Research On Silicon-Based Composite Cathode Field Emission Electron Source

Vacuum electronic devices are widely used in military,national defense,communication,medical and other fields.The electron source is the core of the vacuum electronic device,and the performance of the electron source directly determines the performance of the electron gun and the entire vacuum electronic device.With the development of micro-nano processing technology and low-dimensional materials,new field emission electron sources that are easy to miniaturize and integrate emerge in an endless stream,which greatly promotes the development of vacuum electronic devices.In order to meet the requirements of electron microscopes,X-ray tubes and other vacuum electronic devices for high current density and high brightness electron sources,a high-performance silicon-based composite cathode field emission electron source is prepared through micro-nano processing technology combined with low-dimensional materials.The structural parameters of the silicon substrate were analyzed by numerical simulation,the fabrication process and fabrication parameters of the cathode were optimized,and the emission performance was tested.The results show that the prepared silicon-based composite cathode has excellent emission properties and is expected to be applied in electron microscopes,X-ray tubes,etc.The specific research contents are as follows:(1)The structural parameters of the silicon substrate were analyzed by numerical simulation,and the optimal structural parameters were determined in combination with the fabrication process.the silicon tip-graphene composite cathode was prepared by transfer method,and the emission performance was tested under continuous DC conditions.The test results show that the turn-on electric fields of 2μm,2.5μm,and 3μm silicon tip-graphene are different,which are 5.3V/μm,4.6V/μm,and 3.8V/μm,respectively.The change trend is consistent with the simulation results,and compared with the bare silicon array cathode,the turn-on electric field is significantly reduced.The maximum emission current of the 2.5μm-high silicon tip-graphene composite cathode is about2.5μA,and the current density can reach 26m A/cm~2 when the electric field strength is 6.5 V/μm.The field enhancement factor calculated by F-N fitting is 1078,at the same time,the emission stability is good,and the emission current fluctuates within 5%within 6 hours under 3k V voltage.(2)A new scheme for preparing silicon pillar-carbon nanotube composite cathode was proposed,and a dense catalyst film was successfully prepared on top of the silicon pillar by magnetron sputtering and overlay process.Subsequently,well-oriented carbon nanotubes were prepared on top of the silicon pillars by chemical vapor deposition.Under continuous DC conditions,the repared silicon pillar-carbon nanotube array composite cathode has a turn-on electric field of less than 1V/μm,the emission current of 220μA when the electric field strength is 5.4V/μm,the current density of about 2.2A/cm~2,and the emission current fluctuation rate is 4.7%within 8hours.Under pulsed conditions,when the electric field strength is 12.5V/μm,the emission current can reach about 1.3m A,and the current density can reach about 13.2A/cm~2.(3)The structure of the silicon pillar-carbon nanotube composite cathode was optimized,and a single composite cathode with a smaller emission area(about 80μm~2)was prepared.Under continuous DC conditions,the turn-on electric field is less than 0.7V/μm,the emission current can reach 115μA when the electric field strength is 5V/μm,the current density is as high as 150A/cm~2,and the emission current fluctuation rate is 2.3%in 7.5 hours.Under pulsed conditions,the emission current can reach 400μA when the electric field strength is 5.3 V/μm,and the current density is as high as 520 A/cm~2,which is an order of magnitude improvement compared with the current density of carbon nanotube cathodes and silicon-based composite cathodes reported so far.At the same time,the brightness characteristics of the silicon pillar-carbon nanotube composite cathode were studied,and the brightness of the array cathode could reach 2.964×10~3A/(m~2·sr·V).From the test results,the prepared silicon pillar-carbon nanotube composite cathode has excellent emission characteristics and is expected to be used in future vacuum electronic devices.