Research On Key Technologies Of High Performance Thin Film Transistor

Thin film transistors?TFTs?are one of the critical devices for system on panel and three-dimensional monolithic integration.With the increasing demand of high performance and highly functional portable electronics,TFTs with higher performance are desperately needed to achieve these two advanced integration techniques.However,with the existence of defects in the channel and the requirements of low thermal budget and low cost,there are many challenges in fabricating high performance TFTs.Therefore,this thesis mainly investigates the state of art technologies of high-performance poly-Si anda-InGaZnO TFTs,aiming to make the TFTs meet the requirements of high-level applications.Firstly,in regards to the development of a channel material with high hole mobility,an excimer laser annealing process of poly-SiGe was investigated using a home-built green light laser annealing equipment.With careful design of the optics system,along with optimization of scan mode and laser parameters,the surface topography of the annealed film was significantly improved,and the hole mobility of the annealed film was increased 4.7 times as compared to the as-grown sample.Secondly,with respect to the device structure and manufacturing process,two types of preparation techniques were proposed for nanowire poly-Si TFTs.Using these methods,nanowire poly-Si TFTs can be easily fabricated without using advanced lithography equipment.A poly-Si nanowire TFT with a parallelogram-shaped nanowire channel was successfully demonstrated using the first method.Additionally,a high-?dielectric poly-Si Fin-type TFT formed with a fin-shaped nanowire,of which the height is 230 nm and the width is 22 nm,was fabricated using the second method.Owing to the high gate controllability of the 3D gate to the channel,the demonstrated nanowire TFTs exhibited excellent performance.In addition,the carrier scattering mechanism and positive temperature coefficient mobility of the poly-Si Fin-type TFT were investigated and explained by modeling the temperature-dependent mobility.Additionally,a new fluctuation analytic technique was proposed for the short-channel poly-Si TFT.By combining the location,inclination and rotation of grain boundary,the randomness of the grain boundary in the short channel poly-Si TFT was fully described.Based on the analytic technique,both the fluctuation property and mechanism of poly-Si planar TFT and Fin-type TFT were investigated in detail,and the suppression method of fluctuation was also discussed.Lastly,towards the development of new materials,the preparative processes ofa-InGaZnO TFTs with high-?dielectric were studied and optimized.By optimizing the temperature of Al₂O₃ deposition,a multifaceted influence of hydrogen?H?on the TFT stability was found.On one hand,H can passivate the interface traps and thus improve the stability of the device.On the other side,H can also act as a donor dopant in thea-InGaZnO,thus resulting in a reduction in threshold voltage under a positive gate bias.With a low thermal budget of 150?,a-InGaZnO TFTs with high performance and excellent stability were prepared both on glass with a smooth surface and Parylene flexible substrates with a rough surface.Finally,in terms of the application ofa-InGaZnO TFTs,different function modules such as invertor,charge trapping memory,and ultraviolet light detector were prepared using the optimizeda-InGaZnO TFTs fabrication process and exhibited excellent properties.These discoveries lay the foundation for the future application ofa-InGaZnO TFTs.