【作者】 谢扩军；

【导师】 刘盛纲；

【作者基本信息】 电子科技大学 ， 物理电子学， 2008， 博士

【摘要】 微波功率模块（MPM）是一种新型微波功率组件。它使用高效小型化行波管（TWT）放大器作为功率器件，使用宽带低噪声固态放大器（SSA）驱动行波管，再与行波管电子功率调节器（EPC）集成到一个小型轻重量的封装内成为一个相对独立功能器件，MPM是当今最具发展前景的电真空器件之一。MPM技术关键之一是行波管小型化和微波多芯片模块（MMCM）的高密度集成，TWT小型化要求行波管体积很小，有很高效率和良好的散热能力，散热性能不仅是决定行波管平均输出功率的主要因素，也是直接影响着微波管工作的稳定性与可靠性的主要因素，使用高导热率的夹持材料和采用新型阴极是改进微波器件性能的重要手段之一。金刚石由于具有最高的热导率，最高的机械强度和硬度，低的介电常数和低的介电损耗，极强的抗热震性和抗裂性等优良性能，低功函数，极低的阈值电场，大电流密度、大面积范围内的均匀电子发射以及热化学性质不活泼等。将金刚石应用于TWT慢波结构的夹持杆、场发射阴极（FEA）及MMCM的基板或中间层中，应该对TWT的散热性能的改善，对MPM的小型化和MMCM的高密度集成有良好的作用，对相关的关键技术开展研究具有非常重要的现实意义。本文的主要工作有：1、本课题首先研究了用化学气相沉积（CVD）金刚石厚膜制作宽带大功率行波管的夹持杆取代传统有毒氧化铍瓷杆，改善宽带大功率行波管的散热性能，开展了相关的理论和实验研究，组装了表面沉积金刚石的Al₂O₃夹持杆、BeO夹持杆、金刚石夹持杆的慢波组件，测试了相关的热学和高频电学性能，并进行了对比分析，金刚石夹持杆组装的行波管慢波组件的传热速率明显大于BeO夹持杆组件的传热速率，大约是它的3倍；在此基础上组装了一只金刚石夹持杆慢波结构的C波段行波管整管，对整管进行了冷测和热测，冷测各项指标全部合格，热测整管在4．0～8．0GHz带宽内得到输出功率95W，增益35dB；然后对所用的齿型翼片加载螺旋慢波结构的色散特性了进行理论推导，并通过MAFIA软件和乌克兰2．5D大信号程序软件包Tau对整管进行计算机模拟，得出了其色散、耦合阻抗、增益和效率等特性曲线，并对其电子注相位轨迹和电子注轴向轨迹情况进行了模拟并与实验测试结果进行了对比分析。2、开展了使用金刚石FEA冷阴极代替普通电真空器件中的热阴极的基础性研究，场发射电子的开启电场和更大的发射电流以及场致发射的稳定性和可靠性是场致发射的主要指标，本文在采用MPCVD方法在硅、铜基上沉积了金刚石薄膜，经过多次实验发现采用在铜基上沉积未成膜、晶粒分散分布的金刚石微小颗粒作为发射体可以有效地降低场发射电子的开启电场。本文所制备的金刚石发射体的（宏观）开启场小于2V/μm（对应的发射电流＞10μA，发射电流密度＞0．5mA／cm²）。最大发射电流＞2．08mA，最大发射电流密度＞100mA／cm²，相应的电场强度为E=3．5V／μm。本文所得金刚石薄膜场发射体，开启电压较低的原因在于金刚石薄膜可以看成由很多微小的金刚石发射体微尖锥组成，当颗粒间的间距较大时，发射体尖顶部的场增强因子更大，又因为采用了导电性能优异的金属—无氧铜作为发射基底，有利于在金刚石与基底间形成欧姆接触，所以有利于电子的发射。3、随着微波功率模块（MPM）向大功率、小型化、高可靠及毫米波发展使得其微波多芯片模块（MMCM）也由2D向3D发展，高密度的组装使其散热性能成为主要瓶颈，金刚石具有最高的导热率和非常高的电阻率，且热胀系数与硅匹配，因此吸引人们用它来制作高性能、大功率的薄膜多层基板。本文开展了MPM中金刚石基板MMCM热分析研究，建立了三维多芯片组件的封装模型，分析了多芯片组件的温度场分布，分析了金刚石材料作为中间导热层和基板对组件温度的影响，并分析了散热条件对温度的影响；建立了二维和三维的模型分析了金刚石基板与硅芯片界面间的热应力分布，分析了封装的几何结构对热应力的影响，结果表明：由于金刚石材料具有很高的导热率，不论它作为中间导热层或是基板，都可以显著降低芯片的最高结温，改善组件的散热性能，可做为一种理想的热沉材料，为金刚石在多芯片组件中应用提供了一些参考。总之，CVD金刚石无论是应用于带大功率行波管的夹持杆，FEA冷阴极，还是大功率MPM中的MMCM，都具有非常优良的性能。目前虽然离实际应用还有较大距离，还不成熟，但具有极大的潜力。更多还原

【Abstract】 As a new kind of microwave power modules,MPM is a high density compactmicrowave amplifier which includes a mini-traveling wave tube （TWT）,a solid-statedriver amplifier （SSA）,and a high density electronic power conditioner （EPC）.MPM isa very important part in a next-generation electronic military system,and the millimeterwave power module （MMPM） will be well developed.For the development of widerban d width,high efficiency,high power,reliability and long lifetime of microwavetube,it is important to improve the thermal performance of the mireowave tube.Thethermal management under high temperature affects the reliability of tube and poor heatmanapement will decrease the output power and lifetime and limit the development ofhigh power and small size tube.Using an ideal dielectric material with high thermalconductivity is an important means to improve the performance of the microwave tube.The ideal dielectric materials possess low dielectric losses,high mechanical strength,high thermal conductivity,low thermal expansion,and a low dielectric constant.It is recognized diamond is one of the ideal dielectric materials.It should be usedin the wide-band high power TWT and MMCM to improve the thermal managementgreatly.In the thesis,the thermal dissipation of CVD diamond for vacuum electronicdevices （such as TWT helix rod,power windows and MMCM） has been analyzed.The main results are as follows:1.The project supported by government is to develop a CVD diamond thick filmand possible technology which can be taken over the traditional BeO rod and used in thewide-band high power TWT to improve the thermal management greatly.Havingexperienced over three years’ efforts,we have successfully found a good way tomanufacture the right rectangular diamond rod by CVD,special Laser cutting andpolishing technology.After material tests and evaluation,parts assembly and tests andfinal TWT assembly and tests,we have got the first good results as follows:Thermalconductivity:κ＞12 W/cm.℃,ten times better than BeO Rod;Dielectrical constant:ε=4.75～5.0;RF loss:tgδ＜1×10^-2;Resistivity:ρ＞10¹³Ω/cm;Slow wave partsassembly thermal test:3.0 times better than BeO.The first TWT with diamond rods has passed all cold tests and has got following hot test results:Δf=4～8GHz,P_out=95W,G=35dB.2.Diamond and diamond-like films are excellent field emission materials.Theyare strong candidates for field emission micro-cathodes applied in microwave tubes,because of their low or even negative electron affinity and chemical inertness.Undopeddiamond film on Cu and Si has been successfully fabricated using microwave plasmachemical vapor deposition （MPCVD） technology.Electron emission testing indicateslow turn-on voltages.Current densities from 0.5mA/cm2 to 100mA/cm2 had beenobtained for applied fields of 2-3.5V/μm.The bright light spot had been observed,while emitted electron bombardment fluorescent screen.The application is immaturenow,but their potential is very big.3.CVD diamond films is one of the ideal sink material of 3D-MCM,which isapplicable to the next generation high power MPM and high speed computers.Thisproject has innovative contribution in the following aspects:（1） Discuss the currentstatus of diamond films applied in microwave tubes.Study the merit,operating,physicaldesign and application possibility for microwave power modules and 3D-MCM.（2）Being based on actual multi-chips module packaging structure a three dimensionalthermal analysis model is built,thermal analysis on multi-chips module is conductedusing diamond substrate and thermal interfacial materials;2D and 3Dchip-adhesive-substrate thermal stress model are built,and interfacial thermal stressdistributions are computed based on different area ratios and thickness ratios ofsubstrate to chip.A stacked MCM model was developed,computational fluiddynamics solution was utilized to proceed the thermal dissipation analysis of thestacked MCM with CVD-diamond substrates,to simulate the heat transfer process andthe temperature distribution of the MCM under forced air-cooling conditions,and theeffects of different factors on the 3D-MCM temperature distribution are investigated,the affecting parameters include thermophysical properties and design structuralproperties.Although CVD diamond is one of the ideal dielectric materials,and high-qualitydiamond films have been used in some microwave tubes,there is still a gap to itscommercial application.更多还原