RF Ohmic MEMS Switches Utilizing Printed and Carbon Based Nanomaterials for Space Applications

This thesis is devoted to the development of Radio Frequency (RF) Ohmic (metal-to-metal contact-type) MEMS (micro-electro-mechanical-systems) Switches for Space Applications. Ohmic contact devices void of any dielectric layer are considered exclusively in order to avoid the possibility of dielectric charging during operation, which is a possible failure mode. Cantilevered topologies are solely considered, and all devices are tested unpackaged with a gentle flow of nitrogen gas in standard laboratory conditions. Both DC and RF devices are considered, explored and developed that are each insensitive to stress and temperature effects while utilizing relatively simplistic surface micromachined fabrication processes consisting of no more than six mask steps, developed specifically for this work. For the differing processes, a minimum of three and a maximum of six materials are used for device fabrication. The overall motivation is to realize high-reliability and high-power handling ohmic MEMS switches that are compatible with conventional packaging techniques. With these objectives, both Ni and Au are explored for use as a structural MEMS material while controlling the intrinsic stress of both. Devices consisting of dual contact points utilizing differing contact materials are also explored in order to limit hot-switching damage on the ohmic contacts. Analytically, it is shown that the implementation of a refractory metal (Pt) protection contact would extend the switching lifetime of the device. This was also experimentally verified whereby the dual contact device achieved 6 x 10^6 switching cycles under 10V/10mA switching conditions, compared to only 1 x 10^5 switching cycles for an all Au contact interface device of the same structural design under the same switching conditions. The resistance of the designed dual contact DC MEMS switch is found to be approximately 1.5 Ohms at a biasing voltage of 65 V. In addition, considerations for an efficient RF MEMS switch are implemented to produce devices capable of switching from DC up to 40 GHz while also exploring the utilization of carbon nanotubes (CNTs) as a carbon-based nanocomposite contact material. The experimental validation of an ohmic (metal-to-metal) RF Au-Ru contact interface switch with high reliability and power handling (> 10 x 10^6 cycles at 2 W at 25 degrees Celsius) is presented for DC up to 25 GHz applications, where the device isolation and insertion loss is > -20dB and < -1dB at 10 GHz. In addition, a Au-Au/CNT composite nanomaterial contact interface RF ohmic MEMS switch for DC up to 40 GHz applications is also proposed, designed and experimentally verified. The fabricated devices exhibit > -25dB and < -2dB in terms of RF isolation and insertion loss at a frequency of 10 GHz, respectively. Compared to Au-Au contact device of the same design, the Au-Au/CNT device shows higher switching lifetimes (12 x 10^6 for the Au-Au/CNT device versus 80 x 10^3 for the Au-Au device, under the same test conditions) and less stiction when releasing at elevated temperatures. Raman spectral analysis for the CNT layer post deposition, post fabrication and post lifetime cycling are analysed and compared, showing little change. Finally, further optimization of device arrangement while utilizing dual or multiple contact devices are presented through the use of switching networks in order to extend the hot-switching lifetime of RF MEMS switches while simultaneously improving the on-state device isolation.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2019

Author dc:creator

• Coburn, Nigel J

Advisor dc:contributor.advisor

• Flewitt, Andrew J

• MEMS
• Radio Frequency
• RF
• Nanomaterials
• CNTs
• Carbon Nanotubes
• Microsystems
• Space Applications
• Switching Networks
• Actuators
• Fabrication
• Electroplating

Licence

• https://www.repository.cam.ac.uk/bitstreams/617dd0c4-f429-49d2-8c19-6b693efdabdc/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.55168

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/308073