**Marco Moreira , Emanuel Carlos , Carlos Dias, Jonas Deuermeier , Maria Pereira, Pedro Barquinha \* , Rita Branquinho \* , Rodrigo Martins and Elvira Fortunato**

i3N/CENIMAT, Department of Materials Science, Faculty of Science and Technology, Universidade NOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal

**\*** Correspondence: pmcb@fct.unl.pt (P.B.); ritasba@fct.unl.pt (R.B.)

Received: 4 August 2019; Accepted: 3 September 2019; Published: 6 September 2019

**Abstract:** Solution-processed metal oxides have been investigated as an alternative to vacuum-based oxides to implement low-cost, high-performance electronic devices on flexible transparent substrates. However, their electrical properties need to be enhanced to apply at industrial scale. Amorphous indium-gallium-zinc oxide (a-IGZO) is the most-used transparent semiconductor metal oxide as an active channel layer in thin-film transistors (TFTs), due to its superior electrical properties. The present work evaluates the influence of composition, thickness and ageing on the electrical properties of solution a-IGZO TFTs, using solution combustion synthesis method, with urea as fuel. After optimizing the semiconductor properties, low-voltage TFTs were obtained by implementing a back-surface passivated 3-layer In:Ga:Zn 3:1:1 with a solution-processed high-кdielectric; AlOx. The devices show saturation mobility of 3.2 cm<sup>2</sup> V−<sup>1</sup> s<sup>−</sup>1, *IOn*/*IO*ff of 106, *SS* of 73 mV dec−<sup>1</sup> and *VOn* of 0.18 V, thus demonstrating promising features for low-cost circuit applications.

**Keywords:** IGZO composition; solution combustion synthesis; transparent amorphous semiconductor oxides; low voltage operation
