Inverter circuits on freestanding flexible substrate using ZnO nanoparticles for cost-efficient electronics

Driven by the Internet of Things (IoT), flexible and transparent smart systems have been intensively researched by the scientific community and by several companies. This technology is already available for consumers in a wide range of innovative products, e.g., flexible displays, radio-frequency identification tags and wearable electronic skins which, for instance, collect and analyze data for medical applications. For these systems, thin-film transistors (TFTs) are the key elements responsible for the driving currents. Solution-based materials such as nanoparticle dispersions avail the fabrication on large-area substrates with high throughput processes. In this study, we discuss the integration of ZnO nanoparticle thin-film transistors and inverter circuits on freestanding polymeric substrates enclosing the main issues concerning the transfer of the integration process from a rigid substrate to a flexible one. The TFTs depict VON between −0.2 and 1 V, ION/IOFF > 104 and field-effect mobility >0.5 cm2 V−1 s−1. Additionally, in order to enhance the transistors and inverters performance, an adaptation on the device configuration, from an inverted coplanar to an inverted staggered setup, was conducted and analyzed. By employing the inverted staggered setup a considerable increase in the contact quality between the semiconductor and the drain and source electrodes was observed. As the integrated devices depict electrical characteristics which enable the fabrication of electronic circuits for the low-cost sector, inverters were fabricated and characterized, evaluating the circuit's gain as function of the applied supply voltage and circuit's geometric ratio.