A new approach to 3D printed heterogeneous integration by using steep ramp structures fabricated with UV-curable Norland NEA 121 ink is presented. We demonstrate the ability to achieve ramp angles up to 60 °, steeper than previously achievable by other dielectrics. This improvement allows integrated active devices at lower packaging layers and passive components above. A package using a low-noise amplifier (LNA) on the bottom layer and a patch antenna on the upper layer, connected through 3D printed ramps, is demonstrated. This work serves as a proof of concept for a 3D integrated RF package, with the future goal of directly integrating the antenna on top of the encapsulated active die. We further advance this field by demonstrating steeper, UV-cured Norland ramps capable of 60 ° angles, which will enable true 3DHI in future designs. The demonstrated package achieved an antenna gain of 0.95 dBi, implementing a vertically integrated design.

This article presents an innovative, fully additive manufactured approach to millimeter-wave multilayer circuits. An aerosol jet printer is used to fabricate a multilayer stepped-impedance low-pass filter. By leveraging the second layer for miniaturization, we achieve a more compact design. By precisely controlling conductor separation and utilizing 3-D printing technology, we were able to optimize the width of the high- and low-impedance segments for optimal filter performance. Two filter types were successfully fabricated: a low-pass microstrip filter and a low-pass stripline filter, both with a cutoff frequency near 29 GHz and exhibiting acceptable stopband attenuation. The stripline configuration allows for a 36% decrease in the stripline waveguide conductor area while achieving a great passband insertion loss of just 0.62 dB, enabled by aerosol jet printing (AJP). The line loss of both designs was characterized using a microstrip through line and a stripline through line. Both designs demonstrated low overall loss, with the microstrip line exhibiting a loss of 0.26 dB/mm and the stripline having a loss of 0.37 dB/mm at 29 GHz. This work demonstrates a multilayer integration solution and offers an advantage in reducing the size of RF circuits such as filter banks for next-generation integrated RF front ends.

This paper presents a novel, fully additivemanufactured approach to 3D heterogeneous integration and packaging of RF chips. The proposed solution utilizes an embedded ground plane to create RF transitions using transmission lines. This technique assists with the fabrication of multi-layer structures in the future. By integrating 3D-printed ground planes into fully additive manufactured processes, more flexible impedance matching has been shown in the packaging of RF chips. Using this aforementioned method, impedance matching at higher layers has been achieved, allowing for the fabrication of more complex 3D-printed layered circuits.

An aerosol jet printed (AJP) Ku band patch antenna on top of a thick (>250 um) substrate is presented for the first time. The conductive material used is Clariant Prelect TPS 50G2. The area of the patch antenna is 5.82 x 7.16 mm(2). The material used for the substrate is Benzocyclobutene (BCB) and is approximately 300 mu m tall. The RF circuit will be excited via a CPWG to microstrip transition. The antenna had a simulated gain of 4.95 and a S-11 of -34 dB. These results show that AJP is a viable option to create RF structures on thick printed substrates.

For single crystal diamond (SCD) to gain practical use in technical applications including solid state electronics, thin (<1 μm), doped epitaxial SCD layers with very low (<1 nm) surface roughness are required. Conventional SCD chemical mechanical polishing (CMP) processes are insufficient to meet the requirements of such applications because the material removal rate (MRR) is often characterized inappropriately, and the material removal uniformity is seldom considered. In this study, chemical vapor deposition (CVD) growth of two lightly boron doped (p-) epilayers was performed on 3misoriented (100) high pressure high temperature substrates of 4.5 x 4.5 mm2 area. A subsequent 8-hour oxidative CMP process utilizing potassium permanganate and a novel self-leveling holder design decreased the average surface roughness from 3.83 nm and 1.57 nm to 0.20 nm and 0.16 nm for the two samples, respectively. MRRs were determined by evaluating five circular wear monitor structures in each sample by atomic force microscopy before and after the CMP process. The average MRRs were found to be 38.6 nm/hr and 37.3 nm/hr for the two samples. The purpose of this study is to demonstrate a CMP process suitable for polishing thin SCD epilayers to meet the needs of solid-state electronics applications.

The potential of diamond for electronic materials can be realized by creating well-controlled p- or n-type doping profiles. p-type doping is achieved by ion implantation of boron followed by high temperature annealing to relax the lattice, reduce the defects and create active dopant sites by allowing diffusion of defects in the diamond crystal. It has been found that even after this diffusion the percentage of active dopant sites after high temperature annealing are only a small fraction of the total doping. We perform first principles density functional theory calculations and estimate the migration barrier energy (MBE) for diffusion of carbon vacancies, hydrogen, boron and their complexes in diamond including the boron‑carbon vacancy complex which was recently observed and predicted as a color center for qubit realization. These defects are commonly found after ion implantation of boron in diamond. Here, we use nudged elastic band (NEB) technique to estimate the MBE for these defects and use it to predict the corresponding annealing temperature. Our calculations correctly predict the MBE for carbon vacancy as compared to the available references in literature and extend the calculation to other defects predicted in ion implanted diamond. Our objective of evaluating the MBE is to predict the diffusion processes occurring during post-implantation annealing of diamond.

Printed millimeter-wave (mmW) electronics have been of high interest in the field of communications for some time now due to the potential ability to fabricate mmW systems that utilize 3-D heterogeneous integration (3DHI) to improve performance beyond traditional systems. In this article, a method for fabricating transferable mmW structures via aerosol-jet printing (AJP) is presented. A polydimethylsiloxane (PDMS) stamp-assisted liftoff procedure is developed to separate the printed part from a rigid printing support surface and apply it to an adhesive target surface. Several microstrip (MS) line structures are demonstrated to characterize the effect of stamp transfer on the RF performance of the printed circuits. The effects of printed vias on RF probe pads and shifts in the resonant frequencies of a Beatty standard line after transfer are considered and characterized using S-parameter measurements.

Gallium antimonide (GaSb) is a III-V semiconductor of technological interest for low-power, high-mobility field-effect transistors, as well as for mid-wave infrared detectors. In such devices, GaSb interfaces with other III–V semiconductors with different lattice constants that can induce strain in the GaSb layers. Two dominant limiting factors in hot carrier relaxation are the intra-valley and the inter-valley electron–phonon (e-ph) scattering. In GaSb, these are sensitive to the Γ – L energy ordering, which depend intimately on the strain. Here, we report ab initio calculations of electronic structure, phonon dispersion, e-ph scattering and relaxation times for GaSb as a function of strain. As observed previously for other group IV and III-V semiconductors, our results show strong anisotropy, a strong contribution from LO phonons, and the need to go beyond the deformation potential scattering. For GaSb, the main finding is that a compressive strain between 0.4

Aerosol jet printing (AJP) is gaining attention in additive manufacturing research, especially in the discipline of microwave engineering. Currently, no reliable AJP method exists to fabricate resistors that are both electrically small and with a resistance compatible with waveguide impedances for use in microwave components. In this work, the commercially available Metalon JR-038 is characterized and used to fabricate a resistor that is 100 mu m long by 250 mu m wide for the first time to the best of our knowledge. This resistor was then used to fabricate a Ka-band Wilkinson power divider using only the AJP process.

This work compares the current-voltage characteristics and convergence of two technology computer aided design (TCAD) solvers, a commercial hydrodynamic transport (CHT) solver, Sentaurus by Synopsys (Version R-2020.09), and the Fermi kinetics transport (FKT) solver developed at the Air Force Research Laboratory. These solvers are used to simulate and determine the convergence properties of the large-signal response of a conventional gallium nitride (GaN) high-electron mobility transistor (HEMT) at 1 GHz using drift-diffusion transport with constant electron mobility. We show that the large signal response of the HEMT is virtually the same in CHT and FKT with minor differences in their rate of convergence. This contrasts previous work in static simulations [1] where FKT had better convergence, showing that transient simulations are more computationally robust than static ones.

Advancements in additive manufacturing techniques provide attractive options for RF systems fabrication and development, particularly with respect to heterogeneous integration of bare die components. To facilitate the inclusion of these parts, a new Aerosol-Jet Printed (AJP) die attach method utilizing a patterned combination of adhesive and conductive inks is demonstrated to improve chip leveling and CTE match with die fill materials. In this paper, a patterned combination of printed Benzocyclobutene (BCB) and silver nanoparticle inks are investigated as the primary adhesive and conductive materials respectively. Several dies are tested using this attach method, including S-parameter measurements from attenuator dies with less than 2 dB loss in the 0–20 GHz frequency range. Finally, a Ku-band transmit module where all die level components utilize the proposed attach method is demonstrated, producing more than 34 dBm output power from 13 to 17 GHz.

This work focuses on the unique capabilities that aerosol jet printing (AJP) provides for manufacturing transmit/receive RF front-end modules for microwave and mm-wave applications. We demonstrate an additively manufactured (AM) transmitter system-on-antenna (SoA) at Ku-band, with the transmitter circuit being fully AM packaged on a conventionally manufactured Vivaldi antenna. The entire package is printed on-antenna via AJP around an amplifier die using a chip-first approach. Our transmit module achieves radiated power levels of 0.4-0.66 W, higher than other Ku-band SoAs in the literature. This work shows it is possible to realize high-functional-density RF front-end modules fully via AJP, overcoming the performance bottlenecks introduced by conventional manufacturing methods and reducing prototyping cost and time.

Gallium nitride (GaN) high electron mobility transistors (HEMTs) are a critical technology for radio frequency (RF) power amplifier and low noise amplifier integrated circuits. An important aspect of GaN device engineering is accurate physics-based simulations of the transistors. Technology computer aided design (TCAD) simulations are a staple of device engineering. However, wide bandgap semiconductors like GaN pose considerable challenges for accurate TCAD simulations. This presentation will provide a detailed overview of the Air Force Research Laboratory's custom TCAD solver called Fermi kinetics transport (FKT) and its application to accurate simulations of GaN HEMTs.

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 paper contributes to fully additively manufactured packaged solutions for the integration of millimeter wave devices. We demonstrate the viability of building multiple dielectric layers to achieve interconnects with greater heights. Being able to use vertical space allows for the system to be distributed over multiple layers which allows for more compact systems in horizontal space. Encased printed transmission lines with minimal losses allows for increased compactness of future structures. Both iterations were designed for 30 GHz and in the worst case saw a loss of 0.12 dB/mm at 30 GHz. Our approach provides a flexible packaging solution for next-generation packaging technologies.

This paper presents a robust 23-32 GHz low noise amplifier (LNA) based on 180 nm gate length gallium nitride (GaN) high electron mobility transistor (HEMT) technology. This two stage LNA exhibits the highest reported power handling capability of at least 4. S9W(36.9dBm). The LNA also provides competitive noise figure (NF), gain, and an output third order intercept point (OIP3) of 1.62-2.03 dB, 9-16dB, and 23.4-30.6 dBm, respectively, across the 23-32 GHz frequency band. These results provide an excellent example of a robust GaN-based LNA which could enable next generation receiver topologies without the need for radio frequency input limiters.

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 article presents for the first time a direct connection between gate lag observed in drain current transient measurements of gallium nitride (GaN) high-electron-mobility transistors (HEMTs) and traps located in the barrier of the transistor epitaxy. Semiclassical numerical simulations are presented using the Air Force Research Laboratory’s (AFRL’s) Fermi kinetics transport (FKT) solver and are validated with drain current transient measurements. Capacitance–voltage ( ${C} - {V}$ ) and conductance–voltage ( ${G} - {V}$ ) measurements are also presented to provide further insights into the trap location used in the FKT simulations. These simulations indicate that equivalent defects located specifically at the AlGaN barrier/GaN cap interface of an AFRL GaN HEMT with a density of $7.5\times 10^{{12}}$ cm−2 and positioned 1.464 eV below the GaN cap conduction band edge were the salient traps linked to the gate-lag phenomenon. The study highlights the importance of experimentally benchmarked device simulation for trapping analysis in GaN HEMTs and may provide significant insights into device engineers for mitigating trapping effects in state-of-the-art GaN technologies.

The precision printing of high-conductivity metals is a foundational technology for the realization of additively manufactured electronics integration.For many applications, the quality of the printed metal is a result of a competition between the energetics of metal nanoparticle ink sintering and the tolerance of the active device and substrate materials to sintering conditions.In this work, a quantitative investigation of a novel pulsed-light low-temperature sintering process of silver nanoparticle ink that results in conductivity values competitive with processes requiring temperatures of 150°C or higher is presented.Experimentally determined conductivities are correlated with measured grain sizes, compositions and stoichiometries, and candidate oxide coverages.The impact of dense, uniform, and aligned grains on the observed conductivities is explored.

Raytheon Technologies teamed with Michigan State University and Teledyne Scientific present a zero-IF, mixed-signal, 32-channel millimeter-wave CMOS transceiver design developed under the DARPA/MTO MIDAS program. The architectural choices, design overview, and measured results from two generations of ASIC development are presented. As part of the MIDAS 3D T/R module, element-level digital beamforming provided by this ASIC will allow multiple simultaneous beams over a wide field of regard.