Junctionless Structure Indium-Tin Oxide Thin-Film Transistors Enabling Enhanced Mechanical and Contact Stability

In recent years, considerable attention has focused on high-performance and flexible crystalline metal oxide thin-film transistors (TFTs). However, achieving both high performance and flexibility in semiconductor devices is challenging due to the inherently conductive and brittle nature of crystalline metal oxide. In this study, we propose a facile way to overcome this limitation by employing a junctionless (JL) TFT structure via oxygen plasma treatment of the crystalline indium-tin oxide (ITO) films. The oxygen plasma treatment significantly reduced oxygen vacancies in the ITO films, contributing to the significant reduction in the carrier concentration from 4.67 × 10²⁰ to 1.39 × 10¹⁶. Importantly, this reduction was achieved without inducing any noticeable structural changes in the ITO, enabling the successful realization of ITO JL TFTs with an adjustable threshold voltage. Furthermore, the ITO JL TFTs demonstrate good stability and reliability under various bias stress conditions, aging in the air atmosphere, and high-temperature processes. In addition, the ITO JL TFTs exhibit low light sensitivity due to the wide bandgap of ITO and further suppression of Vo defects, making them suitable for applications requiring stable performance under light exposure. To compare and analyze the flexibility of the JL structure and conventional structure with additional source/drain (S/D) junction in ITO TFTs with nonencapsulation, we utilized mechanical simulations and transmission line method (TLM). By employing the JL structure in ITO TFT through carefully optimized oxygen plasma treatment, we successfully mitigated stress concentration at the S/D-channel interface. This resulted in a JL ITO TFT that exhibited a change in contact resistance of less than 20% even after 20,000 bending cycles. Consequently, a stable and flexible ITO TFT with field-effect mobility (μ_FE) of 12.74 cm²/(V s) was realized, outperforming conventionally structured ITO TFTs with additional S/D junction, where the contact resistance nearly tripled.