Field emission characteristics of a tungsten microelectromechanical system device

We have investigated the field emission properties of free-hanging tungsten microelectromechanical system structures. These tungsten structures are designed to serve as electrodes in a Paul ion trap. Since the outer edges of the trap end cap electrodes are adjacent to the inner edges of the trap ring electrode and approximately 0.5 mu m apart, field emission may occur between these two edges when hundreds of volts are applied, thereby defining an edge field emitter. The arrays were tested under vacuum (10(-5) Torr) and at atmospheric pressure (625 Torr) to understand the field emission behavior. Vacuum tests show turn-on voltages of about 200 V for the 1 and 1.5 mu m radius traps and currents of similar to 80 nA for both sizes of trap with the largest array (10(6)) at 6 MV/cm. The atmospheric tests showed lower turn-on voltages of approximately 150 V for both the 1 and 1.5 Am radius traps. Currents up to a few mu A were achieved at 6 MV/cm for smaller trap size (1 mu m) in the largest array indicating a gas ionization contribution. The measured current-voltage responses fitted the Fowler-Nordheim characteristics well, confirming that the current increase in vacuum was due to field emission. A stable emission current of 2.03 nA was obtained at 10 MV/cm for 11 min. (C) 2005 American Institute of Physics.