High RF Research Articles

Evaluation of Viral Inactivation on Dry Surface by High Peak Power Microwave (HPPM) Exposure.

Previous research has shown that virus infectivity can be dramatically reduced by radio frequency exposure in the gigahertz (GHz) frequency range. Given the worldwide SARS-CoV-2 pandemic, which has caused over 1 million deaths and has had a profound global economic impact, there is a need for a noninvasive technology that can reduce the transmission of virus among humans. RF is a potential wide area-of-effect viral decontamination technology that could be used in hospital rooms where patients are expelling virus, in grocery and convenience stores where local populations mix, and in first responder settings where rapid medical response spans many potentially infected locations within hours. In this study, we used bovine coronavirus (BCoV) as a surrogate of SARS-CoV-2 and exposed it to high peak power microwave (HPPM) pulses at four narrowband frequencies: 2.8, 5.6, 8.5, and 9.3 GHz. Exposures consisted of 2 µs pulses delivered at 500 Hz, with pulse counts varied by decades between 1 and 10,000. The peak field intensities (i.e. the instantaneous power density of each pulse) ranged between 0.6 and 6.5 MW/m2 , depending on the microwave frequency. The HPPM exposures were delivered to plastic coverslips containing BCoV dried on the surface. Hemagglutination (HA) and cytopathic effect analyses were performed 6 days after inoculation of host cells to assess viral infectivity. No change in viral infectivity was seen with increasing dose (pulse number) across the tested frequencies. Under all conditions tested, exposure did not reduce infectivity more than 1.0 log10. For the conditions studied, high peak power pulsed RF exposures in the 2-10 GHz range appear ineffective as a virucidal approach for hard surface decontamination. © 2023 Bioelectromagnetics Society.

Multipacting study for fundamental power coupler of a superconducting cavity

The research work of Hefei Advanced Light Facility (HALF) is in progress. A 499.8 MHz superconducting cavity will be used in the HALF RF system. The preliminary RF design and thermal analysis for the fundamental power coupler (FPC) of HALF 499.8 MHz superconducting cavity have been completed. Multipacting (MP) is one of the major causes of the breakdown in many high power input couplers and RF cavities, thus, MP simulation for our FPC is necessary. In this paper, the MP simulation for the FPC was performed by using the CST. The MP performance of the FPC was studied. The formation process of the MP in the FPC was investigated and the physical mechanism of the delay of the MP establishment was analyzed. The simulation results show that MP will occur when the power level is higher than 175 kW, and the MP location is near the ceramic. Therefore, MP suppression is required in the FPC. In order to suppress the MP, the effect of the biasing DC electric voltage to MP in the FPC was analyzed in this paper. The simulation results indicates that the biasing DC electric voltage not only can suppress the MP, but also can excites new MP in the coupler. Thus, it is crucial to select the appropriate biasing DC electric voltage for the MP suppression in the coupler. The results show that the MP in the FPC can be suppressed very well by using 2 kV or 3 kV biasing DC electric voltage.

Beam optics study for a potential VHEE beam delivery system

VHEE (Very High Energy Electron) therapy can be superior to conventional radiotherapy for the treatment of deep seated tumours, whilst not necessarily requiring the space and cost of proton or heavy ion facilities. Developments in high gradient RF technology have allowed electrons to be accelerated to VHEE energies in a compact space, meaning that treatment could be possible with a shorter linac. A crucial component of VHEE treatment is the transfer of the beam from accelerator to patient. This is required to magnify the beam to cover the transverse extent of the tumour, whilst ensuring a uniform beam distribution. Two principle methodologies for the design of a compact transfer line are presented. The first of these is based upon a quadrupole lattice and optical magnification of beam size. A minimisation algorithm is used to enforce certain criteria on the beam distribution at the patient, defining the lattice through an automated routine. Separately, a dual scattering-foil based system is also presented, which uses similar algorithms for the optimisation of the foil geometry in order to achieve the desired beam shape at the patient location.

Rhizosphere Effect and Bacterial Community Structure in Horizons of Podzolic Soil under Spruce Plants (<i>Picea abies</i> L.)

The relationships between the rhizosphere effects, allocation in soil horizons and bacterial community structure in the rhizosphere and the bulk soil of Retisol under spruce trees (Tver region, Russia) were studied. The rhizosphere factors (Rf) expressed as ratios of soil characteristics in the rhizosphere to that in the bulk soil were determined for the basic indices of microbial respiration, biomass and available nutrients pools in the top AEL (3–15 cm) and deep EL horizons (15–46 cm). The most prominent rhizosphere effects (Rf 1.6) were revealed for microbial biomass C, basal respiration, and SOM turnover rate. Rf value for the SOM turnover rate in humus AEL horizon was approximately 1.5, while in the EL horizon it reached 6. The Rhizosphere had higher microbial diversity, with a significant contribution of both Gram-positive and Gram-negative bacteria, including representatives of Acidobacteria, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Solibacteres and Spartobacteria. The Gram-positive orders Bacillales and Clostridiales predominated in the bulk soil, with the relative contributions of more than 80 and 50% for the AEL and EL horizons, respectively. Based on the number of microbial activity indices with high Rf values (three for the lower EL horizon and only one for the upper humus AEL horizon), the rhizosphere of the lower horizon is probably more pronounced “hot spot” of biological activity than that in the top soil layer.

High-Power and High-Speed Ge/Si Traveling-Wave Photodetector Optimized by Genetic Algorithm

We experimentally demonstrate a 4-stage and an 8-stage Ge/Si distributed traveling-wave photodetectors (TWPDs) with high RF output powers and large bandwidths. The genetic algorithm is utilized to synergistically optimize multiple relevant design parameters, including the dimension of the coplanar waveguide electrode and the aperiodic arrangement of the PD array. After the genetic algorithm optimization, the 3dB bandwidth of the 4-stage TWPD is improved from 46 GHz to 54 GHz under the constraint that the bandwidth of the unterminated single PD element is 50 GHz. Meanwhile, the 3dB bandwidth of the 8-stage TWPD is improved from 33 GHz to 40 GHz. A good agreement between measured and calculated frequency responses is obtained. The measured maximum RF output powers of the aperiodic 4-stage and 8-stage TWPDs at 30 GHz are 2.5 dBm and 6.3 dBm, respectively. Furthermore, the effectiveness of our design methodology is verified by measurement results of devices fabricated at different silicon photonics foundries.

Reverse thermo-responsive biodegradable shape memory-displaying polymers

This study introduces shape memory-displaying (SM), reverse thermo-responsive (RTR) biodegradable polymers consisting of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblocks, and polycaprolactone (PCL) segments. The interplay between their composition, morphology and mechanical properties and their SM and RTR behavior was investigated as the polymers degraded. HO-(CL)n-(PEO-PPO-PEO)-(CL)n-OH pentablocks were synthesized and chain extended using hexamethylene diisocyanate (HDI), whereby a range of PFCLn polyether ester urethanes were generated.The PCL blocks formed two different crystalline phases melting at different temperatures, one acting as the net-points and the other as the switching segments.PFCLn polymers displayed remarkable SM behavior, as revealed by their high Rf and Rr values, and RTR behavior, as demonstrated by the significantly higher water uptake levels they attained below their LCST as opposed to above the transition.The polymers retained their RTR behavior as they degraded over the period investigated, while a gradual enrichment in the PCL content was observed as degradation took place. PFCLn polymers retained their excellent SM properties throughout fifteen SM full cycles conducted over two months.The dual SM/RTR functionality of the polymers developed render them especially suitable for a diversity of applications, such as in drug delivery, robotics and sensors.

Ultrafast Magic Angle Spinning Solid-State NMR Spectroscopy: Advances in Methodology and Applications.

Solid-state NMR spectroscopy is one of the most commonly used techniques to study the atomic-resolution structure and dynamics of various chemical, biological, material, and pharmaceutical systems spanning multiple forms, including crystalline, liquid crystalline, fibrous, and amorphous states. Despite the unique advantages of solid-state NMR spectroscopy, its poor spectral resolution and sensitivity have severely limited the scope of this technique. Fortunately, the recent developments in probe technology that mechanically rotate the sample fast (100 kHz and above) to obtain "solution-like" NMR spectra of solids with higher resolution and sensitivity have opened numerous avenues for the development of novel NMR techniques and their applications to study a plethora of solids including globular and membrane-associated proteins, self-assembled protein aggregates such as amyloid fibers, RNA, viral assemblies, polymorphic pharmaceuticals, metal-organic framework, bone materials, and inorganic materials. While the ultrafast-MAS continues to be developed, the minute sample quantity and radio frequency requirements, shorter recycle delays enabling fast data acquisition, the feasibility of employing proton detection, enhancement in proton spectral resolution and polarization transfer efficiency, and high sensitivity per unit sample are some of the remarkable benefits of the ultrafast-MAS technology as demonstrated by the reported studies in the literature. Although the very low sample volume and very high RF power could be limitations for some of the systems, the advantages have spurred solid-state NMR investigation into increasingly complex biological and material systems. As ultrafast-MAS NMR techniques are increasingly used in multidisciplinary research areas, further development of instrumentation, probes, and advanced methods are pursued in parallel to overcome the limitations and challenges for widespread applications. This review article is focused on providing timely comprehensive coverage of the major developments on instrumentation, theory, techniques, applications, limitations, and future scope of ultrafast-MAS technology.

Unshielded portable optically pumped magnetometer for the remote detection of conductive objects using eddy current measurements.

Electrically conductive objects can be detected using the principle of electromagnetic induction, where a primary oscillating magnetic field induces eddy currents in the object, which in turn produce a secondary magnetic field that can be measured with a magnetometer. We have developed a portable radio-frequency optically pumped magnetometer (RF OPM) working in unshielded conditions with sub-pT/Hz magnetic field sensitivity when used for the detection of small oscillating magnetic fields, setting a new benchmark for the sensitivity of a portable RF OPM in unshielded conditions. Using this OPM, we have detected the induced magnetic field from aluminum disks with diameters as small as 1.5cm and with the disks being ∼25 cm from both the excitation coil and the magnetometer. When used for eddy current detection, our magnetometer achieves a sensitivity of a 2-6 pT/Hz. We have also detected a moving aluminum disk using our RF OPM and analyzed the magnetometer signals, which depend on the position of the disk, illustrating the potential of high sensitivity RF OPMs for remote sensing applications.

Exploring the efficacy of implementing field plate design with air gap on β-Ga2O3 MOSFET for high power & RF applications

In the present work, source field plate design with an air gap has been studied on lateral β – Ga2O3 MOSFET with the objective of achieving improvement in high power as well as RF performance by employing exhaustive TCAD simulations. A comprehensive investigation of various analog Figure of Merits (FoMs) and RF Figure of merits (FoMs) have been carried out and a thorough comparison has been drawn between the proposed device β-Ga2O3 MOSFET with source field plate and air gap, the β-Ga2O3 MOSFET with gate field plate and the conventional β-Ga2O3 MOSFET. It can be noted that the proposed design yields significantly higher breakdown voltage and Power Figure of Merit (PFoM) as compared to gate field plate design and conventional device without any of these designs and also, the proposed design demonstrates improvement in RF performance as compared to gate field plate design.

A Crystal-Less Clock Generation Technique for Battery-Free Wireless Systems

The size of wireless systems is required to be reduced in many applications, such as ultra-low-power sensor nodes and wearable/implantable devices, where battery and crystal are the two main bottlenecks in system miniaturization. In recent years, battery-free radios based on wireless power transfer (WPT) have shown great potential in miniature wireless systems, while a reliable on-chip clock without a crystal remains a design challenge. Conventional methods utilized the RF WPT tone as the reference for clock generation, but the high RF frequency leads to high power consumption. In comparison, using a lower WPT frequency results in an antenna with a larger size. In this work, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2^{\mathrm{nd}}$ </tex-math></inline-formula> -order inter-modulation (IM2) component of the two RF WPT tones is extracted to lock an on-chip oscillator, providing a low-jitter PVT-robust clock. In this way, the wireless systems can benefit from: 1) The clock recovery circuits operate at a low IM2 frequency, reducing the power consumption. 2) The WPT can be set to a high RF frequency to minimize the antenna. Fabricated in 65 nm CMOS process, the proposed crystal-less clock generator takes a small area of 0.023 mm2 in a wireless system chip. Measured results show −92 dBc/Hz@10 kHz phase noise and 6.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> power.

Developing high performance RF heating scenarios on the WEST tokamak

High power experiments, up to 9.2 MW with LHCD and ICRH, have been carried out in the full tungsten tokamak WEST. Quasi non inductive discharges have been achieved allowing to extend the plasma duration to 53 s with stationary conditions in particular with respect to tungsten contamination. Transitions to H mode are observed, and H-modes lasting up to 4 s have been obtained. The increase in stored energy is weak since the power crossing the separatrix is close to the L–H threshold. Hot L mode plasmas (central temperature exceeding 3 keV) with a confinement time following the ITER L96 scaling law are routinely obtained. The weak aspect ratio dependence of this scaling law is confirmed. Tungsten accumulation is generally not an operational issue on WEST. Difficulty of burning through tungsten can prevent the discharge from accessing to a hot core plasma in the ramp-up phase, or can lead to rapid collapse of the central temperature when radiation is enhanced by a slight decrease of the temperature. Except a few pulses post-boronization, the plasma radiation is rather high (P rad/ P tot ∼ 50%) and is dominated by tungsten. This fraction does not vary as the RF power is ramped up and is quite similar in ICRH and/or LHCD heated plasmas. An estimate of the contribution of the RF antennas to the plasma contamination in tungsten is given.

Design RF Magnetic Devices With Linear and Nonlinear Equivalent Circuit Models: Demystify RF Magnetics With Equivalent Circuit Models

Magnetic materials offer a unique combination of properties for RF applications, such as nonreciprocity, high permeability, broad tunability, strong frequency dispersion, and nonlinearity <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> , <xref ref-type="bibr" rid="ref2" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[2]</xref> , <xref ref-type="bibr" rid="ref3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[3]</xref> . In contrast to a dielectric material, where a scalar permittivity constant is often sufficient to represent the property of the material, the permeability of an RF magnetic material is usually a tensor in its linear regime, which is expressed in the form of an asymmetrical matrix; yet each entry in the matrix varies as a function of frequency and biasing field. At high RF power, the magnetic material can be easily driven into a nonlinear regime, which exhibits increased dissipation, drifting of resonant frequency, generation of harmonics, and so on. At a microscale, electromagnetic waves in magnetic materials are often coupled with spin waves that are supported by exchange coupling in quantum mechanics, which adds more complexity to the understanding and applications of the material.

InP/InGaAs Uni-Traveling-Carrier Photodiode (UTC-PD) With Improved EM Field Response

In this article, a unique structure of InP/InGaAs uni-traveling-carrier photodiode (UTC-PD) is proposed. Compared with the one-sided junction photodiode, the UTC-PD has the advantages of a simpler epitaxial layer structure while maintaining the characteristics of high bandwidth and high output power loss profile. Simulated results show that a large built-in electric field can be generated under illumination, which aids UTC carrier velocity. The merits of the new structure are compared to a standard UTC-PD photodiode in terms of improved electric field and carrier concentration response. It is demonstrated that the photogeneration and light absorption of UTC-PDs are improved by incorporating a step-like internal texture of cones and dots profile in the photo absorption layer. The simulated device shows a peak electrical 3-dB bandwidth of 65 GHz at a low light intensity and reverse bias voltage. The performance characteristics of 1-D and 2-D UTC-PD simulations, including internal electric field distribution, energy band diagram, carrier concentration, and power loss distribution, are carefully studied. A theoretical discussion of the working principle and key performance characteristics of a UTC-PD enhanced by heterojunction design is reported. The entire physical environment is modeled and simulated through the finite element method (FEM) using commercial software. The proposed photodiode structure configuration is designed and optimized for photodetectors for high RF frequencies at different light intensities. To the best of our knowledge, the obtained bandwidth and electric field response is the fastest among those reported for other various higher wavelength photodiodes.

A method for extracting sole mechanical properties of Bragg reflector by GHz ultrasonic pulse-echo technique

Solidly mounted resonators (SMRs) with an acoustic Bragg reflector should be more suitable for high power RF filters than a self-standing structure because heat can be transferred to the supporting substrate. Thus, even though the demand for SMRs is expected to increase, the evaluation of the properties of the Bragg reflector that comprise them cannot be separated from the properties of the resonator as a whole. A method to evaluate the mechanical reflection coefficient of the Bragg reflector alone before the piezoelectric layer is grown would, therefore, be attractive, as it would be useful in optimizing the Bragg reflector. In this study, a nondestructive evaluation method of the reflector using a GHz ultrasonic pulse-echo technique is proposed. The Sc0.40Al0.60N film ultrasonic transducers with electromechanical coupling coefficient kt2 of 15.8% and longitudinal wave insertion loss of 7.0 dB with 77% fractional bandwidth were employed for the measurement system. Mo/SiO2 Bragg reflector test samples with various number of pairs were evaluated. The experimental mechanical reflectance of the Bragg reflector agreed well with theoretical results simulated by a mechanical equivalent circuit model.

Silicon nanocrystal synthesis with the atmospheric plasma source HelixJet

AbstractThe HelixJet, a plasma source operating under atmospheric pressure with RF power, was used for the synthesis of silicon nanoparticles (Si‐NPs) in the context of relevance in nanomedicine, sensor technology, and nanotechnology. The HelixJet was operated with a variety of He/Ar/H2/SiH4 gas mixtures to characterize the Si‐NPs in regard to their size, crystallinity, structure, and photoluminescence. Distinct varieties of nanomaterials in the size range from 3 nm to over 100 nm were synthesized depending on the operation parameters of the HelixJet. Admixture of H2 alongside high RF powers led to the formation of crystalline nanoparticles with a strong photoluminescence intensity, where the photoluminescence properties as well as the nanocrystal synthesis yield were tunable by adjustment of the synthesis parameters. Post‐synthesis in‐flight annealing allowed the formation of large crystalline nanoparticles. In addition, the experiments conducted in this study resulted in a design improvement of the HelixJet plasma source that extends the stability of the operating range. Furthermore, the added spatial separation of the He/H2 and He/Ar/SiH4 streams (SiH4 injection on‐axis) minimizes material deposition within the HelixJet and enables continuous long‐term operation.

Hairpin RF resonators for MR imaging transceiver arrays with high inter-channel isolation and B1 efficiency at ultrahigh field 7 T

Electromagnetic decoupling among a close-fitting or high-density transceiver RF array elements is required to maintain the integrity of the magnetic flux density from individual channel for enhanced performance in detection sensitivity and parallel imaging. High-impedance RF coils have demonstrated to be a prominent design method to circumvent these coupling issues. Yet, inherent characteristics of these coils have ramification on the B1 field efficiency and SNR. In this work, we propose a hairpin high impedance RF resonator design for highly decoupled multichannel transceiver arrays at ultrahigh magnetic fields. Due to the high impedance property of the hairpin resonators, the proposed transceiver array can provide high decoupling performance without using any dedicated decoupling circuit among the resonant elements. Because of elimination of lumped inductors in the resonator circuit, higher B1 field efficiency in imaging subjects can be expected. In order to validate the feasibility of the proposed hairpin RF coils, systematical studies on decoupling performance, field distribution, and SNR are performed, and the results are compared with those obtained from existing high-impedance RF coil, e.g., “self-decoupled RF coil”. To further investigate its performance, an 8-channel head coil array using the proposed hairpin resonators loaded with a cylindrical phantom is designed, demonstrating a 19 % increase of the B1+ field intensity compared to the self-decoupled coils at 7 T. Furthermore, the characteristics of the hairpin RF coils are evaluated using a more realistic human head voxel model numerically. The proposed hairpin RF coil provides excellent decoupling performance and superior RF magnetic field efficiency compared to the “self-decoupled” high impedance coils. Bench test of a pair of fabricated hairpin coils prove to be in good accordance with numerical results.

High Rejection and Frequency Agile Optical Filtering of RF Signals Using a Rare Earth Ion-Doped Crystal

While photonics is broadly considered as a leading solution for analog RF processing, photonic RF filters often show a limited out-of-band rejection. In this work we demonstrate a high rejection and high steepness photonic RF bandpass filter based on spectral hole burning in a rare earth ion-doped crystal. The filter is obtained by programming a frequency-selective absorption grating in the crystal. With an experimental and theoretical study we identify the optimal parameters for this filter. We achieve a remarkable rejection of 60 dB and a rejection of 45 dB at 50 MHz from the edge of the filter, compliant with most demanding applications.

An Experimental Study and a Numerical Modelling of Microdroplets Charged in a Helium Atmospheric Pressure Plasma Jet

A droplet passing through a low temperature plasma acquires a net negative charge, Q, and the droplet floating potential increases negatively until positive and negative charge fluxes are balanced. Subsequently electrons arrive at the droplet with a very low net electron energy. Low energy electrons (LEE) may play an important role in for example water chemistry, DNA damage (e.g. in radiotherapy) and electron-initiated nanomaterials synthesis [1]. However obtaining true LEE (< 5 eV) sources compatible with liquid water has not been possible to date. In a previous study, we have shown extremely fast and enhanced metal salt reactions within droplets and it is thought LEE reactions from charge on the droplets was the major contributor, in comparison to radiolysis and electron-beam studies [2]. Charging models of collisional high pressure plasmas have received little experimental validation, especially for particles in the size range (microns) where droplets can survive the plasma-induced evaporation. Measuring the small charge on fast moving droplets, however, in a high plasma RF noise environment presents very significant challenges. We present an experimental study of microdroplets charged in a helium atmospheric pressure plasma jet (APPJ) and, along with numerical modelling, determine the dependence of droplet charge, Q, on droplet diameter (D) and plasma conditions e.g. electron density, ne, and temperature, Te. Our measurements were carried out on aerosol droplet streams under various plasma conditions (power and flow) using a 4 mm plate collector. Without droplets, the collector assumed a mean positive potential. This is likely due to the effect of the upstream plasma potential which is estimated at ~12 V, assuming a Te of 2 eV. The background signal variation due to noise and other sources was ~250 mV. With the addition of droplets, the collector mean potential decreased due to the impact of the negative charge flux. At the maximum power, floating potential (VF) is a factor of ~100 greater at 3 mm collector distance compared to 15 mm. On the addition of droplets, the characteristics remain similar at 3 mm but at 15 mm, the potential remains positive until a much higher power. An image charge model [3] was used to obtain charge per droplet estimates from stream of droplets based on droplet rate and size distribution. High resolution imaging was used to obtain droplet statistics at the edge of the capillary. Here, the maximum droplet rate was ~ 5 x 104 s-1 [4]. The voltage – charge calibration factor, obtained from simulation, varies from 4.6 – 7.6 nV per electron, depending on velocity. The average value of charge per droplet can be obtained from the net potential obtained at different powers. The possible influence of the plasma gas flow (Q2) and liquid delivery rate (QL) on collector potential was explored and maximum charging capability was found to occur around a total gas flow of 3.5 slm and for lower QL values.

Challenges for Sige Bicmos in Advanced-Node SOI

D-band (110-170GHz) spectrum is gaining attention for various applications, including 6G mm-Wave, sub-THz sensing, and radar. These systems require lattice spacing for antenna elements at sub-1mm and a very low loss signal path from antenna to integrated chip. A highly efficient front-end in a very small form factor will be required for these systems. This drives the requirement for a monolithically integrated high-gain, high-efficiency front-end that also leverages the benefits of a high-speed / high-density digital CMOS. Silicon germanium (SiGe) heterojunction bipolar transistors (HBT) integrated along with a high-density CMOS provide such an all-silicon monolithic solution.The US government is fostering the expansion of “unique and differentiated domestic manufacturing” with funding through DARPA’s Technologies for Mixed-mode Ultra Scaled Integrated Circuits (T-MUSIC) [1] program to enable disruptive RF mixed-mode technologies by developing high performance RF analog integrated with advanced digital CMOS. Through the T-MUSIC program, DARPA seeks to: 1) advance RF and mixed-mode devices to support ultra-wideband RF frontends from HF to 100 GHz; 2) integrate those devices with high density digital CMOS electronics at the wafer scale to enable embedded digital intelligence; 3) develop and explore ultra-high resolution broadband mixed-mode circuit building blocks for DoD-relevant applications; 4) explore innovative device topologies and materials to form THz devices in an advanced digital CMOS fabrication platform; and 5) establish a domestic ecosystem that facilitates enduring DoD access to differentiated capabilities for high performance RF mixed-mode SoCs.Under T-MUSIC, GlobalFoundries is demonstrating BiCMOS on 45nm PDSOI, which is the focus of this paper, and 22nm FDSOI CMOS with goals of increasing HBT performance of fT/fMAX from 350/500 GHz to 400/600 GHz and 600/700 GHz. HBTs with fT/fMAX of 380/550GHz GHz have been demonstrated building upon previously published results [2]. This paper will touch on some of the challenges that were encountered in achieving that result and discuss those anticipated in future work.Achieving these results required scaling transistor dimensions. Vertical scaling of the emitter, base and collector layers, with higher doping concentrations, reduces transit time but results in higher current densities and higher electric fields. Lateral scaling of the transistor structure reduces parasitic capacitance and resistance but concentrate the power dissipation in a smaller area. The thermal conductivity of silicon is 148W/m-K whereas that of silicon dioxide is ~1.4W/m-K. Even a thin layer of oxide will significantly increase the self-heating of the HBT. Therefore, we replace the SOI with coplanar epitaxy in regions where the HBTs are formed.The vertical scaling of the HBT requires limiting the thermal cycles that the HBT will experience during processing and suggests forming the HBT as late as possible in the CMOS process. However, the thermal cycles associate with the epitaxy and film depositions to form the HBT impact the CMOS transistors which suggests forming the HBT early in the process. We found a point in the process that offers the best compromise minimizing the impact to the doped-channel PDSOI CMOS while achieving the HBT performance goals. Work is just beginning on integration tradeoffs for FDSOI with metal gate and high-K dielectrics.Advanced-node CMOS processes can form components having smaller dimensions which offers advantages for lateral scaling but also presents challenges for forming the HBT. The contact height in 45nm is significantly less than the height of the HBT structure used in GF’s 9HP process. We changed the formation of the emitter and base so that the emitter and base contacts are almost coplanar in contrast to 9HP where the emitter was almost twice the height of the base. This problem is being further exasperated as we migrate to 22nm.The shrinking of BEOL wiring dimensions, along with the ability of the HBT to drive high currents, presents challenges in designing within limits imposed by electromigration. The use of wider wires is constrained by metal density rules. The use of stacked metal levels and redundant vias impact the parasitic capacitances and resistances of the interconnects.The paper and presentation will review these, and other challenges encountered in achieving BiCMOS integration of SiGe HBTs with fT/fMAX of 380/550GHz GHz [see figure] on a 45nm PDSOI CMOS and touch future work.This research was developed with funding from the Defense Advanced Research Projects Agency (DARPA) and is Approved for Public Release, Distribution Unlimited. The views, opinions and/or findings expressed are those of the author and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.[1] https://www.darpa.mil/attachments/T-MUSIC_Proposers%20Day_Presentations_Combined.pdf [2] J. Pekarik et al., 2021 IEEE BCICTS, 2021, pp. 1-4, Figure 1

Explainable machine learning for breakdown prediction in high gradient rf cavities

The occurrence of vacuum arcs or radio frequency (rf) breakdowns is one of the most prevalent factors limiting the high-gradient performance of normal conducting rf cavities in particle accelerators. In this paper, we search for the existence of previously unrecognized features related to the incidence of rf breakdowns by applying a machine learning strategy to high-gradient cavity data from CERN's test stand for the Compact Linear Collider (CLIC). By interpreting the parameters of the learned models with explainable artificial intelligence (AI), we reverse-engineer physical properties for deriving fast, reliable, and simple rule-based models. Based on 6 months of historical data and dedicated experiments, our models show fractions of data with a high influence on the occurrence of breakdowns. Specifically, it is shown that the field emitted current following an initial breakdown is closely related to the probability of another breakdown occurring shortly thereafter. Results also indicate that the cavity pressure should be monitored with increased temporal resolution in future experiments, to further explore the vacuum activity associated with breakdowns.