High-κ dielectric is regarded as an effective material to reduce the operating voltage of the amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs). However, the dielectric with high permittivity often has the drawbacks of inducing small conduction band offset energy and high interface trap density. Here a bilayer HfO₂/SiO₂ gate dielectric for thin-film transistors (TFTs) is employed to address the issues. Compare to the a-IGZO TFT with solely 15 nm-thick HfO₂ gate dielectric, the TFT with the bilayer HfO₂/SiO₂ (10 nm/5 nm) gate dielectric improves the subthreshold swing (SS) from 0.22 to 0.12 V/decade, the mobility from 1.4 to 7 cm²/V ⋅ s and current on–off ratio from 9 x 10⁶ to 1.3 x 10⁹. Finally, Hooge's parameters (extracted from the low-frequency noise measurement) of a-IGZO TFTs were investigated to understand the defects near the channel/dielectrics interface so that the role of the thin SiO₂ layer can be verified. The device with bilayer HfO₂/SiO₂ structure exhibits a value of 2 x 10^-3, which is an order of magnitude lower than the one with a single HfO₂ layer. The Hooge's parameter of our bilayer dielectric is the lowest among the reported metal–oxide based TFTs on the glass substrate.

© 2012 IEEE

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