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 SiO ₂ /HfO ₂ /Al ₂ O ₃ (OHA) stacked layer structure was proposed as an engineered sensing membrane, and the characteristics were compared with SiO ₂ (O) and SiO ₂ /Si ₃ N ₄ (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.