Management Of Microelectronics Research Articles

Enhanced Far-Field Thermal Radiation through a Polaritonic Waveguide.

We experimentally demonstrate the enhancement of the far-field thermal radiation between two nonabsorbent Si microplates coated with energy-absorbent silicon dioxide (SiO_{2}) nanolayers supporting the propagation of surface phonon polaritons. By measuring the radiative thermal conductance between two coated Si plates, we find that its values are twice those obtained without the SiO_{2} coating. This twofold increase results from the hybridization of polaritons with guided modes inside Si and is well predicted by fluctuational electrodynamics and an analytical model based on a two-dimensional density of polariton states. These findings could be applied to thermal management in microelectronics, silicon photonics, energy conversion, atmospheric sciences, and astrophysics.

PEDOT:PSS/MXene/PEG composites with remarkable thermal management performance and excellent HF-band & X-band electromagnetic interference shielding efficiency for electronic packaging

Recently, the miniaturization of microelectronics has proposed a more urgent demand for the multi-functionalization of packaging materials. Here, a PEDOT:PSS/MXene/PEG composite, which is prepared by vertical directional freezing and vacuum infiltrating, integrates the function of heat management & EMI shielding into single packaging material. The melting & cooling enthalpy (237.6 & 236.1 J g−1) and the phase transition temperature of composite are enhanced synchronously for the first time. The zigzag modification of polyethylene glycol (PEG) crystal is induced by poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The rest of crystal with (7/2) helix conformation packs preferentially along the (120) plane. The stability of the melting composite is enhanced. The PEG leakage is less than 0.66 %, and over 80 % dimension is maintained under the pressure of 1.88 kPa. The composite shows excellent photo-thermal (η = 94.9 %) and electro-thermal (tη = 7.86) conversion performances. The EMI shielding mechanism is reflection-dominated and the total EMI shielding effectiveness (SET) of composite is 29.8 dB at the framework content as low as 1.22 wt%, which is the relatively low filler content and the highest enthalpy efficiency among the reported composites with the equivalent SET. The HF-band shielding capability of composite is verified by the Tesla kit. The assembled heterogeneous asynchrony photo-thermal-electric conversion system identifies its potential application on photo-thermal converters and heat buff. The HF-band & X-band (Sub-6G) EM waves shielding and heat management in microelectronics can be achieved simultaneously by applying this composite.

Linear instability of lid- and pressure-driven flows in channels textured with longitudinal superhydrophobic grooves

It is known that an increased flow rate can be achieved in channel flows when smooth walls are replaced by superhydrophobic surfaces. This reduces friction and increases the flux for a given driving force. Applications include thermal management in microelectronics, where a competition between convective and conductive resistance must be accounted for in order to evaluate any advantages of these surfaces. Of particular interest is the hydrodynamic stability of the underlying basic flows, something that has been largely overlooked in the literature, but is of key relevance to applications that typically base design on steady states or apparent-slip models that approximate them. We consider the global stability problem in the case where the longitudinal grooves are periodic in the spanwise direction. The flow is driven along the grooves by either the motion of a smooth upper lid or a constant pressure gradient. In the case of smooth walls, the former problem (plane Couette flow) is linearly stable at all Reynolds numbers whereas the latter (plane Poiseuille flow) becomes unstable above a relatively large Reynolds number. When grooves are present our work shows that additional instabilities arise in both cases, with critical Reynolds numbers small enough to be achievable in applications. Generally, for lid-driven flows one unstable mode is found that becomes neutral as the Reynolds number increases, indicating that the flows are inviscidly stable. For pressure-driven flows, two modes can coexist and exchange stability depending on the channel height and slip fraction. The first mode remains unstable as the Reynolds number increases and corresponds to an unstable mode of the two-dimensional Rayleigh equation, while the second mode becomes neutrally stable at infinite Reynolds numbers. Comparisons of critical Reynolds numbers with the experimental observations for pressure-driven flows of Daniello et al. (Phys. Fluids, vol. 21, issue 8, 2009, p. 085103) are encouraging.

Effect of Fins Arrangement on Thermal Performance in Microelectronics Devices

Heat sink fins arrangement are important in heat management in microelectronics devices because it helps in the dissipation of heat from the chip level device to the environment and provide an efficiently working device. In this light, investigation was conducted on the effect of fins arrangement on thermal performance in microelectronics devices using the ANSYS finite element design software. The results obtained showed a maximum temperature range of between 95.27 – 126.79 o C, thermal resistance of 1.2 – 1.8 K/W, and thermal efficiency of 15 – 37%. The results demonstrated that, the arrangement of heat sink fins largely affects the thermal resistances and efficiencies of the microelectronic device. In addition, the A1 rectangular fins arrangement exhibited better thermal capabilities over the other fins arrangements investigated. This research can aid the development of future heat sinks to accommodate customer demands. Keywords : heat transfer; fin arrangement; microelectronics

Probing ballistic thermal conduction in segmented silicon nanowires.

Ballistic heat conduction in semiconductors is a remarkable but controversial nanoscale phenomenon, which implies that nanostructures can conduct thermal energy without dissipation. Here, we experimentally probed ballistic thermal transport at distances of 400-800 nm and temperatures of 4-250 K. Measuring thermal properties of straight and serpentine silicon nanowires, we found that at 4 K heat conduction is quasi-ballistic with stronger ballisticity at shorter length scales. As we increased the temperature, quasi-ballistic heat conduction weakened and gradually turned into diffusive regime at temperatures above 150 K. Our Monte Carlo simulations illustrate how this transition is driven by different scattering processes and linked to the surface roughness and the temperature. These results demonstrate the length and temperature limits of quasi-ballistic heat conduction in silicon nanostructures, knowledge of which is essential for thermal management in microelectronics.

Tree-inspired radially aligned, bimodal graphene frameworks for highly efficient and isotropic thermal transport.

Highly-oriented, interconnected graphene frameworks have been considered as promising candidates to realize high-performance thermal management in microelectronics. However, the obvious thermal boundary resistance and anisotropic heat conduction still remain major bottlenecks for efficient heat dissipation. Herein, a biomimetic design enabled by radially aligned, bimodal graphene frameworks (RG-Fin) is proposed to achieve highly efficient and isotropic thermal transport. An interconnected RG skeleton is prepared via a radial ice-template method, serving as the primary expressway for isotropic heat conduction. Tree-leaf-like graphene nanofins are vertically grown on the RG surface to provide additional thermal pathways for bimodal phonon transportation, which can reduce the thermal boundary resistance without degrading the thermal properties of the skeleton. An RG-Fin composite exhibits a superior thermal conductivity of 4.01 W m-1 K-1 (almost 20 times that of a polymer) at an ultralow loading of 1.53 vol%, demonstrating an exceptionally large thermal conductivity enhancement efficiency of 1247%, which far exceeds those of graphene-based polymer composites. Further theoretical analysis and finite element simulations reveal the critical role of the nanofins in significantly decreasing the thermal boundary resistance (by almost 27-fold). Finally, the practical thermal management of running a CPU module is demonstrated, in which the heating-up rate of the RG-Fin composite is ∼2.0 times that of a pure polymer. This strategy provides an innovative avenue for designing radially aligned networks to realize isotropic and efficient thermoconductive composites for thermal management.

Molecular Fin Effect from Heterogeneous Self-Assembled Monolayer Enhances Thermal Conductance across Hard-Soft Interfaces.

Thermal transport across hard-soft interfaces is critical to many modern applications, such as composite materials, thermal management in microelectronics, solar-thermal phase transition, and nanoparticle-assisted hyperthermia therapeutics. In this study, we use equilibrium molecular dynamics (EMD) simulations combined with the Green-Kubo method to study how molecularly heterogeneous structures of the self-assembled monolayer (SAM) affect the thermal transport across the interfaces between the SAM-functionalized gold and organic liquids (hexylamine, propylamine and hexane). We focus on a practically synthesizable heterogeneous SAM featuring alternating short and long molecular chains. Such a structure is found to improve the thermal conductance across the hard-soft interface by 46-68% compared to a homogeneous nonpolar SAM. Through a series of further simulations and analyses, it is found that the root reason for this enhancement is the penetration of the liquid molecules into the spaces between the long SAM molecule chains, which increase the effective contact area. Such an effect is similar to the fins used in macroscopic heat exchanger. This "molecular fin" structure from the heterogeneous SAM studied in this work provides a new general route for enhancing thermal transport across hard-soft material interfaces.

Optimal component sizing in a two-reservoir passive energy harvesting system

We utilize particle swarm optimization to reduce the size of the energy management components in an energy harvesting system, allowing us to eliminate the need for voltage regulators or DC-DC converters without affecting system performance. Prior literature on optimal power management in microelectronics [1, 2] has relied on engineering estimates or exhaustive parameter searches to optimize system design. No prior literature has considered the optimal design of a device with only passive components [3]. By using particle swarm optimization, we demonstrate a 55% reduction in device size relative to conventional engineering calculations of an optimal device design.

Numerical Study of Thermal Spreading Resistance in Body-Fitted Curvilinear Coordinates

One of the most important problems encountered in the thermal management of microelectronics is thermal spreading resistance. This occurs either due to the heat transfer by the conduction mechanism from one solid to another with different cross-sectional areas, or as a result of the heat flow through a conductive solid with a variable cross-sectional area. In this study, both geometric conditions are considered simultaneously. A C++ program code is developed to calculate the thermal spreading resistance in arbitrary curved-edge heat spreaders. A method for automatic numerical generation of a body-fitted curvilinear coordinate system is applied to solve the heat conduction equation on the orthogonal curvilinear grids. A set of Poisson equations is then used to generate two-dimensional grids with grid control along all of the boundaries. The finite difference method is employed to discretize the partial differential equations of the problem. In addition, the Maxwell coordinate system is also used as a special case to demonstrate the similarity of grids generated by numerical and analytical methods. The numerical results of the study are compared with the exact solution, thus illustrating the performance of the approach. Finally, the temperature distribution and thermal spreading resistance are determined for the different shapes of curved edges.

Blocking Phonon Transport by Structural Resonances in Alloy-Based Nanophononic Metamaterials Leads to Ultralow Thermal Conductivity.

Understanding the design rules to obtain materials that enable a tight control of phonon transport over a broad range of frequencies would aid major developments in thermoelectric energy harvesting, heat management in microelectronics, and information and communication technology. Using atomistic simulations we show that the metamaterials approach relying on localized resonances is very promising to engineer heat transport at the nanoscale. Combining designed resonant structures to alloying can lead to extremely low thermal conductivity in silicon nanowires. The hybridization between resonant phonons and propagating modes greatly reduces the group velocities and the phonon mean free paths in the low frequency acoustic range below 4THz. Concurrently, alloy scattering hinders the propagation of high frequency thermal phonons. Our calculations establish a rationale between the size, shape, and period of the resonant structures, and the thermal conductivity of the nanowire, and demonstrate that this approach is even effective to block phonon transport in wavelengths much longer than the size and period of the surface resonant structures. A further consequence of using resonant structures is that they are not expected to scatter electrons, which is beneficial for thermoelectric applications.

Experimental Analysis of a Vapor Chamber Applied to Thermal Management of Microelectronics

In this research, a vapor chamber embedded in the base of a heat sink was experimentally analyzed for the application in thermal management of microelectronics. The vapor chamber was produced by a copper and molybdenum alloy with length of 240 mm, width of 54 mm, thickness of 3 mm, and capillary structures composed by copper screen meshes. The working fluid used was de-ionized water. The pure aluminum heat sink was cooled by air forced convection and the evaporator vapor chamber was heated using an electrical resistor simulating integrated circuit power dissipation. The experimental tests were done in a suction type wind tunnel with open return for a heat load varying from 20 to 80 W and for an airflow velocity varying from 1 to 4 m/s. The experimental results showed that the considered vapor chamber worked successfully, maintaining low operating temperature.

3D porous graphene with ultrahigh surface area for microscale capacitive deionization

Capacitive deionization (CDI) is an emerging technology to supply deionized water as liquid coolant for the thermal management in microelectronics. Graphene has been demonstrated as a promising candidate for CDI electrode. However, the performance of current graphene-based CDI is far below expectation due to the limited specific surface area (SSA) and electrical conductivity of the chemically reduced graphene. Here we presented a KOH-activated graphene that has ultrahigh SSA of 3513m2/g and electrical conductivity of 104S/m. With improved materials properties, an ultrahigh electrosorption capacity of 11.86mg/g and a significant adsorption rate of 20min are achieved.

Design and Fabrication of On-Chip Coupled Inductors Integrated With Magnetic Material for Voltage Regulators

On-chip strip-line coupled inductors integrated with magnetic material are a promising technology option to enable on-chip voltage regulators for improving power management in microelectronics. We report on design methodologies where several examples of parameter tradeoffs are presented. When considered with practical integration constraints, these result in an optimized structure. Strip-line inductors integrated with Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> were then fabricated, electrically characterized, and compared to models. Electrical characterization included frequency dependent measurements of effective self and mutual inductance, effective resistance, coupling coefficient, and saturation effects.

Carbon Nanotubes/Polydimethylsiloxanes Systems for Thermal Management of Miniaturized Electronic Components

The thermal performances of nanocomposite layers formed by Single-walled Carbon Nanotubes (SWCNT) dispersed in 2 different kind of polydimethyl-siloxane (PDMSO) matrices has been investigated by measuring the thermal resistance under conditions similar to the ones used for thermal management in microelectronics. A series of nanocomposite samples with thickness in the range 25 microm(-1) cm have been tested. The nanocomposites were prepared varying the amounts of nanotubes embedded in the matrix (from 0.1 to 5%w). In some cases also microsized graphites were mixed to the nanotube's fillers. For 25 micron thick layers, the thermal resistance of the neat silicone specimen can be reduced of 54% with the addition of 2%w carbon nanotubes. The variation of thermal conductivity as a function of the SWCNT's loading is reported and discussed. Furthermore the dispersion's effects of the nanotubes in the layers and the effects on the realization of a net-like system have been investigated.

The thermal evaluation of the substrate mixed with microencapsulated phase change materials for MEMS packaging applications

The thermal management of microelectronics has become a critical issue in Microsystems and optoelectronic industries. This is particularly evident with the development of high power density and high heat flux in MEMS, IC, and LED components and devices, which has further increased the demand for materials with high thermal performance. To enhance the performance of current thermal modules, the development of advanced materials to replace conventional monolithic materials is crucial. The energy storage characteristics exhibited by materials during phase change helps them to maintain a constant temperature and conserve energy. Microencapsulation is the technique of enclosing phase change materials within a high polymer shell to form microcapsules, called microencapsulated phase change materials (MPCMs). Mixing MPCMs into matrix materials makes it possible to control the temperature of systems. This study evaluates the thermal performance of an MPCM (manufactured as powder with 10–30 μm size) mixed substrate, and results show that the manufacturing process does not destroy the structure of MPCM. The time required for a substrate mixed with MPCM to reach thermal steady state was delayed, compared to the time required for substrates without MPCM. The higher the percentage of MPCM, the longer it took to reach steady state. In addition, the heat transfer efficiency of the MPCM in its solid state was lower than in its liquid state. This heat transfer behavior was quite different from that found in bulk-size materials. These results suggest the application of MPCM for the thermal control of microelectronics, thermal management of modern Microsystems technologies, and the conservation of green house energy.

Thermal Expansion of Graphene Composites

Isolated graphene sheets were achieved by graphite intercalation and charge-induced exfoliation. The resultant graphene oxide sheets were incorporated into polymer composites and thermal expansion was investigated by a thermo-mechanical analyzer. The test results indicated that inclusion of graphene into composites resulted in low coefficients of thermal expansion (CTEs), and increasing graphene fraction reduced CTEs more significantly. The 5 wt % graphene oxide-based composite shows 31.7% reduction below the glass transition temperature. Preliminary measurement of thermal conductivity also indicated that graphene composites significantly improved the thermal conductivity of polymer matrix. Thermal conductivity of 5% graphene composites showed about 4-fold increment in comparison to the polymer matrix. This finding will provide a solid foundation for graphene-enabled thermal management in microelectronics.

Active cooling substrates for thermal management of microelectronics

Heat removal in printed wiring boards (PWB) is primarily accomplished through conduction. This work presents a microelectromechanical system (MEMS) device comprised of an active cooling substrate (ACS) designed and fabricated to add fluidic cooling functionality to the PWB. Thermal management is enhanced through the additional heat convection mode. Synthetic jet technology makes the compact, but easily integrated, MEMS cooling device possible. The fluid control unit, a synthetic jet, has been implemented in an epoxy-glass printed wiring board by multilayer lamination. An air reservoir is drilled through the core of printed wiring board. A flexible polymeric diaphragm and a low profile electromagnetic driver create an active pumping system to produce vibrating air jets downstream of microfluidic channels which transports heat generated by hot microelectronic components. Test heater chips have been directly die attached to the substrate. The integrated packaging system has been characterized mechanically, electrically, and thermally. Peak jet velocities of 14 m/s and average jet velocities of approximately 3 m/s have been achieved at actuator powers of 60 mW. This integrated active cooling substrate has the potential for broad applications in thermal management at the system packaging level.

Design and development of high-frequency thermoacoustic engines for thermal management in microelectronics

Thermoacoustic heat engines provide a practical solution to the problem of heat management in microcircuits where they can be used to pump heat or produce spot cooling of specific circuit elements. There are basically two types of thermoacoustic engines, a prime mover where heat is converted to acoustic energy, and a heat pump or cooler where sound can pump heat up a temperature gradient. Such devices are relatively simple, they can be efficient, and they are readily adaptable to microcircuit interfacing. Since this type of engines is usually operated in a resonant mode, the operating frequency determines its size. The devices presented here are pumped at frequencies ranging from 4 to 24 kHz. They have been developed for interfacing with microcircuits as heat pumps or spot coolers. Results of their performance are presented and suggestions for further improvements are discussed.

Computational and experimental approach to thermal management in microelectronics and packaging

New and ever more demanding applications of microelectronics require advances in design and optimization of components and packages, in relatively short periods of time, while satisfying electrical, thermal, and mechanical specifications, as well as cost and manufacturability expectations, without compromise to reliability and durability. Therefore, time efficient methodologies for detecting, locating and sizing damage early in the product development process are required. In this paper, a novel hybrid methodology, based on a combined use of recent advances in optics and computational modeling, is described and its application is demonstrated by a case study of a microelectronic component subjected to cyclic electro‐thermo‐mechanical loadings. Using the hybrid, optical‐computational approach, displacements and deformations are determined with high spatial resolution and measurement accuracy and provide indispensable data for development, optimization, and thermal management in microelectronics and packaging.