Field emission from silicon

Abstract

A field emitter serves as a cold source of electrons. It has practical applications in various fields such as field emission flat panel displays, multiple electron-beam lithography, ion propulsion/micro-thrusters, radio frequency source, information storage technology, and electronic cooling. Silicon is an attractive material for building electron field emitters. To understand the physics of electron field emission from silicon and to push technologies of making quality field emitter arrays present both opportunities and challenges. This work focuses on an experimental study of electron field emission phenomena from silicon field emitter arrays. We demonstrate electron field emission from both the conduction band and the valence band of silicon simultaneously. A two-band field emission model is presented to explain the experimental data. Theoretical predictions for valence band emission were made in the past; however there was no direct observation until now. Experimental evidence of current saturation in field emission existed in the literature. We also report the observation of current saturation in n-type silicon field emitter arrays. A simple model is presented to account for the results. We report successfully fabricating 1/,m gate-aperture silicon field emitter arrays with a turn-on voltage as low as 14 V. The gate leakage current is observed to be less than 0.01% of the total emission current. Devices show excellent emission uniformity for different sized arrays. The low turn-on voltage is attributed to the small emitter tip radius. It was achieved by isotropic etching of silicon and low temperature oxidation sharpening of the emitter tips.

(cont.) Field emitters with a tip radius of about 10nm can be routinely obtained. Optimization of the oxidation sharpening process further reduced the tip radius to be around lnm. The results were confirmed by Transmission Electron Microscopy (TEM). Device characterization showed agreement with Fowler-Nordheim theory. Analytical and numerical models were introduced to account for the experimental results. We also demonstrate the successful fabrication of the high aspect ratio silicon tip field emitter arrays. Silicon emitters as high as 5-6[mu]m with an aspect ratio larger than 10:1 was achieved in our facilities. Furthermore we have also successfully fabricated and tested the fully gated high aspect ratio field emitter arrays. The experimental current-voltage data agree well with the Fowler-Nordheim theory. A Maxwell Stress Microscope, which is capable of imaging sample topography and the surface potential simultaneously is set up and tested for the purpose of further study of the properties of the surfaces of the silicon field emitters.