Design Of Two Axis Capacitive Accelerometer Using Mems

Author : Ahmad Alfaifi
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (14 download)

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Download or read book Surface-micromachined Capacitive Accelerometers in Above-IC Integration Methods written by Ahmad Alfaifi and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "This thesis proposes a methodology to optimize the design of capacitive accelerometers. This is achieved through a systematic improvement procedure of the closing-gaps accelerometers design. This is used to find the optimum electrode dimensions that would result in the highest sensitivity, within a specified area. The method is verified through the simulation and fabrication of different variations of two designs, then comparing the results with the expected values from analytical optimization methods. The prototypes are fabricated in a commercial process, which imposed limitations on the sizes of the possible accelerometer designs. A survey of prior published works shows the importance of the optimization technique suggested here to increase the performance of these types of sensors, when no fabrication restrictions exist.The thesis also introduces a novel low cross-sensitivity dual-axis capacitive accelerometer design. The device is fabricated in a silicon-on-insulator (SOI) process and its fabrication is finalized by an in-house release step. The device measures 1 mm × 1 mm, with four (4) proof masses that are able to sense accelerations in the X- and Y-axes independently. Two commercial capacitance-to-digital converters are used to read the outputs of both axes of the device in a system in package implementation. The fabricated device exhibits a sensitivity of 16.83 fF/g, while keeping the measured cross-sensitivity to less than 1 % throughout the ±4 g linear range. The rotational motion and Z accelerations have no impact on the device X and Y readings, thanks to the device's particular geometry and differential nature.In addition, the thesis presents a novel design of a 3D high-sensitivity lateral capacitive accelerometer. The accelerometer design utilizes the whole area of the sensor for both the sensing and proof masses, which cancels the tradeoff needed in conventional 2D designs. The design model of the accelerometer is developed to target the highest possible performance. A Z-shaped innovative design of the supporting beams is developed to limit the vertical displacement within the used submicron gap. The accelerometer measures 500 × 500 [mu]m2 and achieves 58 fF/g sensitivity in a ±4 g range in an open-loop system. Suggestions are provided to decrease the 1.4 mg noise floor of the device.Finally, the thesis describes a 3D surface micromachining platform process for above-IC integration. This method uses non-conductive materials with attractive mechanical properties to fabricate micro-electromechanical systems (MEMS) devices. The fixed structures are created using a polyimide layer, while the moving structures are built using silicon nitride (SiN). A 240-nm thin parylene-N polymer layer is used as a sacrificial layer to largely define the capacitive gaps and enable dry release. The photolithography steps are limited to four, in order to ensure a simple and low-cost process. The process has a thermal budget of 300 °C, which should be safe for processing above CMOS integrated circuits. While the used materials provide good results, this process is not limited to these specific materials, and others can be used if needed." --