Development of ceramic microstructures

 For the production of microstructured ceramic parts, development efforts are necessary in the field of powder synthesis as well as in the area of shaping. Several processes have been developed. Powder synthesis was performed starting from metal organic precursors and using a two stage thermal process. Shaping was performed by sol-gel methods, by pressing of a ceramic slurry or an organic precursor paste as well as by direct electrophoretic deposition of gels in a microstructured form. An overview is given on the methods and the results. Received: 30 October 1995 / Accepted: 12 January 1996     

Manufacturing of isolated ceramic microstructures

The design of a micromold for gearwheels and components for a gearwheel micropump were adapted for the fabrication by micro powder injection molding (micro-PIM). Several variations were made to compensate the shrinkage during sintering and to meet the dimensions of the micro features. Mold inserts made by the LIGA- and the UV-LIGA-Process were used. The quality of the models was evaluated by SEM and tests of micro injection molding in PMMA. Subsequently, micro-PIM was carried out using different feedstocks. The green microparts were isolated from the substrate, debound and sintered. At sintered parts, the roughness of the surface was evaluated and the processes were optimized.     

Embossing of 3D ceramic microstructures

 An embossing method based on the viscous polymer processed (VPP) ceramic tape has been used to fabricate 3D ceramic microstructures with high aspect ratios. Examples of lead zirconate titanate (PZT) microrod arrays with feature sizes of 10–150 μm and aspect ratios of 3–10 have been demonstrated. Advantages of the embossing technique over conventional casting and moulding methods are discussed. Received: 10 August 2001/Accepted: 24 September 2001     

Characterisation of high aspect ratio non-conductive ceramic microstructures made by spark erosion

The spark erosion process is widely used for micro structuring. Its possibility to structure materials independent of their material properties like high hardness or melting temperature enables to address a large material diversity. However the process requires a minimal electrical conductivity of 0.1 Scm⁻¹. Nevertheless recent research has shown that the usage of an assisting electrode makes a processing of non-conductive materials possible. Thus even ceramics like Al₂O₃ or ZrO₂ can be processed. These materials are becoming more and more interesting for industrial application and the field of miniaturisation due to their outstanding material characteristics like high hardness, bending strength, melting temperature and chemical inertness. In this study a new lacquer based assisting electrode is used to erode bars in zirconia samples. For this purpose a modular tool concept is established. Bars with aspect ratios of more than 80 are generated. The achieved bar heights are 1.5 mm and the smallest bar width is 8 μm. Furthermore a characterisation of the sidewall angles showed mean values between 0.4° and 2.2° depending on the bar height and width.     

Fabrication of high-aspect-ratio ceramic microstructures byinjection molding with the altered lost mold technique

A fabrication process for complex ceramic microstructures was proposed that combines a lost mold technique and ceramic injection molding. Two key points in this process were studied. First, the solubility of several engineering plastics in various organic solvents was tested to find appropriate combinations of mold material and solvent for dissolving molds. Secondly, the binder extraction rate and the strength of a green body during debinding were investigated. Experimental results indicate that acrylonitrile-butadiene styrene and acetone are the best combinations selected for this lost mold technique. We also propose that using gasoline as the debinding solvent and performing the debinding at room temperature will give a good time-saving effect and avoid toppling the microstructure if paraffin wax, stearic acid, and polyethylene were selected to compound the binder system. This process has been successfully applied to fabricate several ceramic microstructures, such as an integrated punch     

国外高深宽比微细结构制造技术的发展

介绍了国外近年来高深宽比微细结构制造技术的最新发展,其中包括LIGA、准LIGA、深层反应离子刻蚀等主要高深宽比微细结构技术的具体研究现状和研究进展,还介绍了电化学沉积加工、质子束光刻、准LIGA与Si等离子刻蚀复合加工、局部电化学沉积、立体光固化微加工、微细电解加工等一些新发展的高深宽比微细结构技术。     

陶瓷压阻式机油压力传感器研制

针对传统滑线式机油压力传感器不足,设计制作了一种陶瓷压阻式机油压力传感器.利用自搭建的温度压力测试系统对其进行了标定与测试,实验结果显示:其综合检测精度(线性、迟滞、重复性等)达到0.925％F.S,完全符合压力传感器通用技术条件规定的综合误差≤2％F.S的要求,并通过了2～3倍量程的过载、爆破压力测试,性能稳定可靠.加之陶瓷芯片具有耐腐蚀、抗磨损、成本低廉等优点,该传感器可广泛应用于机油压力及其他相关场合的压力检测中.     

E-beam-induced fabrication of microstructures

E-beam-induced deposition of tungsten, W, from a metal-organic gas has been used for the formation of microstructures of various geometries. Three examples have been selected for demonstration: line deposition, needle growth, and bridge formation. Important parameters of the W deposition process from W(CO)₆ gas are given, among them minimum feature size, positional accuracy, and growth rate     

Development of separated micromold system for an efficient replication of high aspect ratio microstructures

In the present study, a separated micromold system (SMS) is newly proposed and developed for an efficient replication of high aspect ratio microstructures. The present SMS basically consists of micromold modules, each having a split structure of the complete microstructure to be replicated. So fabricated micromold modules are assembled for a replication of the microstructures and subsequently separated in a demolding stage. In this manner, serious problems commonly encountered in a conventional fabrication process for high aspect ratio structures can be effectively overcome. For a precise fabrication of the micromold modules, a deep X-ray lithography and nickel electroforming processes were carried out, resulting in nickel SMS including various half circular microstructures. By utilizing the obtained SMS modules, high aspect ratio micro-scale cilium structure and its array were successfully replicated by a hot embossing process.     

Fabrication of high-aspect-ratio hydrogel microstructures

Microfabrication of high-aspect-ratio polymeric microstructures via deep X-ray lithography traditionally involves either crosslinking or scissioning a polymer film spun-cast on a substrate. A post-exposure development procedure is usually employed to remove the unwanted polymer, leaving behind lithographically patterned structures. Instead, we use a novel synthesis technique wherein polymerization of a mixture of monomers in solvent is initiated, through a mask, with hard X-rays. The resulting polymer precipitates out of the solvent, thus limiting the spatial propagation of the reaction only to the exposed regions. Such a technique offers a unique way for the patterned synthesis of polymers from a variety of monomer-solvent systems. Here, we present the first results on the synthesis of high-aspect-ratio microstructures of a thermoreversible hydrogel, poly (N-isopropylacrylamide), and an ionic hydrogel, poly (methacrylic acid). These stand-alone, implantable microstructures are envisioned to be potentially useful in such diverse areas as biosensors, microactuators, controlled release applications, and cell and tissue engineering.This paper was first presented at the High Aspect Ratio Microstructures (HARMST) 2003 conference in Monterey California, June 2003.We would like to thank Dr. Francesco De Carlo (APS) for his discussions on beamline simulations. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Basic Energy Sciences (BES), Office of Science, under contract number W-31-109-ENG-38.     

压电陶瓷片表面缺陷视觉检测系统的研制

压电陶瓷片在生产加工过程中表面会出现空洞、斑点和划伤缺陷,使其压电性、介电性等性能劣化,影响产品质量。目前对压电陶瓷片表面缺陷检测还停留在人工目测的阶段,精度达不到要求,易出现漏检的现象,效率低下。结合压电陶瓷片本身及其待测缺陷的特征,提出一种基于视觉检测技术实现压电陶瓷片表面缺陷检测的方法。将压电陶瓷片放置在二维移动平台上,配合线阵相机进行多张图像采集,获取完整的压电陶瓷片信息,通过所设计的图像处理算法进行缺陷提取与质量判断,最终完成产品样机的研制。     

基于数据融合的陶瓷窑炉温度记录仪的研究

根据陶瓷窑炉的功能和技术指标要求,给出了测温系统的设计方案。设计中采用了基于算术平均值与分批估计的软件数据融合的热电偶线性化处理算法,很好地解决了系统中热电偶测温的不确定性,提高了测量精度,保证了测量数据的可靠性。同时该无纸温度记录仪,具有高测量精度、高可靠性、高稳定性、低成本的特点,通用性强。     

Synchrotron radiation analysis of microstructures

 The outstanding spectral and spatial characteristics of synchrotron radiation make it a powerful analytical tool in microstructure technology. We apply absorption spectroscopy to study foils of electroplated Permalloy (NiFe), and of nickel phosphorus, because they are of interest to microfabrication for their soft magnetic properties and their selective etching behaviour, respectively. In particular, we show that in the electroplated Permalloy foils Ni keeps the structure of pure Ni while Fe changes from b.c.c. to f.c.c. NiP foils become increasingly amorphous with growing P content. In this way, radial elemental distributions which determine magnetic or other properties can be monitored sensitively to improve electroplating process control, even in situ. We also measure the radial thickness profile of a gold layer sputtered on top of a chromium coated silicon wafer. This technique might be extended to measure a given layer in a multilayer structure selectively and non-destructively even when hidden or opaque. Received: 30 October 1995/Accepted: 18 December 1995     

Roll-to-roll hot embossing of microstructures

In this paper we present a new roll-to-roll embossing process allowing the replication of micro patterns with feature sizes down to 0.5 μm. The embossing process can be run in ‘continuous mode’ as well as in ‘discontinuous mode’. Continuous hot embossing is suitable for the continuous output of micro patterned structures. Discontinuous hot embossing has the advantage that it is not accompanied by waste produced during the initial hot embossing phase. This is because in ‘discontinuous mode’, embossing does not start before the foil has reached the target temperature. The foil rests between two parallel heating plates and foil movement and embossing starts only after the part of the foil resting between the heating plates has reached a thermal steady state. A new type of embossing master is used which is based on flexible silicon substrates. The embossing pattern with sub-μm topographic resolution is prepared on silicon wafers by state of the art lithography and dry etching techniques. The wafers are thinned down to a thickness of 40 μm, which guarantees the mechanical flexibility of the embossing masters. Up to 20 individual chips with a size of 20 × 20 mm2 were assembled on a roller. Embossing experiments with COC foils showed a good replication of the silicon master structures in the foil. The maximum depth of the embossed holes was about 70% of the master height.     

Synchrotron radiation analysis of microstructures

The outstanding spectral and spatial characteristics of synchrotron radiation make it a powerful analytical tool in microstructure technology. We apply absorption spectroscopy to study foils of electroplated Permalloy (NiFe), and of nickel phosphorus, because they are of interest to microfabrication for their soft magnetic properties and their selective etching behaviour, respectively. In particular, we show that in the electroplated Permalloy foils Ni keeps the structure of pure Ni while Fe changes from b.c.c. to f.c.c. NiP foils become increasingly amorphous with growing P content. In this way, radial elemental distributions which determine magnetic or other properties can be monitored sensitively to improve electroplating process control, even in situ. We also measure the radial thickness profile of a gold layer sputtered on top of a chromium coated silicon wafer. This technique might be extended to measure a given layer in a multilayer structure selectively and non-destructively even when hidden or opaque.     

Magnetic actuation of hinged microstructures

We have investigated magnetic actuation of hinged, surface micromachined structures. Electroplated magnetic material (Permalloy) is integrated with two types of hinged microstructures and the magnetic actuation process has been experimentally characterized. Under a given external magnetic field, the angular displacement of a hinged structure is determined by the volume of the magnetic material or by the stiffness of an auxiliary flexural loading spring. We have demonstrated parallel actuation of large arrays of hinged microstructures under a global (wafer scale) external magnetic field. The design rules for achieving a prescribed asynchronous actuation sequence among a group of microstructures have been determined to enable efficient parallel assembly of three-dimensional (3-D) microstructures     

Laser bending of etched silicon microstructures

 The process of contactless laser bending using the laser induced thermal stresses that up to this moment is performed with steels and other metal alloys is firstly applied to silicon microstructural elements. One-side-fastened Si beams prepared by anisotropic wet etching were locally heated by a Nd:YAG laser. The beams were bent without additional tools towards the incident laser beam. Bending angles up to 90° are realizable. The degree of bending is strongly dependent on the used laser parameters, the position of heating and the number and distance of the laser scans. Received: 8 February 2000/Accepted: 12 April 2000     

Surface tension driven formation of microstructures

The controlled formation of curved, three-dimensional (3-D) microstructures can be accomplished through solidification from a liquid phase. As a demonstration, we have placed objects in contact with the interface of a photopolymerizable liquid and air to create various liquid menisci that were subsequently solidified with ultraviolet radiation. Geometric control is achieved through variation of physical and environmental parameters; for example, solidified menisci formed at 25/spl deg/C were 300 /spl mu/m taller than those formed at 7/spl deg/C. Comparisons between the polymerized structures and theoretical predictions for liquid menisci indicate that the polymerization process results in repeatable changes in contact angle and meniscus size.     

Magnetically actuated, addressable microstructures

Surface-micromachined, batch-fabricated structures that combine plated-nickel films with polysilicon mechanical flexures to produce individually addressable, magnetically activated devices have been fabricated and tested. Individual microactuator control has been achieved in two ways: (1) by actuating devices using the magnetic field generated by coils integrated around each device and (2) by using electrostatic forces to clamp selected devices to an insulated ground plane while unclamped devices are freely moved through large out-of-plane excursions by an off-chip magnetic field. The present application for these structures is as micromirrors for microphotonic systems where they can be used either for selection from an array of mirrors or else individually for switching among fiber paths     

Multi-channel conical microstructures: perspectives

Known tasks when operating units of a microrobot (sensors, actuators, waveguides, liquid or gas pipelines, etc.) include the need for them to be quickly and precisely sequentially positioned in relation to a relatively tiny object (target). Even using a precision workpiece stage this process can take a long time. The use of conical multi-channel microneedles is proposed as one partial solution. Each channel of such a needle can transport its “own” target -specific liquid to a target (gene, drug). Essentially, all channels of a needle converge in the sharp end of a cone. Positioning of this end enables simultaneous positioning of all its channels. This property of a multi-channel needle has induced the author to consider an opportunity of creating multi-channel cone devices on the basis of the technology of ultra-high aspect ratio fibrous composites. Such an approach enables development of multifunctional cone MEMS/NEMS as in this case each of the channels can be made as an independent embedded device, for example, micromotor, microsolenoid, fluidic storage for micro/nanorobots or living organisms, X-ray or thermal neutron optic guide, photonic crystal, etc. The minimal cross-section size of the channels on the sharp end of experimental cone samples made from lead glass is (250–300?nm), with a cone base of 6,000?nm. The author makes the attempt to estimate the prospects for MEMS/NEMS on basis of multi-channel conical microstructures of fibrous composites.