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Bipolar Dynamic RAM Cell Structure With Low Soft-Error Rate

IP.com Disclosure Number: IPCOM000046546D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Sai-Halasz, GA: AUTHOR [+2]

Abstract

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.

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Bipolar Dynamic RAM Cell Structure With Low Soft-Error Rate

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. The layer 14 serves two purposes. It forms a potential barrier and tends to repel the incoming electrons from the substrate. It also increases the storage node capacitance without the need to increase the cell size. The deep trench isolation 16 in the proposed structure is conducting and acts as a recombination site for the electrons generated by the a-particle. A polysilicon- filled trench or a trench with its wall lined with silicide are both possible choices. The trench thus can sink the electrons diverted by the p-layer underneath the storage node.

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