Fabrication process of silicon-tip-arrays for field emission applications

A micromachined process to assemble homogeneous and reproducible tip arrays for field emission applications is developed and characterized. As substrate material p- as well as n-doped silicon is used. Lateral position of the tips is defined by structuring silicon dioxide to discs in a photolithographic process. Vertical structure of the tips is defined by a combination of RIE dry etching with controlled anisotropy and thermally oxidization of silicon in order to sharpen the tips. Hence field emitter arrays (FEAs) can be assembled both as bare and coated cathodes. To assemble field emission diodes, this fabrication process allows placing a metal anode in a micrometer order distance to the tips by a self-aligning procedure. The anode is placed in an evaporation process whereupon sharpening oxide is used as isolator between anode and cathode. Electrical characterization of the cathodes showed very good homogeneity, well alignment and stability over time of emission current from all tips (i.e. 100% efficiency).

I. Introduction

Field emission characteristics strongly depend on nanoscale geometry and material properties of the emitter structure. Hence to act as replacement for hot cathodes in industrial systems techniques are necessary to fabricate reproducible and homogeneous arrays of microscale sharp tips. Because silicon technology is industrial standard and well characterized it is a predestinated method to achieve this aim. Integration ability of silicon technology offers several possibilities for fabrication of novel monolithic integrated vacuum microelectronic devices [1]. Furthermore field emission current especially out of p-doped silicon saturates in a certain voltage region and is highly photosensitive. This can be used either for stabilization or ultra fast optical modulation of the emission current [3].