Six-Fold Mobility Improvement for All-Solution-Processed Metal Oxide Thin Film Transistors Via a Controlled Humidity Annealing Process

Introducing moisture or water vapor into the annealing process has been proven to enhance the electrical performance of solution-processed metal oxide films. However, there remains a lack of understanding regarding the selection of appropriate pre- and post-annealing relative humidities (RHs). Here, a controlled humidity annealing process is presented to explore the impact of pre- and post-annealing RH on the electrical performance of solution-processed metal oxides. The results indicate that both high RH pre-annealing and high RH post-annealing favor the formation of metal-oxygen-metal bonding states and improve the crystallization of the metal oxide films, leading to an optimized electron percolation path for the indium oxide (In 2 O 3 ) semiconductor channel, decreased leakage current for the aluminum oxide (Al 2 O 3 ) dielectric, and reduced resistivity for the indium tin oxide (ITO) electrodes. All-solution-processed thin film transistors (TFTs) are fabricated utilizing In 2 O 3 as semiconducting channel layers, ITO as source/drain and gate electrodes, and Al 2 O 3 as gate dielectrics. A six-fold improvement in mobility is achieved when increasing the pre- and post-annealing RH from 10% to 70%, attributed to improved electron percolation path, reduced contact resistance, and fewer electron trap sites. Moreover, the TFTs demonstrate outstanding environmental and electrical stabilities and high reproducibility, as evidenced by the minimal threshold voltage shifts observed during stability tests and the small standard deviations of the device parameters.