JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 29, NO. 4, AUGUST 2020 455 Miniature MEMS: Novel Key Components Toward Terahertz Reconfigurability Kazım Demir, Student Member, IEEE, and Mehmet Unlu , Senior Member, IEEE Abstract— We present an overview of the emerging and enabling miniature MEMS-based components for the terahertz frequencies. The usage of miniature MEMS integrated within the terahertz components is an uprising field of research, which offers reconfigurability, improved performance, and ability to perform unprecedented functions that cannot be achieved using the state-of-the-art semiconductor and optical technologies. In this paper, we discuss the recent progress and future of miniature MEMS-based reconfigurable components and present examples including reconfigurable sources, detectors, metamaterials, and guided-wave components. [2019-0099] Index Terms— Detectors, microelectromechanical systems, metamaterials, sources, terahertz. I. I NTRODUCTION T ERAHERTZ band is mostly referred as the part of the electromagnetic spectrum that is located between the infrared and millimeter-wave bands, which has a wavelength range between 30-3000 μm [1]–[3]. The terahertz waves have attracted the attention of the researchers starting almost a century before today [4], thanks to the exciting properties of the terahertz waves that can be achieved neither with infrared, nor with millimeter-wave wavelengths. The terahertz waves cannot only be directed as a ray due to their decreasing wavelength compared to the millimeter-wave wavelengths, but also propagate through most materials except for the metals and water, in contrast to the infrared wavelengths. Moreover, terahertz waves are non-ionizing and the spectral signatures of several molecules reside in the terahertz band [5]. Due to these propitious properties, the terahertz waves enable unparalleled applications in imaging [6], [7], spectroscopy [5], [8], and high-speed communications [9], [10]. It has been recently shown by several groups that the terahertz waves can be Manuscript received May 1, 2019; revised April 6, 2020; accepted April 28, 2020. Date of publication May 18, 2020; date of current version July 31, 2020. This work was supported in part by The Scientific and Technological Research Council of Turkey (TUBITAK) under Grant 114E089, in part by the H2020-MSCA-RI under Grant TERA-NANO, and in part by the 2015 Turkish Academy of Sciences Young Scientist Outstanding Achievement Award Program (TUBA-GEBIP 2015). Subject Editor J.-B. Yoon. (Corresponding author: Mehmet Unlu.) Kazım Demir is with the Department of Electrical and Electronics Engineer- ing, Ankara Yildirim Beyazit University, 06010 Ankara, Turkey, and also with The Scientific and Technological Research Council of Turkey (TUBITAK), 41470 Gebze, Turkey (e-mail: kazimdemir091@gmail.com). Mehmet Unlu is with the Department of Electrical and Electronics Engineer- ing, TOBB University of Economics and Technology, 06560 Ankara, Turkey (e-mail: munlu@etu.edu.tr). Color versions of one or more of the figures in this article are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JMEMS.2020.2992491 used for biomedical imaging [11], quality screening [12], security imaging [13]–[15], detection of defects [16], thick- ness measurement [17], spectroscopic identification of several materials including live tissues [18], and ultrawideband, secure communications [19]. Despite leaving almost a century behind the first research on the terahertz frequencies, we are still unable to close the terahertz “gap” and use the terahertz frequencies as commonly as we use the millimeter-wave and infrared fre- quencies. Unfortunately, the techniques that are employed for the microwave, millimeter-wave or infrared bands can- not be utilized to implement high-power, tunable sources and high-sensitivity, fast detectors, as well as other types of high-performance components, which are the fundamental parts for a terahertz system. There have been a great deal of effort for the development of sources [20], [21], detec- tors [22], [23], switches [24], modulators [25] and passive components [26] such as waveguides [27], filters, power dividers, and couplers [28] for the terahertz band in the last 30 years. Although the performance of these components has increased drastically in the last decade and reached up to a certain point, practical terahertz systems require higher levels of component performance to achieve the desired sys- tem level performance. Moreover, the terahertz systems need to be versatile and programmable in order to satisfy more complicated functions, including the control of the emitted terahertz beam for the imaging, radar, and communication applications, and tunability of the operating frequency for the spectroscopy applications [29]. Therefore, the adoption of reconfigurable terahertz components is inevitable not only to improve the scarce signal level and acquire the desired system level performance, but also to realize more complicated functions for a practical terahertz system. A significant amount of effort has been spent to address the integrability and reconfigurability requirements for the terahertz band using the solid-state technologies [29]–[32]. In view of the progress in the last decade, one can see that GaAs, InP, CMOS, and SiGe technologies are all advancing with a remarkable pace. GaAs Schottky barrier diodes can generate terahertz signals by frequency multiplication up to 3 THz, with mW power levels around 1 THz, which is one of the leading solid-state technologies [33]; unfortunately, the power levels start to drop rapidly beyond 1 THz. Consid- ering the integrated circuit (IC) technologies, the maximum oscillation frequency, f max , for a given technology node is an important figure of merit for the terahertz frequencies, 1057-7157 © 2020 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See https://www.ieee.org/publications/rights/index.html for more information.