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Imaging Technique Pinpoints Cosmic-Ray Damaged Electronics Researchers at Sandia National Laboratories hâve developed an imaging technique to pinpoint weaknesses in integrated circuits caused by ionizing radiation. Called single event upset (SEU) imaging, the technique can isolate malfunctions in single transistor components, and is detailed enough to be used to design more reliable circuits for use in satellites and equipment used in space. Single event upsets are temporary but critical disruptions in an integrated circuit's memory cells resulting from a collision with high-energy cosmic rays. For example, the Hubble space télescope suffers from data loss due to such upsets in a focusing circuit. With today's more densely packed integrated circuits and size réductions,

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radiation-induced failures hâve become more important. The imaging technique can help diagnose circuit weaknesses so the circuits can be redesigned to provide greater radiation hardness. The SEU method is more précise than traditional whole-chip radiation testing for malfunctions, and can furnish information at the individual transistor component levël by direct measurement. The technique involves directing a narrow ion beam (focused to about 1 ^m) at a fixed point on a target. When the ion pénétrâtes the silicon, it leave.s a wake of excited électrons and holes. Electrons that group together and persist can induce memory cells to change their stored logic state. The émission of électrons is recorded by a detector in the target chamber. Because the microbeam can individually irradiate a single memory cell, transistor, or transistor component (like transistor drains or gâtes), SEU imaging can be used to image upset-prone microscopic régions. The researchers use a microbeam generated by Sandia's Tandem Van de Graaff accelerator. The beam's position and component responses are monitored by an external computer which compares the électron image to a circuit design mask, providing detailed information showing which circuit éléments are the origin of the single event upsets. SEU imaging could also be used to measure the cumulative effect of ionizing radiation to a single memory cell, or by engineers to verify software codes used to simulate radiation upset processes.

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