Terahertz MEMS metadevices

Abstract

Terahertz (THz) part of the electromagnetic spectrum (0.1–10 THz) holds the key for next-generation high-speed wireless communication, non-destructive biosensing, fingerprint chemical detection and imaging for astronomy and security surveillance. The limited THz response of naturally occurring materials had left a technological gap in the THz region of the electromagnetic spectrum. Artificially engineered materials termed as ‘metamaterials’, have shown great potential in THz wave interaction and its active counterpart termed as ‘metadevices’ have been widely reported for on-demand manipulation of THz waves. One of the most efficient means of realizing metadevices is to reconfigure the shape of unit cells and hence the corresponding THz response. The 50+ years of development in microelectromechanical systems (MEMS) and the wide array of microactuator designs provide a perfect platform to achieve structural reconfiguration of microscale metamaterial unit cells in both in-plane and out-of-plane directions. In this review, we present a comprehensive overview of various MEMS approaches adopted for the demonstration of THz metadevices, their advantages and limitations. The future research directions of THz MEMS metadevices are also discussed. The seamless integration of matured MEMS technology with incipient THz metamaterials provides significant advantages in terms of enhanced performances, advanced functionalities and large scale manufacturability, that is critical for the development of future THz technologies.

Terahertz Reconfigurable Intelligent Surfaces (RISs) for 6G Communication Links

“…Most existing review papers focused on summarizing various possible applications of RISs in wireless communication [41] or analyzing different tunable metasurfaces according to their tuning mechanisms [42,43]. Several review papers analyzed active metasurfaces for only one tuning element [44][45][46][47]. This paper emphasizes reconfigurable metasurfaces operating in the THz spectrum with the potential to assist 6G communications, i.e., metasurfaces with tunable functions such as pixel-level amplitude modulation or wide-range phase coverage for beam steering.…”

“…Moreover, advanced and developed MEMS manufacturing makes it attractive for reconfigurable THz devices [107]. The simplest microstructure cantilever has been extensively studied and was embedded in a metasurface for active tuning [44]. A wideband spatial light modulator was built using an array of 768 actuatable mirrors, with a length of 220 µm and a width of 100 µm (Figure 10a) [108].…”

Reconfigurable terahertz metamaterials: From fundamental principles to advanced 6G applications

“…Microelectromechanical system (MEMS) technology enables micro/nanoscale mechanical manipulation, which is suitable for meta-atom construction in the THz region, bringing various applications in THz functional devices. The reconfigurable MEMS metamaterials can be further classified by their actuator mechanisms, such as piezoelectric ( Willatzen and Christensen, 2014 ; Amirkhan et al., 2020 ; Le et al., 2022 ), electrothermal ( Lee and Wu, 2005 ; Lee and Yeh, 2005 ; Lee, 2005 ; Lee, 2006 ; Lee, 2007 ; Pitchappa et al., 2017 ), and electrostatic ( Pitchappa et al., 2015a , 2015b , 2015c , 2016a , 2016c ; Shih et al., 2017 ) ( Pitchappa et al., 2021a , 2021b ), and so on ( Lee et al., 2005 ; Lee, 2005 ; Yeh et al., 2006 ). Combining with metamaterial resonator designs, the deformed structures can effectively modify the electromagnetic field distribution inside the resonators.…”

“…Among these tuning mechanisms, two solutions have raised the attention and been reported frequently, microelectromechanical systems (MEMS) technology and tunable two-dimensional (2D) materials. On the one hand, the geometric-dependent metamaterial resonators could be effectively influenced by changing the configuration of unit cells, which can be enabled by MEMS actuators to a broadband frequency ranging from THz to visible light ( Lin and Lee, 2014 ; Dong et al., 2020a ; Ma et al., 2020b ; Ren et al., 2020 ; Dong et al., 2020b ; Lin and Xu, 2020 ; Pitchappa et al., 2021a ; Zhou et al., 2021a ; Wang et al., 2021 ). Moreover, the integration of MEMS actuators and metamaterials are compatible with the current complementary metal-oxide-semiconductor (CMOS) fabrication platform.…”

Cost-Effective Bull’s Eye Aperture-Style Multi-Band Metamaterial Absorber at Sub-THz Band: Design, Numerical Analysis, and Physical Interpretation

“…The THz band covers the distance between the IR and millimeter waves [36][37][38] and has many applications [39][40][41][42][43]. Therefore, THz EM waves have been less discovered than those in the continuous spectrum regime.…”