Development of field emitters for short wave microwave devices and their investigation in SPbPU: Latest achievements

Topic and aim. The data on the latest achievements of the authors on the development and investigation of field emitters for electron-beam microwave devices of millimeter and submillimeter wavelengths range are presented. Methods. The methods for creating and characteristics of new type cathodes, that are of great practical interest, are described: multi-tip silicon cathodes with two-layer metal-fullerene coatings and multilayer nano-structured cathodes, whose emission is determined by the fields at the contacts of materials with a different work function. Numerical calculations and experimental investigation were carried out to optimize the cathodes and to determine their emission characteristics. The most important features of the experimental setup used are as follows: $\bullet$ the operative change of the pressure from the minimal value $10^{-9}$–$10^{-10}$ Torr up to $10^{- 6}$ Torr and back is possible; $\bullet$ it is possible to carry out a number of technological operations directly in the vacuum chamber, including the deposition and treatment of coatings; $\bullet$ it is possible to study the emission characteristics of cathodes in the continuous and pulsed modes over a wide range of voltages (up to 15–25 kV) and currents (up to 0.5 A). Results. A large number of new results have been obtained which particularly include: $\bullet$ fairly simple and reproducible technologies for creating multi-tip and multilayer emitters have been worked out; $\bullet$ the mechanism of functioning of protective fullerene coatings has been defined; $\bullet$ the optimal structure and morphology of the surface of multi-tip cathodes with metal-fullerene coatings have been determined and the possibility of obtaining the field emission currents up to about 100 mA with the current density up to 0.4 A/cm$^2$ has been demonstrated; $\bullet$ the optimal structure of multilayer hafnium-platinum cathodes was determined and the possibility of obtaining the emission currents of about 2 mA at an extremely high current density of about 200 A/cm$^2$ has been demonstrated; $\bullet$ the possibility of a long-term stable operation of the created cathodes at large currents in the conditions of at technical vacuum has been demonstrated. Discussion. Summarizing, it can be said that the created and studied cathodes are promising for use in miniature high-voltage electron-beam microwave devices of the millimeter and submillimeter wavelength range.