Performance Optimization Of Electrical Devices Based On CVD Monolayer Molybdenum Disulfide

As the size of traditional silicon-based devices continues to shrink,the short-channel effect is becoming more and more obvious,and Moore’s Law is about to come to an end.It is urgent to find a new type of semiconductor material to continue Moore’s Law.Molybdenum disulfide layered single crystal material has entered people’s attention at this time.Disulfide with atomic thickness exhibits excellent optical and electrical properties,as well as excellent mechanical properties.It is used in low-power basic logic devices,optoelectronic devices,flexible Devices and other fields have broad application prospects.Although molybdenum disulfide has been widely studied,the current technological level is still difficult to achieve the controllable preparation of high-quality,large-area molybdenum disulfide,and the performance of basic electrical devices based on molybdenum disulfide is far from ideal.In view of this,this paper focuses on the controllable growth of molybdenum disulfide layered single crystals and the preparation of field effect devices.The following are research contents:1.Controlled growth of layered single crystals of molybdenum disulfide.Compared with the traditional mechanical lift-off method,the growth conditions of the chemical vapor deposition method are easier to control.We used the self-built single-temperature zone chemical vapor deposition system to explore the growth of molybdenum disulfide from four aspects:substrate,molybdenum source area,sulfur source heating rate,and airflow.Molybdenum disulfide layered single crystals with an average size of 100μm were stably prepared on the surface.The specific exploration process is as follows:We first explored the growth of molybdenum disulfide layered single crystals on three different substrates:silicon oxide,sapphire,and soda lime glass.The average value is 25μm,35μm,120μm,and soda lime glass wins by obvious advantages;Secondly,on the basis of soda-lime glass as the growth substrate,the influence of different growth conditions（molybdenum source area,sulfur source heating rate,carrier gas flow rate）on the growth of molybdenum disulfide layered single crystal was explored.The epitaxial growth of large-sized molybdenum disulfide is realized on the bottom,the largest single crystal size can reach350μm.2.Improving the transfer method to improve the performance of molybdenum disulfide field effect transistors.At present,two mainstream transfer methods for 2D materials are PMMA water-assisted transfer method and PDMS dry transfer method.However,both methods have certain drawbacks,For example,in the water-assisted transfer method,although the transfer process is clean enough,the two-dimensional material will be in direct contact with water during the transfer process,causing the material to wrinkle,which will destroy the morphology of the two-dimensional material and reduce its electrical properties.In the PDMS dry transfer method,because the PDMS cannot be completely adhered to the growth substrate,a part of the two-dimensional material cannot be taken away due to the lack of contact with the PDMS,resulting in low transfer efficiency and even damage to the material surface.On the basis of the above two transfer methods,this thesis developed a new transfer method named PMMA dry transfer method.Using PMMA as the transfer medium,the two-dimensional materials were dry transferred in a high humidity environment,so that It not only ensures that the two-dimensional material will not directly touch moisture,but also ensures the transfer efficiency.After AFM characterization,it was found that the molybdenum disulfide obtained by the PMMA dry transfer method has almost no wrinkles,while the molybdenum disulfide obtained by the water-assisted transfer method has more surface wrinkles.The electrical properties of the molybdenum disulfide transistors prepared by the two methods were characterized,and the field effect mobility of the PMMA dry transfer electrical device was calculated to be18cm²V^-1S^-1,which was twice that of the PMMA water-assisted transfer method,which was enough to prove Prominent effect of suitable transfer method on improving the performance of molybdenum disulfide field effect transistors3.Improving molybdenum disulfide field effect transistor performance and stability using oxide passivation.At present,due to the limitation of growth technology and transfer technology on the quality of molybdenum disulfide thin films,devices prepared from them generally have many defects and low mobility,which limit the wide application of molybdenum disulfide devices.In view of this,this paper proposes an effective strategy to significantly improve the quality of monolayer molybdenum disulfide grown by chemical vapor deposition using atomic layer deposition oxide encapsulation technology,and investigates different oxide layers,oxide layer thicknesses on the encapsulation effect.Benefiting from the passivation of defects and the suppression of charge Coulomb scattering,the field-effect mobility can be increased by more than 3 times to 36cm²V^-1S^-1compared with the unpackaged field effect transistor under optimal packaging conditions.