Solution-processed p-type copper oxide thin-film transistors fabricated by using a one-step vacuum annealing technique

Abstract

Copper oxide (Cu_xO) thin films were fabricated on SiO₂/Si substrates by using a solution process. The coated Cu_xO gel films were treated using a vacuum annealing method at various temperatures (400–700 °C). X-ray diffraction results indicated that the vacuum annealing technique was effective in transforming CuO into Cu₂O. Atomic force microscopy images showed that the mean grain size and the surface roughness of the resulting films increased with increasing annealing temperature. To verify the possibility of Cu_xO thin films as channel layers, the bottom gate structured thin film transistors (TFTs) were integrated. The electrical properties of the as-fabricated Cu_xO TFTs were improved with increasing processing temperature from 400 to 600 °C. The 600 °C-annealed Cu_xO TFT exhibited the best electrical performances, including a low threshold voltage of −3.2 V, a large field-effect mobility of 0.29 cm² V⁻¹ s⁻¹, a small subthreshold swing of 0.8 V dec⁻¹, and an on/off current ratio of 1.6 × 10⁴, respectively. However, with increasing annealing temperature, the electrical properties of the Cu_xO TFTs were degraded dramatically. These results suggest that solution-processed Cu_xO TFTs achieved by using a one-step vacuum annealing technique could potentially be used for high-performance p-type electronic devices, which represents a great step towards the further development of low-cost and all-oxide CMOS electronics.