Enhanced current sensitivity of AlGaN/GaN pH sensor by combining recessed-gate and increasing the ratio of W/L

The pursuit of enhanced performance in pH sensors is crucial for expanding their applications across various industrial fields. This work presents a systematic investigation into the electrical characteristics and pH sensitivity of AlGaN/GaN sensors, through comparative analysis of sensors with varying W/L ratios (where W and L denote gate width and length, respectively) and with/without recessed-gate. The primary optimization strategy was to enhancing current sensitivity (S_A) by maximizing sensor transconductance. The synergistic combination of recessed-gate implementation and W/L ratio optimization yielded a 16-fold improvement in maximum transconductance (G_M), increasing from 0.82 mS (without recessed-gate, W/L = 800/800 μm) to 13.18 mS (with recessed-gate, W/L = 800/200 μm). This substantial boost in transconductance directly translated to a superior sensing capability. The current sensitivity (S_A) experienced a corresponding 13.2-fold increase, rising from 40.3 μA/pH to 532.7 μA/pH. Furthermore, over the course of 500 repeated measurements, the drift of reference electrode voltage (V_REF) ranged between 35 and 53 mV, demonstrating excellent stability.