Study On Low Resistance Electrodes Of Amorphous Ingazno Thin Flim Transistors

With the increasing requirements of large-size and high-resolution flat panel display?FPDs?,the realtively high resistance of the electrodes of thin film transistors?TFTs?is an important issue to be considered.On the other hand,amorphous InGaZnO?a-IGZO?TFTs have the potential for the applications in FPDs due to their high field-effect mobility,good large-area uniformity,high light transmittance and low temperature fabrication ability,etc.For a-IGZO TFTs mass production,there are still lots of problems to be solved,including the development of low-resistance electrodes for a-IGZO TFTs.In this study,we comprehensively investigated the sputtered low-resistance electrodes used for a-IGZO TFTs based on the experiments and theoretical analysis.Firstly,the exploration of the source and drain?S/D?electrodes of a-IGZO TFTs was conducted.In order to pick out the proper low-resistance electrode materials for the inverted staggered a-IGZO TFTs?Back Channel Etching structure,BCE?,we studed the sheet resistance and contact resistance of the sputtered metal films,such as Cu,Cu alloy?Cu-Mn,Cu-Mg,Cu-Al,Cu-Cr?and Ag.The contact between metal and semiconductor layer might lead to the formation of Schottky barrier,which could influence the contact characteristics.By testing the contact resistances of the a-IGZO TFTs prepard on the wafers and patterened with the shadow masks,we finally proposed the novel Ag/Mo electrodes with low resistance and good contact properties with a-IGZO to serve as the S/D electrodes of a-IGZO TFTs.Then,the process development on both the Ag gate and S/D electrodes of a-IGZO TFTs prepared by photolithography/wet-etching was employed.Ag diffusion was a serious problem to be solved if the Ag electrodes were adopted.The thin layer Mo,acting as the Ag diffusion stopping-layer,was deposited on both the bottom and the top of Ag films.Meanwhile,the thin-Mo could improve the adhesion with the glass substrate and the contact characteristics with a-IGZO layers.Accordingly,the novel Mo/Ag/Mo electrodes were deliberately designed,which possesed many advantages such as low resistance,good contact with a-IGZO,preventing Ag diffusion,easy wet etching,etc.Finally,we successfully fabricated the a-IGZO TFTs with sputtered Mo/Ag/Mo gate and S/D electrodes based on the aforementioned studies,with good performance parameters(V_th of 5.1V,?_FE of 2.42 cm²/V?s,subthreshold swing of 2.2 V/dec,and on-off current ratio of¹0⁶),proving that the sputtered Ag electrodes could be used in a-IGZO TFTs.We believe that the a-IGZO TFTs with high-conductive electrodes developed in this study could be used to drive the large-sized active-matrix FPDs.