The MEMSNAS process: microloading effect for micromachining 3-D structures of nearly all shapes

We propose a technological process for microfabrication of three-dimensional (3-D) structures with nearly all shapes. This is a one-mask process that uses equipment, widespread in the microelectronics laboratories and industry. The main idea is to take advantage from the microloading effect of reactive ion etching (RIE) in order to obtain multiple levels of heights in an array of microholes of different diameters. A 3-D profile results from an overlap of the neighboring microholes due to the isotropic nature of the etching. The final continuous and smooth 3-D structure is obtained after removal of the mask material and a second isotropic RIE step. This fabrication process was validated with the realization of various 3-D structures including microlenses, etched in a 30 /spl mu/m deep cavity, with 375 /spl mu/m in radius and 10 /spl mu/m in height (sag). The resulting structures have shown a roughness down to 25 nm. A quantitative experimental study led to the calibration of three different processes and to an empirical theoretical model, which can serve as a basis of design rules for further fabrication of 3-D microstructures.     

A Supervisory Wafer-Level 3D Microassembly System for Hybrid MEMS Fabrication

Hybrid MEMS (microelectromechanical systems) integrate solid-state ICs with MEMS sensors and actuators. It is widely believed that such systems will bring fundamental technological impacts and significant social benefits. Hybrid MEMS manufacturing requires the development of new fabrication, packaging and interconnection technologies in which microassembly plays a critical role. Microassembly is the assembly of objects with microscale and/or mesoscale features under microscale tolerances. It integrates techniques from many different areas such as robotics, computer vision, microfabrication and surface science. This paper studies the design and implementation of microassembly systems through the introduction of a supervisory microassembly workcell. This workcell is developed for 3D assembly of large numbers of micromachined thin metal parts into DRIE (deep reactive ion etching) etched holes in silicon wafers. It overcomes a major limitation of current MEMS fabrication techniques by allowing the use of incompatiable materials and fabrication processes to build complex-shaped 3D MEMS structures. The system is able to perform reliable and efficient wafer-level microassembly operations within a supervisory framework. Microassembly brings new and unique issues to robotics research. The major components of microassembly systems are analyzed. Results on micromanipulator design, illumination modeling and control, and microgripper design are presented.     

ProTEK PSB coating as an alternative polymeric protection mask for KOH bulk etching of silicon

The utilization of a newly developed photosensitive polymeric coating, ProTEK PSB plays a significant role in realizing simple process steps in the fabrication of MEMS devices using bulk micromachining technology. The photosensitive coating which serves as an alternative to the conventional silicon nitride mask of bulk potassium hydroxide (KOH) etching in devising MEMS devices, particularly in suspended microcantilever structure, is reported in this study. Although the polymeric coating ProTEK PSB acts as an excellent outer protective layer from any pinhole issues, the coating’s lateral etching in the KOH solution is dominant, which results in an undercut problem. Therefore, few investigations have been carried out to identify the most suitable condition for the ProTEK PSB deposition on Si substrate. Initial investigation was done on the effect of Si surface modification on the stability of the ProTEK PSB in KOH etching. It was observed that the surface treatment may reduce the undercut ratio for a short period of KOH etching. However, for the extended hours, the surface treatment is not effective enough to improve the stability of the polymeric coating. Therefore, combinations of ProTEK PSB on three substrates were studied in order to obtain a minimum undercut to etch depth ratio of the polymeric coating in KOH bulk etching. The study showed that the combination of ProTEK PSB patterned on thermal oxide results in the most effective etching condition attributed by minimum undercut ratio. Further investigation was carried out on the effect of the KOH etching concentration on the stability of the ProTEK PSB coating over the long hours of bulk etching process. Three concentrations of KOH etchants, KOH 20 wt%, KOH 45 wt% and KOH with isopropyl alcohol (KOH + IPA) were investigated. The results showed that the stability of the polymeric coating was excellent in KOH 20 wt% concentration with a very minimal undercut ratio of 0.05–0.07. In conclusion, the utilization of the polymeric coating ProTEK PSB serves as an alternative etch mask in KOH wet etching which offers simpler and cheaper device fabrication in bulk micromachining technology.     

Three-dimensional simulation of sacrificial etching

Sacrificial etching is one of the most important process steps in micro-electro-mechanical systems technology, since it enables the generation of free-standing structures. These structures are often the main part of micro-mechanical devices, intended to sense or induce a mechanical movement. The etching process transforms an initial multi-segmented geometry and depends on material properties and several process conditions. One of the crucial issues for etching is the etching selectivity on different materials. The major task for the simulation is to give an answer, how sacrificial layer surfaces regress in time under the influence of process parameters and to which magnitude surrounding material segments are affected by the etching process. For this purpose we have developed a fully three-dimensional topography simulation tool, Etcher-Topo3D, which is capable to deal with realistic process conditions. The main concept is demonstrated in this work. During simulation the topography of the initial multi-segment geometry is changed which is handled by a level-set algorithm. After a simulation is finished, the level-set representation has usually to be converted back to a mesh representation to enable further analysis. To illustrate the main features of our simulation tool several examples of MEMS structures with a sacrificial layer are presented.     

基于B 样条Snake模型的人体运动跟踪方法研究*

提出了一种基于B-样条曲线Snake模型的新的人体运动跟踪方法.Snake算法是通过最小能量来逼近物体的轮廓.采用改进的B-样条曲线Snake模型,每一帧图像中的目标轮廓用三次样条曲线准确地表示,使Snake模型更加稳定和具有较快的收敛速度.计算相邻帧之间的差分图像,通过利用一种基于统计关系双阈值分割方法,有效地检测出图像中运动人体,初步确定目标在每帧图像中的粗略位置.把从上一帧图像中得到的目标轮廓置于该位置,作为B-样条曲线Snake算法中轮廓提取的初始值,经运算后可得到对人体目标的准确分割与跟踪.     

Analytical Solution of the Continuous Cellular Automaton for Anisotropic Etching

The fabrication of micro- and nanoelectromechanical systems (MEMS/NEMS) is based on a wide variety of growth and etching technologies sequentially applied throughout process flows which may involve a dozen or more steps, their realistic simulation having become an essential part of the overall design. By focusing in the simulation of anisotropic etching as a complex example of microfabrication, in this paper, we show how to solve analytically the time evolution of the continuous cellular automaton method, thus providing a particularly suitable choice for the realization of realistic simulations for MEMS and NEMS applications. This paper presents a complete theoretical derivation of the analytical solution based on geometrical and kinetic aspects of step flow on any surface, including a new classification of the surface sites based on a mean-field treatment of the propagation of the steps. The results of the corresponding simulations are in good agreement with the experiments. The study can be seen as an example of a general procedure that is applicable to other interface propagation problems.     

Geometric algorithms for rapidly reconfigurable mold manufacturing of free-form objects

This paper presents geometric algorithms for developing a re-configurable tooling system for fabrication of freeform objects. The proposed method involves a mold block, with n faces, in which the mold cavity is formed by moving a set of discrete pins on each face of the block. The part surfaces are approximated in the mold cavity using the pins from the suitable mold block faces. The geometric algorithms detailed in this paper analyze the part and determine the face of mold block from which the part model is approximated best. Further, the algorithms detect possible interference between pins from different faces, and suitably alter the approximating face to alleviate interferences. By moving these pins in and out of the mold block, the shape of the mold cavity is reconfigured rapidly to suit the changes in part geometry. Since, the proposed method approximates free-form objects with discrete pins, a surface-error calculation method is also developed to control the accuracy. Computer implementation and examples are also presented in this paper.     

Modeling and fabrication of artistic products based on IFS fractal representation

Contemporary computer-aided design (CAD) and computer-aided manufacturing (CAM) theories and systems are well developed for analytical and free-form objects, but neither can deal with all artistically appealing objects efficiently. Artistically appealing objects are common in, for example, jewellery and furniture decoration. Therefore, it is valuable to explore more suitable modeling and manufacturing method for artistically appealing objects.Fractal geometry has been employed for modeling natural objects that cannot be described easily by Euclidean geometry. In this paper, one type of fractal solid — the Iterated Function System (IFS) fractal — is proposed for modeling artistically appealing objects in a computational form. A Radial-Blossoming Tree (RBT) data structure is worked out for fractal solid modeling in a CAD platform. Traversal algorithms have been devised to extract necessary information from the RBT for generating the toolpath for a layered manufacturing (LM) process, so that a physical fractal object can be built and the fabrication of a fractally represented artistic product can be realized.     

Solid-based CAPP for surface micromachined MEMS devices

Process planning for a MEMS device is almost always conducted manually by the designer to date. As the structures of MEMS devices become more and more complicated, in order to release the designers from the hard and tedious work and speed up the development of MEMS products, such a situation should be changed. In this study, a solid based CAPP method for surface micromachined MEMS device is presented. With this method, a MEMS device is designed with a traditional CAD system, and its process planning is conducted automatically based on the solid model created. The process features with engineering semantics are extracted first. Then, the process layer model is constructed with each process layer of the model being coincident with the fabrication layer of surface micromachining. Finally, the masks are synthesized and the fabrication process is generated. Furthermore, to guarantee the manufacturability of the designed MEMS device, a systematic evaluation method is proposed. The proposed design and CAPP methods enable designers to concentrate on functional and shape design of MEMS devices.     

RF MEMS电容式开关结构层释放技术

研究了RF MEMS开关的制造工艺流程和聚酰亚胺牺牲层的去除工艺。在开关的设计和加工中采用在信号线两侧的地线上生长一层绝缘介质层,直流偏置线生成在绝缘介质层之上,与桥的锚点相连接,实现了交直流隔离。讨论了干法刻蚀和湿法刻蚀牺牲层技术。干法刻蚀容易造成绝缘介质层的刻蚀和损伤。采用湿法刻蚀结合临界点干燥技术,可以获得理想的微梁结构。通过测试,开关样品的下拉电压为34 V～40 V,下拉距离为(1.7±0.2)μm,满足设计要求。     

基于窄带水平集的三维平面工艺模拟系统

表面工艺是MEMS制造的一种重要方法,实现其加工过程的计算机仿真可以为相关MEMS工艺研究和器件开发提供技术支持,减少相关MEMS产品的开发成本,缩短其开发周期.基于窄带水平集算法完成了表面加工工艺的三维表面工艺模拟系统.窄带水平集算法稳定,计算速度快处理拓扑变形非常灵活,本文将其应用于该软件仿真系统中,并进行了一列的仿真实验,将仿真结果与实际的流片电镜图对比,验证了仿真系统的精确性.     

Photogrammetric reconstruction of free-form objects with curvilinear structures

The shapes of many natural or man-made objects have curve features. The images of such curves usually do not have sufficient distinctive features to apply conventional feature-based reconstruction algorithms. In this paper, we introduce a photogrammetric method for recovering free-form objects with curvilinear structures. Our method chooses to obtain the topology and geometry of a sparse 3D wireframe of the object first instead of directly recovering a surface or volume model. Surface patches covering the object are then constructed to interpolate the curves in this wireframe while satisfying certain heuristics such as minimal bending energy. The result is an object surface model with curvilinear structures from a sparse set of images. We can produce realistic texture-mapped renderings of the object model from arbitrary viewpoints. Reconstruction results on multiple real objects are presented to demonstrate the effectiveness of our approach.     

Pyrex 7740玻璃深刻蚀掩模研究

玻璃湿法深刻蚀掩模常采用低压化学气相沉积(LPCVD)多晶硅、Cr/Au金属层+光刻胶等,但往往会在玻璃中引入应力,影响后期应用(如阳极键合),而且Cr/Au金属层价格昂贵。为避免以上缺点,引入了SX AR—PC 5000/40保护胶+WBR2075干膜作为玻璃的刻蚀掩模,在HF︰NH4F,HF︰HCl,HF︰HCl︰NH4F刻蚀溶液中进行了大量实验。实验结果表明:SX AR—PC 5000/40抗腐蚀能力强,且成功实现了对Pyrex 7740玻璃131μm的深刻蚀。整个工艺过程与IC工艺兼容,可以进行圆片级批量加工。实验结果对圆片级封装和其他MEMS器件的制作有一定参考作用。     

Simultaneous Surface Approximation and Segmentation of Complex Objects

Deformable models represent a useful approach to approximate objects from collected data points. We propose to augment the basic approaches designed to handle mostly compact objects or objects of known topology.Our approach can fit simultaneously more than one curve or surface to approximate multiple topologically complex objects by using (1) the residual data points, (2) the badly fitting parts of the approximating surface, and (3) appropriate Boolean operations. In 2-D, B-snakes [3] are used to approximate each object (pattern). In 3-D, an analytical surface representation, based on the elements detected, is presented. The global representation of a 3-D object, in terms of elements and their connection, takes the form of B-spline and Bézier surfaces. A Bézier surface is used to connect different elements, and the connecting surface itself conforms to the data points nearby through energy minimization. This way, aG¹continuity surface is achieved for the underlying 3-D object.We present experiments on synthetic and real data in 2-D and 3-D. In these experiments, multiple complex patterns and objects with through holes are segmented. The system proceeds automatically without human interaction or any prior knowledge of the topology of the underlying object.     

Point Signatures: A New Representation for 3D Object Recognition

Few systems capable of recognizing complex objects with free-form (sculptured) surfaces have been developed. The apparent lack of success is mainly due to the lack of a competent modelling scheme for representing such complex objects. In this paper, a new form of point representation for describing 3D free-form surfaces is proposed. This representation, which we call the point signature, serves to describe the structural neighbourhood of a point in a more complete manner than just using the 3D coordinates of the point. Being invariant to rotation and translation, the point signature can be used directly to hypothesize the correspondence to model points with similar signatures. Recognition is achieved by matching the signatures of data points representing the sensed surface to the signatures of data points representing the model surface.The use of point signatures is not restricted to the recognition of a single-object scene to a small library of models. Instead, it can be extended naturally to the recognition of scenes containing multiple partially-overlapping objects (which may also be juxtaposed with each other) against a large model library. No preliminary phase of segmenting the scene into the component objects is required. In searching for the appropriate candidate model, recognition need not proceed in a linear order which can become prohibitive for a large model library. For a given scene, signatures are extracted at arbitrarily spaced seed points. Each of these signatures is used to vote for models that contain points having similar signatures. Inappropriate models with low votes can be rejected while the remaining candidate models are ordered according to the votes they received. In this way, efficient verification of the hypothesized candidates can proceed by testing the most likely model first. Experiments using real data obtained from a range finder have shown fast recognition from a library of fifteen models whose complexities vary from that of simple piecewise quadric shapes to complicated face masks. Results from the recognition of both single-object and multiple-object scenes are presented.     

Arrays of hollow out-of-plane microneedles for drug delivery

Drug delivery based on MEMS technology requires an invasive interface such as microneedles, which connects the microsystem with the biological environment. Two-dimensional arrays of rigid hollow microneedles have been fabricated from single-crystal silicon using a combination of deep reactive ion etching and isotropic etching techniques. The fabricated needles are typically 200 /spl mu/m long with a wide base and a channel diameter of 40 /spl mu/m. The fabrication process allows creating either blunt needles or needles with sharp tips. Their shape and size make these needles extremely suitable for minimally invasive painless epidermal drug delivery. MEMS technology allows for batch fabrication and integration with complex microsystems. Fluid has been successfully injected 100 /spl mu/m deep into sample tissue through arrays of microneedles. Needle breakage did not occur during this procedure. Experiments have shown that the modified Bernoulli equation is a good model for liquid flowing through the narrow microneedle lumen.     

Efficient data structures for model-based 3-D object recognitionand localization from range images

An effective method of surface characterization of 3D objects using surface curvature properties and an efficient approach to recognizing and localizing multiple 3D free-form objects (free-form object recognition and localization) are presented. The approach is surface based and is therefore not sensitive to noise and occlusion, forms hypothesis by local analysis of surface shapes, does not depend on the visibility of complete objects, and uses information from a CAD database in recognition and localization. A knowledge representation scheme for describing free-form surfaces is described. The data structure and procedures are well designed, so that the knowledge leads the system to intelligent behavior. Knowledge about surface shapes is abstracted from CAD models to direct the search in verification of vision hypotheses. The knowledge representation used eases processes of knowledge acquisition, information retrieval, modification of knowledge base, and reasoning for solution     

逆向工程中自由曲面的自适应采样与建模

介绍了将逆向工程与正向设计结合实现自由曲面模型重构的新方法 .由激光线扫描法测量曲面获取截面轮廓数据 ,采用准均匀 B样条逼近算法对离散数据进行拟合 ,然后进行 B样条曲线基于曲率特征的自适应采样以实现数据压缩 ,再生成三维造型软件 Pro/ E的接口文件 *.ibl,最后在 Pro/ E中重构曲面模型 .     

基于切割成型的侧壁表面压阻制作及其参数优化

为了提高MEMS执行器件对面内运动位移（或力学信号）检测的灵敏度并改善侧壁检测电阻制作工艺与其他工艺及其不同器件结构之间的兼容性问题,提出一种基于离子注入工艺和深度反应离子刻蚀（DRIE）工艺相结合制作检测梁侧壁压阻的方法。在此基础上,详细分析了影响位移检测灵敏度和分辨率的各种因素,并对侧壁压阻的结构尺寸及其工艺参数进行优化。最后,给出了侧壁表面压阻在几种不同类型典型MEMS执行器件中的应用,取得了很好的应用效果。