We investigated on electrical performance and storage issues of high efficiency amorphous In-Sn-Zn-O (IZTO) thin film transistor. By capping additional In-Ga-Zn-O (IGZO) layer on IZTO to form the bilayer channel, the device's performance could obviously enhance. The mobility of devices without and with 20 nm, 40 nm IGZO capping layer was 24.2 cm
/Vs, 29.1 cm
/Vs and 33.1 cmVVs, respectively. The threshold voltage and substrate swing were improved proportionally with the thickness of IGZO capping layer. In addition, the storage issues of devices could also be eliminated by using the bilayer channel structure without any threshold voltage shift after placing in ambient environment for half month. Owning to the high performance and better storage stability, the TFTs with IZTO/IGZO bilayer channel is promising for next-generation AMOLEDs displays application.