High Voltage RF Research Articles

A Solid-State High-Voltage RF Oscillator With CLLC-Type Resonant Topology and Its Parameter Optimization

A Solid-State High-Voltage RF Oscillator With CLLC-Type Resonant Topology and Its Parameter Optimization

Arbitrary Shaped High-Voltage RF Switch

Arbitrary Shaped High-Voltage RF Switch

Programmable resonant and forced mode high-voltage RF generator for dielectric barrier discharge and quadrupole mass filter

Dielectric barrier discharge, originally called silent discharge, is the electrical discharge between two electrodes separated by an insulating dielectric barrier. A high-voltage alternating current is required to generate the discharge process. There are two major principles of operation to implement a high-voltage generator: resonant mode and forced mode. While operating in forced mode, the working frequency is forced by the user using internal electronic devices. On the other hand, in resonant mode, the operating frequency is determined by the resonant circuit, which includes the external capacitance, inductance, and resistance of the load. This work shows a flexible circuit based on a real-time digital signal processor and a full H-bridge that combines the two topologies and can be used as a controller for dielectric barrier discharge and a quadrupole mass filter with varying capacitance.

Reflected Signal-Based Feedback Control of a Helical Resonator for Continuous and Efficient Delivery of High Voltage RF to an Ion Trap

Reflected Signal-Based Feedback Control of a Helical Resonator for Continuous and Efficient Delivery of High Voltage RF to an Ion Trap

High-Voltage MOSFET-Based Stacked RF Switch With Extended Bandwidth Down to DC

State-of-art stacked MOSFET-based RF switches cannot handle DC voltages exceeding maximum ratings of individual transistors in stack. In this paper a shunt switch constructed from stacked low-voltage transistors and capable of handling high DC and AC voltages in OFF-state is demonstrated for the first time. The DC voltage handling capability is achieved by introducing a resistive gate bias network coupled to the poles of the switch. An analytical model of the bias network is presented in the paper. A hardware prototype of the proposed device has been implemented in a dedicated 65 nm RF-switch SOI-CMOS process. The measurements of a 20-stack switch demonstrated peak RF and DC voltage handling of 20 V with the potential for further improvement and state-of-art linearity.

A New Phased-Array Magnetic Resonance Imaging Receive-Only Coil for HBO2 Studies.

The paper describes a new magnetic resonance imaging (MRI) phased-array receive-only (Rx) coil for studying decompression sickness and disorders of hyperbaricity, including nitrogen narcosis. Functional magnetic resonance imaging (fMRI) is noninvasive, is considered safe, and may allow studying the brain under hyperbaric conditions. All of the risks associated with simultaneous MRI and HBO2 therapy are described in detail, along with all of the mitigation strategies and regulatory testing. One of the most significant risks for this type of study is a fire in the hyperbaric chamber caused by the sparking of the MRI coils as a result of high-voltage RF arcs. RF pulses at 128 MHz elicit signals from human tissues, and RF sparking occurs commonly and is considered safe in normobaric conditions. We describe how we built a coil for HBO2-MRI studies by modifying an eight-channel phased-array MRI coil with all of the mitigation strategies discussed. The coil was fabricated and tested with a unique testing platform that simulated the worst-case RF field of a three-Tesla MRI in a Hyperlite hyperbaric chamber at 3 atm pressure. The coil was also tested in normobaric conditions for image quality in a 3 T scanner in volunteers and SNR measurement in phantoms. Further studies are necessary to characterize the coil safety in HBO2/MRI.

The DC Performance and RF Characteristics of GaN-Based HEMTs Improvement Using Graded AlGaN Back Barrier and Fe/C Co-Doped Buffer

In this article, the impact of the graded AlGaN back barrier and Fe\C co-doping buffer structure on the AlGaN <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$/$ </tex-math></inline-formula> GaN high electron mobility transistors (HEMTs) is proposed and systematically investigated. Due to effective suppression of Fe tail in unintentionally doped GaN (uid-GaN) layer by the insertion of the thick graded AlGaN back barrier layer, a large maximum drain current density and a transconductance peak are achieved. Meanwhile, the breakdown voltage is significantly improved by the use of Fe\C co-doping GaN buffer design. More importantly, it is revealed that the graded-AlGaN design can reduce the range and intensity of the electrical potential distribution in uid-GaN layer and then effectively suppress the acceptor-induced trapping\detrapping effect under high drain voltage. The RF small-signal performance of Fe-doped GaN (GaN:Fe)\C co-doping buffer HEMT exhibits significant improvement. In addition, load-pull measurement at 8 GHz revealed that a saturation power increases from 38.04 to 41.07 dB, a power gain increases from 9.06 to 10.58 dB, and an associate power-added-efficiency (PAE) increased from 40.27% to 50.18%. Our proposed GaN-based epitaxial structure can not only suppress the gate lag by reduce AlGaN surface electric field, but it can also suppress the drain lag by reduce the amplitude and range of potential distribution. It indicates that our proposed device has great potential for future high-voltage RF power amplifier application.

Design and Fabrication of a Ka Band RF MEMS Switch with High Capacitance Ratio and Low Actuation Voltage.

In this paper a high capacitance ratio and low actuation voltage RF MEMS switch is designed and fabricated for Ka band RF front-ends application. The metal-insulator-metal (MIM) capacitors is employed on a signal line to improve the capacitance ratio, which will not degrade the switch reliability. To reduce the actuation voltage, a low spring constant bending folding beam and bilateral drop-down electrodes are designed in the MEMS switch. The paper analyzes the switch pull-in model and deduces the elastic coefficient calculation equation, which is consistent with the simulation results. The measured results indicated that, for the proposed MEMS switch with a gap of 2 μm, the insertion loss is better than −0.5 dB and the isolation is more than −20 dB from 25 to 35 GHz with an actuation voltage of 15.8 V. From the fitted results, the up-state capacitance is 6.5 fF, down-state capacitance is 4.3 pF, and capacitance ratios is 162. Compared with traditional MEMS capacitive switches with dielectric material Si3N4, the proposed MEMS switch exhibits high on/off capacitance ratios of 162 and low actuation voltage.

Electromagnetic Simulations and Measurements of the K-800 Superconducting Cyclotron RF Cavity at INFN-LNS

In this paper, a complete three-dimensional (3D) RF model of the cyclotron coaxial resonator—including the coaxial sliding shorts, the “Liner” vacuum chamber, the coupler, the trimmer, and the high RF voltage “Dee” structures—has been developed. An eigenmode analysis was used to simulate the tuning of the resonator in the operating frequency range of 15–48 MHz obtained by two movable sliding shorts and a trimmer. A driven analysis has been performed in order to compute the |S11| parameter (or impedance matching) of the cavity excited by a movable coaxial power coupler. The numerical simulations have been performed using the different peculiarities of two commercial tools, COMSOL Multiphysics and CST microwave studio. Experimental validation of the developed model is presented. The evidence of an unwanted electric field component, orthogonal to the accelerating field, was discovered and a mitigation is also proposed. The impact of the proposed modification was evaluated by using a 3D beam dynamics code under development in the framework of the Superconducting Cyclotron upgrade ongoing at INFN-LNS.

Penta-Band Inverted-F Antenna Tuned by High-Voltage Switchable RF Capacitors

A penta-band inverted-F antenna (IFA) tuned by two high-voltage aperture tuning networks is presented in the paper. The design is based on a singe, non-bended radiating arm IFA. Each of the two aperture tuners comprises a high-voltage switchable RF capacitor IC in parallel with an off-chip inductor. The antenna can be tuned to any of the 5 bands of sub-4 GHz cellular spectrum between 690 MHz and 3800 MHz with return loss exceeding 6 dB at the feed over more that 95% of the total frequency range. A systematic design and analysis of the penta-band IFA based on transmission line model is provided, tuning approach for carrier aggregation enablement over two bands at a time is discussed. A nonlinear performance of the designed antenna with RF capacitors fabricated in bulk-CMOS RF-switch technology is demonstrated.

Toward high voltage radio frequency devices in β-Ga2O3

The path to achieving integrated RF and power conversion circuitry using the β-Ga2O3 material system is described with regard to the materials high Johnson's RF figure of merit. Recent results, including large signal data at VD = 50 V, are provided, showing progress in achieving high-voltage RF operation. Additionally, progress in achieving high-gain devices through gate length scaling is also benchmarked by a record RF power device with a gate length of 0.5 μm achieving a 2.1 GHz μm fT−LG product. These results are compared with state-of-the-art RF devices, and the expectations for β-Ga2O3 at this point in its maturity throughout this Letter with future milestones laid out to measure progress. The conclusion includes near- and long-term projections for β-Ga2O3 devices for RF based on the results and projected milestones presented.

Research on VRM in RF PA System Based on Enhancement Mode GaN HEMT

As a key part of the RF PA system, VRM (Voltage-Regulate-Modulator), whose main role is to offer pulse voltage for RF power transistor, is often slighted. As a result, VRM has been a restraining factor now. In order to realize the needs of high speed and high frequency, a new method based on enhancement mode GaN HEMT of designing VRM is proposed in this paper. By using this method, the rise time and fall time of VRM could be as about 10ns with the peak voltage 75V and the peak current 150A, which is quite suitable for driving high voltage and high power GaN-based RF power transistor.

Analysis and design of a novel high capacitance ratio and low actuation voltage RF MEMS switch

Analysis and design of a novel high on/off capacitance ratio and low actuation voltage radio frequency microelectro-mechanical systems (RF MEMS) switch. Circuit topology and electrode topology of RF MEMS switches are analyzed. In order to decrease actuation voltage, the switch, using coplanar waveguide transmission line for signal transmission, are designed with special elastic supported structures and actuation electrode are located on both sides of signal line. Metal–insulator–metal (MIM) fixed capacitors are used to change the up/down-state capacitance without adding more loss to the switches. Through the finite element method to determine the spring constant and the necessary applied voltage, the simulation voltage is 4.5 V. The RF performance are obtained by simulating results in the HFSS tool. The switch exhibits the insertion loss of – 0.2 dB, and isolation of – 20 dB within the range of 10–30 GHz, and the isolation extreme value reaches − 41 dB at resonant frequency, the return loss is less than − 12 dB at the resonant frequency. From the fitted results, the on/off capacitance ratio is 162 for the MEMS switch. Compared with traditional MEMS capacitive switches, the proposed MEMS switch exhibit high on/off capacitance ratios and low actuation voltage.

(Keynote) Fully-Depleted SOI Technology for High-Power RF Applications

FDSOI has shown its benefits, compared to other planar bulk technologies, in low power applications by a better electrostatic control, a reduction in leakage currents and device variability. Thanks to the isolation box in the substrate and the intrinsic channel, the parasitic capacitances are also reduced significantly, including the capacitance between source and drain, and between drain and body. These features help to boost the transistors’ RF performance. The published data shows the measured fT (cut-off frequency) and fMAX (maximum oscillation frequency) of RFMOS in FDSOI processes reach 400 GHz, which is the highest among all advanced CMOS nodes. Moreover, by the process construction (gate-first vs. gate-last), the gate resistance of the transistors in FDSOI processes is smaller, which is beneficial to their RF noise performance. These benefits have been used for small-signal RF blocks in Front-end modules, e.g. LNA, VCO and mixers.In this work, the FDSOI capability for the large-signal RF blocks consisting of integrated power amplifiers (PA) is explored. In previous mobile generations (3G/4G), the base stations need to deliver the peak power more than 100 W, which is solely enabled by GaN or GaAs technologies. Their corresponding handsets also need to transmit a few Watts, which is out of the reach of CMOS-based PA. By moving to massive MIMO with a large number of antennas, the power per RF PA is reduced significantly for both base-stations and handsets in 5G network, with the PMAX per PA varying from 20 dBm to 25 dBm. Such sub-Watt power range opens the opportunities for making silicon-based RF PA, enabling a much larger scale of RF Front-end modules integration. In this paper, two key aspects to make the FDSOI process possible for high-power RF applications in 5G are presented. First, it shows the development of critical active and passive components of high-breakdown and high RF-performance. Second, the 4-port RF test structure designs and in-house characterization to explore the capability of back-bias on RF performance are discussed.Regarding the high-voltage transistors, 3.3V and 5V RF LDMOS have been designed and fabricated without any additional dedicated mask in a sub-28nm FDSOI process. The device was constructed in a non-SOI area. A record high RF-performance, with fT larger than 50 GHz for 5V LDMOS and 100 GHz for 3.3V device, has been achieved. For passive elements, 7V fringe capacitators, inductors and transformers have been developed. The fringe capacitors show their robustness at 7V, with best-in-class quality factor at both 5 GHz and 30 GHz. The matching performance of these capacitors are comparable to the best MOM capacitor mismatch performance in other modern CMOS technologies, which makes them also suitable for high-precision signal processing and filtering. Inductors and transformers have been designed in top 3 metal layers to have state-of-the-art quality factors. An excellent matching between RF measurements and EM simulations has been obtained for these passive elements. Such matching proves that the performance of the passive devices is very well predictable, enabling full design optimization for fringe capacitors and transformers / inductors.To capture the impact of back-bias on RF performance, and facilitate the RF model against silicon validation in the presence of back-bias, this paper shows a 4-port test structure design (GSGSG). The RF measurements for an RFMOS with a back-bias varying from strong reverse to forward are discussed. These results initiate various scenarios for using back-bias in RF applications, e.g. reducing the supply voltage to have the same RF performance, or extending the maximum current density at the same peak fT to have enough RF power.In summary, this paper shows the development of high-voltage RF active and passive devices in a sub-28nm FDSOI process, which are required for building integrated RF power amplifiers at Watt-level in high-performance cost-effective RF front-end ICs. The 3.3V / 5V RF-LDMOS with a cutoff frequency beyond 100GHz has been achieved in silicon, which brings a breakthrough for RF PA designs, both at sub-6GHz and 28GHz. For passive devices, by combining the novel RF design with an RF-compatible metal stack and accurate EM simulation, a record high Q-factor for a 7V-fringe capacitor, a 2-way transformer and 8-shaped inductors are obtained. The developed 4-port measurement for GSGSG structures has been proven as an indispensable tool for RF-FDSOI. These results show FDSOI process can be comparable to RF-HV-centric non-CMOS processes, e.g. SiGe and GaAs, for Watt-level power RF applications.

Development of Large Diameter Semi-Insulating Gallium Oxide (Ga2O3) Substrates

Beta-phase gallium oxide ( ${{\beta }}$ -Ga2O3) is an emerging ultra-wide bandgap semiconductor targeting next generation high power switching and high voltage RF electronics. ${{\beta }}$ -Ga2O3 possesses a bandgap ( ${\text{E}}_{g}$ ) of approximately 4.9 eV and a theoretical critical field strength ( ${\text{E}}_{c}$ ) of 8 MV/cm. The breakdown field for ${{\beta }}$ -Ga2O3 is 2 - 3 times larger than that of silicon carbide (SiC) or gallium nitride (GaN). The Baliga figure of merit for ${{\beta }}$ -Ga2O3 is at least three times GaN and eight times SiC making it a promising low-loss power switch material. Breakdown voltages of 1.6 kV and 740 V have been achieved for ${{\beta }}$ -Ga2O3 Schottky diodes and MOSFETs respectively. Lateral device electric fields of 3.8 MV/cm have also been demonstrated. Critical to this performance realization are the availability of native ${{\beta }}$ -Ga2O3 substrates. ${{\beta }}$ -Ga2O3 single crystals are produced by crystallization from a melt utilizing high growth rate processes such as Czochralski (CZ) or Edge-defined Film-fed Growth (EFG) techniques. Through Air Force Research Laboratory support, Northrop-Grumman SYNOPTICS has successfully scaled the growth of unintentionally doped (UID), Mg-doped and Fe-doped ${{\beta }}$ -Ga2O3 crystals from self-nucleated polycrystalline grains on iridium wire to seeded (010) oriented 50-mm diameter boules. Efforts directed at establishing growth and fabrication processes will be reviewed.

Measurement of Large-Signal C OSS and C OSS Losses of Transistors Based on Nonlinear Resonance

In this letter, we present a new measurement technique to evaluate the large-signal output capacitance ( C OSS) of transistors as well as the C OSS energy dissipation ( E DISS), based on the nonlinear resonance between a known inductor and the output capacitance of the device under test. The method is simple and robust, and only requires a single voltage measurement to extract the large-signal C OSS both in charging and discharging transients. By changing the circuit parameters, it is possible to tune the resonance frequency (even above 40 MHz) and the voltage swing (even above 1 kV) with d v /d t exceeding 100 V/ns, even though the method relies only on a low-voltage dc source, without the need for high-voltage RF amplifiers. The single-pulse operation of the method enables measuring C OSS and E DISS at very high frequency and d v /d t values without any thermal runaway. Using the proposed method, we extracted large-signal C OSS and E DISS of power transistors based on different semiconductor technologies. The obtained results were verified by Sawyer–Tower method and data reported in the literature. In particular, dv/dt-independent C OSS losses were measured in cascode GaN transistors. The precise characterization of large-signal C OSS of transistors presented in this letter is essential for the design of power converters, especially those operating at high switching frequencies.

Analysis of Deep Level and Oxide Interface Defects Using 100V HF Schottky Diodes and MOS CV for Silicon and 4H SiC HV MOSFETs, Advanced Power Electronics, and RF ASIC

AbstractIn this paper we report high voltage MOS and Schottky Diode CV techniques for silicon and SiC power devices. 4H Silicon carbide is a wide bandgap semiconductor suitable for high voltage power electronics and RF applications due to high avalanche breakdown critical electric field, and thermal conductivity. The performance of various power devices, which may include MOSFET and Static Induction Transistor (SIT), can be affected by the deep level traps in the substrate and the oxide interfacial defects. We have characterized deep level trap (High Voltage Schottky Diode HF CV) and oxide interface trap densities (High Voltage HF MOS CV), measured the device channel doping profile for both 4H SiC and silicon, gate metal workfunction, and simulated the effects on DC/AC performance.

Commissioning of the first WEST load-resilient long pulse ICRF launcher in the TITAN testbed and on WEST plasmas

Before the installation of the first ICRF launcher in WEST, dedicated RF, cold and hot leak tests have been performed in the TITAN test bed [1,2] (Bernard et al., 2011a,b). All the water circuits have been controlled in order to avoid any in-vessel leak. The impedance matching has been checked at low level (mW range) and the high RF voltage standoff has been validated at the nominal value of 27 kV peak. During the WEST C3a campaign, the commissioning of the first antenna has been successfully performed. About 0.6 MW of power has been coupled to the plasma, and the launcher’s load-resilience has been proved.

Corrosion-protection of moulded graphite conductive plastic bipolar plates in PEM electrolysis by plasma processing

Proton exchange membrane electrolysis is one of the key technologies for the implementation of renewable energy. The main advantage is the conversion of electrical energy into storable chemical energy. The objective of this work is to enhance our understanding of protective coatings for carbon-polymer composite compound materials used as bipolar plates in acidic electrolysis cells. A two-step plasma process was developed to deposit a corrosion protection. As a first step, the composite compound surface was roughened by applying RF high voltage and using it as a powered electrode. As a second step, titanium coatings were deposited by pulsed DC magnetron sputtering. The plasma process was monitored by in-situ temperature measurements. The corrosion resistance of the coated compound surface was evaluated by cyclic voltammetry and chronoamperometry at 2 V vs. SHE as well as light microscopy. Furthermore, we analysed the activation effect by SEM; the titanium coatings were analysed by the van-der-Pauw method and SEM.

Experimental investigation of mode transitions in asymmetric capacitively coupled radio-frequency Ne and CF4 plasmas

The dependence of the electron density and the emission intensity on external parameters during the transitions of the electron power absorption mode is experimentally studied in asymmetric electropositive (neon) and electronegative (CF4) capacitively coupled radio-frequency plasmas. The spatio-temporal distribution of the emission intensity is measured with phase resolved optical emission spectroscopy and the electron density at the discharge center is measured by utilizing a floating hairpin probe. In neon discharge, the emission intensity increases almost linearly with the rf voltage at all driving frequencies covered here, while the variation of the electron density with the rf voltage behaves differently at different driving frequencies. In particular, the electron density increases linearly with the rf voltage at high driving frequencies, while at low driving frequencies the electron density increases slowly at the low-voltage side and, however, grows rapidly, when the rf voltage is higher than a certain value, indicating a transition from α to γ mode. The rf voltage, at which the mode transition occurs, increases with the decrease of the driving frequency/the working pressure. By contrast, in CF4 discharge, three different electron power absorption modes can be observed and the electron density and emission intensity do not exhibit a simple dependence on the rf voltage. In particular, the electron density exhibits a minimum at a certain rf voltage when the electron power absorption mode is switching from drift-ambipolar to the α/γ mode. A minimum can also be found in the emission intensity at a higher rf voltage when a discharge is switching into the γ mode.