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

To verify the interface state properties of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) with SiN
_x
and SiO
₂
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 (
S
), were measured for comparison. The interface state density (
N
_it
) extracted by
S
for an a-IGZO TFT with SiN
_x
gate dielectrics is only 1.3 times higher than that for an a-IGZO TFT with SiO
₂
gate dielectrics. However, the trap density (
Nt
) extracted by LFN for an a-IGZO TFT with SiN
_x
gate dielectrics is almost 80 times higher than that for one with SiO
₂
gate dielectrics. Moreover, carrier number fluctuations are the dominant mechanism for LFNs in an a-IGZO TFT with SiN
_x
gate dielectrics. This large difference between SiN
_x
and SiO
₂
gate dielectrics in LFN measurement is related to the fast degradation of a-IGZO TFTs with SiN
_x
gate dielectrics by the bias temperature instability or light illumination.