The role of copper in ZnO/Cu/ZnO thin films for flexible electronics

Abstract

ZnO/Cu/ZnO multilayer structures with very high conductivity have been obtained by magnetron sputtering. The Hall resistivity of the films was as low as 6.9×10−5 Ω-cm with a carrier concentration of 1.2×1022 cm−3 at the optimum copper layer thickness. The conduction mechanism has been explained in terms of metal to oxide carrier injection at low copper thickness and metal layer conduction at higher Cu thicknesses. The peak transmittance of the films is 88% and the photopic averaged transmittance is 75%. Optical transmission behavior of the films involves absorption by copper due to d-band to Fermi-surface transitions at short wavelengths and reflectance combined with scattering losses at long wavelengths. A Burstein–Moss shift in the band gap of the films is seen to take place with increase in thickness of the copper layer. The Haacke figure of merit has been calculated for the films with the best value being 8.7×10−3 Ω−1. Pole figure results reveal that the copper midlayer acts as a hindrance to (002) ZnO texturing rather than as a seed layer. These results also confirm the mechanism of conduction. The results of the study assume further significance because annealing at 150 °C for up to 24 h in a reducing (Ar+5% H2) ambient was found to have negligible effect on the properties of the films.

Indium-free Cu/fluorine doped ZnO composite transparent conductive electrodes with stretchable and flexible performance on poly(ethylene terephthalate) substrate

“…However, the increased mobility of thicker Cu layer sample is due to the discontinuous islands are becoming larger and distance between islands is becoming smaller with a result of weak scattering. For the Cu(12 nm)/FZO(250 nm) bilayer, the carrier concentration increases to the 10 22 cm −3 order, which suggests that the Cu layer becomes continuous [30].…”

“…The increase in carrier concentration can be understood by the carrier injection from Cu layer into FZO layer since the work function difference between Cu and FZO. Copper has a work function of ˚ ≈ 4.5 eV [30] and FZO has a work function of ˚ ≈ 4.85 eV [31], as shown in Fig. 7.…”

Transparent conductive Ga-doped ZnO/Cu multilayers prepared on polymer substrates at room temperature

“…Many researches about multilayer coatings on glass substrates have been reported [16][17][18][19][20]. However, reports about multilayer coatings on polymer substrates were very limited [21][22][23]. In this work, we used the polycarbonate (PC) as the polymer substrate, due to its superior optical properties over others [24].…”

Optimization of IGZO/Cu/IGZO Multilayers as Transparent Composite Electrode on Flexible Substrate by Room-temperature Sputtering and Post-Deposition Anneals

“…Singlecomponent TCOs such as zinc oxide [1][2][3] and tin oxide [4] have been studied extensively for the last few decades. Recently, there has been increasing interest in multi-component TCOs with multiple cation oxides such as indium tin oxide [5], indium zinc oxide [6], zinc tin oxide [7] etc. Among them, amorphous indium gallium zinc oxide (a-IGZO) has emerged as a promising candidate due to high-mobility (~10 cm 2 /Vs) and their prospective applications as channel layer materials in transparent thin film transistors (TTFT) in flexible electronics [8].…”