AlGaN/GaN HEMT pH Sensor Simulation Model and Its Maximum Transconductance Considerations for Improved Sensitivity
Aasif Mohammad Bhat, Nawaz Shafi, Chitrakant Sahu, C. Periasamy
Abstract
In this work, AlGaN/GaN high electron mobility transistor (HEMT) pH sensing simulation model is presented along with the sensitivity analysis to different pH values of an electrolyte by considering charged adsorbates systematically. Investigations were performed by studying the effect of pH values on device transfer characteristics and a smooth operation is observed with good pH resolution. The output current sensitivity is analyzed from both linear and saturation regions highlighting the response obtained at different drain bias. The device intricacies and sensing mechanism is also explained and demonstrated by analyzing the channel conductance, conduction band, potential profile and coupling capacitance along with the charge distribution profile at various interfaces using ATLAS Silvaco device simulation tool. The pH of solution is modelled by incorporating charged adsorbates as interface charge density at oxide-semiconductor interface in HEMT for the first time to best of our knowledge. The voltage sensitivity (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> ) of 110 mV/pH was observed which is ~2 times beyond Nernst limit of sensitivity (59 mV/pH) and the current sensitivity (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</sub> ) is 17 mA/mm/pH which is 3 orders higher than silicon based devices. The effects of region of operation is also reported with a maximum upto 8 times higher sensitivity being observed in terms of maximum transconductance (g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> ) considerations and a near zero maximum g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> was found to be optimum condition for higher sensitivity operation in reference electrode free configuration. Therefore high sensitive response along with better biocompatibility of AlGaN/GaN HEMT paves its way in next generation biosensing applications.