Study On Ni-Al-O High K Dielectrics And Integration Of PbZr_0.2 Ti_0.8 O/Ti-Al-O Heterostructures

The different capacitors, Pt/Ni-Al-O/Pt (MIM), Pt/Ni-Al-O/Si (MOS) and Pt/ PbZr_0.2Ti_0.8O₃ (PZT) / Ti-Al-O / Si (MFIS) capacitors, have been successfully fabricated, in which Ni-Al-O and Ti-Al-O dielectric thin films were fabricated by pulsed laser deposition and PZT ferroelectric thin films were prepared by sol-gel method. X-ray diffraction (XRD), Atomic force microscopy (AFM), precision Materials Analyzer (Precision LC Unit), Agilent LCR Meter and Keithley System are used to examine the microstructure, morphology and ferroelectric properties of the samples, respectively.Ni-Al-O thin films have been fabricated on Pt/Ti/SiO₂/Si (111) and n-Si (001) with a Ni3Al alloy target by reactive pulsed laser deposition (PLD). The effects of rapid thermal annealing on structural and electrical properties of Ni-Al-O films have been investigated. It is found that Ni-Al-O thin film annealed up to 750℃is amorphous and the root-mean-square roughness of the film is less than 0.5 nm. With the increase of measurement frequency, dielectric constant of the film decreased, and dielectric loss increased and then decreased for the Pt/Ni-Al-O/Pt structure. The dielectric constant and leakage current density of the film annealed at 700℃are 7.2 and 7.0×10-7 A/cm2, respectively.Ni-Al-O thin films have been fabricated on n-Si (001) substrate using two-step or one-step method by reactive PLD. The electrical and interface properties of all samples have been investigated. It is found that, the biggest dielectric constant, the smallest fixed charge on oxide and interface state density (4.45×1012 eV-1 cm-2) can be obtained for the sample, deposited by two-step method (one-step: thin film is deposited on 5 Pa O₂ at room temperature. Two-step: the deposition temperature is 400℃).To obtain Pt/PZT/Pt and Pt/PZT/Ti-Al-O/Si capacitors, the Ti-Al-O buffer layer has been deposited on n-Si (001) substrate using two-step method by PLD, and then PZT thin film has been prepared on Ti-Al-O/Si and Pt/Ti/SiO₂/Si by sol-gel method. It is found that the PZT thin film annealed at 550℃possesses relatively big remnant polarization and small leakage current density. The MFIS capacitor shows low leakage currents and C– V hysteresis loops which are ascribed to the ferroelectric polarization of PZT films. As the applied voltage increases, the memory window of hysteresis loops increases, and it is 3.36 V at the applied voltage of 10 V.