Thermal-assisted brush printing of water-based In-Ga-Zn oxide transistors

https://doi.org/10.1016/j.jallcom.2020.158001Get rights and content

Highlights

  • Thermal-assisted brush printed In-Ga-Zn oxide thin-film transistors are achieved.

  • Electrical properties of short-time annealing transistors are improved.

  • Synergistic effect of thermal-annealing and brush-printing was investigated.

Abstract

As an environment-friendly technique, the water-based solution process has attracted numerous attention. Due to the ability to fabricate oxide semiconductor films for transistors with acceptable electric properties at relatively low temperatures (~200 °C lower compared with organic solvent), it has great potential in future display technology, and various correlation technologies are keeping emerging. Here, an efficient and facile water route thermal-assisted brush printing is demonstrated, which can be applied to fabricate the semiconductor layer of indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) by the solution process. The synergistic effects of thermal-annealing and brush printing on the film formation process were comprehensively investigated, implying the synergistic effects induce the acceleration of the evaporation of the precursor solvent and promotes the lower surface roughness of as-prepared thin-film, resulting in improved transistor properties. Mechanically, the proposed film-forming model of thermal-assisted brush printing is also elaborated, which is expected to be a general guideline for the solution processing of metal-oxide semiconductor thin-films.

Introduction

Thin-film transistors (TFTs) have been extensively applied in display technologies and optoelectronic devices [1]. Researchers have never stopped exploring new semiconductor materials severed as an active layer in TFTs for next-generation electronics. Recently, innovative semiconductor materials such as metal-oxides, graphene, and conjugated polymers have been investigated and applied to transistors [2], [3], [4], [5]. Among them, metal-oxides semiconductors (MOS) are considered to be competitive for state-of-the-art TFTs semiconductor materials due to their high mobilities, excellent optical transparency [6], [7] and satisfactory environmental stability [8].

The vapor-process technique of manufacturing MOS thin-films is a mature mainstream preparation process, mainly including magnetron sputtering, atomic vapor deposition, pulsed laser deposition, etc. [8]. The indium oxide (In2O3) [9], indium zinc oxide (IZO) [10], and Indium gallium zinc oxide (IGZO) [3] thin-films have been demonstrated to be grown by the vapor-process technique. Nevertheless, all of the above techniques often require a high vacuum environment, leading to the problems of a long time consuming and high costs. Meanwhile, the demand for cost-effective, large-area manufacturing processes in some electronic fields is rapidly rising. Recently, the solution technique represented by spin-coating [11], dip-coating [12], spray pyrolysis [13], and solution shearing [14] has gradually aroused the interest of researchers due to its low cost, simplicity, short time consuming and the possibility of preparation under atmosphere [15].

Typically, the solution process fabricated amorphous MOS thin-films commonly require a high annealing temperature (>500 °C) to achieve a favorable electric performance, which hinders its popularization in specific fields. For IGZO, it has been reported to effectively lower the annealing temperature due to the doping of Gallium (Ga). Ga doping can facilitate the amorphous-oxide semiconductor to form an oxide-lattice structure which is necessary for amorphous-oxide semiconductors to achieve high mobility below 300 °C [16]. Besides, the selection of the precursor solvent is also very important to lower the annealing temperature. Water is considered as an environmentally-friendly solvent and facilitates the dissociation of ionic species due to its high dielectric constant [17]. Metal salts dissolved in organic solvents tend to form organic species [18], that require constant thermal energy to break the chemical bonds. In water precursors, however, metal cation and adjacent aqua ion are bonded by the electrostatic reaction which is easy to break [19].

The brush is a painting tool composed of natural or artificial fibers arranged in parallel. The closely arranged fibers can firmly pin the liquid in the brush without unexpected leakage. When touching the external interface, it can achieve steady, uniform, continuous transferring of precursor onto various substrates directly, even in an uneven surface, effectively reducing the waste of precursor [20]. As a unique solution technique with the possibility of fast large area printing, brush printing attracts considerable attention. In recent, brush printing has been applied to fabricate thin-films of various materials and exhibited great potential in film deposition [21], [22], [23], [24]. It is demonstrated the brush has good adaptability with various low-viscosity precursors and can finely control the wetting and dewetting processes during the printing [23]. However, these previous studies mainly focus on the organic conductor or semiconductor, the application of amorphous MOSs has been rarely reported.

Here, a facile strategy of fabricating amorphous IGZO film via thermal-assisted brush printing was proposed, and the influence of the thermal anneal process include the film morphology and performance during the film formation was explored with the help of thermogravimetry analysis (TGA), X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). Besides, bottom-gate/top-contact MOS TFTs with as-prepared IGZO films as active layers were fabricated to explore the electrical properties. The results showed the importance of thermal-annealing during MOS film fabrication. Compared with the TFTs without thermal-annealing, the performance of the thermal-assisted brush printing TFTs has been significantly improved, especially the short-time annealing devices. Finally, the synergistic effect of thermal-annealing and brush printing during the film fabrication was analyzed in detail.

Section snippets

Synthesis and characterization of IGZO precursor

All precursor materials were purchased from Sigma–Aldrich. 0.11 M Indium nitrate hydrate (In(NO3)3·xH2O, 99.999%), 0.01 M Gallium nitrate hydrate (Ga(NO3)3·xH2O, 99.999%) and 0.03 M Zinc nitrate hydrate (Zn(NO3)2·xH2O, 99.999%) were dissolved in 10 ml deionized water or 2-Methoxyethanol (2ME) and vigorously stirred for 12 h under ambient condition. Prior to the film deposition, the metal-oxide precursor solution was filtered through a 0.22 µm syringe filter. The TGA was performed on TG 409PC

Formation characterization of IGZO films

Fig. 1(a) illustrates the films and TFTs fabrication process via the thermal-assisted brush printing method, and the structure of IGZO TFTs is shown in Fig. 1(b). To understand the formation of IGZO films from the precursor, TGA analysis of IGZO xerogel was performed and the results are shown in Fig. 1(c). Both of water-based and 2ME-based samples gradually decrease from ~50 °C, it is attributed to the evaporation of the residual solvent in the samples, which will induce the thermally driven

Conclusion

In conclusion, a facile and environmental-friendly thermal-assisted brush printing technique for high-performance IGZO TFTs was developed. And the synergistic effect of the thermal annealing and brush printing on the IGZO films was explored. A series of the morphology characterization shows that the brush printing process could effectively limit the disordered microfluidic dynamic behavior of the liquid, and the thermal-annealing process accelerates the evaporation of the solvent, reducing the

CRediT authorship contribution statement

Chenhong Zhang: Conceptualization, Methodology, Validation, Formal analysis. Yanping Chen: Data curation, Writing - review & editing. Chengyi Hou: Investigation. Gang Wang: Funding acquisition, Writing - review & editing. Qinghong Zhang: Writing - original draft, Yaogang Li: Resources, Project administration. Hongzhi Wang: Funding acquisition, Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We gratefully acknowledge the financial support by Science and Technology Commission of Shanghai Municipality (19JC1410600, 20S10601). Gang Wang is grateful for financial support from the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, the Natural Science Foundation of Shanghai (19ZR1470900) and the Fundamental Research Funds for the Central Universities.

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