Gremlins in the Silicon

Abstract

The increasing complexity of semiconductor technologies is exposing limitations in traditional manufacturing test methodologies. Although fault-model-based testing has enabled efficient production screening for decades, growing evidence from advanced logic and memory technologies indicates that many realistic defect mechanisms are insufficiently represented by conventional fault abstractions, leading to test escapes and in-field failures. This paper examines three directions for improving outgoing product quality. First, we discuss the growing mismatch between fault models and actual silicon behavior and emphasize the need for silicon-informed assessment of defect coverage. Second, we investigate timing failures caused by process-variation-induced delay marginalities, which increasingly evade conventional scan-based delay testing. Finally, we present Device-Aware Test (DAT), a defect-centric methodology that derives fault models and test solutions directly from physical defect behavior. Examples from STT-MRAM, RRAM, and FeFET memories demonstrate how DAT enables the detection of realistic defect mechanisms beyond the reach of conventional approaches. Together, these directions support a transition toward defect-aware, data-driven testing for future semiconductor systems.