石墨的微加工工艺研究

石墨具有固态超滑和耐酸、耐碱和耐有机溶剂腐蚀等特性,使其有望成为微机电系统(MEMS)基础材料的一种选择。如能通过微纳米加工工艺对石墨进行微加工并在石墨上大批量、稳定、可控地制备各种掩模图案和石墨微结构,一定程度上可以推动石墨成为MEMS基础材料。故本文通过工艺设计和参数摸索,利用薄膜沉积、光刻、刻蚀等常用的微纳米加工工艺对石墨进行微加工研究,并对加工后的石墨进行表征。结果表明,利用薄膜沉积技术在石墨表面沉积的薄膜可以满足后续光刻和刻蚀等工艺的要求。同时,采用光刻技术能在石墨表面大批量、稳定、可控地加工出不同形状,不同尺寸的光刻胶掩模图案。此外,利用刻蚀技术可以在石墨上大批量、稳定、可控地加工出形状较规则,排列整齐且垂直度较高的石墨微结构。     

利用典型Si(100)微结构对原子力显微镜探针参数进行表征

利用各向异性化学湿法刻蚀工艺在Si(100)上加工了具有本征侧墙角(54.73°)的典型微机电系统(MEMS)梯形结构.用该微结构作为线宽测试结构,对其进行了原子力显微镜(AFM)和扫描电子显微镜(SEM)线宽和轮廓的比对测量.并对AFM探针和样品耦合效应进行了研究,提出了AFM探针参数动态表征的模型,基于几何模型对线宽和轮廓测量中探针针尖形状和针尖位置参数进行了表征,提出了用曲率半径、安装倾角、扫描倾角和针尖半顶角来对原子力显微镜探针针尖进行表征.该方法是对现有AFM探针表征模型的改进和完善.     

基于微PCD刀具的微结构成型制造与应用

本文提出一种基于微聚晶金刚石(PCD)刀具的微结构快速车削成型制造方法.首先利用电火花线切割加工(WEDM)放电蚀除技术实现了微PCD刀具的精密切割成型制造.在WEDM过程中对线切割丝的运动轨迹、电火花加工间隙及加工能量进行了研究分析以提高微切削刀具的制造精度.随后将微PCD刀具安装到精密车削系统,通过铝合金的微车削实验验证了本文所提出的微结构快速成型制造方法的可行性.最后对微刀具的磨损形态进行了实验分析.在微车削过程中,刀具切削刃无明显磨损和破坏,而工件材料粘结于刀具前刀面是造成微结构加工精度降低的主要因素.本文所提出的微细制造技术有望成为微结构快速、大批量生产的潜在工业应用.     

硅基MEMS三维微电极阵列的超电容特性

三维微电极是一种具有空间结构优势、电化学性能比二维微电极更加优越的微型储能结构.本文提出一种基于光刻、感应耦合等离子体刻蚀和溅射等MEMS工艺加工三维结构硅基微电极阵列的新方法.采用电化学阴极沉积工艺在微电极表面制备了纳米氧化钌功能薄膜.借助扫描电子显微镜、循环伏安测试和电化学交流阻抗谱测试等手段对三维微电极的表面形貌和电化学性能进行了表征,系统研究了阴极沉积电流密度、电沉积时间以及硅基微结构表面"微草效应"对三维微电极超电容特性的影响.所制备三维微电极的比电容达到1.57 F/cm2,与平面电极比电容0.42 F/cm2相比明显提高,而电化学阻抗比二维平面微电极显著降低.相关实验数据表明基于MEMS技术加工的三维结构微电极具有优于平面电极的电化学电容储能特性.     

环境振动能收集系统的微型压电悬臂梁设计与制作

研制长寿稳定电源已经成为微型无线传感网络中的关键技术之一,现有的化学电池容量有限,需要不断的逐个更换耗尽的电池,难以满足无线传感网的实际应用.本文提出利用压电材料的机电耦合特性收集环境振动能,该类型微电源有望成为MEMS提供长期电能.首先分析了利用压电材料收集振动能的原理,对微型悬臂梁结构的设计进行了简单的分析,重点介绍了用MEMS工艺加工微型悬臂梁的工艺流程.悬臂梁结构采用体硅和面硅加工工艺相结合,体硅工艺包括湿法和干法刻蚀硅及表面层结构,金属Pt层刻蚀等,面硅工艺包括溅射金属薄膜和利用Sol-Gel方法在Si/SiO2/Ti/Pt衬底上制作锆钛酸铅(Pb(Zr0.52Ti0.48)O3,PZT)压电薄膜等.经过反复工艺实验研究,确定一套稳定的微型压电能源的制作工艺流程.     

氮化镓材料在传感器中的应用

<正>氮化镓(GaN)是直接宽带隙半导体材料,属于第3代半导体。相较于硅、砷化镓等,GaN的禁带宽度更大、击穿电场强度更高,具有更高的电子饱和度和漂移速率、更强的抗辐照能力以及较强的化学稳定性。氮化镓材料与硅、砷化镓材料的电子性能对比如表1所示。目前GaN制备工艺成熟,已经能够利用GaN制造出结构复杂的器件。GaN基紫外探测器由于在可见光和红外光范围内都没有响应,其在可见光和红外光背景下的紫外光探测具     

虚拟MEMS加工工艺建模、实现与系统验证

利用虚拟现实技术对MEMS加工工艺进行仿真,并将其引入设计环节,最终可以解决MEMS生产中设计与加工脱节的问题。MEMS加工工艺的核心是工艺模型。首先,在深入分析单步MEMS加工工艺的基础上给出了规则描述的工艺模型,其次,利用专家系统技术实现了系统。进一步用一种全新的器件微流量泵的工艺设计和虚拟加工过程验证了系统的可扩充性。     

消息报道

苏州纳米所利用氮化镓器件从事核应用研究取得系列成果氮化镓(GaN)是一种III/V直接带隙半导体,作为第三代半导体材料的代表,随着其生长工艺的不断发展完善,现已广泛应用于光电器件领域,如激光器(LD)、发光二极管(LED)、高电子迁移率晶体管(HEMT)等。GaN基材料的良好抗辐射性能和环境稳定性,使得其在核探测领域具有很好的应用前景,在新型核电池领域也具有巨大的应用潜力。因为GaN辐生伏特效应核电池     

纤毛式MEMS矢量水声传感器的仿生组装

提出了一种纤毛式微机电系统（MEMS）矢量水声传感器的仿生组装技术.期望结合MEMS工艺和仿生组装工艺技术,解决复杂结构的仿生制造问题.文中简单介绍了仿生学理论以及定向探测机理.采用MEMS基硅微机械加工技术完成了传感器微结构的加工.通过模仿鱼类侧线器官神经丘感觉器的仿生结构,完成了传感器仿生微结构的组装,制作出纤毛式硅微仿生矢量水声传感器的模型样机.最后,完成了传感器的校准测试.测试结果表明,该水声传感器不但体积小、质量轻、结构简单,而且具有“8”字型的指向特性.该水声传感器的声压灵敏度为-197.7 dB（0 dB=1 V/μPa）.     

基于多掩膜光刻工艺的MEMS体硅加工

本文提出了一种新颖的MEMS多掩膜工艺,实现了带有大台阶和大深宽比窄槽的衬底上的体硅精细加工。通过薄胶多次光刻在衬底上制作出氧化硅(SiO2)、氮化硅(Si3N4)、光刻胶(photo-resist,PR)等材料的多层掩膜图形,每层掩膜可以进行一次衬底刻蚀或腐蚀,刻蚀或腐蚀完毕后去除该层掩膜。该工艺解决了MEMS工艺中的深坑涂胶和光刻问题,结合深反应离子刻蚀(Deep Re-active Ion Etching,DR IE)、湿法腐蚀等工艺可以用于多级台阶、深坑底部精细结构、微结构释放等MEMS工艺。     

Room-temperature red emission from light-emitting diodes with Eu-doped GaN grown by organometallic vapor phase epitaxy

We obtained room-temperature red emission from GaN-based light-emitting diodes (LEDs) using a Eu-doped GaN (GaN:Eu) as an active layer. The bright emission was observed under normal lighting condition, which is associated with the intra-4f shell transition of Eu³⁺ ions. The LED properties depends on the growth condition of GaN:Eu layer. Since the high-quality GaN can be grown at higher growth pressure, the intense electroluminescence (EL) was observed in the LED with a GaN:Eu active layer grown at atmospheric pressure, which is due to the enhancement of the energy transfer efficiency from the GaN host material to the Eu ions. At a d.c. current of 20 mA, the light output power and external quantum efficiency were 17 μW and 0.04%, respectively. These results indicate the feasibility of GaN:Eu to realize a GaN-based red emitter for fabrication of nitride-based monolithic optical devices.     

Enhanced performance of GaN-based light-emitting diodes by using a p-InAlGaN/GaN superlattice as electron blocking layer

The electrical and optical characteristics of GaN-based light-emitting diodes (LEDs) with various kinds of electron blocking layers (EBLs) are analyzed numerically. The results indicate that an enhanced hole injection efficiency and a reduced electron leakage could be achieved with the GaN-based LED where a p-InAlGaN/GaN superlattice (SL) was employed as EBL as compared with the conventional GaN-based LEDs using rectangular p-AlGaN EBL or p-AlGaN/GaN SL EBL. Moreover, it was found that the efficiency droop could be significantly improved at high injection current density for GaN-based LEDs with p-InAlGaN/GaN SL EBL.     

GaN-Based Solar-Ultraviolet Detection Instrument

We report on the fabrication of a solar-UV monitoring system that uses GaN-based photodetectors. GaN photoconductors, p-n junction photodiodes, and Schottky barrier photodiodes have been fabricated and characterized as UV sensors. The best performances are obtained in Schottky photodiodes, which show a linear response, a flat responsivity of 100 mA/W, a visible rejection ratio higher than 10(3), and a noise-equivalent power of 1 nW/Hz(-1/2). Preliminary data on Al(x)Ga(1-x)N (x = 0.15, 0.22) detectors are also presented. Using GaN Schottky diodes, we fabricate and evaluate a complete solar-UV detection head.     

Enhanced performance of GaN-based LEDs via electroplating of a patterned copper layer on the backside

InGaN/GaN multi-quantum well light-emitting diodes (LEDs) are conventionally grown on a sapphire substrate due to a lack of compatible substrates with a high compressive strain. This is a result of the relatively large lattice, and thermal expansion coefficient mismatches between GaN and sapphire. The compressive strain is considered to be a major obstacle to further improve next-generation high-performance GaN-based LEDs. In this paper, we have designed, electroplated, and tested an efficient substrate using a patterned copper (Cu) layer on the backside of sapphire to relax the compressive strain in a GaN epilayer. The patterned Cu layer has a significant function in that it supports the GaN/sapphire LEDs with an external tensile stress. The external tensile stress is capable of compensating for the compressive strain in the GaN/sapphire LEDs by controlling the curvature of the wafer bowing. This patterned Cu layer, when applied to the GaN/sapphire LEDs, suppresses the compressive strain by up to 0.28 GPa. The GaN-based LEDs on this innovative and effective sapphire/Cu substrate offer improved optical and electrical performance.     

Fabrication and performance of GaN electronic devices

GaN and related materials (especially AlGaN) have recently attracted a lot of interest for applications in high power electronics capable of operation at elevated temperatures. Although the growth and processing technology for SiC, the other viable wide bandgap semiconductor material, is more mature, the AlGaInN system offers numerous advantages. These include wider bandgaps, good transport properties, the availability of heterostructures (particularly AlGaN/GaN), the experience base gained by the commercialization of GaN-based laser and light-emitting diodes and the existence of a high growth rate epitaxial method (hydride vapor phase epitaxy) for producing very thick layers or even quasi-substrates. These attributes have led to rapid progress in the realization of a broad range of GaN electronic devices, including heterostructure field effect transistors (HFETs), Schottky and p–i–n rectifiers, heterojunction bipolar transistors (HBTs), bipolar junction transistors (BJTs) and metal-oxide semiconductor field effect transistors (MOSFETs). This review focuses on the development of fabrication processes for these devices and the current state-of-the-art in device performance, for all of these structures. We also detail areas where more work is needed, such as reducing defect densities and purity of epitaxial layers, the need for substrates and improved oxides and insulators, improved p-type doping and contacts and an understanding of the basic growth mechanisms.     

GaN-based stacked micro-optics system

A prototype of a GaN-based stacked micro-optics system is demonstrated. The system consists of a GaN microlens, GaN membrane gratings, six spacers, a spatial filter, and a 980 nm VCSEL. The laser beam is collimated by the GaN microlens and diffracted by the GaN membrane grating. The systems can be used in blue-violet-UV micro-optics systems.     

Synthesis of GaPO4-GaN Coaxial Nanowires

GaPO₄-GaN coaxial nanowires were synthesized by two-step chemical vapor deposition method using H₂ and NH₃ as reactant gas in turn at 950°C. The morphology and microstructures of the GaPO4-GaN coaxial nanowires were studied by scanning elctron microscopy (SEM), X-ray diffraction (XRD) and transmission lectron microscopy (TEM). The nanowires have an average diameter of ~15 nm and length of hundreds of anometers. The core is GaPO₄ crystal and the outer shell is GaN crystal. The formation mechanism was iscussed and the key factors controlling the growth are temperature and the concentration of reactant gases. hese coaxial nanowires may have potential application for piezoluminescence nano-devices, and the two-step ynthetic technique could be used to grow rationally other 1D GaN-based nanowire heterostructures.     

Computer-aided process planning for fabrication of three-dimensional microstructures for bioMEMS applications

In recent years, there has been increasing interest from both academies and industries in developing micro-electromechanical system (MEMS) technology for biological applications, known as bioMEMS or biochips. Targeting at high throughput biomolecule analysis, drug compound screening, and reduction of reagent and sample volume, today's bioMEMS devices come with miniaturised design and increased complexity of microstructures. Fabrication of such a complex bioMEMS structure involves a number of layer fabrication cycles. Moreover, a two-dimensional (2D) mask is required for each process. Thus, manually generating such a complex process plan has become a difficult task. With recent advances in material technology, polydimethylsiloxane (PDMS) silicone material has been widely applied in nowadays bioMEMS fabrication. This paper proposes a novel automated process planning approach for fabrication of three-dimensional (3D) microstructures in bioMEMS. This approach can handle both PDMS casting and traditional micro fabrication processes. It integrates a novel solid decomposition method and a feasibility search algorithm. Also, it can directly handle the solid model of an integrated microstructure with B-rep representation, and automatically generate the data of the fabrication process plan along with masks. A process planner prototype has been implemented. An application example is presented to demonstrate the functionality of the prototype.     

Gallium nitride heterostructures on 3D structured silicon

We investigated GaN-based heterostructures grown on three-dimensionally patterned Si(111) substrates by metal organic vapour phase epitaxy, with the goal of fabricating well controlled high quality, defect reduced GaN-based nanoLEDs. The high aspect ratios of such pillars minimize the influence of the lattice mismatched substrate and improve the material quality. In contrast to other approaches, we employed deep etched silicon substrates to achieve a controlled pillar growth. For that a special low temperature inductively coupled plasma etching process has been developed. InGaN/GaN multi-quantum-well structures have been incorporated into the pillars. We found a pronounced dependence of the morphology of the GaN structures on the size and pitch of the pillars. Spatially resolved optical properties of the structures are analysed by cathodoluminescence.     

类金字塔状GaN微米结构的生长及其形貌表征

采用金属有机化学气相沉积(MOCVD)技术,在非掺杂GaN层上原位生长SiNx掩模层,制备了形貌可控的类金字塔状GaN微米结构,并系统研究了生长温度、生长时间、反应压力和Ⅴ/Ⅲ比等不同生长参数对其形貌的影响。研究结果表明,在生长温度为1 075℃时,所生长的GaN呈现出类金字塔状微米锥结构;当生长时间由3 min延长至20 min时,微米锥的底面直径由3.6μm增大到19.8μm,密度由3.8×10~3cm~(-2)降低至0.8×10~3cm~(-2);压力及Ⅴ/Ⅲ比共同决定该结构顶部的微观形貌(锥状或截顶锥状)。本工作的研究结果为GaN微钠米结构的原位可控生长奠定了一定基础,并有助于三维GaN基LED器件的进一步发展。