Back-channel Surface Decoration In A-IGZO TFTs And The Investigations On The Device Characteristics

Amorphous indium-gallium-zinc-oxide thin film transistor?a-IGZO TFT?,owing to its high electron mobility?mFE?,low deposition temperature,steep subthreshold swing?S.S?and high on/off current ratio?Ion/off ratio?,has received extensive attention and been gradually used in display panels.A-IGZO TFT also shows great potential applications in logic circuits and photodetectors.In this paper,different materials were adopted to modify the back channel of a-IGZO TFTs.The impact of the decoration layer on the TFT performance and the related mechanisms were investigated.Finally,potential applications in logic circuits and photodetectors of the a-IGZO TFTs with back-channel decoration layers were briefly explored.Details are listed as follow:?1?Back-channel surface decoration in a-IGZO TFTs with oxide thin films and their applications in invertersBottom-gate a-IGZO TFTs with excellent performance was obtained by changing oxygen partial pressure and channel thickness.Then,ultrathin NiO,Al₂O₃,and SnO_x decoration layers were adopted to modify the back channel of the a-IGZO TFTs,respectively.The threshold voltage?Vth?of the modified TFTs all shifted negatively.Compared with NiO and Al₂O₃ modified ones,SnO_x modified TFT shows better duration stability.Moreover,the Vth can be tuned in a wide range by changing the thickness of the SnO_x decoration layer.A Vth shift from 15.2 to-9.0 V was observed as the SnO_x thicknesses increased from 0 to 19 nm,accompanying by a sizable increase of the intrinsic electron concentration in the channel layer.According to the composition evolution of the SnO_x capping layers,it was believed that loosely bound oxygen in the IGZO can be consumed by the SnO_x capping layer,resulting in the Vth negative-shift.And loosely bond oxygen in IGZO will result in the decrease of mobility and carrier concentration.The SnO_x capping layer also had some effect in the prevention from moisture or oxygen based on different ambient atmosphere testing,hence inducing a good duration stability of the capped TFT when exposed to the air.On the basis of back-channel surface decoration,the device bias stability can be further improved after passivation with SU-8 photo-resist.Finally,an optimized NMOS inverter with a voltage gain up to 45.9 was achieved by connecting an uncapped TFT with an 8.5 nm-capped one.The proposed inverter demonstrated a great potential in the high-voltage-gain,low-cost and easy-fabrication logic circuits.?2?Back-channel surface decoration in a-IGZO TFTs with p-type semiconductor and the applications in photodetectorIn this part,p-type PEDOT:PSS was used to modify the back channel of a-IGZO TFTs on the purpose of coupling the functions of the TFTs and p-n junctions.Firstly,IGZO/PEDOT:PSS heterojunction was fabricated.The electrical properties of the heterojunctions with IGZO layers treated under different conditions?annealing,plasma treatment,and etc.?were investigated.The results show that the as-deposited and plasma-treated IGZO thin films can form p-n junctions with PEDOT:PSS.Taking the electrical properties of the TFT into consideration,the plasma treatment was chosen to construct the p-n junction coupled TFT.The influence of illumination on the p-n junction coupled TFT performance was investigated.The result shows that the Vth shifted negatively under illumination,which is related to the separation of photo-induced carriers under the built-in electrical field of the p-n junction and subsequent electron injection into the TFT channel.