T-ZnO/AlGaN/GaN HEMT Uric Acid Sensor-Sensitivity Analysis and Effect of Surface Wettability for Improved Performance
Praveen Pal, Yogesh Pratap, Sneha Kabra
Abstract
In this work, a ZnO-Tetrapod (T-ZnO) bio-functionalized AlGaN/GaN HEMT based biosensor has been designed for detection of uric acid (UA) present in human serum. The proposed device is easy to fabricate and offers maximum drain current sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$92.5 \mu \text{A}$ </tex-math></inline-formula> . <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{M}$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> and maximum threshold voltage sensitivity of 0.0229 mV. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{M}$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> at UA concentration of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$55 \mu \text{M}$ </tex-math></inline-formula> . Sensitivity has been evaluated by normalizing the drain current, transconductance and channel conductance with respect to gate width. Maximum transconductance and channel conductance sensitivity obtained are 0.0151 mS/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{M}$ </tex-math></inline-formula> and 0.0521 mS/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{M}$ </tex-math></inline-formula> respectively at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$55\mu \text{M}$ </tex-math></inline-formula> concentration. An analytical model has also been developed for drain current which shows good match with the simulated results and previously reported experimental data. Due to hydrophilic nature of AlGaN barrier layer the sensitivity of the sensor changes rapidly with change in surface wettability conditions thus the impact of variation of aluminum (Al) composition in AlGaN barrier layer and surface wettability on device performance has also been studied. The sensor exhibits a very low threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{th}$ </tex-math></inline-formula> ) hysteresis of 1.9 mV at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{G-sweep}=$ </tex-math></inline-formula> (- 8V, 0V) with a low response time of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$260 \mu \text{s}$ </tex-math></inline-formula> .