Low-Voltage Feedback-Field-Effect-Transistor-Based Ion Sensing: A Novel and Detailed Investigation for Energy-Efficient pH Sensor

In this letter, we present simulation-based results of a vertical nanowire feedback field-effect transistor as an ion sensor (ISFBFET) for accurate pH detection. The sensing mechanism of the investigated ISFBFET draws upon the principles of the Gouy–Chapman–Stern layer and the site-binding model. Along with SiO
₂
only, the deposition of Al
₂
O
₃
on SiO
₂
as a sensitive layer is investigated. Sensitivity parameters are obtained from snap-back characteristics and are evaluated against work function (Φ
_G
) engineering. At optimized conditions, the ISFBFET results in
I
_ON
/
I
_OFF
= 10
¹⁰
and a subthreshold slope = 0.03 mV/dec with Al
₂
O
₃
-SiO
₂
improving the
I
_ON
/
I
_OFF
by a factor of 1.24 (Φ
_G
= 4.7 eV) and 5.53 (Φ
_G
= 5.1 eV) over an oxide-only gate insulator. Up to Φ
_G
≤ 4.3 eV, the sensing response of SiO
₂
is marginally better, whereas for Φ
_G
> 4.3 eV, Al
₂
O
₃
-SiO
₂
has a better sensing response. Peak sensitivity for Al
₂
O
₃
is observed at Φ
_G
= 4.7 eV; the maximum constant current sensitivity and voltage sensitivity are observed as 3927 and 2.73, respectively. In the near future, due to low power functioning, steeper response, and high sensitivity, the Al
₂
O
₃
-SiO
₂
-based ISFBFET can replace conventional oxide-based ion sensors for pH detection in commercial applications.