Single-Event Upsets in Microelectronics: Fundamental Physics and Issues
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Single-Event Upsets
in Microelectronics: Fundamental Physics and Issues
Henry H.K.Tang and Kenneth P. Rodbell Abstract We review the current understanding of single-event upsets (SEUs) in microelectronic devices. In recent years, SEUs have been recognized as one of the key reliability concerns for both current and future technologies. We identify the major sources of SEUs that impact many commercial products: (1) alpha particles in packaging materials, (2) background radiation due to cosmic rays, and (3) thermal neutrons in certain device materials. The origins of SEUs are examined from the standpoint of the fundamental atomic and nuclear interactions between the intruding particles (alpha particles, cosmic rays, and thermal neutrons) and semiconductor materials. We analyze field funneling, which is a key mechanism of charge collection in a device struck by an ionizing particle. Next, we formulate how SEU cross sections and SEU rates are calculated and discuss how these basic quantities are related to experiments. Finally, we summarize the major SEU issues regarding modeling, bulk complementary metal oxide semiconductor technologies, and research on future, exploratory technologies. Keywords: microelectronics, radiation effects, semiconductors, single-event upsets (SEUs), soft error rates.
The Nature of Single-Event Upsets Any charged particle passing through a microelectronic device ionizes the material(s) along its path. A column of transient electron–hole pairs is created around the particle track. These induced free carriers, if left alone in a field-free host medium, will eventually recombine. However, under appropriate operating conditions in a device, recombination of these electrons and holes can be prevented by the intrinsic, strong, internal electric fields. This can generate an electrical pulse large enough to disrupt normal device operation. This disruption caused by one random intruding particle is not associated with any permanent damage to the device. The result is an error in one bit, which, however, cannot be duplicated because of its random nature. In the microelectronics industry, this phenomenon is called a single-event upset (SEU), a soft error, or a soft failure.
MRS BULLETIN/FEBRUARY 2003
Charged particles are not the only agents that can cause SEUs. For reasons explained later, electrically neutral subatomic particles such as neutrons are known to cause soft failures in circuits. SEUs are complex. To understand this subject in depth, one must consider the particle origins, which involve esoteric subjects such as cosmic rays, nuclear reactions, atomic processes, and novel modes of carrier transport in deep submicrometer devices. Radiation effects induced by subatomic particles in electronic devices and circuits have been known for a long time. Yet, with few exceptions, the subject is discussed only in a limited number of research journals and is not readily accessible to a wider technical audience. In recent years, SEUs have been recognized as a key area limiting the reliability of many
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