Electrochromic tunable filters based on nanotubes with viologen incorporation

Electrochromic devices offer a wide potential in microoptics applications owing to their compact set-up, low power consumption, and small control voltage. However, the need to use TiO2 nanoparticle layers (NPL) as efficient electrode material still prevents the development of microstructured optical filters like a tunable optical iris. Here we suggest to replace the TiO2 NPL by a nanotube TiO2 electrode obtained by electrochemical anodization of thin microstructured titanium layers. This renders the complete fabrication route of electrochromic filter devices on base of MEMS compatible processes possible. Process control will be addressed as critical issue because extended anodization may cause the delamination of the TiO2 nanotube film. For the chemisorption of electrochromic viologen molecules a temper process is necessary to turn the nanotube film into the anatase phase. Finally, a fully functional disc shaped tunable intensity filter is presented that relies on the viologen functionalized titania nanotube electrode.