Contacting versus insulated gate electrode for Si nanoribbon field-effect sensors operating in electrolyte

Electric response to pH variations is employed to investigate Si nanoribbon field-effect transistors (SiNRFETs) operating in electrolyte with different gate configurations. For devices with a conducting gate electrode for direct metal-electrolyte contact, a well-defined electrode reaction leading to a stable electrode potential is essential for retaining a stable electrical potential of the electrolyte. However, noble metals such as Pt do not meet the stability requirement and consequently bring severe distortions to the electronic response. For devices with an insulated gate electrode relying on the principle of capacitive gate coupling, the capacitance between the gate electrode and the electrolyte should be made much larger than the gate capacitance established between the SiNR and the electrolyte. In this case, an efficient gate control as well as a high stability against external disturbances can be ensured. Further studies show that surface charging of the gate insulator is the main cause responsible for the pH response of the SiNRFETs. Hence, devices with different gate configurations give rise to a comparable pH sensitivity.