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Proceedings Paper

Implications of scaling on static RAM bit cell stability and reliability
Author(s): Mary Ann Coones; Norm Herr; Al Bormann; Kent Erington; Vince Soorholtz; John Sweeney; Michael Phillips
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Paper Abstract

In order to lower manufacturing costs and increase performance, static random access memory (SRAM) bit cells are scaled progressively toward submicron geometries. The reliability of an SRAM is highly dependent on the bit cell stability. Smaller memory cells with less capacitance and restoring current make the array more susceptible to failures from defectivity, alpha hits, and other instabilities and leakage mechanisms. Improving long term reliability while migrating to higher density devices makes the task of building in and improving reliability increasingly difficult. Reliability requirements for high density SRAMs are very demanding with failure rates of less than 100 failures per billion device hours (100 FITs) being a common criteria. Design techniques for increasing bit cell stability and manufacturability must be implemented in order to build in this level of reliability. Several types of analyses are performed to benchmark the performance of the SRAM device. Examples of these analysis techniques which are presented here include DC parametric measurements of test structures, functional bit mapping of the circuit used to characterize the entire distribution of bits, electrical microprobing of weak and/or failing bits, and system and accelerated soft error rate measurements. These tests allow process and design improvements to be evaluated prior to implementation on the final product. These results are used to provide comprehensive bit cell characterization which can then be compared to device models and adjusted accordingly to provide optimized cell stability versus cell size for a particular technology. The result is designed in reliability which can be accomplished during the early stages of product development.

Paper Details

Date Published: 14 January 1993
PDF: 14 pages
Proc. SPIE 1802, Microelectronics Manufacturing and Reliability, (14 January 1993); doi: 10.1117/12.139349
Show Author Affiliations
Mary Ann Coones, Motorola, Inc. (United States)
Norm Herr, Motorola, Inc. (United States)
Al Bormann, Motorola, Inc. (United States)
Kent Erington, Motorola, Inc. (United States)
Vince Soorholtz, Motorola, Inc. (United States)
John Sweeney, Motorola, Inc. (United States)
Michael Phillips, Motorola, Inc. (United States)

Published in SPIE Proceedings Vol. 1802:
Microelectronics Manufacturing and Reliability
Barbara Vasquez; Anant G. Sabnis; Kenneth P. MacWilliams; Jason C.S. Woo, Editor(s)

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