A carbon-nano tube (CNT) structure comprises a substrate and a plurality of CNTs, each CNT comprising a plurality of first CNTs grown perpendicular to the substrate and a plurality of second CNTs grown on sidewalls of the first CNTs. A method of manufacturing CNTs includes growing first CNTs on a substrate on which a catalyst material layer is formed, and growing second CNTs on surfaces of the first CNTs from a catalyst material on surfaces of the first CNTs. The second CNTs grown on the sidewalls of the first CNTs emit electrons at a low voltage. In addition, the CNT structure exhibits high electron emission current due to the second CNTs being used as electron emission sources, and exhibits uniform field emission due to the uniform diameter of the first CNTs. A display device incorporates the above-described structure.