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Development of High-Performance and High-Reliability NEMS Switches for Smart Antenna Structures

Final Report Summary - NEMSMART (Development of High-Performance and High-Reliability NEMS Switches for Smart Antenna Structures)

Scientific progress and results: The main objective of our project is to address and provide solutions to the ever-increasing performance demands of next-generation wireless communication system requirements with radically innovative approaches and concepts, new materials, and micro/nano-fabrication technologies, which bridge the gap between theory and implementation. NEMSmart focuses on the development of high-reliability, low-contact force DC-contact miniaturized-MEMS (NEMS) switches, which are the main building blocks of the key enabling component of next-generation cognitive wireless communications systems, i.e. NEMS integrated multi-functional reconfigurable antenna (MRA). This project aims to transfer the accumulated knowledge in this area from US institutions to ERA, train researchers in the field and pave the way for new projects in the field.
The fabrication efforts for individual miniaturized NEMS cantilever switches revealed unreliable switching performance mainly due to the limitations and reliability problems of sub-micron lithography systems and processing equipments. Based on these results, our research has been directed towards mainly two alternative RF-switch technologies: liquid-metal based microfluidic switching and smart-material-based switching units. Microfluidic efforts yielded partial success with switching action using the electro-wettin-on-dielectric (EWOD) phenomenon, however typical actuation voltages remained high (80+ V), non-toxic liquid metal droplets suffered from oxidation and metallic residue-leaving problems, as well as being prone to levitation. On the other hand, smart material-based switching differs from electro-mechanical and microfluidic approaches in that it does not suffer from moving parts, stiction, and contamination. The basic idea behind the usage of smart materials as switching components is that with such materials, if we can change the material property in a repeatable and reliable manner, we can place them in between our antenna patch pixels and by changing the conductivity of the smart-material based switch unit we can tune the effective impedance of the antenna surface. Mostly studied smart materials include ferro-electrics (BST) and phase-change materials (GST, VOx). While BST (BaSrTiOx) exhibits tunable dielectric coefficient under electric field, phase change materials show considerable amount of tenability in their conductivity due to the transition between amorphous and crystalline material states. Although the ON/OFF ratio is much less that the MEMS and micro-fluidic counterparts, the main advantage of this architecture is that no movable, fragile parts are involved in the switching scheme. If optimized successfully, smart-material based switching technology might be a strong candidate especially for tunable RF components.
In parallel to the research efforts on alternative novel RF-switching technologies, our research on atomic layer deposition of functional III-nitride and metal-oxide thin-films and nanostructures revealed significant scientific contributions. For the first time, our group demonstrated the successful plasma-assisted ALD growth of GaN and AlGaN alloys in the form of thin films as well as hollow nanofibers. In addition, functional metal-oxide nanofiber templates were synthesized and used for photo-catalysis and dye-synthesized solar cell (DSSC) applications successfully. Moreover, the very first proof-of-concept demonstration of thin-film transistors and UV photodetectors based on low-temperature ALD-grown GaN layers were reported.

Prospects of the research career development and re-integration of the fellow: With the Marie Curie IRG program, Dr. Biyikli was able to build my independent research group, which consists of 5 graduate students and 3 post-doctoral researchers. Dr. Biyikli was influential in attracting top-quality post-doctoral researchers to ERA, hosting 3 researchers from U.S.A. and one researcher from Israel. Three of these scholars have currently secured permanent faculty positions at prestigious national institutes. 13 national and 4 international active scientific collaborations has been created during the grant period. Based on the initial IRG grant and the collaborations formed, Dr. Biyikli was able to secure 6 additional joint project grants with a total of 6.500.000 USD funding. Our students won two prestigious student awards at international conferences, and I received the 2013 research incentive award from a prestigious national foundation. Within the second reporting period, 18 journal articles and 30 conference publications were produced. In addition, Dr. Biyikli gave 30 invited talks at national and international institutes and industrial organizations. The total number of publications during the entire IRG period tolled up to 75 (24 journal + 51 conference) which is a strong indication of the successful integration and level of independent research career of Dr. Biyikli. As an important part of his outreach activities, Dr. Biyikli initiated and served as the main organizer and head of the organization committee for the “International Workshop on Cleanroom Training for Critical and Sustainable Technologies” programs implemented in 2010, 2012, and 2013. A total of 139 international participants out of nearly 30 different countries were trained on cleanroom process technologies and micro/nano-scale device fabrication. Both theoretical lectures and seminars by prominent international scholars as well as hands-on cleanroom lab sessions were provided. Lastly, besides his intense academic research activities, Dr. Biyikli co-founded a hi-tech start-up company with the target of commercializing the RF-switch technologies and smart antenna prototypes which might have a significant impact on the next-generation wireless communication systems. In this way, Dr. Biyikli also contributed to the creation of high-paying salary jobs within the ERA.

None of the above would be possible without the invaluable contributions and research motivation from the EU under this Marie Curie IRG grant. The resources provided enabled Dr. Biyikli to initiate an independent research program at Bilkent University – UNAM focusing on micro/nano-scale functional materials and devices, to travel to the US and Europe to maintain collaborations and establish new ones, as well as networking with the leading pioneers and researchers in the field. The resources also facilitated the training of a number of graduate students and as well as attracting four first class post-doctoral researchers from the US to ERA.