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Influence of electrical conductivity of carbon film nanocomposites on field emission characteristics of planar-end electron sources

DOI 10.18127/j00338486-201907(10)-08


R.K. Yafarov – Dr.Sc.(Eng.), Professor, Head of Laboratory of Submicron Electron-Ion Technology, Saratov Branch of Kotel’nikov IRE of RAS
D.V. Nefedov – Ph.D.(Eng.), Research Scientist, Laboratory of Submicron Electron-Ion Technology, Saratov Branch of Kotel’nikov IRE of RAS

The factors that determine the improvement and stability of the field emission characteristics of field sources of electrons are investigated. As practice shows, the main factor of instability is the strong dependence of field emission from the morphology and electrical properties of the emission surface. Due to the high steepness of the field emission current-voltage characteristics, minor fluctuations in the operating voltage lead to an uncontrolled transition from stable field emission to explosive emission. This causes the destruction of the existing emission centers and changes the mode of operation of the electron source. One of the ways to prevent this transition is a series connection to the emission structure of a sufficiently large ballast resistance, which reduces the total current in the circuit. This, on the one hand, complicates the technology of manufacturing electron sources, and on the other hand, due to the spread of electrophysical properties and parameters of emission centers, does not always lead to the desired results. In this regard, the determination of requirements for the electrophysical characteristics of carbon films from which field cathodes are made, as well as the search for ways to control the transport properties of carriers that ensure longer and more stable operation of vacuum microelectronics devices, is an urgent task. The aim of the work was to study the effect of the electrical conductivity of diamond-graphite film structures and the field current-selection scheme on the field emission characteristics and stability of operation in strong pulsed electric fields of microsecond duration of sources of cold electrons. It has been established that in electron sources based on diamond-graphite film nanocomposites, the use of additional control electrodes makes it possible to reduce the thresholds for the onset of field mission and to increase the maximum densities of field emission currents. When using diamond-graphite film structures with different electrical conductivities, there are optimal grid voltages at which the stability of the field emission mode of electrons increases. To characterize the stability of the field emission mode of electrons, an approximation of the obtained current-voltage characteristics by exponential functions was performed. It is shown that the stability of the field emission, in addition to the optimization of the field current collection circuit, increases with increasing duration of the anode voltage pulses. When using optimal grid voltages corresponding to the extremes of the anodic field strengths, the start of field emission for different resistances of diamond-graphite film structures, the pre-breakdown field emission currents in all cases are greater than in their absence. Anode currents with increasing pulse durations increase. At high resistances, the use of optimal grid voltages increases the pre-breakdown currents, compared with their absence, by more than an order of magnitude. The effectiveness of the use of grid voltages increases with increasing resistance of diamond graphite nanocomposites.

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