Verification of Interface State Properties of a-InGaZnO Thin-Film Transistors With $\hbox{SiN}_{x}$ and $ \hbox{SiO}_{2}$ Gate Dielectrics by Low-Frequency Noise Measurements

Abstract

To verify the interface state properties of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) with SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> and SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectrics, the low-frequency noise (LFN) of various gate-length devices from 5 to 50 μm was measured and evaluated. Before LFN measurements, the dc characteristics, such as the subthreshold slope ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> ), were measured for comparison. The interface state density ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> ) extracted by <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> for an a-IGZO TFT with SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> gate dielectrics is only 1.3 times higher than that for an a-IGZO TFT with SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectrics. However, the trap density ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Nt</i> ) extracted by LFN for an a-IGZO TFT with SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> gate dielectrics is almost 80 times higher than that for one with SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectrics. Moreover, carrier number fluctuations are the dominant mechanism for LFNs in an a-IGZO TFT with SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> gate dielectrics. This large difference between SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> and SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectrics in LFN measurement is related to the fast degradation of a-IGZO TFTs with SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> gate dielectrics by the bias temperature instability or light illumination.