Research On Preparation Method Of Ferroelectric Thin Films

Because of the excellent Electro-optic, pyroelectric and ferroelectric properties, lead lanthanum zirconate titanate (PLZT) thin films are widely used in optoelectronics, microelectronics and integrated optics systems. It is the ideal material for control section on optical commutation, infrared detectors and optical waveguide.In this paper, perovskite-type PLZT(8/65/35) thin films were successfully prepared by a metal-organic decomposition (MOD) method on Pt(111)/Ti/SiO2/Si(100) substrate. In the preparation process, the growth temperature range of PLZT thin film is 600℃-750℃by differential thermal analysis(DTA)。The surface microstructure and crystalline structure of PLZT films were examined by the atomic force microscopy (AFM),scanning electric microscopy (SEM) and X-ray diffraction (XRD).The following are a series of results:(1) the PLZT thin films were respectively annealed at 600,650,700 and 750℃for 1h, and found that the crystalline peak(110) of PLZT thin films annealed at 700℃was the best. Furthermore, the PLZT thin films were respectively annealed at 700℃for 30min,90min and 180min. It was found that the Pb weight percentage of the PLZT thin films surface was the best (46.44%). Therefore, the heat treatment parameters of PLZT thin films was determined to be 700℃and 30min. (2) PLZT thin films with PT seeding layer annealed at 650℃had good crystalline peak (110), and the heat treatment temperature is decreased about 100℃compared with film without PT seeding layers. (3)The PLZT thin films were respectively prepared on Pt substrates of the thickness of 120nm,198nm,290nm and 760nm. It is also reveled that the crystalline peak of PLZT thin films was not affective to the thickness of Pt substrate.The electrical properties of PLZT thin films were studied in this paper. Firstly, theⅠ-Ⅴproperties of PLZT thin films were measured.These results indicated that, the experimental data of leakage current (m=d(logI)/d(logV)=0.89)obeys Ohm'law in low electric field, and the experimental data of leakage current(m=d(logI)/d(logV)=7.8) was consistent with space charge limited current in high electric field. Secondly, The PLZT thin films with thickness of 240nm, 460nm and 956nm were prepared. According to the results of hysteresis loop and C-V properties, when the thickness of the PLZT film was 956nm, the remanent polarization reached its maximum of 25.7uC/cm2 and the coercive field reached its minimum of 68kV/cm; meanwhile, the dielectric tuning rate reached its maximum of 24.79%. Lastly, the results of the dielectric properties showed that the dielectric constant raised with the increasing of the thickness and the PLZT thin films with thickness of 460 nm showed the smallest dielectric loss.The pyroelectric coefficient of PLZT thin films was measured and the pyroelectric coefficient was 720μC/(m2K). Dielectric constant and dielectric loss was 980 and 2.67%at frequency 1kHz. The calculated optimal values of voltage response(Fv) and the detectivity(Fd) were 0.032m2/C and 18.4μPa-1/2, respectively.