Reliability Of Elevated-Metal Metal-Oxide(EMMO) Transistors Under Positive Gate Bias And Illumination Stress

In recent years,thin-film transistors(TFTs)with amorphous indium gallium zinc oxide(a-IGZO)as the active layer have attracted much attention due to their superior characteristics.Elevated-metal metal-oxide(EMMO)TFT is one kind of a-IGZO TFTs,where the conductive source/drain regions and the intrinsic channel region are formed by oxygen annealing.In this study,instabilities of EMMO TFT under both positive gate stress(PBS)and positive gate illumination stress(PBIS)are investigated for different stress gate biases(VG),temperatures(T)and light intensities(?)systematically.The degradation behaviors and mechanisms are investigated and analyzed,and a unified degradation model of PBS and PBIS is proposed.Firstly,we study the degradation of EMMO TFT under PBS.It's found that the degradation behavior of PBS is different from that of traditional a-IGZO TFT,namely continuous negative Vth shift(?Vth)and on-state current(Ion)increase occur here.In addition,there is a much larger negative Von shift than that of Vth,so that a hump in the subthreshold region appearsSecondly,the degradation of EMMO TFT under PBIS is investigated.It is found that degradation is similar to that under PBS.One notes that the stress time,VG and T dependencies are almost the same in both kinds of degradation under PBS and PBIS degradation.In addition,their recovery processes show a great similarity.It strongly suggests that there should be some intrinsic correlation between the NBS and NBIS degradation and underlying mechanisms should be unified.Lastly,a unified model is proposed to explain the PBS and PBIS instabilites of EMMO TFT.In this model,the accumulation of ionized oxygen vacancy(VO2+)at the channel/passivation layer respectively are responsible for the negative Vth shift.