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Mechanochromic luminogenic materials (MCL) can reversibly modify their luminescence properties when exposed to external mechanical stimuli. This smart effect could emerge from physico-chemical characteristics varying in a wider scale, ranging from the transformation of molecular domains to the rearrangement of chemical bonds. MCL has become the fast-emerging group of materials owing to their great application potential as stress sensors, smart switches, optical memories, and optoelectronic and display devices. In recent years, a lot of work has been carried out on these materials leading to the synthesis of various MCL materials. This review discusses various organic MCL materials and their underlying luminogenic mechanisms. Furthermore, a detailed literature review of how different classes of luminescent organic materials respond to mechanical forces has been provided. In particular, the most common chromophores used in such systems including triphenylamine, cyanoethylene, pyrene, tetraphenylethene, and others are described here with an emphasis on their industrial applications. Presumably, this review will provide useful insights into the characteristics and applications of MCL materials to researchers working in this field in the academic community and industry.

Ultralight flexible carbon aerogels have been applied in many fields but are always hampered due to their weak mechanical stability, large energy dissipation, and complex preparation methods. Here, a novel polyimide-derived carbon nanofiber aerogel with high fatigue resistance and excellent flexibility is prepared by using the designed “fiber gluing” to construct the elastic continuous fibrous network. The as-prepared carbon nanofiber aerogels exhibit ultralow density of 6.6 mg cm−3, excellent fire-resistant performance when exposing to alcohol flames (650 °C), and robust elastic resilience even under 55% compressive strain. In particular, the carbon nanofiber aerogels show ultralow plastic deformation (only 1.3%) and low energy dissipation (

Although the mechanism of thermal cracking and the factors affecting the occurrence of this type of cracks are already well documented, the influence of this phenomenon on the structural capacity and the freezing behavior of the roadway near the cracks, as well as the consequence for the pavement of these localized effects is still poorly documented. The objective of the project is to improve the state of knowledge on the effects of cracking on pavement performance and to develop effective approaches for the mitigation of this degradation. Therefore, a pavement structure was built in the experimental pit of Laval University. The structure is composed of a reference section and a section in which an idealized crack has been created. These two sections are dynamically loaded using the Accelerated Transportation Loading System (ATLAS). Mechanical response of the pavement structure has been monitored via various strain and stress sensors, with particular interest for the area around the crack. A quantitative comparison of the two sections shows how the presence of a crack affects the different strain and stress levels measured around the idealized crack area. Results also show the pavement structure’s behavior under different temperature and saturation conditions.

Mechanoluminescence (ML) is generated during exposures of certain materials to mechanical stimuli. Many solid materials produce ML during their fracturing, however, the irreversibility of fracto-induced ML limits the practical applications of these materials. In 1999, Chao-Nan Xu discovered an intense and reproducible ML from trap-controlled materials, including ZnS:Mn2+ and SrAl2O4:Eu2+, and introduced the principles and applications of hybrid inorganic/organic mechanoluminescent (ML) composites, and related sensors to visualize stress/strain in target structures. This discovery has triggered intense research interest in trap-controlled ML materials and composites over the past 2 decades. Notable achievements of this research include the development of trap-controlled materials that exhibit bright ML emission from the ultraviolet to the near infra-red, and multiscale mechano-optical sensitivities. This research has also increased our understanding of the mechanisms of ML phenomena, enabling the rational design of trap-controlled ML materials. Practical applications of ML are also being driven by the discovery that ML composites can serve as “mechano-optical sensitive skin” for structural health diagnosis, stress sensors for biomechanics, and mechanically-activated light sources. This review focuses on the design, synthesis, characterization, optimization and application of trap-controlled ML materials, and concludes with discussions on future directions of ML research and specific challenges to improve ML materials for real-world applications.

Summary Due to the in situ, real-time, and non-destructive properties, mechanoluminescence (ML) crystals have been considered as intelligent stress sensors, which demonstrate potential applications such as in inner crack visualization, light source, and ultrasonic powder recording. Thereinto, it is highly expected that near-infrared (NIR) MLs can realize the visualization of inner biological stress because mechanically induced signals from them can penetrate biological tissues. However, such an energy conversion technique fails to work in biomechanical monitoring due to the limited advances of NIR ML materials. Based on those, some research groups have begun to focus on this field and initially realized this idea in vitro while related advances are still at the early stage. To advance this field, it is highly desirable to review recent advances in NIR ML crystals. In this review, to our knowledge, all the NIR ML crystals have been included in two main groups: oxysulfides and oxides. Besides, the present and emerging trends in investigation of such crystals were discussed. In all, the aim is to advance NIR ML crystals to more practical applications, especially for that of biomechanical visualization in vivo., Graphical Abstract, Medical Imaging; Optical Materials; Biomedical Material

The emergence of new applications, such as in artificial intelligence, the internet of things, and biotechnology, has driven the evolution of stress sensing technology. For these emerging applications, stretchability, remoteness, stress distribution, a multimodal nature, and biocompatibility are important performance characteristics of stress sensors. Mechanoluminescence (ML)-based stress sensing has attracted widespread attention because of its characteristics of remoteness and having a distributed response to mechanical stimuli as well as its great potential for stretchability, biocompatibility, and self-powering. In the past few decades, great progress has been made in the discovery of ML materials, analysis of mechanisms, design of devices, and exploration of applications. One can find that with this progress, the focus of ML research has shifted from the phenomenon in the earliest stage to materials and recently toward devices. At the present stage, while showing great prospects for advanced stress sensing applications, ML-based sensing still faces major challenges in material optimization, device design, and system integration.

A study on the design, simulation and characterization of a reconfigurable terahertz (THz) filter, composed of two frequency-selective surfaces (FSSs) with applications on sensor devices in general and highly sensitive stress sensors, is presented in this paper. Using the developed theoretical model, we found out that by careful tuning the wire parameters, it is possible to control the filter sensitivity and also the energy transmission and reflection that passes through the structure. Numerical modelling of both the mechanical and electromagnetic components (using the elasticity equation and Maxwell&rsquo, s equations, respectively) has been undertaken for two types of the device assemblies based on different thermoplastic polymers transparent to the THz radiation, namely: high-density polyethylene (HDPE) and polytetrafluoroethylene (PTFE), operating in a THz window from 395 to 455 GHz. The numerical results allowed us to characterize the relation between the reflectance/transmittance and the amount of force required to obtain a specific frequency shift along that window. It was found that the device assembled with HDPE presents a more linear response and it is able to pass from a full transparency to almost full opacity using only its linear operating zone. Due to its characteristics, this THz filter might be an interesting solution not only for THz sensors based on reconfigurable filters but also for optical modulators for the THz domain.

[(Na1−xKx)0.5Bi0.5]Ti0.985Ta0.015O3 (abbreviated as Ta-NK100x) lead-free ceramics with good piezoelectric properties were prepared using a solid-state reaction method. The structure and electrical properties of Ta-NK100x had been systemically investigated. The highest bipolar strain of 0.458% and the unipolar strain 0.448% are achieved at x = 0.18 at 60 kV/cm. Meanwhile, the corresponding normalized strain $$ \left( {d_{33}^{*} } \right) $$ reaches 747 pm/V. In addition, the unipolar strain of the poled Ta-NK18 increases to 0.537%, and corresponding $$ d_{33}^{*} $$ increases slightly to 894.5 pm/V at 60 kV/cm. The electric-field-induced phase transition between ferroelectric and relaxor is found to play a dominant role in the origin of the large strain. Moreover, the strain behavior remains stable within 105 switching cycles which indicating the prepared ceramics are promising candidates for actuators and stress sensors.

Embedded stress sensors have previously been employed as part of health monitoring systems for solid rocket motors; however, the sensor readings were used to detect anomalies such as bore cracks an...

The regenerated silk fibroin is developed to soft graphene aerogels for application in stress sensor. The resultant graphene aerogel owns a low density of 14.1 mg cm−3 with high mass specific capacitance of 128.4 F g−1. When a single aerogel serving as elastic medium, a supercapacitive stress sensor is established to offer high sensitivity of 0.73 kPa−1 in ranging 0.01–10 kPa. In contract, the sensor based on original graphene aerogel just shows a sensitivity of 0.04 kPa−1. Further, the sensing stability of the optimized sensor can retain 87% under constant pressure intensity of 1 kPa for 1000 cycles. The soft effect can be attributed to the regenerated silk fibroin by intercalation in preparation, and the simulated results show that the stress response originated from the variation of ion concentration in the electrochemical system.

Visualization and quantitative evaluation of covalent bond scission in polymeric materials are critical in understanding their failure mechanisms and improving the toughness and reliability of the materials. Mechano-responsive polymers with the ability of molecular-level transduction of force into chromism and luminescence have evoked major interest and experienced significant progress. In the current review, we highlight the recent achievements in covalent mechanochromic and mechanoluminescent polymers, leading to a bridge between macroscopic mechanical properties and microscopic bond scission events. After a general introduction concerning polymer mechanochemistry, various examples that illustrate the strategies of design and incorporation of functional and weak covalent bonds in polymers were presented, the mechanisms underlying the optical phenomenon were introduced and their potential applications as stress sensors were discussed. This review concludes with a comment on the opportunities and challenges of the field.

Centimetric capacitive sensors made out of PDMS foams of controlled porosity are fabricated and electromechanically characterized under either normal stress and shear stress. For normal stress characterizations, it can be concluded that the density of the foam strongly affects the sensor performances expressed in sensitivity and measurement range thanks to dedicated behavioral sensor models. Also, it was found that the actual size of the foam pores plays a minor role in the electromechanical behavior of the sensor. Similar conclusions can be derived shear stress sensor characterizations. This work opens the way to the design of flexible sensors with adjustable performances for normal and shear stress measurements.

Combining functional nanomaterials composite with three-dimensional graphene (3DG) is a promising strategy for improving the properties of stress sensors. However, it is difficult to realize stress sensors with both a wide measurement range and a high sensitivity. In this paper, graphene-SiO2 balls (GSB) were composed into 3DG in order to solve this problem. In detail, the GSB were prepared by chemical vapor deposition (CVD) method, and then were dispersed with graphene oxide (GO) solution to synthesize GSB-combined 3DG composite foam (GSBF) through one-step hydrothermal reduction self-assembly method. The prepared GSBF owes excellent mechanical (95% recoverable strain) and electrical conductivity (0.458 S/cm). Furthermore, it exhibits a broad sensing range (0&ndash, 10 kPa) and ultrahigh sensitivity (0.14 kPa&minus, 1). In addition, the water droplet experiment demonstrates that GSBF is a competitive candidate of high-performance materials for stress sensors.

In recent years, mechanoluminescence from polymers is emerging as a new cutting-edge area of polymer mechanochemistry research. It refers to the release of energy from polymers in the form of light when they are under various mechanical stimuli. To spur more researchers to join in such interesting and new burgeoning area, and promote its development to practical applications, in this review, we try to briefly summarize the recent advances in mechanoluminescent polymers with the aspects of non-covalent, covalent, and cascade reactions systems. We pay much attention on the applications of such polymer systems in molecular level failure and stress sensors, and give a perspective of their potential applications in novel energy conversion materials and devices, as well as self-healing materials.

Stress sensors have shown potential to provide “health monitoring” of a wide range of issues related to packaging of integrated circuits, and silicon carbide offers the advantage of much higher temperature sensor operation with application in packaged high-voltage, high-power SiC devices as well as both automotive and aerospace systems, geothermal plants, and deep well drilling, to name a few. This paper discusses the theory and uniaxial calibration of resistive stress sensors on 4H silicon carbide (4H-SiC) and provides new theoretical descriptions for four-element resistor rosettes and van der Pauw (VDP) stress sensors. The results delineate the similarities and differences relative to those on (100) silicon: resistors on the silicon face of 4H-SiC respond to only four of the six components of the stress state; a four-element rosette design exists for measuring the in-plane stress components; two stress quantities can be measured in a temperature compensated manner. In contrast to silicon, only one combined coefficient is required for temperature compensated stress measurements. Calibration results from a single VDP device can be used to calculate the basic lateral and transverse piezoresistance coefficients for 4H-SiC material. Experimental results are presented for lateral and transverse piezoresistive coefficients for van der Pauw structures and p- and n-type resistors. The VDP devices exhibit the expected 3.16 times higher stress sensitivity than standard resistor rosettes.

The conjecture discussed in our previous paper [Jaeger, R. C., Motalab, M., Hussain, S., and Suhling, J. C., 2014, “Four-Wire Bridge Measurements of Silicon van der Pauw Stress Sensors,” ASME J. Electron. Packag., 136(4), p. 041014; Jaeger, R. C., Motalab, M., Hussain, S., and Suhling, J. C., 2018, Erratum: “Four-Wire Bridge Measurements of Silicon van der Pauw Stress Sensors,” ASME J. Electron. Packag., 140(1), p. 017001] was backed up by measurements and simulation results, but not mathematically proven. A proof based upon two-port impedance parameter reciprocity is presented with additional experimental confirmation.

In previous chapters, we discussed the material preparation for the piezotronic strain/stress sensors. This chapter focuses on the sensing mechanism. Different types of strain/stress sensors have been invented for not only conventional applications but also emerging fields like artificial skin [114] and human-machine interface [115]. In spite of the large number of designs, the fundamental mechanisms enabling those sensors fall into only a few categories. One major category is based on the phenomenon that a mechanical strain can affect the charge carrier transport in a homogeneous material with two electrodes. Altering of the transport characteristics can come from the geometric change, the piezoresistive effect that is related to the material resistivity [116], and the piezotronic effect that is related to the interfacial barrier between the material and the electrode [10, 17].

The physical and operating principle of a stress sensor, based on two crossing carbon fibers functionalized with ZnO nanorod-shaped nanostructures, was recently demonstrated. The functionalization process has been here extended to tows made of one thousand fibers, like those commonly used in industrial processing, to prove the idea that the same working principle can be exploited in the creation of smart sensing carbon fiber composites. A stress-sensing device made of two functionalized tows, fixed with epoxy resin and crossing like in a typical carbon fiber texture, was successfully tested. Piezoelectric properties of single nanorods, as well as those of the test device, were measured and discussed.

Magnetoimpedance (MI) and field sensitivity of CoFeSiB amorphous ribbons were investigated at frequencies ranging from 0.2 to 12 MHz after tensile stress applied. Experimental results indicate that the MI of amorphous ribbons can be significantly improved by applying a suitable longitudinal tensile stress. Applying tensile stress induces a rearrangement of domain walls which influences the circumferential anisotropy and magnetic permeability result in improving the MI response. The maximum MI response of 145 % and maximum field sensitivity of 6.32 %/Oe at frequency of 4 MHz were obtained, when tension was equivalent to 120 MPa. So the tensile stress as new method can be effective, cheap, and fast in sensor applications, and result of this investigation can be applied for the design of the stress sensors based on the giant magnetoimpedance effect.

Kinked silicon nanowires (KSiNWs) have many special properties that make them attractive for a number of applications. The mechanical properties of KSiNWs play important roles in the performance of sensors. In this work, the effects of defects on the mechanical properties of KSiNWs are studied using molecular dynamics simulations and indirectly validated by experiments. It is found that kinks are weak points in the nanowire (NW) because of inharmonious deformation, resulting in a smaller elastic modulus than that of straight NWs. In addition, surface defects have more significant effects on the mechanical properties of KSiNWs than internal defects. The effects of the width or the diameter of the defects are larger than those of the length of the defects. Overall, the elastic modulus of KSiNWs is not sensitive to defects; therefore, KSiNWs have a great potential as strain or stress sensors in special applications. Electronic supplementary material The online version of this article (doi:10.1186/s11671-017-1970-7) contains supplementary material, which is available to authorized users.

Packaging-induced die-stresses due to temperature effects on various materials of the package are characterized using piezoresistive van der Pauw stress sensors over a temperature range of −180° C to 80° C. Piezo-resistive coefficients extracted previously are then used to obtain a mapping between change in resistance and corresponding stress at all tested temperatures. The obtained values of stress are compared with finite element simulation results.

Mechanoluminescence (ML) is a type of luminescence induced by any mechanical action on solids. The light emissions induced by elastic deformation, plastic deformation and fracture of solids are called elastico ML (EML), plastico ML (PML) and fracto ML (FML), respectively. Whereas nearly 50% of all organic molecular solids and inorganic salts exhibit FML, only a few solids exhibit EML and PML. The EML and FML of certain solids are so intense that they can be seen during daylight with the naked eye. Mechanolumnescence has a great potential for use in different types of mechano-optical devices such as stress sensors, damage sensors, impact sensors, fracture sensors and safety management monitoring systems. This article reports a survey of the literature from 1605 to 2013. Mechanoluminescence is studied by physicists, chemists, material scientists, geologists, medical scientists, engineers and technologists, among others and researchers will certainly benefit from the literature survey on ML given here. In addition, the field of mechanoluminescence may attract the interest of many new researchers.

In this work, piezoresistive stress sensors test circuit fabricated into the sensitive structure as part of the normal processing procedure is used to measure the stresses difference distribution before and after the assembly. Sensor resistances were recorded before and after the adhesive bonding. Using the theoretical equations, the stresses on the die surface have been calculated from the data of sensor resistances. This technology not only provides a performance diagnostic tool for the sensitive structures and the miniature components, but also presents a design tool for low-stress micro-assemblies of miniature components.

The wearing process of an ultrahigh molecular weight polyethylene (UHMWPE) bearing surface in orthopaedic surgical implants cannot be tracked at present; hence, implant failure only becomes apparent when the patient experiences some discomfort. In exploring the integration of wireless stress sensors into UHMWPE, this paper describes the first step in achieving in vivo monitoring of implant wear using magnetostrictive amorphous ribbons.

We have fabricated p- and n-type resistor stress sensors on (111) silicon surface and investigated the strain effects, which were generally ignored in previous works, for the precise stress measurements. We obtained the corrected values of the pi-coefficients for p- and n-type silicon by considering the strain effects, without which more than 25% discrepancies may be induced for small pi-coefficients. We observed that ignoring the strain effects was one of the potential errors which induce large discrepancies in stress measurements, especially for n-type stress sensors on (111) silicon.

A technical challenge in fabrication of ultra-thin sensor chip (UTSC) is to keep chip integrity in debonding the ultra-thin chips from grinding facilities. This paper presents a new debonding method by utilizing a thermally decomposable polypropylene carbonate (PPC), as the temporary bonding adhesive. Because PPC can readily decompose at relatively low temperature, this method can maintain the chip integrity even the chips have a thickness of tens of microns. UTSCs with thickness of 30μm have been achieved using this method, and stress sensors have been developed to verify the performance of UTSC. The experimental results show that the proposed method is able to fabricate UTSC with good flexibility and characterizations, demonstrating the newly proposed method an enabling technology for fabrication of sensors for flexible and wearable applications.

In this paper, we design, fabricate, and evaluate octagonal nMOSFET multi operation device for normal MOSFET operation, detection of 8 stress direction, and variation of temperatures. In previous works, one sensor device can detect only one physical or chemical phenomenon. If we get some sensing data, such as temperature, stress, and etc., more than two sensor devices must be implemented. According to stress detection, stress sensors reattach along stress direction for measurement, because most of the previous stress sensors can sense only one dimension. However, octagonal MOSFET is not necessary to adjust because this device has radial eight direction output terminals and can accommodate various sensing using these terminals. Furthermore, this device can also measure the variation of threshold voltage using these output terminals. For example, proposed device can get variety of temperatures due to the temperature characteristics of threshold voltage. As the results, we can realize that it can sense 8 stress directions and a variety of temperature.

For many diseases, where a particular organ is affected, chemical by-products can be found in the patient’s exhaled breath. Breath analysis is often done using gas chromatography and mass spectrometry, but interpretation of results is difficult and time-consuming. We performed characterization of patients’ exhaled breath samples by an electronic nose technique based on an array of nanomechanical membrane sensors. Each membrane is coated with a different thin polymer layer. By pumping the exhaled breath into a measurement chamber, volatile organic compounds present in patients’ breath diffuse into the polymer layers and deform the membranes by changes in surface stress. The bending of the membranes is measured piezoresistively and the signals are converted into voltages. The sensor deflection pattern allows one to characterize the condition of the patient. In a clinical pilot study, we investigated breath samples from head and neck cancer patients and healthy control persons. Evaluation using principal component analysis (PCA) allowed a clear distinction between the two groups. As head and neck cancer can be completely removed by surgery, the breath of cured patients was investigated after surgery again and the results were similar to those of the healthy control group, indicating that surgery was successful.

Since GMI changes as a function of external dc magnetic field or applied dc/ac current, it is possible to design and produce GMI-based sensors that can measure either magnetic fields or dc/ac currents. GMI also changes sensitively with applied stress, and this provides a new opportunity to develop stress sensors. A brief description of these typical sensors is given in this chapter. It shows that the high sensitivity of GMI to applied magnetic field, current, and external stress is very useful for a wide range of industrial and engineering applications.

We study the performance of Fiber Specklegram Sensors (FSSs) by using finite element method (FEM). Sensing mechanism is studied by evaluating different stress gauges and numerical apertures of the fibers, which evidence effective design criteria.

In this study, the parameters (i.e., contact stress at the die-sheet interface and the punch velocity) were measured by the installation of film stress sensors in the fine-blanking die. A regression model was established to investigate the degree of importance of the parameters and their interaction on reducing the crack ratio of fine-blanked surface. Analysis of variance (ANOVA) was then performed to check the adequacy of the regression model. The optimal results of the regression model agreed well with the experimental result. The regression analysis indicated that the contact stress have a major influence, followed by the interaction and the punch velocity. The importance of the interaction means that the ability of contact stress in crack ratio reduction depends on the level of punch velocity. The result could be useful to facilitate an improvement in the quality of the fine-blanked parts by the optimization parameters.

Provide the sensor responses for various bonding power from 76 DAC to 200 DAC and use optical microscopy images, Current-Voltage curves and stress responds to find the regions of bondable and bond failures. When the bonding power increased, the stress magnitude of σx, σy and σz all increased. Good bonding could be achieved with bonding power less than 100 DAC. When bonding power is more than 100 DAC, bond failure or sensor damage could be occurred. The bond failure mechanisms include that under Al pad crack and Silicon cratering after wire bonding.

The effect of bond geometry on bond strength and reliability is studied for 25 µm Au wire bonds on standard CMOS Al pads. An accelerated method for parameter optimization is used to produce ball bonds with optimized shear strength (SS) and target values for ball diameter of 56.5 µm, bonded ball height (BH) of 12 µm, 16 µm, and 20 µm for low, medium, and high BH, respectively. Low BH bonds achieve 126.1 MPa strength and endure up to 41.9% US before deformation begins, whereas high BH bonds achieve only 109.8 MPa strength and withstand a maximum of 39.8% US. Low BH bonds achieve higher SS possibly due to the higher level of US that can be used. Bond reliability is assessed non-destructively in high temperature storage (HTS) tests using piezoresistive stress sensors. The bonds are aged at 200 °C for ∼500 h. From features in the stress sensor signals, a characteristic time (t c ) is derived during aging using an improved method. The t c value indicates the time it takes for the bonds to degrade severely due to intermetallics and crack formation. The t c values for low, medium, and high BH bonds were found to be 199.9±8.7 h, 225.9±9.5 h, and 231.9±6.8 h respectively. The result suggests ball bonds with higher BH values are more reliable than the bonds with lower BH for a constant ball bond diameter. This result is corroborated by the SS before and after aging being the same for the high BH bonds whereas SS dropped by 3% for the low BH bonds. The non-destructive method was demonstrated to have an estimated time resolution better than 10 h which allows for precise comparisons of the reliability of various processes.

© 2015 IEEE. In this work the mechanical stress induced in 3D stacks by different packaging process steps is studied. The 3D stacks used in this work are assembled using two identical dies containing a number of stress sensors which are designed and manufactured in 65nm technology. It is observed that the contribution of the package substrate and the die-attach process to the redistribution of mechanical stress inside the 3D stacked IC is more significant than the one of the EMC and that the influence of packaging on the shape and amplitude of local stress around the inter-die interconnects (micro-bumps) is not significant. These observations are supported by the measurements of stress done using micro-Raman spectroscopy and are correlated with the results of finite element modeling and with optical warpage measurements of different packaging configurations. ispartof: pages:354-361 ispartof: IEEE vol:2015-July pages:354-361 ispartof: 2015 Electronic Components & Technology Conference (ECTC) location:CA, San Diego date:26 May - 29 May 2015 status: published

In this paper, the application of magnetoelasticity in static tension monitoring for large steel cables is discussed. Magnetoelastic (EM) stress sensors make contact-free tension monitoring possible for hanger cables and post-tensioned cables on suspension and cable-stayed bridges. By quantifying the correlation of magnetic relative permeability with tension and temperature, the EM sensors inspect the load levels in the steel cables. Cable tension monitoring on Qiangjiang (QJ) 4th Bridge demonstrates the reliability of the EM sensors.

Influences of bending stress on an electrical resistivity of carbon fiber are studied as a basic research to develop high sensitive stress sensors. It is confirmed that an initial bending stress reversibly decreases the electrical resistivity, because the initial stress probably decreases the density of electron scattering sites. On the other hand, an excess stress increases the electrical resistivity.

Piezoresistive stress sensors are widely used to characterize semiconductor die stresses. Packaging stresses induce a small change in resistance in the sensors and they are highly sensitive to factors such as temperature and processing conditions. Thus, accurate stress prediction requires calibration and knowledge of all sources of variation in the resistance response of the sensors. This paper quantifies the effect of process variations and demonstrates that die level tracability is critical to ensure accurate stress prediction.

In this work, a simple assembled structure was designed and fabricated so that the calibration procedures on piezoresistive stress sensors for microelectronic packaging can be simpler, more accurate, and more efficient. After comparing with the previous work results, validity of the aforementioned new structure has been demonstrated through experimental data. Since many accessory experimental facilities employed in traditional calibrations become unnecessary, the new methodology takes great advantage on piezoresistive coefficient extractions, especially for calibration at temperature other than room temperature.

Principles of remote-interrogated stress sensors based on high-frequency magnetic materials showing the inverse magnetostrictive or magnetoimpedance effects are presented. The magnetoelastic behaviour of amorphous single layer films and amorphous/nanocrystalline multilayers is characterized in a frequency range between 10 MHz and 8 GHz with a high-frequency permeameter by applying tensile or compressive stress to the sample. Magnetron-sputtered (Fe50Co50/Co80B20) multilayers have been developed which show ferromagnetic resonance frequencies up to 5 GHz as well as good magnetoelastic properties in the GHz range.

Under the proper orientations and excitations, the transverse output of rotationally symmetric four-contact van der Pauw (VDP) stress sensors depends upon only the in-plane shear stress or the difference of the in-plane normal stresses on (100) silicon. In bridge-mode, each sensor requires only one four-wire measurement and produces an output voltage with a sensitivity that is 3.16 times that of the equivalent resistor rosettes or bridges, just as in the normal VDP sensor mode that requires two separate measurements. Both numerical and experimental results are presented to validate the conjectured behavior of the sensor. Similar results apply to sensors on (111) silicon. The output voltage results provide a simple mathematical expression for the offset voltage in Hall effect devices or the response of pseudo Hall-effect sensors. Bridge operation facilitates use of the VDP structure in embedded stress sensors in integrated circuits.

Different approaches combining Finite Element Simulations and in-situ electrical measurement of stress sensors during a BABSI test are proven to be ideal combination to quantitatively compare the strength of BEOL layers. It is shown that detectable mechanical failures during a shear or BABSI test are insufficient to detect early opens of the metal interconnections. A good agreement was found between the applied loads to the BEOL stack, the response of stress sensors below the Cu pillar and finite element simulations. Next, the risk of cohesive and adhesive failures in the Cu/low-k layers is evaluated in function of stiffness of low-k and design of metal interconnections.

In this work the effects of 3D stacking technology on the performance of devices are systematically studied. For this study a special chip consisting of a number of stress sensors and vertical interconnect loops was designed and manufactured in 65 nm technology. Local variations of stress with a magnitude of up to 300 MPa are detected at different locations along the chip and are being characterized using finite element modeling and micro-Raman spectroscopy measurements.

In order to use NiTi wires as strain or stress sensors, the variations of electrical resistance of Ti-50.8 at%Ni wires during thermo-mechanical loading are studied in this paper. The results show that it is possible to use the NiTi wires as strain sensors, but it is difficult to use NiTi wires as stress sensors.

Cobalt ferrite has been shown to be an excellent candidate material for high sensitivity magnetic stress sensors due to its large magnetomechanical effect and high sensitivity to strain. However, near room temperature, the material exhibits some magnetomechanical hysteresis, which becomes negligible for temperatures of 60/spl deg/C and above. Measurements indicate that doping the cobalt ferrite with silicon lowers the Curie temperature of the material. It was also found that the Curie temperature of the material depends on the fabrication and processing procedure. These results offer the possibility of decreasing the room temperature magnetomechanical hysteresis through control of the Curie temperature, thereby altering the temperature dependence of magnetic and magnetomechanical properties.

The MOSFET (Metal-Oxide-Semiconductor Field-Effective-Transistor) has the potential to be a suitable chip stress monitoring tool for microelectronic packaging because the measurements are nondestructive, in-situ, real-time, and the sensor is relatively small. To this end, this paper studies the stress behaviors of both types of the MOSFET micro stress sensors. In this work, a self-developed four-point bending (4PB) measurement methodology is employed and the stress coefficient calibrations on the MOSFET sensors were next performed. After measurements, stress coefficients for both types of the MOSFET were successfully extracted with discussions. After comparing with the previous extracted temperature coefficients on the same devices, it is also concluded that the temperature effect is extremely important for the MOSFET sensor applications.

The behaviors of piezoresistivity in a new series of composite materials composed of TiC particles in polyvinyl chloride (PVC) insulating polymer are investigated. Experimental results show a pronounced change in resistivity with pressure, making the composite materials attractive candidates for pressure or stress sensors with sensitivities much higher than the conventional semiconductive silicon materials. Piezoresistive effect of TiC-PVC composite is related to the difference in the elastic properties of the TiC particles and PVC polymer, and to the large changes in resistivity with concentration close to 25 vol%TiC in composite.

This paper reports a systematic analysis of the geometry dependent sensitivity of planar piezoresistive stress sensors based on the shear piezoresistance effect, also termed pseudo-Hall effect. The analyzed geometry parameters are: (i) the shape of the device active area, (ii) its aspect ratio, and (iii) the location and size of input and output contacts. Further, the influence of insulating holes in the active device area was investigated. General design rules for the design of piezoresistive stress sensors with improved sensitivity were extracted. These results were obtained using a simulation approach combining affine mapping with the finite element method. The simulation program was tested by comparing simulation results with experimental data. The differences between simulated and measured results were between 1.2% and 3.3%. Novel optimized sensor geometries with insulating holes show simulated and measured sensitivities greatly improved by factors up to 2.30 and 2.39, respectively.