Remco G.P. Sanders

Monolithic fiber-top sensor for critical environments and standard applications

We present a monolithic device obtained by carving a cantilever on the top of a single-mode optical fiber. We show that the vertical position of the cantilever can be determined with accuracy comparable to atomic force microscopes and other commonly used scientific instruments. The device does not require any alignment procedure and can be used in critical environments as well as in standard applications.

Modeling, design, fabrication and characterization of a micro Coriolis mass flow sensor

This paper discusses the modeling, design and realization of micromachined Coriolis mass flow sensors. A lumped element model is used to analyze and predict the sensor performance. The model is used to design a sensor for a flow range of 0–1.2 g h−1 with a maximum pressure drop of 1 bar. The sensor was realized using semi-circular channels just beneath the surface of a silicon wafer. The channels have thin silicon nitride walls to minimize the channel mass with respect to the mass of the moving fluid. Special comb-shaped electrodes are integrated on the channels for capacitive readout of the extremely small Coriolis displacements. The comb-shaped electrode design eliminates the need for multiple metal layers and sacrificial layer etching methods. Furthermore, it prevents squeezed film damping due to a thin layer of air between the capacitor electrodes. As a result, the sensor operates at atmospheric pressure with a quality factor in the order of 40 and does not require vacuum packaging like other micro Coriolis flow sensors. Measurement results using water, ethanol, white gas and argon are presented, showing that the sensor measures true mass flow. The measurement error is currently in the order of 1% of the full scale of 1.2 g h−1.

Use of Selective Anodic Bonding to Create Micropump Chambers with Virtually No Dead Volume

Membrane micropump chambers of 11 mm diam with virtually zero dead volume were realized using selective anodic bonding. The selective bonding was achieved with less than 1 nm thick metallic antibonding layers on the glass wafer. Experiments were carried out to come to a better understanding of the selective anodic bonding process. It was concluded that a conductive antibonding layer on the glass wafer prevents the formation of a bond, because in that case the electrostatic attraction between the Pyrex and silicon wafers will vanish upon contact. Chromium and Platinum were found to be suitable antibonding layers. Furthermore, it was found that during the anodic bonding process, the transport of oxygen ions from Pyrex toward the silicon-Pyrex interface results in the formation of SiO2, which forms the actual bond between both substrates. At positions of an intermediate antibonding layer the oxygen ions form oxygen gas. The Pyrex or silicon substrate may deform locally due to the buildup of oxygen gas pressure. This can be prevented by adding a gas outlet to the design. ©2001 The Electrochemical Society. All rights reserved.

A light detection cell to be used in a micro analysis system for ammonia

This paper describes the design, realization and characterization of a micromachined light detection cell. This light detection cell is designed to meet the specifications needed for a micro total analysis system in which ammonia is converted to indophenol blue. The concentration of indophenol blue is measured in a light detection cell. The light detection cell was created using KOH/IPA etching of silicon. The KOH/IPA etchant was a 31 wt.% potassium hydroxide (KOH) solution with 250 ml isopropyl alcohol (IPA) per 1000 ml H(2)O added to it. The temperature of the solution was 50 degrees C. Etching with KOH/IPA results in 45 degrees sidewalls ({110} planes) which can be used for the in- and outcoupling of the light. The internal volume of the realized light detection cell is smaller than 1 mul, enabling measurements on samples in the order of only 1 mul. Measurements were performed on indophenol blue samples in the range of 0.02 to 50 muM. In this range the measurements showed good reproducibility.

Elastocapillary fabrication of three-dimensional microstructures

We describe the fabrication of three-dimensional microstructures by means of capillary forces. Using an origami-like technique, planar silicon nitride structures of various geometries are folded to produce three-dimensional objects of 50–100 m. Capillarity is a particularly effective mechanism since surface tension forces dominate over bulk forces at small scales. The spontaneous evaporation of water forms the driving mechanism for this microfabrication technique. Therefore the actuating liquid disappears in the final structure. A model describing the elastocapillary interaction of the folding process is compared with experiments. By tailoring the elastic and capillary properties a variety of three-dimensional micro-objects can be realized.

Fibre-top cantilevers: design, fabrication and applications

Fibre-top cantilevers are a new generation of miniaturized devices obtained by carving tiny mechanical beams directly on the cleaved edge of an optical fibre. The light coupled from the other side of the fibre allows measurements of the position of the cantilever with sub-nanometre accuracy. The monolithic structure of the device, the absence of electronic contacts on the sensing head, and the simplicity of the working principle offer unprecedented opportunities for the development of scientific instruments for both standard applications and utilization beyond research laboratories. In this paper we review the results that our group has obtained over the last year in the development of this technology. We describe the working principle and the fabrication procedure, and we present a series of proof-of-concept experiments that demonstrate that fibre-top cantilevers can be used both for atomic force microscopy and for the detection of chemical species.

Improving the performance of biomimetic hair-flow sensors by electrostatic spring softening

We report improvements in the detection limit and esponsivity of biomimetic hair-flow sensors by electrostatic spring softening. Applying a dc-bias voltage to our capacitive flow sensors results in a reduced sensory threshold, improving the mechanical transfer and flow detection limit by more than 6 dB. We further show that the sensor’s responsivity for airflows is also improved on application of high-frequency ac-bias voltages to the sensor’s capacitive structures with little sensitivity to the bias frequency.

Six-axis force-torque sensor with a large range for biomechanical applications

A silicon six-axis force–torque sensor is designed and realized to be used for measurement of the power transfer between the human body and the environment. Capacitive read-out is used to detect all axial force components and all torque components simultaneously. Small electrode gaps in combination with mechanical amplification by the sensor structure result in a high sensitivity. The miniature sensor has a wide force range of up to 50 N in normal direction, 10 N in shear direction and 25 N mm of maximum torque around each axis.

3D Nanofabrication of Fluidic Components by Corner Lithography

A reproducible wafer-scale method to obtain 3D nanostructures is investigated. This method, called corner lithography, explores the conformal deposition and the subsequent timed isotropic etching of a thin film in a 3D shaped silicon template. The technique leaves a residue of the thin film in sharp concave corners which can be used as structural material or as an inversion mask in subsequent steps. The potential of corner lithography is studied by fabrication of functional 3D microfluidic components, in particular i) novel tips containing nano-apertures at or near the apex for AFM-based liquid deposition devices, and ii) a novel particle or cell trapping device using an array of nanowire frames. The use of these arrays of nanowire cages for capturing single primary bovine chondrocytes by a droplet seeding method is successfully demonstrated, and changes in phenotype are observed over time, while retaining them in a well-defined pattern and 3D microenvironment in a flat array.

Electrical properties of low pressure chemical vapor deposited silicon nitride thin films for temperatures up to 650 °C

The results of a study on electrical conduction in low pressure chemical vapor deposited silicon nitride thin films for temperatures up to 650 °C are described. Current density versus electrical field characteristics are measured as a function of temperature for 100 and 200 nm thick stoichiometric (Si3N4) and low stress silicon-rich (SiRN) films. For high E-fields and temperatures up to 500 °C conduction through Si3N4 can be described well by Frenkel–Poole transport with a barrier height of ∼ 1.10 eV, whereas for SiRN films Frenkel–Poole conduction prevails up to 350 °C with a barrier height of ∼ 0.92 eV. For higher temperatures, dielectric breakdown of the Si3N4 and SiRN films occurred before the E-field was reached above which Frenkel–Poole conduction dominates. A design graph is given that describes the maximum E-field that can be applied over silicon nitride films at high temperatures before electrical breakdown occurs.