Graduate Thesis Or Dissertation
 

Assessment of High Mobility Oxide Thin-Film Transistors

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/g732df72j

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  • The trend towards higher resolution, faster refresh rate active-matrix liquid-crystal displays (AMLCDs) as well as the emergence of active-matrix organic light-emitting diode (AMOLED) displays is driving the demand for amorphous oxide semiconductor thin-film transistors (AOS TFTs) with higher mobility. A physics-based model for carrier transport in an amorphous semiconductor is developed to estimate the mobility limits of an AOS TFT to be 71 cm² V⁻¹s⁻¹. Only the effective mass and band tail state density need to be specified, relating to the disorder in the amorphous semiconductor. Three ways are identified to achieve a mobility higher than that of quaternary amorphous indium gallium zinc oxide (a-IGZO) with a cation ratio of 1:1:1. i) Quaternary systems with a higher indium ratio; ii) lower disorder ternary oxides (e.g., boron indium oxide); iii) dual active layer (DAL) TFTs. ITO-IGZO DAL TFTs are directly compared with a-IGZO TFTs. The ITO-IGZO DAL TFT exhibits significantly improved performance with mean mobility of 31 cm² V⁻¹s⁻¹, threshold voltage of -3.6 V, sub-threshold swing of 175 mV dec, minimal hysteresis, and good bias temperature stress stability. Technology computer aided design (TCAD) simulation is used to elucidate the density of states (DOS) of various types of AOS TFTs. A mapping technique is introduced to relate experimental transfer characteristics to the sub-bandgap DOS model.
  • Keywords: Thin-Film Transistor, TCAD Simulation, Amorphous Oxide Semiconductor
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