TCO(Transparent Conducting Oxide)/metal/TCO multi-layer structures have emerged as an interesting alternative because they provide optical and electrical characteristics globally superior to those attainable with a single-layer TCO or metal electrode and can be deposited at low temperatures. Actually, ITO(Indium Tin Oxide)/Ag/ITO structures have allowed the achievement of sheet resistances below 5Ω/sq. and a visible transmittance above 85% with overall thicknesses below 100 nm. Whereas more than 400 nm thickness would be required for single-layer ITO electrodes with 2×10-4Ωcm to obtain the same sheet resistance.
Normally, Ag has been used as the metal layer of TCO/metal/TCO because of its high conductivity and extinction coefficient in visible region. But it is reported that the transparent conductive multi-layer with Ag layer has a severe problem of durability. In particular, the degradation is accelerated by moisture and high temperature. Especially the white dots are appeared on the Ag layer under the heat due to the agglomeration of Ag atoms and also the corrosion of Ag films occurs in a humid environment. One of possible ways to adverse the degradation of Ag layer is to insert the oxidation barrier between TCO and Ag metal layer to minimize the interfacial reaction.
In the present study, the Si3N4/SnZnO/AZO/Ag/Ti/ITO multi-layer film shows sheet resistance of 6.95 ohm/sq. and average transmittance of 87% in the visible range. AFM(Atomic Force Microscope) image suggests that Ti layer plays an important role in reducing the surface roughness and morphology change. With increasing annealing temperature, the sheet resistance of multi-layer films of Si3N4/SnZnO/AZO/Ag/ITO, without Ti layer suddenly increased around 300 oC. On the other hand, a multi-layer films with Ti buffer layer show good thermal stability up to 400 oC, showing higher electrical properties as compared with multi-layer films without Ti layer at 300 oC.