This letter focuses on the unique capabilities that aerosol jet printing (AJP) provides for manufacturing electronics at near-THz frequencies. For the first time, we demonstrate fully aerosol jet-printed passive components above the $W$ -band. Dielectric substrates and conductors are printed on metal carriers via AJP. These components include microstrip (MS) transmission lines (TLs) and radial stubs, and utilize vialess grounded coplanar waveguide (GCPW)-to-MS TL launches. Two separate sets of components and calibration structures are realized, for two different dielectric thicknesses. For the TLs, measured from 140 to 220 GHz, the average loss varies from 0.86 to 2.6 dB/mm. The radial stub return loss, measured from 200 to 220 GHz, is closely aligned with simulations.

This letter focuses on the unique capabilities that aerosol jet printing (AJP) provides for manufacturing electronics at near-THz frequencies. For the first time, we demonstrate fully aerosol jet-printed passive components above the W-band. Dielectric substrates and conductors are printed on metal carriers via AJP. These components include microstrip (MS) transmission lines (TLs) and radial stubs, and utilize vialess grounded coplanar waveguide (GCPW)-to-MS TL launches. Two separate sets of components and calibration structures are realized, for two different dielectric thicknesses. For the TLs, measured from 140 to 220 GHz, the average loss varies from 0.86 to 2.6 dB/mm. The radial stub return loss, measured from 200 to 220 GHz, is closely aligned with simulations.

Three fully 3D printed wideband monopole antennas are presented. The antennas are elliptical monopole. The first antenna is a traditional flat monopole antenna on a dielectric substrate. The second and third antennas feature unique single and double folded dielectric substrate, which enables increase in the bandwidth. The silver conductive traces were aerosol jet printed on the conformal substrate using reactive silver ink. This ink has conductivity close to bulk silver and requires low sintering temperature of 80 °C. The antennas show wideband performance and omnidirectional radiation patterns in the azimuth plane.

Variable-emissivity materials enable "adaptive radiators" to control heat flow and regulate the temperature of spacecraft. Although most variable-emissivity engineering efforts focus on achieving the maximum emissivity contrast (a design variable), the radiator performance is ultimately determined by the resulting temperature profile of the system (the objective function). Here, these temperatures are used to define, evaluate, and optimize the variable-emissivity design space for adaptive radiators that produce desired temperature profiles under prescribed dynamic heat loads. Rather than iterating toward the asymptotic emissivity targets of zero and unity, many quasi-steady and transient systems can achieve optimized thermal control under more relaxed emissivity targets that simplify the radiator design. Examples of thermochromic radiators in dynamic operational environments are considered, where the temperature dependence of the total, hemispherical emissivity is derived from both spectrally engineered metasurfaces and phase-change materials. This reimagination of adaptive radiators shifts the design and optimization of variable-emissivity materials away from simple emissivity extrema and toward system-tailored thermal performance.

Printed radio frequency (RF) electronic components are often prohibitively lossy due to the materials challenges involved in additively manufacturing metals and dielectrics. We use aerosol jet printing of reactive silver inks to fabricate microstrip transmission lines onto commercial RF boards and subsequently extract the insertion loss of the printed silver through bisect de-embedding of the transmission lines. We directly compare the performance of our printed silver microstrips to conventional copper-clad microstrips to benchmark the efficacy of additive manufacturing against traditional processing methods. With an insertion loss nearing that of conventional copper, reactive silver ink printed traces offer dense continuous metals that can reliably act as conductors for RF applications. In addition to the morphological effects on loss from the printed metal itself, we also observe that the effect of substrate surface texture contributes to unexpected loss that may be mitigated by smoothing the surface or aligning the print direction to minimize these effects. Metallizing passive RF components using reactive inks offers a practical approach which will allow RF designers to take advantage of three-dimensional space. This is possible without sacrificing the necessary high conductivity and low loss needed to produce high performance devices for use within aerospace and communications.

Additive manufacturing enables the production of high performance radio frequency device components, but most printable materials are plagued by large losses that render them impractical for robust performance applications beyond rapid prototyping. Here, we demonstrate a set of fully three-dimensional (3D) printed band-stop filters fabricated by printing reactive silver ink onto three different additively manufactured resin substrates with varying dielectric properties. Each of the dielectric substrates were fabricated using stereolithography or digital light processing printing methods. By switching from a dielectric with tan δ = 0.06 to one with tan δ = 0.0073, we can decrease the total loss present in the structure by up to 2 dB. As enabled by 3D additive manufacturing, we also show that regardless of the dielectric material, moving from two-dimensional planar patterns to fully-3D topographies allows us to simultaneously widen the filter stopband by 2 GHz and theoretically increase signal rejection by up to 30 dB. This demonstration of a fully additively-manufactured, 3D band-stop filter that closely matches simulations represents a new class of device construction that was previously inaccessible using only 2- and 2.5-D manufacturing techniques.

In this work, two 3D printed wideband monopole antennas are presented. The antennas are an elliptical monopole. First one is printed on Kapton and the second one is on 3D printed dielectric substrate. The silver conductive traces are printed using a reactive ink with conductivity close to bulk silver. Both antennas show ultra wideband performance and omnidirectional radiation patterns.

Previous efforts to directly write conductive metals have been narrowly focused on nanoparticle ink suspensions that require aggressive sintering (>200 °C) and result in low-density, small-grained agglomerates with electrical conductivities <25% of bulk metal. Here, we demonstrate aerosol jet printing of a reactive ink solution and characterize high-density (93%) printed silver traces having near-bulk conductivity and grain sizes greater than the electron mean free path, while only requiring a low-temperature (80 °C) treatment. We have developed a predictive electronic transport model which correlates the microstructure to the measured conductivity and identifies a strategy to approach the practical conductivity limit for printed metals. Our analysis of how grain boundaries and tortuosity contribute to electrical resistivity provides insight into the basic materials science that governs how an ink formulator or process developer might approach improving the conductivity. Transmission line measurements validate that electrical properties are preserved up to 20 GHz, which demonstrates the utility of this technique for printed RF components. This work reveals a new method of producing robust printed electronics that retain the advantages of rapid prototyping and three-dimensional fabrication while achieving the performance necessary for success within the aerospace and communications industries.

In this work, we study the high critical breakdown field in beta-Ga2O3 perpendicular to its (100) crystal plane using a beta-Ga2O3/graphene vertical heterostructure. Measurements indicate a record breakdown field of 5.2 MV/cm perpendicular to the (100) plane that is significantly larger than the previously reported values on lateral beta-Ga2O3 field-effect-transistors (FETs). This result is compared with the critical field typically measured within the (100) crystal plane, and the observed anisotropy is explained through a combined theoretical and experimental analysis. Published by AIP Publishing.

Herein we report the wafer-scale synthesis of thin-film black arsenic-phosphorus (b-AsP) alloys via two-step solid-source molecular beam deposition (MBD) and subsequent hermetic thermal annealing. We characterize our thin films with a variety of compositional and structural metrology techniques. X-ray photoelectron spectroscopy and energy dispersive spectroscopy determine compositions of As0.78P0.22 for our thin films, while X-ray reflectivity measurements indicate film thicknesses of 6-9 nm. High-resolution transmission electron spectroscopy images reveal a nanocrystalline morphology with orthorhombic b-AsP grains on the order of nm. Raman scattering spectroscopy is employed to characterize the vibrational spectra of our thin films, and the results obtained are in agreement with previously reported b-AsP spectra. Evidence of uniform wafer-scale growth is substantiated by Raman mapping. We simulate crystal structure, band gaps, and Raman spectra from first principles DFT-based computations and find excellent agreement with our experimental results. This work is the first demonstration of on-wafer synthesis of b-AsP. Our large-area growth technique enables the development of next-generation b-AsP devices for optoelectronic, digital, and radio frequency (RF) applications.

Printing methods such as additive manufacturing (AM) and direct writing (DW) for radio frequency (RF) components including antennas, filters, transmission lines, and interconnects have recently garnered much attention due to the ease of use, efficiency, and low-cost benefits of the AM/DW tools readily available. The quality and performance of these printed components often do not align with their simulated counterparts due to losses associated with the base materials, surface roughness, and print resolution. These drawbacks preclude the community from realizing printed low loss RF components comparable to those fabricated with traditional subtractive manufacturing techniques. This review discusses the challenges facing low loss RF components, which has mostly been material limited by the robustness of the metal and the availability of AM-compatible dielectrics. We summarize the effective printing methods, review ink formulation, and the postprint processing steps necessary for targeted RF properties. We then detail the structure-property relationships critical to obtaining enhanced conductivities necessary for printed RF passive components. Finally, we give examples of demonstrations for various types of printed RF components and provide an outlook on future areas of research that will require multidisciplinary teams from chemists to RF system designers to fully realize the potential for printed RF components.

In this effort, a full-3D design of a complementary right/left-handed (CRLH) transmission line structure with a transition frequency of 7.5GHz, which takes advantage of the unique capabilities of additive manufacturing technologies (AMT) is presented. A fully-additive fabrication process, combining SLA dielectric and aerosol conductor printing, is utilized. The fabricated CRLH structure is shown and measured. The approaches reported in this effort may set the foundation for the emergence of novel exotic metamaterial structures, enabled by the unique manufacturing capabilities of AMTs.

Additive manufacturing (AM), also known as 3D printing, is a term that includes a wide range of processes to create 3D objects using layer-by-layer deposition techniques. In addition to their well-known advantages for prototyping and customization, 3D printing technologies have the potential to provide unique capabilities that were previously inexistent or otherwise prohibitively costly or complex. In this unexplored landscape of possibility, the emerging ability to fully 3D print RF or mm-wave components and systems is particularly exciting. Indeed, most such devices (such as couplers or antennas) obtain their operational properties from a spatial arrangement of electrical and dielectric materials, and could therefore benefit greatly from manufacturing technologies that enhance the spatial resolution or increase the range of potential topological arrangements.

Phase change materials (PCMs) provide a high energy density for thermal storage systems but often suffer from limited power densities due to the low PCM thermal conductivity. Much like their electrochemical analogs, an ideal thermal energy storage medium combines the energy density of a thermal battery with the power density of a thermal capacitor. Here, we define the design rules and identify the performance limits for rationally-designed composites that combine an energy dense PCM with a thermally conductive material. Beginning with the Stefan-Neumann model, we establish the material design space using a Ragone framework and identify regimes where hybrid conductive-capacitive composites have thermal power densities exceeding that of copper and other high conductivity materials. We invoke the mathematical bounds on isotropic conductivity to optimize and define the theoretical limits for transient cooling using PCM composites. We then demonstrate the impact of power density on thermal transients using copper inverse opals infiltrated with paraffin wax to suppress the temperature rise in kW cm−2 hotspots by ∼10% compared to equivalent copper thin film heat spreaders. These design rules and performance limits illuminate a path toward the rational design of composite phase change materials capable of buffering extreme transient thermal loads.

Nanomaterials will play a disruptive role in next-generation thermal management for high power electronics in aerospace platforms. These high power and high frequency devices have been experiencing a paradigm shift toward designs that favor extreme integration and compaction. The reduction in form factor amplifies the intensity of the thermal loads and imposes extreme requirements on the thermal management architecture for reliable operation. In this perspective, we introduce the opportunities and challenges enabled by rationally integrating nanomaterials along the entire thermal resistance chain, beginning at the high heat flux source up to the system-level heat rejection. Using gallium nitride radio frequency devices as a case study, we employ a combination of viewpoints comprised of original research, academic literature, and industry adoption of emerging nanotechnologies being used to construct advanced thermal management architectures. We consider the benefits and challenges for nanomaterials along the entire thermal pathway from synthetic diamond and on-chip microfluidics at the heat source to vertically-aligned copper nanowires and nanoporous media along the heat rejection pathway. We then propose a vision for a materials-by-design approach to the rational engineering of complex nanostructures to achieve tunable property combinations on demand. These strategies offer a snapshot of the opportunities enabled by the rational design of nanomaterials to mitigate thermal constraints and approach the limits of performance in complex aerospace electronics.

Recently, non-volatile resistance switching or memristor (equivalently, atomristor in atomic layers) effect was discovered in transitional metal dichalcogenides (TMD) vertical devices. Owing to the monolayer-thin transport and high crystalline quality, ON-state resistances below 10 Ω are achievable, making MoS 2 atomristors suitable as energy-efficient radio-frequency (RF) switches. MoS 2 RF switches afford zero-hold voltage, hence, zero-static power dissipation, overcoming the limitation of transistor and mechanical switches. Furthermore, MoS 2 switches are fully electronic and can be integrated on arbitrary substrates unlike phase-change RF switches. High-frequency results reveal that a key figure of merit, the cutoff frequency ( f c ), is about 10 THz for sub-μm 2 switches with favorable scaling that can afford f c above 100 THz for nanoscale devices, exceeding the performance of contemporary switches that suffer from an area-invariant scaling. These results indicate a new electronic application of TMDs as non-volatile switches for communication platforms, including mobile systems, low-power internet-of-things, and THz beam steering.

Reducing the energy and power dissipation of conductive bridge random access memory (CBRAM) cells is of critical importance for their applications in future Internet of Things (IoT) device and neuromorphic computing platforms. Atomically thin CBRAMs enabled by 2-D materials are studied theoretically by using 3-D kinetic Monte Carlo simulations together with experimental characterization. The results indicate the performance potential of attoJoule energy dissipation for intrinsic filament formation and a filament size of a single atomistic chain in such a CBRAM cell. The atomically thin CBRAM cells also show qualitatively different features from conventional CBRAM cells, including complete rupture of the filament in the reset stage and comparable forming and set voltages. The scaling and variability of the CBRAM cells down to subnanometer size of the switching layer as realized in the experiment are systematically studied, which indicates performance improvement and increased relative variability as the switching layer scales down. The results establish the ultimate limits of the size and energy scaling for CBRAM cells and illustrate the unique application of 2-D materials in ultralow power memory devices.

Four-dimensional (4D) printing overcomes the traditional fabrication limitations by designing heterogeneous materials to enable the printed structures evolve over time (the fourth dimension) under external stimuli. Here, we present a simple 4D printing of self-folding structures that can be sequentially and accurately folded. When heated above their glass transition temperature prestrained polystyrene films shrink along the XY plane. In our process silver ink traces printed on the film are used to provide heat stimuli by conducting current to trigger the self-folding behavior. The parameters affecting the folding process are studied and discussed. Sequential folding and accurately controlled folding angles are achieved by using printed ink traces and angle lock design. Theoretical analyses are done to guide the design of the folding processes. Programmable structures such as a lock and a three-dimensional antenna are achieved to test the feasibility and potential applications of this method. These self-folding structures change their shapes after fabrication under controlled stimuli (electric current) and have potential applications in the fields of electronics, consumer devices, and robotics. Our design and fabrication method provides an easy way by using silver ink printed on polystyrene films to 4D print self-folding structures for electrically induced sequential folding with angular control.

Excitatory and inhibitory postsynaptic potentials are the two fundamental categories of synaptic responses underlying the diverse functionalities of the mammalian nervous system. Recent advances in neuroscience have revealed the co-release of both glutamate and GABA neurotransmitters from a single axon terminal in neurons at the ventral tegmental area that can result in the reconfiguration of the postsynaptic potentials between excitatory and inhibitory effects. The ability to mimic such features of the biological synapses in semiconductor devices, which is lacking in the conventional field effect transistor-type and memristor-type artificial synaptic devices, can enhance the functionalities and versatility of neuromorphic electronic systems in performing tasks such as image recognition, learning, and cognition. Here, we demonstrate an artificial synaptic device concept, an ambipolar junction synaptic devices, which utilizes the tunable electronic properties of the heterojunction between two layered semiconductor materials black phosphorus and tin selenide to mimic the different states of the synaptic connection and, hence, realize the dynamic reconfigurability between excitatory and inhibitory postsynaptic effects. The resulting device relies only on the electrical biases at either the presynaptic or the postsynaptic terminal to facilitate such dynamic reconfigurability. It is distinctively different from the conventional heterosynaptic device in terms of both its operational characteristics and biological equivalence. Key properties of the synapses such as potentiation and depression and spike-timing-dependent plasticity are mimicked in the device for both the excitatory and inhibitory response modes. The device offers reconfiguration properties with the potential to enable useful functionalities in hardware-based artificial neural network.

The morphology and dimension of the conductive filament formed in a memristive device are strongly influenced by the thickness of its switching medium layer. Aggressive scaling of this active layer thickness is critical toward reducing the operating current, voltage, and energy consumption in filamentary-type memristors. Previously, the thickness of this filament layer has been limited to above a few nanometers due to processing constraints, making it challenging to further suppress the on-state current and the switching voltage. Here, the formation of conductive filaments in a material medium with sub-nanometer thickness formed through the oxidation of atomically thin two-dimensional boron nitride is studied. The resulting memristive device exhibits sub-nanometer filamentary switching with sub-pA operation current and femtojoule per bit energy consumption. Furthermore, by confining the filament to the atomic scale, current switching characteristics are observed that are distinct from that in thicker medium due to the profoundly different atomic kinetics. The filament morphology in such an aggressively scaled memristive device is also theoretically explored. These ultralow energy devices are promising for realizing femtojoule and sub-femtojoule electronic computation, which can be attractive for applications in a wide range of electronics systems that desire ultralow power operation.