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1. Modeling of Sub-Millimeter Wave Coplanar Waveguide Graphene Switches

   https://doi.org/10.1109/APUSNCURSINRSM.2019.8889029  

   Theofanopoulos, Panagiotis C. ; Trichopoulos, Georgios C. ( July 2019 , 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting)

   We present a theoretical study on the performance of graphene-loaded coplanar waveguide switches for 5G and beyond applications. Therefore, we exploit the tunable properties of graphene to device cost-effective, large-scale, broadband sub- millimeter-wave switches. Given the sheet impedance of biased and unbiased graphene monolayers, the model provides the optimum switching ratio with respect to insertion loss, characteristic impedance of transmission line, and graphene geometry. Using measured graphene sheet resistance, we compute the optimum switching performance for series and shunt single- pole-single-though sub-millimeter-wave (220-330 GHz) switches.
2. Strongly enhanced THz generation enabled by a graphene hot-carrier fast lane

   https://doi.org/10.1038/s41467-022-34170-3  

   Zhang, Dehui ; Xu, Zhen ; Cheng, Gong ; Liu, Zhe ; Gutierrez, Audrey Rose ; Zang, Wenzhe ; Norris, Theodore B. ; Zhong, Zhaohui ( October 2022 , Nature Communications)

   Semiconductor photoconductive switches are useful and versatile emitters of terahertz (THz) radiation with a broad range of applications in THz imaging and time-domain spectroscopy. One fundamental challenge for achieving efficient ultrafast switching, however, is the relatively long carrier lifetime in most common semiconductors. To obtain picosecond ultrafast pulses, especially when coupled with waveguides/transmission lines, semiconductors are typically engineered with high defect density to reduce the carrier lifetimes, which in turn lowers the overall power output of the photoconductive switches. To overcome this fundamental trade-off, here we present a new hybrid photoconductive switch design by engineering a hot-carrier fast lane using graphene on silicon. While photoexcited carriers are generated in the silicon layer, similar to a conventional switch, the hot carriers are transferred to the graphene layer for efficient collection at the contacts. As a result, the graphene-silicon hybrid photoconductive switch emits THz fields with up to 80 times amplitude enhancement compared to its graphene-free counterpart. These results both further the understanding of ultrafast hot carrier transport in such hybrid systems and lay the groundwork toward intrinsically more powerful THz devices based on 2D-3D hybrid heterostructures.
3. Ultrafast modulation of terahertz waves using on-chip dual-layer near-field coupling

   https://doi.org/10.1364/OPTICA.469461  

   Zhang, Yaxin ; Ding, Kesen ; Zeng, Hongxin ; Kou, Wei ; Zhou, Tianchi ; Zhou, Hongji ; Gong, Sen ; Zhang, Ting ; Wang, Lan ; Liang, Shixiong ; et al ( November 2022 , Optica)

   As a key potential component of future sixth-generation (6G) communication systems, terahertz (THz) technology has received much attention in recent years. However, a lack of effective high-speed direct modulation of THz waves has limited the development of THz communication technology. Currently, most high-speed modulators are based on photonic systems that can modulate electromagnetic waves with high speed using sophisticated optoelectronic conversion techniques. Yet, they usually suffer from low conversion efficiency of light to the THz range, resulting in low output power of the modulated THz waves. Here, we describe a guided-wave modulator for THz signals whose performance nearly matches that of existing in-line fiber-optic modulators. Our results demonstrate a maximum modulation depth greater than 20 dB (99%) and a maximum sinusoidal modulation speed of more than 30 GHz, with an insertion loss around 7 dB. We demonstrate the capabilities of this modulator in a point-to-point communication link with a 25 Gbit/s modulation speed. Our modulator design, based on near-field coupling of a THz transmission line to a single resonant meta-element, represents a powerful improvement for on-chip integrated high-performance THz devices.
4. Observation of solid-state bidirectional thermal conductivity switching in antiferroelectric lead zirconate (PbZrO3)

   https://doi.org/10.1038/s41467-022-29023-y  

   Aryana, Kiumars ; Tomko, John A. ; Gao, Ran ; Hoglund, Eric R. ; Mimura, Takanori ; Makarem, Sara ; Salanova, Alejandro ; Hoque, Md Shafkat ; Pfeifer, Thomas W. ; Olson, David H. ; et al ( December 2022 , Nature Communications)

   Abstract Materials with tunable thermal properties enable on-demand control of temperature and heat flow, which is an integral component in the development of solid-state refrigeration, energy scavenging, and thermal circuits. Although gap-based and liquid-based thermal switches that work on the basis of mechanical movements have been an effective approach to control the flow of heat in the devices, their complex mechanisms impose considerable costs in latency, expense, and power consumption. As a consequence, materials that have multiple solid-state phases with distinct thermal properties are appealing for thermal management due to their simplicity, fast switching, and compactness. Thus, an ideal thermal switch should operate near or above room temperature, have a simple trigger mechanism, and offer a quick and large on/off switching ratio. In this study, we experimentally demonstrate that manipulating phonon scattering rates can switch the thermal conductivity of antiferroelectric PbZrO 3 bidirectionally by −10% and +25% upon applying electrical and thermal excitation, respectively. Our approach takes advantage of two separate phase transformations in PbZrO 3 that alter the phonon scattering rate in different manners. In this study, we demonstrate that PbZrO 3 can serve as a fast (<1 second), repeatable, simple trigger, and reliable thermal switch with a net switchingmore »ratio of nearly 38% from ~1.20 to ~1.65 W m −1 K −1 .« less
5. Non-volatile RF and mm-wave Switches Based on Monolayer hBN

   https://doi.org/10.1109/IEDM19573.2019.8993470  

   Kim, Myungsoo ; Pallecchi, Emiliano ; Ge, Ruijing ; Wu, Xiaohan ; Avramovic, Vanessa ; Okada, Etienne ; Lee, Jack C. ; Happy, Henri ; Akinwande, Deji ( December 2019 , IEEE IEDM)

   Non-volatile radio-frequency (RF) switches based on hexagonal boron nitride (hBN) are realized for the first time with low insertion loss (≤ 0.2 dB) and high isolation (≥ 15 dB) up to 110 GHz. Crystalline hBN enables the thinnest RF switch device with a single monolayer (~0.33 nm) as the memory layer owing to its robust layered structure. It affords ~20 dBm power handling, 10 dB higher compared to MoS 2 switches due to its wider bandgap (~6 eV). Importantly, operating frequencies cover the RF, 5G, and mm-wave bands, making this a promising low-power switch for diverse communication and connectivity front-end systems. Compared to other switch technologies based on MEMS, memristor, and phase-change memory (PCM), hBN switches offer a promising combination of non-volatility, nanosecond switching, power handling, high figure-of-merit cutoff frequency (43 THz), and heater-less ambient integration. Our pioneering work suggests that atomically-thin nanomaterials can be good device candidates for 5G and beyond.