A study of the effect of hydrogen plasma on microfabricated field-emitter arrays

Abstract

The influence of a hydrogen plasma on molybdenum (Mo) tips in microfabricated field-emitter arrays has been investigated using two different methods. During the first process the voltage of the field-emitter array was floating while it was treated by the hydrogen plasma at an operational pressure of 1 × 10 −3 torr. The effect of this plasma on the current-voltage (I–V) characteristics has been studied. The chemisorption of hydrogen on Mo led to a reduction in the work function (Φ) ranging from ∼ 0.3 eV for 10 min plasma exposure to ∼ 0.92 eV for 100 min. Due to this hydrogen adsorption process a temporary enhancement in the emission current of about 15% (at constant applied field) was recorded. Because of the repeatability of the measurements, it was concluded that the changes that take place during this processing are not caused by a tip radius change, but that the process involves an adsorption and desorption mechanism. During the second process the tip, base and gate electrodes of the field-emitter array were all part of the circuit. Under such an arrangement not only are hydrogen molecules chemisorbed by hydrogen ions, but electrons are also attracted to the Mo, resulting in bombardment of the tips. This process has been carried out under a pressure of 1.5 × 10 −1 torr for different lengths of time. Brief treatment resulted in the reduction of the work function while extensive treatment could lead to the destruction of the cathode. Stability measurements were recorded before and after all these processes.