The significance of fluctuation phenomena in vacuum microelectronics

The effect of current fluctuation noise in two classes of devices is considered: first, those that would require a single tip for their operation, such as a microcircuit element that might replace the transistor in an integrated circuit, the gun in a high-resolution, low-voltage scanning electron microscope, or the tip in a scanning tunneling microscope; and second, those that require area arrays of cathode, such as injection guns for klystrons, traveling-wave tubes, accelerators, and free electron lasers. The noise generated in vacuum electron devices derives from two separate sources, namely, random fluctuations in the tube current and a velocity spread among the flowing electrons. In thermionic emission, current fluctuation noise can be reduced by two or three orders of magnitude if the current flow is space-charge-limited with a potential minimum in front of and a retarding field at the cathode. However, field emission requires an intense acceleration field at the cathode which does not allow for any reduction in current fluctuation noise.<>