Enhanced thermal stability of VCSEL array by thermoelectric analysis-based optimization of mesas distribution

The thermal stability of a vertical-cavity surface-emitting laser（VCSEL） array is enhanced by redesigning the mesa arrangement. Based on a thermoelectric coupling three-dimensional（3D） finite-element model, an optimized VCSEL array is designed. The effects of this optimization are studied experimentally. Power density characteristics of VCSEL arrays with different mesa configuration are obtained under different thermal stress in which the optimized device shows improved performance. Optimized device also shows better stability from measured spectra and calculated thermal resistances. The experimental results prove that our simulation model and optimization is instructive for VCSEL array design.

Conductive edge-warping graphite mesas for robust structural superlubricity

Structural superlubricity(SSL) refers to a state of ultralow friction and zero wear when two solid surfaces slide against each other. Recent investigations have identified amorphous carbon at the edge of the graphite mesa as the primary source of friction in such SSL systems. Here, the tensile stress of metal thin film is exploited to engineer vertically conductive edge-warping graphite mesas(EWGM). Through this approach, robust SSL performance is realized, demonstrated by sliding an 8 μm side length square EWGM on an atomically smooth Au substrate for 10000 cycles at a constant voltage of 1 m V. In this SSL system,differential friction coefficients lower than 1.5 × 10^(-4) are achieved, with static contact resistance between EWGM and Au substrate as low as 28Ω and sliding contact resistance as low as 32Ω. Moreover, the EWGM exhibits SSL behavior on polished Si wafer substrates. Furthermore, because of the no-edge contact with the substrate during sliding, friction is independent of the sliding speed of the EWGM. This study presents the first successful fabrication of conductive EWGM. Remarkably, in both EWGM-Au and EWGM-Si SSL systems, the measured frictions are more than one order of magnitude lower than those of ordinary self-retracting graphite mesas with no-edge warping, and no wear is observed during extended current-carrying sliding.Overall, these findings establish a solid groundwork for the future realization of macroscale conductive SSL systems.

Evolution History of Mesas in the Southern Utopia Planitia and Implications for the Ancient Oceans on Mars

As one of the prominent landforms in the Zhurong landing region,mesas are geological features with flat tops and steep marginal cliffs.The mesas are widely distributed along the dichotomy boundary.There are various interpreted origins proposed for the mesas,such as the erosion of sedimentary layers,tuyas eruptions,or surface collapse due to the catastrophic release of groundwater.We investigate the detailed morphological characteristics of the mesas on the Late Hesperian Lowland unit within the Utopia Planitia.We observe morphological evidence for both the ice-bearing interior mesas and the sedimentary origin,including(1)small pits on the crater wall and mesa cliff formed by the release of volatiles like ice;(2)lobate flows at the base of mesas formed by the melting of subsurface ice;(3)layered mesas indicating sedimentary origin;(4)grooves on the top surface of mesas formed by the volumetric compaction of sedimentary deposits.The results indicate that the mesas in the study area are formed by the erosion of sedimentary layers and representative of the Noachian oceanic sediments.We propose an evolutionary model for the mesas.This study will provide some insights into future research of ancient ocean hypothesis of Mars and interesting targets for the exploration of the Zhurong rover.

Stress tensors and quantification of fracture patterns to analyze connectivity and potential fluid flow in a mesa landform of the Northern Andes

This work applies stress tensors inversions and quantification of fracture patterns along the Mesa de Los Santos, in the Eastern Cordillera of Colombia, to better understand the potential fluid flow. It thus contributes to the conceptual hydrogeological model. The area was subdivided into three blocks, separated by the NW Potreros and the Los Santos faults, having minor inner faults of different orientations. This separation facilitates the analysis of the fractures measured in the field, which in general show high dip angles and a conjugate geometry in the northern block, tension fractures(Mode I) in the central block, and a random distribution in the southwestern block. WinTensor treatment of slickensides yielded a maximum horizontal stress(SHmax) of 111o, which coincides with the WNW-ESE tensor observed from the conjugate and tension joints. We then used Frac Pa Q to generate interpolation maps of fracture intensity and density. The maps show the highest values in the central block and the lowest in the northern block,where the precipitation is higher, causing intensive rock weathering and homogenization of the fracture planes. Although the highest values of connectivity by line are found to the south of the mesa, we suggest the possibility of greater flow from the recharge zone(NE) along bedding planes and open NW-SE fractures.

Investigation on Breakdown Characteristics of Various Surface Terminal Structures for GaN-Based Vertical P-i-N Diodes

GaN-based vertical P-i-N diode with mesa edge terminal structure due to electric field crowding effect, the breakdown voltage of the device is significantly reduced. This work investigates three terminal structures, including deeply etched, bevel, and stepped-mesas terminal structures, to suppress electric field crowding effects at the device and junction edges. Deeply-etched mesa terminal yields a breakdown voltage of 1205 V, i.e., 89% of the ideal voltage. The bevel-mesa terminal achieves about 89% of the ideal breakdown voltage, while the step-mesa terminal is less effective in mitigating electric field crowding, at about 32% of the ideal voltage. This work can provide an important reference for the design of high-power, high-voltage GaN-based P-i-N power devices, finding a terminal protection structure suitable for GaNPiN diodes to further enhance the breakdown performance of the device and to unleash the full potential of GaN semiconductor materials.

掩埋异质结激光器的Mesa制备工艺

掩埋异质结结构的半导体激光器具有阈值低、光束质量好的优点。台面(Mesa)制作是掩埋结激光器加工过程中的一步关键工艺,采用传统的全湿法腐蚀工艺制作台面,3英寸圆片内腐蚀深度和器件输出功率水平差异较大。而采用干法刻蚀加湿法腐蚀工艺技术,制备出的台面表面光滑、侧壁连续,腐蚀深度差异为6%,最终器件输出功率水平的差异仅为2%。利用该掩埋结技术制备的1 550 nm大功率激光器均匀性有了较大提升,900μm腔长单管的阈值电流约12 mA,300 mA工作电流时功率输出100 mW。

A polarization mismatched p-GaN/p-Al_(0.25)Ga_(0.75)N/p-GaN structure to improve the hole injection for GaN based micro-LED with secondary etched mesa

A low hole injection efficiency for InGaN/GaN micro-light-emitting diodes(μLEDs) has become one of the main bottlenecks affecting the improvement of the external quantum efficiency(EQE) and the optical power. In this work, we propose and fabricate a polarization mismatched p-GaN/p-Al_(0.25)Ga_(0.75)N/p-GaN structure for 445 nm GaN-based μLEDs with the size of 40 × 40 μm^(2), which serves as the hole injection layer. The polarization-induced electric field in the p-GaN/p-Al_(0.25)Ga_(0.75)N/p-GaN structure provides holes with more energy and can facilitate the non-equilibrium holes to transport into the active region for radiative recombination. Meanwhile, a secondary etched mesa for μLEDs is also designed, which can effectively keep the holes apart from the defected region of the mesa sidewalls, and the surface nonradiative recombination can be suppressed. Therefore, the proposed μLED with the secondary etched mesa and the p-GaN/p-Al_(0.25)Ga_(0.75)N/p-GaN structure has the enhanced EQE and the improved optical power density when compared with the μLED without such designs.

Mesa沟槽终端耦合U型平面结的雪崩型SiC-TVS器件研究

瞬态电压抑制器(Transient Voltage Suppressor,TVS)作为常用的防护型器件具有吸收功率高、响应速度快等特点。目前,雪崩型SiC-TVS器件尚缺乏合理的终端设计,以常用N型衬底为基础的外延P+N-N+/Mesa结构SiC-TVS器件在反偏P+/N-结边缘处易形成负斜角边缘结构,导致器件因边缘电场集中而提前击穿,严重影响器件的工作可靠性。本文基于Sentaurus TCAD数值仿真,研究了一种雪崩型SiC-TVS器件结构,该结构采用离子注入形成大曲率半径的U型平面PN结,并将其边缘与Mesa沟槽终端顶点在器件上表面以距离x进行耦合设计,使器件表面形成正斜角终端,有效地避免了边缘电场集中效应。同时x的选取具有一定余量,在工艺上较易实现。最后利用该结构仿真得到了响应时间约5.3ns、钳位因子达到1.01的雪崩型SiC-TVS器件,仿真结果表明新型耦合结构器件对异常瞬态浪涌信号表现出良好的抑制效果。

IHE互操作性实现机制的研究

IHE基于现有的HL7、DICOM等标准,通过制定技术框架文件来对医疗业务流程进行规范化,为医疗信息系统间的互操作提供通用的解决方案。本文从IHESWF集成模式入手,从信息模型、HL7标准和增强的采用、DICOM标准的采用和增强方面对IHE互操作性的实现机制进行了深入的研究,并就IHE互操作性验证测试在IHE互操作性实现上的重要作用进行了分析,对国内IHE集成测试的开展情况进行了回顾和展望。

隔离技术对SOI PMOSFET中空穴迁移率的影响

在 SIMOX和 Smart- cut SOI衬底上采用 L OCOS和 MESA隔离技术制备了部分耗尽 PMOSFET,虽然 L O-COS隔离器件的阈值电压较小 ,但其跨导和空穴迁移率明显小于 MESA隔离器件 .模拟表明 ,L OCOS场氧生长过程中 ,由于 Si O2 体积膨胀 ,在硅膜中形成较大的压应力 ,从而降低了空穴的迁移率 .

基于Linux的小型无人直升机实时仿真系统构建

小型无人直升机是一个极具挑战性的多学科交叉前沿性研究课题。这里重点介绍基于Linux的小型直升机仿真系统的构建过程及其相关软件实现。首先对小型直升仿真系统的整体架构进行详细的说明。然后基于Linux平台对仿真系统的几个主要程序模块代码进行编写,利用FLTK图形界面库和Mesa/OpenGL实现了小型直升机实时3D飞行状态显示和状态控制面板,可视化仿真及实时运动特性再现的过程。仿真系统的运行结果表明,仿真系统具有独特的优势和很好的开发前景。在今后对小型无人直升机的自主飞行研究当中,可以起到很好的辅助作用。整个仿真系统以模块化实现,具有良好的移植性,便于今后对系统进行功能补充。

VxWorks的三维图形环境的开发

VxWorks作为一种广泛应用于高性能领域中的可裁剪的实时嵌入式操作系统,并没有为用户提供完善的图形界面。为了在VxWorks中实现三维图形的开发和显示,文中通过将OpenGL与WindML(WindRiver Multimedia Library)媒体库相结合,提出VxWorks下三维图形开发环境系统建立和基于该环境的图形开发的方法。完成VxWorks操作系统交叉编译环境的建立、MindML的配置和Mesa3D的编译,并完成VxWorks操作系统下的OpenGL程序开发。通过大量应用程序的测试验证,证明该方法能够完成VxWorks操作系统下的三维图形开发的要求,并且具有操作简单、容易开发等特点。

恶性疟原虫MESA基因的克隆和测序

目的克隆、测定恶性疟原虫海南株(FCC1/HN)成熟疟原虫感染红细胞表面抗原(MESA)基因序列,并进行序列分析。方法根据恶性疟原虫Palo-alto株MESA基因已知序列,设计合成四对引物,用PCR技术从FCC1/HN株基因组DNA中扩增出4个部分序列重叠的MESA基因片段,分别克隆入pMD-18T测序载体。用双脱氧链末端终止法测定这4个基因片段的序列,拼接得到全长MESA基因序列。应用DNAstar、AnthProt软件辅助进行序列同源性比较和抗原表位区预测。结果PCR扩增得到特异的恶性疟原虫FCC1/HN株MESA基因片段,酶切及PCR鉴定获得了包含MESA基因片段的重组质粒。测序结果表明,FCC1/HN株MESA全基因编码区长4102bp,A+T含量为72.11%,G+C含量为27.89%,有1个内含子;编码1323个氨基酸残基,分子量为154470u。序列分析表明,FCC1/HN株与Palo-alto、D10株MESA蛋白在长度和序列组成上呈多态性,序列差异较大区域位于MESA蛋白的氨基酸重复区1、3、4、5和7。经多参数综合分析,有7个潜在的抗原表位区。结论测定、分析了恶性疟原虫FCC1/HN株MESA基因序列。FCC1/HN株MESA基因与其它分离株的MESA基因编码的氨基酸序列存在一定差异。

基于Nakagawa极限理论的硅基IGBT通态特性研究

Nakagawa-limit是基于硅基极窄台面间距IGBT提出的理论假设,发射极区只有电子电流流过,空穴电流只对电导调制有贡献。分别引入载流子存储层和P-ring结构,通过数值模拟分析方法,研究了改进结构对通态压降的降低情况;引入虚拟元胞结构,更进一步降低通态压降。模拟结果表明,4.5kV器件通态比电阻在电流密度为500A/cm^2时可降低至27.2mΩ·cm^2,介于传统SiIGBT和Nakagawa理论预测值的中间。

基于VxWorks操作系统的三维图形驱动开发

通过对Mesa3D库的移植及改进在VxWorks中实现了基于OpenGL1.3的图形API函数,解决了VxWorks下图形驱动开发组件WindML3.0不能使用标准图形API进行图形应用程序开发,不能支持3D图形显示的问题。同时利用硬件双缓冲技术解决了实时显示中画面闪烁、抖动的问题,提高了图形显示的质量。

基于IHE技术框架的测试系统研究

MESA软件是IHE Connectathon(包括IHE-C)的主要辅助测试工具;该软件满足IHE框架的技术要求,为各厂商和软件公司参与IHE测试提供了很多便利。但MESA成型于上个世纪九十年代,距今已有二十多年;且经过测试,MESA在实际使用中也存在不少问题,这些都使得MESA已经不满足当前软件测试的需要。IHE Connectathon需要一款功能完善且符合当今医疗信息化实际的软件测试系统。基于此,提出一种基于B/S架构的测试系统,针对MESA存在的上述问题进行改进和完善。经测试,该系统实现了IHE技术框架的功能性要求且方便易用,为IHE测试提供了方便。

Autumn Daily Characteristics of Land Surface Heat and Water Exchange over the Loess Plateau Mesa in China

The Loess Plateau, located in northern China, has a significant impact on the climate and ecosystem evolvement over the East Asian continent. In this paper, the preliminary autumn daily characteristics of land surface energy and water exchange over the Chinese Loess Plateau mesa region are evaluated by using data collected during the Loess Plateau land-atmosphere interaction pilot experiment （LOPEX04）, which was conducted from 25 August to 12 September 2004 near Pingliang city, Gansu Province of China. The experiment was carried out in a region with a typical landscape of the Chinese Loess Plateau, known as ＂loess mesa＂. The experiment＇s field land utilizations were cornfield and fallow farmland, with the fallow field later used for rotating winter wheat. The autumn daily characteristics of heat and water exchange evidently differed between the mesa cornfield and fallow, and the imbalance term of the surface energy was large. This is discussed in terms of sampling errors in the flux observations-footprint; energy storage terms of soil and vegetation layers; contribution from air advections; and low and high frequency loss of turbulent fluxes and instruments bias. Comparison of energy components between the mesa cornfield and the lowland cornfield did not reveal any obvious difference. Inadequacies of the field observation equipment and experimental design emerged during the study, and some new research topics have emerged from this pilot experiment for future investigation.

WindML中Mesa的应用

研究了在WindML3.0中应用Mesa来改进嵌入式图形界面显示效果的方法。针对实际产生的问题进行了简要的分析,提出了相应的解决方法,达到了预期的效果。

基于Linux和OpenGL/Mesa的数控铣削仿真系统的研究

介绍了在Linux下,利用Qt和OpenGL/Mesa,采用面向对象技术和模块化的设计方式,建立的数控铣削几何仿真的总体结构。阐述了各模块的功能,分析了仿真算法实现。通过验证,系统能检验NC程序是否正确和工艺的合理性,可以发现干涉、碰撞情况。此模型能实时地,交互地显示毛坯材料的去除过程,实现了零件加工的三维实体动态仿真。