(349f) Nanodiamond Lateral Electron Emitter Devices

Chemical vapor deposited (CVD) diamond has unique material properties suitable for electron emission such as low electron affinity, hardness to withstand ion bombardment, and good thermal and electrical conductivity to handle high current. In particular, nanocrystalline diamond, with smaller grain size (1 nm-100 nm) than ?conventional' CVD microcrystalline diamond, has higher volume density of grain boundaries, more sp2-bonded carbon content, uniform surface morphology, and a wider latitude for materials integration *. In this paper, we describe micropatterned nanodiamond films using reactive ion etching (RIE) process and the geometrical field enhancement for electron emission. These nanodiamond films were fabricated with a growth-rate controlled technique on the process of CH4/H2/N2 microwave plasma enhanced chemical vapor deposition. The nucleation rate was increased and the growth rate decreased by adjusting the CVD process parameters, viz., microwave power, reactant pressure and gas flow rate*]. Raman spectroscopic analysis of the nanodiamond film indicates that the degree of sp2-bonded carbon content in the diamond film increases as the grain size decreases. The sp2/sp3 peak ratio of the 5-10 nm grain-sized nanodiamond film is found to be ~ 0.97. The properties of the nanodiamond film, namely, 5 nm grain size, smoother surface morphology, and increased sp2-carbon content are utilized for enhanced field emission devices.

Lateral micropatterned nanodiamond emitters (Figure 1) were fabricated by a process which will be described in the presentation. Figure 1 displays nanodiamond 6-finger, 4-finger, and edge emitters. The aspect ratio of each emitter finger is ~ 46 and ~ 52 in specific cases.

The as-deposited nanodiamond film and the micropatterned nanodiamond emitter structures were characterized for field emission in a vacuum of ~10-6 Torr. Electron emission from the as-deposited nanodiamond film surface was measured using a heavily doped silicon sample as the anode and an insulating spacer of 40 ìm, which defined the anode-cathode spacing. The lateral nanodiamond finger and edge emitters were tested for field emission with the integrated adjacent anode structure. The field emission characteristics of the three different emitters are presented in Figure 2. The highly linear F-N plots clearly confirm that the current is attributed to field emission. The as-deposited nanodiamond film demonstrated a high turn-on field of 18 V/ìm and 3 ìA emission current at an electric field of ~30 V/ìm. The 6-fingered nanodiamond emitter exhibited a very low turn-on electric field of 1.9 V/ìm and a high emission current of ~104 ìA at 20 V/ìm, while the edge emitter, with a 6.5 V/ìm turn-on field, showed 4.6 ìA emission current at the same electric field of 20 V/ìm. The effect of the geometry of the high aspect-ratio fingers and the edge emitters on field emission from the nanodiamond film was studied. The emission data of the different emitters was correlated to the modified Fowler-Nordheim model for electron tunneling emission and the observed field emission enhancement of the micropatterned nanodiamond emitters is explained by an increase in the geometrical enhancement factor as deduced from the F-N slope decreasing significantly for the fingered and edge emitters (see figure 2 (b)). The paper will discuss the field enhancement factor â as regards geometrical field enhancement offered by the fingered emitters for electron emission.