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)