A low-temperature IC-compatible process for fabricatingsurface-micromachined metallic microchannels

In this paper, a low-temperature integrated-circuit (IC)-compatible process for fabricating metallic microchannels is described. Arrays of 1-100 metallic microchannels have been fabricated on silicon and glass substrates. The process can be extended to many planar substrate materials including polymers and ceramics. The microchannels are formed using microelectro-formed metals. The microchannels demonstrated in this paper use nickel as the structural material and gold as the surface coating on the inside walls of the microchannels. The inner dimensions of the individual microchannels fabricated to date range from 30 μm to 1.5 mm in width, 0.5 mm to several centimeters in length, and 5-100 μm in thickness. The wall thickness ranges from 5 to 50 μm. The microchannel fabrication technology enables the fabrication of surface microchannels with a relatively large cross-sectional area. The metallic microchannels can be fabricated to extend from the substrate edge. Interfacing schemes are given for attaching external pressure feeds     

基于MEMS加工技术压力传感器工艺研究

介绍了一种微压力传感器加工技术和加工工艺研究,根据所设计微压力传感器的结构特点和国内现有加工设备,采用了体硅加工技术和表面加工技术相结合的方法,并给进行详细加工步骤研究.     

Characterization and optimization to improve uneven surface on MEMS bridge fabrication

This paper presents an optimized fabrication method for developing a freestanding bridge for RF MEMS switches. In this method, the sacrificial layer is patterned and hard baked a 220 °C for 3 min, after filling the gap between the slots of the coplanar waveguide. Measurement results by AFM and SEM demonstrate that this technique significantly improves the planarity of the sacrificial layer, reducing the uneven surface to less than 20 nm, and the homogeneity of the Aluminum thickness across the bridge. Moreover, a mixture of O₂, Ar and CF₄ was used and optimized for dry releasing of the bridge. A large membrane (200 × 100 μm²) was released without any surface bending. Therefore, this method not only simplifies the fabrication process, but also improves the surface flatness and edge smoothness of the bridge. This fabrication method is fully compatible with standard silicon IC technology.     

High aspect-ratio combined poly and single-crystal silicon (HARPSS)MEMS technology

This paper presents a single-wafer high aspect-ratio micromachining technology capable of simultaneously producing tens to hundreds of micrometers thick electrically isolated poly and single-crystal silicon microstructures. High aspect-ratio polysilicon structures are created by refilling hundreds of micrometers deep trenches with polysilicon deposited over a sacrificial oxide layer. Thick single-crystal silicon structures are released from the substrate through the front side of the wafer by means of a combined directional and isotropic silicon dry etch and are protected on the sides by refilled trenches. This process is capable of producing electrically isolated polysilicon and silicon electrodes as tall as the main body structure with various size capacitive air gaps ranging from submicrometer to tens of micrometers. Using bent-beam strain sensors, residual stress in 80-μm-thick 4-μm-wide trench-refilled vertical polysilicon beams fabricated in this technology has been measured to be virtually zero. 300-μm-long 80-μm-thick polysilicon clamped-clamped beam micromechanical resonators have shown quality factors as high as 85 000 in vacuum. The all-silicon feature of this technology improves long-term stability and temperature sensitivity, while fabrication of large-area vertical pickoff electrodes with submicrometer gap spacing will increase the sensitivity of micro-electromechanical devices by orders of magnitude     

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.     

Fabrication of grids and collimators using SU-8 as a mold

The fabrication process of ultradeep (aspect ratio greater than 25) microchannels in SU-8 photoresist using deep X-ray lithography is described. We have demonstrated that with single-layer coatings, 1-mm-deep trenches in continuous resist layer can be achieved reproducibly. Microchannels with vertical walls and with walls tilted up to 20° from vertical have been fabricated. Electroforming of the channels resulted in metal grids and collimators for various applications. A thickness enhancement method for fabrication of very tall structures is also described.We would like to thank Dr. Francesco De Carlo for support on the beamline, and Judi Yaeger and Ruben Khachatryan for the experimental assistance. The work was supported by NIH SBIR Grants: R44 CA76752 and R43 CA91762, and by the U.S. Department of Energy, under Contract No. W-31–109-ENG-38.     

Microfabrication using one-step LPCVD porous polysilicon films

A simple, one-step LPCVD process was recently reported to allow the repeatable fabrication of polycrystalline silicon (polysilicon) thin films containing through-pores measuring 10-50 nm in diameter, as-deposited, with no additional processing steps required. This paper describes methods for using this one-step porous polysilicon material to quickly and easily fabricate structures of interest to MEMS designers. Among the structures presented are hermetically sealed diaphragms, hollow tube and shell structures, substrate-aligned membranes over one square centimeter in area ("supermembranes"), and permeable fluidic microchannels on silicon and quartz substrates.     

Planar CMOS compatible process for the fabrication of buried microchannels in silicon, using porous-silicon technology

This work presents a new method for the fabrication of buried microchannels, covered with porous silicon (PS). The specific method is a two-step electrochemical process, which combines PS formation and electropolishing. In a first step a PS layer with a specific depth is created at a predefined area and in the following step a cavity underneath is formed, by electropolishing of silicon. The shape of the microchannel is semi-cylindrical due to isotropic formation. The method allows accurate control of the dimensions of both PS and the cavity. The formation conditions of the PS layer and the cavity were optimized so as to obtain smooth microchannel walls. In order to obtain stable structures the area underneath the PS masking layer was transformed into n-type by implantation, taking advantage of the selectivity of PS formation between n- and p-type silicon. With this technique, a monocrystalline support for the PS layer is formed on top of the cavity. Various microchannel diameters with different thickness of capping PS layer were obtained. The process is CMOS compatible and it uses only one lithographic step and leaves the surface of the wafer unaffected for further processing. A microfluidic thermal flow sensor was fabricated using this technology, the experimental evaluation of which is in progress.     

Rapid prototyping of shrinkable BOPS-based microfluidic devices

Biaxially oriented polystyrene (BOPS) is a commercialized packaging material, which has the advantages of biocompatibility, non-toxic, transparency, light-weight and cost-effective. Due to the stress accumulated from both directions in plane during the fabrication process, when BOPS was reheated above the glass transition temperature, an isotropic shrinkage will occur. This study proposed a low-cost and rapid prototyping method for the fabrication of BOPS-based microfluidics device. Both laser ablation and micro-milling were used for the fabrication of microchannels on the surface of the BOPS sheet, after thermal induced shrinkage, microchannels with finer microstructure could be achieved. For the sealing of fabricated microchannels on BOPS, two approaches were made using a layer of BOPS or a layer of polyester adhesive film. The thermal induced shrinkage and bonding strength were carefully studied in this study. Several microfluidic devices, including a droplet generator and a diffusion mixer were also fabricated for demonstration. The proposed fabrication method for BOPS-based microfluidics is simple, rapid, cost-effective and without the requirement of cleanroom facility, with help of thermal induced shrinkage, finer structure with high resolution could be achieved with conventional lab tools.     

A Gap Reduction and Manufacturing Technique for Thick Oxide Mask Layers With Multiple-Size Sub-$mu$m Openings

This paper introduces a technique for the fabrication of thick oxide hard masks on top of a substrate with adjustable opening sizes in the sub-$mu$m regime, while the only lithography step involved has$mu$m-scale resolution. This thick oxide mask layer with sub-$mu$m openings is suitable for etching deep narrow trenches in silicon using deep reactive ion etching (DRIE) tools. Openings of less than 100 nm are realized in a 1.5-$mu$m-thick oxide layer, while the original lithographically defined feature sizes are larger than 1$mu$m in width. This method, combined with modified high aspect ratio DRIE recipes, shows a great potential for single-mask batch-fabrication of high frequency low-impedance single crystalline resonators on silicon-on-insulator (SOI) substrates. Dry-etched trenches with aspect ratios as high as 60:1 are fabricated in silicon using the gap reduction technique to realize 200 nm opening sizes in an oxide mask layer. Various resonator structures with sub-$mu$m capacitive gaps are also fabricated on a SOI substrate using a single-mask process. Measurement results from high-frequency and high-quality factor (Q) all single crystal silicon resonators are presented.1684     

声表面波辅助实现纸基微流分析

纸基微流器件往往难以实现样品前处理操作.提出了一种简单的纸基微通道制作方法及兼具有前处理操作功能的纸基微流分析方法.采用Protel设计微通道图案,采用印刷电路技术制作铜模板,并涂覆石蜡、覆盖滤纸,而后用电烙铁加热铜模板另一侧,熔融石蜡渗透入滤纸形成纸基微通道.制作的纸基器件放置于128°YX-LiNbO3压电基片上,...     

Design and fabrication of a novel microfluidic nanoprobe

The design and fabrication of a novel microfluidic nanoprobe system are presented. The nanoprobe consists of cantilevered ultrasharp volcano-like tips, with microfluidic capabilities consisting of microchannels connected to an on-chip reservoir. The chip possesses additional connection capabilities to a remote reservoir. The fabrication uses standard surface micromachining techniques and materials. Bulk micromachining is employed for chip release. The microchannels are fabricated in silicon nitride by a new methodology, based on edge underetching of a sacrificial layer, bird's beak oxidation for mechanically closing the edges, and deposition of a sealing layer. The design and integration of various elements of the system and their fabrication are discussed. The system is conceived mainly to work as a "nanofountain pen", i.e., a continuously writing upgrade of the dip-pen nanolithography approach. Moreover, the new chip shows a much larger applicability area in fields such as electrochemical nanoprobes, nanoprobe-based etching, build-up tools for nanofabrication, or a probe for materials interactive analysis. Preliminary tests for writing and imaging with the new device were performed. These tests illustrate the capabilities of the new device and demonstrate possible directions for improvement.     

Enhanced wetting properties of silicon mesh microchannels coated with SiO2/SnO2 nanoparticles through layer-by-layer self assembly

The enhanced wetting property of silicon mesh microchannels coated with SiO₂/SnO₂ nanoparticles is presented in this paper. The SiO₂/SnO₂ bi-layers are prepared using layer-by-layer nano self assembly. It is found that the silicon mesh microchannels are super hydrophilic and demonstrated powerful capillary. The capillary rise rate is characterized by measuring the front location of liquid on the silicon mesh surface, laid on a 45° inclined platform. For a silicon mesh sample with an overall dimension of 25 mm × 25 mm, when the microchannel width is 0.5 mm, the liquid front can reach the top edge of the sample in approximately 30 s. The mesh silicon surface with a SiO₂/SnO₂ multilayer film presented in this paper has better wettability and higher capillary pressure than other hydrophilic surfaces reported. The results provide a new way to improve the capillary in microchannels with enhanced super hydrophilic surfaces in microchannels for variety of micro/nanofluidic applications.     

Bonding-less (B-less) fabrication of polymeric microsystems

A new technology of the microsystems fabrication was developed. The process is based on a so-called capillary film, which is a commercially available material. A matrix, master pattern corresponding to the microchannels structure, made of the capillary film emulsion is embedded inside a block of polydimethylsiloxane (PDMS). After polymer cross-linking, the matrix is dissolved and removed as a solution from the PDMS structure leaving network of empty spaces that can act as microchannels. In the paper, the fabrication methods of the microsystems with 2D or sandwich-like microchannels architecture were described.     

Micromechanism fabrication using silicon fusion bonding

Silicon fusion bonding is studied as an enabling technology for the fabrication of microrobotic mechanisms. The effects of both surface activation technique and annealing temperature on bond strength are considered using a crack-opening technique. As part of the study, the relationship between patterned silicon feature size and the resulting bond strength is explored. Based on the experimental results, recommendations for an optimal silicon fusion bonding process for micromechanism fabrication are presented. The experimental results indicate that bulk silicon bonding strength can be achieved independent of feature size at temperatures as low as 300°C, with positive implications for micromechanism fabrication.     

An advanced reactive ion etching process for very high aspect-ratio sub-micron wide trenches in silicon

This paper reports on a practical modification of the two-step time-multiplexed plasma etching recipe (also known as the Bosch process) to achieve high aspect-ratio sub-micron wide trenches in silicon. Mixed argon and oxygen plasma depassivation steps are introduced in between the passivation and etching phases to promote the anisotropic removal of the passivation layer at the base of the trench. Argon does not chemically react with polymers and silicon and removes the passivation layer only by physical sputtering. Therefore, it results in a highly anisotropic polymer etching process. This recipe can be easily integrated on conventional ICP equipment and the scalloping on the trench sidewall can potentially be reduced in size to less than 50 nm. To clean up all the passivation residues, a short oxygen plasma step is also added at the end of the cycle that effectively improves the uniformity of the etching profile over various opening sizes. Excellent anisotropy of the inserted argon depassivation step facilitates narrow trenches down to 130 nm wide and gap aspect-ratios as high as 40:1, extending the application of deep reactive ion etching (DRIE) processes into a new broad regime.     

Plasma planarization for sensor applications

Filling trenches in silicon using phosphosilicate glass (PSG) provides many possibilities for novel device structures for sensors and actuators. This paper describes a plasma planarization technique that provides fully planarized PSG filled silicon trenches for sensor applications. The technique consists of planarizing the substrate using two photoresist layers and plasma etching-back. The lower resist layer is the AZ5214 image reversal resist, which is patterned and then thermally cured. The upper resist layer is a global HPR204 coating. The plasma etching-back is carried out using CHF₃/C₂F ₆ gas mixture with an O₂ addition. It is shown that by using the image reversal photoresist approach, fully planarized surface coating can be obtained without resorting to an additional mask. By adding 25 sccm (14%) O₂ into the 137 sccm CHF₃+18 sccm C₂F₆ gas mixture, the etch rates for the photoresist and PSG can be matched. Process optimization for the two layer resist coating and plasma etching is discussed     

Experimental investigations of liquid flow in rib-patterned microchannels with different surface wettability

The effects of rib-patterned surfaces and surface wettability on liquid flow in microchannels were experimentally investigated in this study. Microchannels were fabricated on single-crystal silicon wafers by photolithographic and wet-etching techniques. Rib structures were patterned in the silicon microchannel, and the surface was chemically treated by trichlorosilane to create hydrophobic condition. Experiments with water as the working fluid were performed with these microchannels over a wide range of Reynolds numbers between 110 and 1914. The results for the rib-patterned microchannels showed that the friction factor with the hydraulic diameter based on the rib-to-upper-wall height was lower than that predicted from incompressible theory with the same height. The friction factor-Reynolds number products for the hydrophobic condition increased as Reynolds number increased in the laminar flow regime. The experimental results were also compared with the predictive expressions from the literature, and it was found that the experimental data for the small rib/cavity geometry was in good agreement with those in the literature.     

A novel polymer microneedle fabrication process for active fluidic delivery

In this article, we explore a new fabrication process for a flexible, all polymer, active fluidic delivery system, incorporating a fusion of laser micromachining and microfabrication techniques as well as rapid prototyping technology. Here, we show selective fluidic delivery from isolated microchannels through an electrochemically driven pumping reaction, demonstrate the dispensing of dose volumes up to 5.5 μl, and evaluate the device’s performance in terms of its delivery speed and ejection efficiency. Finally, we move this work toward an implantable microfluidic drug delivery device by investigating the device’s biocompatibility through a statistical approach that overviews the viability of bovine aortic endothelial cells on polyimide and silicon substrates.     

Sub-Micro-Gravity In-Plane Accelerometers With Reduced Capacitive Gaps and Extra Seismic Mass

This paper presents a robust fabrication technique for manufacturing ultrasensitive micromechanical capacitive accelerometers in thick silicon-on-insulator substrates. The inertial mass of the sensor is significantly increased by keeping the full thickness of the handle layer attached to the top layer proof mass. High-aspect-ratio capacitive sense gaps are fabricated by depositing a layer of polysilicon on the sidewalls of low aspect- ratio trenches etched in silicon. Using this method, requirements on trench etching are relaxed, whereas the performance is preserved through the gap reduction technique. Therefore, this process flow can potentially enable accelerometers with capacitive gap aspect-ratio values of greater than 40:1, not easily realizable using conventional dry etching equipment. Also, no wet-etching step is involved in this process which in turn facilitates the fabrication of very sensitive motion sensors that utilize very compliant mechanical structures. Sub-micro-gravity in-plane accelerometers are fabricated and tested with measured sensitivity of 35 pF/g, bias instability of 8 mug, and footprint of <0.5 cm².