Ultralow-voltage albumen-gated electric-double-layer thin film transistors

Abstract

In recent years, environment-friendly and biocompatible electronics have received extensive attention. As a kind of natural biological material with rich sources, proteins have been widely used in electronic devices. In this work, electric-double-layer (EDL) thin-film transistors (TFTs) gated by natural chicken albumen are fabricated at room temperature. The indium-tin-oxide (ITO) conductive glass is employed as a substrate. The spin coated chicken albumen film is used as the gate dielectric. The indium-zinc-oxide (IZO) is sputtered on an albumen-coated ITO glass as the channel and the source/drain electrodes with only one shadow mask. The capacitance-frequency measurements demonstrate an ultra-large specific capacitance of the albumen film at low frequencies. For the physical understanding of the capacitive coupling within the albumen film, the phase angle is characterized as a function of frequency. The results indicate that such an ultra-large capacitive coupling can be attributed to the proton migration under the electric field, which results in the EDL effect at the interface of the albumen film. By DC sweep measurements, a low leakage current is observed (<3.0 nA at <i>V</i><sub>gs</sub>=1.5 V), which indicates a good isolation of the albumen-based dielectric. By transfer and output measurements, an ultralow operation voltage of 1.5 V, a high field-effect mobility of 38.01 cm<sup>2</sup>/(V·s), a low subthreshold swing of 164 mV/decade, and a large on-off ratio of 2.4×10<sup>6</sup> are obtained for such albumen-gated TFTs. The ultra-large EDL capacitive coupling is responsible for such good electrical characteristics. The dynamic bias stress stability of the albumen-gated TFTs is also investigated. The device exhibits a good reproducibility in response to the repeatedly pulsed gate voltage. A maintainable on-to-off ratio (>10<sup>6</sup>) and no obvious current loss are observed, which suggests that neither chemical doping nor chemical reaction occurs at the albumen-based dielectric/IZO channel interface when the gate potential is biased. After being aged one day in air ambient without surface passivation, the albumen-gated TFTs show a good stability of the electrical properties. Such ultralow-voltage EDL-TFTs gated by albumen electrolyte will be useful for the bioelectronic and low-energy portable electronic products. And our results will also have potential applications in biocompatible artificial neuron networks and brain-inspired neuromorphic systems.