Investigation on Sensitivity Amplification Factor of DGFET Electrochemical Sensors for pH Detection

Abstract

There has been an increasing interest in the development of chemical and biological FET- based sensors due to their remarkable benefits in label-free detection that has been commonly used in both pH and DNA sensing respectively. In this work, recent Double-Gated Field Effect Transistor (DGFET) as transducers is investigated to understand the super- Nernstian response by amplifying the sensitivity capability in back-gate operations. The BioSensorLab tool was employed to evaluate pH-sensitivity amplification by studying the electrolyte screening and conduction modulation mechanisms which modeled by using Poisson-Boltzmann and Drift-Diffusion equations. The pH sensitivity amplification factors were investigated based on different geometrical configurations of DGFET devices, biasing conditions, and top oxide-electrolyte interfaces. pH sensitivity beyond Nernst limit was observed and increased linearly with the back oxide thickness of the DGFETs. DGFET with a sensitivity of 32.1 mV/pH operated through front-gate operation can be amplified to 195.4 mv/pH through the back-gate operation with a drain voltage of 0.5 V when the back gate oxide thickness increased to 150 nm. Higher pH-sensitivity responses of more than 200 mV/pH were observed where Al₂O₃ and Ta₂O₅ are used for the top oxide-electrolyte. It can be concluded that pH sensing of back gate operation ensures the DGFET transducers operated beyond the Nernst limit.