Abstract
Indium tin oxide (ITO) thin films are widely used as transparent electrodes in electronic devices. Many of those electronic devices are heat sensitive, thus their manufacturing process steps should not exceed 100 °C. Manufacturing competitive high-quality ITO films at low temperature at industrial scale is still a challenge. Magnetron sputtering technology is the most suitable technology fulfilling those requirements. However, ITO layer properties and the reproducibility of the process are extremely sensitive to process parameters. Here, morphological, structural, electrical, and optical characterization of the ITO layers deposited at low temperature has been successfully correlated to magnetron sputtering process parameters. It has been demonstrated that the oxygen flow controls and influences layer properties. For oxygen flow between 3–4 sccm, high quality crystalline layers were obtained with excellent optoelectronic properties (resistivity <8 × 10−4 Ω·cm and visible transmittance >80%). The optimized conditions were applied to successfully manufacture transparent ITO heaters on large area glass and polymeric components. When a low supply voltage (8 V) was applied to transparent heaters (THs), de-icing of the surface was produced in less than 2 min, showing uniform thermal distribution. In addition, both THs (glass and polycarbonate) showed a great stability when exposed to saline solution.
Highlights
Transparent conductive oxides (TCOs) have attracted wide interest due to their high optical transmittance in the visible wavelength region combined with high electrical conductivity
Many studies reporting on Indium tin oxide (ITO) deposited by DC magnetron sputtering have shown that ITO thin films could reach high transparency in the visual region (90%) and high conduction properties (ρ = 2 × 10−4 Ω·cm)
The microstructure of the material is strongly dependent on the oxygen flow, changing from amorphous to crystalline ITO layers with very small variation of oxygen amount on the gas mixture
Summary
Transparent conductive oxides (TCOs) have attracted wide interest due to their high optical transmittance in the visible wavelength region combined with high electrical conductivity Due to these properties, they are extensively used as low emissivity layers in architectural glass or as transparent electrodes in multiple devices such as flat panel displays, electrochromic devices, photovoltaic cells, and organic light emitting diodes [1,2], or more recently, in microwave and radio frequency shielding devices [3]. Contemporary car windshields are laminated with polyvinyl butyral (PVB) polymeric foils containing tungsten microwires as heating element. The headlight housings have vent holes with filters to recirculate air and avoid condensation, of which the number and position must be frequently modified after headlight manufacturing to optimize air recirculation, in a difficult and expensive process [5] This has become a challenging issue from a visibility and a safety standpoint for many original equipment manufacturers (OEMs). TCO coatings can improve the performance of conventional heating elements, in terms of demonstrating a high heating power capacity with fast control of temperature and small thermal inertia without detriment to their optical transmission [6]
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