| Recently,transparent semiconducting metal oxide thin-film transistors(TFTs)have been widely attracted by research academia and industry due to the their excellent electrical and optical characteristics such as high field-effect mobility(?FE)and high optical transparency for potential application in the next generation flat panel displays(FPDs).Although the performance of oxide TFTs have been obtained a certain degree of improvement,the stability of oxide TFTs under gate bias,light illumination,temperature stress are still not satisfactory for application in FPDs.In this case,a significant improvements on electrical performance and stability of oxide TFTs should be achieved before they can be widely applied in high resolution FPDs.In this thesis,we have explored on the mechanism of hydrogen(H)doped effects on ZnO-based oxide and H incorporation influence of the electrical performance and stability of ZnO-based oxide TFTs.Therefore,to take the advantage of the hydrogen could act as a defect passivator and a shallow n-type donor in ZnO thin films,the high performance and good stability of ZnO-based oxide TFTs have achieved through using the rational design of bilayer structure and N/H codoping methods.We have demonstrated that the design of bilayer structure TFTs and N/H codoping method have opened up new pathways to the development of high performance,good reliability,and low-cost oxide TFTs.The main research results of this thesis are summarized as follows:Firstly,we have demonstrated a rational design of TFT,which is composed of poly-crystalline Zn0:H/ZnO bilayer structure without using other metal elements for doping.The ?FE and stability of the bilayer structured devices have been improved.In this device structure,the hydrogenated ultra-thin Zn0:H layer(-3 nm)could provide suitable carrier concentration(Ne)and decrease the interface trap density(Dit),while thick pure ZnO layer could control channel conductance.Based on this novel structure,a ?FE of 42.6 cm2/V s,a high on/off current ratio(Ion/Ioff)of 108,desirable threshold voltage(Vth)of 1.8 V and a small subthreshold swing(SS)of 0.13 V/decade have been achieved.Additionally,the bias stress stability of the bilayer structured devices is enhanced compared to that of the single channel layer ZnO TFTs.Secondly,we have investigated the electrical performance and reliability of bilayer a-IGZO:H/IGZO TFTs.The jUFE and bias stress stability of the a-IGZO device were improved by inserting of the a-IGZO:H ultrathin layer(?4 nm)compared to the pure a-IGZO single channel layer device.As a consequence,a ?FE of 55.3 cm2/Vs,a highIon/off of 108,Vth of 0.7 V and a small SSof 0.18 V/decade has been achieved.The X-ray photoelectron spectroscopy(XPS)and low-frequency noise(LFN)analysis suggest that these desirable properties should be attributed to the a-IGZO:H layer,which could provide suitable Ne and reduce the average trap density(Nit)at the channel and insulator layer interface.Meanwhile,the Vth,off current and channel conductance of the bilayer device are controlled by thick a-IGZO layer through formation barrier energy for electron transport at the interface of a-IGZO:H and a-IGZO layer.Lastly,we have investigated the effects of nitrogen and hydrogen(N/H)codoping on the electrical performance and reliability of a-IGZO TFTs.The performance and stability of a-IGZO device were improved by N/H plasma treatment with a ?FE of 45.3 cm2/Vs and small shifts of Vth under gate bias stress.On the basis of XPS analysis,the improved electrical performances of a-IGZO TFTs should be attributed to the N/H codoping,which not only could control the Vth and Ne efficiently,but also passivate the oxygen vacancy defects due to the formation of stable Zn-N and N-H bonds.Meanwhile,LFN analysis indicates that the Nit near at the a-IGZO/Si02 interface reduced by the N/H plasma treatment.Overall,these high performance and good reliability of Zn0-based oxide TFTs have a great potential applications in high resolution FPDs. |
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