Stephanus Büttgenbach

SU-8 Optical Accelerometers

This paper presents the optimization and characterization of SU-8 quad beam optical accelerometers based on intensity modulation. An applied acceleration causes a misalignment between three waveguides, resulting in variation of losses. Mechanical simulations have focused on the evaluation of sensitivity and the design of a robust junction between the mechanical beams and the inertial mass. Results demonstrate that perfectly rounded structures show at least 4.4 times less stress than L-shaped counterparts. Optical simulation predicts that the optimal configuration in terms of sensitivity is obtained when the waveguides are not completely misaligned, since then losses are insensitive to variations in acceleration. Numerical sensitivities ranging between 11.12 and 32.14 dB/g have been obtained. Fabrication has been simplified, now requiring only two photolithographic steps and electroplating Cu as a sacrificial layer. Experimental results show a reproducible experimental sensitivity of at least 13.1 dB/g

Simulation of anisotropic chemical etching of crystalline silicon using a cellular automata model

Abstract Anisotropic chemical etching of crystalline silicon in aqueous KOH is simulated at the atomic level using a cellular automata model. Experimental etch-rate ratios as well as the influence of temperature and concentration of the etchant are taken into account by introducing a stochastic component. With the help of two examples, the underetching of a convex mask corner and mask-corner compensation for mesa-type corners, the capabilities of this model are demonstrated.

Multiple internal reflection poly(dimethylsiloxane) systems for optical sensing

Compact poly(dimethylsiloxane)-based (PDMS) multiple internal reflection systems which comprise self-alignment systems, lenses, microfluidic channels and mirrors have been developed for highly sensitive absorbance measurements. With the proper definition of air mirrors at both sides of the sensing region, the optical path of the light from the LED has been meaningfully lengthened without a dramatic increase of the mean flow cell volume. By recursive positioning of such air mirrors, propagating multiple internal reflection (PMIR) systems have been designed, simulated and characterized. Experimental results confirm the ray-tracing predictions and allow the determining that there are some regions of the mean flow cell volume that do not contribute to the increase of the sensitivity. The tailoring of the sensing region, following the optical path, results in a similar limit of detection (110 nM) for fluorescein diluted in phosphate buffer. Finally, a ring configuration, labelled RMIR, has also been developed. With the addition of a third air mirror, the LOD can be decreased to 41 nM with the additional advantage of a substantial decrease of the length of the sensing region. These results confirm the validity of the proposed systems for high sensitivity measurements.

Poly(dimethylsiloxane) hollow Abbe prism with microlenses for detection based on absorption and refractive index shift.

In this paper we report on an optical detection method that utilizes two physical effects for signal transduction, namely absorption and shift of refractive index. The device consists of a hollow prism and was fabricated by means of soft-lithography. It exhibits a high degree of monolithic integration. In order to keep down the amount of external equipment that is necessary to run the device, we were able to integrate several functions, such as focussing of light and alignment of optical fibres. Since all components are fabricated in the same material and in the same process, compatibility with other microfluidic devices or components can be achieved easily. The functional efficiency and the performance of the detector were tested by investigating solutions containing fluorescein, with concentrations between 5 and 1000 microM. The results clearly show the two regions in which the two physical effects are effective.

Three-axes monolithic silicon low-g accelerometer

In this paper, four different designs for a new three-axes monolithic low-g acceleration sensor are presented. The silicon spring mass system of the sensor is fabricated in a single step by anisotropic wet chemical etching in KOH using [111] planes as physical etch stop. The orientation of the supporting beams of the spring-mass systems allows the seismic mass to move in a direction orthogonal to the [111] planes. Four mass-spring systems, each one rotated by 90/spl deg/, enables the detection of three components of the acceleration vector using capacitive readout. Two alignment structures are presented meeting the high requirements in terms of mask alignment, which are necessary when using the described etch technique. A new space saving compensation structure protecting the convex edges of the seismic masses during the etch process was realized and compared with standard solutions. The sensors performance was characterized and is demonstrated.

A micromachined capillary electrophoresis chip with fully integrated electrodes for separation and electrochemical detection

A novel analytical microsystem with fully integrated electrodes for electrophoresis and amperometrical detection is described. With respect to the lab-on-a-chip concept a capillary electrophoresis (CE) microsystem has been fabricated with a total of six gold electrodes for sample injection, separation and electrochemical detection using standard microfabrication technologies. The device is a ready-to-use system that does not need any extra mechanical apparatus for electrode insertion. The CE-chip has successfully been tested by measuring hydrogen peroxide, ascorbic acid and uric acid simultaneously. All three oxidizable species could be detected in less than 70 s. Glucose was detected by performing an enzymatic reaction along the separation channel. The microsystem showed a very good reproducibility.

Microfluidic reactor for continuous cultivation of Saccharomyces cerevisiae

A diffusion‐based microreactor system operated with a reaction volume of 8 μL is presented and characterized to intensify the process understanding in microscale cultivations. Its potential as screening tool for biological processes is evaluated. The advantage of the designed microbioreactor is the use for the continuous cultivation mode by integrating online measurement technique for dissolved oxygen (DO) and optical density (OD). A further advantage is the broaden application for biological systems. The bioreactor geometry was chosen to achieve homogeneous flow during continuous process operation. The device consisted of a microstructured top layer made of poly(dimethylsiloxane) (PDMS), which was designed and fabricated using UV‐depth and soft lithography assembled with a glass bottom. CFD simulation data used for geometry design were verified via microparticle‐image‐velocimetry (μPIV). In the used microreactor geometry no concentration gradients occurred along the entire reaction volume because of rapid diffusive mixing, the homogeneous medium flow inside the growth chamber of the microreactor could be realized. Undesirable bubble formation before and during operation was reduced by using degassed medium as well as moistened and moderate incident air flow above the gas permeable PDMS membrane. Because of this a passive oxygen supply of the culture medium in the device is ensured by diffusion through the PDMS membrane. The oxygen supply itself was monitored online via integrated DO sensors based on a fluorescent dye complex. An adequate overall volumetric oxygen transfer coefficient KLa as well as mechanical stability of the device were accomplished for a membrane thickness of 300 μm. Experimental investigations considering measurements of OD (online) and several metabolite concentrations (offline) in a modified Verduyn medium. The used model organism Saccharomyces cerevisiae DSM 2155 tended to strong reactor wall growth resembling a biofilm.

Hybrid electronic tongue based on optical and electrochemical microsensors for quality control of wine.

A multiparametric system able to classify red and white wines according to the grape varieties and for analysing some specific parameters is presented. The system, known as hybrid electronic tongue, consists of an array of electrochemical microsensors and a colorimetric optofluidic system. The array of electrochemical sensors is composed of six ISFETs based sensors, a conductivity sensor, a redox potential sensor and two amperometric electrodes, an Au microelectrode and a microelectrode for sensing electrochemical oxygen demand. The optofluidic system is entirely fabricated in polymer technology and comprises a hollow structure, air mirrors, microlenses and self-alignment structures. The data obtained from these sensors has been treated with multivariate advanced tools; Principal Component Analysis (PCA), for the patterning recognition and classification of wine samples, and Partial-Least Squares (PLS) regression, for quantification of several chemical and optical parameters of interest in wine quality. The results have demonstrated the utility of this system for distinguishing the samples according to the grape variety and year vintage and for quantifying several sample parameters of interest in wine quality control.

Microcoils and microrelays — an optimized multilayer fabrication process

Abstract In this paper a complete process technology for the integrated fabrication of inductive micro electromechanical systems (MEMS) is presented. The introduced technology comprises the technologies of 3D-UV–Depth Lithography, electroplating of various metals and alloys, insulation and planarization of magnetic or electrical microstructures using benzocyclobutene (BCB) and anisotropic trench etching of passivation layers to incorporate metallic structures into multilayer systems. By utilizing this technology inductive micro components and systems for use in sensing, actuation and microelectronics can easily be fabricated. To demonstrate the applicability of the introduced technology to complex micro systems microcoils with and without magnetic cores and a microrelay for high current switching have been built by means of this process.

Separate determination of liquid density and viscosity with sagittally corrugated Love-mode sensors

A novel microacoustic sensor is reported for separate determination of liquid density and viscosity. The device is based on a layered quartz/SiO2-system with sagittal corrugations, supporting acoustic waveguide Love-modes. The sensor combines the merits of Love-mode devices, e.g., robustness and high sensitivity, with liquid trapping as an effective approach to separate density and viscosity influences on acoustic shear modes. The outstanding features are extraordinary high and adjustable sensitivity to density changes with inherent large differences between density and viscosity responses. A model is discussed to describe the frequency response to liquid loading. Furthermore, studies of attenuation changes have shown that only little extra damping occurs due to the corrugations. Moreover, strategies are discussed for device optimisation in terms of temperature stability and sensitivity enhancement.