The effects of the oxygen-argon ratio on electric properties of Ta2O5 film prepared by radio-frequency magnetron sputtering were investigated.The Ta2O5 partially transforms from the amorphous phase into the crystal phase when annealing temperatures are 800℃ or higher.The lattice constant of Ta2O5 decreases with the increase of the O2/Ar ratio,which indicates that oxygen gas in the working gas mixture contributes to reducing the density of oxygen vacancies during the deposition process.For the films deposited in working gas mixtures with different O2/Ar ratios and subsequently annealed at 700℃,the effective dielectric constant is increased from 14.7 to 18.4 with the increase of the O2/Ar ratio from 0 to 1.Considering the presence of an SiO2 layer between the film and the silicon substrate,the optimal dielectric constant of Ta2O5 film was estimated to be 31.Oxygen gas in the working gas mixture contributes to reducing the density of oxygen vacancies,and the oxygen vacancy density and leakage current of Ta2O5 film both decrease with the increase of the O2/Ar ratio.The leakage current decreases after annealing treatment and it is minimized at 700℃.However,when the annealing temperature is 800℃ or higher,it increases slightly,which results from the partially crystallized Ta2O5 layer containing defects such as grain boundaries and vacancies.
The rapid thermal annealing （RTA） nano-crystallization method is widely used in the metal nanocrystal fabrication process. However, the high temperature （usually 600 900 ℃） in the RTA process will worsen the per- formance and reliability of devices. A novel method has been proposed to grow metal nanocrystal by synchronous in situ nano-crystallization of metal thin film （SINC）, which is able to resolve the problems mentioned above. Com- pared with Ni nanocrystals （NCs） formed by RTA, Ni NCs prepared by SINC can obtain more energy to crystallize, and its crystallization temperature is greatly reduced. A large memory window （2.78 V） was observed for Ni NCs deposited by SINC at 300 ℃. However, the largest window is only 1.26 V for Ni NCs formed by RTA at 600 ℃. A large change （from 0.20 to 4.59 V） of the memory window was observed while the operation voltage increased from 0 to 4-10 V, which is due to an occurrence of strong carrier trapping in Ni NCs. Flat-band voltage shift rapidly increases to its saturation value, which indicates that electron/hole trapping in Ni NCs mainly occurs at the initial stage of the program/erase process. A theoretical model was proposed to characterize the charging and discharging processes.
Large-scale In2O3 nanotowers with different cross sections were synthesized by a thermal evaporation and oxidation technique using metal as the catalyst. The morphologies and structural characterizations of In2O3 nanotowers are dependent on growth processes, such as different metal （Au, Ag or Sn） catalysts, the relative position of the substrate and evaporation source, growth temperature, gas flow rate, and growth time. In2O3 nanotowers cannot be observed using Sn as the catalyst, which indicates that metal liquid droplets play an important role in the initial stages of the growth of In2O3 nanotowers. The formation of an In2O3 nanotower is attributed to the competitive growth model between a lateral growth controlled by vapor-solid mechanism and an axial vaporliquid-solid growth mechanism mediated by metal liquid nanodroplets. The synthesized In2O3 nanostructures with novel tower-shaped morphology may have potential applications in optoelectronic devices and gas sensors.
