N.F. de Rooij

Vertical mirrors fabricated by deep reactive ion etching for fiber-optic switching applications

We report on vertical mirrors fabricated by deep reactive ion etching of silicon. The mirror height is 75 /spl mu/m, covering the fiber core of a single-mode fiber when the latter is placed into a groove of equal depth and etched simultaneously with the mirror. To obtain a uniform etch depth, etching is stopped on a buried oxide layer. Using the buried oxide as a sacrificial layer allows to fabricate mirrors with suspension and actuation structures as well as fiber-alignment grooves in one and the same processing step. A minimal mirror thickness of 2.3 /spl mu/m was achieved, resulting in an aspect ratio higher than 30. The verticality was better than 89.3/spl deg/. In the upper part of the mirror a surface roughness below 40 nm rms was obtained. At a wavelength of 1300 nm the reflectivity of the aluminum-coated mirrors was measured to be higher than 76%. Using a reactive ion etched mirror we have fabricated an optical fiber switch with electrostatic actuation. The coupling loss in the bar state of two packaged prototypes was between 0.6 and 1.7 dB and between 1.4 and 3.4 dB in the cross state. The switching time is below 0.2 ms.

Planar microcoil-based microfluidic NMR probes

Microfabricated small-volume NMR probes consisting of electroplated planar microcoils integrated on a glass substrate with etched microfluidic channels are fabricated and tested. 1H NMR spectra are acquired at 300 MHz with three different probes having observed sample volumes of respectively 30, 120, and 470 nL. The achieved sensitivity enables acquisition of an 1H spectrum of 160 microg sucrose in D2O, corresponding to a proof-of-concept for on-chip NMR spectroscopy. Increase of mass-sensitivity with coil diameter reduction is demonstrated experimentally for planar microcoils. Models that enable quantitative prediction of the signal-to-noise ratio and of the influence of microfluidic channel geometry on spectral resolution are presented and successfully compared to the experimental data. The main factor presently limiting sensitivity for high-resolution applications is identified as being probe-induced static magnetic field distortions. Finally, based on the presented model and measured data, future performance of planar microcoil-based microfluidic NMR probes is extrapolated and discussed.

Design and fabrication of high-temperature micro-hotplates for drop-coated gas sensors

Note: 243 Reference SAMLAB-ARTICLE-2000-004 Record created on 2009-05-12, modified on 2016-08-08

Planar amperometric enzyme-based glucose microelectrode

Note: 32 Reference SAMLAB-ARTICLE-1989-009doi:10.1016/0250-6874(89)87015-5 Record created on 2009-05-12, modified on 2016-08-08

Comparison of the hysteresis of Ta2O5 and Si3N4 pH-sensing insulators

Abstract It has been shown that the accuracy of pH sensor devices based on insulator/electrolyte interface is limited by a slow response, which manifests itself as hysteresis and drift. In this paper, we use hysteresis measurement to compare the performance of Ta2O5 and Si3N4 as pH-sensing surfaces. The results depend on the time taken to perform a complete pH loop. At short loop times (960-9600 s) Ta2O5 is superior to Si3N4 is reduced. These data can be combined with earlier measurements of the hysteresis of Al2O3 surfaces to establish the following order to hysteresis magnitude at a loop time of 1920 s: si3N4 > Al2O3 > Ta2O5.

Hysteresis in Al2O3-gate ISFETs

Abstract When used as pH-sensing surfaces, insulators such as SiO2, Si3N4 and Al2O3 are subject to non-idealities such as hysteresis and drift. These effects limit the accuracy obtainable from pH-sensitive ISFETs. This paper studies the hysteresis effects in Al2O3-gate ISFETs by exposing the devices to a cycle of pH values. When the pH is cycled between 3 and 11 in a 0.1 M NaCl solution, hysteresis of 3 to 6 mV is seen, which corresponds to 0.8 to 1.6% of the total response. The hysteresis is somewhat less when background phosphate buffers are used rather than a Tris buffer. Oxalate and aluminate ions have no significant effect. The presence of fluoride ions in acid solutions causes a strong irreversible drift. Alkaline solutions also induce such a drift, but to a much smaller extent. The observations can be explained by the presence of two different effects: first, part of the pH response is delayed, resulting in hysteresis. Secondly, OH− and F− ions cause an irreversible drift towards more negative threshold voltages, which will also affect measured hysteresis values.

Integrated flow-regulated silicon micropump

Abstract A piezoelectric silicon micropump with a controlled output flow is presented. A closed-loop controller regulates the liquids flow. The system can maintain a constant output flow when the pressure difference between the pumps output and input varies. This regulation has been demonstrated for flow rates from 10 to 100 μl/min, and for pressure differences up to 100 mbar. The main components of the system as well as the results obtained are discussed.

Applications of SOI-based optical MEMS

After microelectromechanical systems (MEMS) devices have been well established, components of higher complexity are now developed. Particularly, the combination with optical components has been very successful and have led to optical MEMS. The technology of choice for us is the silicon-on-insulator (SOI) technology, which has also been successfully used by other groups. The applications presented here give an overview over what is possible with this technology. In particular, we demonstrate four completely different devices: (a) a 2 /spl times/ 2 optical cross connector (OXC)with an insertion loss of about 0.4 dB at a switching time of 500 /spl mu/s and its extension to a 4 /spl times/ 4 OXC, (b) a variable optical attenuators (VOA), which has an attenuation range of more than 50 dB (c) a Fourier transform spectrometer (FTS) with a spectral resolution of 6 nm in the visible, and (d) an accelerometer with optical readout that achieves a linear dynamic range of 40 dB over /spl plusmn/6 g. Except for the FTS, all the applications utilized optical fibers, which are held and self-aligned within the MEMS component by U-grooves and small leaf springs. All devices show high reliability and a very low power consumption.

Fabrication of multilayer systems combining microfluidic and microoptical elements for fluorescence detection

This paper presents the fabrication of a microchemical chip for the detection of fluorescence species in microfluidics. The microfluidic network is wet-etched in a Borofloat 33 (Pyrex) glass wafer and sealed by means of a second wafer. Unlike other similar chemical systems, the detection system is realized with the help of microfabrication techniques and directly deposited on both sides of the microchemical chip. The detection system is composed of the combination of refractive microlens arrays and chromium aperture arrays. The microfluidic channels are 60 /spl mu/m wide and 25 /spl mu/m deep. The utilization of elliptical microlens arrays to reduce aberration effects and the integration of an intermediate (between the two bonded wafers) aluminum aperture array are also presented. The elliptical microlenses have a major axis of 400 /spl mu/m and a minor axis of 350 /spl mu/m. The circular microlens diameters range from 280 to 300 /spl mu/m. The apertures deposited on the outer chip surfaces are etched in a 3000-/spl Aring/-thick chromium layer, whereas the intermediate aperture layer is etched in a 1000-/spl Aring/-thick aluminum layer. The overall thickness of this microchemical system is less than 1.6 mm. The wet-etching process and new bonding procedures are discussed. Moreover, we present the successful detection of a 10-nM Cy5 solution with a signal-to-noise ratio (SNR) of 21 dB by means of this system.

Scanning force microscopy in the dynamic mode using microfabricated capacitive sensors

We report on the first successful operation of a scanning force microscope using microfabricated capacitive force sensors. The sensors, which are made from single crystal silicon on insulator wafers, consist of a cantilever spring with integrated tip at the free end and an electrically insulated counter electrode. Dynamic force gradient sensing is the preferred operating mode. Here, tip–sample interactions are detected by letting the sensor act as a resonator in a phase controlled oscillator setup and measuring corresponding shifts of the oscillation frequency. Experiments were performed in vacuum using a standard tunneling microscope. A Cr grating on a quartz substrate served as the test sample. Topographic images showing details on a 10 nm scale were obtained operating at a constant force gradient of the order of 0.01 N/m. In addition, critical design parameters are discussed based on an analysis of the electromechanical properties of the sensors.