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Title: Metal microstructures for shock protection of MEMS
Author: Delahunty, Aifric Kyne
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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With MEMS (Micro-electro-mechanical systems) becoming increasingly commonplace in many different industries, the need for more robust microstructures that can withstand high-shock environments is growing in importance. Literature currently available is yet to reveal a MEMS shock-absorber which meets our set of requirements, namely that it is suitable for both space and terrestrial applications, is easily incorporated into current MEMS fabrication methods and can absorb significant amounts of energy without needing a power source or without adversely affecting the performance of the device. This thesis presents a novel solution for the shock protection of MEMS which successfully satisfies the requirements stated above. Metal microstructures, created through the reflow of solder, are successfully used to armour and protect delicate silicon MEMS suspensions. A brittle silicon-silicon impact is replaced with a ductile metal-metal impact. The metal protects the silicon from fracturing at the point of impact during a high-shock event and absorbs a significant proportion of the collision energy through plastic deformation. A model suspension system is used to assess the performance of metalarmouring as a MEMS shock-absorber. Two metal-bumper designs, surface-mounted solder bumpers and solder bumpers integrated into the sidewalls of the suspension system are fabricated and tested in a drop-test rig at acceleration levels of up to 6000g. The surface-mounted bumpers, formed by reflowing solder on metallised pads (plated on the suspension surface), were found to fail on impact at the pad-wafer interface. The integrated bumpers are designed to combat the short-comings of the surface-mounted bumpers. Two solder balls are reflowed in through-wafer conduits within the suspension sidewalls, creating substantial solder bumpers which are mechanically keyed in place. The integrated bumpers proved to be shear resistant and to double overall the shock resistance of the MEMS suspension.
Supervisor: Pike, William Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available