We investigated the effects of bias stress on a passivation-free InZnO thin-film transistors ͑a-IZO TFTs͒ exposed to either the atmosphere or a vacuum. The magnitude of threshold voltage shift increased with the application duration of bias stress, to an extent that was much larger in the atmosphere than in the vacuum. The threshold voltage recovered slowly to its nearly initial value when the gate bias stress was removed. The electrical metastability was attributed to the interaction between the exposed a-IZO backchannel and oxygen/moisture from the atmosphere, and a dynamic equilibrium was finally achieved, regardless of the polarity of stress voltage.

No abstract

This work presents the electrical characteristics of the nitrogenated amorphous InGaZnO thin film transistor (a-IGZO:N TFT). The a-IGZO:N film acting as a channel layer of a thin film transistor (TFT) device was prepared by dc reactive sputter with a nitrogen and argon gas mixture at room temperature. Experimental results show that the in situ nitrogen incorporation to IGZO film can properly adjust the threshold voltage and enhance the ambient stability of a TFT device. Furthermore, the a-IGZO:N TFT has a 44% increase in the carrier mobility and electrical reliability and uniformity also progress obviously while comparing with those not implementing a nitrogen doping process.

Ambipolar thin film transistors ͑TFTs͒ with InGaZnO/pentacene heterostructure channels are demonstrated for a high-voltage-gain complementary metal oxide semiconductor ͑CMOS͒ inverter. The ambipolar TFT exhibits a electron mobility of 23.8 cm 2 / V s and hole mobility of 0.15 cm 2 / V s for the InGaZnO and pentacene, respectively. The thermal annealing process was also studied to adjust electron concentration reducing operating voltage of the CMOS inverter. The voltage gain achieves as high as 60 obtained in the first and third quadrants of the voltage transfer characteristic. The high performance and simple manufacture of the heterostructure CMOS inverter show promise as critical components in various electrical applications.

The role of oxygen in amorphous InGaZnO thin film transistor (a-IGZO TFT) is studied for the device ambient stability. The threshold voltage (Vth) value of 350 • C annealed a-IGZO TFT decreased apparently with the staying duration, and the average value shifted from 10.2 V to 5.8 V after a 9-day staying at the atmosphere. After raising the annealing temperature to 450 • C, the electrical stability issue was improved significantly with superior electrical parameters, including low threshold voltage (V th), low subthreshold swing, high carrier mobility and a small V th variation of ±0.5 V. It can be attributed to the enhancement of bonding energy of oxygen in the thermally-annealed a-IGZO film with the increase of thermal annealing temperatures. Besides, the stronger oxygen bonding could also suppress the absorption/desorption and UV-induced migration at the back surface, causing better electrical reliability and immunity against UV radiation, respectively. All these results showed the ambient stability is greatly related to the oxygen in a-IGZO film, and the desired electrical characteristic can be achieved via the optimization of thermal annealing process.