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Real-time imaging of transient structure of the electronic excited state is fundamentally critical to understand and control ultrafast physics and chemistry. However, the coherent nuclear motion in a specific excited state is yet to be captured accurately. Here, snapshots of the vibrational wave-packets of the excited (A) and ground states (X) of D$\rm_{2}$O$^{+}$ were acquired simultaneously with sub-10 picometer and few-femtosecond spatiotemporal precision, using a novel approach based on electron recollision-assisted Coulomb explosion. We visualised large amplitude bending and stretching motions for the A state, which significantly increased $\rm \theta _{DOD}$ and R$\rm_{OD}$ by approximately 50$^\circ$ and 10 pm, respectively, within 8 fs after initial tunneling ionization. In contrast, for the X state, only the prominant stretching motion is initialised with a bond extension of 7 pm within 5 fs. Another higher excited state with an asymmetric folding structure is experimentally established, which can be efficiently populated via the excitation of electron recollision. We demonstrate the remarkable dynamical vibrational fingerprints of these excite states and pave the way towards to make a movie of excited state-resolved ultrafast molecular dynamics and light-induced chemical reaction.

Granular flow has solid-, liquid-, or even gas-like behaviors, which can be described through discrete element method (DEM)-based simulations. Although the DEM simulation has advantages in studying particle-scale information, it is computationally intensive. Alternatively, this work proposes to combine the DEM and deep learning methods to predict granular flow behaviors in a wedge-shaped hopper. As the image-based labels are extracted from the DEM simulation, an Alexnet-fully connection (FC) model can make point-to-point predictions about the discharge time. Furthermore, when the first 20% of image-based datasets in the timing sequence are used to train a convolutional neural network (CNN)-long short-term memory (LSTM) network, it can make process predictions about the number ratio of remaining particles (NRRP) in the hopper vs. the discharge time. Although these attempts have some shortcomings at the present stage, more efforts are encouraged to stimulate the future potential of image-based prediction through the combined methods.

A hopper has very wide and vital applications in handing the granular materials in daily life and industrial production, and the full understanding of the granular flow inside a hopper is of great importance to control and optimize the discharge process. By employing experimental and numerical methods, the influence of particle packed pattern on the transient granular flow is investigated in terms of the particle-scale kinetics and structure. For the mono-sized particles packed pattern, despite the similar particle-scale structure, smaller particles achieve greater kinetic energy conversion efficiency, which helps shorten the discharge time. For the binary-sized particles uniform mixing pattern, the interaction between particles increases the individual kinetic energy and transient average coordination number (CN) of large particles, while decreases that of small ones. Then the in-between kinetic energy and the disperse structure are reached. For the layer by layer mixing pattern, the strong percolation effect caused by the upper small particles hinders the increase of the individual kinetic energy at the beginning of the discharge process, and the transient average CN at the layer interface abruptly reaches 8. By contrast, when the small particles are placed at the bottom, more particles are active in the larger space, and subsequently, a looser structure is achieved in a shorter period.

A four-body coincident measurement of carbonyl sulfide dimers is conducted using a femtosecond laser-induced Coulomb explosion. Sequential and concerted processes that occur during the Coulomb explosion are distinguished. Four isomers of carbonyl sulfide dimer are resolved, and their structures are retrieved from the measured coincident momenta of the fragment ions generated in the concerted process, with the help of a classical trajectory simulation. As a result of our study, we can resolve the isomers of a weakly bound molecular cluster and determine their stereo configuration by using the Coulomb explosion. There is also the potential in femtosecond time-resolved imaging for structural evolution of molecular complexes in dissociation.

The novel strong field autoionization (SFAI) dynamics is identified and investigated by channel-resolved angular streaking measurements of two electrons and two ions for the double-ionized CO. Comparing with the laser-assisted autoionization calculations, we demonstrate the electrons from SFAI are generated from the field-induced decay of the autoionizing state with a following acceleration in the laser fields. The energy-dependent photoelectron angular distributions further reveal that the subcycle ac-Stark effect modulates the lifetime of the autoionizing state and controls the emission of SFAI electrons in molecular frame. Our results pave the way to control the emission of resonant high-harmonic generation and trace the electron-electron correlation and electron-nuclear coupling by strong laser fields. The lifetime modulation of quantum systems in the strong laser field has great potential for quantum manipulation of chemical reactions and beyond.

The inevitable particle segregation behaviors of granular materials are undesirable in the industrial processes. It will directly affect the heat transfer efficiency between gas and solid phases during the ironmaking process of blast furnace. Therefore, the understanding and prediction on the particle segregation behaviors are vital to optimize the process and improve the production efficiency. This work first employs the Discrete Element Method (DEM) to investigate the effects of the parameters, such as the particle density, the mean diameter, the mass of particles, the particles mass ratio, and the angle of chute, on the mass segregation and size segregation behaviors at the bell-less top blast furnace with the serial type hopper. Then, the Artificial Neural Network (ANN) model is proposed to predict the aforementioned behaviors in the radial direction based on the numerical data. The results show that the predicted segregation behaviors by the established ANN model are in a good agreement with the simulated results.

Elliptically polarized laser pulses (EPLPs) are widely applied in many fields of ultrafast sciences, but the ellipticity~($\varepsilon$) has never been in situ measured in the interaction zone of the laser focus. In this work, we propose and realize a robust scheme to retrieve the $\varepsilon$ by temporally overlapping two identical counter-rotating EPLPs. The combined linearly electric field is coherently controlled to ionize Xe atoms by varying the phase delay between the two EPLPs. The electron spectra of the above-threshold ionization and the ion yield are sensitively modulated by the phase delay. We demonstrate that these modulations can be used to accurately determine $\varepsilon$ of the EPLP. We show that the present method is highly reliable and is applicable in a wide range of laser parameters. The accurate retrieval of $\varepsilon$ offers a better characterization of a laser pulse, promising a more delicate and quantitative control of the sub-cycle dynamics in many strong field processes., Comment: Phys. Rev. Lett., in press (2018), 4 figures

In the present work we design, model and experimentally characterize a two-phase vapor venting parallel microchannel heat exchanger capped with a 220 nm pore, hydrophobic PTFE membrane that vents the vapor phase into separate vapor transport channels. We compare the performances of a traditional non-venting heat exchanger and the vapor-separating version operating at heat fluxes of up to 820 kW/m2 and water mass fluxes of between 102 and 420 kg/s m2. We find ∼60% improvement in the normalized pressure drop and up to 4.4 °C reduction in the average substrate temperature between the control and vapor venting device under similar operating conditions.

We studied the relative yields and dissociation dynamics for two- and three-body Coulomb explosion (CE) channels from highly charged carbonyl sulfide molecules in intense laser fields using the CE imaging technique. The electron recollision contributions are evaluated by comparing the relative yields for the multiple ionization process in linearly polarized and circularly polarized (LP and CP) laser fields. The nonsequential multiple ionization is only confirmed for the charge states of 2 to 4 because the energy for further ionization from the inner orbital is much larger than the maximum recollision energy, 3.2U p . The novel deviations of kinetic energy releases distributions between LP and CP pulses are observed for the charge states higher than 4. It can be attributed to the stronger molecular bending in highly charged states before three-body CE with CP light, in which the bending wave packet is initialed by the triple or quartic ionization and spread along their potential curves. Compared to LP light, CP light ionizes a larger fraction of bending molecules in the polarization plane.

Phase-change technology has been widely used in rewritable disks for optical recording applications. Recently, it has also received attention as a candidate for future high-storage-density nonvolatile random access memory, due to its much longer cycle life (∼1013) and fast data access time (∼100 ns) compared with the existing flash memory technology. In this article, we present thermal conductivity data and models for phase-change GeSbTe material that would be helpful in performance optimization and improvement in the reliability of phase change–based data storage devices and systems. We present thermal conductivity data for a 40-nm-thick Ge2Sb2Te5 phase-change layer in both amorphous and crystalline states using electrical resistance joule heating and thermometry techniques. The limits of lattice and electronic thermal conductivities are investigated to determine their relative contributions to the total thermal conductivity as a function of tellurium concentration, crystalline structures, and temperature.

A new setup for small-scale differential scanning calorimetry (DSC) studies based on a suspended bridge configuration is presented. The new setup has three major advantages over previously reported DSC setups: 1) superior temperature uniformity in the bridge cross section; 2) less heat loss to the surroundings by at least two orders of magnitude; and 3) a faster transient response by three orders of magnitude. This paper includes a thermal analysis to support these improvements. A major contribution of the new thermal analysis over previous reports is the inclusion of the thermal mass of the substrate in calculations, which makes thermal design more detailed, dramatically affecting accuracy and sensitivity in measurements. Furthermore, the new thermal analysis more accurately accounts for heat loss to the substrate and the surroundings in efforts to resolve suspected inconsistencies in previously reported data. Experimental validation of the new setup is presented by measuring the specific heat of thin layers of Si02 and CoFe. The specific heat of Si02 was found to be 2.2 times 106 Jm -3 K-1 which is nearly 10% different from the literature values of bulk specimens. For CoFe, the specific heat value of 3.16 x 106 Jm -3 K-1 is obtained using differential Cu/Si02 and Cu/Si02/CoFe structures compared to the value of 3.5 times 106 Jm -3 K-1 obtained using single CoFe suspended structure.

In this manuscript, different aspects of nanoscale thermal transport in strained silicon transistors will be addressed. The two-dimensional Boltzmann transport equations for phonons in Si and SiGe alloy layers, along with the acoustic mismatch model for the interface, are used to capture the sub-continuum heat conduction effects in the device. It is shown that the lateral thermal conductivity of a 10-nm strained-Si layer grown on the SiGe underlayer can vary from 14 to 20W/m-K, depending on the interface specularity parameter. The resulting temperature distribution in the device is used to predict the impact of self-heating on performance of future generations of strained-Si devices. The analysis shows that the merits of strained-Si technology can be suppressed by excessive self-heating; therefore, additional considerations in the design of these devices need to be taken into account

Giant magnetoresistance (GMR) head technology is one of the latest advancements in the hard disk drive (HDD) storage industry. The GMR head multilayer structure consists of alternating layers of extremely thin metallic ferromagnetic and nonmagnetic films. A large decrease in the electrical resistivity from antiparallel to parallel alignment of the film magnetizations is observed, known as the GMR effect. The present work characterizes the in-plane electrical and thermal conductivities of Cu/CoFe GMR multilayer structures in the temperature range of 50 K to 340 K using Joule-heating and electrical resistance thermometry on suspended bridges. The thermal conductivity of the GMR layer monotonically increases from 25 W m -1 K -1 (at 55 K) to nearly 50 W m -1 K -1 (at room temperature). We also report a GMR ratio of 17% and a large magnetothermal resistance effect (GMTR) of 25% in the Cu/CoFe multilayer structure.

In recent years, the magnetic recording storage industry has developed a growing interest in increasing recording density of the magnetic disks. Since dimensions of the recording head read transducer have been scaled down to increase areal density, all other parameters being equal, the energy required to cause damage by an ElectroStatic Discharge (ESD) event is reduced substantially. The reduction of insulator thickness between the leads and shields, to increase linear density, further lowers the threshold for ESD breakdown voltage. This problem will become increasingly acute with use of a large number of new and exotic passivation materials having low dielectric constants and thermal conductivities. The present work characterizes the thermal transport properties of Al2 O3 Gap layer, which are essential to address the ESD failure in GMR head. This study provides data for out-of-plane (normal) thermal conductivity of thin Al2 O3 layers. Thermal conductivity data is obtained using steady-state Joule heating and electrical-resistance thermometry technique.Copyright © 2003 by ASME

If a laser beam illuminates a continual deformation object surface, it will lead to a temporal speckle pattern on the observation plane. Recording this time-dependent speckle pattern the deformation of the surface of an object can be obtained. Two methods, scanning phase method (SPM) and time sequence phase method (TSPM), have been introduced for measuring the displacement caused by the deformation in temporal speckle pattern interferometry (TSPI). Their principle is that by capturing a series of speckle interference patterns related to the object deformations, the fluctuations in the intensity of the interference patterns can be obtained. Through scanning these fluctuations and estimating both the average intensity and modulation of the temporal speckle interference patterns, the phase maps for whole-field displacements are calculated. In this way one is capable of quantitatively measuring continual displacements simply using a conventional electronic speckle pattern interferometry (ESPI) system without phase shifting or a carrier. The elaboration on the new methods is given in this paper and experiments are performed to demonstrate their performance with a conventional ESPI system.

The highly nonuniform transient power densities in modern semiconductor devices present difficult performance and reliability challenges for circuit components, multiple levels of interconnections and packaging, and adversely impact overall power efficiencies. Runtime temperature calculations would be beneficial to architectures with dynamic thermal management, which control hotspots by effectively optimizing regional power densities. Unfortunately, existing algorithms remain computationally prohibitive for integration within such systems. This work addresses these shortcomings by formulating an efficient method for fast calculations of temperature response in semiconductor devices under a time-dependent dissipation power. A device temperature is represented as output of an infinite-impulse response (IIR) multistage digital filter, processing a stream of sampled power data; this method effectively calculates temperatures by a fast numerical convolution of the sampled power with the modeled system's impulse response. Parameters such as a steady-state thermal resistance or its extension to a transient regime, a thermal transfer function, are typically used with the assumption of a linearity and time-invariance (LTI) to form a basis for device thermal characterization. These modeling tools and the time-discretized estimates of dissipated power make digital filtering a well-suited technique for a run-time temperature calculation. A recursive property of the proposed algorithm allows a highly efficient use of an available computational resource; also, the impact of all of the input power trace is retained when calculating a temperature trace. A network identification by deconvolution (NID) method is used to extract a time-constant spectrum of the device temperature response. We verify this network extraction procedure for a simple geometry with a closed-form solution. In the proposed technique, the amount of microprocessor clock cycles needed for each temperature evaluation remains fixed, which results in a linear relationship between the overall computation time and the number of temperature evaluations. This is in contrast to time-domain convolution, where the number of clock cycles needed for each evaluation increases as the time window expands. The linear dependence is similar to techniques based on FFT algorithms; in this work, however, use of z-transforms significantly decreases the amount of computations needed per temperature evaluation, in addition to much reduced memory requirements. Together, these two features result in vast improvements in computational throughput and allow implementations of sophisticated runtime dynamic thermal management algorithms for all high-power architectures and expand the application range to embedded platforms for use in a pervasive computing environment.

The industry trend toward reduced feature size and faster operating speed has generated demand for higher powered devices. The increased power and reduced overall area creates higher thermal loads for the package. This has led to the need for new thermal materials with high thermal conductivity. High-performance thermal interface greases, gels, and adhesives significantly improve the transmission of the heat generated by the high power densities out of the system. Thermal greases generally have higher thermal conductivity than gels or adhesives with similar fillers. Unfortunately, greases typically pump out and separate during use. Additionally, some applications that require higher thermal conductivity materials cannot go through a cure profile normally used for non-grease thermal interface materials (TIMs). Use of integrated heat spreaders avoids some of the processing restrictions placed on board-level thermal solutions, but many applications -- particularly in mobile electronics -- have little space or have significant weight constraints that interfere with the use of a built-in heat spreader. A new 4 W/mK silicone thermal grease with dramatic property improvements has been developed with significant resistance to in-package bleed-out or pump-out, eliminating the reliability problem most commonly encountered with traditional thermal greases.

Increase of non-uniform power density and high switching frequency has presented new challenges in predicting transient temperature response to fast-changing power inputs in advanced electronic devices. While the computational effort with direct calculation through the finite element model (FEM) is expensive, various methods of model reduction with drastically improved computing speed have been developed for calculation of dynamic thermal responses of the electronic systems. However, those methods’ still-considerable computational time consumption inhibits their practices in real-time temperature prediction and dynamic thermal management (DTM) applications. This work presents a fast algorithm for predicting temperature evolution in electronic devices subjected to multiple heat source excitations. It utilizes the equivalent thermal RC network for model reductions, and adopts recursive infinite impulse response (IIR) digital filters for accelerated computation in discrete time-domain. The algorithm is validated by comparison to existing convolution integral methods, yielding excellent agreement with several orders of magnitude improvement in computation efficiency. Due to its simplicity in implementation, the algorithm is very suitable for run-time evaluation of temperature response for dynamic power management applications.Copyright © 2010 by ASME

The evolution of microprocessor architectures has driven semiconductor manufacturers making transition from ceramic to organic package substrate technology in order to take full advantage of the silicon advances. However, large mismatch in coefficients of thermal expansion (CTE) between silicon die and organic substrate results in significant die/package warpage that adversely impact the package's thermomechanical performance during assembly processes and longterm reliability in use conditions. In contrast to the extensive studies in various mechanical failures, little research effort has been pursued in the investigation of impacts from die warpage on package thermal performance and TIM degradations, mainly due to the limitation of existing steady-state and transient thermal characterization techniques. This work explores the application of frequency-domain thermal impedance measurement technique in study of impact on thermal resistance at TIM1 level from temperature-dependent die warp behavior in field conditions. Hysteresis loop of thermal impedance at TIM1 level as a function of junction temperature is observed which indicates the TIM delamination due to its failure to accommodate the temperature-dependent die warpage. Evaluations of TIM candidates with different bond-line thicknesses (BLT), TIM curabilities, and die sizes suggest that optimizations of BLT are required in order to meet both mechanical and thermal performance requirements.

We present a methodology for optimizing footprint, metal mass and thermal performance of an aluminum extruded heatsink for cooling chipset microprocessors in server form-factor. The analysis is based on predefined volume flow rate of air at a constant temperature assumed to be available upstream of the package. The front-to-back cooling assumption covers the worst case ambient conditions, typical of chipset boundary condition in servers. We present studies covering a range of heatsink footprints in order to compare and minimize the heatsink footprint, at the same time satisfying thermal specification of the chipset microprocessor. The study also focuses on the system-level assessment of the optimum 60×40 mm2 footprint and corner cases by studying the effect of motherboard thermal conductivity as well as blockages on the heatsink case-to-ambient thermal resistance.Copyright © 2009 by ASME

Increase of power densities has become the primary constraint for semiconductor industry to sustain the Moore’s law for microprocessor evolution. Further development of packaging technology and advanced thermal interface materials (TIMs) requires both maximization of the total thermal throughput of the system and mitigation of the thermal impact from non-uniformly distributed hotspots. Therefore, thermal characterization techniques capable of resolving partial thermal resistances at the component level have received increased emphasis in development of advanced packaging technologies. This work develops a practical method for thermal characterization of IC packages using the frequency-domain measurement technique. It is well suited for investigation of package thermal performance during various application-specific tests in field conditions, as well as a tool for development of TIM and optimization of packaging process. Both steady-state and dynamic thermal characterizations of the IC packages can be achieved using this technique. Various applications, such as thermal structure function measurement, silicon die hot-spot detection, and in-situ thermal/mechanical characterization of TIMs are discussed.Copyright © 2009 by ASME

In this paper, a thermal analysis of thermoelectric coolers (TECs) is conducted for processors based on TEC module parameters. Two sets of analytical solutions for TECs in system constraints are derived for the junction temperature Tj at a fixed power Qc, and for Qc at fixed Tj, respectively. The major advantage of the present models lies in the fact that the solutions can be obtained based on the module parameters without prior knowledge of pellet details and iterative solution procedure, as often reported in literature. Two cooling scenarios, the processor test and the processor cooling under end-user conditions, are analyzed based on the present analysis models for two commercial TECs with high power capacities. Results show that significant thermal enhancements are achievable based on optimized current and power dissipation. The validation is also conducted through experimental measurements and comparison with previous iterative solutions.

As the increase of power densities became the primary constraint for semiconductor industry to sustain the Moore's law for microprocessor evolution, multi-core architecture has been introduced in order to meet the growing demands for performance. Non-uniform power distribution, increased die-size and multiple-chip packaging present new challenges for the thermal management of modern CPUs. Further development of packaging technology and advanced thermal interface materials (TIMs) requires both maximization of the total thermal throughput of the system and mitigation of the thermal impact from non-uniformly distributed hotspots introduced by individual cores. Therefore, thermal characterization techniques capable of resolving thermal resistance distribution at TIM1 level need increased emphasis in package development. This work aims to develop practical techniques for such characterization. Steady-state measurements are supplemented by transient techniques to allow thorough characterization of thermal performance of CPU packages. Such techniques would aid with development of optimized thermal packaging to meet new challenging thermal requirements imposed by modern computing architectures.

It is well known theoretically and experimentally that spin waves can be excited by current in magnetic trilayer and multilayer structures where the current is spin polarized by one of the magnetizations and interacts with the others. However, it has also been observed experimentally that a nonpolarized dc current flowing through a point contact into a single ferromagnetic thin film can induce spin waves. We investigate this phenomenon using a model in which the spins of the conduction electrons interact with a nonuniform magnetization and the current is treated perturbatively. To a first-order approximation, the spin-wave modes excited by the injected current have been characterized and the relationship between the dynamic properties of the spin waves and the applied current and applied magnetic field has been established. Calculated results are then used for comparison with the experimental observations.

Phase-change technology has been widely used in rewritable disks for optical recording applications. Recently, it has also received attention as a candidate for future high storage density non-volatile random access memory, due to its much longer cycle life (∼1013 ) and fast data access time (∼100ns) compared with the existing Flash memory technology. In this paper, we present thermal conductivity data and models for phase-change GeSbTe material that would be helpful in performance optimization and improvement in the reliability (i.e., enhancement of data rate, cyclability, control of mark-edge jitter) of phase-change-based data storage devices and systems. We perform the thermal characterization of Ge4 Sb1 Te5 and Ge2 Sb2 Te5 phase-change materials for the application of optical recording and phase-change memory cell using the techniques of thermoreflectance and electrical resistance thermometry. The limits of lattice and electronic thermal conductivities are investigated to determine their relative contributions as a function of tellurium concentration at different crystalline structures.Copyright © 2007 by ASME

The discovery of the giant magnetoresistance effect in metallic multilayers and alloys has led to extensive theoretical and experimental investigations of this effect for the past few decades. Recently, we discovered that Cu/CoFe giant magneto-resistance layers exhibit a giant magnetothermal resistance effect (GMTR), in which the thermal conductivity shows a “giant” change under a magnetic field. In the present study, we adopted the Fuchs-Sondheimer extension of the semiclassical Boltzmann theory to predict the in-plane giant magneto-resistance (GMR) and giant magnetothermal resistance (GMTR) ratios in the Cu/CoFe multilayer structure. The present model has been implemented in an attempt to explain the measured differences in the giant magnetoresistance and giant magnetothermal resistance ratios, which have previously been attributed to the different mechanisms for charge and heat transport in the Cu/CoFe multilayer structure.Copyright © 2007 by ASME

By definition, a differential scanning calorimetry (DSC) requires a sample structure and a refrence structure to obtain the latent heat of a speicman. We propose a novel approach, named Phase Transition Calorimetry (PTC), to obtain the specimen’s latent heat by using only the signal from the sample bridge. The new setup and procedure are primarily based on electrical resistance heating and thermometry and the parametric estimation method by solving the heat conduction equation with and without the phase transformation. The new setup has two major advantages over widely used DSC setups: there are no errors associated with heat loss to the surroundings, and the uncertainty resulting from the difference between the sample and the reference is eliminated by removing the reference structure. Experimental validation of the new setup and procedure is demonstrated by measuring the latent heat of thin layers of tin. This was found to be 4.1×108 Jm−3 , which is different within 5% from the literature values of bulk specimens.Copyright © 2007 by ASME

This paper presents the experimental and theoretical study on the effects of electron scattering at grain and boundaries on the reduction of effective thermal conductivity. The present study measures the electrical resistivity and lateral thermal conductivity of thin copper layers of thicknesses 50 and 144 nm at temperatures between 40 and 400 K, using Joule heating and electrical-resistance thermometry in suspended micro fabricated structures. A fitting model including the size effect and grain boundary scattering is used to model the thermal conductivity and electrical resistivity of thin copper film simultaneously and is consistent with the experimental results. The thermal conductivity of the 50 nm thick copper layer is ~150 W m-1 K-1, which is much smaller than the bulk value (~400 W m-1 K-1) at room temperature. The experimental and modeling data are essential to address performance and reliability issues for future device and interconnect technologies

It has been recognized that future improvements in performance and reliability of the microelectronic devices may only be possible through the use of new high-thermal-conductivity materials for thermal management in compact packaging systems. The diamond-like dielectric materials, in bulk form or thin film configurations are the likely choice, due to their high thermal conductivity and their excellent mechanical and electrical properties. However, the accurate thermal characterization of these materials has proven to be extremely challenging due to variations in fabrication processes and therefore their microstructures, as well as the practical difficulties in measuring small temperature gradients during the thermal characterization process. The variations in microstructure of these materials (e.g., CVD diamond) would manifest into anisotropic, nonhomogeneous, and thickness-dependent thermal properties that may vary by several orders of magnitude. As a result of these complications, a wide range of experimental techniques have been developed over the years, which may or may not be appropriate for thermal characterization of high-thermal-conductivity material of given microstructure and physical dimension. We will describe and critically review the existing thermal-characterization techniques for high-thermal-conductivity dielectric materials. In addition, we propose a number of techniques that are particularly tailored for accurate thermal characterization of diamond, silicon nitride (Si3N4), aluminum nitride (AlN), and silicon carbide (SiC) films and substrates. In each case, specific comments about the experimental technique and procedure, detailed description of the heat transfer process, and sensitivity analysis are provided.

When crystalline solids are confined to the nanometer range, phonon transport within them can be significantly altered due to various effects, namely (i) increased boundary scattering; (ii) changes in phonon dispersion relation; and (iii) quantization of phonon transport. For example, theoretical studies (e.g., Chung et al., 2000) have suggested that, as the diameter of a silicon nanowire (NW) becomes smaller than 20 nm, the phonon dispersion relation, and therefore its density of states, could be modified due to phonon confinement. This in turn impacts the phonon group velocities and scattering rates that can further reduce the thermal conductivity of confined structures.

Giant Magnetoresistance (GMR) head technology is one of the latest advancement in hard disk drive (HDD) storage industry. The GMR head superlattice structure consists of alternating layers of extremely thin metallic ferromagnet and paramagnet films. A large decrease in the resistivity from antiparallel to parallel alignment of the film magnetizations can be observed, known as giant magnetoresistance (GMR) effect (Baibich et al., 1988; Binasch et al., 1989). The GMR effect is generally due to the spin dependent electron bulk and interfacial scattering in the GMR multilayer structures (Zhang et al., 1992). However, in order to understand the nature of the spin-dependent electron scattering mechanism responsible for the GMR effect, both electrical and thermal transport properties of such multilayer structures must be measured and understood. It is suggested that the thermal transport property measurements in GMR can be used to judge whether the scattering processes responsible for the GMR have elastic and/or inelastic components (Shi et al., 1996). Moreover, the GMR effect is anticipated to have a thermal counterpart, known as giant magnetothermal resistance (GMTR) effect in which the thermal conductivity shows a ‘giant’ change under magnetic field.

Design/optimization of the phase change recording media to create proper marks, in size, shape, and quality, needs a robust modeling tool to predict temperature distribution in the constituting layers and model the phase formation during writing/erasure of the information bits. This requires a modeling of the heat transfer (thermal performance) and the crystallization processes. The thermal modeling, which is based on the solution of the heat diffusion equation for finding temperature distribution in the multilayer media, has been done before, using the finite difference techniques. These techniques have limited potentials for modeling real phase change recording media that have a rather more complex geometry. The finite elements method has, on the other hand, the required flexibility for such applications. In this work, we are reporting on development of a numerical simulation tool that uses the finite elements method for heat transfer simulation. ANSYS is used as the source code for the heat transfer simulation, in this application, with the crystallization model then being built into this media. This code has been used to simulate mark formation during writing on grooved plain and planer patterned media. Patterning the phase change material layer looks very promising in controlling the mark size and the mark edge irregularity which lead to timing jitter.Copyright © 2005 by ASME

Lack of an efficient thermal management strategy and system can often lead to overall system failure in advanced microprocessors. This can be avoided by utilization of the high thermal conductivity materials, as heat spreader/sink, in compact packaging systems. The diamond-like dielectric materials such as diamond, silicon nitride (Si/sub 3/N/sub 4/), aluminum nitride (AlN), silicon carbide (SiC), etc, are the likely choices. However, thermal characterization of such high thermal conductivity material has proven to be challenging due to variations in fabrication process and therefore their microstructures as well as the practical difficulties in measuring small temperature gradients during the characterization process. In this paper, we will report a novel film on substrate technique that can be used conveniently for repeated measurements of the lateral thermal conductivity of the high thermal conductivity films, with thicknesses between 100 to 500 /spl mu/m.

With the dramatic scaling of the transistors, the important issues like RC delay, electromigration failure and heat dissipation emerge, which need to be addressed urgently. Substitution of copper for aluminum has been suggested to reduce the RC delay of interconnects. While the electrical and mechanical properties of thin copper films have been extensively investigated; their thermal characterizations have received less attention. The lateral thermal conductivity of a 144 nm thick copper film is measured using the electrical resistance Joule heating and thermometry in a suspended bridge. The thermal conductivities at 300 K and 450 K are 240 and 280 W/m-K, respectively, which is smaller than the corresponding bulk values. The impact of the interconnect dimension and thermal conductivity on the self-heating is investigated as a function of interconnect via density. It is concluded that for via separation distances less than 5 /spl mu/m, the combination of Cu interconnect and vias can significantly reduce the average temperature rise in multilayer interconnects.

Accurate modeling of heat transport in multi-level interconnects of advanced microprocessors requires accurate knowledge of the thermal properties in thin film structures. The commonly used suspended bridge structures for the lateral thermal conductivity measurements of the metallic thin films involves significant microfabrication process and often cannot produce suspended structures with dimensions near 100 nm/spl times/100 nm. In this paper, a novel technique for the in-plane thermal conductivity measurements of electrically conductive structures is presented. Thin interconnects or nanostructures can be deposited on a silicon dioxide layer of thickness near /spl sim/1 /spl mu/m and then patterned to form a bridge with the width comparable to or less than 100 nm. Joule-heating in the patterned bridge results in a temperature distribution that is strongly dependent on the lateral conduction along the bridge itself through the silicon dioxide layer. The feasibility of the proposed structure for thermal conductivity measurement is investigated by performing careful sensitivity analysis.

The thermal response of the GMR sensor during the ESD pulse is investigated using finite element model. The simulation compares the transient temperature rise in GMR sensor when they are subjected to the Human Body Model (HBM) and Charged-Device Model (CDM) waveforms. The results indicate that the ESD threshold damage for GMR head depends on both the thermal time constant and the ESD transient current.

The fundamental study of phase transformations continues to be a key for successful implementation of metals and alloys in micro- and nano-scale structures in integrated circuitry and magnetic recording devices and systems. The thermodynamic and thermokinetic properties of extremely thin layers can be altered due to the relative effect of boundaries and interfaces on the volume of the material. Calorimetry at the nano-scale requires measurement sensitivity on the order of 1 nJ or better, which requires improved thermal design, development of thermal modeling, and development of experimental measurement techniques. In this report, the specific heat of 144 nm thick CoFe layer is measured, using frequency-domain Joule heating and thermometry (3ω-technique), on Cu/SiO2 and Cu/SiO2 /CoFe suspended bridges. Analyses of the heat transfer in suspended structures are performed to establish guidelines for design and fabrication of small-scale differential scanning calorimeters.Copyright © 2004 by ASME

The amorphous/crystalline phase formation during writing or erasure of the written marks, in the rewritable phase change (PC) optical recording media, is controlled by the temperature distribution in the media and its variation with time. Temperature distribution, on the other hand, strongly depends on the thermal properties of its constituent layers in particular the ZnS-SiO2 dielectric layer that separates the phase change media from the substrate and aluminum heat sink. The reported values for the thermal conductivity of thin dielectric layers are however limited in the literature. In this manuscript, we report thermal conductivity data for dielectric layers of thickness near 50, 100 and 225 nm using the steady sate Joule-heating and electrical resistance thermometry technique. The boundary resistance at the interface is estimated to be near 7.0×10−8 m2 K W−1 , which would limit the thermal time constant for cooling of PC layer and potentially impact data rate and jitter in optical recording technology.Copyright © 2004 by ASME

This manuscript investigates the relevance and impact of nanoscale thermal phenomena in the state-of-the-art semiconductor device technologies such as: silicon-on-insulator (SOI), strained silicon, and tri-gate CMOS transistors. The experimental data and predictions for thin silicon layer thermal conductivity and the solutions of the Boltzmann transport equations (BTE) for phonon transport in strained-Si/Ge bi-layer configuration are used to estimate the thermal resistance of the SOI, tri-gate, and strained-silicon-on-SiGe-on-insulator (SGOI) transistors, respectively. In particular, the impact of SiGe underlayer and interface roughness on the lateral thermal conductivity of the silicon layer at room temperature is investigated. In order to avoid the complexity of the BTE for predictions of the temperature distribution, Lumped Analytical (LA) models are introduced that are simple to implement and also adequate enough to capture the sub-continuum effects. It is concluded that the SOI, SGOI and tri-gate transistors are all susceptible to self-heating for very thin silicon device layers.Copyright © 2004 by ASME

The performance and reliability of GMR heads are influenced by the level of temperature rise, which may occur in the device during the normal operation or during an electrostatic discharge (ESD) event. However, the reliable electro-thermal modeling of the GMR sensor to predict the temperature rise, demands an accurate knowledge of the thermal properties of its constituent materials such as Al2 O3 passivation and GMR layers. The lateral thermal conductivity of the GMR layer, which has not been measured previously, can largely influence the maximum temperature rise in the GMR sensor. The present effort will be directed at thermal characterization of the CoFe/Cu multilayer structures made of extremely thin periodic layers, using steady-state and frequency domain heating and thermometry in suspended bridges. The measurements are performed on several suspended structures with the lengths and widths in the range of 250 to 500 μm and 16 to 20 μm, respectively.Copyright © 2003 by ASME

With the further miniaturization of the GMR heads, the electrostatic discharge (ESD) failure has become the primary reliability issue in manufacturing of these sensors. The Joule heating effect during the ESD events result in both thermal and magnetic damages in GMR heads. In this paper, the thermal response of the GMR read head to the excessive current/voltage during an ESD event is investigated numerically using a 3-D finite element analysis. Unlike the previous studies, the thermal properties of the GMR and Al2 O3 gap layers used in the simulation are the experimentally measured values. The temperature-rise in GMR heads under human-body-model (HBM) source current is obtained for a range of GMR dimensions and thermal properties of its constituent materials. The simulation results show that temperature in the GMR element sharply increases as the GMR dimensions are reduced, indicating the future GMR heads are more susceptible to the ESD damages. In addition, thermal properties of the GMR and gap materials play key roles in accurate prediction of the temperature field in GMR head during ESD events.Copyright © 2003 by ASME

By all measures, the data storage industry is one of the most important components of the Information Technology (IT) revolution. In recent years, many of the emerging technologies rely heavily on energy transport at extremely short time and length scales as a mean to overcome the superparamagnetic limit - a serious impediment to future advancement of storage technology. Additionally, thermally induced failure and reliability issues at the nanoscale are becoming increasingly important due to rapid device miniaturization in data storage applications. Further advances in high-technology data storage systems will be difficult, if not impossible, without rigorous treatment of nanoscale energy transport. This manuscript reviews the thermal design issues and challenges in thermally assisted magnetic disk recording, thermally assisted scanned probe recording, phase change optical data recording, magnetoresistive random access memory (MRAM) and giant magnetoresistive (GMR) heads. Relevant thermally induced failures in GMR heads, write coil, interconnects and MRAM will be discussed as well.Copyright © 2002 by ASME