Recessed Trench Gate AlGaN/GaN HEMT for pH Monitoring: Design and Sensitivity Evaluation

This work proposed a recessed trench gate AlGaN/GaN HEMT for a potential of hydrogen ion ($\rm H^+$) sensing by eliminating the need for a reference electrode. The proposed device performance has been optimized by simulating the device with the help of the ATLAS device simulation tool, considering the pH model. The sensing surface has been functionalized with APTES to improve the sensor's performance to activate the binding sites. The impact of pH solution on the device characteristic alters the threshold voltage sensitivity, drain current sensitivity, and signal-to-noise ratio. The effect of gate voltage in terms of maximum $\rm g_{m}$ has also been optimized for the maximum sensitivity of the device to the pH solution. The device linearity has been utilized for $\rm VIP_{3}$, $\rm IIP_{3}$, and $\rm IMD_{4}$. The average threshold voltage sensitivity obtained is 160.56 mV/pH, higher than the Nernstian limit (59 mV/pH), and the current sensitivity obtained is 22.93 mA/mm.pH. The device's reliability has been optimized by addressing sensor output drift across various temperature and humidity conditions. These findings suggest that the proposed structure presents a promising alternative to current ion sensing techniques.