Effects of carbon fillers on the tribological and mechanical properties of an epoxy-based polymer (SU-8)

SU-8, an epoxy-based negative photoresist polymer, is highly suitable for making micro-electro-mechanical systems (MEMS) structures. Despite fabrication advantages, its bulk mechanical and tribological properties are the main limitations for application as MEMS material. Carbon filler materials such as graphene, graphite and multi-walled carbon nanotube (MWCNT) are added to SU-8 for tribological and mechanical property enhancements. SU-8/(5 wt%) graphite composite has performed better for the steady-state coefficient of friction at all loads including for the speed effect. SU-8/(5 wt%) MWCNT has shown excellent wear resistance. At 10 wt% graphite content, SU-8/graphite is superior in tribological performance to other composites tested.     

Self-lubricating SU-8 Nanocomposites for Microelectromechanical Systems Applications

SU-8 is an industrially useful photoresist polymer for micro-fabrication because of its unique UV-sensitive curing property. It is also used as a structural material for micro-machines such as micro-electro mechanical systems (MEMS). However, it has poor tribological and mechanical properties which make SU-8 inferior to Si, the mainstay MEMS material today. In this paper, we report the fabrication of SU-8 nanocomposites which are self-lubricating and have better mechanical properties. The liquid lubricant i.e., perfluoropolyether (PFPE) and nanoparticles such as SiO₂, CNTs, and graphite were added into SU-8 for this purpose. These self-lubricating SU-8 + PFPE and SU-8 + PFPE + nanoparticle composites have shown a reduction in the initial coefficient of friction by ~6?C9 times and increased wear life by more than four orders of magnitude. The mechanical properties such as the elastic modulus and the hardness have increased by ~1.4 times. These SU-8 nanocomposites can be used as a self-lubricating structural material for MEMS applications requiring no external lubrication. As well, these nanocomposites can find applications in many tribological components of traditional machines.     

超声时效技术在微注塑模具制作中的应用

针对金属微注塑模具UV-LIGA制作过程中由于SU-8胶内应力过大而引起的胶膜破裂、变形甚至脱落等问题,提出将超声时效技术应用于微注塑模具的制作工艺.首先,利用紫外光刻工艺制备了电铸胶膜,在显影前使用自制的超声时效装置对胶膜进行超声处理.然后,采用无背板生长方法在38CrNiMnMo模具钢基底上直接进行镍金属的电铸生长,讨论并解决了工艺过程中遇到的SU-8胶浮胶变形、非圆形基片的匀胶、胶膜中的气泡以及微电铸层结合不牢等问题.最后,制作出微通道宽度和高度分别为80 μm和35 μm的微注塑模具.实验结果表明,超声时效技术的使用避免了由于SU-8胶内应力过大引起的破裂、变形甚至从基底脱落等缺陷,增强了UV-LIGA技术制作微注塑模具的能力,提高了制作微注塑模具的成功率.     

Effects of temperature on mechanical properties of SU-8 photoresist material

A representative fabrication processing of SU-8 photoresist, Ultraviolet (UV) lithography is usually composed of spin coat, soft bake, UV exposure, post exposure bake (PEB), development and optional hard bake, etc. The exposed region of SU-8 is crosslinked during the PEB process and its physical properties highly depend on UV exposure and PEB condition. This work was initiated to investigate if thermal baking after fabrication can affect the mechanical properties of SU-8 photoresist material because SU-8 is trying to be used as a structural material for MEMS operated at high temperature. Since a temperature of 95°C is normally recommended for PEB process, elevated temperatures up to 200°C were considered for the optional hard bake process. The viscoelastic material properties were measured by dynamic mechanical analyses (DMA). Also, pulling tests were performed to obtain Young’s modulus and Poisson’s ratio as a function of strain rate in a wide temperature range. From this study, the effects of temperature on the elastic and viscoelastic material properties of SU-8 were obtained.     

Surface roughness and geometrical characterization of ultra-thick micro moulds for ceramic micro fabrication using soft lithography

Ceramic micro fabrication using soft lithography is a well-known technique used to pattern high-aspect-ratio microstructures. The quality of the pattern highly relies on the quality of the moulds. This paper describes the surface roughness and geometrical characterization of soft lithography technique for the fabrication of ceramic micro components. Effects of patterning materials and methods on the produced geometry, repeatability and surface roughness were studied and a comparative study was performed for the optimization process. UV lithography of BPR100 and SU-8 and deep reactive ion etching are the methods for fabricating the master mould. In addition, polydimethylsiloxane and Dragon Skin elastomeric have been used in the fabrication of the soft moulds. Mould geometry was inspected using SEM images while surface roughness was measured using stereo imaging. The results show that the maximum obtained thicknesses are 1,000, 250 and 500 μm for SU-8, BPR100 and DRIE moulds. In addition, their surface roughness values are higher than the SU-8. On the other hand, Dragon Skin shows demoulding problems despite it has smoother surface than PDMS mould.     

基底材料对石墨烯膜F-P声压传感器灵敏度的影响分析

文中以多层石墨烯膜为敏感膜片,分别制备了基于P DMS、SU-8、氧化锆的石墨烯膜F-P声压传感器,应用薄膜与基底之间吸附理论,分析了石墨烯膜与基底间吸附能相对于基底材料的杨氏模量成正向变化的趋势,并实验测试了所制备的声压传感器灵敏度.实验结果表明,制备的PDMS和SU-8基底具有较大的表面粗糙度,其虽降低了与石墨烯膜...     

Friction and wear durability studies on the 3D negative fingerprint and honeycomb textured SU-8 surfaces

The effects of two different textures (a 3D negative fingerprint texture and a honeycomb texture) on the tribological performance of SU-8 polymer surface have been investigated with a ball-on-disc tribometer. Friction and wear behaviors of the textured surfaces are conducted against a 4 mm diameter silicon nitride (Si₃N₄) ball counterface. The coefficient of friction for the negative fingerprint textured surface (μ=∼0.08) is much lower than that of the untextured surface (∼0.2) and the honeycomb textured surface (∼0.41) under a normal load of 100 mN and a rotational speed of 2 rpm. The coefficients of friction of the textured surfaces decrease with increasing normal loads between 100 mN and 300 mN. Above the normal load of 300 mN, the coefficient of friction of the negative fingerprint textured surface increases due to the occurrence of plastic deformation. The honeycomb textured surface has shown the highest coefficient of friction. The wear durability tests are also conducted at a normal load of 100 mN and a rotational speed of 500 rpm on the untextured/textured surfaces on SU-8 in the presence of an overcoat of a nano-lubricant, perfluoropolyether(PFPE). Six samples i.e. the untextured surface (Si/SU-8 and Si/SU-8/PFPE), the 3D negative fingerprint textured surface (Si/SU-8/FP and Si/SU-8/FP/PFPE) and the honeycomb textured surface (Si/SU-8/HC and Si/SU-8/HC/PFPE), each with and without PFPE nano-lubricant, have been investigated for their tribological behaviours. The negative fingerprint pattern on SU-8 with PFPE coating has shown the highest wear life of 60,000 cycles under a normal load of 100 mN. The reasons for excellent tribological performance of 3D fingerprinted SU-8 surface are analyzed using the Hertzian contact area calculation.     

SU-8胶光刻工艺研究

SU-8胶是一种基于环氧SU-8树脂的环氧型的、近紫外光、负光刻胶.其专门用于在非常厚的底层上需要高深宽比的应用.但是SU-8胶对工艺参数的改变非常敏感.本文对影响光刻后图形质量的主要工艺参数前烘温度和时间、中烘温度和时间、曝光时间及显影时间进行了研究,发现前烘时间和显影时间是影响图形分辨率及高深宽比的最主要的参数.随后给出了200μm厚SU-8光刻胶的建议工艺条件:200μm/s甩胶,1h的95°C前烘,近紫外光(400nm)接触式曝光,95°C的中烘 30min,PGMEA中显影20min.另外对实验中实现的主要问题基片弯曲和光刻胶的难以去除作了一定的探讨,给出了合理化建议:对于基片弯曲可采用以下四种措施来降低,降低中烘的温度同时增加中烘的时间、用厚硅片来代替薄硅片、对于薄硅片在前烘后可用金刚刀切成4～8小片、适当的设计掩模板;对于光刻胶的去除用热丙酮泡、超声清洗、反应离子刻蚀和高温灰化法相结合,能达到较好的效果.     

超声处理对UV-LIGA工艺中SU-8胶溶胀的影响

首次将超声处理引入UV-LIGA工艺中,研究了超声处理对SU-8胶模溶胀的影响,并探讨了其影响机理,从而获得了减小胶模溶胀及提高电铸微器件尺寸精度的方法.试验研究了超声处理对显影过程及电铸过程中SU-8胶模溶胀的影响,分析了不同超声时间下SU-8胶表面亲水性的变化趋势,并计算了不同超声时间下胶模的溶胀去除率.讨论了超声处理对不同结构微器件尺寸精度的影响.试验结果表明:SU-8胶模在显影过程中的溶胀不明显,并且超声处理对显影过程中胶模的溶胀影响很小,其主要影响SU-8胶模在电铸过程中的溶胀.随着超声时间的增加,胶模溶胀及其表面亲水性均呈现先减小后增大的趋势.当超声时间为10 min时,胶模溶胀最小,其溶胀去除率a值可高达70％,并且超声处理后电铸微器件的尺寸误差与结构尺寸无关.根据超声波的机械断键作用与聚合物吸水机理,从亲水性和内应力两个方面,探究了SU-8胶模溶胀随超声时间的增加而变化的原因.文中提出的减小SU-8胶溶胀的方法不依赖于工艺参数也不会增加掩模图形设计的复杂性,是一种实用的减小SU-8胶溶胀的新方法.     

Alleviation of the adhesive protrusion problem at the bonding interface of free-standing microstructures

The vertically allocated free-standing SU-8 microstructures are typically bonded to a glass cover by the usage of uncrosslinked SU-8 adhesives. Such a phenomenon can easily cause SU-8 protrusion and eventually result in the SU-8 cantilever to be immovable. Traditional methods are sensitive to the bonding conditions and have a short bondable thickness of SU-8 adhesives. In this study, we propose an approach, that is, improved structural features, to alleviate the protrusion problem while extending the bondable thickness for the freestanding SU-8 microstructures in an enclosed channel. We used concave and moat microstructures as solutions of the improved structural features. We investigated the influence of both microstructures on the bonding quality and compared the bondable thickness with the previous one. THB-151N was used in another example to demonstrate the availability of our method. The bonding quality at the interfaces was evaluated by SEM images and direct inspection through a transparent glass cover. The bonding method is advantageous to other microfluidic systems, particularly those with long narrow channels.

     

UV-LIGA技术制作微型螺旋形加速度开关

微型加速度开关是用于空间飞行体中感受加速度并完成致动的重要惯性器件。本文采用UV-LIGA技术,结合SU-8厚胶工艺、微电铸工艺以及牺牲层技术,制作了微型螺旋形加速度开关。研究了牺牲层工艺、SU-8光刻技术以及螺旋形弹簧形变控制等微细加工的工艺细节;分析了多种牺牲层材料的特性,优选了与工艺相适应的Zn牺牲层体系,解决了微结构易脱落的工艺问题。通过优化微电铸工艺来减小金属膜层的内应力,优化牺牲层释放工艺来避免腐蚀过程对弹簧膜结构的冲击。实验结果表明,通过工艺优化可得到平整的微型螺旋形弹簧—质量块结构,螺旋弹簧厚度为20μm,质量块厚度达200μm,本文的工作可为大批量、低成本地研制微型加速度开关提供工艺基础。     

Photoplastic near-field optical probe with sub-100 nm aperture made by replication from a nanomould

Polymers have the ability to conform to surface contours down to a few nanometres. We studied the filling of transparent epoxy‐type EPON SU‐8 into nanoscale apertures made in a thin metal film as a new method for polymer/metal near‐field optical structures. Mould replica processes combining silicon micromachining with the photo‐curable SU‐8 offer great potential for low‐cost nanostructure fabrication. In addition to offering a route for mass production, the transparent pyramidal probes are expected to improve light transmission thanks to a wider geometry near the aperture. By combining silicon MEMS, mould geometry tuning by oxidation, anti‐adhesion coating by self‐assembled monolayer and mechanical release steps, we propose an advanced method for near‐field optical probe fabrication. The major improvement is the possibility to fabricate nanoscale apertures directly on wafer scale during the microfabrication process and not on free‐standing tips. Optical measurements were performed with the fabricated probes. The full width half maximum after a Gaussian fit of the intensity profile indicates a lateral optical resolution of ≈ 60 nm.     

Micro-scale Realization of Compliant Mechanisms:Manufacturing Processes and Constituent Materials——A Review

Compliant micromechanisms (CMMs) acquire mobility from the deflection of elastic members and have been proven to be robust by millions of silicon MEMS devices.However,the limited deflection of silicon impedes the realization of more sophisticated CMMs,which often require larger deflections.Recently,some novel manufacturing processes have emerged but are not well known by the community.In this paper,the realization of CMMs is reviewed,aiming to provide help to mechanical designers to quickly find the proper realization method for their CMM designs.To this end,the literature surveyed was classified and statistically analyzed,and representative processes were summarized individually to reflect the state of the art of CMM manufacturing.Furthermore,the features of each process were collected into tables to facilitate the reference of readers,and the guidelines for process selection were discussed.The review results indicate that,even though the silicon process remains dominant,great progress has been made in the development of polymer-related and composite-related processes,such as micromolding,SU-8 process,laser ablation,3D printing,and the CNT frameworking.These processes result in constituent materials with a lower Young's modulus and larger maximum allowable strain than silicon,and therefore allow larger deflection.The geometrical capabilities (e.g.,aspect ratio) of the realization methods should also be considered,because different types of CMMs have different requirements.We conclude that the SU-8 process,3D printing,and carbon nanotube frameworking will play more important roles in the future owing to their excellent comprehensive capabilities.     

Micromachined fragment capturer for biomedical applications

Due to changes in modern diet, a form of heart disease called chronic total occlusion has become a serious disease to be treated as an emergency. In this study, we propose a micromachined capturer that is designed and fabricated to collect plaque fragments generated during surgery to remove the thrombus. The fragment capturer consists of a plastic body made by rapid prototyping, SU-8 mesh structures using MEMS techniques, and ionic polymer metal composite (IPMC) actuators. An array of IPMC actuators combined with the SU-8 net structure was optimized to effectively collect plaque fragments. The evaporation of solvent through the actuator's surface was prevented using a coating of SU-8 and polydimethylsiloxane thin film on the actuator. This approach improved the available operating time of the IPMC, which primarily depends on solvent loss. Our preliminary results demonstrate the possibility of using the capturer for biomedical applications.     

SU-8胶紫外光刻的尺寸精度研究

研究了衍射效应对SU-8胶紫外光刻尺寸精度的影响。根据菲涅耳衍射理论建立了紫外曝光改进模型,预测微结构的尺寸,分析了光刻参数变化对尺寸的影响。为了更好地与数值模拟结果进行比较,以硅为基底,进行了SU-8胶紫外光刻的实验研究。实验分四组,实验中掩模的特征宽度分别取50 μm、100 μm、200 μm和400 μm,SU-8胶表面的曝光剂量取400 mJ/cm²。用扫描电镜测量了微结构的顶部线宽、底部线宽和SU-8胶的厚度,用MATLAB软件对紫外曝光过程中SU-8胶层内曝光剂量的分布情况进行了数值模拟,数值模拟结果与实验结果基本吻合。数值模拟结果为进一步的实验研究提供了光刻参数的参考值。     

Tribological analysis of tip-cantilever made of SU-8, talc and PFPE composite

ABSTRACT

SU-8 polymer with talc particle (30?wt-%) and liquid perfluoropolyether (PFPE) (30?wt-%) fillers was used as a composite to fabricate conical tip-cantilever device. The composite tip demonstrated lower coefficient of friction (～0.22) when compared with a tip made of pure SU-8 (～0.65). Fluorine was detected on the wear track and the tip surface, which resulted from the transfer of PFPE from the tip to the wear track. The counterface made of pure SU-8 remained smooth and unworn when slid against the composite tip even after 1000 cycles of sliding. This composite with improved tribological and mechanical properties can be used for fabricating small component devices such as for micro-electro-mechanical systems (MEMS).     

基于MEMS微加工技术的高灵敏度隧道传感器的研究

基于硅加工的高灵敏微型隧道传感器在过去15年里得到了充分的发展.多种隧道传感器被开始出来,例如加速度计,角速度计,红外传感器,磁性传感器等.首先对基于硅加工的隧道传感进行了简单的总结.对四种传感器进行了总结和讨论,包括几种器件的结构设计,加工过程,器件性能,控制电路和系统噪音.特别介绍了一种新型的基于高分子聚合物的隧道加速度计,并讨论了其结构,加工与测试,隧道效应得到了进一步验证.同时给出了这种新型高灵敏传感器在很多领域的应用展望.     

Polymer Jet Printing of SU-8 Micro-Dot Patterns on Si Surface: Optimization of Tribological Properties

Tribological properties of optimized SU-8 patterns (micro-dots with varying pitch) on Si (silicon) were evaluated using a ball-on-disk tribometer. Sliding tests on the patterns were conducted against a 2-mm diameter Si₃N₄ ball at varying normal loads and sliding velocities. It was observed that the pitch of the SU-8 pattern on Si substrate had a significant effect on the initial coefficient of friction and wear durability. Initial coefficient of friction studies have concluded that the SU-8 polymeric micro-dots improved the tribological properties by sharing the normal force and reducing the contact area. For the wear durability test, ultra-thin layer of perfluoropolyether was over-coated onto SU-8 micro-dot specimens, and the optimized pitch specimens have shown wear durability of more than 100,000 cycles at a normal load of 350 mN.     

模糊神经网络在UV-LIGA工艺优化中的应用

将模糊神经网络理论和算法应用于负性光刻胶(SU-8)加工高分辨率和高深宽比微结构的工艺研究,在正交试验的基础上对网络进行训练,建立了光刻图形质量与前烘时间、前烘温度、曝光量、后烘时间之间的预测模型。该模型采用五层前向模糊神经网络,学习算法为梯度下降法。进行了实验,实验结果表明,前烘温度与前烘时间对光刻质量影响最大。对120~340 μm厚的光刻胶,前烘温度取95℃,前烘时间100 min时,图形的相对线宽差最小;超声搅拌能缩短显影时间,显著改善图形质量,试验结果与计算结果十分吻合。将模糊神经网络应用于UV－LIGA工艺中,能实现光刻加工微结构的工艺参数优化。     

SU-8胶光弹性性能显微测试

考虑获知SU-8胶的光弹性性能有利于拓展其在微纳米领域中的应用范围,本文设计了材料应力光学系数显微测量光路,完成了SU-8胶应力光学系数的测量实验。首先,基于光弹性原理设计了测量光路,推导了求解应力光学系数的计算公式;然后,根据所设计的光路搭建了应力光学系数显微测量实验装置,在SU-8胶试样光弹性条纹的单个半级数范围内进行了单向拉伸实验;最后,利用Matlab提取实验照片组中光强值信息,得到了不同拉力下透过SU-8胶试样的单色光光强值,计算求解出了SU-8胶的应力光学系数。实验结果以及测量公式计算显示,SU-8胶的应力光学系数为(3.007±0.149)×10–11 m2/N,大于光学玻璃等材料的应力光学系数,也远大于二氧化硅等MEMS领域常用材料的应力光学系数。实验结果可为以SU-8胶为材料,通过光弹性原理进行微力测量的微探针、微夹钳等的设计与制作打下基础。