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We have developed a fast and simplistic AlGaN/GaN high electron mobility transistor (HEMT) for the detection of heavy metals such as mercury, lead, copper and zinc in water with a dynamic range of 1 nM to 1 mM. Four device designs have been fabricated where the gate structure and the distance between the source and the drain have been varied. It is observed that the device with meander gated (MG) structure and larger sensing area showed better response. A detailed analysis of the surface of the samples has been also investigated using SEM, EDS and Raman spectroscopy which confirms the re-usability of the sensor for a longer period of time. The response of the sensor stabilizes at 35 and 27 s for mercury and copper ions respectively. The response time of the sensor also shows a concentration dependent behavior. The sensor exhibits the high sensitivities of 31, 38, 35, and 24 mV/decade [M] for mercury, copper, zinc and lead ions respectively.

In this paper, a GaN-high electron mobility transistor (HEMT) based sensor is designed, fabricated and characterized for polar liquid sensing. The fabricated HEMT sensor chip is packaged by using low temperature co-fired ceramic (LTCC) technique. The sensor shows a typical drain current of 21.2 mA at 3.3 V. The fabricated sensor shows a percentage change of 1.78%, 2.18% and 6.3% in drain current for mercury chloride, copper chloride and sodium chloride respectively with respect to the drain current of pure water. The readout circuit shows a change of 0.15, 0.20 and 0.34 mA in drain current for acetone, water and methanol respectively and ensures the detection of different polar liquids. Due to the novel inter-digital structure, the sensor shows a sensitivity of 5.98 mA/mm/Debye at a drain voltage of 3.3 V. Sensing mainly depends on the dipole moment because the change in the dipole moment of the liquid causes a change in surface potential at the gate sensing area. This paper gives a theoretical and practical perspective on polar liquid detection using both, the sensor and system.