Ionic Liquid Channel Field Effect Transistor Fabricated Using Silicon Dioxide Trench

This work explores the fabrication and characterization of an ionic liquid channel field effect transistor (FET) incorporated within the trench structure on SiO
₂
. The trench structure allows any liquid to be accommodated, thereby eliminating the mold creation on the device or the requirement for an intricate architecture to store liquid. For the fabrication of the trench, we followed a standard photolithography process with the help of selective etching of aluminum and SiO
₂
. The fabricated trench surface is characterized using atomic force microscopy (AFM) and contact angle analysis. The electrical characterization of the proposed FET structure is also performed with 0.01-mM potassium chloride (KCl) solution as an ionic channel. We tested both the n-FET and p-FET type characteristics which can be controlled by the back gate biasing condition. The dc characterization shows a high I
_ON
/I
_OFF
ratio of 10
⁵
for both the n-FET and p-FET. The device further shows an improvement in K
⁺
mobility and Cl
^-
mobility of 2.24 ×10
^-4
m
²
/Vs and 4.96 ×10
^-4
m
²
/Vs, respectively. We also carried out the FET structure modeling to estimate the effective C
_ox
for the trench SiO
₂
structure. It is observed that the total capacitance after the inclusion of Debye length is 1.29 ×10
^-4
F/m
²
. Furthermore, the number of ions is also calculated from the electrical characteristics, and it is almost comparable with the number of ions in the molar solution. Overall, the proposed fabricated structure, although simple, enables to accommodate any liquid as a channel and provides an easy way to develop electrolyte-based sensors.