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.     

A simple and cost-effective method for fabrication of integrated electronic-microfluidic devices using a laser-patterned PDMS layer

We report a simple and cost-effective method for fabricating integrated electronic-microfluidic devices with multilayer configurations. A CO₂ laser plotter was employed to directly write patterns on a transferred polydimethylsiloxane (PDMS) layer, which served as both a bonding and a working layer. The integration of electronics in microfluidic devices was achieved by an alignment bonding of top and bottom electrode-patterned substrates fabricated with conventional lithography, sputtering and lift-off techniques. Processes of the developed fabrication method were illustrated. Major issues associated with this method as PDMS surface treatment and characterization, thickness-control of the transferred PDMS layer, and laser parameters optimization were discussed, along with the examination and testing of bonding with two representative materials (glass and silicon). The capability of this method was further demonstrated by fabricating a microfluidic chip with sputter-coated electrodes on the top and bottom substrates. The device functioning as a microparticle focusing and trapping chip was experimentally verified. It is confirmed that the proposed method has many advantages, including simple and fast fabrication process, low cost, easy integration of electronics, strong bonding strength, chemical and biological compatibility, etc.     

Rapid,simple and low cost fabrication of a microfluidic direct methanol fuel cell based on polydimethylsiloxane

In this paper a simple and rapid fabrication method for a microfluidic direct methanol fuel cell using polydimethylsiloxane (PDMS) as substrate is demonstrated. A gold layer on PDMS substrate as seed layer was obtained by chemical plating instead of conventional metal evaporation or sputtering. The morphology of the gold layer can be controlled by adjusting the ratio of curing agent to the PDMS monomer. The chemical properties of the gold films were examined. Then catalyst nanoparticles were grown on the films either by cyclic voltammetry or electrophoretic deposition. The microfluidic fuel cell was assembled by simple oxygen plasma bonding between two PDMS substrates. The cell operated at room temperature with a maximum power density around 6.28 mW cm^?2. Such a fuel cell is low-cost and easy to construct, and is convenient to be integrated with other devices because of the viscosity of the PDMS. This work will facilitate the development of miniature on-chip power sources for portable electronic devices.     

SU-8 microchannels for live cell dielectrophoresis improvements

In this work a novel highly precise SU-8 fabrication technology is employed to construct microfluidic devices for sensitive dielectrophoretic (DEP) manipulation of budding yeast cells. A benchmark microfluidic live cell sorting system is presented, and the effect of microchannel misalignment above electrode topologies on live cell DEP is discussed in detail. Simplified model of budding Saccharomyces cerevisiae yeast cell is presented and validated experimentally in fabricated microfluidic devices. A novel fabrication process enabling rapid prototyping of microfluidic devices with well-aligned integrated electrodes is presented and the process flow is described. Identical devices were produced with standard soft-lithography processes. In comparison to standard PDMS based soft-lithography, an SU-8 layer was used to construct the microchannel walls sealed by a flat sheet of PDMS to obtain the microfluidic channels. Direct bonding of PDMS to SU-8 surface was achieved by efficient wet chemical silanization combined with oxygen plasma treatment of the contact surface. The presented fabrication process significantly improved the alignment of the microstructures. While, according to the benchmark study, the standard PDMS procedure fell well outside the range required for reasonable cell sorting efficiency. In addition, PDMS delamination above electrode topologies was significantly decreased over standard soft-lithography devices. The fabrication time and costs of the proposed methodology were found to be roughly the same.

     

Fabrication of layered polydimethylsiloxane/perfluoropolyether microfluidic devices with solvent compatibility and valve functionality

The development of multilayer soft lithography methodology has seen polydimethysiloxane (PDMS) as the preferred material for the fabrication of microfluidic devices. However, the functionality of these PDMS microfluidic chips is often limited by the poor chemical resistance of PDMS to certain solvents. Here, we propose the use of a photocurable perfluoropolyether (PFPE), specifically FOMBLIN^® MD40 PFPE, as a candidate material to provide a solvent-resistant buffer layer to make the device substantially impervious to chemically induced swelling. We first carried out a systematic study of the solvent resistance properties of FOMBLIN^® MD40 PFPE as compared with PDMS. The comparison presented here demonstrates the superiority of FOMBLIN^® MD40 PFPE over PDMS in this regard; moreover, the results permitted to categorize solvents in four different groups depending on their swelling ratio. We then present a step-by-step recipe for a novel fabrication process that uses multilayer lithography to construct a comprehensive solvent-resistant device with fluid and control channels integrated with a valve structure and also permitting easy establishment of outside connections.     

Patterning of carbon nanotube films on PDMS using SU-8 microstructures

In this paper, we propose a simple and low-cost fabrication technique for patterning carbon nanotube (CNT) films on polydimethylsiloxane (PDMS), which can be used in flexible sensors and electronics. We demonstrate CNT patterning on both recessed and flat PDMS surfaces using a standard photolithography method. By this proposed technique, we were able to fabricate a CNT film, having a high flexibility and good conductivity, on a PDMS surface. A CNT pattern with a minimum feature resolution of 150 μm was obtained using the proposed fabrication technique. The sheet resistance of the CNT film on the PDMS surface was determined to be in the 100–280 Ω/sq range. The thickness and resultant resistivity of the CNT film can be easily controlled by controlling just the spray duration. Furthermore, the gauge factor of the proposed device is higher than that of metal and it increases as the thickness of the CNT film increases.     

Low-cost polymer microfluidic device for on-chip extraction of bacterial DNA

A polymer microfluidic device for on-chip extraction of bacterial DNA has been developed for molecular diagnostics. In order to manufacture a low-cost, disposable microchip, micropillar arrays of high surface-to-volume ratio (0.152 μm⁻¹) were constructed on polymethyl methacrylate (PMMA) by hot embossing with an electroformed Ni mold, and their surface was modified with SiO₂ and an organosilane compound in subsequent steps. To seal open microchannels, the organosilane layer on top plane of the micropillars was selectively removed through photocatalytic oxidation via TiO₂/UV treatment at room temperature. As a result, the underlying SiO₂ surface was exposed without deteriorating the organosilane layer coated on lateral surface of the micropillars that could serve as bacterial cell adhesion moiety. Afterwards, a plasma-treated PDMS substrate was bonded to the exposed SiO₂ surface, completing the device fabrication. To optimize manufacturing throughput and process integration, the whole fabrication process was performed at 6 inch wafer-level including polymer imprinting, organosilane coating, and bonding. Preparation of bacterial DNA was carried out with the fabricated PDMS/PMMA chip according to the following procedure: bacterial cell capture, washing, in situ lysis, and DNA elution. The polymer-based microchip presented here demonstrated similar performance to Glass/Si chip in terms of bacterial cell capture efficiency and polymerase chain reaction (PCR) compatibility.     

Vertically aligned multi-walled CNT arrays coated by gold nanoparticles for surface-enhanced Raman scattering

A unique substrate for surface-enhanced Raman scattering on vertical multi-walled carbon nanotube (MWCNT) arrays coated by Au nanoparticles was reported. The vertically aligned MWCNT arrays were prepared by thermal chemical vapor deposition at temperature of 720 °C, and then coated by gold nanoparticles by sputtering. The possible mechanisms for the SERS sensitivity were discussed. Raman spectroscopy experiments for detecting Rhodamine6G were carried on and some obvious Raman peaks were observed and analyzed.     

具有3D微纳结构PDMS阵列免疫传感芯片研制

介绍了一种简便快速加工微阵列免疫传感芯片的新方法。采用化学刻蚀技术加工具有μm级山脉状起伏和nm级表面粗糙度结构(简称为3D微纳表面)的玻璃阳模,以该阳模为模板浇注法制得表面具有3D微纳表面结构的PDMS基片,再借助于物理吸附,将抗体直接固定于该PDMS表面,形成具有3D微纳结构的PDMS微阵列免疫传感器。利用光学显微镜和原子力显微镜对玻璃阳模和PDMS基片表面形貌进行表征,研究了PDMS表面微纳结构化处理对抗体吸附能力的影响。结果表明:3D微纳结构的PDMS由于具有大的比表面积,能显著增强抗体的吸附能力。将研制所得的3D微纳表面结构的PDMS芯片用于微阵列荧光免疫分析,其灵敏度是平板PDMS的5倍。     

Shrinkage ratio of PDMS and its alignment method for the wafer level process

In the research area known as Lab-on-a-Chip, poly-dimethylsiloane (PDMS) is a popular material whose fabrication method is the replication of patterns by curing on a mold. Shrinkage of PDMS occurs when it is cured; this is a problem related to the alignment between the PDMS layer and the rigid substrate during the wafer-level processing. In this paper, the 2D shrinkage ratio of PDMS is measured experimentally for various curing conditions including the temperature, thickness, and mixing ratio of the curing agent and dilutant. In order to measure this, scale marks were patterned onto a 4 in. wafer and replicated onto a PDMS substrate. When the patterned Si wafer and PDMS substrate were aligned, the difference of each scale mark was observed. A cross-shaped groove was patterned with a scale mark as a align key for the easy alignment of substrates. For a general recipe, the measured shrinkage ratios of PDMS were 1.06, 1.52 and 1.94% for curing temperature of 65, 80 and 100°C, respectively. Considering the shrinkage ratio of PDMS, the design offset applied in a photomask is 1.07, 1.54 and 1.98% for curing temperature of 65, 80 and 100°C, respectively.     

Fabrication of miniature Clark oxygen sensor integrated with microstructure

A miniature Clark-type oxygen sensor has been integrated with a microstructure using a novel fabrication technique. The oxygen chip consists of a glass substrate with a three-electrode configuration, which is separated and connected by a groove, and a poly(dimethylsiloxane) (PDMS) container with an immobilized PDMS oxygen-permeable membrane. The assembly of the different substrates only uses the O₂ plasma bonding technique, and the fabrication temperatures do not exceed 95 °C. Characteristics of the miniature sensor include the fastest response time of 6.8 s, good linearity with a correlation coefficient of 0.995, and a long lifetime of at least 60 h. The present miniature Clark oxygen sensor can be readily integrated with a microfluidic system to form a μ-TAS.     

New approach for batch microfabrication of silicon-based micro fuel cells

This paper reports a novel and straightforward approach to the development of a compact micro direct methanol fuel cell. The device consists of a hybrid polymer membrane as a feasible microintegrable electrolyte to be used together with silicon current collectors. These current collectors consist in microfabricated silicon chips that incorporate a fine electrode grid. The membrane combines two polymers with different functionalities, Nafion^® as a proton conducting material and PDMS as a flexible mechanical support. The compatibility of this membrane with MEMS fabrication processes lies in the acknowledged bonding capabilities of the PDMS polymer to materials typically used in microsystems technologies—such as silicon, silicon dioxide and glass—as well as its ability to withstand variations of the Nafion^® volume. The compatibility of all the components with microfabrication processes will permit the application of batch fabrication techniques for the whole device, so contributing to a significant lowering of the fabrication costs.     

Chemiluminescence detection for Cu (II) based on 1,10-Phenanthroline-hydrogen peroxide reaction on a PDMS microfluidic chip

A simple, rapid and effective method for the determination of copper (II) in water on a PDMS microfluidic chip with chemiluminescence (CL) detection is presented. The CL reaction was based on oxidation of 1,10-phenanthroline by hydrogen peroxide in basic aqueous solution. Polydimethylsiloxane (PDMS) was chosen as material for fabricating the microfluidic chip with two steps lithography method. Optimized reagents conditions were found to be 6.0 × 10^?5 mol/L 1,10-phenanthroline, 1.2 × 10^?3 mol/L hydrogen peroxide, 6.5 × 10^?2 mol/L sodium hydroxide and 2.0 × 10^?3 mol/L Hexadecyl trimethyl ammonium Bromide (CTMAB). In the continuous flow injection mode the system can perform fully automated detection with a reagent consumption of only 3.4 μL each time. The linear range of the Cu (II) ions concentration was 1.0 × 10^?8 mol/L to 1.0 × 10^?4 mol/L, and the detection limit was 9.2 × 10^?9 mol/L with the S/N ratio of 3. The relative standard deviation was 2.8 % for 1.0 × 10^?6 mol/L Cu (II) ions (n = 8). The most notable features of the detection method are simple operation, rapid detection and easy fabrication of the microfluidic chip.     

Improvement of capillary electrophoresis property for microchannels fabricated by deep X-ray lithography

We fabricated the electrophoresis microchips using the UV polymerization technique. We employed plastic substrates that were suitable for rapid prototyping instead of glass and quartz. A thick UV negative photo resist was used to form molds and poly-dimethylsilozane (PDMS) was polymerized by a thermal curing process on the mold to obtain replica microchips. Electroosmotic flow (EOF) was measured to evaluate the surface. Characteristic differences between UV-fabricated and SR-fabricated microchips were evaluated by electro osmotic flow (EOF) measurement. It was observed that microchannels fabricated by SR lithography show constant peak heights and FWHMs. We also investigated the effect of the change of the channel width along the EOF direction. It is demonstrated that broadening width channel significantly restricts the sample diffusion towards the EOF direction and leads to the high resolusion separation on the PDMS microchips. Thus the advantage of the application of SR lithography to the mold fabrication is also demonstrated.     

Embedding off-the-shelf filter in PDMS chip for microbe sampling

Filtration for microfluidic sample-collection devices is desirable for sample selection, concentration, preprocessing, and manipulation, but microfabricating the required sub-micrometer structures is an elaborate process. This article presents a simple method to integrate filters in polydimethylsiloxane (PDMS) devices to sample microorganisms in aqueous environments. An off-the-shelf membrane filter with 0.22-μm pores was embedded in a PDMS layer and sequentially bound with other PDMS channel layers. No leakage was observed during filtration. This device was validated by concentrating a large amount of biomass, from 15 × 10⁷ to 3 × 10⁸ cells/ml of cyanobacterium Synechocystis in simulated sample water with consistent performance across devices. The major advantages of this method are low cost, simple design, straightforward fabrication, and robust performance, enabling wide-utility of chip-based devices for field-deployable operations in environmental microbiology.     

聚二甲基硅氧烷微流体芯片的制作技术

基于MEMS技术的微流体芯片在分析化学和生物医学领域显示了巨大的应用潜力。作为构建微流体芯片的基底材料———聚二甲基硅氧烷(PDMS)已经表现出了许多的优点:良好的电绝缘性、较高的热稳定性、优良的光学特性以及简单的加工工艺等。采用浇注法制作了PDMS电泳微芯片,对PDMS微流体芯片的加工工艺、封装方法和结构特征进行了探讨,并提出了相应的解决方案。     

Preparation of normally open microvalves with fluorinated ethylene propylene membrane and poly(methyl methacrylate) substrates

Substitution of PDMS membrane with fluorocarbon membrane serving as the actuating elements has been reported in preparation of normally closed pneumatic valves, but rarely reported in fabrication of normally open valves. We presented a photoresist-free method to fabricate normally open valves using fluorinated ethylene propylene (FEP) film as the actuating membrane to close PMMA-based microfluidic channels. An arched FEP film top wall of compressed-gas-filled channel was used as the relief pattern to prepare a positive epoxy resin stamp, which was employed to hot-emboss the fluid channels with round cross section into PMMA substrates. An adhesive-assisted bonding technique was used to irreversibly bond the PMMA substrates to the FEP membrane. The chemical resistance, small molecule absorption and valve/pump properties of the fabricated pneumatic valves were characterized.     

Temporary bond—debond technology for high‐performance transistors on flexible substrates

Abstract— A processing technology based upon a temporary bond—debond approach has been developed that enables direct fabrication of high‐performance electronic devices on flexible substrates. This technique facilitates processing of flexible plastic and metal‐foil substrates through automated standard semiconductor and flat‐panel tool sets without tool modification. The key to processing with these tool sets is rigidifying the flexible substrates through temporary bonding to carriers that can be handled in a similar manner as silicon wafers or glass substrates in conventional electronics manufacturing. To demonstrate the power of this processing technology, amorphous‐silicon thin‐film‐transistor (a‐Si:H TFT) backplanes designed for electrophoretic displays (EPDs) were fabricated using a low‐temperature process (180°C) on bonded‐plastic and metal‐foil substrates. The electrical characteristics of the TFTs fabricated on flexible substrates are found to be consistent with those processed with identical conditions on rigid silicon wafers. These TFTs on plastic exhibit a field‐effect mobility of 0.77 cm²/V‐sec, on/off current ratio >10⁹ at Vds = 10 V, sub‐threshold swing of 365 mV/dec, threshold voltage of 0.49 V, and leakage current lower than 2 pA/μm gate width. After full TFT‐array fabrication on the bonded substrate and subsequent debonding, the flexible substrate retains its original flexibility; this enables bending of the EPD display without loss in performance.     

Leak detection methods for glass capped and polymer sealed MEMS packaging

This paper presents the limitations of the helium leak test when applied to typical MEMS packages. A novel closed-form expression is presented which allows the determination of the minimum cavity volume package that can be accurately tested using the helium leak test method in conjunction with a standard gross leak test. This expression can be used to find optimum test parameters for packages with cavity volumes greater than 2.6 × 10⁻³ cm³. Hermeticity testing using FTIR and Raman spectroscopy are considered as potential methods to overcome the limitations of the helium leak test method.     

一种新型可调光栅的制作方法

介绍了一种可调光栅的制作方法。首先通过紫外线光刻的方法,制作出微米尺度的光栅结构(周期8μm),然后将光栅复制在聚甲基硅氧烷(PDMS)薄膜上,形成内嵌式PDMS光栅。利用PDMS优异的弹性,将此薄膜沿着光栅栅线的方向拉伸,随着栅线的伸长,光栅常数也随之变小,周期调节极限为5μm。传统方法制作可调光栅,工艺条件苛刻,制作过程复杂,难以控制,制作成本高,周期较长。提出的制作可调光栅的方法成本低,周期短,工艺过程简单易控制,可广泛应用于微型光谱仪、扫描仪、光通信等领域。