*Article* **Fully Printed Zinc Oxide Electrolyte-Gated Transistors on Paper**

#### **José Tiago Carvalho 1, Viorel Dubceac 1, Paul Grey 1, Inês Cunha 1, Elvira Fortunato 1, Rodrigo Martins 1, Andre Clausner 2, Ehrenfried Zschech 2 and Luís Pereira 1,\***


Received: 28 December 2018; Accepted: 22 January 2019; Published: 30 January 2019

**Abstract:** Fully printed and flexible inorganic electrolyte gated transistors (EGTs) on paper with a channel layer based on an interconnected zinc oxide (ZnO) nanoparticle matrix are reported in this work. The required rheological properties and good layer formation after printing are obtained using an eco-friendly binder such as ethyl cellulose (EC) to disperse the ZnO nanoparticles. Fully printed devices on glass substrates using a composite solid polymer electrolyte as gate dielectric exhibit saturation mobility above 5 cm<sup>2</sup> V−<sup>1</sup> s<sup>−</sup><sup>1</sup> after annealing at 350 ◦C. Proper optimization of the nanoparticle content in the ink allows for the formation of a ZnO channel layer at a maximum annealing temperature of 150 ◦C, compatible with paper substrates. These devices show low operation voltages, with a subthreshold slope of 0.21 V dec−1, a turn on voltage of 1.90 V, a saturation mobility of 0.07 cm<sup>2</sup> V−<sup>1</sup> s<sup>−</sup><sup>1</sup> and an Ion/Ioff ratio of more than three orders of magnitude.

**Keywords:** zinc oxide; nanoparticles; paper transistors; printed electronics; electrolyte-gated transistors
