In the last 30 days

• Open/close Plasma removal of Parylene C

  Ellis Meng et al  2008 J. Micromech. Microeng. 18 045004 Tag this article

  Article References Full text PDF (1.41 MB)

  Parylene C, an emerging material in microelectromechanical systems, is of particular interest in biomedical and lab-on-a-chip applications where stable, chemically inert surfaces are desired. Practical implementation of Parylene C as a structural material requires the development of micropatterning techniques for its selective removal. Dry etching methods are currently the most suitable for batch processing of Parylene structures. A performance comparison of three different modes of Parylene C plasma etching was conducted using oxygen as the primary reactive species. Plasma, reactive ion and deep reactive ion etching techniques were explored. In addition, a new switched chemistry process with alternating cycles of fluoropolymer deposition and oxygen plasma etching was examined to produce structures with vertical sidewalls. Vertical etch rates, lateral etch rates, anisotropy and sidewall angles were characterized for each of the methods. This detailed characterization was enabled by the application of replica casting to obtain cross sections of etched structures in a non-destructive manner. Application of the developed etch recipes to the fabrication of complex Parylene C microstructures is also discussed.

• Open/close The mechanical properties of the rubber elastic polymer polydimethylsiloxane for sensor applications

  J C Lötters et al  1997 J. Micromech. Microeng. 7 145 Tag this article

  Article References Full text PDF (62 KB)

  Polydimethylsiloxane (PDMS) is a commercially available physically and chemically stable silicone rubber. It has a unique flexibility with a shear elastic modulus due to one of the lowest glass transition temperatures of any polymer . Further properties of PDMS are a low change in the shear elastic modulus versus temperature , virtually no change in G versus frequency and a high compressibility. Because of its clean room processability, its low curing temperature, its high flexibility, the possibility to change its functional groups and the very low drift of its properties with time and temperature, PDMS is very well suited for micromachined mechanical and chemical sensors, such as accelerometers (as the spring material) and ISFETs (as the ion selective membrane). It can also be used as an adhesive in wafer bonding, as a cover material in tactile sensors and as the mechanical decoupling zone in sensor packagings.

• Open/close Droplet merging in a straight microchannel using droplet size or viscosity difference

  B-J Jin et al  2010 J. Micromech. Microeng. 20 035003 Tag this article

  Article References Full text PDF (1.41 MB)

  In the present study, a novel droplet-merging technique is proposed, which enables two nanoliter or picoliter droplets to merge in a straight microchannel with high precision. Two dispersed phase fluids are supplied respectively from two side channels in a certain range of flow rates to generate droplets of different sizes or different viscosities in a regularly alternating mode at a cross-channel intersection prior to the straight microchannel, in such a manner that the droplets are spontaneously synchronized by themselves due to the competition of the two interfaces formed at the cross-channel intersection. Then they are autogeneously merged in the downstream straight microchannel with or without a sudden expansion of the cross section, due to their velocity difference which is induced as they are transported aboard the continuous phase fluid. This droplet-merging method has no desynchronization or secondary-merging problems. Thus, it can be applied efficiently to mixing or encapsulating one target sample with another material for the purposes of nanoparticle synthesis, hydrogel-bead production, cell transplantation and so forth.

• Open/close Low-frequency two-dimensional resonators for vibrational micro energy harvesting

  U Bartsch et al  2010 J. Micromech. Microeng. 20 035016 Tag this article

  Article References Full text PDF (1.67 MB)

  The fabrication, characterization and theoretical analysis of a novel two-dimensional silicon resonator with threefold rotational symmetry are described. The resonator consists of a 4 mm wide disk-shaped seismic mass having the full-wafer thickness of 525 µm and suspended by a system of concentric circular springs. The device is structured using two-sided deep reactive-ion etching of silicon. With its current spring thickness and height, the device has two closely spaced resonance frequencies at 370.5 and 373.9 Hz and a quality factor of 1800 at ambient pressure. The spring height and thus the resonance frequency of the device are easily tuned by simple adjustment of a single etch duration in the entire fabrication process. The dynamic response of the structure is modeled under the two assumptions that silicon is elastically (i) isotropic and (ii) anisotropic. In comparison with the isotropic model, the elastic anisotropy leads to a predicted mode splitting by 6.2 Hz, with oscillation directions aligned with the cubic crystal axes. Even small geometrical imperfections are found to significantly rotate the eigenmodes and to further modulate their frequency splitting. Experimental and numerical results corroborate these conclusions. Overall the present resonator design has the potential for a higher energy harvesting efficiency than a combination of two separate one-dimensional oscillators.

• Open/close Optically induced electrokinetic concentration and sorting of colloids

  Stuart J Williams et al  2010 J. Micromech. Microeng. 20 015022 Tag this article

  Article References Full text PDF (1.29 MB)

  We demonstrate an optically induced ac electrokinetic technique that rapidly and continuously accumulates colloids on a parallel-plate electrode surface resulting in a crystalline-like aggregation. Electrothermal hydrodynamics produce a microfluidic vortex that carries suspended particles toward its center where they are trapped by local ac electrokinetic hydrodynamic forces. We characterize the rate of particle aggregation as a function of the applied ac voltage, ac frequency and illumination intensity. Hundreds of polystyrene particles (1.0 µm) suspended in a low conductivity solution (2.4 mS m ⁻¹) were captured at a range of voltages (5–20 V _pp) and frequencies (20–150 kHz) with an optical power of approximately 20 mW. This technique was not restricted to near infrared (1064 nm) illumination and was also demonstrated at 532 nm. The sorting capability of this technique was demonstrated with a solution containing 0.5 µm, 1.0 µm and 2.0 µm polystyrene particles. This dynamic optically induced technique rapidly concentrates, sorts and translates colloidal aggregates with a simple parallel-plate electrode configuration and can be used for a variety of lab-on-a-chip applications.

• Open/close Anisotropic etching of {100} and {110} planes in (100) silicon

  Oliver Powell and H Barry Harrison  2001 J. Micromech. Microeng. 11 217 Tag this article

  Article References Full text PDF (334 KB)

  Anisotropic etching of (100) silicon using KOH with 45° alignment to the primary 110 wafer flat was investigated. It was shown that in KOH solution with isopropyl alcohol added, high KOH concentration and temperature caused the selection of {100} instead of {110} walls, allowing reliable fabrication of {100} walls with improved surface smoothness due to the isopropyl alcohol. TMAOH solutions with methanol and isopropyl alcohol were also found to produce both types of wall, with excellent surface smoothness for the {110} walls. A new maskless etching technique was developed for corner compensation of structures bounded by {110} walls.

• Open/close Microfluidics-a review

  P Gravesen et al  1993 J. Micromech. Microeng. 3 168 Tag this article

  Article References Full text PDF (1.48 MB)

  An overview is given of research activities in the field of fluid components or systems built with microfabrication technologies. This review focuses on the fluidic behaviour of the various devices, such as valves, pumps and flow sensors as well as the possibilities and pitfalls related to the modelling of these devices using simple flow theory. Finally, a number of microfluidic systems are described and comments on future trends are given.

• Open/close Force-controlled automatic microassembly of tissue engineering scaffolds

  Guoyong Zhao et al  2010 J. Micromech. Microeng. 20 035001 Tag this article

  Article References Full text PDF (1.58 MB)

  This paper presents an automated system for 3D assembly of tissue engineering (TE) scaffolds made from biocompatible microscopic building blocks with relatively large fabrication error. It focuses on the pin-into-hole force control developed for this demanding microassembly task. A beam-like gripper with integrated force sensing at a 3 mN resolution with a 500 mN measuring range is designed, and is used to implement an admittance force-controlled insertion using commercial precision stages. Visual-based alignment followed by an insertion is complemented by a haptic exploration strategy using force and position information. The system demonstrates fully automated construction of TE scaffolds with 50 microparts whose dimension error is larger than 5%.

• Open/close A self-assembled 3D microelectrode array

  Ming-Fang Wang et al  2010 J. Micromech. Microeng. 20 035013 Tag this article

  Article References Full text PDF (3.44 MB)

  Recording a neural ensemble has been an extremely successful experimental paradigm allowing real-time interpretation of neural codes as well as the detection of dynamic changes within a process. In recent years, microfabricated electrodes have attracted a great deal of attention for recording neural ensembles with superior resolution and spatial density. A 3D microfabricated electrode is particularly attractive since it yields enhanced performance with regard to spike sorting and single unit detection. In this paper, we describe a self-assembly process for fabricating 3D microelectrode arrays in silicon. The electrode array is composed of four silicon shanks (200 µm wide, 4 mm long and 30 µm thick) with polyimide-filled V-groove joints at the back end and four 20 × 20 µm ² recording sites (200 µm separation) at the tip. The shanks automatically fold to a vertical configuration upon proper heat treatment, hence creating a 3D configuration without the need for any manual assembly. Impedance and electrical test-signal measurements were used to verify the electrode functionality after the folding process.

• Open/close Piezoelectric energy harvesting from flow-induced vibration

  D-A Wang and H-H Ko  2010 J. Micromech. Microeng. 20 025019 Tag this article

  Article References Full text PDF (1006 KB)

  A new piezoelectric energy harvester for harnessing energy from flow-induced vibration is developed. It converts flow energy into electrical energy by piezoelectric conversion with oscillation of a piezoelectric film. A finite element model is developed in order to estimate the generated voltage of the piezoelectric laminate subjected to a distributed load. Prototypes of the energy harvester are fabricated and tested. Experimental results show that an open circuit output voltage of 2.2 V _pp and an instantaneous output power of 0.2 µW are generated when the excitation pressure oscillates with an amplitude of 1.196 kPa and a frequency of about 26 Hz. The solution of the generated voltage based on the finite element model agrees well with the experiments. Based on the finite element model, the effects of the piezoelectric film dimensions, the fluid pressure applied to the harvester and types of piezoelectric layer on the output voltage of the harvester can be investigated.