Dual-gate amorphous InGaZnO thin film transistors ( DG a-IGZO TFTs) have better electrical characteristics than single-gate a-IGZO TFTs.In this paper,on the basis of a model describing the exponential distribution of defect states of a-IGZO/SiO₂ interface,the effects of the active layer thickness of DG a-IGZO TFTs on their electrical characteristics are investigated by taking into consideration the interface defect states.The results show that,as the active layer becomes thinner,the two gates of DG a-IGZO TFTs get coupled more strongly,which causes the conduction channels initially locating at the front and back interfaces of active layer to extend into the bulk of a-IGZO,thus greatly increasing the field effect mobility of DG a-IGZO TFTs.In addition,with the decrease of the active layer thickness,the field effect mobility of DG a-IGZO TFTs gradually becomes immune to the interface defect states,while the subthreshold swing becomes more sensitive to the interface defect states.