Fabrication of high-aspect-ratio microstructures in polymer microfluid chips for in vitro single-cell analysis

Technologies and methods of prototyping microfluidic devices are widely used in solving many biological problems and testing of operability of new microanalytic systems. This study is devoted to analyzing the features of the formation of microstructures in SU-8 photoresist and the preparation of replicas in polydimethyl siloxane by the soft lithography method. It has been shown that the aspect ratio of the resultant microstructures is determined by their shape, size, and the force of resist adhesion to the silicon substrate and the efficiency of the circulation of the developer around microstructures. In the replication of complex microstructures, an aspect ratio of ~25 is attained. The technology considered here is used to prepare microfluidic chips with mechanical traps for fixation and the in vitro analysis of living cells.     

355nm激光曝光SU-8胶的XPS谱和FT-IR谱研究

SU-8光胶因具有良好的光刻性能,并可获得稳定的高深宽比而在微加工领域得到了广泛的应用。众多研究采用不同的光源对其进行了多种光刻研究,本文应用355nm激光对SU-8胶进行曝光,分别采用XPS谱和FT-IR谱分析了SU-8胶与激光相互作用过程中,355nm激光对SU-8胶的作用以及反应前后主要成分含量、分子结构的变化,初步探讨了SU-8胶中激光曝光能量与透入深度的关系。     

Simulation of 3D inclined/rotated UV lithography and its application to microneedles

A 3D model is set up to simulate the exposure process of inclined/rotated UV lithography for negative SU-8 resists. The formation of inclined resist pillars and microstructures with truncated cone shapes is simulated based on a 3D exposure model in combination with a post exposure bake model for chemically amplified resists and the Mack development model. As one of the interesting applications employing this promising lithography technique for MEMS fabrication, a solid microneedle for drug delivery is simulated.     

严格电磁场波导方法的三维厚胶光刻工艺仿真（英文）北大核心CSCD

无论是在微机电系统(MEMS)还是集成电路(IC)领域,SU-8厚胶光刻已经成为制造高深宽比结构的主流工艺。为了取代昂贵而耗时的光刻实验,一套能够良好预测显影形貌,从而为优化光刻制造提供有效帮助的光刻仿真软件就成为必要而有价值的工具。基于严格电磁场波导法的理论,给出一种针对SU-8光刻胶在紫外光下的三维光刻仿真模型。利用该模型,能很好地预测显影后的光刻胶内光强分布和立体形貌。并完成了一系列仿真和实验结果来验证模型的有效性。仿真结果给出横截面光强分布图和显影立体形貌模拟图形,并与相应的实验结果进行对照。结果验证了本文提出的仿真模型的正确性,并且表明三维混合模型在保证精确性的前提下,较之其他仿真算法运算速度更快。     

SU-8 based planar metamaterials with fourfold symmetry as selective terahertz absorbers

We report on the absorption properties of polarization-insensitive transmissive and reflective metamaterial absorbers based on two planar aluminium periodic structures and SU-8 epoxy resist. These absorbers were investigated using numerical simulation and experimental methods in the terahertz range (below 2 THz). SU-8 is a very promising organic material for dielectric layers in planar metamaterials, because its application simplifies the process of fabricating these structures and significantly reduces the fabrication time. The experimental absorption of the metamaterial absorbers has narrowband characteristics that were consistent with the numerical simulations. Power flow analysis in the transmissive metamaterial unit cell shows that the absorption in the terahertz range occurs primarily in the SU-8 layer of the absorber.     

A novel design and micro-fabrication for copper (Cu) electroforming bipolar plates

A novel design and micro-fabrication were developed for micro-proton exchange membrane (PEM) fuel cell stack bipolar plates with cross section of 5 cm² and thickness of about 650 μm. Copper metals were used to make bipolar plates (BPs) by using a LIGA-like micro-fabrication process of deep UV lithography in order to obtain SU-8 resist patterns/and SU-8 mould. Through two-sided exposure and development, copper metal bipolar plates with serpentine (meandering) flow field configurations for a micro PEM fuel cell stack, were fabricated and performance tests through polarization characteristics were conducted; this made it possible for the first time to consider copper sheets as suitable for BPs in micro PEM fuel cell stacks.     

Direct removal of SU-8 using focused laser writing

SU-8 photoresist is an important material used in the development of micro-devices [1]. Cross-linked SU-8 structures have been known for their thermal stability and their strong resistance to standard solvent, acid and base. Due to the inert properties of this polymer, it is difficult to further modify or remove SU-8 once it is completely cured. We report an effective process to pattern cured SU-8 photoresist on glass using focused laser beam. Laser fabrication has been an important tool in various fields of research [2]. We made use of this laser cutting method to create interesting and useful two-dimensional SU-8 structures. The shapes and sizes of the structures created can be controlled by varying the power of the laser, angle of incident of the focused laser beam, the relative speed with which the laser beam traverse through the SU-8 film and the magnification of objective lens used. Besides two-dimensional structures, we can also create three-dimensional structures. In this case, we made use of a combination of controlled depth cutting and undercutting where focused laser beam is transmitted through the transparent substrate. Some possible applications of the laser patterned SU-8 film are also demonstrated in this work. PACS 42.62-b; 42.82.Cr; 79.60.Fr; 79.20.Ds; 78.66.-w     

SU-8去胶工艺对电铸Ni材料力学性能的影响（英文）北大核心CSCD

SU-8负胶具有优异的力学性能、抗化学腐蚀性、热稳定性和生物兼容性,在MEMS工艺和器件中得到广泛应用。镍金属具有良好的力学性能和抗腐蚀性,因此常用来制作MEMS器件。在MEMS执行器中,弹性元件常采用电铸镍制作。SU-8经过经曝光显影后形成致密的交联网络结构是一种高分子聚合物,这种聚合物非常稳定,不溶于强酸强碱及常见的有机溶剂,尤其是在电铸金属结构后的SU-8胶的去除更为困难。目前的SU-8去胶技术,按去胶原理可分:机械物理去胶技术和氧化去胶技术。氧化去胶技术可以有效去除SU-8胶,但氧化去胶方法不同程度地损坏电铸金属,使其力学性能与去胶前相比发生显著的变化。因此需要研究去胶对Ni金属弹性模量的影响,从而为执行机构设计提供准确的基本数据。针对目前运用比较普遍的两种去除SU-8胶方式:微波等离子下游化学刻蚀和强碱熔盐浴,分别进行了去胶实验,对去胶前后的电铸Ni金属进行了弹性模量和硬度测试。实验结果表明,电铸镍的杨氏模量在经过微波等离子下游化学刻蚀后下降18%,而经过强碱熔盐浴后下降36%,但硬度下降不明显。     

Reduction of capillary force for high-aspect ratio nanofabrication

The wet processing of SU8 resist was modified in order to achieve a high-aspect ratio patterning with feature size of 100 nm. A final rinse in water, which makes a large contact angle on the resist (less wetting) was added to the procedure. This allowed considerable reduction of the capillary force, which is responsible for pattern distortions in three-dimensional (3D) lithography. 3D recording of high-aspect ratio (f_ar=18) structures by holographic exposure using femtosecond pulses in SU8 resist was achieved using this modified development procedure. The thickness of the free-standing planes was approximately 100 nm. High fidelity of this recording method was confirmed by a Moiré pattern transfer into a developed SU8 pattern. In terms of focusing, the 100 nm feature size comprised 1/13-th of the diffraction limit. This modified development is applicable for wet processing when super-critical drying cannot be used. PACS 81.05.-t; 81.07.-b; 81.16.-c; 81.40.-z; 81.65.-b     

Soft X-ray optimization studies on a dense plasma focus device operated in neon and argon in repetitive mode

This paper investigates the emission characteristics of a high-performance low-energy (3-kJ) repetitive dense plasma focus device, NX2, operated at up to 1-Hz repetition rate to develop it as an intense source of soft X-rays (SXR) for microlithography and micromachining. Various SXR yield optimization studies with argon and neon as filling gases were performed under different operating conditions (charging voltage, filling pressure, anode length, and insulator sleeve length). The SXR yield was computed using signals obtained from a PIN diode SXR spectrometer with appropriate filters. When operated in neon, the average optimum SXR (/spl lambda//spl sim/1 nm) yield in 4/spl pi/ steradians was found to be up to 140 J/shot, which corresponded to a wall plug efficiency of 5.6%. Operation in argon showed that optimized SXR (/spl lambda//spl sim/0.4 nm) yield was up to 1.3 J/shot. While operating with neon under optimized conditions with a water-cooled anode in repetitive mode, the NX2 device was used as a SXR source to imprint a test lithograph on a highly sensitive chemically-amplified resist SU-8. Test structures showing the effect of a stepper with aspect ratio 3:1 on 10-/spl mu/m-thick SU-8 resist film were obtained.     

Integrated SU-8 photonic gas sensors based on PANI polymer devices: Comparison between metrological parameters

In this work, we have designed and developed three families of integrated photonic sensors for ammonia detection. These photonic sensors are integrated onto single-mode TE₀–TM₀ SU-8 polymer planar waveguides and based on a polyaniline (PANI) sensitive polymer material. The first family relies on the deposit of a PANI–polymethyl methacrylate (PMMA) composite sensitive layer on a given SU-8 waveguide. The second family relies on a PMMA passive layer deposited on the SU-8 waveguide before applying the PANI sensitive layer on the PMMA passive layer. The third family takes advantage of a PANI layer deposited by plasma technique directly onto the SU-8 waveguide. The working principle of such sensors is based on the optical intensity modulation induced within the single-mode waveguide owing to the interaction between the evanescent field and the sensitive layer. The sensing proprieties of these integrated photonic sensors to ammonia gas at room temperature were characterized and the comparison between these different families of photonic sensors is presented. Experimental results show that the sensor based on new plasma–PANI as sensitive layer has the better metrological parameters.     

The three-dimensional photonic crystals coated by gold nanoparticles

We report on the fabrication of metallodielectric photonic crystals by means of interference lithography and subsequent coating by gold nanoparticles. The grating is realized in a SU-8 photoresist using a He-Cd laser of wavelength 442 nm. The use of the wavelength found within the photoresist low absorption band enables fabricating structures that are uniform in depth. Parameters of the photoresist exposure and development for obtaining a porous structure corresponding to an orthorhombic lattice are determined. Coating of photonic crystals by gold nanoparticles is realized by reduction of chloroauric acid by a number of reductants in a water solution. This research shows that the combination of interference lithography and chemical coating by metal is attractive for the fabrication of metallodielectric three-dimensionally periodic microstructures.     

SU-8光刻胶应变分布光学全场检测方法

由于SU-8光刻胶的内应力将会影响高深宽比结构的全金属光栅的制作质量,本文针对近年来SU-8光刻胶应力测量困难的情况,提出了一种基于激光剪切散斑干涉技术的SU-8光刻胶应变分布测量的新方法。该方法通过对被测胶体加载前后两幅干涉图像的处理,直接得到被测胶体结构的全场应变分布情况,由胶体的应变变形数据即可反映出内应力的变化和分布趋势。同时使用ANSYS有限元分析软件对同一被测胶体进行应变仿真模拟研究,获得胶体结构的变形场仿真数据。组建了实验系统,进行了实验验证,结果表明:实际测量变形量约为1.189μm,仿真的最大变形量为1.088μm,测量误差在允许范围内,且测量的形变趋势与仿真模拟结果相一致,表明激光剪切散斑干涉技术可应用于SU-8光刻胶的应变分布全场无损检测。     

基于NOA73微球与SU-8微柱的微探针制作

集成紫外固化胶NOA73微球与SU-8微柱制造的亚毫米探针,可以作为关键部件应用于三坐标测量机。NOA73微球通过NOA73对其他溶液的界面张力形成,柱子由深紫外光穿过微球曝光SU-8形成。这种新技术利用甘油补偿NOA73与空气折射率差,使得紫外光透过NOA73微球后保持接近平行。最终得到高深宽比的探针结构,高度超过1 200 m,微柱侧壁与基底呈89。     

Development and application of chip calorimeter as an X-ray detector

Radiotherapy for cancer patients requires accurate measurement of the absorbed dose of radiation in a treatment planning step. Various types of radiation detectors are currently utilized for dose measurement. Among them, calorimeters are known to be the most precise detector for measuring absorbed dose, but their on-site application is limited by the large size of the equipment. We developed a miniaturized chip calorimeter for application as a radiation detector. The calorimetric radiation detector was built using micro/nano fabrication techniques, and consists of an SU-8 photoresist absorber and high-sensitivity vanadium oxide (VO_x) thermistors. The thermistors had a temperature resolution of 135 μK, and the calorimeter showed a thermal conductance of 11 μW/K. The detector was irradiated with various X-ray dose rates from a linear accelerator, and the absorbed dose to SU-8 was measured. The detector responses showed high linearity with dose rates, demonstrating the feasibility of the radiation detector for practical uses.     

Single-shot two-photon exposure of commercial photoresist for the production of three-dimensional structures

We report the use of an amplified femtosecond laser for single-shot two-photon exposure of the commercial photoresist SU-8. By scanning of the focal volume through the interior of the resist, three-dimensional (3-D) structures are fabricated on a shot-by-shot basis. The 800-nm two-photon exposure and damage thresholds are 3.2 and 8.1TW/cm(2), respectively. The nonlinear nature of the two-photon process allows the production of features that are smaller than the diffraction limit. Preliminary results suggest that Ti:sapphire oscillators can achieve single-shot two-photon exposure with thresholds as low as 1.6TW/cm(2) at 700 nm, allowing 3-D structures to be constructed at megahertz repetition rates.     

Polymerization of SU-8 under irradiation stimulated by temperature increase

X-ray irradiation of thick polymer layers (a deep X-ray lithography procedure) results in a temperature distribution over the exposed area. The induced inhomogeneous temperature increase can reach several tens of degrees and it affects direct SU-8 polymerization depending on the microstructure size and area.     

锆英石的抗γ射线辐照能力和Rietveld结构精修

为研究放射性核素固化介质备选矿物锆英石的抗γ射线辐照结构稳定性,以澳大利亚锆英石为研究对象,通过⁶⁰Co源γ射线辐照装置对样品施以1728 kGy的γ射线辐照.利用X射线荧光光谱仪、扫描电子显微镜和X射线衍射仪对样品的元素含量、γ射线辐照前后的微观形貌及物相变化进行表征,同时利用Rietveld方法对γ射线辐照前后的样品进行了结构精修.结果表明:澳大利亚锆英石经1728 kGy剂量的γ射线辐照后未发生物相变化,射线辐照前后样品的晶胞参数仅发生了10^-4 量级的变 关键词： 锆英石 γ射线 辐照 Rietveld结构精修     

聚合物自写入光波导的时域有限差分模拟

利用时域有限差分方法,对非线性光学聚合物SU-8环氧树脂在激光作用下,其折射率会升高的过程进行了数值模拟与分析,得到SU-8薄膜与激光作用一定时间之后,其内部折射率的分布。分别对表面是平面及表面带有微透镜的SU-8薄膜进行了模拟。结果表明,利用折射率升高引起的自聚焦效应,可以在SU-8薄膜内自写入波导;写入的波导以自聚焦焦点为分界点,分为锥形波导和柱形波导。写入的波导长度随着与激光作用时间的增加而增长;在与激光相同的作用时间里,表面带有微透镜的SU-8薄膜,与表面是平面的SU-8薄膜相比,锥形波导的旁瓣更收敛,写入的波导长度更长;在微透镜底面半径保持不变以及曝光时间一定时,微透镜冠高与底面半径比例为0.08时比比例为0.24时写入的波导长度要长12.2%,其中锥形波导部分要长19.2%。     

一种新型声学超材料平板对机械波吸收性能的模拟与实验研究

基于质量-弹簧微结构通过光学振动模式对机械波进行选择性吸收的原理, 本文设计了一个由集中质量与弹性薄膜构成的二维声学超材料等效平板结构. 利用有限元法对等效平板代表性胞元的振动特性模拟结果表明, 二维超材料平板结构表现出与质量-弹簧微结构相同的振动模式. 基于模拟结果, 制作加工了一个正方形超材料平板, 并通过Polytec扫描式激光测振仪(PSV)对其振动特性进行了试验测试, 结果表明, 本文设计制作的超材料平板可以对频率157.5 Hz的机械波进行选择吸收.