Solution-Processed Flexible Fluorine-doped Indium Zinc Oxide Thin-Film Transistors Fabricated on Plastic Film at Low Temperature

Abstract

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.

Metal oxide semiconductor thin-film transistors for flexible electronics

“…If the semiconductor deposition is performed at lower temperatures ( 150 C), also PES foils (T G around 200 C) can be utilized. 226 In an attempt to reduce the substrate cost, especially when cost-effective high throughput fabrication processes are targeted, less expensive (but also less thermally resistance) polymer substrates like PEN 190,[195][196][197]227,228 and PET 76,194,229,230 have been employed. Additionally, the use of paper substrates for flexible solution-processed ZnO TFTs has been investigated.…”

“…The contact materials used in n-type solution-processed metal oxide semiconductor TFTs are generally similar to those employed for their vacuum-processed counterparts. Source/drain and gate electrodes are mostly made of Al and Au, 145,193,231 but also of transparent conducting metal oxides, such as ITO, 76,83,190,196,197 IZO, 220,221 or zinc indium tin oxide (ZITO). 192 In addition to the above mentioned materials, gate contacts are also made of Cr 145 or dual layers of Cr/Au, 220,221 which yield a good adhesion.…”

“…244 The commonly high thermal budget required in approach (B) strongly limits the choice of the flexible substrates to materials such as PI 145,193 or PAR. 192 Nevertheless, recent efforts have been devoted to the reduction of the annealing temperatures required to solution-process metal oxide semiconductors (and also gate dielectrics) 87,116,119,237,245 which consequently allows selecting a wider range of substrate materials, including PEN, 196,197,228 and PET. 194,229 c. Deposition methods.…”

“…As for vacuum-processed devices, also for flexible n-type solution-processed metal oxide semiconductor TFTs, standard vacuum deposition techniques are widely used, especially to manufacture the conductive and insulating materials. To grow barrier, gate dielectrics, and passivation layers, vacuum-deposition tools like ALD (for Al 2 O 3 ) 83,145,196,197,200 and PECVD (for SiO 2 and SiN x ) 76,83,145,199,222 are commonly utilized. For source/ drain and gate contact deposition, thermal and e-beam evaporation 145,193,220,221,231 as well as sputtering 76,83,190,192,196,197,220,221 are mainly employed.…”

“…250 f. Device configuration. The majority of the reported flexible n-type solution-processed metal oxide semiconductor TFTs are fabricated in BG staggered configuration with only few devices in BG coplanar, 145,196 TG staggered, 226 or TG coplanar setup. 231 Only electrolyte gated devices present a configuration where source/drain and gate electrodes are all in the same plane (in-plane configuration).…”