Investigation of the thermal properties of thin solid materials at different temperature levels using a set of microresistors

The measurement of thermal properties of solid materials at different temperatures above ambient is investigated using a set of microresistors. Samples consisted of suspended films with sets of long, parallel resistive wires deposited on their surfaces. One resistive wire was heated by an alternating current. Surface temperature changes in DC and AC regimes were then detected by measuring the change in electrical resistance of the other wires deposited on the surface. The length of wires was chosen so that they may be assumed isothermal and such that heat diffusion acts perpendicularly to their axes. By measuring the dependence of the surface alternating temperature oscillation on the modulation frequency f and on the separation between the heating wire and the probing wires, the thermal diffusivity of the sample was determined. Through adjustment of the alternating current amplitude in the source wire, the temperature at which the thermal diffusivity of the sample was evaluated was finely controlled. For the validation of the method, pure silicon samples were first studied. An experimental bench was set up and resistive source and probes were experimentally characterized. Results obtained from ambient temperature to 500 K for pure silicon are in accordance with reference data found in the scientific literature.     

Modelling and IR measurement of the electronic substrate thermal conductivity

The temperature distribution on a ceramic substrate with a small heating element in the middle has been measured by infrared thermography. By comparing the experimental data with a theoretical analysis, the thermal conductivity could be easily obtained.     

Photoacoustic study of optical and thermal properties of alloyed CdTexS1−x nanocrystals

Photoacoustic (PA) technique has been applied to study the optical and thermal properties of the alloyed CdTe_xS_1−x (nanocrystals (NCs) with different (Te/(S+Te)) molar ratio (x=0, 0.2, 0.4, 0.6, 0.8 and 1). Increasing x value causes clearly observed red shift of the corresponding exciton peak in PA spectra. The same spectra were compared to those obtained by a regular UV–Vis. absorption. The effective mass approximation (EMA) model was applied to determine the size of the NCs. The calculated sizes of the alloyed NCs are in a good agreement with the directly measured values obtained using high resolution transmission electron microscopy (HRTEM). The values of thermal diffusivity and thermal conductivity obtained using PA technique show at least an order of magnitude larger than that of the bulk values.     

Robust snubberless soft-switching power converter using SiC power MOSFETs and bespoke thermal design

A number of harsh-environment high-reliability applications are undergoing substantial electrification. The converters operating in such systems need to be designed to meet both stringent performance and reliability requirements. Semiconductor devices are central elements of power converters and key enablers of performance and reliability. This paper focuses on a DC–DC converter for novel avionic applications and considers both new semiconductor technologies and the application of design techniques to ensure, at the same time, that robustness is maximized and stress levels minimized. In this respect close attention is paid to the thermal management and an approach for the heatsink design aided by finite element modelling is shown.     

The interferometric mirage effect method: The determination of the thermal diffusivity of CdMnTe

A Michelson interferometer was used as a precise detector in the Mirage effect configuration in order to determine the thermal diffusivity of the diluted magnetic semiconductor Cd_1−xMn_xTe, in the concentration range 0<x<0.6 at room temperature. This zinc-blende ternary alloy exhibits an almost linear behavior of the thermal diffusivity as a function of Mn concentration. This trend is similar to that of the energy gap against Mn concentration, which increases linearly as the nominal x value increases. The latter result was tested by electrolytic electroreflectance measurements.     

碳化硅材料发光特性研究进展

碳化硅作为一种优秀的微电子材料,在高频、高温、大功率、强辐射环境中颇具应用潜力。然而由于其间接带隙的特点,碳化硅LED不能像氮化镓、磷化镓LED那样有效发光,因此人们竞相研究能提高碳化硅发光效率的方法,其中包括非晶碳化硅、多孔单晶碳化硅、用CVD方法制备的纳米碳化硅和用离子注入方法制备的多孔碳化硅。在最近几年,这些研究已取得巨大进展,从而使其成为适用于发展中的OEIC技术的颇具潜力的材料。     

液相烧结SiC陶瓷性能的研究

以Al2O3、Y2O3(质量比为2:3)为烧结助剂,在氮气氛或氩气氛中、1900～1970℃、30 MPa下热压制备SiC陶瓷.根据Archimedes原理测量烧结体的体积密度和显气孔率;采用XRD、SEM(EDS)及瞬态热导率测试仪分别对材料的物相、显微结构和热导率进行表征.研究了烧结温度、烧结气氛和烧结助剂含量对材料烧结性能和热导率的影响.结果表明,当烧结助剂质量分数为10%,获得SiC致密体(气孔率＜0.30%),热导率高达182.50 W/(m·K);随着烧结助剂的质量分数降至6%,材料的致密度和热导率皆明显下降;在氩气氛中SiC与Al2O3、Y2O3具有更好的润湿性.     

Investigation of the thermal performance of micro-whisker structured silicon heat spreaders for power devices

The driving forces of developments in power electronics are the continuing miniaturization and enhancement of power densities. New packaging concepts are required allowing the dissipation of a power loss density of up to several hundred W/cm² at operation temperatures as low as possible. A promising attempt to decrease the thermal resistance to the ambient is the development of silicon substrates structured with microwhiskers perpendicular to its surface. An industrial application of this new heat spreader technology in power electronic modules makes necessary the specification of the substrate properties. In this work, a new method for determination of thermal qualities based on laser heating of the heat spreader, surface temperature measurement by thermovision, and dynamic reverse modeling is described. For numerical determination of the thermal characteristics, the measured data are evaluated with the help of a thermal model of the heat spreaders under various boundary conditions. The respective temperature distributions are calculated with a new simulation tool using an alternating-direction implicit algorithm (ADI-method). Results obtained from heat spreaders with microwhisker treatment are compared with those from reference samples with a polished surface. Based on these results a view on future applications for power electronics assemblies are derived.     

无压浸渗SiC/A1的电镀和应用

无压浸渗SiC／A1新材料集高导热性、低热膨胀系数(并在一定范围内可调)、轻量化几大优势于一身,导热性可与W-Cu相当,热膨胀系数可与Si、GaAs等芯片,A12O3,AIN,BeO等瓷件相匹配,比重则不到W-Cu的20％,且可加工性强,成本低,未来可望在封装领域大量替代W-Cu、Mo-Cu等材料。实验证明,此复合材料前处理用有机溶剂和中性化学除油,HNO3,HF混合酸液浸蚀后浸锌,然后化学镀镍,经适当热处理后镀镍、镀金,完全能满足后道封装工艺要求,器件性能经考核完全符合GJB33A-97和GJB128A-97要求。     

The influence of minor titanium addition on thermal properties of diamond/copper composites via in situ reactive sintering

A minor amount of titanium addition is proposed to improve interfacial bonding between diamond particles and copper matrix for diamond/copper composites. The volume fractions of diamond and minor titanium in the sintering process are optimized. The microstructures, thermal properties, interface reaction production, and the effects of minor amount of titanium on the properties of the composites are investigated. The results show that the interfacial bonding of the composites could be strengthened by changing the volume fraction of titanium and diamond. The 45 vol%-diamond/copper composites with 3 vol% titanium at 945 °C for 5 min exhibits thermal conductivity as high as 670 W/(m K), which is 90% of the theoretical prediction value. High thermal conductivity is achieved by forming the titanium carbide (TiC) and intermetallic compounds (Cu₃Ti₂) at the diamond/copper interface to obtain a good interface.     

SiC纳米晶/非晶复合纳米纤维的制备和场发射性能研究

采用阵列碳纳米管作为模板制备出了SiC纳米晶/非晶复合纳米纤维(以下称SiC纳米纤维),并对其晶体结构、形貌和精细结构使用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和高分辨透射电子显微镜(HR-TEM)进行了表征.比较了SiC纳米纤维和碳纳米管模板的场发射性能,研究了SiC纳米纤维直径的变化对其绝对场增强因子的影响.结果表明:SiC纳米晶/非晶复合纳米纤维具有特殊的"树状"结构,顶端及"树枝"中分布着大量的SiC纳米晶粒.SiC纳米晶粒以及特殊的分支结构增强了SiC纳米纤维的场发射性能,开启场强低至1.1 V/μm,仅为相同直径碳纳米管模板的1/2.随着SiC纳米纤维直径的减小,绝对场增强因子β0呈明显增大趋势.     

掺氮6H—SiC材料电学性质温度依赖关系测量与分析

测量了７－１０００Ｋ的掺氮６Ｈ－ＳｉＣ材料基本电学性质，用电子性方程对载流子浓度温度倒数关系曲线进行拟合，利用化全物半导体散射机构计算了行 率。数据拟合分析得到样品的掺杂浓度、补偿浓度、杂质激光活能和载波子有效质量。分析结果表明，控制杂质能级和表观杂质激活能由补偿度和杂质浓度决定。掺氮６Ｈ－ＳｉＣ材料预期有０．０８ｅＶ、０．１２ｅＶ两个能级，当补偿杂质浓度大于较小能级浓度时，材料将由较高的能级控制     

Co掺杂SiC稀磁半导体薄膜的磁与电阻率特性

采用射频磁控溅射法制备了不同Co掺杂浓度的SiC薄膜。X射线衍射（XRD）、X射线光电子能谱（XPS）、Hall以及电阻率-温度（-ρT）曲线测试结果表明,Co掺杂SiC薄膜具有4H-SiC（100）晶体结构和典型的半导体导电特征,未发现Co金属团簇以及其它CoSi第二相化合物生成,显示了Co原子以替位掺杂的形式进入了...     

窗片介质材料对输出窗功率容量的影响

本文介绍了研制大功率速调管的过程中输出窗的失效现象,比较了两种窗片介质材料氧化铍与氧化铝的性能特点;通过实际制管后的热测数据证明,相同条件下窗片材料氧化铍比氧化铝对输出窗的功率容量的提高更显著,在研制大功率速调管过程中窗片材料氧化铍是比氧化铝更为优良的介质材料.     

Structures and physical properties of sputtered amorphous SiC films

Optical and electrical properties have been measured for amorphous SiC films prepared by rf sputtering in a pure Ar atmosphere with a sintered 6H-SiC target. The absorption edge E₀ determined from the relation of αhΝ = B(hΝ-E₀)² ranged from 1.45 to 1.80 eV depending on the film thickness and the substrate temperature. The room temperature electrical conductivity is in the range of 5.4×10⁻¹¹ and 1.4×10⁻⁵ Ω⁻¹cm⁻¹. The absorption edge decreases and the conductivity increases with increasing film thickness. The absorption edge shifts to shorter wavelengths (blue shift) and the conductivity decreases during annealing below 400‡C for 60 min, whereas the absorption edge shifts to the longer wavelength side (red shift) and the conductivity increases during annealing at 800‡C It is proposed that the two annealing processes cause structural changes in amorphous SiC films, one of which involves removal of defects or voids while the other involves rearrangement or rebonding of the component atoms.     

Characterization of the thermal conductivity of insulating thin films by scanning thermal microscopy

This paper reports on the abilities of a Scanning Thermal Microscopy (SThM) method to characterize the thermal conductivity of insulating materials and thin films used in microelectronics and microsystems. It gives a review of the previous works on the subject and gives new results allowing showing the performance of a new method proposed for reducing the thermal conductivity of meso-porous silicon by swift heavy ion irradiation. Meso-porous silicon samples were prepared by anodisation of silicon wafers and underwent irradiation by 845 MeV ²⁰⁸Pb ions, with fluences of 4×10¹¹ and 7×10¹¹ cm⁻². Thermal measurements show that irradiation reduced thermal conductivity by a factor of up to 2.     

In-situ analysis of thermal properties of polymer composites by embedded LED temperature sensor

Real time and accurate measurement of thermal conductivity of polymer composites with thermal conductive fillers challenges researchers in industrial application. Here, we present an in-situ measurement approach by embedding a LED or diode as a combined heat source and temperature sensor into the filled polymer and using the well-established transient measuring method based on forward voltage variation to determine the temperature response of the sensor in polymer. Numerical model fitting is applied to estimate the thermal conductivity of the polymer composites with different filler/polymer ratios. These findings are compared with other thermal conductivity test methods such as the laser flash method and the Modular Differential Scanning Calorimeter (MDSC). The proposed approach provides a quick way of measuring the thermal conductivity in relatively thin polymer composites and agrees well with the MDSC method. Another advantage is that it can work with the real samples made for the application in mind, so its results can be used directly.     

键合界面对面发射激光器的光、热性质影响

分析了采用双面键合长波长面发射激光器时,键合界面光吸收系数和电、热导率的变化对器件的光、热性质的影响。对于1λ光学腔的面发射激光器,键合界面吸收系数对器件光学性能影响较大,而对于1.5λ光学腔的面发射激光器,其光学性能基本不受键合界面吸收系数的影响。由有限元方法对面发射激光器的温度分布计算结果可知,当键合界面电、热导率小于GaAs电、热导率的1%时,激光器有源层的温度会有较大的上升。     

Three-dimensional modeling of the heat flow into a GaAs substrate. Influence of thermal phenomena on the RF behavior of power HBTs and technological optimization

Using three-dimensional modeling of the heat flow into the substrate, and taking into account the variation of thermal conductivity with temperature, we study the sensitivity of the thermal resistance R_TH to parameters such as the substrate thickness, its nature (GaAs, Si, AlN or diamond), the topology of the power source (length and width) or even the power density. Thus, we show that the transfer of active GaAs layers onto a host substrate with a higher thermal conductivity such as Si, AlN or diamond is of greater interest than the thinning of the substrate.We developed an accurate electrothermal model for the AlGaAs/GaAs heterojunction bipolar transistor (HBT) allowing prediction of the static and mainly dynamic (RF) behavior at a high signal operating mode. We show that if the HBT layers are transferred onto a diamond substrate, a 50% gain in RF power can be expected at 10 GHz.Finally, we present the technological solutions investigated for the transfer and the heteroassembly of HBT active layers on substrates better suited for thermal dissipation.     

Influence of boron doping on the properties of amorphous and microcrystalline SiC films prepared using ECR-CVD

Hydrogenated silicon carbide films (SiC:H) were deposited using the electron cyclotron resonance plasma chemical vapor deposition (ECR-CVD) method from a mixture of methane, silane, and hydrogen, with diborane as the doping gas. The effect of changes in the percentage of the diborane to reactant gas mixture on the deposition rate, optical bandgap, and photoconductivity were investigated. There is evidence from Raman scattering analysis to show that films deposited at a low microwave power of 150 W were all amorphous and the bandgap decreases as the diborane level is increased whereas films deposited at a high microwave power of 800 W at low diborane levels are highly photoconductive and contain microcrystalline silicon inclusions. These films become amorphous as the diborane level is increased, while the optical bandgap remains relatively unaffected throughout the entire range of diborane levels investigated. The effect of the microwave power was also investigated. The conductivity increases rapidly to a maximum, followed by rapid reduction at high microwave powers. Raman scattering analysis showed evidence of the formation and increase of microcrystalline silicon inclusions and diamond-like components in the films, the former of which could account for the rapid increase and the latter the subsequent decrease in the conductivity.