On the Electrical Origin of Flicker Noise in Vacuum Devices

We have recently shown that thermal noise in the space-charge regions of solid-state devices can account for most of their excess noise, whose 1/f spectrum is produced by the dc bias that was used to convert resistance noise into a voltage noise to be measured. This spectrum reflects the modulation of an energy barrier that confines carriers along the channel of such devices-a feature that was also found for electrons around cathodes of vacuum tubes. Using this novel theory, we can predict a flicker noise in vacuum tubes-a noise whose origin has eluded scientists since its early report by Johnson in 1925.