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1. 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. 

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2. Ultra‐High Interfacial Thermal Conductance via Double hBN Encapsulation for Efficient Thermal Management of 2D Electronics

   https://doi.org/10.1002/smll.202205726  

   Ye, Fan ; Liu, Qingchang ; Xu, Baoxing ; Feng, Philip X. ‐L. ; Zhang, Xian ( February 2023 , Small)

   Heat dissipation is a major limitation of high‐performance electronics. This is especially important in emerging nanoelectronic devices consisting of ultra‐thin layers, heterostructures, and interfaces, where enhancement in thermal transport is highly desired. Here, ultra‐high interfacial thermal conductance in encapsulated van der Waals (vdW) heterostructures with single‐layer transition metal dichalcogenides MX₂(MoS₂, WSe₂, WS₂) sandwiched between two hexagonal boron nitride (hBN) layers is reported. Through Raman spectroscopic measurements of suspended and substrate‐supported hBN/MX₂/hBN heterostructures with varying laser power and temperature, the out‐of‐plane interfacial thermal conductance in the vertical stack is calibrated. The measured interfacial thermal conductance between MX₂and hBN reaches 74 ± 25 MW m⁻²K⁻¹, which is at least ten times higher than the interfacial thermal conductance of MX₂in non‐encapsulation structures. Molecular dynamics (MD) calculations verify and explain the experimental results, suggesting a full encapsulation by hBN layers is accounting for the high interfacial conductance. This ultra‐high interfacial thermal conductance is attributed to the double heat transfer pathways and the clean and tight vdW interface between two crystalline 2D materials. The findings in this study reveal new thermal transport mechanisms in hBN/MX₂/hBN structures and shed light on building novel hBN‐encapsulated nanoelectronic devices with enhanced thermal management.

    

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3. Guided Mid‐IR and Near‐IR Light within a Hybrid Hyperbolic‐Material/Silicon Waveguide Heterostructure

   https://doi.org/10.1002/adma.202004305  

   He, Mingze ; Halimi, Sami I. ; Folland, Thomas G. ; Sunku, Sai S. ; Liu, Song ; Edgar, James H. ; Basov, D. N. ; Weiss, Sharon M. ; Caldwell, Joshua D. ( February 2021 , Advanced Materials)

   Silicon waveguides have enabled large‐scale manipulation and processing of near‐infrared optical signals on chip. Yet, expanding the bandwidth of guided waves to other frequencies will further increase the functionality of silicon as a photonics platform. Frequency multiplexing by integrating additional architectures is one approach to the problem, but this is challenging to design and integrate within the existing form factor due to scaling with the free‐space wavelength. This paper demonstrates that a hexagonal boron nitride (hBN)/silicon hybrid waveguide can simultaneously enable dual‐band operation at both mid‐infrared (6.5–7.0 µm) and telecom (1.55 µm) frequencies, respectively. The device is realized via the lithography‐free transfer of hBN onto a silicon waveguide, maintaining near‐infrared operation. In addition, mid‐infrared waveguiding of the hyperbolic phonon polaritons (HPhPs) supported in hBN is induced by the index contrast between the silicon waveguide and the surrounding air underneath the hBN, thereby eliminating the need for deleterious etching of the hyperbolic medium. The behavior of HPhP waveguiding in both straight and curved trajectories is validated within an analytical waveguide theoretical framework. This exemplifies a generalizable approach based on integrating hyperbolic media with silicon photonics for realizing frequency multiplexing in on‐chip photonic systems.

    

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4. Stochastic FDTD Modeling of Propagation Loss due to Random Surface Roughness in Sidewalls of Optical Interconnects

   https://doi.org/10.23919/USNC-URSINRSM51531.2021.9336433  

   Guiana, Brian ; Zadehgol, Ata ( February 2021 , 2021 United States National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM))

   null (Ed.)

   The dielectric waveguide (WG) is an important building block of high-speed and high-bandwidth optical and opto-electronic interconnect networks that operate in the THz frequency regime. At the interface of Si/SiO 2 dielectric waveguides with width above w = 2.5 μm and anisotropic surface roughness, transverse electric (TE) mode surface wave propagation can experience a loss of approximately a = 2 dB/cm; however, propagation losses increase rapidly to near a = 44 dB/cm as the width decreases to w = 500 nm, due to increased interaction of surface waves and sidewall surface roughness that exhibits random distribution inherent to the manufacturing process. Previous works have developed analytic expressions for computing propagation loss in a single dielectric waveguide exhibiting random roughness. More recent works report a = 0.4 dB/cm noting the non-trivial estimation errors in previous theoretical formulations which relied on planar approximations, and highlight the discrepancy in planar approximations vs. the 3-D Volume Current Method. A challenge that remains in the path of designing nanoscale optical interconnects is the dearth of efficient 3-D stochastic computational electromagnetic (CEM) models for multiple tightly coupled optical dielectric waveguides that characterize propagation loss due to random surface roughness in waveguide sidewalls. Through a series of theoretical and numerical experiments developed in the method of finite-difference time-domain (FDTD), we aim to develop stochastic CEM models to quantify propagation loss and facilitate signal & power integrity modeling & simulation of arbitrary configurations of multiple tightly-coupled waveguides, and to gain further insights into loss mechanisms due to random surface roughness in optical interconnects. 

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5. FDTD Simulations Of The Impedance Of A Dipole Antenna in A Plasma

   https://doi.org/10.1109/APUSNCURSINRSM.2019.8888864  

   Spencer, E. ; Latif, S. ( July 2019 , 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting)

   The impedance of a dipole antenna in the earth’s ionospheric plasma is dependent on the ambient plasma properties such as electron density and electron neutral collision frequency. Depending on the length of the dipole, it is possible to not only measure the plasma properties, but in addition, receive plasma waves that are found propagating in the ionosphere. Here we report on some FDTD simulations of a dipole antenna in a cold plasma, and present some approximate expressions that can be used to analyze this behavior. When the dipole antenna resonant wavelength /4 and associated frequency is far from the upper hybrid, cyclotron and plasma frequencies of the local plasma, the expressions work fairly well. However, when the length of the antenna is such that it’s resonant wavelength coincides or is close to the plasma resonances, the expressions fail, and a full-wave FDTD simulation has to be performed to extract meaningful plasma data. 

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