deposition voltage, and 5 minutes deposition time. However, transmission values
higher than 80% just can be obtained for deposition time inferior to 2 minutes.
PVD MULTILAYER COATINGS WITH ELECTROCHROMIC BEHAVIOUR
Alcino João dos Santos Cunha Monteiro
Braga, 15 September 2004
ABSTRACT
The fossil and nuclear energy environmental impact and limited resources, in today’s would, made the use of alternative energy sources a fact of the most importance. The simple fact of coatings deposition in “smart windows” opens the possibility to increase energetic efficiency and comfort in a house. The importance of electrochromic thin films is due to its applications on optics devices. The electrochromic effect can be defined as a light transmission or reflection reversible modification in the result of a voltage application. Tungsten oxide is a very well study electrochromic material, and it can be deposited by magnetron sputtering. Structural, optical and electrical properties of coatings can be modulated as a consequence of deposition conditions, and techniques. The deposition and optimization of W, WO3 and ITO coatings is the main objective of this work. Vacuum atomistic deposition of PVD thin films gives the possibility to obtain dense (or porous) coatings, with a defects level control. Low pressure tungsten coatings deposited show high reflection and electrical conductivity values, ß-W crystallographic phase, and compressed stress. At medial deposition pressure (2Pa) the optical and electrical properties degraded, the mechanical stress is tensile, and the crystallography shows a mixture of W and ß-W phases. The accentuated degradation of optical and electrical properties, and the obtained of amorphous coatings, is a consequence of high pressure deposition conditions. Experimental results of tungsten oxide thin films give the possibility to conclude that coatings properties are dependent of a deficient oxygen phase (W20O58). It is possible to obtain transmission levels higher than 80%, for reactive gas concentration bigger than 30%. The deposition of tungsten oxide coatings on ITO/glass substrates gives the possibility to apply a bias polarization. The electrons bombardment of the growing thin film increase the crystalline phases. In the other hand, the ions bombardment takes us to the coating amorphous phases. Electrochromic tests give the possibility to observe the coloration effect of H+ ions insertion on the tungsten oxide layer. The ions intercalation reduces the transmission to 90% of the normal state. The bias polarization of the tungsten oxide layer, during sputtering deposition, result in the best color efficiency of the glass/ITOWO3 multilayer structure. The best commitment between optical and electrical properties of ITO coating was obtained for deposition with negative polarization (-60V), at a 0,06Pa pressure, 430 deposition voltage, and 5 minutes deposition time. However, transmission values higher than 80% just can be obtained for deposition time inferior to 2 minutes.
