pH sensor based on an AlGaN/GaN HEMT structure

pH sensor based on a gateless AlGaN/GaN high electron mobility transistor (HEMT) structure is reported in this paper. The sensing characteristics of the devices have been measured in hydrochloric acid solutions in pH=2 to pH=6 respectively. The device with gate sensing area of 250×400μm2 shows sensitivity of 0.0944mA/mm-pH in the linear region (Vds=0.5 V), while the one with gate sensing area of 15×400μm2 shows sensitivity of 2.19 mA/mm-pH in the saturation region (Vds=13 V). The results show that the carrier sheet density of the two dimensional electron gas (2DEG) could be effectively tuned by the solutions with different H+ concentration at AlGaN gate region, and higher sensitivity could be obtained in the saturation region than in the linear region. It is analyzed that the device with shorter gate length could reach saturation at lower voltage. Furthermore, sensing in the saturation region helps to overcome the measurement error caused by voltage fluctuations.