Ferroelectric properties of YMnO3 epitaxial films for ferroelectric-gate field-effect transistors

Ferroelectric properties of ${\mathrm{YMnO}}_3$ epitaxial films were studied. The ferroelectric properties of epitaxially grown (0001) ${\mathrm{YMnO}}_3$ films on (111)Pt/(0001)sapphire (epi-YMO/Pt) with an excellent crystallinity were compared to (0001)-oriented poly crystalline films on $\text{(111)}{\mathrm{Pt/ZrO}}_2/{\mathrm{SiO}}_2/\mathrm{Si}.$ The epi-YMO/Pt had saturated polarization–electric-field (P–E) hysteresis loops, with a remanent polarization ${\mathrm{(P}}_r)$ of 1.7 $\mu {\mathrm{C/cm}}^2$ and a coercive field ${\mathrm{(E}}_c)$ of 80 kV/cm. The fatigue property showed no degradation up to ${10}^{10}$ measured cycles. These results suggested that the ${\mathrm{YMnO}}_3$ epitaxial films were suitable ferroelectric material for the ferroelectric-gate field-effect transistors. Consequently, epitaxially grown $\text{(0001)}{\mathrm{YMnO}}_3$ films on epitaxial ${\mathrm{Y}}_2{\mathrm{O}}_3/\mathrm{Si}$ (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 ${10}^4$ s was obtained in the epi-YMO/Si capacitor.