In-plane-gate a-IGZO thin-film transistor for high-sensitivity pH sensor applications

In this paper, we propose a thin-film transistor (TFT) with an in-plane-gate (IPG) structure, in which the channel and bottom-gate electrodes are located on the same plane to enhance the sensitivity of the pH sensor. The transistor was applied to an extended-gate field-effect transistor (EGFET) system for disposable sensor implementation. The fabricated IPG pH sensor exhibited amplified pH sensitivity owing to the improved capacitive coupling effects. Moreover, we measured the dependence of the pH sensitivity on the IPG area and evaluated the performance of the pH sensor with the IPG structure. The fabricated IPG pH sensor showed a linearity of 99% or more even for a small IPG area, and the amplification of the sensitivity was improved with further reduction in the area. Notably, we achieved a high sensitivity of 387.58 mV/pH, which is significantly greater than the Nernst limit (59 mV/pH), at the lowest IPG area. To evaluate the stability and reliability of the fabricated IPG pH sensor, non-ideal effects, such as hysteresis and drift characteristics, were considered. The IPG structure exhibited enhanced stability and reliability. Accordingly, we believe that EG-type biosensors with an IPG structure can be useful for biomedicine, clinical diagnosis, environmental monitoring, and point-of-care-testing (POCT) systems.