Vacuum microelectronic devices and vacuum requirements

With the emergence of microfabrication and thin film deposition techniques developed by the semiconductor industry, it became apparent that miniature vacuum microelectronic devices could be developed. Using approaches as diverse as controlled evaporation, chemical etching (both wet isotropic and anisotropic and dry plasma etching) and controlled oxidation, sharp tips were formed in both metals and semiconductor materials with a radius of less than 50 nm. When integrated with a gate electrode, field enhancement at the tip showed the promise of very high field emission electron currents, especially when arrays of more than one million tips per square centimeter could be produced. Even though currents above 1 mA have been achieved, vacuum microelectronic devices have not been adapted into widespread use. The vacuum environment of the device leads to changes in emission performance and premature failure that has limited the acceptance of the devices. Numerous approaches have been explored to improve and maintain the vacuum environment of the devices and enhance the vacuum conductance. In addition, device structures have been proposed that are less sensitive to the vacuum level and less susceptible to failure. An overview of these issues will be provided from a historical perspective.