Transparent flexible fluorine-doped indium zinc oxide (IZO:F) thin-film transistors (TFTs) were demonstrated using the spin-coating method of the metal fluoride precursor aqueous solution with annealing at 200°C for 2 hrs on polyethylene naphthalate films. The proposed thermal evolution mechanism of metal fluoride aqueous precursor solution examined by thermogravimetric analysis and Raman spectroscopy can easily explain oxide formation. The chemical composition analysed by XPS confirms that the fluorine was doped in the thin films annealed below 250°C. In the IZO:F thin films, a doped fluorine atom substitutes for an oxygen atom generating a free electron or occupies an oxygen vacancy site eliminating an electron trap site. These dual roles of the doped fluorine can enhance the mobility and improve the gate bias stability of the TFTs. Therefore, the transparent flexible IZO:F TFT shows a high mobility of up to 4.1 cm2/V·s and stable characteristics under the various gate bias and temperature stresses.
Electrostatic doping aims at replacing donor/acceptor dopant species with free electron/hole charges induced by the gates in ultrathin MOS structures. Highly doped N + /P + terminals and virtual P-N junctions can be emulated in undoped layers prompting innovative reconfigurable devices with enriched functionality. The distinct merit is that the carrier concentration and polarity (i.e., electrostatic doping) are tunable via the gate bias. After presenting the fundamentals, we review the family of electrostatically-doped devices fabricated with emerging or mature technologies (nanowires, nanotubes, 2D materials, FD-SOI). The multiple facets of the Hocus Pocus diode are discussed by underlining the difference with classical physical diodes. Electrostatic doping gave rise to a number of band-modulation devices with outstanding memory and sharp-switching capability. The concept, intrinsic mechanisms and typical applications are described in detail.
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