The Fabrication And Performance Investigation Of ITO Thin Film Transistors

Thin film transistors as electronic switching device play an important role in the fields of sensors, flat panel display and integrated circuit. In recent years, because of their high transparency, compatibility with flexible substrates, good electrical properties, transparent oxide-based TFTs have become a hot shot. It is widely regarded that transparent oxide-based TFTs will replace traditional a-Si:H TFT and become the mainstream in the next few years.In this thesis, my research is about ITO TFTs. The advantages of ITO film are good light transmission, high carrier concentration(10²⁰¹0²¹cm^-3) , high carrier mobility（10³0cm²/Vs）, good physical and chemical stability. In addition, they can be deposited by a variety of methods. All the advantages of ITO film indicate that it suit for the channel materials for transparent TFT. However, large operating voltage is a weak point for traditional transparent TFT. In my work, we prepared ITO TFTs operating at 0.8V, and they have good light transmission.My thesis includes four parts. The first part gives the basic theory of TFTs, such as working mechanism, electrical theory and basic properties. In the second part, the preparing technology, performance testing methods of ITO TFTs are presented.In the third part, ITO TFTs with an operating voltage of 1.5V were fabracited at room temperature. These TFTs exhibit a good performance with a VTH of 0.32V, a large current on/off ratio of 1.2×10⁶, a field-effect mobility of 13.5cm²/Vs, and a low subthreshold swing of 130 mV/decade.In the fourth part, I prepared ITO TFTs with an operating voltage of 0.8V. The channel and source/drain electrode layers were deposited by one shadow mask, and the channel and source/drain electrode are prepared at the same time. In order to realize the low operating voltage, the SiO₂ gate dielectric was immersed in 43.5% LiCl aqueous solution, and a large number of ions enter the SiO₂ gate dielectric. Owing to an enhanced electric double layer in the interface between ITO channel/SiO₂, the devices show a large special capacitance of 9.2μF/cm². ITO TFTs gated by such ion-incorporated SiO₂ show a field-effect mobility of 28.4cm²/Vs, a current on/off ratio of 10⁷, a subthreshold swing of 98mV/decade.Good results of the experiment demonstrate that our preparing TFTs are suitable for low power consumption transparent electronic devices. However, the mechanism of the electric double layer and the stability of the TFT devices need more detailed reaserch.