Study On Materials And Processes For Source/drain Electrodes Of Amorphous Oxide Thin Flim Transistors

With the continuous development of flat panel display?FPDs?,the requirements on the performance of displays becomes higher and higher?e.g.larger size,higher resolution,shoter response time,etc?.On one hand,researchers find that a-IGZO TFTs have good performances?such as high field-effect mmobility,good large-area uniformity,flexible and low temperature fabrication ablility,etc?,which have the potential to be the core driving devices for FPDs.On the other hand,there still remain many problems to be solved for processes of a-IGZO TFTs,including the better choices of low-resistance electrodes and the improvements of the related processes.In this study,we comprehensively investigated the sputtered low-resistance electrodes used for a-IGZO TFTs based on detailed comparative experiments.We also studied and determined the best fabrication conditions and tried to explain what brought these changes by theoretical analysis.To test the performances of a-IGZO TFTs with Mo electrodes,we fabricated the Mo electrode films at various powers and measured their adhension properties,surface roughness and sheet resistances.The Mo electrodes showed good adhension properties to the substrates.With the sputtering power of Mo films increasing,their surface roughness increased and their resistivity decreased.Then,we prepared the a-IGZO TFTs with Mo electrodes on silicon substrates with shadow masks as well as on the glass substrates with photolithography/wet-etching.By extracting the related parameters,we found that although Mo eletrodes could be well used in a-IGZO TFTs,they were not the best choice for their high resistances.Next,we fabricated the Cu electrode films and the corresponding a-IGZO TFTs.It was found that Cu has poor adhension with substrates and could easily diffuse into the transportion layers.To solve these problems,we prepared the a-IGZO TFTs with Mo/Cu bilayer electrodes to achieve the complementary advantages of both metal films.The good electrical performance parameters were finally obtained(e.g.,V_th of 6.0 V,?_FE of8.33 cm²/V?s,subthreshold swing of 2.0 V/dec,and on-off current ratio of1.3×10⁷),which might meet the requirements from FPDs.This proved that the sputtered Mo/Cu electrodes could possibaly be used for the mass productions of a-IGZO TFTs.However,some problems may occur for the applicaitons of Mo/Cu electrodes due to the different etching rates of Mo and Cu.To find better canditates of low-resistance electrodes,we comparatievely studied the properties of Cu-Mn alloy films and Cu-Mg alloy films and their corresponding a-IGZO TFTs.Compared with those of Mo and Cu electrodes,he resistivity of Cu alloys was proved a median.With no enough improving studies,the devices with Cu alloy electrodes exhibited poorer properties than those with pure Cu electrodes.But,the testing results of single films proved that Cu-Mg might be better than Cu-Mn to be used as source/drain electrodes of a-IGZO TFTs because the former had better adhension properties to substrates.