Effect of organic-buffer-layer on electrical property and environmental reliability of Ga-doped ZnO films prepared by RF plasma assisted DC magnetron sputtering on plastic substrate

Ga-doped ZnO (GZO) transparent conductive films have been prepared by RF plasma assisted DC magnetron sputtering under a reductive atmosphere on organic-buffer-layer (OBL) coated polyethylene telephthalate (PET) substrates without intentionally heating substrates. Electrical and optical properties, crystallinity, and environmental reliability of the GZO films have been investigated. The distributional characteristic of resistivity is observed in the GZO film deposited on the OBL-coated PET substrates. The high resistivity at facing the erosion area in the source target is reduced by providing the RF plasma and H₂ gas near the substrate, resulting in a uniform distribution of the sheet resistance. It has been also found that the increase of resistivity by an accelerated aging test performed under a storage condition at 60 °C and at a relative humidity of 95% is suppressed by employing the OBL. The OBL suppresses the formation of cracks, which are induced by the aging test. These facts are thought to contribute to a high environmental reliability of GZO films on PET substrates. Values of resistivity, Hall mobility and carrier concentration are obtained: 5.0-20 × 10⁻³ Ω cm, 4.0 cm²/Vs, and 3.8 × 10²⁰ cm⁻³, respectively. An average transmittance of the GZO film including OBL and PET substrate is 78% in a visible region. The OBL enables to realize the practical use of GZO films on PET sheets.