Electrothermal Properties Research Articles

Condition monitoring for solder layer degradation in multi‐device system based on neural network

Power semiconductor devices (chips) are usually arranged in parallel to increase the power rating of the modules for high power applications like renewable energy. In multi-device systems uneven degradation of the devices is inevitable. The uneven solder layer degradation of the parallel chips translates into higher thermal resistances for the degraded chips and, according to the electrothermal properties of the devices, the current sharing and temperature distribution between the devices will be affected. This phenomenon will have implications on the global reliability of the power module. In this study, a two-stage neural network (NN) approach is proposed for the diagnosis of the degradation: the first stage NN estimates the power losses of the parallel devices, whose deviations from the reference values are then applied to the NN in the second stage to classify the health condition. This condition monitoring method has been evaluated in on-state experiments at different constant current values, indicating that it could be a suitable strategy for improving the operational reliability of converters employing multi-chip power modules.

Ethylene-octene copolymer and carbon black composite electro-thermal properties for self-regulating heating

Carbon black - ethylene-octene copolymer (EOC-CB) composite electro-thermal properties were investigated for using the composite as self-regulating heating material. The materials electrical resistance change with temperature change was investigated. Additionally, while a voltage of 30 V was applied, the sample temperature and electrical current strength was measured. The samples with 15 to 20 phr CB showed positive temperature coefficient of resistivity and could be used as self-regulating heating materials. For different concentrations of CB the achieved equilibrium temperatures were between 30°C to 60°C (with 30 V) and could be used to comfortably warm the human body.

Characterization of Bitumen Modified with Pyrolytic Carbon Black from Scrap Tires

Pyrolytic carbon black (CBp) from scrap tire pyrolysis is a potential modifier for the bitumen industry. Binders containing different contents of CBp were prepared and experimentally investigated to examine the effects of CBp on the electrical and thermal conductivity, conventional physical properties, rheological properties, high-temperature antirutting performance, aging resistance, and storage stability. Laboratory test results indicated that the incorporation of CBp effectively improves the electrothermal properties, rheological properties, high-temperature rutting resistance, and aging resistance. It also increases the viscosity and decreases the storage stability of bitumen. The study confirms that CBp-modified bitumen with proper selection of content can be a multifunctional paving material.

RF magnetron-sputtered Al–ZnO/Ag/Al–ZnO (AAA) multilayer electrode for transparent and flexible thin-film heater

We report the electrothermal properties of AAA trilayer on polyethylene terephthalate substrate which allowed the development of low-cost high-performance transparent thin-film flexible heater (TTFFH) using RF magnetron sputtering. The structural, electrical, and optical properties of the AAA trilayer were investigated at different thickness of the Ag interlayer. The AAA trilayer-based TTFFH yielded saturation temperatures beyond 100 °C at 10 V at optimized Ag interlayer thickness of 5 nm. The time-dependent temperature profile along with its highly stable and reversible thermal behavior was studied. Most importantly, the AAA trilayer-based TTFFH provides a high-performance alternative to the conventional and expensive ITO electrodes at a much lower cost.

Experimental evaluation of artificial defects using SMArt thermography

SMArt termography is an innovative and promising technique that could be useful for the detection of damages of large components subjected to in-service loads, like wind blade. This technique requires building traditional carbon or glass fiber reinforced composite laminates adding a regular net of Shape Memory Alloy (SMA) wires in the matrix. These wires confer to the composite material additional features. In particular, the electro-thermal properties of SMA could be used as an internal heat source to be used for the control of the component using the traditional numerical technique used to elaborate the raw thermal data. Despite of other thermography techniques, SMArt thermography is characterized by a quite reduced amount of heating power, which produces a limited increasing of the temperature of the component subjected to control. On the other hand, the numerical elaboration of thermal data acquired from IR camera is more sensitive and require a deeper comprehension of the phenomena. In this work, a GFRP composite panel containing several artificial defects has been studied both from a numerical and experimental point of view, in order to determine the sensitivity of the technique, the limit of applicability and practical indications about the reliability of the technique.

Orthotropic electro-thermal behaviour of highly-aligned carbon nanotube web based composites

A ‘forest’ of vertically aligned carbon nanotubes (CNTs), synthesised by chemical vapour deposition with an iron catalyst on a silicon substrate, is drawn into a horizontally-aligned CNT web. Previous work has shown that the electro-thermal properties of this web may be tuned by altering the individual length of the CNTs and the number of layers. This paper demonstrates, for the first time, that the orientation and multi-directional layering of the web provides further scope for tuning the electrical conductivity and heat distribution of the composite system. An analytical model based on the thermal conduction theory of anisotropic solids is proposed to predict the electrical conductivity of general multi-layered and multi-directional CNT webs.Specimens with different aspect ratios and web orientations were manufactured and their electrical conductivity and resistive heat distribution measured. All of them were shown to exhibit electrical properties and heating distributions which could be predicted or bounded by the analytical model. Consequently, through tuning the CNT web orientation and layup, various heating patterns may be obtained and designed for specific requirements.

Potential of ITO thin film for electrical probe memory applications

ABSTRACTElectrical probe memory has received considerable attention during the last decade due to its prospective potential for the future mass storage device. However, the electrical probe device with conventional diamond-like carbon capping and bottom layers encounters with large interfacial contact resistance and difficulty to match the experimentally measured properties, while its analog with titanium nitride capping and bottom layers also faces serious heat dissipation through either probe and silicon substrate. Therefore, the feasibility of using indium tin oxide (ITO) media for the capping and bottom layers of the electrical probe device is investigated by tailoring the thickness and electrothermal properties of the ITO capping and bottom layers within experimentally established range and subsequently calculating the resultant temperature at several predefined points based on a previously developed three-dimensional model. To meet the required temperature and to fit the experimentally reported values, the thickness, electrical conductivity, and thermal conductivity of the ITO capping and bottom layers are found to be 5 nm, 103 Ω−1 m−1, 0.84 W m−1 K−1, and 200 nm, 1.25 × 106 Ω−1 m−1, 0.84 W m−1 K−1, respectively. The practicality of using this optimized device to achieve ultrahigh density, ultralow energy consumption, ultrafast switching speed, low interfacial contact resistance, and high thermal reliability has also been demonstrated.

Electrothermal regeneration by Joule heat effect on carbon cloth based MnO2 catalyst for long-term formaldehyde removal

Carbon-based materials (e.g., activated carbon) have been widely used as contaminant removal media due to their unique adsorption properties. However, some of their other characteristics, such as electrothermal properties, have been greatly ignored in the field of environmental remediation. Herein, a kind of carbon cloth (CC)-supported MnO2 composite (MnO2-CC) was prepared and investigated for catalytic oxidation of gaseous formaldehyde (HCHO) under the assistance of electric power. The MnO2-CC composite exhibited unique Joule heat property and could efficiently convert electrical energy into heat energy. The surface temperature of MnO2-CC composite could be increased to as high as 138 °C within 20 s when 8 V input voltage was imposed. In addition, porous MnO2 nanosheets dispersed uniformly on the surface of CC surface, forming a kind of hierarchical core-shell structure. The close contacted interface could reduce energy loss during heat transfer. As a result, the used MnO2-CC composite could exhibit long-term HCHO removal efficiency by highly effective electrothermal regeneration. This work represents a convenient and fast approach that allows direct utilization of electric power to accelerate the complete mineralization of HCHO. The in-situ fast electric heating process along with the uniform dispersion of porous MnO2 on CC make the MnO2-CC fabric an excellent material for indoor HCHO abatement.

Transient Analysis for Electrothermal Properties in Nanoscale Transistors

Due to the significance of electron and heat transfer in designing the nanoscale semiconductor devices, the transient analysis of electrothermal properties has attracted extensive attention. In this paper, the density-gradient and dual-phase-lag (DPL) equations are first combined to predict the electron and heat transport in nanoscale transistors. The DPL equation is solved with the consideration of the temperature jump boundary condition that dealing with phonon–wall collisions. We have shown that the temporal and spatial distributions of related physical variables can be obtained by self-consistently solving these equations. Furthermore, the spectral element time-domain method is used to discretize these equations. Numerical results of electrothermal properties for both 2-D and 3-D field-effect transistors have been demonstrated to show the robustness and universality of the proposed model. Therefore, the model we proposed can be used with the temporal and spatial distributions, which could be helpful for evaluating the electrothermal performance and computational designing of nanoscale transistors.

In-Situ Electrical Characterization of Low Temperature Getter Thin Films Activation

Thanks to their reactivity to gases, getter materials are involved in vacuum packaging to compensate leaks and permeation through the package. After deposition, the material is passivated due to the contact with the air, and must be thermally activated to force the diffusion of the passivation layer inside the film. However, new MEMS technologies imply more fragile devices thus processes with a limited temperature. In this frame, we investigate getter materials presenting a low activation temperature, such as Zr-based alloys. Moreover, in most investigations of getter films, activation and sorption are characterized separately by room temperature surface analysis techniques in UHV and by sorption experiments under specific gases, respectively. In this work, we have studied the behavior of getter thin films in vacuum as a function of the temperature and the pressure to be as close as possible to the conditions of integration, i.e. wafer bonding. This consisted in following the sheet resistance measured by using the 4-probes technique and comparing electro-thermal properties (resistivity, Temperature Coefficient of Resistance TCR) to pre- and post- characterization (composition, structure). Thin films of Zr, V, Ti, Zr-Ti, Zr-V and Zr-Co with thicknesses of 300-400 nm have been deposited by co-evaporation in UHV. Their sheet resistance was measured as a function of the temperature under vacuum. The control of the pressure, from 10-6 to 10-3 mbar, allowed to activate the films in different conditions. For as-deposited films, results show that the resistivity and TCR are linked and follow the Mooij rule: the TCR decreases with the resistivity and becomes negative for resistivities higher than 150 µW.cm. The values globally depend on the composition, but separated groups are also linked to the disorder of the structure, from the lowest to the highest: pure metals, Zr-Ti, Zr-V then Zr-Co. In case of Zr-Ti, the grain size directly impacts the evolution of the coupled TCR and resistivity. The activation in vacuum involves simultaneous and continuous diffusion inside the films and sorption at the surface. The latter cannot be avoided, even at 10-6 mbar, and the resistivity increases with the square root of the time. However, differences of behavior as a function of the pressure can be linked to the gettering efficiency and the diffusion length of oxygen in the material, which depends on both the composition and the microstructure. Crystalline Zr-Ti films behave as Zr and Ti and the grain size directly impacts the diffusion, thus the quantity of oxygen sorbed in the film. The structure of Zr-V or Zr-Co is more complex, which can be either crystalline or amorphous depending on the composition. Large variations in the sheet resistance can be obtained and the high disorder of the structure allow them to sorb more gaseous species than Zr-Ti.

Nanoscale thermal cross-talk effect on phase-change probe memory

Phase-change probe memory is considered as one of the most promising means for next-generation mass storage devices. However, the achievable storage density of phase-change probe memory is drastically affected by the resulting thermal cross-talk effect while previously lacking detailed study. Therefore, a three dimensional model that couples electrical, thermal, and phase-change processes of the Ge2Sb2Te5 media is developed, and subsequently deployed to assess the thermal cross-talk effect based on a Si/TiN/ Ge2Sb2Te5/diamond-like carbon (DLC) structure by appropriately tailoring the electro-thermal and geometrical properties of the storage media stack for a variety of external excitations. The modeling results show that the DLC capping with a thin thickness, a high electrical conductivity, and a low thermal conductivity is desired to minimize the thermal cross-talk, while the TiN underlayer has a slight impact on the thermal cross-talk. Combining the modeling findings with the previous film deposition experience, an optimized phase-change probe memory architecture is presented, and its capability of providing ultra-high recording density simultaneously with a sufficiently low thermal cross-talk is demonstrated.

Amorphization Optimization of Ge₂Sb₂Te₅ Media for Electrical Probe Memory Applications.

Electrical probe memory using Ge2Sb2Te5 media has been considered a promising candidate in the future archival storage market due to its potential for ultra-high density and long data retention time. However, most current research efforts have been devoted to the writing of crystalline bits using electrical probe memory while ignoring the viability of writing amorphous bits. Therefore, this paper proposes a physical, realistic, full three-dimensional model to optimize the practicable media stack by spatially and temporally calculating temperature distributions inside the active media during the writing of amorphous bits. It demonstrates the feasibility of using an optimized device that follows a Silicon/Titanium Nitride/Ge2Sb2Te5/Diamond-Like Carbon design with appropriate electro-thermal properties and thickness to achieve ultra-high density, low energy consumption, and a high data rate without inducing excessive temperature. The ability to realize multi-bit recording and rewritability using the designed device is also proven, making it attractive and suitable for practicable applications.

In-Situ Electrical Characterization of Low Temperature Getter Thin Films Activation

Thanks to their reactivity to gases, getter materials are involved in vacuum packaging to compensate leaks and permeation through the package. After deposition, the material is passivated due to the contact with the air, and must be thermally activated to force the diffusion of the passivation layer inside the film. However, new MEMS technologies imply more fragile devices thus processes with a limited temperature. In this frame, we investigate getter materials presenting a low activation temperature, such as Zr-based alloys. Moreover, in most investigations of getter films, activation and sorption are characterized separately by room temperature surface analysis techniques in UHV and by sorption experiments under specific gases, respectively. In this work, we have studied the behavior of getter thin films in vacuum as a function of the temperature and the pressure to be as close as possible to the conditions of integration, i.e. wafer bonding. This consisted in following the sheet resistance measured by using the 4-probes technique and comparing electro-thermal properties (resistivity, Temperature Coefficient of Resistance TCR) to pre- and post- characterization (composition, structure). Thin films of Zr, V, Ti, Zr-Ti, Zr-V and Zr-Co with thicknesses of 300-400 nm have been deposited by co-evaporation in UHV. Their sheet resistance was measured as a function of the temperature under vacuum. The control of the pressure, from 10-6 to 10-3 mbar, allowed to activate the films in different conditions. For as-deposited films, results show that the resistivity and TCR are linked and follow the Mooij rule: the TCR decreases with the resistivity and becomes negative for resistivities higher than 150 µW.cm. The values globally depend on the composition, but separated groups are also linked to the disorder of the structure, from the lowest to the highest: pure metals, Zr-Ti, Zr-V then Zr-Co. In case of Zr-Ti, the grain size directly impacts the evolution of the coupled TCR and resistivity. The activation in vacuum involves simultaneous and continuous diffusion inside the films and sorption at the surface. The latter cannot be avoided, even at 10-6 mbar, and the resistivity increases with the square root of the time. However, differences of behavior as a function of the pressure can be linked to the gettering efficiency and the diffusion length of oxygen in the material, which depends on both the composition and the microstructure. Crystalline Zr-Ti films behave as Zr and Ti and the grain size directly impacts the diffusion, thus the quantity of oxygen sorbed in the film. The structure of Zr-V or Zr-Co is more complex, which can be either crystalline or amorphous depending on the composition. Large variations in the sheet resistance can be obtained and the high disorder of the structure allow them to sorb more gaseous species than Zr-Ti.

Electrothermal and Optical Properties of Hybrid Polymer Composites

Electrothermal and Optical Properties of Hybrid Polymer Composites

A powerful dual-responsive soft actuator and photo-to-electric generator based on graphene micro-gasbags for bioinspired applications.

Soft actuators with large deformation and high output force in response to multi-stimuli are highly demanded for the development of biomimetic applications. Here, a bilayer actuator composed of spongy graphene with internal gasbag microstructures and the commercial polyimide adhesive tape is fabricated by a simple and fast method. This actuator produces large deformation, high output force, and dual-stimuli response, owing to the deformation of graphene micro-gasbags coupled with the thermal expansion of polyimide, and the electrothermal and photothermal properties of graphene. Experiments show that upon low voltage (16 V) stimulation the fabricated actuator with a length of 30 mm could generate a bending curvature of 0.55 cm-1 in 5 s, and can simultaneously produce high output force and lift an object 20 times heavier than its own weight. Moreover, a curvature of 0.45 cm-1 can be achieved for the actuator upon light irradiation for 10 s. Based on this bilayer actuator, diversely biomimetic motions including kicking a ball, grabbing a vegetable leaf, human hand movement, and creeping motion are realized, revealing its potential application in soft robotics, artificial muscles, wearable electronics, and biomedical devices. Besides the mechanical deformation output, a photo-to-electric generator is also assembled by associating this actuator with commonly triboelectric materials, further enriching the application range of soft actuators.

A possible use of SMArt thermography for the control of GFRP composite laminate

The development of techniques able to check the structural health of a wind blade is very important. An innovative and promising technique applicable at this aim is the SMArt thermography. It exploits the electro-thermal properties of SMArt composites, in order to detect the structural flaws using an embedded source. Such a system enables a built-in, fast, cost-effective and in-depth assessment of the structural damage as it overcomes the limitations of standard thermography.With the aim for developing a reliable diagnostic method based on SMArt thermography, a preliminary numerical model was implemented in order to simulate the heating and the subsequent cooling of a GFRP composite laminate with embedded SMA wires. The heat source was represented by the Joule effect originated in the SMA wires and supplied as power density. The analysis of the resulting thermal maps at different values of power density provided the optimal levels of current amplitude and period to be applied in the subsequent experimental applications.

Failure and Reliability Analysis of a SiC Power Module Based on Stress Comparison to a Si Device

The superior electro-thermal properties of silicon carbide (SiC) power devices permit higher temperature of operation and enable higher power density compared with silicon devices. Nevertheless, the reliability of SiC power modules has been identified as a major area of uncertainty in applications which require high reliability. Traditional power module packaging methods developed for silicon chips have been adopted for SiC and the different thermomechanical properties cause different fatigue stresses on the solder layer of the chip. In this paper, a 2-D finite element model has been developed to evaluate the stress performance and lifetime of the solder layer for Si devices, which has been validated using accelerated power cycling tests on Si IGBTs. The proposed model was extrapolated for SiC devices of the same voltage and current rating using the same solder material and the results show that under the same cyclic power loss profile the induced stress and strain energy in the die attach layer is much higher and concentrates on the die/solder interfacial area for SiC chips. Using the validated stress-based model, the lifetime can be quantified when SiC chips are used. This ability to extrapolate the available power cycling and lifetime data of silicon chips to SiC chips would be a key element for developing reliable packaging methods for SiC devices.

Composite process and electrothermal properties of a new-type electric heating plywood made with melamine resin adhesive film

A new type of electric heating plywood used for indoor heating products was made using melamine resin adhesive film (MRAF) as the bonding material and carbon fiber paper (CFP) as the electric heating material. Hot-press pressure greatly affected the permeation of the adhesive into the CFP and bonding performance, resulting in a bonding strength above 1.8 MPa. The conducting path in the electric heating layer was the main factor affecting the drop rate of resistance (DRR). Pressure of around 1.3 MPa was beneficial in controlling power deviation. Use of the MRAF improved insulation and water resistance. The plywood exhibited a surface temperature difference of 6 °C under commonly used power. Temperature rise exhibited an exponential relationship with heating time, and surface equilibrium temperature had a linear relationship with power density. The plywood had good power stability because the maximum resistance changed by only 0.44% when electricity was overloaded for 24 h at a power density of 500 W/m2. Stable resistance was presented after power was cycled 40 times, and the maximum DRR was 1.25% after 120 power cycles. This scheme offers a simple process for large-scale manufacture of the adopted MRAF, which has good bonding performance and electric heating stability.

Analysis of multifinger power HEMTs supported by effective 3-D device electrothermal simulation

The influence of the metallization layer geometry on the electrothermal behavior of the multifinger power high-electron mobility transistors (HEMTs) is studied. The analysis of thermal and electrical behavior is supported by effective 3-D electrothermal device simulation method developed for Synopsys TCAD Sentaurus environment using mixed-mode setup. The proposed methodology allows fast simulation of complex systems from individual semiconductor layers at a frontend up to package and cooling assemblies at a backend. More accurate electrothermal model of power HEMT is proposed and validated by finite element method (FEM) simulations. The analysis points on significant influence of metallization geometry design on electrothermal properties and reliability of the multifinger power HEMTs. The unique identification and visualization of the critical regions allows effective device optimization. Very good comparison between simulation results and experimental data demonstrate validity of the proposed simulation methodology and HEMT structures analysis.

Microstructures and electrothermal properties of AlxCrFeNi multi-component alloys

AlxCrFeNi multi-component alloys were fabricated by vacuum arc-melting to study the effect of homogenization on microstructures of as-cast and homogenized alloys using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Besides, electrical resistivity and thermal conductivity of as-cast and homogenized alloys were also investigated. The results showed that no obvious differences of crystal structures and phase compositions between these as-cast and homogenizing alloys were presented. However, transmission electron microscope indicated that the ordered B2 NiAl intermetallic nanoparticles, which were distributed on the disordered BCC [Fe, Cr] solid solution of as-cast Al1.2CrFeNi alloy, disappeared after homogenization. For AlxCrFeNi alloys, the electrical resistivity increased with Al addition and dramatic increase of thermal conductivity was presented with increasing the homogenization temperatures. However, homogenization could decrease both electrical resistivity and thermal conductivity of as-cast alloys. The main factors influencing the changes of electrothermal properties of AlxCrFeNi alloys were the electron scattering affected by crystal defects, phase boundaries and temperatures.