Thermal Management Approach Research Articles

Thermal management challenges and mitigation techniques for transistor-level 3-D integration

For beyond 2-D CMOS logic, transistor-level 3-D integrations such as monolithic 3-D [1], Skybridge [2], SN3D [3] hold the most promise. However, such 3-D architectures within small form factor increase hotspots and demand careful consideration of thermal management at all levels of integration [4] as additional thermal resistance imposed by vertical layer stacking escalate the temperature, especially for the layers that are far detached from the substrate. Traditional system-level approaches such as liquid cooling [5], heat spreader [6], etc. are inadequate for transistor-level 3-D integrations and have huge cost overhead [7]. Previously, we introduced the concept of heat management in 3-D ICs through architecting physical fabric features [8]. In this paper, we elaborate on the thermal management approach, show its application for emerging transistor-level 3-D ICs through Finite Ele ment Method (FEM) based modeling and simulations, quantify results and compare for various scenarios. The modeling approach accounts for details of the 3-D device structure, nanoscale material properties, and 3-D circuit operations. The simulations were performed for both static and transient scenarios. Our simulation results show that without any heat extraction feature, the temperature for monolithic 3-D, Skybridge and SN3D, can be increased by almost 100 K, 200 K & 20 K, respectively. However, the proposed heat extraction feature is very effective in heat management, reducing the temperature from the heated area by up to 175 K, 320 K, and 20 K for monolithic 3-D, Skybridge and SN3D, respectively.

Investigation of phase change materials for efficient thermal management of electronic modules

Abstract Power electronics is a key technology for the advancement and spreading of electromobility applications and compact power supply devices on the market. The use of new WBG semiconductors (e.g. SiC, GaN) as well as highly integrated silicon-based power electronics enables a significant increase in power density with increasing integration. At the same time, however, this development requires costly thermal management solutions, since the power semiconductors generate considerable heat loss during operation. To ensure the robustness of the systems, the components must be protected from critical temperatures. Nowadays, a considerable effort for active and passive cooling by fans, microfluidic systems or heat pipes is operated. Compared with that, the usage of phase change materials (PCM) is a novel approach for sophisticated thermal management [1], [2]. In this paper some selected results of research project SWE-eT (Heat-retaining coatings for next-generation, efficient, compact power electronics) funded as part of KomroL program (Compact and robust power electronics of the next generation) of German Federal Ministry of Education and Research are presented. Main goal of this project is development, investigation and testing of efficient thermal management solutions based on heat-storing layer systems through phase transition processes. The research project was focused on investigation of sugar alcohols as PCM because of its wide range of melting temperature, high enthalpy of fusion and low cost.

Pulsed laser melting of bismuth telluride thermoelectric materials

While laser melting, deposition, and annealing of semiconductor thin films are well-established, pulsed laser processing of bulk semiconductor material powders has been minimally investigated. This work investigates nanosecond pulsed laser melting of bismuth telluride, a common thermoelectric material. Using both experimental and computational modeling methods, a process window was determined in which melting is achieved before ablation occurs. The process window was determined for Bi2Te3 powder compacts, with melt depths on the order of 20–100 μm. The melted region had a fine-grained, columnar microstructure and showed typical selective laser melting defects such as microcracking. Stroboscopic imaging was used as an in situ imaging technique to observe molten pool features, revealing a teardrop-shaped molten pool with little resolidification between pulses. A simplified thermal model of the nanosecond pulsed laser melting process was developed, and two models for the solid phase thermal conductivity were used to investigate the impact of thermal conductivity on the size, shape, and duration of the molten pool. The results demonstrate the narrow process window available for pulsed laser processing of bulk bismuth telluride powders, and the discussion includes thermal management approaches possible for reducing defects such as microcracking.

A novel approach for Lithium-ion battery thermal management with streamline shape mini channel cooling plates

The mini-channel cooling plate has been widely used in the Lithium-ion battery thermal management for electric vehicles. The technology development of high efficiency and good temperature uniformity cooling plate can promote the application of electric vehicles by improving the lifespan of the battery. In this study, streamline concept, which is commonly used for the external design of car, aerospace and submarine system to improve the system performance, has been introduced to design and optimise the performance of inner mini channel cooling plate. The flow resistance was proved to be minimised when the streamline shape design was adopted. Moreover, the results have proven the novel designed mini channel cooling plate can keep the heat exchange ability within the acceptable level. The maximum improvement of the heat exchanger efficiency with streamline shape design could be as high as 44.52%. Results indicated the temperature uniformity could also be effectively improved. The streamline shape mini channel cooling plate could be a promising solution for Lithium-ion battery thermal management.

Experimental and numerical investigation of heat transfer in Li‐ion battery pack of a hoverboard

Li-ion cells are used for energy storage and conversion in electric vehicles and a variety of consumer devices such as hoverboards. Performance and safety of such devices are severely affected by overheating of Li-ion cells in aggressive operating conditions. Multiple recent fires and accidents in hoverboards are known to have originated in the battery pack of the hoverboard. While thermal analysis and measurements have been carried out extensively on large battery packs for electric vehicles, there is relatively lesser research on smaller devices such as hoverboards, where the extremely limited thermal management design space and the critical importance of user safety result in severe thermal management challenges. This paper presents experimental measurements and numerical analysis of a novel approach for thermal management of the battery pack of a hoverboard. Measurements indicate that temperature rise in cells in the pack can be as large as 30°C at 4C discharge rate, which, although unlikely to be a standard discharge rate, may result from a malfunction or accident. A novel thermal management approach is investigated, wherein careful utilization of air flow generated by hoverboard motion is shown to result in significant temperature reduction. Measurements also indicate the key role of the metal housing around the battery pack in thermal management. Measurements are found to be in good agreement with finite element simulations, which indicate that the battery pack can be cooled as effectively in presence of a perforated metal casing as without the casing at all. Experimental data and simulation model presented here offer critical insights into the design of hoverboard thermal management and may result in safer, high performance hoverboard battery packs.

Plasma Assisted Cooling of Hot Surfaces on Hypersonic Vehicles

Electron transpiration cooling (ETC) is a proposed thermal management approach for the leading edges of hypersonic vehicles that utilizes thermionic emission to emit electrons to carry heat away from the surface. A modeling approach for assessing ETC in a computational fluid dynamics (CFD) framework and is evaluated using previously completed experiments. The modeling approach is presented includes developing boundary conditions to account for space-charge-limited emission to accurately determine the level of electron emission from the surface. The effectiveness of ETC for multiple test cases are investigated including sharp leading edges and blunt bodies. For each of these test cases, ETC affects the surface properties, most notably the surface temperature, suggesting that ETC occurs for bodies in thermally intense, ionized flows, no matter the shape of the leading edge. An approximate approach is also presented to assess ETC in an ionized flow and compares its cooling power to radiative cooling.

Thermal Characterization of Quasi-Vertical GaAs Schottky Diodes Integrated on Silicon Using Thermoreflectance and Electrical Transient Measurements

Thermal management and design have been understood, for many years, as critical factors in the implementation of submillimeter-wave Schottky-diode-based circuits and instruments. Removal of heat is particularly important for frequency multipliers, as these circuits generally exhibit low-to-modest conversion efficiencies, and are usually driven with high-power sources to achieve usable output power in the submillimeter-wave region of the spectrum. Elevated diode junction temperature due to inadequate heat sinking is known to degrade performance, accelerate aging effects (for example, due to electromigration, ohmic contact deterioration, or thermally-induced stress), and can ultimately lead to device failure. The relatively-low thermal conductivity of GaAs (the predominant material technology for submillimeter-wave diodes), coupled with restrictions on diode anode size and geometry needed to minimize parasitics and achieve the device impedances required for high-frequency operation, present significant challenges and trade-offs between electrical and thermal designs of these devices. Recognition that heating is a major factor limiting efficiency and output power has prompted a number of approaches to mitigate excessive temperature rise in the junction of planar Schottky diodes, including the use of AlN or diamond as low-loss substrates that act as heat spreaders. A new diode topology, based on a quasi-vertical geometry that is realized through heterogeneous integration of GaAs with high-resistivity silicon, was recently developed at the University of Virginia for submillimeter-wave applications. Unlike planar diodes, the device structure of the quasi-vertical diode consists of a metal contact that underlies the diode's anode and epitaxial mesa, thus providing a large-area ohmic cathode contact that also serves as an integrated heat sink. Measurement of high-efficiency multipliers based on this technology suggest the quasi-vertical architecture provides an effective approach for heat removal and thermal management in Schottky diodes. This paper presents the first results reporting thermal performances of terahertz quasi-vertical GaAs Schottky diodes integrated on silicon. The devices are characterized using a thermoreflectance measurement technique, a method based on the change in refractive index, and therefore surface reflectivity, with changes in temperature. Heating and cooling temperature profiles and 2-D temperature maps are obtained for 3.5 micron and 5.5 micron diameter diodes. From these measurements, the device thermal resistances, junction temperatures, and thermal time-constants are extracted. Equivalent thermal circuit and finite element models are developed to study the device geometry, and extract material thermal parameters. The devices are also characterized using an electrical transient method, and the temperature and cooling transients found from this technique are found to be comparable to those obtained from thermoreflectance measurements. The quasi-vertical diodes studied in this work are shown to demonstrate a faster transient thermal response compared to flip-chip bonded terahertz diodes reported in the literature.

Adaptive Periodic Thermal Management for Pipelined Hard Real-Time Systems

This paper proposes a novel dynamic thermal management approach named Adaptive Periodic Thermal Management (APTM) for multi-core pipelined processors with hard real-time constraints. During online execution, the approach optimizes the peak temperature of the processor by dynamically calculating and deploying new adaptive periodic thermal management schemes, which periodically switch the stages to sleep state until next adapting. At each such instant of adapting, new APTM schemes which optimize the peak temperature under real-time constraints are calculated according to the extended pay-burst-only-once principle. To reduce the overhead of online computation, our approach utilizes thermal properties obtained from offline experiments in searching the ATPM scheme minimizing the temperature. We evaluate our APTM with simulation on the Intel SCC chip as well as real experiments on an Intel I7 processor. Compared to existing approaches, our approach reduces the peak temperature by up to 8 K for the Intel I7 processor, and 7.5 K for the Intel SCC using four to sixteen processor cores.

Machine Learning-Based Quality-Aware Power and Thermal Management of Multistream HEVC Encoding on Multicore Servers

The emergence of video streaming applications, together with the users’ demand for high-resolution contents, has led to the development of new video coding standards, such as High Efficiency Video Coding (HEVC). HEVC provides high efficiency at the cost of increased complexity. This higher computational burden results in increased power consumption in current multicore servers. To tackle this challenge, algorithmic optimizations need to be accompanied by content-aware application-level strategies, able to reduce power while meeting compression and quality requirements. In this paper, we propose a machine learning-based power and thermal management approach that dynamically learns and selects the best encoding configuration and operating frequency for each of the videos running on multicore servers, by using information from frame compression, quality, encoding time, power, and temperature. In addition, we present a resolution-aware video assignment and migration strategy that reduces the peak and average temperature of the chip while maintaining the desirable encoding time. We implemented our approach in an enterprise multicore server and evaluated it under several common scenarios for video providers. On average, compared to a state-of-the-art technique, for the most realistic scenario, our approach improves BD-PSNR and BD-rate by 0.54 dB, and 8 percent, respectively, and reduces the encoding time, power consumption, and average temperature by 15.3, 13, and 10 percent, respectively. Moreover, our proposed approach enhances BD-PSNR and BD-rate compared to the HEVC Test Model (HM), by 1.19 dB and 24 percent, respectively, without any encoding time degradation, when power and temperature constraints are relaxed.

TheSPoT: Thermal Stress-Aware Power and Temperature Management for Multiprocessor Systems-on-Chip

Thermal stress including temperature gradients in time and space, as well as thermal cycling, influences lifetime reliability and performance of modern multiprocessor systems-on-chip (MPSoCs). Conventional power and temperature management techniques considering the peak temperature/power consumption do not provide a comprehensive solution to avoid high spatial and temporal thermal variations. This work presents TheSPoT, a novel multilevel thermal stress-aware power and thermal management approach for MPSoCs. At the top level, core consolidation and deconsolidation is performed based on peak temperature, thermal stress, and power consumption constraints. These constraints are also used at the next level, where operating frequencies are determined. At this level, we obtain optimal core frequencies by solving a convex optimization problem. However, thereafter, to reduce the runtime overhead in large MPSoCs, we alternatively propose to use a fast heuristic algorithm. The efficacy of the proposed approaches in reducing the thermal cycles and temporal/spatial temperature gradients is evaluated by comparing the results with the state-of-the-art methods. The evaluation performed on 4-core, 8-core, and 16-core MPSoCs, using PARSEC benchmarks, reveals a considerable reduction in thermal stress. For the 8-core MPSoC case study, on average, for the proposed heuristic(optimal) approach, the mean time to failure improved by 47(35)% compared to the state-of-the-art techniques with only 6(4)% performance degradation. Also, our simulations show that TheSPoT is more efficient in thermal stress reduction when more heterogeneous workloads are used.

Phenomenon and Mechanism of Spray Cooling on Nanowire Arrayed and Hybrid Micro/Nanostructured Surfaces

Enhancing spray cooling with surface structures is a common, effective approach for high heat flux thermal management to guarantee the reliability of many high-power, high-speed electronics and to improve the efficiency of new energy systems. However, the fundamental heat transfer enhancement mechanisms are not well understood especially for nanostructures. Here, we fabricated six groups of nanowire arrayed surfaces with various structures and sizes that show for the first time how these nanostructures enhance the spray cooling by improving the surface wettability and the liquid transport to quickly rewet the surface and avoid dry out. These insights into the nanostructure spray cooling heat transfer enhancement mechanisms are combined with microstructure heat transfer mechanism in integrated microstructure and nanostructure hybrid surface that further enhances the spray cooling heat transfer.

A Thermal Diode Based on Nanoscale Thermal Radiation.

In this work we demonstrate thermal rectification at the nanoscale between doped Si and VO2 surfaces. Specifically, we show that the metal-insulator transition of VO2 makes it possible to achieve large differences in the heat flow between Si and VO2 when the direction of the temperature gradient is reversed. We further show that this rectification increases at nanoscale separations, with a maximum rectification coefficient exceeding 50% at ∼140 nm gaps and a temperature difference of 70 K. Our modeling indicates that this high rectification coefficient arises due to broadband enhancement of heat transfer between metallic VO2 and doped Si surfaces, as compared to narrower-band exchange that occurs when VO2 is in its insulating state. This work demonstrates the feasibility of accomplishing near-field-based rectification of heat, which is a key component for creating nanoscale radiation-based information processing devices and thermal management approaches.

Experimental investigation on the thermal performance of Si micro-heat pipe with different cross-sections

Increasing component densities of the integrated circuit (IC) and packaging levels has led to thermal management problems. Si substrates with embedded micro-heat pipes (MHPs) couple good thermal characteristics and cost savings associated with IC batch processing. The thermal performance of MHP is intimately related to the cross-sectional geometry. Different cross-sections are designed in order to enhance the backflow of working fluid. In this experimental study, three different Si MHPs with same hydraulic diameter and various cross-sections are fabricated by micro-fabrication methods and tested under different conditions of fluid charge ratios. The results show that the trapezoidal MHP associated with rectangular artery which is charged with 40% of vapor chamber’s volume has the best thermal performance. This silicon-based MHP is a passive approach for thermal management, which could widen applications in the commercial electronics industry and LED lightings.

Parametric study of thin film evaporation from nanoporous membranes

The performance and lifetime of advanced electronics are often dictated by the ability to dissipate heat generated within the device. Thin film evaporation from nanoporous membranes is a promising thermal management approach, which reduces the thermal transport distance across the liquid film while also providing passive capillary pumping of liquid to the evaporating interface. In this work, we investigated the dependence of thin film evaporation from nanoporous membranes on a variety of geometric parameters. Anodic aluminum oxide membranes were used as experimental templates, where pore radii of 28–75 nm, porosities of 0.1–0.35, and meniscus locations down to 1 μm within the pore were tested. We demonstrated different heat transfer regimes and observed more than an order of magnitude increase in dissipated heat flux by operating in the pore-level evaporation regime. The pore diameter had little effect on pore-level evaporation performance due to the negligible conduction resistance from the pore wall to the evaporating interface. The dissipated heat flux scaled with porosity as the evaporative area increased. Furthermore, moving the meniscus as little as 1 μm into the pore decreased the dissipated heat flux by more than a factor of two due to the added resistance to vapor escaping the pore. The experimental results elucidate thin film evaporation from nanopores and confirm findings of recent modeling efforts. This work also provides guidance for the design of future thin film evaporation devices for advanced thermal management. Furthermore, evaporation from nanopores is relevant to water purification, chemical separations, microfluidics, and natural processes such as transpiration.

Thermal management approaches of Cu(Inx,Ga1−x)Se2 micro-solar cells

Concentrator photovoltaics (CPV) is a cost-effective method for generating electricity in regions that have a large fraction of direct solar radiation. With the help of lenses, sunlight is concentrated onto miniature, highly efficient multi-junction solar cells with a photovoltaic performance above 40%. To ensure illumination with direct radiation, CPV modules must be installed on trackers to follow the sun’s path. However, the costs of huge concentration optics and the photovoltaic technology used, narrow the market possibilities for CPV technology. Efforts to reduce these costs are being undertaken by the promotion of Cu(Inx,Ga1−x)Se2 solar cells to take over the high cost multi-junction solar cells and implementing more compact devices by minimization of solar cell area. Micrometer-sized absorbers have the potential of low cost, high efficiencies and good thermal dissipation under concentrated illumination. Heat dissipation at low (<10×) to medium (10 × to 100×) flux density distributions is the key point of high concentration studies for macro- and micro-sized solar cells (from 1 µm2 to 1 mm2). To study this thermal process and to optimize it, critical parameters must be taken in account: absorber area, substrate area and thickness, structure design, heat transfer mechanism, concentration factor and illumination profile. A close study on them will be carried out to determine the best structure to enhance and reach the highest possible thermal management pointing to an efficiency improvement.

Electrochemical-thermal Modeling to Evaluate Active Thermal Management of a Lithium-ion Battery Module

Lithium-ion batteries are commonly used in hybrid electric and full electric vehicles (HEV and EV). In HEV, thermal management is a strict requirement to control the batteries temperature within an optimal range in order to enhance performance, safety, reduce cost, and prolong the batteries lifetime. The optimum design of a thermal management system depends on the thermo-electrochemical behavior of the batteries, operating conditions, and weight and volume constraints. The aim of this study is to investigate the effects of various operating and design parameters on the thermal performance of a battery module consisted of six building block cells. An electrochemical-thermal model coupled to conjugate heat transfer and fluid dynamics simulations is used to assess the effectiveness of two indirect liquid thermal management approaches under the FUDC driving cycle. In this study, a novel pseudo 3D electrochemical-thermal model of the battery is used. It is found that the cooling plate thickness has a significant effect on the maximum and gradient of temperature in the module. Increasing the Reynolds number decreases the average temperature but at the expense of temperature uniformity. The results show that double channel cooling system has a lower maximum temperature and more uniform temperature distribution compared to a single channel cooling system.

Mitigation of Failure Propagation in Multi-Cell Lithium Ion Batteries

Lithium ion batteries are one of the main energy storage devices that have the potential to be fully integrated in electric grid applications and electric vehicles. Despite years of research in battery safety, there are still challenges associated with the complexity of system-level safety for large battery systems. There is a major gap of safety knowledge at the module or pack level on the effects on adjacent cells in a large-scale battery pack as one cell experiences failure. After the impacts and consequences are identified it is also important to determine mechanisms to mitigate the effects of a single cell failure to the entire pack. In this study, we analyze the failure behavior of small battery packs with 5 stacked pouch cells (LiCoO2 cathode, 3Ah) after thermal runaway is induced to a single cell with nail penetration as the failure initiation method. The first part of the study was to determine the SOC in which full propagation was identified. Different states of charge were tested, including 50%, 75%, 80% and 100% SOC. Complete propagation was observed for 80% and 100 % SOC as shown in Figure 1. The second part of the investigation focused on identifying passive thermal management approaches to mitigating failure propagation. Figure 2 presents the preliminary results using an aluminum heat sink, in which partial propagation was achieved. The results of this study could provide insightful information of the impacts of single battery failure in a pack and a base for future battery designs. Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. Figure 1

A Bio-Inspired Hybrid Thermal Management Approach for 3-D Network-on-Chip Systems.

3-D network-on-chip (NoC) systems are getting popular among the integrated circuit (IC) manufacturer because of reduced latency, heterogeneous integration of technologies on a single chip, high yield, and consumption of less interconnecting power. However, the addition of functional units in the -direction has resulted in higher on-chip temperature and appearance of local hotspots on the die. The increase in temperature degrades the performance, lifetime, and reliability, and increases the maintenance cost of 3-D ICs. To keep the heat within an acceptable limit, floorplanning is the widely accepted solution. Proper arrangement of functional units across different layers can lead to uniform thermal distribution in the chip. For systems with high density of elements, few hotspots cannot be eliminated in the floorplanning approach. To overcome, liquid microchannel cooling technology has emerged as an efficient and scalable solution for 3-D NoC. In this paper, we propose a novel hybrid algorithm combining both floorplanning, and liquid microchannel placement to alleviate the hotspots in high-density systems. A mathematical model is proposed to deal with heat transfer due to diffusion and convention. The proposed approach is independent of topology. Three different topologies: 3-D stacked homogeneous mesh architecture, 3-D stacked heterogeneous mesh architecture, and 3-D stacked ciliated mesh architecture are considered to check the effectiveness of the proposed algorithm in hotspot reduction. A thermal comparison is made with and without the proposed thermal management approach for the above architectures considered. It is observed that there is a significant reduction in on-chip temperature when the proposed thermal management approach is applied.

Towards Intelligent Thermal Energy Management of Eco-industrial Park through Ontology-based Approach

An ontology-based approach for thermal energy management of eco-industrial park is proposed in this paper. The ontology captures core concepts of this domain as well as the relationships between them; together with instances, the ontology can serve as knowledge base for related energy management tools. The development of this application ontology is based on existing knowledge base, e.g. OntoCAPE in this paper. The advantages of ontology-based approach are shown by an application case, the case shows how ontology can overcome data heterogeneity both structurally and semantically through its own reasoning ability, then allow intelligent decision making by using disparate data from remote databases, which implies the possibility of self-optimization without human intervention in the future scenario. With properly designed cyber-infrastructure systems, the prospective application of the ontology-based approach can unleash the potential of artificial intelligence for eco-industrial park thermal energy management in the future.

Multi‐stack fuel cell efficiency enhancement based on thermal management

Automotive manufacturers face serious difficulties concerning the expected fossil fuel depletion and the emitted pollutants during combustion. The fuel cell (FC) vehicle is considered a promising solution for greener and sustainable transportation. The integration of FC in vehicles is limited by some technological constraints and technical barriers which can be partially met by splitting the power and energy into different ‘downsized’ FCs named multi-stack FCs. This study aims at proposing a multi-stack FC configuration for electric vehicles (EVs) to minimise its start-up time, heating/cooling and cycling problems. To properly reach such desired operating conditions, a novel thermal management technique is proposed. Using the modularity provided by multi-stack solution, each FC is activated depending on the FCs temperature and the required vehicle power. Simulation results, using MTCSim© software, demonstrate the capability of the proposed thermal management approach to effectively enhance the EV's multi-stack FC's life span, cycling and efficiency, besides optimising its operation performance.