Optimized diagnostic strategy for embedded memories of Automotive Systems-on-Chip

Embedded memories in Automotive Systems-on-Chip usually occupy a large die area portion. Consequently, their defectivity can strongly impact production yield for any automotive device. Along with the technology ramp-up phase and for statistical process control reasons during volume production, it is a good automotive industry practice to collect diagnostic information in addition to pure testing data. Designers and technology experts must receive accurate diagnostic results from failing devices to react to misbehavior by identifying and correcting the related issues at their source and drawing correct repair strategy conclusions. A commonly used approach resorts to the generation of failure bitmaps based on collecting all failing bits coordinates to be sent one by one to the tester. More efficiently, the encountered faults can be compacted or compressed in on-chip memory resources to be retrieved by the tester at the end of the memory test.This paper presents an on-chip method to compact diagnostic information during embedded memory testing. More specifically, the method is applied to diagnose embedded FLASH memories. This strategy permits the reconstruction of failure bitmaps without any loss, while compression approaches obtain an approximation. The proposed method uses a fraction of the memory requested by a coordinate-based bit mapping approach and is comparable to compression methods. At the cost of a moderate test time overhead, the proposed strategy permits dramatically increasing the number of devices that can be fully diagnosed without any bitmap reconstruction loss. Most failing devices in a real embedded FLASH production scenario were diagnosed after a single transfer from on-chip to the tester host computer.