Abstract
The sensitivity of conventional ion-sensitive field-effect transistors is limited to the Nernst limit (59.14 mV/pH). In this study, we developed a pH sensor platform based on a coplanar gate AlGaN/GaN metal-oxide-semiconductor (MOS) high electron mobility transistor (HEMT) using the resistive coupling effect to overcome the Nernst limit. For resistive coupling, a coplanar gate comprising a control gate (CG) and a sensing gate (SG) was designed. We investigated the amplification of the pH sensitivity with the change in the magnitude of a resistance connected in series to each CG and SG via Silvaco TCAD simulations. In addition, a disposable extended gate was applied as a cost-effective sensor platform that helped prevent damages due to direct exposure of the AlGaN/GaN MOS HEMT to chemical solutions. The pH sensor based on the coplanar gate AlGaN/GaN MOS HEMT exhibited a pH sensitivity considerably higher than the Nernst limit, dependent on the ratio of the series resistance connected to the CG and SG, as well as excellent reliability and stability with non-ideal behavior. The pH sensor developed in this study is expected to be readily integrated with wide transmission bandwidth, high temperature, and high-power electronics as a highly sensitive biosensor platform.
Highlights
AlGaN/GaN MOS high electron mobility transistor (HEMT) exhibited a pH sensitivity considerably higher than the Nernst limit, dependent on the ratio of the series resistance connected to the control gate (CG) and sensing gate (SG), as well as excellent reliability and stability with non-ideal behavior
We developed a pH sensor based on an AlGaN/GaN MOS HEMT using the resistive coupling of a coplanar gate structure comprising a control gate (CG) and a sensing gate (SG)
We developed a pH sensor based on a coplanar gate AlGaN/GaN MOS HEMT with increased sensitivity using the resistive coupling effect
Summary
Developments in big data, artificial intelligence, deep learning, and internet of things in the fourth industrial revolution have led to increased human-machine interactions and, the requirement of the miniaturization and functionalization of electronic devices. We developed a pH sensor based on an AlGaN/GaN MOS HEMT using the resistive coupling of a coplanar gate structure comprising a control gate (CG) and a sensing gate (SG). We designed an AlGaN/GaN MOS HEMT transducer unit that converts biochemical signals into electrical signals and an extended gate (EG) sensing unit that is directly exposed to the pH solution This separate structure of the transducer and sensing units fundamentally prevents damage to the expensive HEMT and provides a cost-effective sensor platform by replacing the damaged low-cost sensing unit. The variation in the sensitivity of the pH sensor was evaluated according to the ratio of the series resistance connected to the CG (RCG ) and SG (RSG ) of the AlGaN/GaN MOS HEMT transducer, and an amplified sensitivity that exceeded the Nernst limit was obtained. Non-ideal behaviors, such as hysteresis and drift effects, were investigated to verify the stability and reliability of the sensor
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