Solvothermal Synthesis of Gallium-Indium-Zinc-Oxide Nanoparticles for Electrolyte-Gated Transistors Lídia Santos,* Daniela Nunes, Toma ́ s Calmeiro, Rita Branquinho, Daniela Salgueiro, Pedro Barquinha, Luís Pereira, Rodrigo Martins, and Elvira Fortunato* Departamento de Ciê ncia dos Materiais, CENIMAT/I3N, Faculdade de Ciê ncias e Tecnologia, Universidade Nova de Lisboa and CEMOP/Uninova, 2829-516 Caparica, Portugal * S Supporting Information ABSTRACT: Solution-processed field-effect transistors are strategic building blocks when considering low-cost sustainable flexible electronics. Nevertheless, some challenges (e.g., pro- cessing temperature, reliability, reproducibility in large areas, and cost effectiveness) are requirements that must be surpassed in order to achieve high-performance transistors. The present work reports electrolyte-gated transistors using as channel layer gallium-indium-zinc-oxide nanoparticles pro- duced by solvothermal synthesis combined with a solid-state electrolyte based on aqueous dispersions of vinyl acetate stabilized with cellulose derivatives, acrylic acid ester in styrene and lithium perchlorate. The devices fabricated using this approach display a I ON /I OFF up to 1 × 10 6 , threshold voltage (V Th ) of 0.3-1.9 V, and mobility up to 1 cm 2 /(V s), as a function of gallium-indium-zinc-oxide ink formulation and two different annealing temperatures. These results validates the usage of electrolyte-gated transistors as a viable and promising alternative for nanoparticle based semiconductor devices as the electrolyte improves the interface and promotes a more efficient step coverage of the channel layer, reducing the operating voltage when compared with conventional dielectrics gating. Moreover, it is shown that by controlling the applied gate potential, the operation mechanism of the electrolyte-gated transistors can be modified from electric double layer to electrochemical doping. KEYWORDS: electrolyte-gated transistor, electrochemical, electric double layer, solvothermal synthesis, GIZO nanoparticles 1. INTRODUCTION The aim of low-cost and sustainable devices, for a broad range of fully disposable commodities, has resulted in an increased interest in solution based deposition technologies and nano- materials that are able to produce devices with enhanced per- formance and low power consumption. 1 The first work of electrolytes used in transistors was reported in 1954 by Brattain and collaborators at Bell Laboratories. 2 At that time, the main goal was to reduce the surface defects of point contact in germanium transistors by adjusting the surface potential. Only 30 years later the use of electrolyte-gated tran- sistors (EGTs) became popular, especially for organic transis- tors with the pioneer work of Wrighton et al., 3 taking profit of the reversible electrochemical oxidation of the semiconducting polymers. Recently, EGTs are once again attracting significant attention mainly because of the low operating voltage compared to con- ventional thin-film transistors (TFTs). This arises from the high capacitance of the electrolytes, usually in the order of 1-10 μF cm -2 , which exceeds the capacitance of high-κ dielec- trics like Ta 2 O 5 by at least 1 order of magnitude and even the one of ultrathin dielectrics based on self-assembled monolayers by a factor of ∼5. 4 Furthermore, the static capacitance of the electrolyte is nearly thickness independent, resulting in large process margins, hence in increased yield when scaling the device fabrication to industrial applications. In particular, mak- ing this type of transistors attractive for roll-to-roll printing on flexible substrates. 5 Figure 1 schematically illustrates and com- pares a conventional dielectric and an electrolyte-gate insulator, showing the voltage profile and the electric field distribution when a positive voltage is applied to the gate electrode. So far, the drawbacks of the EGTs are related to large leakage currents and high switching times, as well as large parasitic capacitances, especially when integrated in an electric circuit. 4 Recent studies have been reported describing several attempts to overcome such issues nevertheless, the operation behavior of these transistors is still not fully understood. In the present study, the operation mechanism of the EGTs have been distin- guished in two different types, depending on the semiconductor material permeability to ions existing in the electrolyte and on the applied gate voltage. 4 When a positive gate voltage is applied, negative and positive ions accumulate at the gate/electrolyte and Received: October 3, 2014 Accepted: December 17, 2014 Research Article www.acsami.org © XXXX American Chemical Society A DOI: 10.1021/am506814t ACS Appl. Mater. Interfaces XXXX, XXX, XXX-XXX