Finite element simulation of the micromachining of nanosized-silicon-carbide-particle reinforced composite materials based on the cohesive zone model

A finite element method based on the cohesive zone model was used to study the micromachining process of nanosized silicon-carbide-particle(SiCp) reinforced aluminum matrix composites. As a hierarchical multiscale simulation method, the parameters for the cohesive zone model were obtained from the stress-displacement curves of the molecular dynamics simulation. The model considers the random properties of the siliconcarbide-particle distribution and the interface of bonding between the silicon carbide particles and the matrix.The machining mechanics was analyzed according to the chip morphology, stress distribution, cutting temperature, and cutting force. The simulation results revealed that the random distribution of nanosized SiCp causes non-uniform interaction between the tool and the reinforcement particles. This deformation mechanics leads to inhomogeneous stress distribution and irregular cutting force variation.

Forecast of the Luminescent Phenomena of Silicon Rich Oxide Films off Stoichiometry by Means of the Global Reaction Model

The Global Reaction Model describes a set of chemical reactions that can potentially occur during the process of obtaining silicon rich oxide (SRO) films, regardless of the technique used to grow such films which are an outside stoichiometry material. Particularly, chemical reactions that occur during the process of growing of SRO films by LPCVD technique are highlighted in this model. We suggest and evaluate either some types of molecules or resulting nanostructures and we predict theoretically, by applying the density functional theory, the contribution that they may have to the phenomenon of luminescence which is measured in SRO films. Also, we have calculated the opto-electronic properties of SRO films. The suggested model provides enough information required to identify the molecular structures resulting from the presence of defects in SRO films and also those corresponding to charged structures. It is also possible to detect the molecular structures which are modified due to the effect of heat treatment, and identify the presence of different oxidation states inclusive the formation of siloxanes.

The model developed for stress-induced structural phase transformations of micro-crystalline silicon films

The nanoindentations were applied to island-shaped regions with metal-induced Si crystallizations. The experimental stress-strain relationship is obtained from the load-depth profile in order to investigate the critical stresses arising at various phase transitions. The stress and strain values at various indentation depths are applied to determine the Gibbs free energy at various phases. The intersections of the Gibbs free energy lines are used to determine the possible paths of phase transitions arising at various indentation depths. All the critical contact stresses corresponding to the various phase transitions at four annealing temperatures were found to be consistent with the experimental results.

Breakdown voltage model and structure realization of a thin silicon layer with linear variable doping on a silicon on insulator high voltage device with multiple step field plates

Based on the theoretical and experimental investigation of a thin silicon layer（TSL） with linear variable doping（LVD） and further research on the TSL LVD with a multiple step field plate（MSFP）,a breakdown voltage（BV） model is proposed and experimentally verified in this paper.With the two-dimensional Poisson equation of the silicon on insulator（SOI） device,the lateral electric field in drift region of the thin silicon layer is assumed to be constant.For the SOI device with LVD in the thin silicon layer,the dependence of the BV on impurity concentration under the drain is investigated by an enhanced dielectric layer field（ENDIF）,from which the reduced surface field（RESURF） condition is deduced.The drain in the centre of the device has a good self-isolation effect,but the problem of the high voltage interconnection（HVI） line will become serious.The two step field plates including the source field plate and gate field plate can be adopted to shield the HVI adverse effect on the device.Based on this model,the TSL LVD SOI n-channel lateral double-diffused MOSFET（nLDMOS） with MSFP is realized.The experimental breakdown voltage（BV） and specific on-resistance（R on,sp） of the TSL LVD SOI device are 694 V and 21.3 ·mm 2 with a drift region length of 60 μm,buried oxide layer of 3 μm,and silicon layer of 0.15 μm,respectively.

Modeling of a triple reduced surface field silicon-on-insulator lateral double-diffused metal–oxide–semiconductor field-effect transistor with low on-state resistance

An analytical model for a novel triple reduced surface field（RESURF） silicon-on-insulator（SOI） lateral doublediffused metal–oxide–semiconductor（LDMOS） field effect transistor with n-type top（N-top） layer, which can obtain a low on-state resistance, is proposed in this paper. The analytical model for surface potential and electric field distributions of the novel triple RESURF SOI LDMOS is presented by solving the two-dimensional（2D） Poisson＇s equation, which can also be applied to single, double and conventional triple RESURF SOI structures. The breakdown voltage（BV） is formulized to quantify the breakdown characteristic. Besides, the optimal integrated charge of N-top layer（Q_（ntop）） is derived, which can give guidance for doping the N-top layer. All the analytical results are well verified by numerical simulation results,showing the validity of the presented model. Hence, the proposed model can be a good tool for the device designers to provide accurate first-order design schemes and physical insights into the high voltage triple RESURF SOI device with N-top layer.

美日科学城创办的实践及对中国科创中心建设的启示——基于三重螺旋和创新生态系统视角的分析

党的二十大报告中提及:“加快建设世界重要人才中心和创新高地,促进人才区域合理布局和协调发展,着力形成人才国际竞争的比较优势”“以海纳百川的宽阔胸襟借鉴吸收人类一切优秀文明成果,推动建设更加美好的世界。”那么,如何加快建设适应中国式现代化发展进程的人才中心与创新高地?这其中,该有着怎样可能的建设途径?能否更有效借鉴吸收像美日等发达国家在相应人才中心和创新高地建设方面的已有成果经验?鉴于这些考虑,本文先回顾了三重螺旋理论的来源、文献梳理及实践应用,接着回顾了创新生态系统理论的组成要义、作用机理,从而建立了结合三重螺旋理论的创新生态系统模型图。基于此,进而以硅谷、筑波为例,从创新核心层和创新支撑层深入探究这一独特、高效且持续引领创新发展的国外著名科学城建构过程和机理,进一步分析中国科技创新中心建设实践中所存在的一些问题、困境或障碍,并给出了一些相应的引领性建议和可能性借鉴。

计及时变演化特征的硅泡沫垫层非线性黏弹性模型研究

基于黏弹性基本理论,引入材料非线性特征,考虑了材料加载、保载应力松弛历史、老化效应以及黏弹性模型各运动单元退化的差异性,并从两种老化机制出发,获得了老化硅泡沫垫层力学模型以及长时应力松弛硅泡沫垫层接续加载力学模型.模型机理清晰,能够反映材料服役历史信息及其对力学效应的影响.

一种低耦合电容的高压SiC MOSFET驱动隔离电源设计

高压SiC MOSFET更快的电压变化率dv/dt,导致其驱动遭受更严重的共模干扰,而现有高隔离电压驱动电源大多又存在耦合电容高、共模瞬态抗扰度(CMTI)能力弱、转换效率低等问题,因此该文设计一种兼具高隔离电压、高转换效率的低耦合电容驱动隔离电源。首先,基于有源钳位反激变换器,提出一种驱动隔离电源耦合电容等效简化解析模型,并通过仿真、实验验证解析模型可行性;其次,基于该模型分析耦合电容影响因素及其优化方法,为低耦合电容的驱动电源设计提供参考;最后,通过实验评估所提低耦合电容高压SiC MOSFET驱动隔离电源性能。结果表明,该文驱动隔离电源额定转换效率约80%,工频耐压高达18 kV,且耦合电容不足2 pF,CMTI能力强。

硅橡胶压缩力学性能及率相关本构模型

研究了典型超弹性材料硅橡胶压缩力学性能及率相关本构模型.采用Instron万能材料试验机和分离式Hopkinson压杆(SHPB)试验装置对硅橡胶进行了准静态和动态压缩测试,基于测试结果分析了硅橡胶材料在0.001、0.01、0.1、1750、2300和3000 s^(−1)应变率下的力学行为.测试结果表明,硅橡胶在静态载荷下有显著的超弹性特性,动态载荷下表现出明显的应变率效应,弹性模量与应变率比值对数之间存在非线性关系;据此,建立了率相关本构方程来描述硅橡胶在静、动态压缩载荷下的力学行为,与现有模型相比,所建立的本构方程参数仅有5个,在试验应变范围内应力最大误差保持在15%以内,与试验结果有良好一致性.

基于灰色关联分析和机器学习的高炉铁水硅含量预测

高炉铁水硅含量通常被用作表征“炉温”和高炉经济效益的重要指标,建立及时准确的高炉铁水硅含量预报模型,对于高炉稳定生产具有重要意义。本工作考虑时间延迟及灰色关联分析(GRA)并结合主成分分析(PCA)和长短期记忆网络(LSTM)建立了一种新的预测模型。首先,从硅的还原氧化行为角度出发,选出高炉生产中与铁水硅含量相关的操作参数、状态参数和结果参数。其次,通过GRA确定各参数与铁水硅含量的关联度大小,筛选出硅含量的主要影响因素。在此基础上,对国内某3200 m^(3)级高炉一年共计8544组生产数据进行降维处理。模型输入变量由降维得到的13个主成分组成,以铁水硅含量作为输出变量,建立了预测模型。该预测模型具有合理的泛化能力、鲁棒性和准确性。预测结果分析表明,该模型的决定系数(R^(2))为0.9297,均方误差(MSE)和平均绝对误差(MAE)分别为0.0012和0.0254,实现了对高炉铁水硅含量精确预测。

硅橡胶绝缘材料表面剥离力预测模型

选用室温硫化硅橡胶作为修复材料,分别与4种基底黏合制备成剥离试样,通过构建的材料表面剥离力计算数学模型预测了材料间的剥离力理论值,同时通过剥离力测试获取了不同材料间的剥离力实验值。结果表明,所有试样中剥离力理论值与实验值的相对大小关系一致,并且单一试样的剥离力理论值与实验值的绝对偏差均在1 N以下。该数学模型计算结果能很好地反映不同材料间剥离强度的相对强弱。

不同金属镀层单晶硅靶板的冲击受力特性

为了探究金属镀层对单晶硅靶板抗冲击性能的影响,建立了金属/单晶硅复合靶板理论分析模型,分析讨论了单晶硅靶板表面的最大应力与镀层材料动态屈服应力的关系,应用有限元法在LS-DYNA软件中对金属/单晶硅复合靶板进行瞬态动力学计算,得到了不同金属镀层单晶硅靶板冲击受力后的力学响应。根据实验结果总结得到金属镀层对单晶硅靶板冲击受力具有一定的抗冲击效果,能够延迟和减弱出现在靶板正、背面的应力峰值,减小在靶板上产生的应力。

水分侵入高温硫化硅橡胶扩散行为的仿真研究(一):数值建模与计算

硅橡胶复合绝缘子在高湿多雨环境下容易发生劣化,但由于受到实验方法和观测表征技术的限制,难以判断硅橡胶复合材料中水分的来源及侵入路径。借助数值建模与可视化仿真,通过两篇系列论文分别研究液态水和气态水在高温硫化硅橡胶内部的扩散行为,该文是系列论文第一篇。首先,基于Langmuir扩散模型研究水分侵入过程的数值建模方法,结合时域有限差分法和牛顿–拉夫逊法实现精确建模与高效解算。然后,使用MATLAB软件编程,对高温硫化硅橡胶内部的液态水扩散行为开展仿真,实现对自由态水分和结合态水分的解耦,获得液态水侵入过程的时空分布及质量演变规律。通过硅橡胶样品吸水增重实验,验证数值模型和仿真的正确性。最后,研究氢氧化铝和温度两种因素对水分扩散行为的影响,揭示亲水性氢氧化铝填料和温度对水分侵入过程的影响规律。所提出的数值仿真方法可为研究水分侵入复合绝缘子提供新的思路。

纳米Fe_(3)O_(4)增强硅橡胶与铁氧体的界面黏结特性试验研究

目的探究纳米Fe_(3)O_(4)增强硅橡胶与铁氧体的界面黏结特性。方法分别开展准静态拉伸试验、界面法向和切向黏结强度试验。采用超弹性理论,分析纳米Fe_(3)O_(4)增强硅橡胶材料的拉伸行为,采用双线性和指数内聚力模型,分析纳米Fe_(3)O_(4)增强与铁氧体的界面破坏行为。结果通过拉伸试验获得了不同纳米Fe_(3)O_(4)含量的硅橡胶的工程应力应变曲线及两参数Mooney-Rivlin模型,小变形范围的模型误差在1%以内,大变形范围的最大误差为3.8%。通过界面强度试验,获得了不同纳米Fe_(3)O_(4)含量的硅橡胶和铁氧体界面的法向和切向力-位移曲线、黏结强度和界面断裂能,得到了界面法向和切向黏结强度内聚力模型参数。结论随着纳米Fe_(3)O_(4)含量增加,硅橡胶的拉伸强度增加,界面法向黏结强度和断裂能增大,而切向黏结强度和断裂能变化不显著。双线性内聚力模型更适合作为纳米Fe_(3)O_(4)增强硅橡胶与铁氧体的界面黏结强度表征模型,界面法向和切向黏结强度变化规律与实测值的吻合程度更高。

饱和砂土地基中碳化硅能源桩的传热特性测试与分析

采用标准试块测试与模型试验,对碳化硅能源桩的传热特性进行研究。通过桩基混凝土试块导热系数和力学性能测试,确定碳化硅能源桩的桩身材料配合比;通过饱和砂土地基中能源桩高温释热工况模型试验,分析饱和砂土地基中碳化硅能源桩的传热性能以及轴向和径向温度分布及变化规律。结果表明:碳化硅代砂率达到16.0%时,桩基混凝土试块的导热系数、抗压强度以及抗折强度会分别提升64.1%、19.9%和11.4%,该代砂率下的碳化硅能源桩桩身材料配合比为最佳配合比。碳化硅能源桩的最高温度出现在桩体中部。相较于普通能源桩,碳化硅能源桩具有更高的桩体温度、温度增长速率和换热功率,表现出更优的传热性能。在碳化硅能源桩进行热循环时,桩土间的热量传递效率自桩身向外沿径向递减;热循环后,桩周土体呈现热量堆积现象,且这种现象随着接近桩身区域而逐渐增强。研究结果可为碳化硅能源桩的设计及其在饱和砂土地基中的应用提供试验依据。

藏品保存环境中的硅胶型被动调湿材料吸放湿模型研究进展

综述了几种常见的硅胶型被动调湿材料吸/放湿模型,包括湿度半衰期模型、集总参数模型、硅胶颗粒扩散模型、多孔材料扩散模型、硅胶床层扩散模型、温度耦合扩散模型等;结合博物馆藏品保存环境的特点和需求,对不同吸/放湿模型的适用性进行了分析,比较了各模型在博物馆湿度控制应用场景中的优势和局限性。指出被动调湿材料和藏品保存环境相关参数的准确测定对吸/放湿模型的应用效果非常重要,并提出有必要继续开展被动调湿材料吸/放湿模型精准性、使用操作便利性等方面的研究。

硅片磨床伺服进给系统仿真模型与分析

在硅片磨削时,硅片加工质量与硅片磨床的进给系统性能密切相关。为了提升硅片磨床进给系统的精度和稳定性,提出了采用上位机、运动控制卡、伺服驱动器、位置传感器进行闭环控制进给的技术方案。研究了伺服系统和机械系统两者之间的相互耦合关系,建立了动力学模型,搭建了基于PID控制的三闭环控制系统,采用MATLAB中Simulink模块对进给系统进行仿真分析。仿真结果表明,磨床进给系统速度波动量在1%以下满足硅片磨削对进给精度的要求。

多元嵌段有机硅防热涂层制备及性能研究

面向未来高速飞行器的热防护需求,为解决有机硅防热涂层在气动热条件下易粉化剥蚀的问题,开展了多元嵌段有机硅防热涂层制备及性能研究。基于树脂分子结构创新的思路,设计并合成了具有嵌段结构的有机硅树脂,制备出了适用于高热流环境的有机硅防热涂层,并采用FT-IR、TG、SEM-EDS、电弧风洞试验等微观和宏观手段分别对树脂基体和涂层材料进行了表征分析;此外,通过对多元嵌段有机硅涂层高温下的烧蚀产物研究,分析了高温下涂层材料微结构演化规律。结果表明,目标产物多元嵌段有机硅树脂纯度较高、热稳定性较好,在1000℃氮气环境下的质量保留率为55.97%;以此为基体的防热涂层具有优异的综合性能,密度、伸长率、热导率三项关键指标分别为0.70~0.72 g/cm^(3)、16%~25%、0.05~0.06 W/(m·K)(20℃);在最高1044℃、310 s的风洞烧蚀条件下,涂层表面陶瓷化效果显著,无烧蚀后退,验证了由表及里分别为瓷化层、热解层、原始层的有机硅防热涂层烧蚀模型。

硅酮密封胶体系中增塑剂扩散性能的分子动力学模拟

采用分子动力学模拟方法在COMPASS II力场下分析了3种增塑剂(白油、甲基硅油和双端乙烯基硅油)在脱酮肟硅酮密封胶中的扩散性能。研究结果表明:(1)在相同温度(298 K)下,增塑剂的扩散系数大小顺序为:白油>甲基硅油>双端乙烯基硅油。随着温度升高,3种增塑剂的扩散系数均随之升高。当温度超过318 K后,白油扩散系数急剧增加,双端乙烯基硅油增加最缓慢。随着增塑剂含量的升高,3种增塑剂在硅酮密封胶体系中的扩散系数均随之升高,增塑剂的扩散能力随着其含量的增加而增加。(2)在3种混合体系中,脱酮肟密封胶/白油体系的相容性最差,体系分子间的自由体积和自由体积分数最大,增塑剂分子的占有体积及尺寸最大,这些因素综合作用均导致白油具有较强的扩散能力,而双端乙烯基硅油具有较好的抗迁移能力。(3)温度升高使脱酮肟密封胶与增塑剂分子间作用减弱,同时体系的自由体积和自由体积分数增大,增加了增塑剂分子的运动空间,提高了增塑剂分子的扩散能力。(4)增塑剂含量越高,与脱酮肟密封胶分子间形成的相互作用能及范德华作用力能也越大,但同时体系的自由体积和自由体积分数也随着增塑剂含量的增加而增加。增塑剂分子扩散能力是分子间相互作用的力学效应及空间效应共同作用的结果。

Numerical and analytical investigations for the SOI LDMOS with alternated high-k dielectric and step doped silicon pillars

This paper presents a new silicon-on-insulator(SOI) lateral-double-diffused metal-oxide-semiconductor transistor(LDMOST) device with alternated high-k dielectric and step doped silicon pillars(HKSD device). Due to the modulation of step doping technology and high-k dielectric on the electric field and doped profile of each zone, the HKSD device shows a greater performance. The analytical models of the potential, electric field, optimal breakdown voltage, and optimal doped profile are derived. The analytical results and the simulated results are basically consistent, which confirms the proposed model suitable for the HKSD device. The potential and electric field modulation mechanism are investigated based on the simulation and analytical models. Furthermore, the influence of the parameters on the breakdown voltage(BV) and specific on-resistance(R_(on,sp)) are obtained. The results indicate that the HKSD device has a higher BV and lower R_(on,sp) compared to the SD device and HK device.