TCAD Simulation And Key Process Preparation Of Field Effect Transistor Based On Two-Dimensional Material

The performance of graphene FETs is related to the material of the top gate dielectric and substrate.At present,the characteristic of interface between the gate dielectric with graphene and the electrical properties of the gate dielectric are the key to limit the improvement of the device performance.Therefore,the impact of the gate dielectric on the device of the top-gate graphene field effect transistor is focused in this work.The preparation and properties of graphene field effect gate dielectric were studied.The key process of alumina gate dielectric preparation was optimized,and the electrical properties of alumina gate dielectric were further improved.In addition,hexagonal boron nitride(h-BN)has an atomic structure similar to that of graphene,and its two-dimensional planar structure also gives the material an ultra-flat surface with no dangling bonds and charge traps on the surface.At room temperature,the carrier mobility in graphene on h-BN is very high,and h-BN as a substrate and gate dielectric has great advantages in improving the radio frequency characteristics of graphene field effect transistors.Based on the experimental results of the existing devices,silvaco TCAD was used to model the boron nitride/graphene/boron nitride structure graphene field effect transistor to study its mechanism.The core content of this paper is as follows:1)A water pretreatment ALD method for graphene was used to make the alumina compact.Then,the design of pretreatment details in ALD process are optimized,and the results showed that the roughness of alumina grown on graphene for pretreatment was smaller.In addition,a method which use copper net as hard mask to evaporate metal was discovered to test breakdown characteristics and leakage current for dielectric,which was used to evaluate the compactness of alumina.The leakage current of alumina was one order of magnitude smalle than which fabricated by normal ALD method,the results combined with roughness showed that the pretreatment ways can make the alumina more compact.2)A method which alumina is grown on the surface of molybdenum sulfide by using Al seed layer is studied.This method is more effective and can be used in many two-dimensional materials.The leakage current decreases by four orders of magnitude after growth on molybdenum sulfide which are compared with the results for the water pretreatment method,and the breakdown electric field is 8MV/cm,so the alumina,which fabricated by using Al seed layer,is enough to be used to fabricate FETs with top gate structure or other devices.3)The Boron Nitride as gate dielectrics and substrates also has some advantages,so the field effect transistors with BN/graphene/BN structure are simulated in this paper.The model of graphene field effect transistors on SiO2 substrates is simulated by SILVACO TCAD at first.On this basis,the model of BN/graphene/BN structure is established and simulated.The output characteristics including transfer characteristic under different bias voltage are obtained,and the parasitic capacitance,resistance and RF characteristics are also obtained.The specific scattering mechanism of graphene field effect transistors w when BN materials are used as graphene gate dielectrics and substrates is studied from simulation which combine with experimental results.In this paper,some achievements have been made in improving the performance of gate dielectrics for two-dimensional material field effect transistor.The output characteristics of field effect devices have been studied from simulation,which has certain guiding significance for improving the performance of graphene devices and FETs for two-dimensional materials.