The reflectivity and colour variation in SnO2/Ag/SnO2/SiO2/Nb2O5 multi layer films on glass substrate were investigated with respect to the top layer SnO2 thickness and IM (Index matching layer) layer. Initially SnO2/Ag/SnO2/SiO2/Nb2O5 multi layer films on glass substrate were deposited at room temperature by RF/DC magnetron sputtering method. EMP simulation results suggested that the multilayered thin film of SnO2 (40 nm)/Ag (10 nm)/SnO2 (30 nm)/SiO2 (10 nm)/Nb2O5 (10 nm) exhibited the highest visible transmittance of 90.1% at 550 nm, whereas experimentally measured transmittance showed 85.1%, somewhat lower than simulation data. Reflectivities of SnO2 (40 nm)/Ag (10 nm)/SnO2 (30 nm)/SiO2 (10 nm)/Nb2O5 (10 nm) multi layer film at 450 nm and 550 nm of visible range, were 10.4% and 10.6% measured on the top of multi-layer film stackup, respectively. However, reflectivities with IM layer only were 10.8% and 12.4%, suggesting that reflectivity variation was approximately within 2%. From the L*a*b* colour space represented by reflectivity spectra, it was found that the lightness (+ L*) decreased from 91.2 to 89.4, whereas the yellowness (+ b*) increased from 0.77 to 1.47, with increasing SnO2 top layer thickness in multi-layer film.

Keywords: TMT structure, Reflectivity, Index matching layer, L*a*b* colour space.