Intellectual Merit: The objective of this BRIDGE research project is to design and develop terahertz integrated circuits using dielectric waveguides. In particular, integrated ribbon-waveguide based structures are proposed to make passive and tunable devices such as phase shifters, attenuators, switches, and power splitters. Research will focus on using high-index silicon and polymer-ceramic nanocomposites to fabricate these devices on a planar substrate. These dielectric waveguide based devices will be used to design novel terahertz-integrated circuits for application in antenna arrays and sensors. The proposed technology is a significant advancement when compared to traditional quasi-optical approaches, and in particular provides an avenue to overcome the integration bottleneck of terahertz systems and circuits.
Broader Impacts: The proposed research provides advancements in the general field of terahertz technology, yielding fundamentally new approaches to integrating circuits and systems. Applications of such a system includes security, biological studies, high-data rate communications, and spectroscopy. Under this project several graduate and undergraduate students will be trained in an exceptionally interdisciplinary manner as part of the research on integrated terahertz circuits. Integrating with the research program, a new project-based interdisciplinary course that includes terahertz circuit design and fabrication will be developed. Ongoing university programs will be leveraged to attract underrepresented students to engineering.
Terahertz (THz) holds significant potential for a range of applications, from biomedical imaging to high bandwidth communications. In comparison to X-rays, THz provides the benefit of imaging without the use of high energy radiation. One of the fundamental road blocks to building low-cost, compact and highly functional THz system is the lack of availability of THz integrated circuits. Interconnects or waveguides form the basic building block of an integrated circuit and approaches to form low-loss planar THz waveguides has been lacking. Approaches to integrate THz waveguides and passive circuits on a large area substrate is the subject of this study. Under this research, a host of THz waveguide designs were studied: micro-injection molded metalized plastic, surface plasmonics and thin dielectric ribbon waveguides. Among these, the ribbon waveguide structures were determined to be compatible with fabrication of planar circuits on large area substrates and have wide band frequency operation. Thin silicon (Si), alumina and polymer-ceramic nanocomposite were investigated for the fabrication of ribbon waveguides. From these, polymer-ceramic nanocomposites provides a practical approach to fabricate THz waveguides and circuits at the wafer level. Photopolymer based polymer-ceramic nanocomposites can be tailored to achieve desired dielectric properties and can be patterned using conventional microlithography on a large area substrate. Several THz circuits based on ribbon waveguides were demonstrated. Dielectric waveguide based wafer probes were designed and used for on-wafer probing of THz circuits. Overall, a new and practical approach to integrate THz circuits at the wafer level was demonstrated. The THz waveguides were also adopted in the design and demonstration of THz microfluidics sensors. These sensors will be useful in drug discovery and environment monitoring applications. In order to characterize the materials needed for the fabrication of THz circuits, several materials in thin-film form were characterized. In addition, new methods to characterize materials in the THz spectral region were demonstrated that overcome the challenges associated with system calibration and characterization of stacked dielectric layers. A total of 4 graduate students and 3 undergraduate students worked directly on this project. This research work resulted in in two Ph.D. and one M.S. thesis, and 18 conference and 4 journal papers. Furthermore, a new course was developed by the PI and a website was established that houses the dielectric properties of thin films measured under this program. Educational kits were also developed for K-12 students.
