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Amorphous IZO-based Thin Film Transistors: Native Defect-based Doping, Amorphous Phase Instabilities, Threshold Voltage Shifts, and Metallization Strategies

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Abstract:
Amorphous oxide semiconductor (AOS) thin film transistors (TFTs) based on In2O3 have attracted much interest for use as pixel switching elements in next generation active-matrix liquid crystal (AM-LCD) and active-matrix organic light emitting diode (AM-OLED) displays. The high field effect mobility of In2O3-based AOS devices (10–25 cm2/Vsec) offers significant performance improvements over present-day a-Si TFTs (&lt;1 cm2/Vsec) technology. Additional advantages of AOS materials include low temperature processing (RT–300 °C), isotropic wet etch characteristics, and high optical transparency (&lt;85 % in the visible regime) all of which make this material suitable for large area, flexible, and transparent devices on inexpensive polymer substrates.<br/> We have investigated the electrical and structural stability of a-IZO TFTs. Pure amorphous In2O3 is unstable and crystallizes to the bixbyite phase at &lt;150 °C. However, the amorphous phase can be stabilized to temperatures up to 600 °C by the addition of 10 wt% ZnO (a-IZO). We reported high performance long-channel a-IZO n–MOSFETs which operate in depletion-mode (VTh~ –3.21 V) and have saturation field effect mobility of (μsat) of ~&gt;18 cm2/Vsec and on/off ratio of &gt;106. These demonstration devices were fabricated on thermally oxidized Si that used the Si as a bottom-gate, thermal SiO2 as the gate dielectric, semiconducting a-IZO as the channel and conducting a-IZO as the source/drain metallization. We have also deposited TFTs with sputtered dielectric layers to demonstrate an all-room temperature TFT fabrication process.<br/> Challenges for the implementation of a-IZO as a TFT channel material which include dominant doping mechanism, contact properties, and their effect on the field effect mobility measurements, metallization-induced amorphous phase and threshold voltage instability, and metallization strategies were investigated. Research findings in this thesis may be significant to some amorphous IZO and IGZO TFTs to understand fundamental characteristics of materials and devices for the potential use of ultra high definition display device applications such as active-matrix organic light-emitting diodes (AMOLED).
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Thesis (Ph.D. -- Brown University (2013)

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Citation

Lee, Sunghwan, "Amorphous IZO-based Thin Film Transistors: Native Defect-based Doping, Amorphous Phase Instabilities, Threshold Voltage Shifts, and Metallization Strategies" (2013). Materials Science Engineering Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z0WD3XW7

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