Nanoscale Multimodal Characterization of Operating Electrolyte-Gated Transistors

Programa de Doctorat en Biomedicina / Tesi realitzada a l'Institut de Bioenginyeria de Catalunya (IBEC) [eng] Electrolyte-gated transistors (EGTs) have emerged as key platforms for transducing and amplifying biological and biochemical signals, making them an integral part of diverse biosensing and bioelectronic applications ranging from single molecule biosensors to neuromorphic devices. Despite being the foundational architecture, the fundamental understanding of the nanoscale electronic and ionic transport governing the device operation remains poor, which hinders further progress in the rational and targeted optimization of devices for various applications. The limitation mainly stems from the lack of characterization methods that can probe ionic and electronic transport processes in operating devices at the nanoscale under electrolyte environments and in application-relevant conditions. Further complexity arises due to diverse molecular design of organic semiconductors that expresses wide variety of coupled electrical and mechanical behaviours. In this thesis, we developed an advanced multimodal characterization method based on in-liquid Scanning Dielectric Microscopy (SDM) that simultaneously probes relevant electrical and mechanical properties at the nanoscale in functional EGTs. The presented method significantly advances an earlier implementation of in-liquid SDM for the same purpose by adding automated data acquisition and analysis functionalities along with technical improvements for the comprehensive characterization of EGTs. We introduced a straightforward and robust approach for data interpretation and representation that effectively eliminated experimental artefacts and the calibration procedures, enabling rapid and accurate analysis. The approach also enabled quantification of the local electric potential directly from raw experimental data, thereby providing direct access to fundamental charge transport parameters such as contact access resistances, inter-and intra-domain charge transport, and anisotropy, which weren't accessible earlier at the nanoscale in operating EGTs. We studied two varieties of EGTs, namely Electrolyte-Gated Organic Field-Effect Transistors (EGOFETs) and Organic Electrochemical Transistors (OECTs), which exhibit distinct operating mechanisms. We first focused on EGOFETs based on a blend of organic semiconducting material diF-TES-ADT and the insulating polymer polystyrene (PS), where we investigated the local electrica