M.T. Blom

Design and fabrication of a hydrodynamic chromatography chip

A chromatography chip is presented in which the analysis is performed by polymer separation entirely based on geometry. Design and fabrication are discussed for a chip incorporating an injection structure and a separation channel. The injection is characterized by fluorescence measurements. Chromatographic performance was shown by separation of fluorescein and 26 nm fluorescent particles.

Local anodic bonding of Kovar to Pyrex aimed at high-pressure, solvent-resistant microfluidic connections

Local anodic bonding of a common Kovar alloy to Pyrex is presented. This technique is ideally suitable for temperature-, solvent- and pressure-resistant microfluidic connections. In this paper we mainly concentrate on the stress problems occurring during and after bonding. Because of the different thermal expansion coefficients of Kovar and Pyrex a structure is added in order to release the thermal stresses induced during bonding. Optimum bonding conditions in vacuum on Pyrex and on a Pyrex-Si bonded wafer pair are investigated. In the latter case bonding for 3 h at 250 °C and 1.5 kV results in a high-quality bond.

Production of silicon mirror plates

Silicon pore optics are currently under development for missions such as the International X-ray Observatory (IXO) as an alternative to the glass or nickel shell mirrors that were used in previous generation X-ray telescopes. The unprecedented effective area requirement of the IXO requires a modular optics design suitable for mass production. In this paper we discuss the current state-of-the-art in plate manufacturing technology. We provide examples of process innovations that have directly impacted the cost per mirror plate and have reduced the manufacturing cost of a mirror module. We show how a switch from silicon to silica as the reflective surface results in a simplified process flow without a corresponding change in the optical performance. We demonstrate how standard photolithographic techniques, applied in the semiconductor industry, can be used to pattern a reflective layer. The 5 arc-second angular resolution requirement of the IXO has stimulated a theoretical analysis of engineering tolerances in relation to angular resolution. We prove that improved control of the wedge angle by means of etch rate monitoring results in improved angular resolution. The results of this investigation will be used as the basis for future development in design for mass production.

A differential viscosity detector for use in miniaturized chemical separation systems

We present a micromachined differential viscosity detector suitable for integration into an on-chip hydrodynamic chromatography system. The general design, however, is applicable to any liquid chromatography system that is used for separation of polymers. The micromachined part of the detector consists of a fluidic Wheatstone bridge and a low hydraulic capacitance pressure sensor of which the pressure sensing is based on optical detection of a membrane deflection. The stand-alone sensor shows a resolution in specific viscosity of 3/spl times/10/sup -3/, in which specific viscosity is defined as the increase in viscosity by a sample, relative to the baseline viscosity of a solvent.

A low hydraulic capacitance pressure sensor for integration with a micro viscosity detector

A design is presented for a micromachined differential viscometer, that is suitable for integration into a planar hydrodynamic chromatography system (HDC) for polymer analysis. The viscometer consists of four equal flow restrictions and two pressure sensors, connected in a Wheatstone bridge configuration. Since this viscometer requires an ultra-low hydraulic capacitance differential pressure sensor, a pressure sensor is presented of which the internal volume displacement was reduced considerably compared to commercially available sensors. An optical method was used to detect membrane deflections with a magnitude of approximately 0.01 nm. This method lead to a linearity of 1% over the measured pressure range and a resolution of 2 Pa. With this pressure sensor integrated into the viscosity detector, viscosity measurements were performed on the viscosity difference of ethanol and water.

A Micro Viscosity Detector for Use in Miniaturized Chemical Separation Systems

A novel micromachined differential viscosity detector is presented that is suitable for integration with an on-chip hydrodynamic chromatography system. Viscosity detection is demonstrated using a prototype that shows a resolution in the specific viscosity of 3.0*10−3.

A Micro Viscosity Detector for a Planar Hydrodynamic Chromatography (HDC) System

A design is presented for a micromachined differential viscometer, suited for integration in a planar Hydrodynamic Chromatography System. The viscometer consists of four equal flow restrictions and two pressure sensors, connected in a Wheatstone bridge configuration.

Laser assisted and hermetic room temperature bonding based on direct bonding technology

A novel method for laser assisted room temperature bonding of two substrates is presented. The method enables the packaging of delicate (bio)structures and/or finished (MEMS) devices, as there is no need for a high temperature annealing process. This also allows the bonding of two substrates with non-matching thermal expansion coefficients. The basis of the presented technology is the ability to create a direct pre-bond between two substrates. These can be two glass substrates, of which one has a thin film metal coating (e.g. Cr. Ti, Ta, Au…), or a silicon-glass combination. After (aligned) pre-bonding of the two wafers, a laser (e.g. a Nd:YAG laser) is used to form a permanent bond line on the bond interface, using the metal layer as a light absorber (or the silicon, in the case of a glass-silicon combination). The permanent bond line width is in the order of 10-50μm. The use of a laser to form the permanent bond ensures a hermetic sealing of the total package; a distinctive advantage over other, more conventional methods of room temperature bonding (e.g. adhesive bonding). He-leak testing showed leak rates in the order of 10-9 mbar l/s. This meets the failure criteria of the MIL-STD-883H standard of 5x10-8 mbar l/s. An added functionality of the proposed method is the possibility to create electrical circuitry on the bond interface, using the laser to modify the metal interlayer, rendering it electrically non-conductive. Biocompatible packages are also possible, by choosing the appropriate interlayer material. This would allow for the fabrication of implantable packages.

Solute dispersion by electroosmotic flow in nonuniform microfluidic channels

In this work the effect of nonuniform channel shape on the dispersion of a solute by electroosmotic flow in microfluidic systems was studied using fluorescence imaging.

Failure mechanisms of pressurized microchannels, model and experiments

Microchannels were created by fusion bonding of a Pyrex and a thermally oxidized silicon wafer. The maximum pressure which can be applied to these channels was investigated. In order to find the relation between this maximum pressure, channel geometry, material elasticity and bond energy, an energy model was developed. It was shown that the model is substantiated by the pressure data, from which it could be calculated that the effective bond energy increased from 0.018 J/m/sup 2/ to 0.19 J/m/sup 2/ for an annealing temperature ranging from 310/spl deg/C to 470/spl deg/C.