An Integrated Experimental and Computational System for the Thermal Characterization of Complex Three-Dimensional Submicron Electronic Devices

This work presents the creation of a coupled analysis engine and experimental system capable of fully characterizing the thermal behavior of complex, 3D, active, submicron, electronic devices. First, the surface temperature field of an activated device is non-invasively measured with submicron spatial resolution. Next, the thermal conductivity of each thin-film layer composing the device is measured and a numerical model is built using these values. The measured temperature distribution map is then used as input for an ultra-fast inverse computational solution to fully characterize the thermal behavior of the complex 3D device. By bringing together measurement and computation, it becomes possible for the first time to non-invasively extract the 3D thermal behavior of nanoscale embedded features that cannot otherwise be accessed. The power of the method was demonstrated by verifying that it can extract details of interest of a representative MOSFET device.     

Power Generator Modules of Segmented Bi2Te3 and ErAs:(InGaAs)1−x (InAlAs) x

The thermoelectric properties of ErAs:InGaAlAs were characterized by variable-temperature measurements of thermal conductivity, electrical conductivity, and Seebeck coefficient from 300 K to 600 K, which shows that the ZT(, where and T are the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively) of the material is greater than 1 at 600 K. Power generator modules of segmented elements of 300 μm Bi₂Te₃ and 50 μm thickness ErAs:(InGaAs)_1−x (InAlAs) _x were fabricated and characterized. The segmented element is 1 mm × 1 mm in area, and each segment can work at different temperature ranges. An output power up to 5.5 W and an open-circuit voltage over 10 V were measured. Theoretical calculations were carried out and the results indicate that the performance of the thermoelectric generator modules can be improved further by improving the thermoelectric properties of the element material, and reducing the electrical and thermal parasitic losses.     

Controlling n-Type Carrier Density from Er Doping of InGaAs with MBE Growth Temperature

Under certain growth conditions in molecular beam epitaxy, erbium, indium, gallium, and arsenic form a two-phase composite, consisting of ErAs nanoparticles embedded in dilute Er-doped In_0.53Ga_0.47As. This paper further explores the effect of growth conditions, specifically growth temperature, on the nanostructure of this material and the resulting thermal and electrical transport properties. For a set of samples grown with substrate temperatures varying from 430°C to 525°C, we find that the thermal conductivity decreases slightly with increasing growth temperature (from 4.8 W/m K to 4.1 W/m K) while the electrical conductivity decreases dramatically with increasing growth temperature (from 2100 S/cm to 110 S/cm), which is largely due to decreasing carrier concentration. At higher growth temperatures, more erbium precipitates out of solution and the size and density of the ErAs nanoparticles increase, as characterized by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), while the total erbium concentration does not change with growth temperature, as characterized by Rutherford backscatter spectrometry (RBS). Measurement of the erbium concentration by secondary-ion mass spectrometry suggests that the Er bonding configuration changes with growth temperature. These results indicate that increasing the ratio of solute Er atoms in the In_0.53Ga_0.47As host to precipitated Er atoms in ErAs particles increases the carrier density and electrical conductivity of the total composite material.     

Effect of Nanoparticles on Electron and Thermoelectric Transport

Recent experimental results have shown that adding nanoparticles inside a bulk material can enhance the thermoelectric performance by reducing the thermal conductivity and increasing the Seebeck coefficient. In this paper we investigate electron scattering from nanoparticles using different models. We compare the results of the Born approximation to that of the partial-wave method for a single nanoparticle scattering. The partial-wave method is more accurate for particle sizes in the 1 nm to 5 nm range where the point scattering approximation is not valid. The two methods can have different predictions for the thermoelectric properties such as the electrical conductivity and the Seebeck coefficient. To include a random distribution of nanoparticles, we consider an effective medium for the electron scattering using the coherent potential approximation. We compare various theoretical results with the experimental data obtained with ErAs nanoparticles in an InGaAlAs matrix. Reasonably good agreement is found between the measured and theoretical electrical conductivity and Seebeck data in the 300 K to 850 K temperature range.     

Thermoelectric Properties of Off-Stoichiometric Ti-Ni-Sn Half-Heusler Systems

The Ti-Ni-Sn half-Heusler compound exhibits a high power factor but relatively low figure of merit due to its high thermal conductivity. In this paper, we propose an effective and inexpensive way to reduce the thermal conductivity, and independently increase the power factor. To this end, we have systematically synthesized off-stoichiometric Ti-Ni-Sn half-Heusler compounds and introduced Y-Sb dilute co-doping at Ti-Sn sites. Excess Ni introduces interstitial defects in the half-Heusler crystal and results in significant reduction of the thermal conductivity, which drops below 3?W/mK at room temperature. In addition, the Y-Sb dilute co-doping at Ti-Sn sites improves the power factor while the thermal conductivity remains reasonably small. As a result, the figure of merit at room temperature is eight times larger than that of nondoped Ti-Ni-Sn.     

PCB glass-fibre laminates: Thermal conductivity measurements and their effect on simulation

Accurate values of thermal conductivity are required for the simulation of temperature phenomena in electronic circuits. This paper presents the results of measurements carried out to determine the thermal conductivity along and normal to the plane of fibre glass laminates used in the manufacture of printed circuit boards. It has been found that the reinforced fibre-glass substrates used in PCBs are strongly anisotropic with the conductivity normal to the boards being much smaller than tangential to it. The test samples were type FR4 epoxy/glass laminates. An experiment has been designed which determines the thermal conductivity in-the-plane of the laminates by matching the measured temperature distribution along a heated specimen with a finite difference solution. An electrically heated Lees’ disc apparatus is also used to measure the thermal conductivity of these boards in a direction normal to their plane. The samples tested yielded values of 0.343 W/mK and 1.059 W/mK for thermal conductivity through and along the plane of the boards, respectively.     

MCM用氮化铝共烧多层陶瓷基板的研究

通过实验优化AlN(氮化铝)瓷料配方及排胶工艺,对共烧W(钨)导体浆料性能及AlN多层基板的高温共烧工艺进行了研究,并对AlN多层基板的界面进行了扫描电镜分析。采用AlN流延生瓷片与W高温共烧的方法,成功地制备出了高热导率的AlN多层陶瓷基板,其热导率为190 W/(m·K),线膨胀系数为4.6106℃1(RT~400℃),布线层数9层,W导体方阻为9.8 m,翘曲度为0.01 mm/50 mm,完全满足高功率MCM的使用要求。     

SIMOX硅片埋氧层垂直方向热导率的测量

提出了一种简单、有效而且准确的测量SOI硅片埋氧层垂直方向热导率的方法,并采用这种方法测量了用SIMOX工艺制作的SOI硅片的埋氧层垂直方向的热导率.测量结果显示至少在5 5nm以上的尺度上对于SIMOX硅片的埋氧层垂直方向经典的热导率定义仍然成立,且为一明显小于普通二氧化硅的热导率(1 4W/mK)的常数1 0 6W/mK .测量中发现硅/二氧化硅边界存在边界热阻,并测量了该数值.结果表明,边界热阻在SOI器件尤其是薄二氧化硅背栅的双栅器件热阻的计算中不可忽略.     

Nanoscale Thermal Transport and Microrefrigerators on a Chip

In this paper we review recent advances in nanoscale thermal and thermoelectric transport with an emphasis on the impact on integrated circuit (IC) thermal management. We will first review thermal conductivity of low-dimensional solids. Experimental results have shown that phonon surface and interface scattering can lower thermal conductivity of silicon thin films and nanowires in the sub-100-nm range by a factor of two to five. Carbon nanotubes are promising candidates as thermal vias and thermal interface materials due to their inherently high thermal conductivities of thousands of W/mK and high mechanical strength. We then concentrate on the fundamental interaction between heat and electricity, i.e., thermoelectric effects, and how nanostructures are used to modify this interaction. We will review recent experimental and theoretical results on superlattice and quantum dot thermoelectrics as well as solid-state thermionic thin-film devices with embedded metallic nanoparticles. Heat and current spreading in the three-dimensional electrode configuration, allow removal of high-power hot spots in IC chips. Several III-V and silicon heterostructure integrated thermionic (HIT) microcoolers have been fabricated and characterized. They have achieved cooling up to 7 /spl deg/C at 100 /spl deg/C ambient temperature with devices on the order of 50 /spl mu/m in diameter. The cooling power density was also characterized using integrated thin-film heaters; values ranging from 100 to 680 W/cm/sup 2/ were measured. Response time on the order of 20-40 ms has been demonstrated. Calculations show that with an improvement in material properties, hot spots tens of micrometers in diameter with heat fluxes in excess of 1000 W/cm/sup 2/ could be cooled down by 20 /spl deg/C-30 /spl deg/C. Finally we will review some of the more exotic techniques such as thermotunneling and analyze their potential application to chip cooling.     

Thermal characterization of embedded electronic features by an integrated system of CCD thermography and self-adaptive numerical modeling

This work provides a practical application of a coupled experimental-computational system devised for the full characterization of the thermal behavior of complex three-dimensional active submicron electronic devices. A thermoreflectance thermography (TRTG) technique is used to non-invasively measure the 2D surface temperature field of an activated device, with submicron spatial resolution. The measured planar temperature distribution field is then used as input for an ultra-fast inverse computational solution to derive the three-dimensional temperature distribution throughout the device. For the purposes of this investigation, test micro-heater devices were constructed on epitaxial layers of natural (Si) and isotopically pure (Si²⁸) silicon. Then, all devices were activated and measured with the TRTG technique. In order to demonstrate the coupled experimental-computational system, the measured temperature fields of the samples whose thermal properties are known (Si) were used to extract critical physical parameters (the oxide layer thickness and the effective heater length). Then, since the devices with unknown thermal properties (Si²⁸) share the same construction with the Si devices, the extracted parameters were used together with the measured planar temperature fields to derive the thermal conductivity of Si²⁸. The extracted oxide layer thickness and thermal conductivity of Si²⁸ compared very closely to values obtained by other independent direct methods.     

Optical properties of InGaAs/InGaAlAs quantum wells for the 1520–1580 nm spectral range

The optical properties of elastically strained semiconductor heterostructures with InGaAs/InGaAlAs quantum wells (QWs), intended for use in the formation of the active region of lasers emitting in the spectral range 1520–1580 nm, are studied. Active regions with varied lattice mismatch between the InGaAs QWs and the InP substrate are fabricated by molecular beam epitaxy. The maximum lattice mismatch for the InGaAs QWs is +2%. The optical properties of the elastically strained InGaAlAs/InGaAs/InP heterostructures are studied by the photoluminescence method in the temperature range from 20 to 140°C at various power densities of the excitation laser. Investigation of the optical properties of InGaAlAs/InGaAs/InP experimental samples confirms the feasibility of using the developed elastically strained heterostructures for the fabrication of active regions for laser diodes with high temperature stability.     

Thermodisplacement imaging of current in thin-film circuits

We present initial results on a novel scheme for measuring current distribution in thin-film circuits. When an AC current passes through a thin-film circuit, the resulting periodic heating sets up a dynamic surface displacement which can be detected using a phase-sensitive laser probe. Results indicate that the present system has a sensitivity of 4 × 10?3 ? for displacement and 2.7 × 10?2°C for temperature in a 1 Hz bandwidth. The spatial resolution can be as small as an optical wavelength and is currently limited to 2 ?m by the optics used. As the surface displacement amplitude depends on the thermal properties of the substrate material, the technique can also be used to detect defects beneath the metallisation in integrated-circuit structures.     

Thermal characteristics of submicron vias studied by scanning Jouleexpansion microscopy

Thermal characteristics of submicron vias strongly impact reliability of multilevel VLSI interconnects. The magnitude and spatial distribution of the temperature rise around a via are important to accurately estimate interconnect lifetime under electromigration (EM), which is temperature dependent. Localized temperature rise can cause stress gradients inside the via structures and can also lead to thermal failures under high current stress conditions, such as electrostatic discharge (ESD) events. This letter reports the first use of a novel thermometry technique, scanning Joule expansion microscopy, to study the steady state and dynamic thermal behavior of small geometry vias under sinusoidal and pulsed current stress. Measurement of the spatial distribution of temperature rise around a submicron via is reported with sub-0.1 μm resolution, along with other thermal characteristics including the thermal time constant     

Thermal Conductivity Measurement of Low-k Dielectric Films: Effect of Porosity and Density

The thermal conductivity of low-dielectric-constant (low-k) SiOC:H and SiC:H thin films has been measured as a function of porosity using a heat transfer model based on a microfin geometry and infrared thermometry. Microscale specimens were patterned from blanket films, released from the substrate, and subsequently integrated with the experimental setup. Results show that the thermal conductivity of a dense specimen, 0.7 W/mK, can be reduced to as low as 0.1 W/mK by introducing 30% porosity into it. The measured thermal conductivity shows a nonlinear decrease with increasing porosity that approximately follows the porosity-weighted simple medium model for porous materials. Neither the differential effective medium nor the coherent potential model could predict the density dependence of the thermal conductivity. These results suggest that more careful consideration is required for application of generic porous materials modeling to low-k dielectrics.     

显微拉曼光谱法对多孔硅热导率的研究

多孔硅优良的热学性能使其成为MEMS领域新兴的热绝缘材料。文中采用一种简便且无损的多孔硅热导率测量技术——显微拉曼光谱技术对电化学腐蚀法制备的不同孔隙率和厚度的多孔硅试样热导率进行了测量,结果表明在多孔硅的拉曼谱峰位置与其温度间存在线性对应关系。在所有样品中,厚度为110μm空隙率为65%的多孔硅显示出最好的绝热性能,其热导率为0.624W/mK。且随多孔硅孔隙率和厚度的减小,其热导率有迅速增加的趋势(厚度和孔隙率为9μm和40%时,其热导率升至25.32W/mK)。     

Measurement of Thermal Conductivity Using Steady-State Isothermal Conditions and Validation by Comparison with Thermoelectric Device Performance

A new technique for measuring thermal conductivity with significantly improved accuracy is presented. By using the Peltier effect to counterbalance an imposed temperature difference, a completely isothermal, steady-state condition can be obtained across a sample. In this condition, extraneous parasitic heat flows that would otherwise cause error can be eliminated entirely. The technique is used to determine the thermal conductivity of p-type and n-type samples of (Bi,Sb)₂(Te,Se)₃ materials, and thermal conductivity values of 1.47?W/m?K and 1.48?W/m?K are obtained respectively. To validate this technique, those samples were assembled into a Peltier cooling device. The agreement between the Seebeck coefficient measured individually and from the assembled device were within 0.5%, and the corresponding thermal conductivity was consistent with the individual measurements with less than 2% error.     

Thermal characteristics of InP, InAlAs, and AlGaAsSb metamorphic buffer layers used in In0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistors grown on GaAs substrates

In_0.52Al_0.48As/In_0.53Ga_0.47As heterojunction bipolar transistors (HBTs) were grown metamorphically on GaAs substrates by molecular beam epitaxy. In these growths, InAlAs, AlGaAsSb, and InP metamorphic buffer layers were investigated. The InAlAs and AlGaAsSb buffer layers had linear compositional grading while the InP buffer layer used direct binary deposition. The transistors grown on these three layers showed similar characteristics. Bulk thermal conductivities of 10.5, 8.4, and 16.1 W/m K were measured for the InAlAs, AlGaAsSb, and InP buffer layers, as compared to the 69 W/m K bulk thermal conductivity of bulk InP. Calculations of the resulting HBT junction temperature strongly suggest that InP metamorphic buffer layers should be employed for metamorphic HBTs operating at high power densities.     

Thermal Conductivity of an Individual Bismuth Nanowire Covered with a Quartz Template Using a 3-Omega Technique

Thermal conductivity is estimated using a 3-omega technique for an individual bismuth nanowire (diameter: 595 nm, length: 2.24 mm) covered with a quartz template. To evaluate the thermal conductivity of the nanowire, we propose a simple model of thermal and electrical transfer functions for the nanowire that assumes a linear combination of that of the line heater on the substrate and a suspended wire. Since the out-of-phase third-harmonic component of the electrical transfer function depends only on the thermal diffusivity of the nanowire, measurement of the frequency dependence is carried out. A distinct extreme value of the frequency has been observed, as expected, and estimation of the thermal conductivity of the nanowire covered with the quartz is attempted. Although the thermal conductivity at 300 K is 9.8 W/mK, somewhat smaller than that of bulk bismuth, the temperature dependence of the thermal conductivity is quite different from that of bulk bismuth, and decreased linearly with decreasing temperature. In particular, this shows that the thermal conductivity obtained is suppressed in the low-temperature region by phonon confinement in the nanowire.     

Development of a Measurement Method for the Thermal Conductivity of a Thick Film Prepared by a Screen-Printing Technique

We propose a method that allows us to evaluate the thermal conductivity of a conductive material that has thickness on the order of microns. The key feature of the proposed method is use of a complete thermoelectric device with electrodes and a substrate, while conventional methods measure the temperature gradient of thermoelectric materials directly without electrodes. The measured thermal conductivity of a ZnSb film annealed at 380°C in N₂ ambient for 16?min to 26?min is 1.2?W/m?K to 1.4?W/m?K. The measurement shows that thermoelectric film prepared by a screen-printing technique has lower thermal conductivity than bulk material (2.2?W/m?K to 2.4?W/m?K) because the screen-printing technique generates high porosity in the film. The lower measured thermal conductivity of the porous films compared with bulk material supports the reliability of the proposed measurement method.     

Efficient electrooptic modulator in InGaAlAs/InP optical waveguides

A single heterostructure InGaAlAs/InP phase modulator utilizing the quadratic electrooptic effect (QEO) is reported for the first time. The calculated value of the QEO coefficient from the measurements is 3.7×10^-19 m²/V² at 80 meV below the band edge. In addition, the linear electrooptic effect (LEO) coefficient is estimated to be 1.2×10^-12 m/V, which is comparable to that of GaAs. The propagation loss of a single mode ridge waveguide is in the range of 1.5-1.7 dB/cm, which is better than the previously reported value in this material system. The measured single mode phase shifts are 5.5 and 2.8°/V mm for TE and TM polarizations, respectively. These values are the largest reported so far in an InGaAlAs system