Stability improvement of solution-processed IGZO TFTs by fluorine diffusion from a CYTOP passivation layer

Abstract

This study investigated the effects of fluorine (F) diffusion from a CYTOP passivation layer into amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). The F contained in the CYTOP passivation layer was diffused into a-IGZO through 350 °C annealing. The similar ionic radii of F and oxygen (O) allowed the passivation of oxygen vacancy (Vo) and weakly bonded oxygen by F. As a result, the a-IGZO TFTs with CYTOP passivation were highly stable under various stresses. The threshold voltage (Vth) shifts of a-IGZO TFTs without CYTOP passivation and with CYTOP passivation under a negative bias stress test for 10 000 s were −6.7 V and −2.5 V, respectively. In addition, the Vth shifts of each device under a negative bias illumination stress test for 4000 s were −10.9 V and −5.3 V, respectively. This improvement was caused by a reduction of Vo and a widened band gap of a-IGZO through the F diffusion effect. In addition, the CYTOP passivation layer maintained excellent properties as a barrier against moisture after 350 °C annealing.