Vertically Graded Oxygen Deficiency for Improving Electrical Characteristics and Stability of Indium Gallium Zinc Oxide Thin-Film Transistors

Abstract

We investigated a facile fabrication method, which is an insertion of a carrier-induced interlayer (CII) between the oxygenrich a-IGZO channel and the gate insulator to improve the electrical characteristics and stability of amorphous indium−gallium−zinc− oxide thin-film transistors (a-IGZO TFTs). The a-IGZO channel is deposited with additional oxygen gas flow during a-IGZO channel deposition to improve the stability of the a-IGZO TFTs. The CII is a less than 10 nm thick deposited thin film that acts to absorb the oxygen from the a-IGZO front channel through oxidation. Through oxidation of the CII, the oxygen concentration of the a-IGZO front channel is decreased compared to that of the oxygen-rich back channel, which forms a vertically graded oxygen deficiency (VGO) in the a-IGZO channel. Therefore, the electrical characteristics of the VGO TFTs are improved by increasing the carrier concentration of the front channel as the oxygen vacancy concentration in the front channel is increased through the oxidation of the CII. At the same time, the stability of the VGO TFTs is improved by maintaining a high oxygen concentration in the back channel even after oxidation of the CII. The field-effect mobility (μ FET ) of the VGO TFTs improved compared to that of the a-IGZO TFTs from 7.16 ± 0.6 to 12.0 ± 0.7 cm 2 /V•s. The threshold voltage (V th ) shifts under positive bias temperature stress and negative bias temperature illumination stress decreased from 6.00 to 2.95 V and −15.58 to −8.99 V, respectively.

Multifunctional Oxygen Scavenger Layer for High-Performance Oxide Thin-Film Transistors with Low-Temperature Processing

“…Figure a,b shows the XPS results of the O 1s spectra of the a-IGZO film. There was almost no change in the area ratio of M–O bonds (O I ) and V O (O II ) at the front/back channel, with values of 59.26/59.37% and 37.51/37.39%, respectively . On the other hand, the XPS results of the O 1s spectra of the OSL/a-IGZO film after thermal annealing (200 °C) show that the area ratio of M–O bonds (O I ) in the front channel was 57.11% while that in the back channel was 64.39%, as shown in Figure c,d .…”

“…Figure 6 18 On the other hand, the XPS results of the O 1s spectra of the OSL/a-IGZO film after thermal annealing (200 °C) show that the area ratio of M−O bonds (O I ) in the front channel was 57.11% while that in the back channel was 64.39%, as shown in Figure 6c,d. 18 Also, the area ratios of V O (O II ) were 40.51% in the front channel and 33.30% in the back channel.…”

“…Also, the area ratios of V O (O II ) were 40.51% in the front channel and 33.30% in the back channel. In the case of the OSL/a-IGZO film before thermal annealing, the area ratio of M–O bonds (O I ) in the front channel was 25.91% while that in the back channel was 33.71%, as shown in Figure S8a . In addition, the area ratios of V O (O II ) were 72.86% in the front channel and 65.30% in the back channel, as shown in Figure S8b.…”

“…Many studies have tried to find a way to control the oxygen vacancy (V O ) distribution and concentration in AOS films as V O plays a significant role in determining the stability and field-effect mobility (μ FE ) of AOS TFTs. − To improve stability, most studies have focused on decreasing the V O concentration (e.g., vertically graded V O , a heterogeneous organic passivation layer, plasma treatment) as V O is a well-known cause of instability. − However, V O is also a carrier source for AOS; thus, the reduction in V O concentration also reduces the μ FE of the AOS TFTs. For this reason, it is difficult to improve both the μ FE and stability of AOS TFTs due to their trade-off relationship. , Furthermore, in the case of a low-temperature annealing process, it is further challenging to improve both the μ FE and stability of AOS TFTs as V O control becomes more difficult.…”

Surface Passivation Treatment to Improve Performance and Stability of Solution‐Processed Metal Oxide Transistors for Hybrid Complementary Circuits on Polymer Substrates

“…[ 21 , 22 ] Oxygen deficiency in metal oxide films is able to be reduced by an additional oxygen gas flow during the film formation and the vertically controlled oxygen ratio improves FET mobility and stability. [ 23 ] Recent thermal crystallization approach also improves oxygen stoichiometry, resulting in enhanced carrier mobility and electrical stability. [ 24 ] However, these approaches are not directly applicable to solution‐processed metal oxide films due to the difficulty in adjusting oxygen concentration during sol–gel processing in ambient air.…”