Ultra-low Thickness Titanium Nitride Thin Films for Spintronic Devices

TiN thin films were deposited using a pulsed laser deposition method in the thickness range of 9-45 nm. Temperature-dependent resistivity measurement showed a metal-to-insulator (MI) the transition of the TiN thin films below 15 nm. This value represents a critical thickness at which the properties of TiN films are strikingly different from the bulk TiN material. The thickness-dependent MI transition was free from structural phase transition and can be attributed to the localization of 3d¹ electrons in the valence band. This localization takes place due to the separation in the energy states larger than the gaps between the valence and conduction bands. The analysis of transport resistivity data demonstrated that the Arrhenius law governs the transport properties of TiN films in the 300-350 K range, while the transport properties are governed by a thickness-dependent variable range hopping mechanism below 300 K. Both metallic and semiconducting TiN films showed ferromagnetic behavior at room temperature. There was a marked correlation between coercivity (H_c) and saturation magnetization (M_s) with TiN film thickness. At room temperature, H_c increased from 66 to 134 Oe as the thickness decreased from 45 nm to 9 nm. The M_s at room temperature was also highest for the 9 nm sample (2.8 emu/g). The observed magnetic behavior of TiN films due to the localized 3d¹ electron. These electrons become more localized with the decrease in film thickness due to the size-dependent enhanced separation of energy states.