超大尺寸IGZO(InGaZnO)产品在高温高湿(50℃/80%)信赖性评价中易发生异常显示不良(Abnormal Display,AD).其不良原因主要是集成栅极驱动电路(Gate Driver On Array,GOA)的关键器件M2转移特性曲线(IDS-VGS)在评价中发生了严重正移.本文通过脉冲实验,模拟GOA关键器件M2的实际工作环境,重现了转移特性曲线严重正移的不良现象.通过设置不同的脉冲实验,揭示了造成不良的主要影响因素:M2器件关闭时,漏极与源极之间的压差VDS过大,使IGZO膜层内的氧空位V+O在电场作用下同时向IGZO与GI(Gate Insulator)的边界及源极端迁移,由于氧空位V+O对电子的捕获作用,最终导致转移特性曲线发生正移,并发现迁移的氧空位V+O经过加热后可以复原.此外,在不改变IGZO成膜条件下,通过减小M2器件关闭时的VDS压差,导入超大尺寸IGZO产品,高温高湿信赖性评价2 000 h未发生AD不良.
Effect of pulse on performance of InGaZnO thin film transistor
Ultra-large IGZO(InGaZnO)products were prone to Abnormal Display(AD)during reliability evaluation at high temperature and humidity(50℃/80%).The main reason was that the key device's(M2)transfer characteristic curve(IDS-VGS)of GOA(Gate Driver on Array)had a serious positive shift in the evaluation.In this paper,the real working environment of GOA's key device(M2)was simulated by pulse experiment,and the bad phenomenon of serious positive shift of transfer characteristic curve was reproduced.By setting different pulse experiments,the main influencing factor was revealed.When the device(M2)was turned off,the VDS(pressure difference between Drain and Source)was too large,so that the oxygen vacancy V+O in the IGZO layer migrated to the boundary of IGZO and GI(Gate Insulator)and to the Source at the same time under the electric field.Due to the electrons trapping effect of oxygen vacancy V+O,the transfer characteristic curve would eventually shift positively.It was found that the migrated oxygen vacancy V+O can be restored after heating.In addition,without changing the IGZO film forming conditions,by reducing the VDS pressure when the device(M2)was turned off,the ultra-large IGZO product did not occur AD defects during the reliability evaluation at high temperature and humidity for 2 000 h.
InGaZnO thin film transistorgate driver on arrayabnormal displaythreshold voltage shift
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