Multiscale modeling of organic electronic biosensor response
- Autores: Larissa Huetter
- Directores de la Tesis: Gabriel Gomila Lluch (dir. tes.)
- Lectura: En la Universitat de Barcelona ( España ) en 2022
- Idioma: inglés
- Tribunal Calificador de la Tesis: Carlo Augusto Bortolotti (presid.), Anna Maria Vilà Arbonés (secret.), Tobias Cramer (voc.)
- Programa de doctorado: Programa de Doctorado en Biomedicina por la Universidad de Barcelona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
There have been significant advances in organic bioelectronic devices in recent years. These devices are capable of stimulating excitable cells and can generate data to facilitate disease diagnostics and monitoring. Electrolyte-gated organic field-effect transistors (EGOFETs) are powerful organic bioelectronic devices. EGOFETs are a group of thin-film transistors used as the sensing units within organic bioelectronic devices due to their ability to strongly amplify the signal and natural biocompatibility. EGOFETs can detect minor voltage variations of electrically excitable cells or when analyzing biomarkers. Organic semiconductors offer various advantages over inorganic ones, such as low-cost production, flexibility, printability as well as allowing easy integration into sensing devices or textiles.
Due to the lack of specific physical-mathematical modeling of EGOFETs, they are often approximated using ideal field-effect transistor (FET) models. Whilst these models can be useful, they are not capable of accommodating ionic diffusion effects generated by nanoscale variations at the electrolyte/semiconductor and electrolyte/gate interfaces within EGOFETs. This thesis presents the physical modeling of EGOFETs to provide a deeper physical understanding of these devices. We show the changes in the macroscale current correlated to the nanoscale conductivity when changing the device geometries. Further, we observe the voltage shifts due to ionic concentrations and evaluate the role of interfacial layers and fixed charges at the gate electrode. We address these problems with finite-element models coupling the device physics of the electrolyte and the semiconductor.
Different levels of complexity of the models have been considered. The simpler Helmholtz model, where the electrolyte is mimicked as a Helmholtz capacitance, was selected initially. Using this, we determined that many of the transfer and output current-voltage curves of EGOFETs could be reproduced. This enabled the identification of local conductivity changes in the different operating regimes.
We subsequently expanded the physical model by incorporating the electrolyte's ionic diffusive effects and compact interfacial layers' presence using the NPP framework. Initially, a one-dimensional capacitor structure model was used to gain fast results without neglecting the physics of the device. This model demonstrated the change in device characteristics following the addition of biorecognition layers to the gate electrode for biosensing applications. Developing this further, we considered the NPP model in two-dimensional structures, which allowed investigating changes to devise geometry, including channel and gate length in the NPP framework. This provides a deep insight into the voltage and charge density distributions to reveal the formation of space charge layers, including accumulation and ionic diffusive layers. The potential profiles over semiconductors and electrolytes demonstrate the differences in charge accumulation for gate modifications with self-assembled monolayers, ion concentrations, and material parameters. We correlate the charge accumulation along the conductive channel with the distribution of ions.
The results of these studies allowed us to provide further explanations of the behavior of EGOFETs and have opened the door to a rational design and characterization of the devices for future biosensing applications.
