Development of Engineered Sensing Membranes for Field-Effect Ion-Sensitive Devices Based on Stacked High- $\kappa$ Dielectric Layers

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.