Diagnostic Circuit for Latent Fault Detection in SRAM Row Decoder

Functional safety is crucial in automotive life-critical systems. Early diagnosis of unanticipated faults and failures is necessary to prevent hazardous implications. ISO 26262, Functional Safety-Road Vehicles, is an automotive industry-specific functional safety standard that describes the course for classification, detection and control of potential risks. Electromigration induced open and short defects and Bias Temperature Instability (BTI) are critical failure mechanisms and pose severe reliability concerns as they may escape tests at fabrication and cause failures when the chip eventually wears out. This paper analyzes the independent and combined impact of partial resistive defects and BTI on row decoders at 55nm technology node. The presence of resistive defects causes an additional delay which gets further increased due to aging (BTI). Due to the combined impact of 10 years of aging and a $25\mathrm{K}\Omega$ resistive defect, the activation delay increases by about 16.15% and the deactivation delay increases by about 22.14%. A novel technology-agnostic diagnostic test circuit and method is proposed to detect small resistive defects as low as $5\mathrm{K}\Omega$ before they can result in functional failure.