RADIATION-INDUCED INTEGRATED CIRCUIT LATCHUP

This paper discusses integrated circuit (IC) structures and associated physical mechanisms which are responsible for the phenomenon of radiation-induced latchup. Laboratory measurements on selected IC's have verified that the structures described will support latchup. These measurements are briefly discussed. An important result of the laboratory measurements has been to establish that electrical tests can be used to identify latchup-prone structures within an IC. These measurements, together with an understanding of the biasing conditions that must exist in order to initiate the latchup path, can be used to determine the susceptibility of an IC, in normal operation, to radiation-induced latchup. A careful analysis of a given IC's topology can uncover all latchup-prone structures. Once such structures have been identified, appropriate electrical testing can be implemented during the IC production phase to determine the V-I characteristics of these paths. This procedure will supply the necessary information regarding the biasing conditions required for the initiation of the latchup paths when the IC is exposed to an ionizing radiation environment. One-hundred percent electrical testing may be required, depending upon the results of the analyses, in order to uncover the single latchup-prone individual, among several hundred IC chips, which might possess an anomalous V-I characteristic. It is concluded that four-layer (p-n-p-n) action is the primary latchup sustaining mechanism, while transistor sustaining voltage breakdown is of little concern and second breakdown is probably of minor importance for most IC's. Second breakdown must be given careful consideration, however, before a given IC can be considered to be latchup free. Four layer structures that will support p-n-p-n action are common in IC's that are constructed by utilizing triple or quadruple diffusions. The available evidence suggests that inter-element p-n-p-n paths in IC's constructed with epitaxial processes, and utilizing a highly-doped buried layer, are not sensitive to latch-up initiation by photocurrents. Semiconductor junctions that will sustain second breakdown are present in all IC's. However, in view of the usual magnitude of holding voltage and the energy required to initiate second breakdown, it is not usually observed in a radiation environment. Copyright © 1969 by The Institute of Electrical and Electronics Engineers, Inc.