Holding Time Degradation in Dynamic MOS RAM by Injection-Induced Electron Currents

The holding time degradation of a dynamic MOS RAM caused by a peripheral MOS device operated in the saturation region is discussed. It is shown that the process taking place is injection of electrons into a positively biased substrate region from a grounded junction. This junction becomes forward biased due to the resistive potential drop on the substrate caused by the high substrate current of the short-channel MOS device operated in the saturation region. The model presented in the literature of secondary-impact ionization of holes in the depletion-region edge being responsible for the degradation phenomenon is shown to be inconsistent with experimental results and theoretically improbable.