Ultra-sensitive Floating Gate Transistor Gas Sensor Based On Carbon Nanotube Film

With the development of Internet of Things(IOT),the need for low power sensors with high sensitivity and environmental compatibility become more and more urgent.With the emergence of many new nanomaterials,a variety of nanomaterials and different technologies have been widely used in the sensing field.Among these emerging nanomaterials,its ultra-high specific surface area,ultra-thin volume,low noise and stability make carbon nanotubes(CNTs)to be one of the most promising candidate for gas sensing field.Nevertheless,it's still challenging to provide an ultra-sensitive carbon based gas sensor with a sub-ppm Limit of Detection(LOD).To date,the focus of CNTs based gas sensors is mainly based on the material optimization and some device parameter improvement based on the resistance-type(R-type)structure to enhance the sensitivity.As a clean energy,Hydrogen(H₂)has been widely used in many fields.Nowadays,most of the hydrogen detections concerned on the concentration around the flammable point(4%)of hydrogen,but the detection at trace level or ppb level is essential in some applications,such as in deep-space,leakage monitoring in nuclear power plants and so on.However,it is a big challenge to detect H₂,the smallest atoms,with an ultra-low concentration.Few research studies alternative device architecture to achieve co-optimization of the sensitivity,selectivity,bias stress stability and life of CNT gas sensors.In this work,a floating gate FET structure is applied to improve the sensing performance synthetically.The floating sensitive gate(Pd nanoparticles)is separated from the conduction CNTs channel by a thin layer of high-?Y₂O₃ dielectric,reducing the scattering introduction and realizing the complete isolation between the channel and sensing materials,protecting the channel from being possible damaged,regulating the channel as a whole,leading the optimization of sensitivity.Compared with conventional R-type sensors,the FG FET sensors exhibit more than one magnitude enhancement on response at 100 ppm.Meanwhile,by avoiding the diffusion of gas molecules in the environment into the active channel,the non-specific absorption sites can be effectively shielded and thus result in the improvement of selectivity and stability.Significant reduction of the baseline drift under 10 hours'bias-stress and 168 times improvement of the selecting ratio to the interference gases achieved.Moreover,we discussed the sensing mechanism and proposed our response model based on Langmuir adsorption isotherm and find it fitting well with our data,which reflects the superiority of the floating gate structure.Moreover,we achieved the LOD of 90 ppb at room temperature and 5 ppb at?100?,which is the first time for carbon-based H₂ sensors meet the nuclear leak monitoring requirements and is also the lowest H₂ limit of detection(LOD)so far.The co-optimization of the floating-gate H₂ sensors has expanded the potential application field of carbon-based hydrogen sensors,greatly improves its environmental compatibility.Its carbon-based electronic compatibility makes it possible to achieve a carbon-based sensing system and will no doubt promote the development of carbon-based sensors with high sensitivity,high selectivity,stability and low power consumption,which is of great significance for the practical application of carbon-based sensors.