Development of a nitrogen incorporated ultrananocrystalline diamond film based field emitter array for a flat panel X-ray source

As an alternative to conventional X-ray sources, a flat panel transmission X-ray source is being developed. A field emitter array (FEA) prototype to be incorporated as cold cathode in this flat panel X-ray source was fabricated for this work. Using the Particle-in-Cell code OOPIC Pro, an initial FEA was designed through simulations. Based on the simulation results, a FEA prototype was fabricated using conventional microfabrication techniques. Planar nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) films were used as field emitters. This N-UNCD based FEA prototype was composed of 9 pixels distributed in a 3x3 array, with a pixel size of 225x225 mum, and a 500 mum pitch. Each pixel was composed of a N-UNCD-based cathode and a free-standing copper grid used as extraction grid. Field emission from each pixel could be addressed individually. Emission currents per pixel in the order of 0.05 - 3.0 muA were obtained for extraction fields between 4 and 20 V/mum. Delamination issues were found in the microfabrication of the first FEA prototype. Consequently, a second generation N-UNCD based 3x3 FEA was designed and fabricated. In this design, the free-standing grid was replaced by a tungsten layer composed of a matrix of 11x11 extraction gates. Each extraction gate had a circular aperture of 6 mum in diameter. These design changes solved the delamination issues found for the first prototype. Also, for an extraction field of 7 V/mum, an emission current around 0.14 muA per pixel was measured; this value is higher than the 0.08 muA per pixel obtained from the initial FEA prototype at the same extraction field.