测，确认了MFS-FET的基本动作，但仍存在较大的漏电流。(2)为了弄清漏电流的来源，我们对大量样品进行了检验。发现Mn的价态涨落导致漏电流的增加，Yb取代A位原子和Zr的掺杂降低了漏电流。Yb的取代降低了工艺温度。我们相信，我们的研究将有助于实现MFS-FET的RMnO_3。

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.