Study On The Effects Of Electrode Buffer Layer On The Performance Of IGZO Thin Film Transistor

Since2004, K. Nomura et al. reported indium-gallium-oxide thin film transistor(InGaZnO Thin Film Transistor, IGZO TFT) with indium-gallium-zinc-oxidesemiconductor as the active layer, it caused widespread attentions of academia andindustry due to the characters of high field effect mobility, good uniformity on largearea and amorphous. At present, IGZO TFT is considered to be the most promisingbackplane technology of display development toward the direction of large size andflexibility.In IGZO TFT, oxygen vacancy is the main source of carriers, but an excess ofoxygen vacancy can lead to more defects in active layer, and then cause adegradation of performance. Therefore, IGZO TFT must be annealing in the air oroxygen environment, to eliminate excess oxygen vacancy and defects in the activelayer. Oxygen content on the surface or in the internal of IGZO film will increaseafter annealing, and lead to the resistivity increased2~3orders of magnitude. Theatoms of Source/Drain electrode are easy to form contact oxidation with the oxygenin the active layer, after the preparation of Source/Drain electrode is complete.This article studied the effects of Source/Drain electrode buffer layer on theperformance of IGZO TFT, to decrease the contact oxidation and contact resistance.Detail works are as follows:1、Prepared the IGZO TFT with bottom gate and top contact structure by usingalumina(Al2O3) as insulation layer materials. Obtained a good performance of IGZOTFT by optimize the active layer thickness of the devices and the temperature ofannealing.2、Analyzed the effects of contact resistance between Source/Drain electrodeand active layer on the performance of IGZO TFT. Conductive channel formed ininterface between insulation layer and active, when the devices work in saturatedzone. The body resistance can be ignored compared with the contact resistance. Total resistance mainly depends on the contact resistance of the device. Namely theSource/Drain current and field effect mobility can be only influenced by contactresistance. However, the metal contact oxidation between source/drain electrode andactive layer can increase the contact resistance, and then cause performancedegradation. With common electrode material Al as the example, Al atoms ofSource/Drain diffuse to the active layer, and combined with oxygen in the activelayer or on the surface, form groups similar with alumina, which will greatlyincrease the contact resistance between the active layer and Source/Drain electrode.3、IGZO film without annealing has the characters of more oxygen vacanciesand high electrical conductivity. This article proposed using IGZO film withoutannealing as drain/source electrode buffer layer to reduce the contact oxidation andreduce contact resistance. Using the same material with active layer as buffer layercan simplify the process compared with other material as buffer layer in industrialproduction with single rectangular target. Experimental results indicated that the bestperformance of device can be obtained, when inserting4nm IGZO film withoutannealing between active layer and source/drain electrode, and the mobility wasimproved by11.6%, and the threshold voltage reduced3.8V compared with thedevice without buffer layer. In conclusion, the buffer layer can effectively reduce thecontact oxidation, and improve the performance of device.