Unified Subthreshold Coupling Factor Technique for Surface Potential and Subgap Density-of-States in Amorphous Thin Film Transistors

Abstract

We report a unified subthreshold coupling factor technique for a simultaneous extraction of the surface potential (ψ S ) and the subgap density-of-states [DOS: g(E)] over the bandgap in amorphous semiconductor thin film transistors (TFTs). It is fully based on the experimental gate bias-dependent coupling factor [m(V GS )] under subthreshold bias. Through the proposed technique only with current-voltage data under subthreshold operation, a unified extraction of the DOS with a consistent mapping of the gate bias (V GS ) to the subgap energy is obtained. Applying to amorphous InGaZnO TFTs, g(E) is obtained to be a superposition of two exponential functions with N TA = 1.62 × 10 17 eV −1 cm −3 and kT TA = 0.026 eV for the tail states while N DA = 6.5 × 10 16 eV −1 cm −3 and kT DA = 0.22 eV for the deep states. Index Terms-Amorphous InGaZnO (a-IGZO), coupling factor, subgap density-of-states (DOS), subthreshold current, surface potential, thin film transistors (TFT).

Water-Mediated Photochemical Treatments for Low-Temperature Passivation of Metal-Oxide Thin-Film Transistors

“…To evaluate the operational stability of the diversely processed devices, a positive gate bias stress (PBS) test and a negative gate bias illumination stress (NBIS) test were performed without a passivation layer in ambient conditions with RH 28% at 24 °C, which easily revealed the effect of oxygen vacancy as defect states (shallow and deep states), and the results are shown in Figure and Figure S4. Generally, the passivation layer can improve the electrical stability of the devices due to protecting the adsorption of oxygen and water in the surrounding atmosphere on the back channel of TFTs. − However, in order to clearly understand the effect of water treatment, the passivation layer was not applied to all devices in this study. The prolonged DUV irradiation improved the operational stability of the a -IGZO TFTs.…”

“…To fully exploit the correlation between the structural imperfections in the a -IGZO films and the operational stability of the a -IGZO TFT devices, the density of states (DOS) under the conduction band edge ( E c ) for each of the a -IGZO films was extracted using the unified subthreshold coupling factor technique Figure shows the DOS distribution as a function of energy for the differently processed a -IGZO thin films.…”

Theoretical Modeling of a Temperature-Dependent Threshold-Voltage Shift in Self-Aligned Coplanar IZTO Thin-Film Transistors

“…Indeed, a device with a T PDA of 320 °C achieved the fastest decline in V GS , which is reminiscent of the lowest subgap DOS distribution among the three devices. Figure e depicts the extracted subgap DOS distributions according to the MN rule. ,− The subgap DOS distributions extracted by the IV–CV combination method were consistent with those produced by the MN rule. Similar subgap DOS profiles can be obtained using both methods, as shown in Figure S2 of the SI.…”

Electrothermal Annealing (ETA) Method to Enhance the Electrical Performance of Amorphous-Oxide-Semiconductor (AOS) Thin-Film Transistors (TFTs)

“…Figure a shows the subgap density-of-state (DOS) of bulk traps in the a-IGZO channel. In the a-IGZO TFTs, a quantitative analysis of the subgap DOS over the bandgap is a significant issue when estimating the reliability and stability when affected by long-term degradation. − As shown in Figure a, the subgap DOS can be determined by the V G -dependent coupling factor obtained from the measured transfer curve of the a-IGZO TFTs . With I - V data under the subthreshold region, a nonuniform distribution of the subgap DOS over the bandgap energy can be obtained.…”

“…28−30 As shown in Figure 5a, the subgap DOS can be determined by the V G -dependent coupling factor obtained from the measured transfer curve of the a-IGZO TFTs. 31 With I-V data under the subthreshold region, a nonuniform distribution of the subgap DOS over the bandgap energy can be obtained. After ETA, accordingly, the SS is improved due to a reduction of the bulk trap states originating from subgap DOS near the conduction band (E C ).…”