Impact of (111)-oriented TiN conductive layers for the growth of vanadium dioxide films and the effect of grain boundary diffusions

We report on advantage of (111)-oriented TiN conductive layers for realizing low temperature crystalline growth of vanadium dioxide (VO2) films with phase transition. Comparison between (111)-oriented TiN and random polycrystalline TiN layers was performed to clarify the effect of oriented TiN for succeeding VO2 growth. Oriented growth of VO2 (010) on (111)-oriented TiN suggests feasibility of most dense TiN (111) surface with pseudo-hexagonal lattice fitted against VO2 (010) surface with monoclinic angle β of 122°. Abrupt resistance change nearly three orders of magnitude was achieved in the films prepared at substrate temperatures of 250 ～ 300 °C. XPS depth profiles clearly showed abrupt interface between VO2 and TiN at deposition temperatures lower than 300 °C. On the other hand, it was found that (111)-oriented TiN layers enhance diffusions of Ti and O atoms through the grain boundaries, which act as direct path for diffusion at temperatures higher than 350 °C. Strictly unchanged composition of TiN layers confirms the superior property as anti-diffusion barrier material, however, grain boundaries arrangements are supposed to be crucial factors for the maintanance of layerd structure. Obtained results tell us the impact of (111)-oriented TiN layers not only for succeeding growth of VO2 films, but also for design of layerd device introducing TiN as electrodes.