The development of a field emission electron source for a cathode ray tube

Abstract

Computer techniques have been used to design two-anode electrostatic field emission guns of focal length 300 mm and 50mm. These were subsequently tested using a demountable proto-type cathode ray tube (CRT) with a carbon fibre field emission source. It has been demonstrated that such guns have a satisfactory electron optical performance in this application. Subsequently, two commercial "thermionic" CRTs, one a standard type, and the other a miniature high resolution type, were adapted to contain field emission guns. The successful operation of these tubes highlighted the great potential of carbon fibre as a field emission electron source. Initially, the final display of these CRTs exhibited a flickering which was found to be due to an inherent instability associated with the carbon fibre field emission source. This undesirable effect was satisfactorily eliminated firstly by using an external electronic feed-back system, and secondly by using a pulsed field technique which had the effect of reducing the instability by ~ 90%. By using scanning electron microscopy, it was shown that this instability was during the initial "switch-on" of "virgin" carbon fibre cathodes. This destructive process was eliminated using a pre-heat treatment of the emitter, which resulted in considerably longer life times and a significant reduction in the noise in the total emission current. The energy spectra of the field emitted electrons from heat-treated cathodes were measured using an UHV high resolution spectrometer, and cathodes were shown to be both single and multi-peaked. Foe single peaked spectra, the half width is found to increase with field, whereas the spectral shift from the Fermi level decreases. These and other properties of carbon fibre emitters have been interpreted in terms of a hot-electron emission mechanism.