The Pros and Cons of Very-Low-Voltage Testing

Albert-Ludwigs University of Freiburg, Germany
Abstract: IC test application at reduced power supply voltage (Very Low Voltage or VLV testing) has been reported to increase the defect coverage of a test set, with no need for expensive testers or design for test (DFT). VLV testing can detect both defects that lead to a catastrophic failure but are missed by the test set at nominal conditions, and undetectable defects (flaws). The detection of flaws is important, as they could deteriorate and become catastrophic, resulting in early-life failures (ELF). On the other hand, lowering the power supply voltage necessitates a reduction of the frequency at which the test vectors are applied. If the test time is fixed, this results in fewer vectors being applied, and thus in a potential coverage loss. Moreover, there are instances of defects detectable under nominal conditions but undetectable by VLV testing.
In this talk, the defect coverage increase induced by VLV testing is compared with the coverage loss caused by performance degradation. The analysis is based on the resistive bridging fault model that allows determination of the detection conditions as a function of the power supply voltage. The model and its extensions will be presented in depth. It is accurate enough to explain phenomena such as pattern dependency and the Byzantine Generals Problem. At the same time, its computational overhead is reasonable, so that larger blocks can be treated. Some preliminary ideas on the use of the model for diagnosis will conclude the presentation.

Biography: Dr. Ilia Polian is a Senior Researcher with the Computer Architecture Group at the University of Freiburg, Germany, where he received his MS and PhD degrees in 1999 and 2003, respectively. His research interest are in fault modeling, reliability, test methods, and verification. He received the Wolfgang-Gentner Award 2004 for outstanding research in 2004. He was European Champion and Vice World Champion at the ACM Collegiate Programming Contest in 1999.