Self-encapsulated hollow microstructures formed by electric field-assisted capillarity

Hollow microstructures serve many useful applications in the fields of microsystems, chemistry, photonics, biology and others. Current fabrication methods of artificial hollow microstructures require multiple fabrication steps and expensive manufacturing tools. The paper reports a unique one-step fabrication process for the growth of hollow polymeric microstructures based on electric field-assisted capillary action. This method demonstrates the manufacturing of self-encapsulated microstructures such as hollow microchannels and microcapsules of around 100-??m height from an initial polymer thickness of 22???m. Microstructure caps of several microns thickness have been shown to keep their shape under bending or delamination from the substrate. The inner surface of hollow microstructures is shown to be smooth, which is difficult to achieve with current methods. More complicated structures, such as a microcapsule array connected with hollow microchannels, have also been manufactured with this method. Numerical simulation of the resist growth process using COMSOL Multiphysics finite element analysis software has resulted in good agreement between simulated and experimental results on the overall shape of the resulting structures. These results are very positive and demonstrate the speed, versatility and cost-effectiveness of the method.     

Microfabrication of high-temperature silicon devices using waferbonding and deep reactive ion etching

As part of an effort to develop a micro gas turbine engine capable of providing 10-50 W of electrical power in a package less than one cubic centimeter in volume, we report the fabrication and testing of the first hydrogen combustor micromachined from silicon. Measuring 0.066 cm ³ in volume, and complete with a fuel manifold and set of fuel injector holes, the fabrication of the device was largely enabled by the use of deep reactive ion etching (DRIE) and aligned silicon wafer bonding. The 150-W microcombustor has a power density in excess of 2000 MW/m³ and has been successfully demonstrated to provide turbine inlet temperatures up to 1800 K. After 15 h of experimental tests, the combustor maintained its mechanical integrity and did not exhibit any visible damage. Combined with the results of a materials oxidation study, these tests are used to demonstrate the satisfactory performance of silicon in the harsh oxidizing environment of a combustion chamber     

Fabrication of metallic microstructures by electroplating usingdeep-etched silicon molds

A new technology is presented here to fabricate three-dimensional micromachined metal structures. The microstructures are manufactured by electroplating in deep-etched silicon structures followed by a separation from their mold. Up to 140-μm-deep silicon structures with vertical sidewalls are realized by an anisotropic plasma etching process producing the mold for electroplating. An etching gas mixture of SF_6s and CBrF₃ is used to achieve both an anisotropic etching behavior by protective film formation of CF₂ -radicals and high etching rates. The anisotropy is due to photoresist masking, which enhances the polymer formation. The vertical trenches are electroplated from the trench base filling the structures uniformly to the substrate surface. By avoiding overplating across the whole substrate the resulting structures are suitable for micromechanical devices. If needed, released microstructures from the silicon mold can be obtained by direct lift-off     

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     

Fracture behaviour of single crystal silicon microstructures

The fracture behaviour of single crystal silicon (SCSi) microstructures is analysed based on microme-chanical torsional and tensile experiments. The uniaxial testpieces are characterised by the presence of sharp not-ches at the gauge length extremities. The critical loading conditions are reproduced in a finite element model in order to identify the analogies of the failure conditions in tension and torsion. The stress field in the vicinity of the notch tip (were cracks originate) is analyzed, and fracture mechanics parameters are determined. In the finite element model a crack, reproducing the failure process observed in the experiments, is included. The crack area is incrementally increased and the energy release rate for the critical loading conditions in tension and torsion is calculated. Based on these results a failure criterion is formulated along with a procedure for the mechanical integrity analysis of SCSi microstructures of arbitrary shape and loading conditions.     

Mechanical characterization and design of flexible silicon microstructures

A variety of different silicon structures has been fabricated and characterized mechanically to optimize the design of silicon ribbon cables used in neural probes and multichip packaging structures. Boron-doped 3-/spl mu/m-thick silicon beams were tested in three modes: bending in plane, twisting (along beam axis), and pushing. Various cable configurations were investigated (straight beams, curved beams, meandered beams, etc.) as well the effects of length, width, cable termination, and the presence of reinforcing spans between multistranded cables. The results along with finite element modeling indicated that many simple modifications could be made to increase the strength and flexibility of silicon ribbon cables. One structure, a meandered beam 200-/spl mu/m wide and 2-mm long could be twisted up to 712/spl deg/. It also was seen that structures having multiple 20-/spl mu/m-wide beams were generally more robust than those with a single 500-/spl mu/m-wide beam. Finally, a method for easy determination of the bending fracture strain is analyzed and verified. It was seen that the silicon structures tested broke after a strain slightly above 2%.     

Fabrication of three-dimensional microstructures byelectrochemically welding structures formed by microcontact printing onplanar and curved substrates

This paper describes two convenient techniques for the fabrication of three-dimensional (3-D) structures with micron-sized features. The methods use microcontact printing (μCP) to define patterns with feature sizes as small as 20 μm both on planar substrates and on cylinders (diameter ~2 mm). Electrodeposition serves as a micron-scale tool for metal deposition and welding that transforms these patterned surfaces and cylinders into metallic complex 3-D microstructures (e.g., tetrahedra). Final tetrahedra (~2-cm sides) have feature sizes as small as 50 μm     

Investigation of attractive forces between PECVD silicon nitride microstructures and an oxidized silicon substrate

A troublesome phenomenon encountered during the realization of free-standing microstructures, for example, beams, diaphragms and micromotors, is that initially released structures afterwards stick to the substrate. This effect may occur during wafer drying after the etching process has been completed, as well as during normal operation as soon as released structures come into contact with the substrate. In this paper the most important types of attractive forces are discussed with respect to their possible influence on the performance of micromachined structures. It is concluded that the main reason for sticking of PECVD silicon nitride micromachined structures is adsorption of water molecules. The water molecules, adsorbed on both surfaces, attract each other as soon as the surfaces come into contact. It is shown that a chemical surface modification, in order to achieve hydrophobic surfaces, is an effective method for avoiding adsorption of water, and therefore reduces sticking. Sticking of micromachined structures during drying is reduced by rinsing with a non-polar liquid before wafer drying.     

Injection molding for microstructures controlling mold-core extrusion and cavity heat-flux

 In this work we constructed an injection press molding system with a mold-core extrusion mechanism and a small sensor assembly for effectively duplicating microstructures to the mold products. The mold-core extrusion mechanism is driven by a piezo element to apply force on important area with microstructures. For example, after injection it increases the cavity pressure from 20 to 34 MPa. Small sensors consist of the pressure, displacement, and heat flux sensor assemblies, arranged around the small cavity. The signals showed us the physical phenomena inside the mold and may be further used as control signal. In order to evaluate this injection press molding system, we formed micro triangular grooves of pitch 1 μm and angle 140°. The mold-core extrusion gave better diffraction intensity by several percents. Received: 16 May 2001/Accepted: 24 July 2001 The authors would like to thank FANUC Ltd. for cutting the triangular grooves on the mold-core. This paper was presented at the Conference of Micro System Technologies 2001 in March 2001.     

Testing of "Venetian-Blind" silicon microstructures with optical methods

In this paper, we illustrate the design and testing of new silicon microstructures, fabricated by means of a conventional planar process. These "Venetian-blind" structures consist of arrays of narrow, rectangular suspended masses (width =31 /spl mu/m, length =400 /spl mu/m, thickness =15 /spl mu/m), which can be tilted using electrostatic actuation. Characterization of their static and dynamic behavior was performed with optical methods. The diffraction patterns in monochromatic light were analyzed and vibration measurements were performed by means of semiconductor laser feedback interferometry: experimental data on the tilt angle as a function of the applied voltage and on the resonance frequencies are reported. A maximum tilt angle of approximately 1.9/spl deg/ was obtained with a driving voltage in the range of 70-95 V. All the tested devices showed resonance frequencies higher than 80 kHz, which is fast enough (i.e., switching time in the millisecond range) for future use in optical interconnections. Numerical analyses were performed to evaluate the coupled electromechanical behavior of the microstructures, confirming the observed experimental behavior.     

Plastic reshaping of silicon microstructures: process, characterization and application

 The plastic reshaping is applied to Si microstructures prepared by wet anisotropic etching. The performed processes are the deformation in a furnace with tools also prepared from Si and the laser beaming. The generation of dislocations necessary for the plastic deformation of the monocrystalline dislocation free material and the bending fracture strength of undeformed and deformed Si are investigated. Demonstrators for possible applications are presented.     

A CMOS compatible process for monolithic integration of high-aspect-ratio bulk silicon microstructures

We report a CMOS compatible bulk micromachining method for the integration of high-aspect- ratio single crystal silicon MEMS （micro electromechanical systems） devices and signal conditioning circuit on a standard silicon wafer. The trench refilling and residual silicon removing techniques are used to acquire a proper electrical insulation between the different actuation and sensing elements situated on either fixed or movable parts of an MEMS device. To demonstrate the compatibility of the process, an integrated MEMS accelerometer was implemented. Test results show that the resistance between different elements of the device is larger than 1012 Ω. The electrical properties of the transistors that experienced MEMS fabrication agree well with those without ]VIEMS process, indicting the CMOS compatibility of the process.     

超声波密闭容器液位传感器设计

针对现有超声波液位检测方法存在安装时需对容器开孔,从而破坏容器结构和声波受挥发性介质影响的问题,设计了一种非接触式超声波液位传感器,分析了传感器超声波频率的选取并给出了具体硬件电路的实现方案。该传感器根据超声波液位检测原理,以AT89S52为控制核心,采用收发一体超声波换能器,选取nRF2401作为无线收发模块,实现了密闭容器内液位数据的测量与无线传输。测试结果表明,该传感器测试精度较高,相对误差在3%以内,满足了现场液位实时测量的需要。     

Design of periodic elastoplastic energy dissipating microstructures

The design of periodic elastoplastic microstructures for maximum energy dissipation is carried out using topology optimization. While the topology optimization of elastic microstructures has been performed in numerous studies, microstructural design considering inelastic behavior is relatively untouched due to a number of reasons which are addressed in this study. An RVE-based multiscale model is employed for computational homogenization with periodic boundary constraints, satisfying the Hill-Mandel principle. The plastic anisotropy which may be prevalent in materials fabricated through additive manufacturing processes is considered by modeling the constitutive behavior at the microscale with Hoffman plasticity. Discretization is done using enhanced assumed strain elements to avoid locking from incompressible plastic flow under plane strain conditions and a Lagrange multiplier approach is used to enforce periodic boundary constraints in the discrete system. The design problem is formulated using a density-based parameterization in conjunction with a SIMP-like material interpolation scheme. Attention is devoted to issues such as dependence on initial design and enforcement of microstructural connectivity, and a number of optimized microstructural designs are obtained under different prescribed deformation modes.

     

Electroplated metal microstructures embedded in fusion-bonded silicon: conductors and magnetic materials

Fabrication methods for integrating thick (tens or hundreds of micrometers) electroplated metallic microstructures inside fusion-bonded silicon wafers are proposed and validated. Cu and Ni/sub 80/Fe/sub 20/ (permalloy) test structures were embedded inside of cavities in silicon wafers, which were fusion-bonded at 500/spl deg/C for 4h with nearly 100% yield. Resistance tests validated the electrical integrity of the metals after annealing, and magnetic measurements indicated the Ni-Fe maintained its magnetic performance after annealing. Additional mechanical tests verified a strong, uniform bond, and that the presence of the metals does not degrade the bond strength. These results demonstrate the ability to integrate conductive and magnetic materials in wafer-bonded silicon, a method useful for a variety of multiwafer, MEMS devices.     

Pre-buried mask wet etching for suspended silicon microstructures applied in rocking mass micro-gyroscope

Microsystem Technologies - A pre-buried mask method to fabricate suspended silicon microstructures by using pure wet etching in TMAH solution is presented in this paper. Pre-buried mask method...     

硅悬臂梁脉象传感器温度补偿

阐述了采用硅悬臂梁制造的脉象传感器结构、设计和温度补偿原理。实验结果表明:补偿后的传感器具有灵敏度高、稳定性好,线性度为1%FS(0~5 N),重复性为0.5%FS,灵敏度为50 mV/N。给出的温度补偿晶体管对该脉象传感器的灵敏度温度漂移补偿效果好,有推广应用前景。     

硅--蓝宝石绝压传感器陶瓷密封结构设计与分析

介绍了硅—蓝宝石绝压传感器中氧化铝陶瓷—钛合金的真空密封参考腔小型化结构设计,探讨了异质材料不匹配引起的陶瓷断裂问题,对陶瓷—钛合金封装结构的应力情况进行了计算和分析,通过中间缓冲层设计、减小陶瓷承受的结构残余应力,消除了由陶瓷断裂导致的密封失效;选择热胀系数相近的可伐中间层材料,对比不同厚度缓冲层产生的残余应力,优化中间层结构,采用LTCC加工技术与真空钎焊工艺结合制作了陶瓷—可伐—钛合金密封组件,并通过了高、低温度试验考核:组件密封漏率小于1×10-10 Pa·m3/s,密封可靠,满足绝压传感器使用寿命的要求.     

Laterally vibrating MEMS resonant vacuum sensor based on cavity-SOI process for evaluation of wide range of sealed cavity pressure

Microsystem Technologies - This paper reports a laterally vibrating MEMS resonant vacuum sensor which senses ambient pressure based on the squeeze-film damping effect. The single-anchored...