Fabrication of metallic double-gate field emitter arrays and their electron beam collimation characteristics

Abstract

The fabrication of double-gate metallic field emitter arrays with large collimation gate apertures and their field emission beam characteristics are reported. The device fabrication steps, including the molding technique for array fabrication, the electron extraction gate fabrication by the self-aligned resist etch-back method, and the fabrication of the collimation gate electrode using a focused ion beam assisted method are described in detail. The experimental results of 2 × 2 tip arrays with the proposed double-gate structure demonstrate an order of magnitude enhancement in beam brightness with minimal current loss.

Electron beam collimation with a 40 000 tip metallic double-gate field emitter array and in-situ control of nanotip sharpness distribution

“…25,26,[33][34][35] The 4 Â 10 4 emitter tips were aligned with 10 lm pitch in a circular area measuring 2.26 mm in diameter. The gate electrodes consisted of 0.5 lm thick molybdenum films.…”

“…The FEA and G ext were separated by a 1.2 lm thick SiO 2 layer, whereas G col and G ext were separated by a 1.2 lm thick SiON layer. 26 To pattern the apertures of G col , a process using focused ion beam milling was formally developed for arrays up to 20 Â 20 tips. 25,26 This maskless and flexible method is ideal for prototyping small arrays but difficult to apply to larger FEAs because of the required milling time of $90 s per aperture.…”

“…26 To pattern the apertures of G col , a process using focused ion beam milling was formally developed for arrays up to 20 Â 20 tips. 25,26 This maskless and flexible method is ideal for prototyping small arrays but difficult to apply to larger FEAs because of the required milling time of $90 s per aperture. With the newly developed e-beam process, we successfully prepared the 4 Â 10 4 tip FEA having a G col aperture diameter of 6.5 6 0.1 lm, which is a factor of 3 larger than that of the G ext apertures (2.0 6 0.1 lm).…”

“…These so-called double-gate FEAs have been proposed as high current and high brightness cathodes 15,16 and have been actively studied. [17][18][19][20][21][22][23][24][25][26] One of the critical obstacles for the realization of high performance double-gate FEAs is the reduction of the emission current during the beam collimation. Recent developments show that this can be circumvented by devising the gate aperture shapes as demonstrated with volcano-shaped FEAs 23 and stacked double-gate device with large G col apertures.…”

“…Recent developments show that this can be circumvented by devising the gate aperture shapes as demonstrated with volcano-shaped FEAs 23 and stacked double-gate device with large G col apertures. [24][25][26] For the practical application of FEAs it is important to prepare an array with uniform nanotip apex distribution. Due to the exponential sensitivity of the field emission current on the electric field at the emitter apexes, even a small nonuniformity of the emitter tip apex radius of curvature r tip results in a highly non-uniform beam across the array and limits the total current, making the requirement for the r tip uniformity stringent.…”