Among many commercial applications using TCO material, touch screens in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their cost effectiveness. However, when the touch sensor panel in touch screens composed with TCO and adhesive is used in a bright environment, the light reflected from interfaces can give rise to the appearance of fringes on the touch sensor panel, which can be visually distracting. It was already known that the presence of an index matching layer can reduce the amount of reflection between the adhesive-ITO interface.
In this study, a hybrid structure of SnO2/Ag/SnO2 film with SiO2 and Nb2O5 layer has been designed. SiO2 (n = 1.46) and Nb2O5 (n = 2.34) with low and high refractive indices, which have been the most successful application in electronic industry as electrical contact, were selected as index matching materials. SnO2/Ag/Nb2O5/SiO2/SnO2 and SnO2/Ag/SnO2/SiO2/Nb2O5 multi-layered thin films were initially designed and deposited on glass substrate by RF/DC magnetron sputtering system. In order to estimate and compare with the experimental results, the simulation program, EMP (Essential Macleod Program) was adopted. EMP results suggested that the multi-layered thin film of SnO2(45nm)/Ag(10nm) /Nb2O5(10nm)/SiO2(10nm)/SnO2(30nm), SnO2(40nm)/Ag(10nm)/SnO2(30nm)/ SiO2(10nm)/Nb2O5(10nm) exhibited high transmittance of 89.7 and 90.1 % at 550 nm, whereas the experimentally measured transmittance showed 85.8 and 85.1 %, somewhat lower than simulation data, respectively.
The lowest Rs and ρ value were about 5.81Ω/sq, 3.21Ω/sq and 5.81×10-5Ω·cm, 3.21×10-5Ω·cm, acquired at the multi-layers with the structure of SnO2(45nm)/Ag(10nm)/Nb2O5(10nm)/SiO2(10nm)/SnO2(30nm) and SnO2(40n m)/Ag(10nm)/SnO2(30nm)/SiO2(10nm)/Nb2O5(10nm).
Reflectivities of SnO2(45nm)/Ag(10nm)/Nb2O5(10nm)/SiO2(10nm)/SnO2(30n m) and SnO2(40nm)/Ag(10nm)/SnO2(30nm)/SiO2(10nm)/Nb2O5(10nm) multi layer film at 550 nm of visible range, were 10.6% and 10.6% measured on the top of multi-layer film stackup, respectively. However, reflectivities with IM layer only were 11.3% and 11.3%, suggesting that reflectivity variation was approximately within 1%. From the L*a*b* colour space represented by reflectivity spectra, it was found that the lightness (+L*) decreased from 91.5 to 89,9 and 91.2 to 89.4, whereas the yellowness (+b*) increased from 1.24 to 1.97 and 0.77 to 1.47, with increasing SnO2 top layer thickness in multi-layer film.
The obtained results show that SnO2/Ag/SnO2 multilayer films with Nb2O5 and SiO2 index matching layers can be possibly used as transparent multilayer electrode for display applications.