Study On Passivation Materials And Fabrication Process Of Amorphous Indium-Gallium-Zinc-Oxide Thin-Film Transistors

In recent years, Amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) thin film transistors (TFTs) have attracted great attention for high mobility, low temperature fabrication, good uniformity and high transparency, however there still are some factors, like fabrication process and device stability principle, need to be further studied. In this work, we researched the effect of passivation material and fabrication process on the performance and stability of a-IGZO TFT by combing experiment and theory, and the results can be references for the application of a-IGZO TFT.In this paper, common used SiO2was used as reference. Besides, we selected another five materials (TiO2、Ta2O5、Al2O3、Y2O3and ZrO2) as passivation, and single films were deposited by RF sputtering on the glasses. To study the characteristics of the single films, we measured the deposition rate, crystal structure, surface morphology, transmittance and so on. The results show that Ta2Os and SiO2have fast deposition rate, while Al2O3is the smallest one; all films were still amorphous after high temperature annealing; Al2O3and TiO2possess small surface roughness; TiO2has a low transmittance of ultraviolet, which is useful to the light stability of a-IGZO TFT. From the results of deposition rate and surface morphology, we found that low deposition rate may lead to smooth surface, and dense structure which is good for a-IGZO TFT as passivation.On the basic study of single films, we introduced the materials into the a-IGZO TFT and did a lot of performance and stability tests. We found that passivation with low deposition rate and small surface roughness show better performance, like Al2O3and TiO2; The others (SiO2、Ta2Os、Y2O3and ZrO2) were inferior. By analysising the results, the plasma damage during passivation deposition,which can be partly reflected by the deposition rate and surface roughness, was responsible for that.At last, we compared the stability of a-IGZO TFTs passivated by Al2O3and TiO2. The results show that Al2O3passivation can provide good bias-stress stability, but inferior environment and light stability, while TiO2exhibits excellent stability under all above conditions except for PBS test. According to our experiment, the PBS instability of TiO2passivated a-IGZO TFT is caused by the interface between TiO2and a-IGZO, and is eliminated by adding a SiO2-middle-layer. However, SiO2middle-layer can make Vth of the TFT negatively shifted, so new middle-layer material and proper process need to be studied.