A conceptual design for a microelectronic ionization vacuum gauge

Abstract

A novel cold emission microelectronics vacuum gauge is proposed and its operation is analysed theoretically. The device is based on the controlled motion of field emission (FE) electrons in a vacuum working space subject to crossed electric E and magnetic B fields. The arrangement is cylindrically symmetrical around the B axis while the radial electric field is applied between two coaxial surfaces. The electrons obtained from a circular FE cathode array placed between these surfaces are shown to move on a cycloid-like closed trajectory. Some electrons with enough kinetic energy ionize the residual gas molecules. The ions are collected by an external electrode. The sensitivity of the vacuum gauge is computed taking into account different cross sections for the ionization process of nitrogen molecules as function of electron kinetic energy and integrating over the electron path. The electron `time of flight' inside the device is computed assuming an uniform (repelling) electric field in the Z direction. An analysis is performed in order to find the conditions (geometrical and operational) necessary to improve the vacuum gauge sensitivity. It is shown that the device should be operated to allow large electron loops, but at the same time the device dimensions should be large enough to allow the electron to acquire enough kinetic energy for an efficient ionization process to take place.