Controllable doping and passivation of ZnO thin films by surface chemistry modification to design low-cost and high-performance thin film transistors

Solution-processed metal oxide thin-film transistors have become more popular as they can be used to fabricate transparent and flexible electronics at low cost. However, additional and complex processes for trap-site passivation and doping hinder the potential of the low-cost solution process. This study introduces a surface passivation process involving treatment with 3-aminopropyltriethoxysilane (APTES) that can enhance the electrical properties of ZnO sol–gel thin films. Optical, chemical, and structural analyses of ZnO sol–gel thin films revealed that their trap sites were passivated successfully through APTES treatment under basic conditions. Taking advantage of this process, high-mobility and negligible-hysteresis ZnO thin-film transistors were successfully fabricated, showing an I_on/I_off of 10⁵, hysteresis as low as 1.13 V, and mobility of up to 0.117 cm²/Vs. Furthermore, a characteristic transition of ZnO sol–gel thin films from semiconductive to semimetallic was observed during investigations with various APTES concentrations.