Bipolar Dynamic RAM Cell Structure With Low Soft-Error Rate
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
All dynamic memory cells are susceptible to soft error when the cell is hit by ionizing particles, such as a-particles. Bipolar dynamic cells are of no exception. This article describes a cell structure that is less susceptible to soft error. Fig 1 shows a conventional bipolar dynamic random-access memory (RAM) cell. The storage node is the n+ subcollector 10. The cell is isolated by a trench 12 which is an insulator. The substrate doping density is 1016 cm-3 . When an a-particle hits the cell, the electron generated from the substrate diffuses up and into the n+ subcollector which may cause error. Fig. 2 shows the cell structure proposed in this article. A p-layer 14 of 1017cm-3 doping density and about 1 mm thick is added to the bottom of the n+ subcollector 10, and the trench 16 is made conductive.