Photopatternable Solid-State OECTs for Monolithic and Advanced Organic Electronics

Owing to their ability to transport ions and translate them to electronic charges, organic mixed ionic-electronic conductors (OMIECs) have been at the forefront of research in the fields of bioelectronics and neuromorphic (brain-inspired) computing.

One of the building blocks of many of these applications is the organic electrochemical transistor (OECT), which relies on the injection of ions from an electrolyte to modulate its channel current. The complexity of organic circuits using OECTs is however limited, due to the electrolyte generally used for the devices. Their poor mechanical properties or loose entrapment of ions do not allow the deposition of subsequent layers, restricting the overall circuit to a planar architecture. Moreover, due to the sensitivity of OMIECs towards traditional fabrication techniques, mechanical lift-off is still widely used for the patterning of these materials. However, this process is cumbersome, unscalable and poorly reproducible.

We introduce a photocrosslinkable semi-interpenetrating network (SIN) to micropattern an OMIEC (PEDOT:PSS) and a solid-state polyelectrolyte (PSSH). Using conventional lithographic system, the UV-exposed SIN traps the organic polymers and renders them insoluble during the development step. The entrapment of the polyelectrolyte increases its mechanical stability without hindering its ionic conductivity, and enables the deposition of subsequent layers. The gate of the OECT can therefore directly be fabricated below the channel (bottom gate OECT) or above it (top gate OECT), allowing to vertically gate the solid-state transistor. This new architecture and fabrication technique open the creation of monolithic, highly advanced and miniaturized circuits. The implications of such solid-state devices are multiple: front-end amplification and multiplexing for microelectrode arrays, independent transconductance tuning for organic transistors, micropatterning of internal electrolyte reservoir for ion-selective OECTs, faster spiking circuits, upscaling of hardware neural network crossbar arrays, improved ionotronic circuits, or even fundamental research for in-operando analysis.