Kun-Han Tsai

Embedded deterministic test for low cost manufacturing test

This paper introduces embedded deterministic test (EDT) technology, which reduces manufacturing test cost by providing one to two orders of magnitude reduction in scan test data volume and scan test time. The EDT architecture, the compression algorithm, design flow, experimental results, and silicon implementation are presented.

Timing-Aware ATPG for High Quality At-speed Testing of Small Delay Defects

In this paper, a new ATPG methodology is proposed to improve the quality of test sets generated for detecting delay defects. This is achieved by integrating timing information, e.g. from standard delay format (SDF) files, into the ATPG tool. The timing information is used to guide the test generator to detect faults through the longest paths in order to improve the ability to detect small delay detects. To avoid propagating faults through similar paths repeatedly, a weighted random method is proposed to improve the path coverage during test generation. During fault simulation, a new fault-dropping criterion, named dropping based on slack margin (DSM), is proposed to facilitate the trade-off between the test set quality and the test pattern count. The quality of the generated test set is measured by two metrics: delay test coverage and SDQL. The experimental results show that significant test quality improvement is achieved when applying timing-aware ATPG with DSM to industrial designs

Compactor independent direct diagnosis

In scan test environment, designs with embedded compression techniques can achieve dramatic reduction in test data volume and test application time. However, performing fault diagnosis with the reduced test data becomes a challenge. In this paper, we provide a general methodology based on circuit transformation technique that can be applied for performing fault diagnosis in the context of any compression technique. The proposed methodology enables seamless reuse of the existing standard ATPG based diagnosis infrastructure with compressed test data. Experimental results indicate that the diagnostic resolution of devices with embedded compression is comparable with that of devices without embedded compression.

Multiple fault diagnosis using n-detection tests

We study the relationship between multiple fault diagnosability and fault detection count. Instead of developing a complex diagnostic algorithm for multiple fault behavior, we change the test sets used in test and diagnosis. This allows us to apply a simple single-fault based diagnostic algorithm, and yet achieve very good diagnosability for the failure test cases caused by multiple faults. We have verified experimentally the effectiveness of n-detection tests for multiple-fault cases and explained the results in probabilistic terms.

Analysis and methodology for multiple-fault diagnosis

In this paper, we propose a multiple-fault-diagnosis methodology based on the analysis of failing patterns and the structure of diagnosed circuits. We do not consider the multiple-fault behavior explicitly, but rather partition the failing outputs and use an incremental simulation-based technique to diagnose failures one at a time. Our methodology can be further improved by selecting appropriate diagnostic test patterns. The n-detection tests allow us to apply a simple single-fault-based diagnostic algorithm, and yet achieve good diagnosability for multiple faults. Experimental results demonstrate that our technique is highly efficient and effective. It has an approximately linear time complexity with respect to the fault multiplicity and achieves a high diagnostic resolution for multiple faults. Real manufactured industrial chips affected by multiple faults can be diagnosed in minutes of central processing unit (CPU) time.

Delay-fault diagnosis using timing information

In modern technologies, process variations can be quite substantial, often causing design timing failures. It is essential that those errors be correctly and quickly diagnosed. Unfortunately, the resolution of the existing delay-fault diagnostic methodologies is still unsatisfactory. In this paper, the feasibility of using the circuit timing information to guide the delay-fault diagnosis is investigated. A novel and efficient diagnostic approach based on the delay window propagation (DWP) is proposed to achieve significantly better diagnostic results than those of an existing delay-fault diagnostic commercial tool. Besides locating the source of the timing errors, for each identified candidate the proposed method determines the most probable delay defect size. The experimental results indicate that the new method diagnoses timing faults with very good resolution.

Timing-Aware Multiple-Delay-Fault Diagnosis

With feature sizes steadily shrinking, manufacturing defects and parameter variations often cause design timing failures. It is essential that these errors be correctly and quickly diagnosed. In this paper, we analyze the multiple-delay fault diagnosis problem and propose a novel, simulation-based approach to solve it. We enhance the diagnostic resolution by processing failure logs at various slower- than-nominal clock frequencies. We experimentally determined our diagnosis algorithm s sensitivity to delay variations.

Star test: the theory and its applications

In this paper, we introduce a hierarchical test set structure called star test, derived from the experimental observation of the fault clustering phenomena. Based on the concept of star test, two applications are studied: one applied to built-in-self-test (BIST); the other to automatic test pattern generation (ATPG). First, a very high quality and low-cost BIST scheme, named STAR-BIST is proposed. Experimental results have demonstrated that a very high fault coverage can be obtained without any modification of the logic under test, no test data to store and very simple BIST hardware which does not depend on the size of the circuit. Second, an efficient test generator, named STAR-ATPG, is developed which speeds up the ATPG performance by a factor of up to five for large industrial circuits.

Enhancing Transition Fault Model for Delay Defect Diagnosis

With nanometer processes, at-speed testing is required to filter out failing chips with delay defects to ensure high product quality. Locating delay defects is important not only for improving yield but also providing important information to enhance at-speed test methods to meet quality goals. In this paper, a method that leverages successful static defect diagnosis method to diagnose delay defects is presented. To avoid missing any defect suspects, transition fault model is used with special considerations of self masking, glitch detection and passing bit mismatch. The effectiveness of this approach is demonstrated with simulation experiments as well as two case studies on failing chips from Renesas Technologys 130nm process.

Scan encoded test pattern generation for BIST

This paper presents an improved scan-based BIST scheme which achieves very high fault coverage without any modification of the mission logic, i.e. no test point insertion, no test data to store and very simple BIST hardware which does not depend on the size of the circuit. The approach utilizes scan order and its polarity in scan synthesis, effectively converting it into a ROM encoding a few test vectors which serve as centers of clusters from which the other vectors are derived by complementing at random their coordinates. The proposed method successfully tests the random pattern resistant faults, which is the major problem of traditional LFSR-based BIST, with lower hardware cost and a more efficient algorithm than previous methods. Experimental results demonstrate that a very high fault coverage can be achieved with much smaller test set than other pseudorandom pattern generation methods published so far.