*David V. Tsu¹, Christian Linke², Matthias Muehle³, Joerg Winkler², Harald Köstenbauer^2
1Mackinac Technology Co., Grand Rapids, MI; ²Plansee SE, Reutte, Austria; ³Fraunhofer USA CCD, East Lansing, MI
To further improve the optical clarity of visual displays in electronic devices, it is essential to hide the metal conducting lines addressing display elements. This demands a material that can act as anti-reflective (AR) layers for metals like aluminum or copper. For this, MoO_x may be an ideal candidate. Since this oxide exists in both insulating-transparent (MoO₃) and conductive-reflective (MoO₂) phases, we prepare a range of oxide stoichiometries from MoO_x targets (x from 2.1 to 2.8) and sputter deposit thin films using pure Ar gas. By measuring the [R,T], we directly solve for the film’s [n,k] at each wavelength point measured, using non-linear numerical methods. Once we have the [n,k] of these MoO_x materials, we perform both (i) physical modeling the materials, and (ii) optical modeling of device performance. For (i), we find that MoO_x is an unusual material having two distinct optical bandgaps: the low energy band (LEB) accounts for the absorption in the VIS and NIR bands; and the high energy band (HEB) accounts for absorption in the UV region. As the carrier concentration grows, the E_g of both LEB and HEB decrease in energy. For (ii), we identify the stoichiometry having the optimal AR response over metals.