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Low-Cost Fabrication Techniques for RF Microelectromechanical systems (MEMS) Switches and Varactors

Obuh, Isibor Ehi (2018) Low-Cost Fabrication Techniques for RF Microelectromechanical systems (MEMS) Switches and Varactors. PhD thesis, University of Leeds.

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A novel low-cost microfabrication technique for manufacturing RF MEMS switches and varactors is proposed. The fabrication process entails laser microstructuring and non-clean room micro-lithography standard wet bench techniques. An optimized laser microstructuring technique was employed to fabricate the MEMS component members and masks with readily available materials that include, Aluminum foils, sheets, and copper clad PCB boards. The non-clean room micro-lithography process was optimized to make for the patterning of the MEMS dielectric and bridge support layers, which were derived from deposits of negative-tone photosensitive epoxy-based polymers, SU-8 resins (glycidyl-ether-bisphenol-A novolac) and photoacid activated ADEX™ dry films. The novel microfabrication technique offers comparatively reasonably yields without intensive cleanroom manufacturing techniques and their associated equipment and processing costs. It is an optimized hybrid rapid prototyping manufacturing process that makes for a reduction in build cycles while ensuring good turnarounds. The techniques are characterized by analysing each contributing technology and dependent parameters: laser structuring, lithography and spin coating and thin film emboss. They are developed for planar substrates and can be modified to suit specific work material for optimized outcomes. The optimized laser structuring process offers ablation for pitches as small as 75 µm (track width of 50 µm and gap 25 µm), with a deviation of 3.5 % in the structured vector’s dimensions relative to design. The lithography process also developed for planar and microchannel applications makes for the realization of highly resolved patterned deposits of the SU-8 resin and the laminated ADEX™ polymer from 1 µm to 6 µm and with an accuracy ±0.2 µm. The complete micro-fabrication technique fabrication techniques are demonstrated by realizing test structures consisting of RF MEMS switches and varactors on FR4 substrates. Both MEMS structures and FR4 substrate were integrated by employing the micro-patterned polymers, developed from dry-film ADEX™ and SU-8 deposits, to make for a functional composite assembly. Average fabrication yield up to 60 % was achieved, calculated from ten fabrication attempts. The RF measurement results show that the RF MEMS devices fabricated by using the novel micro-fabrication process have good figure-of-merits, at much lower overall fabrication costs, as compared to the devices fabricated by conventional cleanroom process, enabling it to be used as a very good micro-fabrication process for cost-effective rapid prototyping of MEMS.

Item Type: Thesis (PhD)
Keywords: Micro electromechanical systems (MEMS), rapid prototyping, laser microstructuring, non-clean room micro-lithography standard wet bench techniques
Academic Units: The University of Leeds > Faculty of Engineering (Leeds) > School of Electronic & Electrical Engineering (Leeds) > Institute of Microwaves and Photonics (Leeds)
Identification Number/EthosID: uk.bl.ethos.755121
Depositing User: Isibor Obuh
Date Deposited: 05 Oct 2018 10:49
Last Modified: 18 Feb 2020 12:32
URI: http://etheses.whiterose.ac.uk/id/eprint/21479

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