Tin Dioxide Electrolyte-Gated Transistors Working in Depletion and Enhancement Modes

Metal oxide semiconductors are interesting for next-generation flexible and transparent electronics because of their performance and reliability. Tin dioxide (SnO₂) is a very promising material that has already found applications in sensing, photovoltaics, optoelectronics, and batteries. In this work, we report on electrolyte-gated, solution-processed polycrystalline SnO₂ transistors on both rigid and flexible substrates. For the transistor channel, we used both unpatterned and patterned SnO₂ films. Since decreasing the SnO₂ area in contact with the electrolyte increases the charge-carrier density, patterned transistors operate in the depletion mode, whereas unpatterned ones operate in the enhancement mode. We also fabricated flexible SnO₂ transistors that operate in the enhancement mode that can withstand moderate mechanical bending

Photolithographically Patterned TiO₂ Films for Electrolyte-Gated Transistors

Metal oxides constitute a class of materials whose properties cover the entire range from insulators to semiconductors to metals. Most metal oxides are abundant and accessible at moderate cost. Metal oxides are widely investigated as channel materials in transistors, including electrolyte-gated transistors, where the charge carrier density can be modulated by orders of magnitude upon application of relatively low electrical bias (2 V). Electrolyte gating offers the opportunity to envisage new applications in flexible and printed electronics as well as to improve our current understanding of fundamental processes in electronic materials, e.g. insulator/metal transitions. In this work, we employ photolithographically patterned TiO₂ films as channels for electrolyte-gated transistors. TiO₂ stands out for its biocompatibility and wide use in sensing, electrochromics, photovoltaics and photocatalysis. We fabricated TiO₂ electrolyte-gated transistors using an original unconventional parylene-based patterning technique. By using a combination of electrochemical and charge carrier transport measurements we demonstrated that patterning improves the performance of electrolyte-gated TiO₂ transistors with respect to their unpatterned counterparts. Patterned electrolyte-gated (EG) TiO₂ transistors show threshold voltages of about 0.9 V, ON/OFF ratios as high as 1 × 10⁵, and electron mobility above 1 cm²/(V s)

Conducting Polymer Transistors Making Use of Activated Carbon Gate Electrodes

The characteristics of the gate electrode have significant effects on the behavior of organic electrochemical transistors (OECTs), which are intensively investigated for applications in the booming field of organic bioelectronics. In this work, high specific surface area activated carbon (AC) was used as gate electrode material in OECTs based on the conducting polymer poly­(3,4-ethylenedioxythiophene) (PEDOT) doped with poly­(styrenesulfonate) (PSS). We found that the high specific capacitance of the AC gate electrodes leads to high drain-source current modulation in OECTs, while their intrinsic quasi-reference characteristics make unnecessary the presence of an additional reference electrode to monitor the OECT channel potential

Protonic and Electronic Transport in Hydrated Thin Films of the Pigment Eumelanin

The electrical properties of eumelanin, a ubiquitous natural pigment, have fascinated scientists since the late 1960s. For several decades, the hydration-dependent electrical properties of eumelanin have mainly been interpreted within the amorphous semiconductor model. Recent works undermined this paradigm. Here we study protonic and electronic charge carrier transport in hydrated eumelanin in thin film form. Thin films are ideal candidates for these studies since they are readily accessible to chemical and morphological characterization and potentially amenable to device applications. Current–voltage (<i>I</i>-<i>V</i>) measurements, transient current measurements with proton-transparent electrodes, and electrochemical impedance spectroscopy (EIS) measurements are reported and correlated with the results of the chemical characterization of the films, performed by X-ray photoelectron spectroscopy. We show that the electrical response of hydrated eumelanin films is dominated by ionic conduction (10^–4–10^–3 S cm^–1), largely attributable to protons, and electrochemical processes. To propose an explanation for the electrical response of hydrated eumelanin films as observed by EIS and <i>I</i>-<i>V</i>, we considered the interplay of proton migration, redox processes, and electronic transport. These new insights improve the current understanding of the charge carrier transport properties of eumelanin opening the possibility to assess the potential of eumelanin for organic bioelectronic applications, e.g. protonic devices and implantable electrodes, and to advance the knowledge on the functions of eumelanin in biological systems