The effect of SiO2/SiNx bilayer structure on the bias and light-induced instability in InGaZnO TFTs

We investigated the effect of gate dielectric structure on the light-induced bias-temperature instability of IGZO TFT. After the application of light-induced negative bias stress, the SiO₂/SiN_x bilayer gate dielectric TFT exhibited the superior stability than single layer gate dielectric TFTs. Total applied electric field to bilayer gate dielectric layer(Device C) is -1.91MV/cm. However, electric field applied bilayer gate dielectrics divided between SiN_x(-0.76MV/cm) and SiO₂(-1.15MV/cm). In case of SiO₂ single layer(Device A) effective electric field is -1.52MV/cm. This result indicates that bilayer gate dielectric structure has reducing electric field to gate dielectric. In addition, we observed different recovery behavior after negative bias temperature illumination stress. SiO₂/SiN_x bilayer TFT showed quickly recovery after stress as same as SiO₂ single layer gate dielectric. This results can be explained photo-created charge temporary trapping at the SiO₂/active interface. On the other hand, photo-created charge deeply injection to SiN_x gate dielectric as well as trapping at the gate dielectrics/active interface.