Research On The Application Of La-Based High-k Gate Dielectric In Graphene Field Effect Transistors

Graphene has been attracting much attention since its discovery.Its unique chemical structure enables it to have ultra-high carrier mobility and natural thickness advantage,which brings new opportunities and challenges to the research of nano-electronic devices.With the continuous improvement of chip integration,GFET will also face problems such as the increase of leakage current and the decrease of device reliability caused by the reduction of device size.Therefore,it is particularly important for the long-term development of GFET to prepare the high k gate dielectrics with compatible technology and superior performance to replace the traditional silicon dioxide gate dielectric.At present,the focus of graphene research is mainly on the growth and transfer of graphene,opening of graphene band gap,optimization of graphene-related device technology and other aspects,but there is little research on the application of high k gate dielectric in GFET.Based on this,rf magnetron sputtering technology was used to deposit Hf doped lanthanide binary oxide film in this work,and on this basis,full back gated GFET was prepared to explore the effect of lanthanide high k gate dielectric film properties on the performance of graphene FETs.The specific research contents and results are as follows:Based on rf magnetron sputtering technology,HfLaO_x thin films were deposited at room temperature using Hf/La alloy single target.The effects of sputtering power and sputtering oxygen partial pressure on the growth of thin films were systematically investigated.The properties of thin films were optimized by annealing after deposition.The experimental results show that when the sputtering power is 120 W and the sputtering oxygen flow is 6 sccm,the k value and EOT of HfLaO_x film after annealing for 10 min at 400?nitrogen are 33 and 6 nm respectively.Based on the monolayer graphene grown from copper foil CVD,GFET with micron channel size was prepared by PMMA assisted transfer,photoligraphy,plasma etching and other techniques.According to the electrical test results,compared with the 300 nm SiO₂based GFET,the mobility of the GFET with HfLaO_x gate medium is increased by 4 times,the current switching ratio is up to 12,and the Dirac point of the device is between 0 V and 8 V,and the lowest is up to 1.8 V.In order to further explore the effect of HfLaO_xgate dielectric properties on GFET performance,HfLaO_x thin films with different thickness and different La/Hf element ratio were prepared,and GFET was prepared on this basis.The experimental results show that the 30 nm HfLaO_x has better gate control ability,and the Dirac voltage of the GFET decreases with the increase ofLaelement ratio.In this thesis,high-performance HfLaO_x films were deposited by magnetron sputtering,and GFET with HfLaO_x full back-gated structure was constructed on this basis.Compared with traditional Silicon-based GFET,its performance was greatly improved.The research results in this thesis verify that lanthanide high k materials are compatible with GFET,and show some unique tunable effects,providing a new choice of gate dielectric materials for the following study of graphene field effect transistors,and laying a foundation for the preparation of high-performance GFET.