Uniformity and stability of field emission from bare and metal coated Si tip arrays

Field emitter arrays of tips of some micrometers in height have been fabricated from p- and n-doped Si substrates by photolithographic techniques and partially coated with 7.5 nm thick W, Pt, or Cr layers by magnetron sputtering. The emission uniformity of these tip arrays was investigated with a field emission scanning microscope. The local current stability was measured with a spectrum analyzer. The bare Si tips show low average extraction fields (∼35 V/μm for 10 nA) but moderate uniformity and pronounced current noise and switches. In comparison, the metal-coated Si tips yield improved emission uniformity with up to 100% of emitting tips and sufficient stability up to 700 nA (1 μA) in the case of Pt (W) coating, but also a factor of 2 higher extraction fields. Noise power spectra of W and Pt coated samples showed a typical 1/fγ dependence up to the kHz range with a spectral density index γ of about 3.