Research On Preparation Process And Optimization Of P-type NiO_x-TFT Device

Nowadays,n-type oxide thin-film transistors（TFTs）have been able to meet the needs of flat panel display devices.However,more complex applications require complementary metal-oxide-semiconductor（CMOS）structures based on n-type and p-type semiconductors.The CMOS device composed of n-type and p-type thin-film transistors is the cornerstone of complex logic circuits.Unfortunately,p-type oxide semiconductors are unusually rare and performance（device mobility,etc.）lags far behind n-type materials,which severely restricts the development of oxide semiconductor CMOS devices.In recent years,NiO_x attracts extensive attention due to its excellent optical properties and chemical stability.It is a very promising p-type oxide semiconductor material.However,the research on p-type NiOx-TFT is still in a preliminary stage and needs further exploration.This dissertation systematically studies the p-type NiOx thin films and TFT devices.The main contents are of this thesis as follows:At first,we studied the effect of different annealing temperatures on NiO_x-TFT devices.The electrical performance of the device improves with the rise of annealing temperature and then falls.This is mainly due to the gradual elimination of organic residues（C-,N-and related components）in NiO_x films as the annealing temperature increases and so that improve carrier transport characteristics.As a result,device performance has been significantly improved.However,with the further increase of the annealing temperature,frequent scattering events are aggravated due to clustering of surface atoms.Besides,Ni²⁺vacancies are further reduced with the rise of annealing temperature.Both of that lead to poor device performance at high annealing temperature.The results show that 250°C is the optimum annealing temperature for NiO_x-TFT devices.Secondly,we investigated the effect of active layer thickness on NiO_x-TFT devices.We found that when the active layer thickness is too thin,the hole carriers are affected by the scattering of the back surface of the NiO_x thin film and the device cannot be turned on.When the thickness of the active layer is too large,the defect state increases sharply and increases the probability of hole carriers scattering and trapping during transport.Thirdly,in order to further improve the electrical properties of NiO_x-TFT devices,the effects of different source and drain electrodes and the role of MEA in precursor solutions were studied respectively.The results show that the choice of metal electrodes has a great impact on the performance of NiO_x-TFT devices.Besides,we also found that the incorporation of MEA in the precursor solution directly affects the hole carrier concentration of NiO_x thin film and device performance.NiO_x-TFT devices exhibit good electrical performance by optimizing experimental conditions:μ=0.48 cm²v^-1s^-1,S=1.22 V/Dec,V_th=11.8 V,I_on/off=1.7×10³.Finally,we use the high-k Al₂O₃ instead of the traditional SiO₂ as insulating layer.The NiO_x/Al₂O₃ TFT devices exhibit excellent electrical properties:μ=5.92 cm²v^-1s^-1,S=0.13V/Dec,V_th=-0.83 V,I_on/off=3.5×10⁶.Compared with NiO_x/SiO₂ TFT,the mobility of NiO_x/Al₂O₃ TFT increases by 10 times and the threshold voltage by 15 times.The excellent performance of NiO_x/Al₂O₃ TFT devices could be attributed to the large of Al₂O₃ dielectric and the low interface trap density between NiO_x and Al₂O₃.