Fabrication of Planar Diamond Electron Emitters for Flat Panel Displays
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electron emission from isolated particles enables us to discuss the electron-emission mechanism without having to consider the effects of unknown factors in grain boundaries. From engineering point of view, however, the electron emission from isolated particles required the high driving voltage (Vd - 150 V) and the lowering its threshold was demanded. In this study, we fabricated planar diamond electron emitters employing continuous diamond films and the low threshold emission was realized. We also discussed the electron-emission mechanism from diamond by making a comparison between continuous films and isolated particles. EXPERIMENT Samples were fabricated as follows. First, Cr film was deposited on quartz substrate by resistively heated evaporation, and then, Au film was also deposited on Cr film in situ in order to prevent the oxidation of Cr film surface. Second, the surface of Au film deposited on Cr was scratched in diamond powder for the nucleation enhancement of the diamond growth. After photolithography, the gap of 4 lam in width was formed in the center of Au/Cr film by ion milling. Finally, undoped CVD diamond was deposited at 800 'C by the electron cyclotron resonance (ECR) microwave-plasma assisted chemical vapor deposition (MPCVD) method using a mixture of CO and H 2 gases. Due to the side-growth of diamond at Au/Cr film, the gap was narrowed into 2 lam. The Au/Cr film has three functions in this device. First, it is used as a buffer layer for overcoming the weak adhesion of diamond to quartz substrate. Second, it acts as a seeding layer for the selective growth of diamond because diamond is grown on the Au/Cr film and not on bare quartz substrate. Third, it can serve as an electrode that contacts the measurement system. Figure 1 shows a secondary electron microscope (SEM) image of the planar diamond electron emitter. The characterization of this cathode was performed at less than lx10"6 Torr by the system shown in Fig. 2. Anode volatage, V., was fixed at 700 V, and driving voltage, Vd, was varied from 0 to 130 V. Quartz substrate
Diamond film
Anode Screen (Phosphors/ITO/Glass)
Va Diamond/Au/Cr Quartz Substrate
d
_
2gm Fig. 1 SEM image of a planar diamond electron emitter.
Vd
Fig. 2 Setup for measuring the electron-emission properties.
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EXPERIMENTAL
RESULTS
The current-voltage (Id-Vd) characteristics of the planar electron emitters are shown in Fig. 3(a). The observed current increased rapidly over about 10 V, which was defined as the threshold voltage of the device. From the Fowler-Nordheim (F-N) plot shown in Fig. 3(b), we can say that the current obtained was due to the tunneling effect because it could be described 10 well by the modified F-N law, ) 1-54 x 102 (f3E)
2
(-6.83 x 10303(
SP3E where J is the current density in A/cm2 , F the fraction of the area emitting electrons, E the field in V/gm, 0 the effective work function in eV, and /3 the factor of the geometrical field enhancement which is mainly controlled by the cathode radius of curvature. Solid lines shown in Figs. 3(a
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