Accelerated Lifetime Testing Research Articles

Multiparameter laser performance characterization of liquid crystals for polarization control devices in the nanosecond regime

Interactions of liquid crystals (LC’s) with polarized light have been studied widely and have spawned numerous device applications, including the fabrication of optical elements for high-power and large-aperture laser systems. Currently, little is known about both the effect of incident polarization state on laser-induced–damage threshold (LIDT) and laser-induced functional threshold (LIFT) behavior at sub-LIDT fluences under multipulse irradiation conditions. This work reports on the first study of the nanosecond-pulsed LIDT’s dependence on incident polarization for several optical devices employing oriented nematic and chiral-nematic LC’s oriented by surface alignment layers. Accelerated lifetime testing was also performed to characterize the ability of these devices to maintain their functional performance under multipulse irradiation as a function of the laser fluence at both 1053 nm and 351 nm. Results show that the LIDT varies as a function of input polarization by 30–80% within the same device, while the multipulse LIFT (which can differ from the nominal LIDT) depends on irradiation conditions such as laser fluence and wavelength.

Accelerated Lifetime Testing and Analysis of Delta-Doped Silicon Test Structures

As transistor features shrink beyond the 2 nm node, studying and designing for atomic scale effects become essential. Being able to combine conventional CMOS with new atomic scale fabrication routes capable of creating 2D patterns of highly doped phosphorus layers with atomic precision has implications for the future of digital electronics. This work establishes the accelerated lifetime tests of such doped layers, showing that these materials survive high current (>3.0 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and 300°C for greater than 70 days and are still electrically conductive. The doped layers compare well to failures in traditional metal layers like aluminum and copper where mean time to failure at these temperatures and current densities would occur within hours. It also establishes that these materials are more stable than metal features, paving the way toward their integration with operational CMOS.

Investigation on Parylene-C based neural electrodes by accelerated life test and reliability improvement using polyimide flexible cable

Since the encapsulation layer of the neural electrode plays an important role in determining the reliability of the device, more studies on the long-term reliability of Parylene-C are required. In this paper, we described the long-term reliability of Parylene-C based neural electrodes through an accelerated lift test and proposed a method to improve the reliability using polyimide flexible cable (PFC) attached to the Parylene-C device. The accelerated lifetime test was performed in phosphate-buffered saline at 50 °C. The electrochemical characteristics were acquired and analyzed to evaluate the reliability of the Parylene-C coated neural electrode for up to 56 days, which is equivalent to 115 days as an accelerated time. The proposed PFC method showed improved long-term stability of the device, demonstrating an increased lifetime, showing that testing conditions and device setup affect overall results. This study will help make reliable Parylene-C based neural electrode systems with improved moisture protection.

A Comparative Study on Reliability and Ruggedness of Kelvin and Non-Kelvin Packaged SiC Mosfets

This article evaluates silicon carbide (SiC) <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet’</small> s reliability and ruggedness comprehensively between two widely employed device package types: common source and Kelvin source. Multiple accelerated lifetime tests are conducted to comprehensively investigate SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> ’s reliability at both package and die levels. Specifically, a conventional high electric field test is applied to induce gate oxide degradation, whereas package degradation is investigated by the widely adopted power cycling test. To mimic gate oxide degradation patterns closer to realistic cases, an active channel gate bias test is proposed in this study, and a fair comparison is made regarding the device's degradation pattern in the conventional high electric field test. Throughout accelerated lifetime tests, devices’ electrical parameters, consumable lifetime, and end-of-life failure modes are comprehensively evaluated. For ruggedness comparison, a single-shot short-circuit test is conducted on both common-source and Kelvin-source packaged devices with the same die technique and configuration. Other than analytical discussions with experimental waveforms, failure analysis is also conducted to investigate the device's failure mode and root cause. In respect of experimental results in accelerated lifetime tests and short-circuit tests, the existence of the common-source inductance and resistance may mitigate the electrothermal stress applied on the chip with lower gate–source voltage under load current and results in mitigated device instability and longer consumable lifetime.

High-performance Ti/IrO2-RhOx-TiO2/α-PbO2/β-PbO2 electrodes for scale inhibitors degradation

The extensive evaporation-induced aggregation of scale inhibitors in the wastewater of recirculating cooling systems causes severe environmental pollution. In this study, Amino Trimethylene Phosphonic Acid (ATMP), an ordinary scale inhibitor, was degraded via electrochemical oxidation using a multi-layered Ti/IrO2-RhOx-TiO2/α-PbO2/β-PbO2 electrode. The electrochemical oxidation experimental results verified the superior electro-catalytic properties of the β-PbO2 electrode. Accelerated lifetime tests suggested that Ti/IrO2-RhOx-TiO2/α-PbO2/β-PbO2 possesses a service lifetime of 201 h under a current density of 40000 A/m2, which is 3.4–100.5 times as long as other β-PbO2 electrodes reported by other researchers. Four major operational parameters, namely electrolyte, current density, initial ATMP concentration, and pH, were discovered to significantly affect the ATMP degradation rate and electrical efficiency. The direct oxidation mechanism predominated in the degradation process of ATMP, achieving a 55.11% and 38.82% removal efficiency in Na2SO4 and NaCl solutions, respectively. In addition, two possible degradation pathways of ATMP were proposed: induced by the breaking of either C-P or C-N bonds.

Piezoresistive 3D graphene–PDMS spongy pressure sensors for IoT enabled wearables and smart products

Recently, 3D porous graphene–polymer composite-based piezoresistive sensors have gained significant traction in the field of flexible electronics owing to their ultralightweight nature, high compressability, robustness, and excellent electromechanical properties. In this work, we present an improved facile recipe for developing repeatable, reliable, and linear 3D graphene–polydimethylsiloxane (PDMS) spongy sensors for internet of things (IoT)-enabled wearable systems and smart consumer products. Fundamental morphological characterization and sensing performance assessment of the piezoresistive 3D graphene–polymer sensor were conducted to establish its suitability for the development of squeezable, flexible, and skin-mountable human motion sensors. The density and porosity of the sponges were determined to be 250 mg cm−3 and 74% respectively. Mechanical compressive loading tests conducted on the sensors revealed an average elastic modulus as low as ∼56.7 kPa. Dynamic compressive force-resistance change response tests conducted on four identical sensors revealed a linear piezoresistive response (in the compressive load range 0.42–2.18 N) with an average force sensitivity of 0.3470 ± 0.0794 N−1. In addition, an accelerated lifetime test comprising 1500 compressive loading cycles (at 3.90 N uniaxial compressive loading) was conducted to demonstrate the long-term reliability and stability of the sensor. To test the applicability of the sensors in smart wearables, four identical graphene–PDMS sponges were configured on the fingertip regions of a soft nitrile glove to develop a pressure sensing smart glove for real-time haptic pressure monitoring. Similarly, the sensors were also integrated into the Philips 9000 series electric shaver to realize smart shaving applications with the ability to monitor shaving motions. Furthermore, the readiness of our system for next-generation IoT-enabled applications was demonstrated by integrating the smart glove with an embedded system software utilizing the an open source microcontroller platform. The system was capable of identifying real-time qualitative pressure distribution across the fingertips while grasping daily life objects, thus establishing the suitability of such sensors for next-generation wearables for prosthetics, consumer devices, and personalized healthcare monitoring devices.

Aging Mechanisms and Accelerated Lifetime Tests for SiC MOSFETs: An Overview

Accelerated lifetime tests (ALTs) play a critical role in long-term reliability studies of SiC MOSFETs, including lifetime estimation, failure analysis, and condition monitoring. This article presents a comprehensive review of state-of-the-art ALTs circuits, operating principles, and induced failure modes for SiC MOSFETs. First, the weak spots and corresponding aging mechanisms in both device chip and package are summarized. Next, based on the system operating conditions, ALT configurations and working principles are discussed. Specifically, SiC MOSFET ALTs under normal operation, third-quadrant conduction, and extreme conditions are comprehensively described and compared. Requirements and future trends on ALTs selection and development are comprehensively discussed corresponding to various reliability research directions. Finally, suitable ALTs, corresponding failure locations, and mechanisms are tabulated as the conclusion. This review intends to provide insight on SiC MOSFET reliability test selection, platform development, and test parameter adjustments depending on application requirements.

New Driving Structure to Increase Pixel Charging Ratio for UHD TFT-LCDs With High Frame Rate

This paper proposes a new driving structure of the thin-film transistor liquid crystal display (TFT-LCD) for use in notebook displays with ultra-high definition (UHD) and a high frame rate. The proposed pixel circuit improves the pixel charging ratio by reducing the RC loadings of the data lines and extending the available row-line time for pixel charging. A new gate driver circuit that generates two output waveforms in a single stage is presented to reduce the cost and occupied layout area of gate driver ICs, enabling the realization of high-resolution displays with a narrow bezel. To verify the feasibility of the proposed driving structure, a 12.3-inch panel with UHD (3840 &#x00D7; 2160) and a frame rate of 120 Hz is fabricated. Experimental results demonstrate that the proposed driving structure yields a measured pixel charging ratio of more than 97.09% for a heavy loading pattern with a gray level of 255. Following an accelerated lifetime test, the measured waveforms of the proposed gate driver circuit are stable without any malfunction, demonstrating its high reliability. Therefore, the proposed driving structure and the gate driver circuit are highly suitable for use in UHD TFT-LCD notebook applications.

Statistical Inference for a Simple Step Stress Model with Competing Risks Based on Generalized Type-I Hybrid Censoring

Abstract This paper investigates a simple step-stress accelerated lifetime test (SSALT) model for the inferential analysis of exponential competing risks data. A generalized type-I hybrid censoring scheme is employed to improve the efficiency and controllability of the test. Firstly, the MLEs for parameters are established based on the cumulative exposure model (CEM). Then the conditional moment generating function (MGF) for unknown parameters is set up using conditional expectation and multiple integral techniques. Thirdly, confidence intervals (CIs) are constructed by the exact MGF-based method, the approximate normality-based method, and the bias-corrected and accelerated (BCa) percentile bootstrap method. Finally, we present simulation studies and an illustrative example to compare the performances of different methods.

Nanofibrous PEDOT-Carbon Composite on Flexible Probes for Soft Neural Interfacing.

In this study, we report a flexible implantable 4-channel microelectrode probe coated with highly porous and robust nanocomposite of poly (3,4-ethylenedioxythiophene) (PEDOT) and carbon nanofiber (CNF) as a solid doping template for high-performance in vivo neuronal recording and stimulation. A simple yet well-controlled deposition strategy was developed via in situ electrochemical polymerization technique to create a porous network of PEDOT and CNFs on a flexible 4-channel gold microelectrode probe. Different morphological and electrochemical characterizations showed that they exhibit remarkable and superior electrochemical properties, yielding microelectrodes combining high surface area, low impedance (16.8 ± 2 MΩ µm2 at 1 kHz) and elevated charge injection capabilities (7.6 ± 1.3 mC/cm2) that exceed those of pure and composite PEDOT layers. In addition, the PEDOT-CNF composite electrode exhibited extended biphasic charge cycle endurance and excellent performance under accelerated lifetime testing, resulting in a negligible physical delamination and/or degradation for long periods of electrical stimulation. In vitro testing on mouse brain slices showed that they can record spontaneous oscillatory field potentials as well as single-unit action potentials and allow to safely deliver electrical stimulation for evoking field potentials. The combined superior electrical properties, durability and 3D microstructure topology of the PEDOT-CNF composite electrodes demonstrate outstanding potential for developing future neural surface interfacing applications.

Accelerated lifetime testing of thin‐film solar cells at high irradiances and controlled temperatures

AbstractWithin this study, we investigate the intrinsic photostability of thin‐film solar cells, here organic photovoltaic cells. Since degradation under natural sun light proceeds within the timeframe of months and years, the process needs to be speeded up for fast material analysis and screening, using high‐concentration accelerated lifetime testing (high‐C ALT). For this purpose, we established setups allowing irradiances of up to 730 sun equivalents (SE). One key finding of our study is that accelerating the testing procedure by such large intensities is possible but a precise measurement and control of the solar cell temperature is absolutely essential. Accordingly, we developed an innovative method of determining the temperature of the active layer which offers significant advantages over commonly used measurement methods. Furthermore, it was found that the degradation process under high illumination densities can be well described by a stretched exponential law. We demonstrate that the temperature kinetics of P3HT:PCBM was found to be Arrhenius governed with an activation energy of 27.2 kJ/mol under continuous illumination of 300 SE. Finally, it was shown that the velocity of light‐induced degradation of short‐circuit current depends linearly on the used irradiance dose at a given temperature starting from normal illumination conditions up to at least 300 SE. This makes high‐C ALT a very valuable tool for swift screening of the lifetime of novel thin‐film solar cells and materials.

Highly Efficient and Solution‐Processed Single‐Emissive‐Layer Hybrid White Organic Light‐Emitting Diodes with Tris(triazolo)triazine‐Based Blue Thermally Activated Delayed Fluorescence Emitter

AbstractSolution processable organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters show inferior efficiency to devices produced via vacuum deposition. In this context, solution‐processed hybrid white OLEDs are fabricated using a TADF molecule and iridium complex as the blue and red dopants, respectively. First, solution‐processed OLEDs employing a tristriazolotriazine‐based TADF as the blue dopant are designed and fabricated, yielding maximum external quantum efficiency (EQEmax) of 23.23% with an emission peak at 492 nm. Use of the optimized tristriazolotriazine‐based TADF OLED structure and additional red phosphor achieves highly efficient white light emission with an EQEmax of 22.57%, stable Commission International de l'Eclairage (CIE) coordinates of (0.34, 0.34), a correlated color temperature of 5000 K, and a color rendering index of 73. Impressively, accelerated lifetime testing shows the white OLED possessing a lifetime to 80% of initial luminance (LT80) of 40 h, and an LT50 of 298 h. To the best of knowledge, the device performance demonstrated in this work is one of the best comprised of solution‐processed blue and fluorescent‐phosphorescent hybrid white OLEDs. This research provides a reliable method for high efficiency solution processable blue TADF and TADF‐phosphorescent hybrid OLEDs.

Evaluation of the ZnO Nanopillar Surface for Disinfection Applications.

Much attention has been devoted to the synthesis and antimicrobial studies of nanopatterned surfaces. However, factors contributing to their potential and eventual application, such as large-scale synthesis, material durability, and biocompatibility, are often neglected in such studies. In this paper, the ZnO nanopillar surface is found to be amenable to synthesis in large forms and stable upon exposure to highly accelerated lifetime tests (HALT) without any detrimental effect on its antimicrobial activity. Additionally, the material is effective against clinically isolated pathogens and biocompatible in vivo. These findings illustrate the broad applicability of ZnO nanopillar surfaces in the common equipment used in health-care and consumer industries.

Bias dependent admittance spectroscopy of thin film solar cells: KF post deposition treatment, accelerated lifetime testing, and their effect on the CVf loss maps

Modern solar cell designs include an always larger variety of elements and additional layers. This approach is usually successful and leads to the development of increasingly efficient materials. However, scientifically, it makes the drawing of accurate conclusions always more challenging, due to the growing number of elements, possible defects, interfaces, and barriers. To try and remedy this problem, we developed a novel way to investigate solar cells by representing bias dependent admittance spectroscopy (CVf) measurement data in the form of a 2D loss map. In this contribution, we elaborate how this technique can be used experimentally, present some concrete results we obtained from measurements on ultra-thin CIGS solar cells and explain how they can be interpreted. We identify 3 major response domains on our typical CVf loss maps. One at high frequency that covers most of the bias range and can be related to series resistance. One at low frequency, mostly visible at strong positive and negative biases, which is related to shunt and dissipation. The last response domain, close to 100 kHz and impacting most of the bias range, can be identified as a defect response of the material. Using CVf measurements on samples with KF post deposition treatment, known for its grain boundary passivation properties, and samples that were previously submitted to accelerated lifetime testing in damp heat conditions, the impact of bulk defects, grain boundaries and conduction band offsets are investigated.

Highly accelerated lifetime testing in power electronics

Abstract This paper presents case studies on application of accelerated mechanical fatigue testing for evaluation of wire bond interconnects and interfaces in electronic devices. A dedicated experimental set-up is designed to induce fatigue failure in the weak sites of the devices by reproducing the failure modes occurring during operation. Acceleration is achieved by increasing the mechanical testing frequency enabling determination of lifetime curves in a very short time. Exemplary studies on the degradation and fatigue failure of heavy wire bonds typically used in power electronics are presented and advantages and some restrictions of the proposed method are briefly discussed.

Structural color coatings for high performance BIPV

Building integrated photovoltaics (BIPV) offer aesthetics and freedom of design for architects and home owners. This can accelerate implementation and free up new spaces for solar energy harvesting at building level, which is a necessary step towards a climate neutral built environment. Colored solar panels with high conversion efficiency and low cost price are an important development for large scale market penetration of BIPV. Here we report a solution processed structural color coating for solar panels and solar collectors. We show that virtually any color can be prepared, that the desired coating stack can be designed using optical calculations and that the exact color can be produced via a low cost solution process. Furthermore, we show that the light transmission for the colored glass plates is still very high, exceeding commonly used absorbing colors and enables very high solar cell efficiency. The colored PV panels have been tested in real environment and via accelerated lifetime testing for 3 years without any performance decline or degradation.

Biopolymer Degradation Analysis: Accelerated Life Testing Study to Characterize Polylactic Acid Durability.

While the degradation of Polylactic Acid (PLA) has been studied for several years, results regarding the mechanism for determining degradation are not completely understood. Through accelerated degradation testing, data can be extrapolated and modeled to test parameters such as temperature, voltage, time, and humidity. Accelerated lifetime testing is used as an alternative to experimentation under normal conditions. The methodology to create this model consisted of fabricating series of ASTM specimens using extrusion and injection molding. These specimens were tested through accelerated degradation; tensile and flexural testing were conducted at different points of time. Nonparametric inference tests for multivariate data are presented. The results indicate that the effect of the independent variable or treatment effect (time) is highly significant. This research intends to provide a better understanding of biopolymer degradation. The findings indicated that the proposed statistical models can be used as a tool for characterization of the material regarding the durability of the biopolymer as an engineering material. Having multiple models, one for each individual accelerating variable, allow deciding which parameter is critical in the characterization of the material.

Improvement of stability and reduction of energy consumption for Ti-based MnOx electrode by Ce and carbon black co-incorporation in electrochemical degradation of ammonia nitrogen

Abstract Ti-based electrode coated with MnOx catalytic layer has presented superior electrochemical activity for degradation of organic pollution in wastewater, however, the industrial application of Ti-based MnOx electrode is limited by the poor stability of the electrode. In this study, the novel Ti-based MnOx electrodes co-incorporated with rare earth (Ce) and conductive carbon black (C) were prepared by spraying-calcination method. The Ti/Ce:MnOx-C electrode, with uniform and integrated surface and enhanced Mn(IV) content by C and Ce co-incorporation, could completely remove ammonia nitrogen (NH4+-N) with N2 as the main product. The cell potential and energy consumption of Ti/Ce:MnOx-C electrode during the electrochemical process was significantly reduced compared with Ti/MnOx electrode, which mainly originated from the enhanced electrochemical activity and reduced charge transfer resistance by Ce and C co-incorporation. The accelerated lifetime tests in sulfuric acid showed that the actual service lifetime of Ti/Ce:MnOx-C was ca. 25 times that of Ti/MnOx, which demonstrated the significantly promoted stability of MnOx-based electrode by Ce and C co-incorporation.

Highly Reliable BaTiO3‐Polyphenylene Oxide Nanocomposite Dielectrics via Cold Sintering

AbstractIn the design of the ceramic capacitor, high capacitance, temperature stability, and high operating voltage must be balanced against the failure mechanisms of degradation. Cold sintering is used to develop dense BaTiO3 – poly (p‐phenylene oxide) (PPO) nanocomposites with PPO throughout the grain boundary microstructure. To obtain the desired PPO distribution, a process is introduced that distributes the polymers on the BaTiO3 powders prior to the cold sintering process. With the cold sintering enabled by a Ba(OH)2·8H2O transient phase, theoretical densities ≈95% could be obtained at a sintering temperature ≈225 °C with up to 15 vol% PPO content. The rationale is to influence the local electric field distribution within the dielectric, to maximize resistivity (1013–1014 Ω cm) and degradation resistance, minimize temperature dependence of permittivity, and minimize the field dependent permittivity. All these properties are investigated as a function of the volume fraction of PPO. The magnitude of the permittivity follows a logarithmic mixing law: 1460 to 680 for the nanocomposite with 5 to 15 vol% PPO content, respectively, at room temperature. The BaTiO3‐PPO composite dielectrics are contrasted under accelerated lifetime testing conditions, noting superior resistance toward degradation kinetics, indicating an important breakthrough opportunity towards the development of high reliability dielectrics.

DC resistance degradation of SrTiO3: The role of virtual‐cathode needles and oxygen bubbles

AbstractThis study of highly accelerated lifetime tests of SrTiO3, a model semiconducting oxide, is motivated by the interest in reliable multilayer ceramic capacitors and resistance‐switching thin‐film devices. Our analytical solution to oxygen‐vacancy migration under a DC voltage—the cause of resistance degradation in SrTiO3—agrees with previous numerical solutions. Yet all solutions fail to explain why degradation kinetics feature a very strong voltage dependence, which we attribute to the nucleation and growth of cathode‐initiated fast‐conducting needles. While they have no color contrast in SrTiO3 single crystals, hence nominally “invisible,” needle’s presence in DC‐degraded samples—in silicone oil and in air—was unambiguously revealed by in‐situ hot‐stage photography. Observations in silicone oil and thermodynamic and kinetic considerations further revealed that copious oxygen bubbling and general reduction mark the onset of final accelerating degradation toward failure. Conversely, if oxygen vacancies cannot be sufficiently depleted from the near‐anode region to render it sufficiently conductive, then final failure is postponed, which is often the case at lower temperatures and voltages when the lifetime tests are incomplete. Remarkably, both undoped and Fe‐doped SrTiO3 can emit electroluminescence at higher current densities, thus providing a vivid indicator of resistance degradation and a metal‐to‐insulator resistance transition during cooling. The implications of these findings to thin ceramic and thin‐film SrTiO3 devices are discussed, along with connections to similarly DC‐degraded fast‐ion yttria‐stabilized zirconia.