Comparative Study on the Separate Extraction of Interface and Bulk Trap Densities in Indium Gallium Zinc Oxide Thin-Film Transistors Using Capacitance–Voltage and Current–Voltage Characteristics

The interface and bulk trap densities were separately extracted from self-aligned top-gate (SA-TG) coplanar indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) using the low-frequency capacitance–voltage (C–V) characteristics and space-charge-limited current (SCLC) under the flat-band condition. In the method based on the C–V curve, the energy distribution of the interface trap density was extracted using the low-frequency C–V characteristics, and that of the bulk trap density was obtained by subtracting the density of interface trap states from the total subgap density of states (DOS) at each energy level. In the SCLC-based method, the energy distribution of the bulk trap density was extracted using the SCLC under the flat-band condition at high drain-to-source voltages, and that of the interface trap density was obtained by subtracting the density of bulk trap components from the total subgap DOS at each energy level. In our experiments, the two characterization techniques provided very similar interface and bulk trap densities and showed that approximately 60% of the subgap states originate from the IGZO/SiO2 interface at the conduction band edge in the fabricated IGZO TFTs, although the two characterization techniques are based on different measurement data. The results of this study confirm the validity of the characterization techniques proposed to separately extract the interface and bulk trap densities in IGZO TFTs. Furthermore, these results show that it is important to reduce the density of interface trap states to improve the electrical performance and stability of fabricated SA-TG coplanar IGZO TFTs.