High transparent and stability indium praseodymium oxide thin-film transistors with tungsten doping by solution method

Abstract

Indium-oxide-based thin-film transistors are widely investigated and exhibit higher carrier mobility than amorphous silicon. Lanthanide-doped Indium oxide TFTs show relatively high negative bias illumination stress (NBIS) stability but at the cost of mobility. To improve the NBIS stability by the solution method, we doped Tungsten (W) into Praseodymium-doped Indium oxide (InPrO) and fabricated InPrWO TFT. We proposed that W doping could densify the films and suppress oxygen vacancy. With the increase of W doping concentration from 0 to 3 mol%, the contact angle of precursor solutions first decreased and then increased, reaching minimums of ∼13° at 1 mol%. When the W doping concentration increased from 0 to 1 mol%, the density of films increased from 6.155 to 6.479 g/cm3. While doping concentration increased from 1 to 3 mol%, the density of films decreased. Transmittance of InPrWO films was higher than 90 % from 300 to 800 nm. The localized defects of InPrWO films were investigated by μ-PCD. With 1 mol% W doping, deep-level and shallow-level defects were relatively the least. XPS result revealed that W was successfully doped into the films. Besides, the oxygen vacancy ratio first decreased and then increased when the W doping concentration increased. InPrWO film with 1 mol% W doping had the least oxygen vacancy ratio, resulting in the highest stability. The TFT fabricated with optimal 1 mol% W doped InPrWO film showed excellent electrical characteristics (μsat = 5.4 cm2/Vs, Vth = -0.3 V, Ion/Ioff = 8.0 × 105, and SS = 0.30 V/dec). With the W doping concentration increased, the NBIS stability first increased and then decreased, having minimum shift ΔVth = -2.1 V at 1 mol%. We improved the quality of films and NBIS stability of TFT by doping W into InPrO and appropriate post-processing, satisfying the development trend of high transparency and high stability TFTs for future displays.