RF Characteristics Research Articles

Design and RF Characterization of High-Power Ferrule-Loaded Folded Waveguide SWS for mm-Wave TWT

Design and analysis of ferrule-loaded folded waveguide slow wave structure is carried out for a high-power millimeter-wave traveling-wave tube (TWT). The design of the structure is carried out by numerical simulation. A typical structure has been designed and fabricated at the Ka-band, and cold test measurement is carried out for the cold circuit parameters and the results are compared against numerical analysis. To compare the efficacy of the ferrule-loaded folded waveguide structure, a conventional folded waveguide structure is also designed for the same operating bandwidth, and cold circuit parameters are compared. The comparison results shows that the interaction impedance of the ferrule-loaded folded waveguide structure is double compared with the conventional structure at the cost of reduction in cold bandwidth. Furthermore, particle-in-cell (PIC) simulation is also carried out to estimate the output power and gain for both the structures for the same operating band, and the results are compared. The comparison results show that the cross section is reduced by 22% and the overall interaction length is reduced by 50% for the ferrule-loaded FW-SWS compared with the conventional FW-SWS for the same output power of about 500 W.

Electrical properties of high permittivity epitaxial SrCaTiO3 grown on AlGaN/GaN heterostructures

Epitaxial integration of perovskite oxide materials with GaN has unlocked the potential to improve functionality and performance in high-power RF and power-switching applications. In this work, we demonstrate structural and electrical properties of high dielectric constant Sr1−xCaxTiO3 epitaxial layers grown on AlGaN/GaN/4H-SiC high-electron-mobility transistor structures with compositions ranging from x = 0 to x = 0.53 and oxide film thicknesses ranging from 7 to 126 nm. We show (111) orientation in the SrCaTiO3 (SCTO) thin films using a 1 nm (100) TiO2 buffer layer grown by RF-plasma-assisted oxide molecular beam epitaxy. Current–voltage measurements show up to 5 orders of magnitude reduced leakage with SCTO films when compared to Schottky contacted samples. Capacitance–voltage measurements show minimal hysteresis, an extracted dielectric constant (κ) as high as 290, and a fixed positive interface charge density of 2.38 × 1013 cm−2 at the SCTO/AlGaN interface. The direct integration of the SCTO layer does not significantly affect the two-dimensional electron gas (2DEG) density or the channel mobility with the 2DEG density as a function of SCTO thickness having good agreement with 1D Poisson–Schrödinger simulations. RF characterization of interdigitated capacitors using the SCTO films on unintentionally doped GaN/SiC shows that the films maintain their high κ into microwave frequencies and only exhibit a slight reduction in κ with increased lateral electric fields. These results demonstrate that the integration of a high-κ oxide with GaN can potentially improve electric field management in RF high-electron-mobility transistors and increase the device breakdown voltage without significant degradation to channel transport properties.

Soil rock fragments: Unquantified players in terrestrial carbon and nitrogen cycles

Soils with a significant proportion of rock fragments (RFs, with diameter >2 mm) are widely distributed in terrestrial ecosystems. However, a lack of quantitative information about RF characteristics restricts our ability to explain and predict the related soil carbon (C) and nitrogen (N) processes, and induces biases of C and N investigations in areas where soils contain significant RFs. In this paper, we reviewed the direct and indirect effects of RFs on soil C and N cycles, including via affecting soil C and N stocks, hydrology, temperature, and via chemical weathering that releases C, N, cations and anions, consumes CO2 and regulates pH. Based on this, we discussed current challenges and potential solutions in investigating C and N cycles of high RF content soils. First, we proposed a series of approaches to quantifying the effects of RFs on C and N stocks and soil hydrology across scales. Second, we emphasized the evolutions of soil RFs’ properties over time, and recommended including RF physicochemical properties in the routine soil inventory. Third, we suggested that both the effects of RFs and the evolutions of soil RFs over time should be considered in model simulation. Finally, we provided a framework by coupling monitoring, mapping and modelling to investigate the roles of RFs on soil C and N cycles from earth’s critical zone to global scale. This review will improve our understandings of RFs and terrestrial C and N cycles, and their responses to global change.

Monolithic Integration of Nano-Ridge Engineered InGaP/GaAs HBTs on 300 mm Si Substrate.

Nano-ridge engineering (NRE) is a novel method to monolithically integrate III–V devices on a 300 mm Si platform. In this work, NRE is applied to InGaP/GaAs heterojunction bipolar transistors (HBTs), enabling hybrid III-V/CMOS technology for RF applications. The NRE HBT stacks were grown by metal-organic vapor-phase epitaxy on 300 mm Si (001) wafers with a double trench-patterned oxide template, in an industrial deposition chamber. Aspect ratio trapping in the narrow bottom part of a trench results in a threading dislocation density below 106∙cm−2 in the device layers in the wide upper part of that trench. NRE is used to create larger area NRs with a flat (001) surface, suitable for HBT device fabrication. Transmission electron microscopy inspection of the HBT stacks revealed restricted twin formation after the InGaP emitter layer contacts the oxide sidewall. Several structures, with varying InGaP growth conditions, were made, to further study this phenomenon. HBT devices—consisting of several nano-ridges in parallel—were processed for DC and RF characterization. A maximum DC gain of 112 was obtained and a cut-off frequency ft of ~17 GHz was achieved. These results show the potential of NRE III–V devices for hybrid III–V/CMOS technology for emerging RF applications.

Electron irradiation effects on InP-based HEMTs with different gate widths

In this paper, the influence of electron irradiation on DC and RF characteristics of InP-based HEMTs with different gate widths were studied by irradiation experiment. The results show that the value of channel current (IDS) and transconductance (gm) are decreased for device with different gate width after electron irradiation, which is mainly due to the reduction of mobility in the channel by the irradiation-induced defects. However, the carrier concentration in the channel has a little change. Compared with the device with 100 μm gate width, IDS and gm of the device with 40 μm gate width were decreased by 1.5% and 3%. Meanwhile, the forward gate current decreased due to the increase of series resistance of gate contact caused by electron irradiation. The interface defects induced by electron irradiation induced the increase of the reverse gate current. Additionally, the current gain cut-off frequency (fT) and maximum oscillation frequency (fmax) were reduced by 19.8% and 10.9% for device with 40 μm gate width, and the fT and fmax were only reduced by 7.1% and 8.2% for device with 100 μm gate width. The experimental results indicate that designing a reasonable structure is an effective method to enhance the radiation resistance in InP-based HEMTs, and this method can also be utilized in other semiconductor devices.

Effect of different layer structures on the RF performance of GaN HEMT devices

In this paper we have studied AlGaN/GaN high electron mobility transistor devices with three different buffer layer structures and their effect on the RF performance of the devices. Detailed DC and pulsed IV measurements were carried out to investigate the effect of bulk traps on the performance of the devices. Activation energy of buffer traps is also investigated by low frequency S-parameter measurements of the devices at variable temperature. The effect of buffer structure and quality of buffer on RF gain has been observed for the devices. Using the S-parameters, the equivalent circuit model parameters of the devices were also extracted. All the characterizations revealed that the presence of low C-doped buffer shows less vulnerability towards traps and produces better RF performance. It was also observed that the device with only low C-doped thin buffer reproduces better RF characteristics.

DC and RF characteristics improvement in SOI-MESFETs by inserting additional SiO2 layers and symmetric Si wells

This paper presents an efficient structure for silicon on insulator metal semiconductor FETs. In this structure, by using two symmetrical SiO2 pieces on both sides of the channel and creating two Si wells in the buried oxide along with an extra dent, it has caused DC characteristics and frequencies to be higher than conventional structure. In the proposed device, the breakdown voltage boosts from 15.5 V in the basic structure to 19.5 V in the novel device which indicates about 25% growth. Also, the maximum output power has increased from 0.69 W/mm in the basic structure to 2.4 W/mm in the proposed one which shows an improvement more than 3 times. Also, attributable to lessening of the gate-drain and the gate-source capacitances, the frequency characteristics such as the cut-off and maximum oscillation frequencies have been improved. Therefore, the investigations demonstrate that suggested structure has proper high power and high frequency characteristics.

RF wave coupling, plasma heating and characterization of induced plasma-material interactions in WEST L-mode discharges

Plasma heating in the full tungsten (W) environment in a steady-state tokamak (WEST) relies on electromagnetic waves in both the lower hybrid (LH) and ion cyclotron range of frequencies (ICRF). The present study focuses mostly on the optimization of discharges heated with ICRF, by reporting different methods to first optimize wave coupling, optimize their absorption and reduce the impurity production. It is shown that ICRF coupling can be optimized by moving the plasma closer to antennas, increasing the plasma density, wave frequency and LH power. We show that the absorption efficiency correlates with the hydrogen concentration with the existence of an optimum between 7% and 10% as expected for a minority heating scenario. Absolutely calibrated visible spectroscopy sightlines were used to monitor ion fluxes in different locations as part of an effort to quantitatively estimate the contribution of different impurity sources to the core contamination by tungsten. It is typically found that in discharges with high total RF-power (above 5 MW of LH and 3 MW of ICRF), divertor and antenna limiter sources can reach a similar order of magnitude during the ICRF phase.

Cap layer effect in DC and RF characteristics of InP based n-p-n metamorphic δ-doped heterojunction bipolar transistor

ABSTRACT The effect of InGaAsP and InGaAs cap layers in InP n-p-n heterojunction bipolar transistor (HBT) is presented. The common figures of merit (FOM) in each case are compared to assess their potentials for operation at high frequency. The Gummel-Poon plot of experimental reported result has been used to validate the data obtained from simulation using ATLAS module of Silvaco software tool. After models validation in TCAD tool, the DC and RF characteristics of the HBTs with different cap layers are examined and then a comparative analysis is carried out based on the characteristics such as I–V behaviour, frequency response, minimum noise figure and maximum cut-off frequency. With the change in InGaAs cap to InGaAsP cap, the DC current gain increases from 255 to 300, VCE,offset is reduced from 131 to 76 mV, Early Voltage (VA) increases from −42 to −190 V, cut-off frequency ft is increased from 24.34 MHz to 8.04 GHz, and the maximum oscillation of frequency(fmax) is improves from 13.79 to 37.11 GHz

Composite‐channel In 0. 17 Al 0 . 83 N /In 0. 1 Ga 0 . 9 N / GaN /Al 0. 04 Ga 0 . 96 N high electron mobility transistors for RF applications

In this work, we present the high performance of composite channel based In0.17Al0.83N/In0.1Ga0.9N/GaN/Al0.04Ga0.96N high electron mobility transistors (HEMTs) on a sapphire substrate. A numerical simulation is carried out for the proposed and conventional GaN channel-based HEMTs using TCAD. Due to the strong polarization of InAlN/InGaN, enhanced electron confinement and high electron mobility of composite channel based proposed device shows excellent DC and RF characteristics with improved linearity than conventional GaN channel based HEMTs. A 55 nm T-gate device demonstrates 4.45 A/mm drain current density (IDS) at VGS = 0 V, 0.7 S/mm stable transconductance (GM) for a wide range of gate bias, and excellent FT/Fmax of 274/288 GHz. Benefiting from the Al0.04Ga0.96N buffer (back-barrier), the device shows a very low sub-threshold drain leakage current and high breakdown voltage (VBR) of 43.5 V. The combination of high FT/Fmax, stable transconductance, and high breakdown voltage of the proposed HEMTs shows the great promise for high power and wide-bandwidth millimeter-wave applications.

Design and low-power RF test of a C-band cryogenic RF gun

Next-generation photoinjectors with high brightness are under development for advanced accelerator facilities, such as Free-Electron Laser, Ultrafast Electron Diffraction, and Ultrafast Electron Microscopy. A feasible and prospective method to produce electron beams with higher quality is based on high gradient acceleration technology. The gradient could be as high as 200 MV/m at the photocathode in a C-band RF gun in a 20 K cryostat. In this paper, a new cryogenic C-band photocathode electron gun is systematically designed and optimized in both beam dynamics and RF design. Moreover, a test platform has been set up for some preliminary experiments with a 3-cell prototype. The results on the RF characteristics at cryogenic temperatures are in good agreement with the design and simulation, and will pave the way for the practical operation of the cryogenic electron gun and the design of other cryogenic structures.

Heat sink implementation in back-end of line for self-heating reduction in 22 nm FDSOI MOSFETs

This work studies the effect of heat sink in the back-end of line (BEOL) on the self-heating (SH) parameters of transistors in a Fully Depleted Silicon-on-Insulator (FDSOI) technology. The RF characterization technique, which involves S-parameter measurements over a wide frequency range, is used to evaluate SH parameters. Two types of sink configurations in the BEOL are considered; one connected to the gate and the other left floating. We experimentally demonstrate that gate-connected heat sink allows for a reduced self-heating in 22 nm FDSOI devices. Around 15% to 30% reduction in thermal resistance is observed for the gate-connected heat sink in comparison to the floating sink.

Physical Analysis on the DC and RF Operations of a Novel SOI-MESFET with Protruded Gate and Dual Wells

In this article, a novel SOI MESFET which can be suitable for high power applications is proposed. In order to upgrade its electrical characteristics, a protruded gate and dual wells (PGDW) n-type silicon in the buried oxide are formed. This strategy by using a protruded gate and a right well at the drain side increases the channel thickness causing a rise in the drain current. Besides, a reduction in the electric field maximum value near the drain side leads to improving the maximum power density of the PGDW- structure 143% over a Conventional MESFET. A left well in the proposed structure has been used to absorb the created holes due to the impact ionization mechanism and causes improvement of floating body effect. Also, the PGDW-MESFET demonstrates the improved performance in the RF characteristics, consequently, two parameters h21, Unilateral power gain boost almost 14%, and 11%, respectively compared to the C-MESFET.

RF network analysis of the WEST TWA mock-up in TITAN

WEST represents the ideal device to test a reactor relevant travelling wave array (TWA) due to its long pulse capability and full metal wall configuration. Moreover, the already installed ICRF high power launchers will allow a direct comparison between a classical in-port antenna and the TWA. The design and exploitation of a high power (2 MW) TWA mock-up to be tested in TITAN represent the first step towards its integration in WEST. This paper presents the progress in the RF characterization of this high power mock-up. An integrated modelling scheme based on the full-wave code HFSS and on Python packages for RF circuit simulations is developed and used to parametrically analyse the response of the mock-up inside TITAN. The sensitivity of the antenna to geometrical deformations, e.g. thermal dilatation or manufacturing tolerances, is analysed. The use of trimmers to compensate those deformations is discussed and results from a manufactured trimmer test-bed are presented. A diagnostic system is proposed to measure electric field and current on the straps. Aspects like sensitivity and calibration are briefly discussed. In conclusion, the next steps of the project are outlined.

Optimized vertical RF-MEMS switch design with a small actuation voltage

A vertical RF-MEMS (Radio Frequency Micro ElectroMechanical Switch) switch design is proposed in this work that features a shunt capacitive configuration and can operate at a very low actuation voltage. Besides operating on a low switching voltage, the switch behold a small value of insertion loss in Up (ON) state and offers a towering isolation factor in Down (OFF) state. A horizontal structure of bridge membrane is used in the proposed design and the switch function (with ON and OFF operating states) is provided by the vertical movement of this membrane structure that is controlled by the electrostatic actuation technique. The actuation pad is centrally fed by a Coplanar Waveguide structure. The switch performance has been analysed over a wide frequency range from 1 to 40 GHz. For obtaining a 1.5 μm vertical displacement of the bridge membrane, a sheer 3.0 Volts of pull-in voltage (VPI) is required. CoventorWare and HFSSv13 tools are used in this work for designing and analysing the proposed switch. The use of fixed-fixed flexure beam configuration is chosen for switch design. Simulation results showcase excellent RF characteristics with isolation factor of −47 dB (at 32.5 GHz) and insertion loss in range of −0.01 to −1.10 dB (for 1−40 GHz frequency).

Investigation of high threshold voltage E-mode AlGaN/GaN MIS-HEMT with triple barrier layer

A comprehensive study on an E-mode AlGaN/GaN MIS-HEMT with triple barrier layer is conducted by Silvaco TCAD software. The effect of geometric parameters of gate dielectric layer, including the length of both sides and the recessed depth, on the device is studied. The simulation results show that the optimized device can reach a high threshold voltage (from 1.24 V to 2.06 V), a large maximum drain current (from 0.925 A/mm to 1.044 A/mm), and a large gate-source capacitance (from 1837 fF/mm to 3100 fF/mm) on the condition that frequency is 1 MHz. Furthermore, based on the analysis of different combinations of the triple structural parameters, two types suitable for specific conditions are concluded, which is helpful to further improve DC and RF characteristics of E-mode AlGaN/GaN MIS-HEMT.

Study of Effective Graded Oxide Capacitance and Length Variation on Analog, RF and Power Performances of Dual Gate Underlap MOS-HEMT

Comparative analysis of a Symmetric Heterojunction Underlap Double Gate (U-DG) GaN/AlGaN Metal Oxide Semiconductor High Electron Mobility Transistor (MOS-HEMT) on varying the effective capacitance by using different oxide materials on source and drain sides, and determination of optimum length of oxides for the superior device performance has been presented in this work. This paper shows a detailed performance analysis of the Analog Figure of Merits (FoMs) like variation of Drain Current (IDS), Transconductance (gm), Output Resistance (R0), Intrinsic Gain (gmR0), RF FoMs like cut-off frequency (fT), maximum frequency of oscillation (fMAX), gate to source resistance (RGS), gate to drain resistance (RGD), gate to drain capacitance(CGD), gate to source capacitance (CGS) and total gate capacitance (CGG) using Non-Quasi-Static (NQS) approach. Power analysis includes Output power (Pout), Gain in dBm and power output efficiency (POE) have been studied. Studies reveal that the device with higher dielectric material towards source side shows superior performance. On subsequently changing the proportion of two oxides in a layer by varying length, it is observed that as the proportion of oxide increases the device demonstrates more desirable Analog and RF characteristics while best power performance is obtained from device with equal lengths of HfO2 and SiO2.

Preliminary RF characterization of DEMO in-port ion cyclotron heating system for toroidal and poloidal geometry variations

Ion cyclotron Resonance Heating (ICRH) is one of the auxiliary heating schemes considered for the future DEMOnstration Power Plant (DEMO). The ICRH system in DEMO should couple 50 MW using three equatorial ports. Compared to the ITER one, the current DEMO port design has a smaller toroidal and a larger poloidal extent.One of the ICRH pre-conceptual design options for DEMO, an in-port antenna based on the current ITER design, is investigated using the ANTITER II code. To make optimal use of the port larger poloidal extent, the possibility to use quadruplets instead of the ITER triplets is explored. The impact on the power coupling is evaluated for two different antenna geometry considering a possible toroidal extension of the antenna in the blanket. The ITER matching-decoupling system is adapted to the new antenna front geometries considered.

30 GHz GeSn photodetector on SOI substrate for 2 µm wavelength application

We report the demonstration of a normal-incidence p-i-n germanium-tin ( Ge 0.951 Sn 0.049 ) photodetector on silicon-on-insulator substrate for 2 μm wavelength application. The DC and RF characteristics of the devices have been characterized. A dark current density under − 1 V bias of approximately 125 mA/ cm 2 is achieved at room temperature, and the optical responsivity of 14 mA/W is realized for illumination wavelength of 2 μm under − 1 V reverse bias. In addition, a 3 dB bandwidth ( f 3 dB ) of around 30 GHz is achieved at − 3 V , which is the highest reported value among all group III–V and group IV photodetectors working in the 2 μm wavelength range. This work illustrates that a GeSn photodetector has great prospects in 2 μm wavelength optical communication.

Measurement‐based analysis of GaAs HEMT technologies: Multilayer D‐H pseudomorphic HEMT versus conventional S‐H HEMT

AbstractThe key objective of this study is to check out the performance of two multilayer processed double‐heterojunction pHEMTs with different gate width as well as one conventional single‐heterojunction HEMT. Different types of investigation have been undertaken by means of on‐wafer DC, small‐signal, and nonlinear two‐tone measurements. The modeling of the DC output characteristics was successfully accomplished using the FET's Curtice model for all of three tested devices. The main figures of merit for microwave and millimeter wave applications have been determined from scattering parameter measurements and then discussed in detail. Furthermore, to attain a better insight of the device behavior, the nonlinear intermodulation distortion behavior has been also studied and compared for the three devices over different bias conditions. A careful analysis of the DC and RF characteristics over a wide range of working conditions is necessary to ensure adequate transistor operation, depending on the given application of interest.