Ferroelectric HfO2-based thin films, which can exhibit ferroelectric properties down to sub-10 nm thicknesses, are a promising candidate for emerging high density memory technologies. As the ferroelectric thickness continues to shrink, the electrode-ferroelectric interface properties play an increasingly important role. We investigate the TaN interface properties on 10 nm thick Si-doped HfO2 thin films fabricated in a TaN metal-ferroelectric-metal stack which exhibit highly asymmetric ferroelectric characteristics. To understand the asymmetric behavior of the ferroelectric characteristics of the Si-doped HfO2 thin films, the chemical interface properties of sputtered TaN bottom and top electrodes are probed with x-ray photoelectron spectroscopy. Ta-O bonds at the bottom electrode interface and a significant presence of Hf-N bonds at both electrode interfaces are identified. It is shown that the chemical heterogeneity of the bottom and top electrode interfaces gives rise to an internal electric field, which causes the as-grown ferroelectric domains to preferentially polarize to screen positively charged oxygen vacancies aggregated at the oxidized bottom electrode interface. Electric field cycling is shown to reduce the internal electric field with a concomitant increase in remanent polarization and decrease in relative permittivity. Through an analysis of pulsed transient switching currents, back-switching is observed in Si-doped HfO2 thin films with pinched hysteresis loops and is shown to be influenced by the internal electric field.
We have investigated the adsorption of dodecanethiol on zinc- and oxygen-terminated ZnO surfaces. Strong enthalpic adsorption is demonstrated by the stability of sulfur on both ZnO surfaces for temperatures up to 400°C. The minimal presence of the S 2p3∕2 170eV peak suggests absorption of the sulfur as an unoxidized thiol. The results indicate a higher surface coverage of the thiol on the zinc-terminated surface. Evidence from reflection high energy electron diffraction measurements for the surface ordering after thiol treatment of the oxygen-terminated ZnO surface suggests that the dodecanethiol molecules can adsorb in a highly ordered manner. These results further open the possibility for biofunctionalization of ZnO for biosensing applications.
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