Bidirectional Scan Chain for Stuck-At Defect Detection
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Solution Overview
Problem
The testing of application-specific integrated circuits (ASICs) is complicated by the inaccessibility of internal connections between core cells, rendering standard test methods ineffective, and defects in scan chains can prevent proper testing of integrated circuits.
Innovation Solution
A bi-directional scan chain structure is introduced, which includes additional multiplexers and different wirings, allowing for both forward and backward shift operations through a selector signal, enabling efficient detection of defects in ASICs by serially shifting data bits in one direction for a certain number of clock cycles and then reversing direction for another set of cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional one-directional scan chain is used, then the structure is simple and easy to manufacture, but it cannot detect certain defects (such as stuck-at defects) effectively
Solution Approach 1:
The patent applies inversion by enabling the scan chain to operate in reverse direction. By adding backward scan capability to the conventional forward-only scan chain, the system can detect defects that would be invisible in a single-directional configuration. The inverted operation mode allows test patterns to propagate through the circuit in both directions, revealing stuck-at defects and other failures that a unidirectional chain would miss.
Solution Approach 2:
The patent implements dynamics by making the scan chain direction changeable rather than fixed. The scan chain can dynamically switch between forward and backward directions based on test requirements. This dynamic capability is achieved through control logic that selectively enables forward or backward shifting, allowing the same hardware structure to adapt its operation mode for comprehensive defect detection.
2Measurement precision
If additional multiplexers and bidirectional wiring are added to enable forward and backward shift operations, then defect detection accuracy improves, but device complexity increases
Solution Approach 1:
The patent applies universality by designing multiplexers that serve multiple functions. The same multiplexer structure is used for both forward and backward scanning operations, as well as for normal circuit operation. This multi-functional design eliminates the need for separate dedicated components for bidirectional control, reducing overall complexity despite the enhanced capability.
Solution Approach 2:
The scan chain structure serves itself by using its own components (multiplexers and flip-flops) to enable bidirectional operation without requiring entirely separate test infrastructure. The existing scan chain elements are reconfigured through control signals to provide both forward and backward functionality, allowing the system to self-test in multiple directions using its own hardware resources.
3Adaptability or versatility
If a bidirectional scan chain is implemented, then multiple defect types can be detected and located, but the testing procedure becomes more complex
Solution Approach 1:
The patent applies periodic action by structuring the test procedure as a sequence of alternating forward and backward scan phases. Test patterns are applied in systematic cycles: forward scan to detect certain defect types, then backward scan to detect others. This periodic alternation provides a methodical approach that covers multiple defect types while maintaining procedural organization and ease of execution.
Data Source
AI summary
A bi-directional scan chain includes a plurality of cell structures, each cell structure having a storage device and at least one multiplexer, the plurality of cell structures coupled to one another in a series configuration, wherein an output of a (K−1)-th cell structure is provided as input to the K-th cell structure to provide a forward data shifting operation, and an output of the K-th cell structure is provided as an input to the (K−1)-th cell structure to provide a backward data shifting operation, where K is an integer greater than 1.