Scanning spreading resistance microscopy for failure analysis of nLDMOS devices with decreased breakdown voltage

Scanning Spreading Resistance Microscopy (SSRM) is successfully applied to investigate failing nLDMOS test devices that exhibit a lowered break down voltage (BVDSS) in electrical test. Cross-sectional, two-dimensional maps of the local sample resistivity from fail and reference (pass) devices reveal significant differences of the dopant concentration in individual, specific regions. This important information enables unambiguous identification of the root cause of the device failure to be dopant related. Furthermore, from a set of hypothesis, which explains the failed electrical test, SSRM results confirm exactly one and rule out the other. These are two important steps towards root cause identification. Since a relative comparison of fail and pass SSRM scans is sufficient for this failure analysis, an extensive data calibration for the absolute dopant concentration by means of additional SSRM measurements on test samples with known dopant concentration is not required. The ability of SSRM to prove or disprove miscellaneous fail hypothesis even without data calibration makes this method a very powerful tool for analysis of dopant related failure types.     

Localization of temperature sensitive areas on analog circuits

We introduce a novel easy to apply method to detect critical temperature sensitive areas on analog circuits. Our method is based on heat diffusion on a silicon micro-chip: the corners of a temperature sensitive micro-chip are heated up directly by ESD diodes or infrared laser light. This heat stimulus at the corners results in an inhomogeneous temperature distribution. Thus, the temperature is a function in time and space. The elapsed time to change the chip status from “fail” to “pass” as a reaction to the heat stimulus correlates with the distance to the heat source. This correlation is extracted from COMSOL simulations and experimental results. A numerical program based on that correlation succeeded in localization of the temperature sensitive chip module.Micro-chips affected by corner MOSFETs in the subthreshold regime are used to demonstrate our method.     

Micro-stress analysis and identification of lightweight aggregate’s failure strength by micromechanical modeling

This work is based on a dual approach of experiments and micromechanical modeling in order to characterize the failure behaviors of lightweight aggregate concretes (LWAC). Many classes of LWAC were tested, based on five families of lightweight aggregates (LWA) and three types of mortar matrices: normal, high performance (HP) and very high performance (VHP). Micromechanical modeling is based on an iterative homogenization approach and associated localization: local stress distributions during the uniaxial compression tests can be predicted in LWAC’s components and at their interface. Experimental compressive strengths were measured on manufactured 16 × 32 cm cylindrical specimens. The confrontations between micromechanical modeling and experiments were used to identify LWA’s failure strengths which are difficult to measure, and to quantify the inaccuracies related to conventional methods. These corrected values of LWA’s failure strength were introduced into a failure criterion modeling: associated predictions of LWAC’s compressive strength are in good agreement with the experimental measurements.     

Investigate the causes of cracks in welded 310 stainless steel used in the Flare tip

The present study examines the causes of the cracks in welded 310 stainless steel that has been used in the Flare tip. According to the tests, including metallographic examination, macroscopic hardness test and scanning electron microscopic analysis, the reasons for the nucleation and growth of the cracks in the weld zone have been discussed. The results show that, because of the service temperature of Flare tip between 500 and 900 °C, and hydrocarbon gases such as methane, ethane, sour gas and carbon dioxide that are the combustion products, the component surface has been oxidized and carburized. Thus, the surface carburized oxide layer and also the subsurface damage can be fertile field for the nucleation of cracks. Likewise, the presence of sigma phases, austenite dendrites and interdendritic delta ferrite can cause a drop in toughness in the weld zone and provide fields for the crack growth in the weld zone.     

Computational micromechanics of fatigue of microstructures in the HCF–VHCF regimes

Advances in higher resolution experimental techniques have shown that metallic materials can develop fatigue cracks under cyclic loading levels significantly below the yield stress. Indeed, the traditional notion of a fatigue limit can be recast in terms of limits associated with nucleation and arrest of fatigue cracks at the microstructural scale. Although fatigue damage characteristically emerges from irreversible dislocation processes at sub-grain scales, the specific microstructure attributes, environment, and loading conditions can strongly affect the apparent failure mode and surface to subsurface transitions. In this paper we discuss multiple mechanisms that occur during fatigue loading in the high cycle fatigue (HCF) to very high cycle fatigue (VHCF) regimes. We compare these regimes, focusing on strategies to bridge experimental and modeling approaches exercised at multiple length scales and discussing particular challenges to modeling and simulation regarding microstructure-sensitive fatigue driving forces and thresholds. We conclude by discussing some of the challenges in predicting the transition of failure mechanisms at different stress and strain amplitudes.     

Experimental study of the performance of geosynthetics-reinforced soil walls under differential settlements

The deformation performance and settlement failure mechanism of geosynthetics-reinforced soil (GRS) walls are the two key points of engineering design under the differential settlement. This paper presents model tests of deformation performance and failure mechanism of the GRS wall with and without lateral restriction under differential settlement conditions. The observation and measurement results, including force and vertical displacement of geosynthetics and lateral deformation of facing panels, indicate good settlement control performance of GRS wall during construction and under differential settlement. Results indicate that the influence of the stress state of facing panels on the settlement control performance of GRS wall cannot be ignored. And the differential settlement failure of GRS wall is likely to occur in the joint of facing panels and geosynthetics. For good illustrations, two analytical approaches about deformation and stress of geosynthetics were proposed based on elastic cable theory, in GRS wall with and without lateral restriction. The expressions exclude the necessity to carry out sophisticated numerical analyses to stress and deformation and may help to develop the design guidelines for such GRS wall.     

Comparison of different failure criteria for fiber-reinforced plastics in terms of fracture curves for arbitrary stress combinations

For fiber-reinforced plastics exists a big number of different criteria for the failure prediction. The intention of this paper is to compare the TSAI-HIL-, the LaRC04- and PUCK’s criterion in terms of their fracture curves for a unidirectional glass-fiber reinforced composite layer. Therefore after the implementation of these three criteria, the two-dimensional fracture curves for all possible stress combinations, which can be derived from a general spatial stress tensor, are computed. In this way, the characteristics of the criteria, similarities and differences and possible weak points become obvious.     

Deformation and failure in nodular cast iron

Ductile failure in nodular cast iron is explored through uniaxial tension and notched tension experiments. Specimens obtained through tests interrupted at various stages of deformation and failure evolution were examined through quantitative microscopy to discern the mechanisms of failure and to quantitatively evaluate the local strain evolution. Fractographic observations were used to identify the onset and evolution of damage processes during the deformation and failure of nodular cast iron. These tests and observations reveal that void growth and coalescence occurred only within a narrow localized band, whose size is comparable with the size of the graphite nodules; no statistically significant changes in the porosity were observed outside this zone.     

Signal noise perturbation on automotive mixed-mode semiconductor device generated by graded substrate defect

The semiconductor technologies evolution allows greatly reducing noise impact on products and many structures have been created to reduce its effect. However, this paper presents the apparition of a noise issue during the production of a mixed-mode device dedicated to automotive applications. The research investigations concerned the fact that failure was not detected at test level but at customer level; therefore, it was determinant to understand the root cause of this failure mode to drive corrective actions in order to secure customer. The challenge was to analyse noise in Failure Analysis (FA) without fault spatial localization results. Indeed, Light Emission Microscopy (EMMI) and Thermal Laser Stimulation (ex: Soft Defect Localization – SDL) were unable to provide any defective area in the product. The lack of failing device identification led us to combine electrical and design analyses in order to define hypothesis on the failure origin. It was then possible to drive physical investigations through different approaches, using physical cross-section, Secondary Ion Mass Spectrometry (SIMS) and Scanning Capacitance Microscopy (SCM) techniques. Finally, the obtained complementary results will be discussed and an explanation of the failure mechanism will be presented as the root cause issue, allowing defining the defective step in production process.     

Failure analysis on abnormal wall thinning of heat-transfer titanium tubes of condensers in nuclear power plant Part II: Erosion and cavitation corrosion

In Part I of the failure analysis on abnormal wall thinning of heat-transfer titanium tubes used in condensers in nuclear power plant, we analyzed the causes and mechanisms of abnormal thinning that commonly happened at the contact part between the tubes and the support plates. This kind of failure was the mainstream failure type in our case and the main causes were found to be eccentric contact wear and three-body contact wear rooted in processing defect of internal borings, corrosion products deposit and sagging, and foreign particles. However, there were still some individual failure tubes with different failure sites and modes and were located under the bypass pipes at the shoulder of the tube tower instead of in its lower part, obviously telling another failure story. In Part II of the failure analysis, material analysis, metallographic examination, mechanical performance tests, macro- and microstructure analysis and composition analysis were conducted. The failure causes were found to be erosion and cavitation corrosion and the synergetic effect of them. Finally, corresponding countermeasures were suggested.