Homojunction solution-processed metal oxide thin-film transistors using passivation-induced channel definition

Area of Science:

• Materials Science
• Electronics Engineering
• Semiconductor Physics

Background:

• Solution-processed metal oxide thin-film transistors (TFTs) offer potential for low-cost, large-area electronics.
• Developing simple and effective methods for channel passivation and device definition is crucial for improving TFT performance and stability.

Purpose of the Study:

• To develop a photoresist-free method for channel passivation and physical definition of aluminum oxide (AlOx) and indium oxide (InOx) thin-film transistors (TFTs).
• To investigate the effects of aluminum diffusion on the electrical properties of indium oxide channels.
• To fabricate and characterize a coplanar homojunction-structured metal oxide TFT using the novel passivation-induced channel-defining (PCD) method.

Main Methods:

• A photoresist-free ultraviolet (UV) patterning process was employed to define indium oxide (InOx) source/drain regions and an aluminum oxide (AlOx) passivation layer.
• Thermal annealing was used to induce diffusion of Al from the AlOx layer into the InOx channel.
• The electrical characteristics of the fabricated TFTs were measured, including field-effect mobility, threshold voltage, subthreshold swing, and on/off current ratio.

Main Results:

• The developed PCD method successfully defined both the InOx source/drain and AlOx passivation layers without photoresist.
• Aluminum diffusion into the InOx thin film during annealing resulted in a low-resistivity electrode and a low carrier concentration channel.
• The diffused Al acted as a carrier suppressor, reducing oxygen vacancies in the InOx thin film.
• The fabricated PCD TFT exhibited a field-effect mobility of 0.02 cm²/V·s, a threshold voltage of -1.88 V, a subthreshold swing of 0.73 V/decade, and an on/off current ratio of 2.75 × 10⁶.

Conclusions:

• The passivation-induced channel-defining (PCD) method provides a simple and effective approach for fabricating coplanar homojunction-structured metal oxide TFTs.
• The AlOx/InOx bilayer system and the PCD method enable precise control over channel properties, leading to improved TFT performance.
• This technique holds promise for the development of advanced solution-processed oxide electronics.