Research On Room Temperature SO₂ Gas Sensor Based On Reduced Graphene Oxide Field Effect Transistors

Gas sensors play a vital role in many application fields such as industrial manufacturing,medical diagnosis,national defense,and environmental protection.Sulfur dioxide(SO₂)is being as one of the main air pollutants,and its concentration detection is considered as one of the key research directions in the field of gas sensing.In this thesis,a SO₂ gas sensor based on reduced graphene oxide(r GO)field effect transistor(FET)is proposed,in which the composite film of r GO and Ti O₂nanoparticles(NPs)is used as the gas sensing layer to realize the detection of SO₂ gas at room temperature.At the same time,based on the realization of 2D Ti O₂/r GO FET,the3D Ti O₂/r GO FET is fabricated by self-rolled up technique.It has been detected that the device area for the 3D structure is effectively reduced compared with 2D counterpart,which is expected to realize the miniaturization,integration and high performance of SO₂ gas sensing.The main research contents of this thesis are as follows:Firstly,a FET-type room temperature SO₂ gas sensor based on Ti O₂ NPs and r GO composite gas-sensing thin film(Ti O₂/r GO)is proposed in this thesis.By adopting the buried-gate structure,the problem of large circuit power consumption caused by the large gate voltage for the back-gate structure has been avoided.Meanwhile,the problem that the top grid structure blocks the gas sensing film has been avoided.In addition,by using the interdigital electrode contact electrode,the contact area between the electrode and the gas-sensing thin film has been increased,while,the contact resistance has been reduced.Hence,the gas-sensing performance has been further improved.The Ti O₂/r GO FET type SO₂ gas sensor can adopt either 2D planar structure or 3D"microtubular"structure.Secondly,the controllable fabrication for 2D and 3D Ti O₂/r GO FET devices are realized by using Micro-Electro-Mechanical-System(MEMS)technology.The Ti O₂/r GO composite gas-sensing thin film was prepared by means of thin film forming technology and simple thermal reduction method.By applying the sacrificial layer and the self-rolled up technique based on the Si N_x stress layer,2D devices are self-rolled up into 3D"microtubular"structure,where 3D Ti O₂/r GO FET devices are obtained.The morphology and structure of the 2D/3D devices were characterized by the optical microscope and scanning electron microscope(SEM).Then,the electrical properties of 2D and 3D Ti O₂/r GO FET devices were investigated and characterized.The experimental results show that the 2D and 3D devices exhibited typical bipolar characteristics before and after self-rolled up,and the Dirac point voltage changes slightly.However,the resistance of 3D device is slightly higher than that of 2D device due to the introduction of curling stress at the same gate voltage.Finally,the performance of 2D Ti O₂/r GO FET for SO₂ detections at room temperature was investigated.A responsibility of a round 3.46%is obtained for 20 ppm SO₂ with a gate voltage of 0 V and a source-drain voltage of 2 V.Moreover,the responsivity of 2D Ti O₂/r GO FET to SO₂ increases with the increase of source and drain voltage.Considering that the chip area of 3D Ti O₂/r GO FET is only half of that of 2D devices with the same gas sensing area,3D devices are expected to achieve higher performance for SO₂ gas sensing.