Simulation Of Suspended Graphene-Based Pressure Nano-Sensors

Graphene membrane can be applied as the sensitive material of micro-pressure sensor, because it has high strength,2D properties, high electron transfer rate, zero band gap, and its band gap can be opened through specific direction of strain, any gas can't penetrate it. Comparing with the traditional pressure sensor with Si membrane, graphene-based pressure sensor has better performance, such as high sensitivity, high range, nanoscale. However, currently only basic structure of sensor has been reported, and some actual experiments showed the sensor performance was unstabile. Therefore, improving suspended graphene-based pressure sensor's performance through the structure optimization has become a key point to solve the application problem of grahene pressure sensor.In this thesis, firstly, the influences of strain, band gap, carrier density and mobility on the graphene piezoresistive effect was studied by using the knowledge of semiconductor physics. The tight binding model and Hamiltonian were used to explain why the graphene band gap can be opened by strain. The relationship between the carrier mobility and the bandstructure in graphene was studied by using the exact solution of the linear Boltzmann equation. Combining with the impact of these factors, it was found that the strain on graphene membrane could increase its resistivitty. Then, the finite element method (FEM) software was used to improve the performance by changing the structure parameters and geometry shapes of piezoresistive sensors. The simulation results reveal that circular vacuum cavity structure is better than rectangular vacuum cavity in general pressure sensor, and increasing the aspect radio between the top plate and the contact point areas can bring a high sensitivity in ultrasensitive graphene-based pressure sensor. In order to improve stability of the pressure sensor, the capacitive pressure sensor is designed on the basis of influencing factors reduction, and the effect of changing the structure parameters and geometry shapes on the sensor performance is also studied. According to the simulation results, it is found that decreasing the distance between the two electrodes and increasing the electrodes'area can improve the performance of the sensor.The above results show that a suspended graphene-based pressure sensor with good performance is achieved by using FEM simulation, and the sensor structure designed by simulation can be a useful reference to the experiments.