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Developments in Ceramic Materials Research

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Field Emission Display on <strong>Ceramic</strong> 251<br />

process. The thickness of this buffered alum<strong>in</strong>ium layer was around 0.2 µm. The sample<br />

holders were turned back to their normal position after the alum<strong>in</strong>ium deposition process.<br />

The molybdenum micro cone form<strong>in</strong>g process is the key process to produce the micro<br />

field emitters. Sample holders were rotat<strong>in</strong>g as satellites around their orbit centre, from which<br />

the molybdenum evaporation source was located 600 mm below; the sample holders were<br />

also sp<strong>in</strong>n<strong>in</strong>g on their own axis dur<strong>in</strong>g the deposition process so as to form cone structures<br />

<strong>in</strong>side the gate cavities. Radiation energy transmitted from the halogen lamp heaters to the<br />

ceramic samples dur<strong>in</strong>g the deposition was <strong>in</strong> an attempt to release the stress build<strong>in</strong>g up<br />

upon the deposited film. In order to fully form conical shape, the thickness of molybdenum<br />

film was monitored dur<strong>in</strong>g the process to be just beyond an empirical value. Over dose<br />

deposition of molybdenum not only leads to material wasted unnecessarily, but also <strong>in</strong>creases<br />

the risk of a th<strong>in</strong> film peel<strong>in</strong>g, which is due to an extensive stress built <strong>in</strong> a thick molybdenum<br />

film. A SEM photograph shows a cross section of a molybdenum cone tip after deposition<br />

process <strong>in</strong> the Figure 5.<br />

The f<strong>in</strong>al photo lithography process to pattern the top molybdenum film <strong>in</strong>to open<strong>in</strong>g<br />

w<strong>in</strong>dows is designed for the lift-off process. The mask aligner was re-used here for this<br />

lithography pattern<strong>in</strong>g. Followed the lithography and photo resist develop<strong>in</strong>g process, a wet<br />

etch<strong>in</strong>g method was employed to etch away the molybdenum down to the alum<strong>in</strong>ium layer<br />

through the photo resist mask open<strong>in</strong>g w<strong>in</strong>dows. The lift off process was performed <strong>in</strong> a fresh<br />

NaOH solution to dissolve the alum<strong>in</strong>ium buffer layer, and thus lift<strong>in</strong>g materials above. The<br />

entire fabrication process ended with nitrogen blow-dry of the samples. Figure 6 shows an<br />

array of the micro field emitters after the entire fabrication processes. The emitter tips with<br />

gate structures are evenly distributed.<br />

Figure 5. Micro cone tip formed after molybdenum deposition. Vertical crystallized molybdenum film<br />

on the top layer and larger gra<strong>in</strong> structure with irregular shape ceramic substrate <strong>in</strong> the low layer are<br />

visible.

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