We have been proposing the use of RMnO_3 (R: rare earth elements)f ilms for metal-ferroelectric-semiconductor field effect transistor (MFSFET)-type ferroelectric random access memories (Ferroelectic RAMs). This report describes the progress of YMnO_3 and YbMnO_3 films for FET type FeRAM application.Although highly (0001)-oriented YMnO_3 films are easily obtaine don a MgO, ZnO/Sapphire, Pt/Sapphire and Pt/Si substrates, it was very hard to obtain the crystalline films directly on Si or on SiO_2/Si substrate. A Y-Mn-O buffer layer improved the crystallinity of the YMnO_3 films on Si, and we got the C-V curve with ferroelectric hysteresis. The real ferroelectric component responsible for the C-V hysteresis was calculated to be just 8.4 nC/cm~2 by pulse measurements. On the other hand, Y_2O_3 buffer layer drastically improved the dielectric properties. The window width of the C-V hysteresis does not change by changing the sweep rate and measurement frequency.
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