The Study Of Oxide Thin-Film Transistors And Novel Active-layer Materials

In the information age,displays are seeing an increasing tendency of complanation and are becoming more energy efficient.Thin film transistors are the most widely used technology in Flat Panel Display?FPD?,which at present is the most popular display technique.Amorphous silicon thin film transistors technique,current mainstream TFT technique,is unable to meet such current and future display technology requirements as ultra-high resolution,ultra-large size and solution processing.Comparatively,metal-oxide thin film transistors?MOTFTs?have better performance because of its high mobility,good uniformity,low process temperature and its compatibility with current amorphous silicon production lines.Therefore,MOTFTs are considered one of the most promising TFT technologies for the next generation display and attracts major attention from domestic and foreign academia and industry.The fast-growing flat panel display industry put forward higher requirements for oxide TFTs: higher mobility,better stability,and better solution processability.In order to develop higher-mobility and better-stability MOTFTs,this research mainly focuses on the exploitation of novel oxide active layer materials.In this research,a ternary In-Nd-O oxide system with Nd-doped In₂O₃ is developed and high-mobility InNdO TFTs are fabricated in order to deal with the low mobility of traditional InGaZnO oxide material? 10 cm²/Vs?.It was found that the incorporation of Nd atoms would effectively broaden the optical band gap,suppress the grain growth,and reduce the free carrier concentration.The InNdO-5 TFT shows a mobility of 46.7 cm²/Vs,an on-to-off current ratio of 3×10⁶ and a subthreshold swing of 0.23 V/decade.It is also found that when the concentration of Nd is too low,the electronic structure of |Nd3d_5/2⁵4f⁴O2p^-1> charge-transfer electron configuration is easy to be formed due to the lattice geometric constraints.The |Nd3d_5/2⁵4f⁴O2p^-1> charge-transfer electron configuration will generate holes and degrade the stability under negative-bias-stress.In order to improve the poor negative bias stability of InNdO TFT,a ternary In-La-O oxide material system with La-doped In₂O₃ is developed and the influence of La element doping and Nd element doping is compared.By contrast with Nd,the binding bond between La and oxygen is stronger,which is more favorable for regulating the carrier concentration in the film,and the La³⁺ ion radius is closer to the In³⁺ ion radius,which leads to less lattice mismatch defects.In addition,due to the difference between the 4f energy level positions of the La and Nd,the |La3d_5/2⁵4f¹O2p^–1> charge-transfer electron configuration is less likely to be formed in the InLaO system.Thus,the InLa O TFT shows both high mobility and high stability.InLa O-2 TFTs show a maximum mobility of 50.2 cm²/Vs,and the device exhibits excellent positive and negative bias stability.The devices show a turn-on voltage shift of 1.2 V under positive bias stress and-1.2 V under negative bias stress.In view of the In content scarcity issue,three kinds of SnO-based oxide system,Sn-Si-O,Sn-Zr-O and In-Sn-Ba-O,were developed.These three kinds of material systems show high acid etch resistance ability,which can effectively reduce the damage of the acid etching solution to the active layer during the patterning process of the source and drain in the BCE structure.We found out that Si and Zr elements can strongly bond with O and effectively curb the overhigh carrier concentration in SnO₂ films,and by adjusting the content of doped elements the performance of TFT devices will be effectively regulated.The SnSiO TFT,SnZrO TFT and InSn BaO TFT devices shows mobilities of more than 10 cm²/Vs by optimizing the performance of the device from the preparation of the active layer,substrate temperature,film thickness,doping concentration etc..This project provides a novel idea for the choice of In-free and low-cost active-layer materials.In order to reduce the production cost and meet the needs of future printing technique,a surface-selective deposition technique associated with ultraviolet irradiation that allows for the formation of metal oxide from aqueous precursor solution is proposed.Selective modification of the insulator layer surface is performed by being exposed to the UV light for a long time.The long-time exposed surface is wettable by the aqueous precursor solution likely due to the polar interaction between the surface and the solvent,while the unexposed region is unwettable.Since the mobility of the traditionally solution-processed MOTFT is very low,we used InNdO aqueous solution as a precursor and fabricated high-performance InNdO TFTs based on gel-like precursor.Similar to the InNdO material prepared by sputtering,the Nd element in the InNdO system prepared by the solution method can effectively suppress the crystallization of the film and regulate the carrier concentration in the film.When the doping concentration of Nd decreases from 10 at.% to 2 at.%,the mobility of InNdO TFT devices increases from 0.9 cm²/Vs to 15.6 cm²/Vs.The solution-processed InNdO-2 TFT shows a mobility of 15.6 cm²/Vs,a turn-on voltage of-3.6 V,a subthreshold swing of 0.34 V/decade and a threshold voltage shift of 1.2 V under positive bias stress.