University of Twente Student Theses


Characterisation of a micromachined Wobbe index sensor

Breazu, B. (2020) Characterisation of a micromachined Wobbe index sensor.

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Abstract:This report presents the calculations, measurements and simulations of the TCR (Temperature coefficient of resistance) for silicon and platinum inside multiple MEMS (micro-electromechanical system) chips used for microfluidic applications. The chips were designed as a Wobbe index meter and uses a silicon strip as a heater and a gold-platinum-tantalum alloy as a temperature sensor. The report aims to prove the working principles of the chips design as well as show the performance achieved during experiments. The theoretical calculations use models (parallel plate approximation) so all the limitations are discussed separately. The design and performance of the chips is influenced by aspects as the distribution of the heat transfer along the silicon heaters and the limitations of the SCT fabrication technology. During the experiment the chips are evaluated from the visual point of view using a microscope and also technically trough the probe measurement and joule heating process. The report records all the progress and steps taken by the chips during the experiment as well as verdicts at different checkpoints. During the experiment, one chip obtained a great performance, achieving a temperature of 325⁰C at a power of 0.35W, one chip achieved an average performance, a temperature of 118⁰C at a power of 0.20W and one chip broke down after only 0.20W. The paper also discussed the reliability of each design and future improvements. The simulations do not reflect the real world design and aim to prove the calculations of the theory. The heat dissipation along the silicon strip is considered to have the shape of a hyperbolic cosine function, so the most heat dissipation is in the middle and the least on the sides. Also the temperature difference between the Silicon and the platinum was calculated as a linear function that increases linearly with the power. The temperature difference varies from chip to chip depending on the length of the silicon strip but ranges from 0.5⁰C to 2⁰C at a dissipated power of 0.35W
Item Type:Essay (Bachelor)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:53 electrotechnology
Programme:Electrical Engineering BSc (56953)
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