基于MEMS技术的SU-8胶被动微阀片的设计与研制

为解决微流体在微流控芯片上的单向流动,进而实现生化反应的片上系统,采用微机电系统（MEMS）技术加工出SU-8胶微型阀片．SU-8胶阀片具有弹性模量和弹性常数低、开启压力小、反向泄漏小、易于加工等特点．从理论上分析了不同厚度（10μm,15μm,20μm,25μm）的微型阀片在不同压力作用下的挠度和应力分布,在相同尺寸和压力下,SU-8微阀片的挠度与传统的硅阀片的挠度相比要大10倍左右．讨论了有阻尼作用下的谐振频率以及过流特性。可知阀臂和阀座的尺寸是影响阀片性能的主要因素．给出了加工工艺,测试了阀片的正反向过流性能,以水作为工作物质,得到3种厚度阀片的过流曲线,其最大正向流速达到7000μL／min．     

SU-8胶制备三维微电极结构研究

为了增大MEMS超级电容器电极结构的表面积,提高MEMS超级电容器的电荷存储能力,研究了利用SU-8胶制备高深宽比三维电极微结构.经过基片清洗、涂胶、前烘、曝光、后烘、显影、坚膜等过程,制备了深宽比为6的微结构.分析讨论了微结构制备过程中基底洁净度和升降温速度及曝光、显影时间等因素对结构制备的影响.实验结果表明,用SU...     

Tensile mechanical properties of SiC whiskers

An initial evaluation has been made of the tensile mechanical properties of SiC whiskers synthesized by a vapour-liquid-solid process. A micro-tensile tester and associated testing techniques were developed for this purpose. The SiC whiskers exhibit an average tensile strength of 8.40 GPa (1 220 000 psi) and an average elastic modulus of 581 GPa (84 300 000 psi), and were considerably stronger and stiffer than continuous, polycrystalline SiC fibres. These results indicate the significant potential of SiC whiskers as short-fibre reinforcement elements for ceramic matrix composites.     

Optical and structural properties of SiC nanocrystals

This paper presents the results of porous SiC characterizations using photoluminescence, scanning electronic microscopy and X-ray diffraction techniques. It is shown that the intensity of defect-related PL bands (2.13 and 2.54 eV) increases monotonically with PSiC thickness rise from 2.0 up to 12.0 μm. These luminescence centers are assigned to surface defects which appear at the PSiC etching process. Intensity enhancement for exciton-related PL bands (2.84, 3.04 and 3.24 eV ) is attributed to the exciton recombination rate increasing as result of electron-hole confinement realization in big size SiC NCs (6H-PSiC with inclusions of 15R- and 4H-PSiC) and/or quantum confinement exciton recombination in small-size 4H-PSiC NCs.     

Multifunctional polymer nanocomposites with enhanced mechanical and anti-microbial properties

The paper reports the results of a project aiming to obtain multifunctional binary and ternary polymer nanocomposites with enhanced mechanical and anti-microbial properties. To this end a DGEBA-based epoxy resin is loaded using montmorillonite clays and later used as matrix for glass fibre reinforced laminates. Both binary and ternary nanomodified specimens are manufactured and subjected to mechanical testing. An accurate analysis of the effect of nanomodification on the biological activity is carried out as well.     

Morphological, structural and optical properties of thin SiC layer growth onto silicon by pulsed laser deposition

Crystalline silicon carbide thin layers were grown on a p-type Si(1 0 0) substrate by pulsed laser deposition (PLD) using KrF excimer laser at λ=248 nm from a 6H-SiC hot-pressed target. The target “SiC” used to elaborate our SiC films is realized from a mixture of 1SiO₂ with 3C (carbon) “1SiO₂+3C” heated in an oven at 2500 °C (the target was a hot-pressed material and supplied by Goodfellow). The morphological, structural and optical properties of SiC layers were investigated by scanning electronic microscopy (SEM), high-resolution X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and UV-visible spectrophotometer. XRD analysis of the target showed that this latter is a hexagonal structure (6H-SiC). The XRD pattern shows that a 1.6 μm crystalline SiC layer was formed. In addition, a SIMS analysis gives a ratio Si/C of the thin SiC layer around 1.15 but the ratio Si/C of the target was found equal to 1.06, whereas one should have 1.0. This is due to the degree of the sensitivity of the SIMS technique and due to the higher ionization efficiency of Si compared to C atoms, all these which give different ratios. It is known that the PLD technique reproduces the same macroscopic property (optical, mechanical, structural, etc.) of the target. An optical gap (E_Gap) of the SiC layer of about 2.51 eV was obtained by reflectance measurement. Finally, a crystalline thin SiC layer of 1.6 μm was elaborated using PLD method at low-temperature deposition.     

Development of carbon nanofiber reinforced hydroxyapatite with enhanced mechanical properties

In order to improve fracture toughness, carbon nanofibers (CNF) were used as reinforcement for hydroxyapatite (HA) composites. The powder mixture of CNF/HA were obtained with ball-milling technique. CNF/HA composites were sintered by hot-pressing with 7.81 and 15.6 MPa sintering pressure. Maximum sintering pressure was 1200 °C. Mechanical and physiological bio-compatibility were evaluated by four-point bending tests, indentation tests and immersion tests in simulated body fluid (SBF). The strength values of 10 vol.% CNF/HA composites sintered at 15.6 MPa is 90 MPa, which is within those of cortical bone. The fracture toughness values for CNF/HA composites are around 1.6 times higher than those obtained for HA. Equal bioactivity are obtained for CNF/HA composites.     

SiC埋层的制备与性质研究

在衬底温度400℃条件下对n型(100)单晶硅进行剂量分别为5×1017cm-1和1×1018cm-1的C+注入,经过在1050℃氮气氛下进行60min退火形成β-SiC埋层。通过X射线光电子能谱(XPS),俄歇电子能谱(AES)及付立叶变换红外吸收光谱(FTIR),对所形成的碳化硅埋层进行了测试与分析。结果表明在此条件下,在Si中可以形成一定的SiC埋层,并且C+离子注入硅衬底可以形成β-SiC和α-SiC。SiC埋层主要由非立方相的α-SiC和立方相的β-SiC所构成。     

Fabrication and mechanical properties of oriented SiC short-fiber-reinforced SiC composite by tape casting

SiC fiber-reinforced SiC composites with nearly unidirectionally and randomly aligned SiC short fiber were prepared by tape-casting and hot-pressing (HP). Volume fractions of fibers were 10 and 20 vol.%. Three-point bending test was carried out at room temperature. The SiC short-fiber-reinforced SiC composites showed completely brittle fracture for any fiber volume fraction and orientation. The maximum strength increased with increasing sintering temperature regardless of orientation of short fiber. In the unidirectionally and randomly aligned composites sintered at 1700 °C containing 20 vol.% fiber, the maximum bending strength was about 390 and 280 MPa, respectively.     

Probabilistic Weibull behavior and mechanical properties of MEMS brittle materials

The objective of this work is to present a brief overview of a probabilistic design methodology for brittle structures, review the literature for evidence of probabilistic behavior in the mechanical properties of MEMS (especially strength), and to investigate whether evidence exists that a probabilistic Weibull effect exists at the structural microscale. Since many MEMS devices are fabricated from brittle materials, that raises the question whether these miniature structures behave similar to bulk ceramics. For bulk ceramics, the term Weibull effect is used to indicate that significant scatter in fracture strength exists, hence requiring probabilistic rather than deterministic treatment. In addition, the material's strength behavior can be described in terms of the Weakest Link Theory (WLT) leading to strength dependence on the component's size (average strength decreases as size increases), and geometry/loading configuration (stress distribution). Test methods used to assess the mechanical properties of MEMS, especially strength, are reviewed. Four materials commonly used to fabricate MEMS devices are reviewed in this report. These materials are polysilicon, single crystal silicon (SCS), silicon nitride, and silicon carbide.     

Analysis of mechanical properties and SEM for laminated SiC/W composites

In this letter, it is reported that a laminated SiC/W composite has been developed using the hot pressing method. It is found that a chemical reaction between W and SiC occurs during the preparation process. Making use of SEM, the components within the sandwiched-in metal and the fracturing crack for the laminated SiC/W composite are determined. Testing mechanical properties of the laminated SiC/W composite indicates that fracture toughness increases while bending strength reduces, with an increase of the thickness of the sandwiched-in metal ranging from 10–50-μm thickness.     

微机电器件的稳健设计

微机电系统（MEMS）是一个新兴的跨学科研究领域,成本和可靠性是MEMS商品化的关键。与传统的机械加工和IC加工相比,MEMS加工的尺寸偏差比较大,而且很难控制,因此需要在设计过程中充分考虑加工的不确定性。稳健设计可以在不提高制造成本的前提下提高设计方案的稳健性。稳健优化设计方法主要包括 Taguchi方法和基于容差模型的方法,后者特别适合于处理带约束的优化设计问题。以微加速度计和微阀为例给出了稳健设计在MEMS设计中的应用,验证了稳健设计可以显著提高MEMS器件的信噪比。     

The effect on the tensile properties of PIP-processed SiC/SiC composite of a chemical vapor-infiltrated SiC layer overlaid on the pyrocarbon interface layer

A chemical vapor-infiltrated (CVI) SiC layer is often deposited on the pyrocarbon (PyC) fiber–matrix interface layer in SiC fiber-reinforced SiC matrix (SiC/SiC) composites. It is normally applied to protect the PyC layer from reacting with molten Si or sintering aids during manufacturing, and to guard against the effects of high temperature, oxidation and moisture during use. In this study, we investigated the effect of this SiC layer on the tensile properties of a composite. Tensile tests of our composite samples showed the SiC layer to have no noticeable effects on its ultimate load or fracture strain, whereas it decreased the load-to-strain ratio and proportional limit. The test results were analyzed by carrying out element tests on filaments and fiber bundle samples, fracture mirror analysis of pullout fibers, and finite element analysis (FEA) of residual thermal stress around the interface.     

Synthesis and high temperature mechanical properties of Ti3SiC2/SiC composite

A high density Ti₃SiC₂/20 vol % SiC composite was hot pressed under a uniaxial pressure of 45 MPa for 30 min in an Ar atmosphere at 1600 °C. The grain size of the Ti₃SiC₂/SiC composite was finer than that of monolithic Ti₃SiC₂, though the composite was hot pressed at a higher temperature, due to the dispersion of SiC particles in the Ti₃SiC₂ matrix. Room temperature fracture toughness of the composite and Vickers hardness were measured as 5.4 MPa m^1/2 and 1080 kg mm^–2, respectively. A higher flexure strength of the composite compared to that of monolithic Ti₃SiC₂ was measured both at room temperature and up to 1200 °C. At 1000 °C, the composite showed a lower oxidation rate than that of monolithic Ti₃SiC₂.     

Processing, microstructure and mechanical properties of hot-pressed SiC continuous fibre/SiC composites

SiC (SCS-6TM) continuous fibre/SiC composites were fabricated by hot-pressing at 1700°C in vacuum using an Al sintering additive. Analytical transmission electron microscopy was used to investigate the microstructure of the composites. The room-temperature mechanical and high-temperature creep properties of the composites were investigated by four-point bending. The SiC powders used were sintered at a relatively low sintering temperature to high density (97% of theoretical density) with the addition of the Al sintering additive. It is believed that the Al additive is very efficient for the densification of SiC. The SiC fibres maintained their original form and microstructure during fabrication. The SiC matrix reacted with the outermost carbon sublayer in the fibre, forming a thin (1.8–4.8m) interfacial layer, which was composed of Al4C3, Si–Al–C, and Si–Al–O phases. The incorporation of SiC fibre into a dense SiC matrix significantly increased the room-temperature failure strain and improved the high-temperature creep properties. In addition, the incorporation of SiC fibre into a porous SiC matrix increased the room-temperature failure strain, but did not contribute to the high-temperature creep properties.