薄膜导热系数的测量方法及技术

随着微型机电系统及集成电路的发展,器件中大量使用了微米、纳米量级厚度的薄膜,对其导热系数测量的研究有助于器件的设计和热优化工作。综述了当前几种测量薄膜导热系数的主要方法及技术,分析了各自的优点及不足,并对其以后的发展趋势做了简要分析。     

国产石墨薄膜低温导热系数测量

在90-350K温度范围内,设计了1套实验装置,用以测量一种国产石墨薄膜的导热系数.介绍了实验装置的结构和原理,以及相关的数据处理方法.最终利用该装置得出了石墨薄膜导热系数与温度的关系.结果表明,该石墨薄膜在低温下可以作为铜的理想替代材料.     

基于激光热成像的薄膜面向导热系数测试方法

提出一种基于激光热成像的薄膜面向导热系数测试方法。仿真论证了激光加热相较于常规电加热方案的热损失差异;分析了激光加热功率、表面换热系数、测温模型增益系数等关键参数标定问题,并设计了相应的方案。基于15个不同材料或厚度的薄膜和薄片样品进行了实验,测试结果和参考值相对偏差均<6%,其中导热系数<3 W/(m·K)的样品测试误差显著优于常规方法,这表明该方法可有效改善热流环路积分法对低导热薄膜的测试精度。     

NZP陶瓷的导热系数研究

测定了NZP陶瓷中CZP、CM、CMS三种组成的导热系数随温度的变化,计算了三种组成的声子平均自由程,认为复杂的结构与组成是NZP陶瓷导热系数小的主要原因．     

SiO2二维纳米链的导热系数尺寸效应数值模拟

纳米隔热材料具有优良的隔热性能,在高超声速飞行器热防护技术中有着广泛应用前景。针对纳米隔热材料固体构架导热系数的尺寸效应,基于声子辐射传输方程建立了声子导热的二维计算模型,采用离散坐标法进行数值计算,以SiO2二维纳米链为例,对其横向及纵向导热系数尺寸效应进行了数值模拟。模拟结果表明,SiO2纳米隔热材料的二维纳米链导热具有明显尺寸效应,导热系数主要受纳米链直径影响,对直径2～4nm的纳米链,其导热系数比块材的导热系数小15%以上,研究结果对认识纳米隔热材料内固体构架热量传递机理具有一定指导作用。     

基于细观尺度的再生混凝土多相导热系数理论模型

为分析再生混凝土导热系数变化机理,进行了再生混凝土导热系数理论模型研究。在细观尺度上,将再生混凝土看作由新硬化砂浆、天然骨料、界面过渡区、孔隙相组成的四相复合材料。采用等效化方法,建立了界面过渡区导热系数模型并进行了验证,同时定义了等效界面过渡区(NITZ)影响系数η,η与再生混凝土导热系数有显著的线性关系。基于复合材料导热系数计算模型,利用η建立再生混凝土导热系数理论模型,计算结果与测试结果吻合较好,误差小于6%。在此基础上,根据该模型分析了各相组分导热系数、水灰比、骨料取代率、孔隙饱和度等因素对再生混凝土导热系数的影响,揭示了再生混凝土与普通混凝土传热差异,为再生混凝土传热机理的进一步研究提供了理论基础。     

碳纳米管/导热硅脂复合材料的导热性能

为了提高导热硅脂的导热性能,本文研究了一种新型的碳纳米管/导热硅脂复合材料。研究结果表明,酯化处理后的碳纳米管有利于其在导热硅脂中的分散,并由此在导热硅脂中形成一个有效的导热网络,达到提高导热硅脂导热性能的目的。     

非线性弹性薄膜表面效应的尺寸相关性研究

在Mindlin假设的前提下，考虑了几何非线性条件及表面效应的影响，建立了纳米尺度下尺寸相关的板状各向同性弹性薄膜模型；从哈密尔顿变分原理出发，导出了薄膜的控制方程，用公式明确阐述了由表面张力引起的符合经典板理论且与薄膜变形相关的残余膜力和弯矩；通过微小尺寸薄膜弯曲的算例，说明了表面效应与薄膜厚度的相关性，当薄膜厚度等于或者小于其内禀尺度时，表面效应对薄膜厚度表现出很强的敏感性。     

导热系数测试仪校准中压力影响研究

根据防护热板法导热系数测试仪的原理和特点,通过专门的压力实验测试,研究了多孔绝热材料导热系数参比板在不同温度、压力条件下的厚度变化,提出了实际校准中建议采用的压力设定值,在实际校准工作具有一定的参考价值。     

硅掺杂类金刚石薄膜微米尺度摩擦性能研究

采用微米级别的AFM球头探针对硅掺杂类金刚石薄膜进行了摩擦实验。研究了微米尺度下,外加载荷和扫描速率对薄膜摩擦性能的影响。考虑粘附的影响,提出了适用于微观低载荷接触摩擦力表征的修正Amonton公式。分析了摩擦系数与表面形貌粗糙峰之间的关系,根据薄膜表面粗糙峰的分布,建立了微米尺度下球头探针与薄膜表面粗糙峰的等效接触模型,并推导出了摩擦力f关于载荷参数(p)和形貌参数()的函数表达式f(p,),表明单位面积接触粗糙峰密度对摩擦力大小起着主导作用。所建接触模型成功解释了摩擦实验现象产生的原因。     

Temperature-Dependent Thermal Conductivity of Undoped Polycrystalline Silicon Layers

Polycrystalline silicon is used in microelectronic and microelectromechanical devices for which thermal design is important. This work measures the in-plane thermal conductivities of free-standing undoped polycrystalline layers between 20 and 300 K. The layers have a thickness of 1 m, and the measurements are performed using steady-state Joule heating and electrical-resistance thermometry in patterned aluminum microbridges. The layer thermal conductivities are found to depend strongly on the details of the deposition process through the grain size distribution, which is investigated using atomic force microscopy and transmission electron microscopy. The room-temperature thermal conductivity of as-grown polycrystalline silicon is found to be 13.8 W·m^-1·K^-1and that of amorphous recrystallized polycrystalline silicon is 22 W·m^-1·K^-1, which is almost an order of magnitude less than that of single-crystal silicon. The maximum thermal conductivities of both samples occur at higher temperatures than in pure single-crystalline silicon layers of the same thickness. The data are interpreted using the approximate solution to the Boltzmann transport equation in the relaxation time approximation together with Matthiessen's rule. These measurements contribute to the understanding of the relative importance of phonon scattering on grain and layer boundaries in polysilicon films and provide data relevant for the design of micromachined structures.     

Thermal Conductivity Measurement of Thermally-Oxidized SiO<Subscript>2</Subscript> Films on a Silicon Wafer Using a Thermo-Reflectance Technique

This paper describes the development of an advanced method to measure the normal-to-plane thermal conductivity of very-thin insulating films. In this method the metal film layer, which is deposited on thin insulating films, is Joule heated periodically and the ac-temperature response at the center of the metal film surface is measured by a thermo-reflectance technique. The one-dimensional thermal conduction equation of the three-layered system was solved analytically, and a quite simple and accurate approximate equation was derived. In this method, calibration factors of the thermo-reflectance coefficient were determined using the known thermal effusivity of the substrate. The present method was examined for thermally-oxidized SiO₂ films (1000--20 nm thick) on a silicon wafer. The present results of the thermal conductivity agree with those of VAMAS TWA23 within ±10%.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22--27, 2003, Boulder, Colorado, U.S.A.     

Measurements of Thermal Conductivity and Thermal Diffusivity of CVD Diamond

The thermal conductivity of natural, gem-quality diamond, which can be as high as 2500 Wm^–1 K^–1 at 25°C, is the highest of any known material. Synthetic diamond grown by chemical vapor deposition (CVD) of films up to 1 mm thick exhibits generally lower values of but under optimal growth conditions it can rival gem-quality diamond with values up to 2200 Wm^–1 K^–1. However, it is polycrystalline and exhibits a columnar microstructure. Measurements on free-standing CVD diamond, with a thickness in the range 25–400 m, reveal a strong gradient in thermal conductivity as a function of position z from the substrate surface as well as a pronounced anisotropy with respect to z. The temperature dependence of in the range 4 to 400 K has been analyzed to determine the types and numbers of phonon scattering centers as a function of z. The defect structure, and therefore the thermal conductivity, are both correlated with the microstructure. Because of the high conductivity of diamond, these samples are thermally thin. For example, laser flash data for a 25-m-thick diamond sample is expected to be virtually the same as laser flash data for a 1-m-thick fused silica sample. Several of the techniques described here for diamond are therefore applicable to much thinner samples of more ordinary material.     

金刚石膜内晶粒尺寸和取向对其热导率的影响

研究了金刚石膜内晶粒尺寸和取向程度对金刚石膜热导率的影响。通过对衬底表面进行不同研磨时间的处理和适当的工艺条件，采用灯丝热解化学气相沉积（ＨＦＣＶＤ）的方法在单晶硅衬底上形成了具有不同晶粒尺寸和不同程度（１００）晶面取向的金刚石膜，并研究了其热导率。结果表明，由大晶粒和较高程度（１００）晶面取向的晶粒构成的金刚石膜具有热导率特性。     

颗粒填充型复合材料有效导热系数的数值计算方法

基于Monte Carlo随机摆放方法,建立颗粒填充型两相复合材料的随机分布模型.应用有限差分法对导热微分方程进行离散,获得差分格式的热传导方程.将复合材料模型中的微观随机结构单元的数据信息导入计算机,应用循环迭代法对差分格式热传导方程进行求解,实现了对二维稳态导热温度场的数值模拟.采用此方法对可以理论求解的特殊情形进行模拟验证,结果表明其准确可靠.同时模拟了导热增强颗粒含量、颗粒与基体的导热系数比对复合材料有效导热系数的影响,并将模拟结果与Maxwell-Eucken、Bruggeman模型进行了比较,发现该方法的模拟结果在低填充量时与Maxwell-Eucken模型、在高填充量时与Bruggeman模型吻合良好.研究表明所述方法能够较好地计算颗粒填充型复合材料的导热系数.     

A Thermal Conductivity Experimental Method Based on the Peltier Effect

The objective of this work was to test a novel experimental technique to determine the thermal conductivity of low-thermal conductivity materials and tropical foods. The experimental method was based on the Peltier effect and its application to the thermoelectric heat pump. This device became practical recently with the development of semiconductor thermocouple materials. The module assembly used in this work had 127 thermocouples connected in series electrically and in parallel thermally. The heat transfer area of the module was 3.96×3.96 cm². The equipment was calibrated using standard materials of known thermal conductivity: Plexiglas and Bakelite. Then the values were easily computed from a steady-state energy balance equation.     

纳米氧化锆涂层晶粒度与隔热性能的关系

将纳米热障涂层隔热性能与微观组织联系起来并进行定量描述的工作还处于起步阶段,采用纳米ZrO2团聚体粉末在不同的喷涂参数下制备了3种不同的纳米热障涂层,利用扫描电子显微镜、IA-32定量金相分析软件、X射线衍射仪对其进行了观察和分析,并结合非稳态激光脉冲法与差示扫描量热仪测量了涂层的热导率.研究表明:涂层中同时存在柱状组织和纳米级等轴组织,并以柱状组织为主;随着喷涂参数的改变,二者的相对比例发生变化;纳米级等轴组织含量对涂层的平均晶粒度和热导率都有重要影响;随着涂层晶粒度的减小,热导率随之降低.     

Thermal Conductivity Measurements of Thin Amorphous Silicon Films by Scanning Thermal Microscopy

Thermal conductivity measurements of thin amorphous silicon films performed with a micro-thermistance mounted on an atomic force microscope are presented. A specific thermal model is implemented, and an identification procedure is proposed to extract the film contribution from the apparent thermal conductivity. Results show agreement with the literature regarding interface resistance data, but lower thermal conductivity values are obtained.