Heteroepitaxial growth of oxide thin film on Si substrate by controlling the interface

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After the Y content dependence of YSZ film material properties was investigated, we confirmed usefulness of the YSZ buffer layr for the PZT film on Si.(1) 100-nm-thick cubic YSZ films with Y content ratios R_Y=2.3-19.7 at.% were heteroepitaxially grown on Si (100) at 800ﾟC and the crystal phase was kept at room temperature. Also, YSZ films with R_Y=1.2 at.% were kept to be cubic phase even at room temperature until their thickness were 20 nm. However, they were monoclinic at room temperature and were cubic at 800ﾟC when their thickness was more than 30 nm.(2) In the case of ZrO_2 without Y content, the 10-nm-thick (100) film grew heteroepitaxially on Si (100) substrate and the 100-nm-thick film had monoclinic (100) oriented grains which is about 9ﾟ off from the surface of the substrate.(3) We obtain electric characteristics of the YSZ films as follows : When the Y content was decreased and cubic phase was kept, the leakage current and the hysteresis width of the C (capacitance) -V (voltage) curve were increased. The hysteresis was due to ion drift. However, further decreasing Y content so that the crystal phase of the film was changed to monoclinic, the leakage current and the hysteresis width were decreased. This is probably because the crystalline quality of the film was degraded by decreasing the Y content in the state of the cubic phase.(4) When PZT film was deposited on the 10-nm-thick YSZ film with R_Y=9.4At.%, no reaction was found between the Si substrate and the PZT film and the ferroelectric property was observed. But, since the thickness of the YSZ film is not thin enough to reduce the operation voltage to 3V,we need to decrease its thickness and to improve the material quality of the film.