Verification of Interface State Properties of a-InGaZnO Thin-Film Transistors With SiNₓ and SiO₂ 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 SiNxand SiO2gate 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 (Nit) extracted bySfor an a-IGZO TFT with SiNxgate dielectrics is only 1.3 times higher than that for an a-IGZO TFT with SiO2gate dielectrics. However, the trap density (Nt) extracted by LFN for an a-IGZO TFT with SiNxgate dielectrics is almost 80 times higher than that for one with SiO2gate dielectrics. Moreover, carrier number fluctuations are the dominant mechanism for LFNs in an a-IGZO TFT with SiNxgate dielectrics. This large difference between SiNxand SiO2gate dielectrics in LFN measurement is related to the fast degradation of a-IGZO TFTs with SiNxgate dielectrics by the bias temperature instability or light illumination.