Abstract
We evaluated the pH-sensing properties of engineered sensing membranes fabricated by stacking high-κ dielectric layers to improve the sensitivity and long-term stability of field-effect ion-sensitive device applications. The SiO2/HfO2/Al2O3 (OHA) stacked layer structure was proposed as an engineered sensing membrane, and the characteristics were compared with SiO2 (O) and SiO2/Si3N4 (ON) membranes. As a result, the engineered OHA sensing membrane revealed higher capacitance and better sensitivity and stability than the O and ON membranes. The electrolyte-insulator-semiconductor device with the OHA membrane exhibited a high sensitivity level of 54.4 mV/pH, a low hysteresis voltage of 14.26 mV, and a small drift rate of 2.15 mV/h. Therefore, the use of engineered OHA sensing membranes is suitable for increasing pH sensitivity and is promising for long-term stable field-effect pH sensor applications.

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