Advancements in Metal Oxide Thin Film Quality in Solution-Processed High-κ Dielectrics for High-Performance Transistors

The present spotlight article addresses the challenges associated with metal oxide dielectric thin films deposited from liquid-phase precursors, which are often deemed inferior in thin film quality; suboptimal film quality adversely impacts the performance of electronic devices, particularly thin film transistors (TFTs). The traditional spin-casting method contributes to porous film masses due to the evaporation of solvent, and thermal annealing results in rough interfaces. Also, the presence of a high concentration of oxygen vacancies introduces traps, leading to hysteresis. To overcome these, the present article explores various film treatment methodologies, including Ar/O2 plasma treatment, the use of high-oxygen affinity dopants, and spray deposition of prepurified solution precursors. These treatments significantly improved film characteristics and TFT performance. Aluminum-doped zirconium oxide (ZAO) dielectrics treated with Ar/O2 plasma showed enhanced density (4.16 g/cm3). ZAO/amorphous indium gallium zinc oxide TFTs exhibited hysteresis-free characteristics with a field effect mobility (μ) of >15 cm2/V-s and an on:off (ION:IOFF) switching ratio of 108. Using purified precursors for depositing dielectric ZrOx, along with amorphous indium gallium zinc oxide, resulted in μ and ION:IOFF values exceeding 15 cm2/V-s and 109, respectively. Additionally, incorporating substitutional dopants such as hafnium in ZrOx improved TFT performance. TFTs composed of ZrOx and lanthanum zinc oxide demonstrated a μ of 22.2 cm2/V-s and ION:IOFF of 108. These performance parameters were observed across a variety of devices and demonstrated stability. These enhanced performance parameters are attributed to improved film quality, including reduced roughness and defect-traps, facilitating seamless electrical conduction at the interface.