Demonstration of Extended-Gate Structure for Ion Sensors based on Amorphous Indium-Gallium-Zinc Oxide Thin-Film Transistors

Abstract

This paper presents our work towards improving the reliability of high-sensitivity pH sensor based on the top-gate effect in an amorphous indium-gallium-zinc oxide thin-film transistor (a-InGaZnO TFT) and its application to the sensing of a sodium ion and a potassium ion. Here, we propose an extended-gate a-InGaZnO TFT pH sensor with an atomic layer deposition (ALD)-AlOx/sputtered-TaOx layered top-gate insulator and a Ti extended-gate electrode. We discuss our primary results for the extended-gate a-InGaZnO TFT pH sensor, including its pH sensitivity and ability to respond to a pH change of 0.001. The extended-gate a-InGaZnO TFT pH sensor resulted in over Nernstian pH sensitivity of 625 mV/pH. The pH sensor indicated the possibility of detecting a pH change of 0.001 with some signal processing techniques. Furthermore, we demonstrated the sensing of a sodium ion and a potassium ion with a-InGaZnO TFT and an ion-sensitive extended-gate electrode. The sensors indicated a clear response to the concentration changes of sodium and potassium ions with a sensitivity of 1030 mV/decade and 866 mV/decade, respectively. These results demonstrate that our extended-gate structure has the potential to detect with high sensitivity concentration changes in various ions just by replacing the extended-gate electrode with various ion-sensitive membranes.