Abstract-We fabricated top-gate and self-aligned In-Ga-Zn-O thin-film transistors (TG-SA IGZO TFTs) at a maximum process temperature of 150 °C using a coatable organic gate insulator (OGI). By forming a damage and contamination-free interface between the IGZO channel and OGI, and forming low-resistive source/drain (S/D) regions by Al reaction method, we achieved good TFT properties, such as field effect mobility of 9.8 cm 2 /Vs, subthreshold swing of 0.21 V/dec., and hysteresis of 0.3 V, with minimizing a parasitic capacitance. Although the TFT showed an abnormal degradation behavior under positive gate bias stress testing in an ambient air, it was suppressed by forming an additional organic passivation layer.Index Terms-Indium-gallium-zinc-oxide (IGZO), Organic gate insulator (OGI), Self-aligned structure, Thin-film transistor (TFT).
The negative gate bias and illumination stress (NBIS) stability and photo-response of In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) with either silicon oxide (SiO X ) or fluorinated silicon nitride (SiN X :F) passivation were investigated. NBIS degradation can be suppressed when the fluorine (F) in SiNx:F diffused into an IGZO channel during long annealing period. Photo-response analysis revealed that F passivated effectively electron traps in the IGZO channel existing at an energy level close to the valence band maximum (near-VBM state). The fluorine-passivated IGZO TFT is thus advantageous for achieving highly reliable IGZO TFT for next-generation displays. An amorphous In-Ga-Zn-O (a-IGZO) semiconductor is widely accepted as a promising channel material for TFT applications owing to its outstanding electrical properties.3 However, it is recognized that degradation under negative gate bias and illumination stress (NBIS) is a unique but serious issue for oxide TFTs.4 When a negative gate voltage and illumination stresses are simultaneously applied to oxide TFTs, the enhancements of negative threshold voltage (V th ) shift and hysteresis were observed due to photo-excitation of electrons from high-density electron traps existing in an IGZO at an energy level close to the valence band maximum (near-VBM state). [5][6][7][8][9] The origin of the near-VBM state has been actively investigated from both experimental and theoretical standpoints. Kamiya et al. reported the oxygen vacancy with void in oxygen deficient IGZO film is an origin of the near-VBM state.10 In addition, weakly-bonded oxygen, interstitial oxygen, undercoodinated oxygen, and peroxide have been reported as origins of the near-VBM state in an IGZO film.11-14 Moreover, the -OH groups in the film have also been reported to relate the density of the near-VBM state. [15][16][17] Although the origin of the near-VBM state is still debatable, passivation or reduction of the near-VBM state originating from oxygen-related defects is essential to improve NBIS reliability. Wet-O 2 annealing has been reported to improve the NBIS reliability of the IGZO TFT. 17,18 It has also been reported that formation of OH-bonds in an IGZO is an important factor to passivate the near-VBM state.17 A theoretical study also indicated that a hydrogen atom preferentially binds to undercoordinated oxygen, resulting in a passivation of the near-VBM state.14 Although many researches have made numerous efforts to improve the NBIS reliability of oxide TFTs, NBIS degradation has as yet not been suppressed.We reported that reliability of the IGZO TFT under positive gate bias and temperature stress (PBTS) was drastically improved by a fluorine-passivated IGZO TFT. 19 It was found that fluorine (F) effectively passivated electron traps and weakly bonded oxygen in an IGZO channel and at a gate insulator (GI)/channel interface when F diffused into an IGZO channel. However, both the F passivation effect of the near-VBM state and its influence on the NBIS stability of the IGZO TFT have not bee...
The electrical properties of InGaZnO (IGZO) thin-film transistors (TFTs) with SiO X and fluorinated silicon nitride (SiN X :F) passivation were investigated. The IGZO TFTs with SiN X :F passivation showed excellent performance and positive bias temperature stress (PBTS) stability as compared with those with SiO X passivation after annealing in N 2 ambient at 350 C for 3 hours. Long time annealing could promote fluorine (F) diffusion through an etch stopper layer to an IGZO film. The diffused F could passivate the electron traps, which were the main factor to improve the performance and bias stability of oxide TFTs. The SiN X :F passivation layer will supply F to IGZO channel layer through post-fabrication annealing, which is a novel method for making high performance and stability TFT used in next generation display.
High performance and highly-stable In-Ga-Zn-O thin-film transistor (IGZO TFT) have been achieved by using fluorine passivation method of defects in an IGZO. Degradations under positive gate bias and temperature stress and negative gate bias with illumination stress were almost suppressed by the fluorinated IGZO TFT. Proposed method is advantageous for improving reliability of oxide TFTs for next generation displays.
A novel doping method of fluorine in IGZO for making thermally stable source and drain (S/D) regions of self-aligned oxide TFTs is presented. Thermally stable IGZO homo-junction could be achieved by the selective deposition of fluorinated silicon nitride (SiNx:F) on top of the IGZO. Electrical properties of self-aligned IGZO TFT drastically improved owing to the reduction of parasitic and offset resistances in S/D regions, and the field effect mobility of 10.6 cm2×V-1×s-1 was achieved. The proposed method is an essential for making self-aligned oxide TFTs with thermally stable S/D regions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.