Improvement in the bias stability of amorphous InGaZnO TFTs using an Al2O3 passivation layer

This work presents the light–color-dependent negative bias stress (NBIS) effect on amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) with Al2O3 passivation layer. The colors of incident photon are varied from red to blue, that incident photon energies are all lower than the optical band gap of IGZO (3.2 eV). The experimental results show that the Al2O3 passivated devices present stable electrical behaviors under different incident lights (ΔVT < 0.1 V of dark and red, ΔVT < 1 V of green, and ΔVT < 4 V of blue), whereas the unpassivation devices exhibit observable negative shifts during NBIS (ΔVT < 1 V of dark and red, ΔVT > 8 V of green, andΔVT > 15 V of blue). The degradation mechanism of the negative bias stress under illumination of a-IGZO TFTs is dominated by the photo-generated hole trapping at the gate insulator and/or interface between insulator and channel. In this result, the Al2O3 passivation layer can effectively passivate the defect in the a-IGZO film, reducing electron hole pair generated during the illumination processed.

► The Al2O3 passivation layer enhancing the illumination stable was investigated.
► Al2O3 passivation suppresses gas adsorption/desorption in back channel of a-IGZO film.
► The NBIS induced instability of electrical properties was investigated.
► The Al2O3 passivation device exhibits a slighter Vth negative shift under NBIS.
► The Al2O3 is an effective passivation layer to decrease photo-excitation behavior.