SnO₂/Carbon Nanotube Floating-Gate Field-Effect Transistor Gas Sensor for ppb-Level CO Detection

Carbon monoxide (CO) poses significant health risks to humans, impacts the lifespan and efficiency of hydrogen fuel cells as a primary impurity, and is also used for early insulation fault diagnosis in equipment. However, portable CO detectors with low detection limits are still lacking. In this work, we demonstrate a floating-gate field-effect transistor (FG-FET) for a CO gas sensor, in which the carbon nanotubes (CNTs) and tin oxide (SnO 2 ) film are separated by Y 2 O 3 layer and act as channel and sensing layer, respectively. Thanks to the wettability of Y 2 O 3 and the secondary annealing process in the preparation of SnO 2 by sol–gel method, the structure not only ensures the stability of the channel but also possesses an optimized interface state with sensing material, protecting the stability of the device and facilitating excellent transmission of the sensing signal. The SnO 2 /CNT FG-FET sensor achieved effective monitoring of 1 ppb of CO at 150 °C, breaking the current CO detection limit. Furthermore, the sensor demonstrates good regular response in the range of 1–30 ppb CO gas concentration. The prepared CO sensor features an extremely low detection limit, ultrahigh sensitivity, and excellent selectivity, providing an idea for high-performance FET gas sensor development.