Integration Investigation Of Transparent ZnO Film With Ferroelectric Film

Ferroelectric random access memory(FeRAM) based on a single ferroelectric field effect transistor(FFET) in principle has a great advantage over other types of memory since it is nonvolatile, low power consumption, non-destructively readable and possesses a fast access time. The recent development of transparent thin-film transistors (TTFTs) represents a major advance in the emerging field of transparent electronics. TTFTs could find many applications in light-emmetting displays, smart windows, solar cells, security or military systems, and even toys. Integration of TTFTs with a ferroelectric insulator has become a hot topic of numerous studies because of their memory function and non-destructive readout properties.Firstly, the high-quality Zinc oxide (ZnO) films and Al-doped ZnO (AZO) films were prepared and the microstructural, optical and electrical properties were studied; then, the infulence of experiment parameters on the microstructure and physical properties of Pt/Pb(Zr_0.4Ti_0.6)O₃(PZT)/Pt and Pt/BiFe_0.95Mn_0.05O₃(BFMO)/Pt ferroelectric capacitors were investigated. At last, the PZT and BFMO thin films were respectively prepared on the high-quality AZO films, and the microstructure and electrical properties of the integrated films were studied. The main results are as follows:Epitaxial ZnO thin films were deposited on sapphire (0001) substrates by radio frequency (RF) magnetron sputtering. The influence of sputtering power, oxygen gas content and substrate temperature on the structural and optical properties of ZnO thin films was studied. The optimal experimental conditions of depositing ZnO films were obtained. The ZnO films were investigated by atomic force microscope (AFM), X-ray diffraction (XRD), UV-spectrophotometer. It is found that the surface of ZnO films fabricated under optimal experiment conditions has good crystallinity, smooth surface and uniform grain-size distribution. The average optical transmittance is over 90% in visible-light region.Base on the experimental parameters for the high quality ZnO Films, AZO films were fabricated on the Sapphire (0001) and single crystalline Si (001) by RF magnetron sputtering and pulsed laser depositon. The infuence of growth temperature on the microstructural, optical and electrical characteristics of AZO films was mainly studied. The high-quality AZO films were obtained. PZT thin films were grown on the Pt(111)/TiO₂/Si or LaNiO₃/Pt(111)/TiO₂/Si substrates by Sol-gel method, and Pt film was used as the top electrodes of PZT films. The impact of oxygen content, annealing time and temperature on the microstructual and electrical properties of Pt/PZT/Pt and Pt/PZT/LaNiO₃/Pt ferroelectric capacitor were studied. The results show that the high quality PZT thin films were obtained through annealing in oxygen gas at 600℃for 120 seconds and the Pt/PZT/Pt ferroelectric capacitors have good ferroelectric properties. The analysis of the leakage current mechanism indicates that Pt/PZT/Pt capacitor meets Ohmic-like behaviour at low voltages (<1V) and Schottky emission at high voltages (>1 V). The Pt/PZT/LaNiO₃/Pt capacitors annealed at the temparature of 550℃possess the large remnant polarization (Pr) (⁴4μC/cm²).Pt/BFMO/Pt capators were fabricated on the Si substrate, in which BFMO film was prepared by sol-gel method. The results show that the BFMO film has good crystallin quality annealed at 650℃in air and Pt/BFMO/Pt capators possesses good ferroelectric properties. When the anneal atmosphere is high pure netrogen, the BFMO film annealed at 600℃has optimal crystalline quality and good ferroelectric properties. The Pr and coercive voltage (Vc) of the ferroelectric capacitor are ⁵0μC/cm² and ⁵ V, respectively. The leakage current density measured at 4 V is 3×10^-2 A/cm² and the leakage current mechanism satisfied Ohmic-like behaviour when the voltage is less than 4 V.PZT and BFMO films were prapared on the AZO(002)/Si(001) substrates using Sol-gel method. It is found that the Pr and Vc of Pt/PZT/AZO capacitors, measured at 5 V, annealed at 550 OC in 0.5% oxygen atmosphere are 1.3μC/cm² and 2.4 V respectively. The Pr and Vc of Pt/BFMO/AZO annealed at 600 OC for 2 min in pure netrogen are ³.5μC/cm² and ⁰.68 V respectively. The leakage current density, measured at 5 V, is 7.8×10--3 A/cm². The analysis of the leakage current mechanism indicates that Pt/BFMO/AZO capacitor meets Ohmic-like behaviour at low voltages (<0.7 V) and Schottky emission at high voltages (>0.7 V).