In this article, we describe the improvement in cold emission characteristics of a device termed HEED (high efficiency electro-emission device) by optimizing the emission site structures. The advanced HEED consists of a bottom electrode, a Si layer, a SiOx, layer, a top electrode, and a carbon layer. The electron emission properties were significantly improved by appropriately arranging emission sites of "dimplelike" forms with a diameter of I Am on the device surface. The applied voltage was significantly lowered to 20 V (1/5 of that in the previously reported HEED), and a high emission current density of 1.8 mA/cm(2) was obtained at a applied voltage of 20 V with an electron emission efficiency of 1% under a pulse operation. The energy distribution measurement of emitted electrons showed that the device emits considerably high-energy electrons as compared with conventional field emitters. Using this emitter as an excitation source, a 4 in. prototype flat display panel has been fabricated with a vacuum spacing of 9 mm between glass substrates. The panel operates well at a practical brightness of 2000 cd/m(2). (C) 2004 American Vacuum Society.