Chitosan-gated low-voltage transparent indium-free aluminum-doped zinc oxide thin-film transistors

• Chitosan shows a large specific capacitance (0.4 μF/cm2) due to the strong electric-double-layer effect.
• Low-cost indium-free AZO film is developed for replacing the traditional ITO/IZO electrodes.
• The junctionless electric-double-layer TFTs with 30 nm AZO thickness shows the best performance.

Low-voltage transparent indium-free aluminum-doped zinc oxide (AZO) thin-film transistors (TFTs) are demonstrated by using chitosan polymer electrolyte as the gate dielectric. Chitosan with a large specific capacitance (0.4 μF/cm2) is obtained possibly due to the strong electric-double-layer (EDL) effect through the mobile-proton hopping mechanism. Herein, low-cost indium-free AZO film is developed for replacing the traditional ITO/IZO electrodes. A simple method is developed to fabricate all of the channel and source/drain electrodes during one-step sputter process by using such a low-cost indium-free AZO film. The optimized TFTs with 30 nm AZO thickness shows the best performance with a low operation voltage of 1.5 V, a large on-off ratio of 105, and a field-effect mobility of 8.3 cm2/Vs, respectively. The chitosan-gated AZO TFTs may provide a good candidate for the applications of next-generation transparent flexible low-cost portable electronics.

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