Thickness Dependence of Cu-layer-based Transparent Heaters

Abstract

In this study, ultrathin (4-40 nm) Cu-layer-based transparent heaters prepared on glass substrates were investigated for cost-effective applications. The Cu heaters were embedded between ZnO layers serving as anti-reflection and anti-corrosion layers. The Cu layer thicknesses varied in the range of 4-40 nm, and the corresponding structural, electrical, optical and thermal properties were evaluated. Cu was found to follow the Volmer-Weber 3D growth mode in the early deposition stage, where isolated islands grow and coalesce to form a continuous layer at ~12 nm. In the thickness regime of discontinuous Cu layers, a significant increase in sheet resistance was observed due to the reduced current paths and the high severity of electron scattering at the Cu/ZnO interfaces. Because of light absorption associated with the localized surface plasmon resonance (LSPR) in the presence of pores in the films, visible transparency peaks near the thickness of the complete film-closure, beyond which stronger light absorption decreases transparency. The sheet resistance of the transparent heaters was modulated in the range of 0.8-96.2 Ω/sq. The heating characteristics well follow Joule’s law which predicts a higher temperature for a lower-resistance heater at a given voltage. The measured temperature-power relation is linear, from which the important heater parameter of convective heat transfer coefficient is extracted.