Fabrication and Simulation of Silicon Structures with High Aspect Ratio for Field Emission Devices

To obtain higher field enhancement factors of Si-tip structures, we present an improved fabrication process utilizing reactive-ion etching (RIE) with an inductively coupled plasma (ICP). In our design, a pillar under the tips is realized by a combination of RIE with ICP. With adjusted power settings approximate to 240 W) and step times (< 5 s), vertical slopes with a low roughness of approximately 10 nm to 20 nm are possible. The remaining silicon is oxidized thermally to sharpen the emitters. A final tip radius of R < 20 nm is obtained for the tips of the emitters. The pillar height H-P can be mainly adjusted by the duration of the ICP-etching step. A total emitter height of H approximate to 6 nm with a pillar height of H-P approximate to 5 nm is achieved. Simulations with COMSOL Multiphysics (R) are applied to calculate the field enhancement factor beta. A two-dimensional model is used in rotational symmetry. In addition to the previous model, a pillar with a varying diameter phi(P) and height H-P is added. A conventional emitter (H = 1 mu m and R = 20 nm) placed on a pillar of the height H-P approximate to 5 Itm approximately results in a three times higher beta-factor (beta approximate to 105). By decreasing the diameter O a slight increase of the beta-factor is observed. However, the aspect ratio of the emitter mainly influences on the beta-factor.