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

在研究了Y含量对YSZ薄膜材料性能的影响后，我们证实了YSZ缓冲层对在Si上生长PZT薄膜的有效性。(1)在800ﾟC下，在Si(100)衬底上异质外延生长了Y含量比R_Y=2.3-19.7at.%的100 nm厚的立方YSZ薄膜，晶相保持在室温下。在室温下，R_Y=1.2at.%的YSZ薄膜仍保持立方相结构，直到厚度达到20 nm。(2)在没有Y含量的情况下，10 nm厚的(100)薄膜在Si(100)衬底上异质外延生长，100 nm厚的薄膜具有与衬底表面相差约9ﾟ的单斜晶系(100)取向的晶粒。(3)我们获得了如下的电学特性：当Y含量降低而立方相保持不变时，薄膜的(100)晶面呈单斜晶型。C(电容)-V(电压)曲线的漏电流和磁滞宽度增大。磁滞是由于离子漂移引起的。随着Y含量的进一步降低，薄膜的晶相转变为单斜晶系，漏电流和磁滞宽度减小。这可能是由于立方相中Y含量的降低降低了PZT薄膜的结晶质量。(4)在R_Y=9.4at.%的10 nm厚的YSZ薄膜上沉积PZT薄膜时，没有发现硅衬底与PZT薄膜发生反应，并且观察到了铁电性质。但是，由于YSZ薄膜的厚度不够薄，不足以将工作电压降低到3V，因此需要减小其厚度并提高薄膜的材料质量。

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.