Preparation Of Metal Oxide Nanofibers And Their Application In Thin Film Transistors

Compared with 2D metal oxide film（2D-MO）,the one-dimensional metal oxide nanofibers（MONFs）,fabricated by electrospinning,have advantages of higher specific surface area,higher optical transmittance,unique electronic transmission characteristics,easy to dope and prepare,and better mechanical flexibility,etc.MONFs show a wide application prospect in the Thin Film Transistor（TFT）.Among many MONFs materials,In₂O₃ nanofibers have received a lot of research attention due to the excellent electrical properties.However,In₂O₃nanofibers also have severval disadvantages.Firstly,indium is a rare element with few reserves and high price;Secondly,In₂O₃ nanofibers have a mass of oxygen vacancies（V_O）with excessive carrier concentration,making In₂O₃ nanofibers TFT in depletion mode（D-mode）;Thirdly,under illumination,V_O tends to lose two electrons and transform into V_O²⁺excited states,resulting in illumination instability of In₂O₃ nanofibers TFT with serious threshold voltage shift.These problems seriously affect the practical application of In₂O₃ nanofibers-based TFT.Finally,In₂O₃-based nanofibers TFT needs to be calcined at high temperature to achieve ideal electrical properties,which limits the application of In₂O₃-based nanofibers in flexible and stretchable TFT.In this thesis,In₂O₃-based nanofibers TFT with E-mode and light stability were prepared by electrospinning combined with precursor solution adjusting and doping.Nitrate was used to reduce the calcination temperature of In₂O₃ nanofibers for producing flexible TFT.The strechable TFT was prepared by transfering In₂O₃ nanofibers from the rigid substrate with Ge O₂sacrificial layer to stretchable substrates.With the increasement of diameter of In₂O₃ nanofibers,the V_O increases and the electrical performance of In₂O₃ nanofibers TFT deteriorates.The diameter of In₂O₃ nanofibers can be controlled by adjusting the mass ratio of indium chloride and PVP in the precursor.With the decrease of indium chloride ratios,the diameter of the nanofiber gradually decreases.The In₂O₃nanofibers with minimum diameter（～50 nm）was obtained by the mass ratio of 0.1:1.The In₂O₃ nanofibers TFT with minimum diameter has good electrical properties and controllability,with the I_on/off ratio(I_on/I_off)of～10⁶ and carrier mobility(μ_FE)of 7.83 cm²/V·s.However,In₂O₃nanofibers with larger diameter show high conductivity and cannot be modulated.In addition,due to the zinc has low binding energy of oxygen atoms,and higher V_O formation energy than that of indium,it can be doped into In₂O₃ nanofibers with a large proportion.These properties can reduce the amount of indium and the formation of V_O effectively,improving its electrical properties.When the molar ratio of indium to zinc is 0.5:0.5,the In_0.5Zn_0.5O nanofiber TFT shows the best electrical performance withμ_FE of 4.64 cm²/V·s,I_on/I_off of～2.0×10⁷,threshold voltage(V_TH)of～0.17 V,and good bias stability.Because the Pr not only exhibits good V_O suppression performance but also acts as blue light down-conversion medium with a low charge transfer transition energy,the Pr doping can suppress the formation of V_O,keep the high mobility,enhance illumination and environmental stability of In₂O₃ nanofibers.When Pr doping concentration is 3 mol%,In Pr O nanofiber TFT has the best electrical performance,with theμ_FE of 6.92 cm²/V·s,I_on/I_offratio of～5.4×10⁷,and V_TH of 5.2 V.Moreover,with the doping of 5 mol%Pr,the as-prepared FETs exhibites a good illumination stability with the turn-on voltage shift of-7.7 V under NBIS,comparing to the In₂O₃nanofibers-based FETs of-17.5 V.In addition,the TFT has been successfully applied as a switch to bright the LED.The above In₂O₃-based nanofibers TFT needs to calcin at high temperature to achieve ideal electrical properties,which greatly limits its application in flexible TFT.To solve this problem,the chloride was replaced with nitrate in the precursor solution.The nitrate will release heat during thermal decomposition,which can assist in the decomposition of PVP,reducing the calcination temperature of the nanofibers.In the end,In Pr_3%O nanofibers with high quality can be prepared at 380℃,which makes In Pr_3%O nanofibers TFT achieve the best comprehensive electrical performance withμ_FE of 2.92 cm²/V·s.Subsequently,In Pr_3%O nanofibers flexible TFT was prepared on Al₂O₃/Al PI glass substrate.The electrical properties of the TFT did not change significantly at the bending radius of 50 mm,20 mm,and 5 mm.When the bending radius reaches 2 mm,the TFT will be destroyed.In addition,the electrical properties of the TFT remained stable after 1000 bending folds at a bending radius of 5 mm.It is proved that MONFs have application potential in the field of flexible electronics.However,the calcination temperature of 380℃is still far beyond the temperature which stretchable substrates can withstand,which limits the application of MONFs in intrinsic stretchable TFT.In order to solve this problem,In Pr O nanofibers were prepared on the heat resisting substrates with Ge O₂ sacrificial layer,and then transferred to stretchable substrates.Based on the sacrificial layer transfer printing method,the structure and preparation process of intrinsic stretchable TFT based on In Pr O nanofibers were designed.The preparation process and transfer effect of Ge O₂sacrificial layer on nanofibers,the performance matching of stretchable electrode and In Pr O nanofibers,and the performance matching of stretchable dielectric layer and In Pr O nanofibers were studied.Finally,the intrinsic stretchable TFT based on In Pr O nanofiber was prepared by integrating all functional layers together.In the original state,the I_on is～3.4×10^-6 A,with poor switching characteristics.When the strain reached 5%and recovered,the I_on decreased to～1.9×10^-6 A,and when the strain reached 10%and recovered,the I_on further decreased to 6.2×10^-7 A.It is proved that the method is feasible to prepare the intrinsically stretchable TFT.