Preparation, Property And Applications Of TiSi Nanowires/Titanium Silicide Thin Film

Titanium silicide has received great interests due to its low resistivity, high thermal and chemical stability as well as high compatibility with Si technology. One-dimentional nanostructures have been given great concerns since CNT was reported in 1991. Titanium silicide nanowires thus receive great developments in its preparation, properties and applications. In this paper, titanium silicide thin films and nanowires are prepared on glass and Si substrates with APCVD method by using SiH4 and TiCl4 as precursors of Si and Ti, respectively, and N2 as diluted gas and carrier gas. The field emission properties of the titanium silicide thin films and nanowires are investigated. The titanium silicide thin films and nanowires as-prepared are also used as electrode substrates for preparing dielectric thin films. The formation and the field emission property of the thin films and the nanowires as well as the applications for it being used as electrodes in dielectric thin films are investitated. The paper mainly focuses on the following aspects.1. Preparation and the electrical properties of the titanium silicide thin films at different deposition conditions. It shows that the Ti5Si3 crystalline phases with hexagonal structure are formed at lower SiH4/TiCl4 while TiSi2 crystalline phases with face-centered orthorhombic structure are formed at higher SiH4/TiCl4. Species of the phases as-prepared are independence on the others deposition conditions in these cases. However, species of the phases in the thin films can be adjusted by the others deposition conditions, such as the deposition temperature, with a moderate SiH4/TiCl4. A higher temperature favors the formation of the Ti5Si3 phases while a lower temperature favors the formation of the TiSi2 phases. The thermodynamics is critical in forming the phases.2. Formation of the TiSi nanowires with morphologies of nanowires, nanopins and rocket nanowires, on different thin films of the Ti5Si3, the TiSi2, and the mixture of them. It shows that the TiSi nanowires are formed due to its anisotropic growth of the TiSi crystal planes. The nucleation and growth of the nanowires depend not only on the deposition temperature, the concentration of the source gases, but also on the properties of the thin films underneath the nanowires. The higher the contents of the crystalline phase in the thin films, the easier the nucleation of the nanowires is. The formation of the nanowires depends seriously on the deposition conditions in the CVD process other than the substrates. The verticality of the nanowires to the substrate depends mainly on the properties of the thin films underbeneath.3. Field emission properties of the titanium silicide thin films and TiSi nanowires. Effects of the thicknesses, morphologies and the distribution of the nanowires as well as the species of the thin films on the field emission properties of the TiSi nanowires/titanium silicide thin films were investigated. It shows that the turn on voltage of the TiSi rocket nanowire with thin films underneath is as low as 2.33V/μm (when the current density larger than 10μA/cm2) and the current density is 917.43μA/cm2 as the electric field reaches 4.18V/μm. The lower the thickness of the nanowires is, the stronger the intensity of the electric field at the tip is. Intensity of the electric field at the tip of the nanopins is larger compared with that of normal nanowires and rocket nanowires. The bunch nanowires have the lower screening effect of the electric field and thus can get both lower turn on voltage and larger current density. The turn on voltage of the nanowires prepared on TiSi2 thin film is lower than that of Ti5Si3 thin film and the current density of the former is also larger than that the latter.4. Ti5Si3 thin films, TiSi nanowire/Ti5Si3 thin films and TiSi nanowire/Ti5Si3 and TiSi2 thin films were used as electrodes and substrates for preparing BT, BST and PST thin films by Sol-gel method and RF-sputtering method respectively. The dielectric properties of the BT, BST and PST thin films as-prepared were also investigated. It shows that the dielectric thin films formed on the titanium silicide thin films with nanowires have higher crystallinity, higher capacitance, low dielectric loss and lower dependence of the capacitance and dielectric loss on the frequency than that of ITO. Furthermore, the capacitance of the dielectric thin films formed on the titanium silicide thin films with nanowires is larger than that on titanium silicide thin films without nanowires. The capacitance of the dielectric thin films formed on the TiSi nanowire/Ti5Si3 and TiSi2 thin films is larger than that of Ti5Si3 thin films. Nonoxide titanium silicide gives the dielectric thin films prepared on the titanium silicide thin films the lower dependence of the dielectric properties on the frequency than that of ITO while the large surface area of the nanowires and large electric field around the nanowires give the higher capacitance and lower dependence of the dielectric properties on the frequency of the titanium silicide thin films with nanowires than the titanium silicide thin films without nanowires.