Reconfigurable Multi-Bit Scan Flip-Flop for Cell-Aware Diagnosis

Conventional diagnosis methods are performed at the library cell level, whereby only defective cells are identified. In reality, many defects affecting the inside of the cells cannot be identified, thus limiting yield improvement. Although cell-aware diagnosis has been introduced to overcome this limitation, it is rarely used in the scan-chain domain due to the characteristics of scan flip-flops. Designing a scan flip-flop is complex, and only a few of the I/O pins are controllable and observable. Moreover, there are many equivalent defects due to the two identical latches that are serially connected. In this brief, the multi-bit scan flip-flop design was modified to reconfigure the scan path inside the cell, thereby making defects that are not easily identifiable more distinguishable. Since the proposed method is not affected by logic and proceeds at the layout level of the scan flip-flops, it is immune to the type, size, or complexity of the circuit. A new modified cell view for the intracell scan-chain diagnosis was developed based on the layout data and some analog simulations. Compared to the conventional method, cell-aware diagnosis using the modified scan flip-flop is available in the scan-chain domain and the area overhead is decreased.