A study on materials interactions between Mo electrode and InGaZnO active layer in InGaZnO-based thin film transistors
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Kyungseok Son, Jang-Yeon Kwon, and Sangyun Lee Display Laboratory, Samsung Advanced Institute of Technology, Suwon 440-600, Korea (Received 6 July 2009; accepted 7 October 2009)
This study examined the degradation of the device performance of InGaZnO4 (IGZO)based thin-film transistors after annealing at high temperatures in air ambient. Using various characterization methods including scanning electron microscopy, x-ray diffraction, and transmission electron microscopy, we were able to disclose the details of a two-stage phase transformation that led to the device performance degradation. The Mo electrodes first succumbed to oxidation at moderate temperatures (400500 C) and then the Mo oxide further reacted with IGZO to produce an In–Mo–O compound with some Ga at higher temperatures (600700 C). We analyzed our results based on the thermodynamics and kinetics data available in the literature and confirmed that our findings are in agreement with the experimental results.
I. INTRODUCTION
Transparent oxide semiconductors possess several technologically important features—high electron mobility, high transparency, the capability for low temperature processing, etc.—which make them an excellent candidate for the active layer of thin-film transistors (TFTs).1,2 Successfully developing the materials of such features would usher in the world of next-generation electronics, such as flexible1–4 and transparent electronics.1–3 Among many possible transparent oxide semiconductors, one key material is amorphous InGaZnO4 (IGZO), which was first introduced by Hosono and collaborators.2 Researchers have successfully exploited the material and demonstrated the fabrication of IGZObased TFTs with excellent electrical properties including a high electron mobility (>10 cm2/Vs) and a high on/off current ratio (>106).5 Despite the success in the research of this material, the material’s aspects (e.g., thermal stability) remain largely unexplored. Understanding such aspects would critically help us to fully use this technologically relevant material. For example, postannealing at elevated temperatures has been reported to be a key process step to ensure high device performance.6,7 However, from a materials science perspective, such annealing could instigate undesirable materials interactions, depending on the reactivity of the IGZO with materials that share an interface with it a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0032
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J. Mater. Res., Vol. 25, No. 2, Feb 2010
(electrode, dielectric, etc.). Thermodynamic data for this material is scarcely available in the literature and thus systematically predicting its thermal stability would prove to be an extremely difficult task; some peculiar aspects of this material, such as its amorphous nature8 and its major constituents being low-melting-temperature elements (In: 157 C, Ga: 30 C, Zn: 419 C),9,10 hint that it might have a relatively low thermal stability and a tendency to react with surrounding materials. Thus, examining
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