Study On Metal Electrodes Of Amorphous Oxide Thin-film Transistors

Amorphous oxide semiconductor thin film transistors (AOS TFTs),especially amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) TFTs isexpected to drive next generation flat panel displays (FPDs) instead ofamorphous silicon (a-Si) TFTs. However, there are still lots of issuesremained to be solved for mass production of a-IGZO TFTs, including theissues about electrodes.For a-IGZO is very sensitive to most acid and alkaline solutions,adopting etching stopper seems necessary during mass production ofa-IGZO TFTs, which increases the cost greatly; on the other hand, theresistance of the electrodes of a-IGZO TFTs is another important issue tobe considered especially for large area panel. In this study, I discussed thetopic which is closely related to the issues mentioned above based onexperiments:(1) Study on source and drain (S/D) electrodes of a-IGZO TFTs formass production and corresponding process development of a-IGZO TFTs.In order to pick out proper electrode material, we study the wet etchingproperty of five metal films (Al, Cu, Ti, Ta and Cr) in various solutions atfirst. Wet etching rates of them in various solutions and correspondingetching selectivity to a-IGZO film were acquired. Then we produceda-IGZO TFTs without etching stopper (Back Channel Etching structure,BCE) by typical photolithography process based on the researchmentioned above successfully. And it shows relative good electrical andstability characteristics.(2) Study on silver gate and S/D electrodes of a-IGZO TFTs. FerricNitrate solution in the concentration of200g/L is the best choice foretching Ag electrode of a-IGZO TFTs in our study, which shows not only proper etching rate of Ag film but also good etching selectivity of Ag toa-IGZO film. Al2O3and TiO2films are picked out to be the buffer layermaterials of a-IGZO TFTs with wet-etched Ag electrodes for their goodadhesion property among five candidate materials. Further, Al2O3filmshows better transmittance but TiO2film shows even better adhesionproperty and higher deposition rate. Besides, adopting double layerstructure for gate insulator (GI) can decrease the plasma damage to Ag gateduring GI deposition effectively. At last, we produced a-IGZO TFTs (BCE)with wet-etched Ag gate and S/D electrodes based on the researchmentioned above successfully.