Under manufacturing process variation, a path through a net is called longest if there exists a process condition under which the path has the maximum delay among all paths through the net. There are often multiple longest paths for each net, due to different process conditions. In addition, a local defect, such as resistive open or a resistive bridge, increases the delay of the affected net. To detect delay faults due to local defects and process variation, it is necessary to test all longest paths through each net. Previous approaches to this problem were inefficient because of the large number of paths that are not longest. This paper presents an efficient method to generate the set of longest paths for delay test under process variation. To capture both structural and process correlation between path delays, we use linear delay functions to express path delays under process variation. A novel technique is proposed to prune paths that are not longest, resulting in a significant reduction in the number of paths. In experiments on International Symposium on Circuits and Systems (ISCAS) circuits, our number of longest paths is 1-6% of the previous best approach, with 300/spl times/ less running time.

Longest-path selection for delay test under process variation

In this paper, we present a fault dictionary based scan chain failure diagnosis technique. We first describe a technique to create small dictionaries for scan chain faults by storing differential signatures. Based on the differential signatures stored in a fault dictionary, we can quickly identify single stuck-at fault or timing fault in a faulty chain. We further develop a novel technique to diagnose some multiple stuck-at faults in a single scan chain. Comparing with fault simulation based diagnosis technique, the proposed fault dictionary based diagnosis technique is up to 130 times faster with same level of diagnosis accuracy and resolution.

Fault Dictionary Based Scan Chain Failure Diagnosis

Under manufacturing process variation, a path through a fault site is called longest for delay test if there exists a process condition under which the path has the maximum delay among all paths through that fault site. There are often multiple longest paths for each fault site in the circuit, due to different process conditions. To detect the smallest delay fault, it is necessary to test all longest paths through the fault site. However, previous methods are either inefficient or their results include too many paths that are not longest.This paper presents an efficient method to generate the longest path set for delay test under process variation. To capture both structural and systematic process correlation, we use linear delay functions to express path delays under process variation. A novel path-pruning technique is proposed to discard paths that are not longest, resulting in a significantly reduction in the number of paths compared with the previous best method. The new method can be applied to any process variation as long as its impact on delay is linear.

Longest path selection for delay test under process variation

We propose to achieve and maintain ultra-high quality of digital circuits on a per-design basis by (i) monitoring the type of failures that occur through volume diagnosis, and (ii) changing the test patterns to match the current failure population characteristics. Opposed to the current approach that assumes sufficient quality levels are maintained using the tests developed during the time of design, the methodology described here presupposes that fallout characteristics can change over time but with a time constant that is sufficiently slow, thereby allowing test content to be altered so as to maximize coverage of the failure types actually occurring. Even if this assumption proves to be false, the test content can be tuned to match the characteristics of the fallout population if the fallout characteristics are unchanging. Under either scenario, it should be then possible to minimize DPPM for a given constraint on test costs, or alternatively ensure that DPPM does not exceed some pre-determined threshold. Our approach does not have to cope with situations where fallout characteristics change rapidly (e.g. excursion), since there are existing methods to deal with them. Our methodology uses a diagnosis technique that can extract defect activation conditions, a new model for estimating DPPM, and an efficient test selection method for reducing DPPM based on volume diagnosis results. Circuit-level simulation involving various types of defects shows that DPPM could be reduced by 30% using our methodology. In addition, experiments on a real silicon chip failures show that DPPM can be significantly reduced, without additional test execution cost, by altering the content (but not the size) of the applied test set.

Controlling DPPM through Volume Diagnosis

The application of Dynamic Voltage Scaling (DVS) to reduce energy consumption may have a detrimental impact on the quality of manufacturing tests employed to detect permanent faults. This paper analyses the influence of different voltage/frequency settings on fault detection within a DVS application. In particular, the effect of supply voltage on different types of delay faults is considered. This paper presents a study of these problems with simulation results. We have demonstrated that the test application time increases as we reduce the test voltage. We have also shown that for newer technologies we do not have to go to very low voltage levels for delay fault testing. We conclude that it is necessary to test at more than one operating voltage and that the lowest operating voltage does not necessarily give the best fault cover.

/pdf/dynamic-voltage-scaling-aware-delay-fault-testing-3f3eolxb79.pdf

Dynamic Voltage Scaling Aware Delay Fault Testing

Test application at reduced power supply voltage (low-voltage testing) or reduced temperature (low-temperature testing) can improve the defect coverage of a test set, particularly of resistive short defects. Using a probabilistic model of two-line nonfeedback short defects, we quantify the coverage impact of low-voltage and low-temperature testing for different voltages and temperatures. Effects of statistical process variations are not considered in the model. When quantifying the coverage increase, we differentiate between defects missed by the test set at nominal conditions and undetectable defects (flaws) detected at non nominal conditions. In our analysis, the performance degradation of the device caused by lower power supply voltage is accounted for. Furthermore, we describe a situation in which defects detected by conventional testing are missed by low-voltage testing and quantify the resulting coverage loss. Experimental results suggest that test quality is improved even if no cost increase is allowed. If multiple test applications are acceptable, a combination of low voltage and low temperature turns out to provide the best coverage of both hard defects and flaws.

On Detection of Resistive Bridging Defects by Low-Temperature and Low-Voltage Testing

A procedure for using fault dominance in a large volume diagnosis environment is described. Fault dominance is shown to be useful for reducing the fault simulation time during diagnosis when used together with the concept of pattern dependence and maximally dominating faults. Results for both ISCAS benchmarks and industrial circuits are reported. The results show 9 % to 44% average reduction in the fault simulation time for these circuits.

Dominance based analysis for large volume production fail diagnosis

Path delays in deep submicron designs are sensitive to the operating point of the design, which is defined by the temperature and supply voltage. Moreover, a change in the operating conditions may affect different paths differently. We study a path selection technique for pathdelay fault test generation that takes into account possible variations in operating conditions. In developing the path selection procedure, we assume that the operating conditions are uniform across multiple gates, however, they are unknown and may assume one of a large range of values. The paths selected for test generation must include the critical paths for anyoperating point in this range. The study provides a quantitative analysis of path criticality at different operating conditions.

https://ieeexplore.ieee.org/iel5/8721/27596/01231681.pdf

On Path Selection for Delay Fault Testing Considering Operating Conditions

Path delays in deep submicron designs are sensitive to the operating point of the design, which is defined by the temperature and supply voltage. Moreover, a change in the operating conditions may affect different paths differently. We study a path selection technique for path delay fault test generation that takes into account possible variations in operating conditions. In developing the path selection procedure, we assume that the operating conditions are uniform across multiple gates, however, they are unknown and may assume one of a large range of values. The paths selected for test generation must include the critical paths for any operating point in this range. The study provides a quantitative analysis of path criticality at different operating conditions.

On path selection for delay fault testing considering operating conditions [logic IC testing]

We propose techniques to speed up diagnostic fault simulation for circuits without full-scan which may need multi-cycle tests. First, we introduce the concept of z-sets for circuits without full scan and show how z-sets can be used in a preprocessing step to improve the performance of diagnostic fault simulation. Further, an implementation of an equivalence identification tool that executes concurrently with diagnostic fault simulation is described along with methods to increase its efficiency by prioritizing fault pair selection and reducing interprocess communication. Finally, a combination of both these techniques is analyzed and the performance benefit is presented. Experimental results on ISCAS'89 benchmarks and industrial circuits indicate that diagnostic fault simulation is substantially faster by 20.6 to 46.9% when z-sets are used along with concurrent equivalent fault identification.

B. Seshadri

Papers

On Detection of Resistive Bridging Defects by Low-Temperature and Low-Voltage Testing

Dominance based analysis for large volume production fail diagnosis

On Path Selection for Delay Fault Testing Considering Operating Conditions

On path selection for delay fault testing considering operating conditions [logic IC testing]

Accelerating diagnostic fault simulation using z-diagnosis and concurrent equivalence identification