Radio Frequency Loss Research Articles

Effects of Low Boron Concentration on Electrical Properties of Commercial Trap-Rich High Resistivity SOI Substrate

Electrical properties of boron lightly doped trap-rich layers of trap-rich high resistivity silicon-on-insulator (trap-rich HR-SOI) substrates are investigated. Secondary Ion Mass Spectroscopy (SIMS) is used to measure boron distribution. Resistivity profiles are studied by means of Spreading-resistance profiling (SRP). Moreover, radio frequency (RF) performance of the trap-rich HR-SOI substrates is evaluated using coplanar waveguide (CPW) lines. It is found that RF losses and harmonic distortions keep unchanged when boron concentration of the trap-rich layer is lower than 5 × 1014 cm−3. It is suggested that the trap-rich layer can still effectively restrain the parasitic surface conductance (PSC) effect.

12-Way 100 kW Reentrant Cavity-Based Power Combiner With Doorknob Couplers

We present radio frequency (RF) and thermal characterization of a compact 12-way power combiner designed for operation at 352 MHz at a power level of 100 kW with 5% duty factor. The combiner is based on a reentrant cavity with 12 input doorknob couplers and one output coupler that is integrated with the post of the cavity and forms doorknob type geometry. We introduce convenient design formulas that allow easy identification of a suitable parameter space, which is then refined with numerical simulations. Low-power RF measurements of a prototype show 0.2% insertion loss and a relative rms amplitude imbalance between the ports of 0.1% and phase imbalance of 0.036° rms. The matching is better than −25 dB over a 3-dB bandwidth around the design frequency. We also tested the combiner up to 200 kW and found the RF loss to be comparable to that of the low-power measurement. In a long test run at 100 kW with 5% duty factor, the combiner temperature stabilized at 10° above ambient.

Printable Materials for the Realization of High Performance RF Components: Challenges and Opportunities

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.

Improvement of both bandwidth and driving voltage of polymer phase modulators using buried in-plane coupled micro-strip driving electrodes

A large performance improvement of polymer phase modulators is reported by using buried in-plane coupled microstrip (CMS) driving electrodes, instead of standard vertical Micro-Strip electrodes. The in-plane CMS driving electrodes have both low radio frequency (RF) losses and high overlap integral between optical and RF waves compared to the vertical designs. Since the optical waveguide and CMS electrodes are located in the same plane, optical injection and microwave driving access cannot be separated perpendicularly without intersection between them. A via-less transition between grounded coplanar waveguide access and CMS driving electrodes is introduced in order to provide broadband excitation of optical phase modulators and avoid the intersection of the optical core and the electrical probe. Simulation and measurement results of the benzocyclobutene polymer as a cladding material and the PMMI-CPO1 polymer as an optical core with an electro-optic coefficient of 70 pm/V demonstrate a broadband operation of 67 GHz using travelling-wave driving electrodes with a half-wave voltage of 4.5 V, while satisfying its low RF losses and high overlap integral between optical and RF waves of in-plane CMS electrodes.

Electrowetting-actuated liquid metal for RF applications

Electrowetting is well-established as a fluid manipulation technique in such areas as lab-on-a-chip, visible light optics, and displays, yet has seen far less implementation in the field of radio-frequency (RF) electronics and electromagnetics. This is primarily due to a lack of appropriate materials selection and control in these devices. Low loss RF conductive fluids such as room temperature liquid metals (i.e. Hg, EGaIn, Galinstan) are by far the leading choice of active material due to their superior electrical properties but require high actuating voltages due to their inherently high surface tensions (>400 mN m−1) which often lead to dielectric breakdown. While the toxicity of Hg encourages the pursuit of non-toxic alternatives such as gallium alloys, the native surface oxide formation often prohibits reliable device functionality. Additionally, traditional electrowetting architectures rely on lossy electrode materials which degrade RF transmission efficiencies and result in non-reversible material diffusion at the electrode/liquid metal contact. In this work, we report on approaches to utilize liquid metals in electrowetting on dielectric (EWOD) devices that resolve all of these challenges by judicious choice of novel electrode materials, dielectric fluid, and device architecture. A functional RF device, namely an electromagnetic polarizer, is demonstrated that can be activated on demand through EWOD and provides an average signal attenuation of 12.91 dB in the on state and 1.46 dB in the off state over the range of 8–9.2 GHz, with a switching speed of about 12 ms. These results can be further extended to other RF applications such as tunable antennas, transmission lines, and switchable metasurfaces.

Triarylmethyl Radical OX063d24 Oximetry: Electron Spin Relaxation at 250 MHz and RF Frequency Dependence of Relaxation and Signal-to-Noise.

The triarylmethyl radical OX063d24 is currently used for pulsed electron paramagnetic resonance oximetry at 250 MHz. Both 1/T 1 and 1/T 2 increase with increasing oxygen concentration. The dependence of 1/T 1 on probe concentration is smaller than for 1/T 2. To inform the selection of the optimum frequency for in vivo oximetry 1/T 1, 1/T 2 and signal-to-noise were measured as a function of frequency between 400 and 1000 MHz on a variable-frequency spectrometer with an adjustable-frequency cross-loop resonator. 1/T 1 and 1/T 2 decrease with increasing frequency and signal-to-noise increases with increasing frequency, which are all favourable for imaging at higher frequencies. However, depth of penetration of the radio frequency (RF) into an animal decreases with increasing frequency. Assuming that the RF loss in the animal to be studied determines the resonator Q, our results indicate that the optimum frequency for in vivo imaging will be determined by the desired depth of penetration in the tissue.

Gold nanoparticle-based sensors activated by external radio frequency fields.

A novel molecular beacon (a nanomachine) is constructed that can be actuated by a radio frequency (RF) field. The nanomachine consists of the following elements arranged in molecular beacon configuration: a gold nanoparticle that acts both as quencher for fluorescence and a localized heat source; one reporter fluorochrome, and; a piece of DNA as a hinge and recognition sequence. When the nanomachines are irradiated with a 3 GHz RF field the fluorescence signal increases due to melting of the stem of the molecular beacon. A control experiment, performed using molecular beacons synthesized by substituting the gold nanoparticle by an organic quencher, shows no increase in fluorescence signal when exposed to the RF field. It may therefore be concluded that the increased fluorescence for the gold nanoparticle-conjugated nanomachines is not due to bulk heating of the solution, but is caused by the presence of the gold nanoparticles and their interaction with the RF field; however, existing models for heating of gold nanoparticles in a RF field are unable to explain the experimental results. Due to the biocompatibility of the construct and RF treatment, the nanomachines may possibly be used inside living cells. In a separate experiment a substantial increase in the dielectric losses can be detected in a RF waveguide setup coupled to a microfluidic channel when gold nanoparticles are added to a low RF loss liquid. This work sheds some light on RF heating of gold nanoparticles, which is a subject of significant controversy in the literature.

100 GHz silicon–organic hybrid modulator

AbstractElectro-optic modulation at frequencies of 100 GHz and beyond is important for photonic-electronic signal processing at the highest speeds. To date, however, only a small number of devices exist that can operate up to this frequency. In this study, we demonstrate that this frequency range can be addressed by nanophotonic, silicon-based modulators. We exploit the ultrafast Pockels effect by using the silicon–organic hybrid (SOH) platform, which combines highly nonlinear organic molecules with silicon waveguides. Until now, the bandwidth of these devices was limited by the losses of the radiofrequency (RF) signal and the RC (resistor-capacitor) time constant of the silicon structure. The RF losses are overcome by using a device as short as 500 µm, and the RC time constant is decreased by using a highly conductive electron accumulation layer and an improved gate insulator. Using this method, we demonstrate for the first time an integrated silicon modulator with a 3dB bandwidth at an operating frequency beyond 100 GHz. Our results clearly indicate that the RC time constant is not a fundamental speed limitation of SOH devices at these frequencies. Our device has a voltage–length product of only VπL=11 V mm, which compares favorably with the best silicon-photonic modulators available today. Using cladding materials with stronger nonlinearities, the voltage–length product is expected to improve by more than an order of magnitude.

Amorphous silicon carbide nitride layer as an alternative to a disordered silicon surface to suppress RF/microwave losses

A large number of dielectric layer stacks of different combinations of SiC, SiN and SiO2 are studied with respect to their ability to suppress surface-channel currents that give radio-frequency (RF) and microwave losses in coplanar waveguides (CPWs), integrated on high-resistivity silicon (HRS) substrates. Measurements are performed of the Space Charge Layer sheet resistances (SCL-RSH) and the RF losses in CPWs. The lowest, bias-independent losses of 1.6dB/cm are achieved on thin Low-Pressure Chemical Vapor Deposition (LPCVD)-nitrated Plasma-Enhanced Chemical Vapor Deposition (PECVD) amorphous (α-) SiC layers, for which the surface currents are conducted away from the crystalline HRS into the α-SiC:N. The nitridation appears to have changed the surface of the SiC from an insulating to a highly resistive layer, where the presence of SiC:N compounds suggests a possible n-doping by nitrogen. The α-SiC/SiC:N layer is known to remain stable during high-temperature thermal treatments typically used for dopant activation as indicated previously.

Properties and Printability of Inkjet and Screen-Printed Silver Patterns for RFID Antennas

We report the modeling, and geometrical and electrical characterization, of inkjet and screen-printed patterns on different polymeric substrates for use as antennas in radio-frequency identification (RFID) applications. We compared the physical and electrical characteristics of two silver nanoparticle-based commercial inkjet-printable inks and one screen-printable silver paste, when deposited on polyimide (PI), polyethylene terephthalate (PET), and polyetherimide (PEI) substrates. First, the thickness of the inkjet-printed patterns was predicted by use of an analytical model based on printing conditions and ink composition. The predicted thickness was confirmed experimentally, and geometrical characterization of the lines was completed by measuring the root-mean-square roughness of the patterns. Second, direct-current electrical characterization was performed to identify the printing conditions yielding the lowest resistivity and sheet resistance. The minimum resistivity for the inkjet-printing method was 8.6 ± 0.8 μΩ cm, obtained by printing four stacked layers of one of the commercial inks on PEI, whereas minimum resistivity of 44 ± 7 μΩ cm and 39 ± 4 μΩ cm were obtained for a single layer of screen-printed ink on polyimide (PI) with 140 threads/cm mesh and 90 threads/cm mesh, respectively. In every case, these minimum values of resistivity were obtained for the largest tested thickness. Coplanar waveguide transmission lines were then designed and characterized to analyze the radio-frequency (RF) performance of the printed patterns; minimum transmission losses of 0.0022 ± 0.0012 dB/mm and 0.0016 ± 0.0012 dB/mm measured at 13.56 MHz, in the high-frequency (HF) band, were achieved by inkjet printing on PEI and screen printing on PI, respectively. At 868 MHz, in the ultra-high-frequency band, the minimum values of transmission loss were 0.0130 ± 0.0014 dB/mm for inkjet printing on PEI and 0.0100 ± 0.0014 dB/mm for screen printing on PI. Although the resistivity achieved is lower for inkjet printing than for screen printing, RF losses for inkjetted patterns were larger than for screen-printed patterns, because thicker layers were obtained by screen printing. Finally, several coil inductors for the HF band were also fabricated by use of both printing techniques, and were used as antennas for semi-passive smart RFID tags on plastic foil capable of measuring temperature and humidity.

Muon spin rotation studies of niobium for superconducting rf applications

In this work we investigate superconducting properties of niobium samples via application of the muon spin rotation/relaxation (muSR) technique. We employ for the first time the muSR technique to study samples that are cutout from large and small grain 1.5 GHz radio frequency (RF) single cell niobium cavities. The RF test of these cavities was accompanied by full temperature mapping to characterize the RF losses in each of the samples. Results of the muSR measurements show that standard cavity surface treatments like mild baking and buffered chemical polishing (BCP) performed on the studied samples affect their surface pinning strength. We find an interesting correlation between high field RF losses and field dependence of the sample magnetic volume fraction measured via muSR. The muSR line width observed in ZF-muSR measurements matches the behavior of Nb samples doped with minute amounts of Ta or N impurities. An upper bound for the upper critical field Hc2 of these cutouts is found.

Comparison of complex permittivities of isotonic colloids containing single‐wall carbon nanotubes of varying chirality

The application of bio-compatible, conductive nanoparticles in combination with radiofrequency (RF) irradiation to raise tissue temperatures between 40 and 60 °C for hyperthermia and ablation spurred interest in the complex permittivities of isotonic nanoparticle-based colloids. Nanoparticles with large aspect ratios and high permittivities increase the bulk permittivity of the colloid and RF losses at the macroscopic scale. The complex permittivities of isotonic colloids with and without single-wall carbon nanotubes (SWCNTs) containing either metallic, semiconducting, or mixed chiralities were measured from 20 MHz to 1 GHz at room temperature. The colloids were made with one of three different isotonic solvents: phosphate buffered saline (PBS), and Dulbecco's modified eagle medium (DMEM) with and without 0.5% weight/volume bovine serum albumin to simulate cytosol and blood, respectively. The concentration of elemental carbon from the SWCNTs in the colloids ranged from 16 to 17 mM. The permittivities were corrected for electrode polarization effects by fitting the data to the Cole-Cole relaxation model with a constant phase angle element. The presence of SWCNTs increased both the real and imaginary components of the permittivities of the colloids. For all three solvents, the direct current (DC) components of the real and imaginary permittivities were greatest for the colloids containing the mixed chirality SWCNTs, followed by the colloids with semiconducting SWCNTs, and then metallic SWCNTs.

High-performance evanescently-coupled uni-traveling-carrier photodiodes

A new evanescently-coupled uni-traveling-carrier photodiode (EC-UTC PD) based on a multimode diluted waveguide (MDW) structure is fabricated, analysed and characterized. Optical and electrical characteristics of the device are investigated. The excellent characteristics are demonstrated such as a responsivity of 0.36 A/W, a bandwidth of 11.5 GHz and a small-signal 1-dB compression current greater than 18 mA at 10 GHz. The saturation current is significantly improved compared with those of similar evanescently-coupled pin photodiodes. The radio frequency (RF) bandwidth can be further improved by eliminating RF losses induced by the cables, the probe and the bias tee between the photodiode and the spectrum analyzer.

Critical RF losses in fine particles of La 1−xAg yMnO 3+δ: Prospects for temperature-controlled hyperthermia

Temperature and frequency dependencies of the real ( χ′) and imaginary ( χ″) parts of the dynamic magnetic susceptibility were studied experimentally in fine particles of La–Ag manganites prepared by various methods. The samples under study have the Curie points in the range T C=42–48 °C, which is a medical hyperthermia range of interest. When approaching T C from below, a critical peak of χ″ was revealed, followed by a steep drop while passing to the paramagnetic phase. The experiments on the magnetic radio-frequency (RF) heating of the manganite aqueous suspensions demonstrated good autostabilization of the temperature near T C. Peculiar instability is found in the heating kinetics, caused by the observed critical behavior of the RF losses. The prospects of the La–Ag manganites as candidates for application in the temperature-controlled hyperthermia are discussed.

An wide-range tunable on-chip radio-frequency LC-tank formed with a post-CMOS-compatible MEMS fabrication technique

An on-chip-micromachined tunable LC-tank, which consists of a metal inter-digitated variable capacitor and a metal solenoid inductor, is developed for wide-range radio-frequency (RF) tuning in multi-GHz band. A low-temperature metal MEMS process is developed to on-chip fabricate the passives. The process can be used for post-CMOS-compatible integration with RF ICs. Both the varactor and the inductor are suspended with a gap from the low-resistivity silicon wafer (i.e. standard CMOS wafer) for effectively depressing RF loss. The fabricated variable capacitor part, the inductor part and the whole tunable LC resonator are sequentially tested, finally resulting in a wide resonance-frequency tuning range of 72% (between about 3.5 and 6.0GHz) under a low tuning voltage range of 0–4V, while the Q-factor ranged within 23 and 8.

Development of a diffusion bonding method for fabrication of lower hybrid current drive grills

A diffusion bonding method has been developed to fabricate a LHCD (Lower Hybrid Current Drive) grill with a large number of waveguides. The grill is composed of several thin septum plates and pairs of rods, and is constructed by diffusion bonding. This method simplifies the fabrication process and the grill can have a high mechanical strength at high temperature. A 24×4 multijunction grill, which consists of 24 waveguides and 4 waveguides in the toroidal and poloidal directions, respectively, has been successfully fabricated by this method and has demonstrated a power handling capability of up to 26 MW/m 2 on JT-60U. Moreover, the diffusion bonding method can make a grill composed of two different kinds of material: one has a high thermal conductivity for the septum plates to remove RF (Radio Frequency) losses, and the other has a low electrical conductivity for the rods to reduce eddy currents during a plasma disruption. A test module composed of Dispersion Strengthened Copper and Stainless Steel has been fabricated and has shown the practical application of diffusion bonding in the fabrication of a LHCD grill for steady-state operation.