飞秒脉冲激光沉积Si基a轴择优取向的钛酸铋铁电薄膜

在钛酸铋(Bi4Ti3O12)薄膜的制备过程中容易获得晶粒c轴垂直于基片表面的薄膜,而压电和铁电存储器主要利用a轴的自发极化分量,因而制备a轴择优取向的Bi4Ti3O12铁电薄膜具有特别的意义。采用飞秒脉冲激光作用在钛酸铋陶瓷靶上,采用Si(111)作为衬底,制备了a轴择优取向的钛酸铋薄膜。采用X射线衍射(XRD)的薄膜附件和场发射扫描电镜(FSEM)研究了薄膜的结构和形貌;采用傅里叶红外光谱仪测量了室温(20℃)下在石英基片上沉积的样品的光学特性;室温下沉积的钛酸铋薄膜呈c轴择优取向,晶粒的平均大小为20 nm,其光学禁带宽度约为1.0 eV。在500℃沉积的钛酸铋薄膜呈a轴择优取向,晶粒大小在30~300 nm之间,薄膜的剩余极化强度Pr为15μC/cm2,矫顽力Er为48 kV/cm。

a-Axis Oriented Bi4 Ti3 O12 Thin Films Deposited on Si (111) by Femtosecond Laser Ablation

The crystalline grains of Bi4Ti3O12 thin films are tended to c-axis-orientation in a usually deposited process on planar substrates, but the piezoelectric and ferroelectric storage devices largely utilize the a-axis-oriented component of spontaneous polarization. So, it is importance to investigate the way to gain a-axis-oriented Bi4Ti3O12 thin films. The polycrystalline Bi4Ti3O12 thin films successfully prepared by femtosecond laser deposition on Si(111) wafers are reported in this paper. The structural properties and crystallographic orientation of the films were investigated by X-ray diffraction (XRD) method in 2θ only scan, the surface morphology of the films was observed using the field scanning electron microscope (FSEM). The Bi4Ti3O12 thin film deposited at room temperature (20 ℃) was highly c-axis-oriented; but the film deposited at 500 ℃ was highly a-axis-oriented. It was observed that the films were composed of well-distributed grains, the grains of the 20 ℃-sample was about 20 nm in diameters, the grains of the 500 ℃-sample was 30～200 nm, large particles (≥1 μm) were not found in the surface of the two samples. A Fourier-transform infrared spectroscopy (FT-IR) was used to measure the transmittance and reflectance of the film deposited on quartz at room temperature, and then to determine the optical forbidden gap of the film, the optical forbidden gap of it was 1.0 eV. The remnant polarization (Pr) of the a-axis-oriented sample was measured to be 15 μC/cm2 by RT-66A the coercive force (Er) was 48 kV/cm.