High Cutoff Frequency Research Articles

Modulation of ballistic injection velocity in phosphorene nanodevices by bias and confinement effects

Atomistic quantum transport simulations are employed to study the electron injection velocity (vinj) and ballistic performance of phosphorene nanoribbon (PNR) field-effect transistors (FETs). We show that PNR bandstructure is immune to quantum confinement effects, which is seen in a rather constant vinj≈2.1 × 107cm/s down to the PNR width of 1.5 nm. Moreover, we demonstrate that the modulation of vinj by gate bias is available only for PNRs wider than 2.1 nm, with the maximum enhancement being 33%. Finally, it is reported that PNR FETs combine high cut-off frequencies above 526 GHz with acceptable bandgap that ranges from 0.7 eV to 1.6 eV in the examined PNR width range, which proves the plausibility of PNRs as channel material for future ultra-scaled high-speed FETs.

Fast electrochemical response of PEDOT:PSS electrodes through large combined increases to ionic and electronic conductivities

Conducting polymers serve as the active materials in flexible electrochromic displays, organic electrochemical transistors, supercapacitors, artificial muscle and other electrochemical devices. poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) is often employed in these devices since it is widely available, suitable for spraying, printing or casting, and can be treated to obtain high electronic conductivity. However, the ionic resistance limits charging rate and switching speed in this high volumetric capacitance polymer. Here we show that treatments that increase electronic conductivity can also increase ionic conductivity – by a factor of 300. Symmetric PEDOT:PSS supercapacitors with electrode thicknesses of 4.7 µm charge 40 times faster due to the combination of improved ionic and electronic conductivity. In these devices, PEDOT:PSS was deposited on two sides of a porous polymer separator by spray coating, and then soaked in either methanol, methanol mixed with the ionic liquid EMITFSI (50%v/v), ethylene glycol, ethylene glycol mixed with EMITFSI (50%v/v), or dimethyl sulfoxide. Ionic resistance dictates the charging time in untreated films. Treatment with methanol combined with EMITFSI results in the highest ionic conductivity (0.02 S/m), combined with an electronic conductivity of 498 S/m and the highest cut-off frequency. In addition, these treatments increase volumetric capacitance. The increases are most likely due to the removal of insulating PSS by the polar solvents, resulting in the formation of an open polymer structure in which ions can move more freely. Improving the charge/discharge speed has implications on the response times of color displays, energy storage devices, neural recording devices and actuators.

Optically controlled n −Si/p −SeO2/p −SiO2 microwave resonators designed for 5G/6G communication technology

Herein n−Si/p−SiO2 interfaces comprising layers of p-SeO2 are employed as an optically controllable microwave resonators. The stacked layers of SeO2 (500 nm) and SiO2 (50 nm) were deposited onto type Si thin crystals by the thermal evaporation technique under a vacuum pressure of 10−5 mbar. Ytterbium and Au metals were coated onto SiO2 and Si layers, respectively, to form Schottky arms. Energy band diagram analyses were performed to confirm the formation of doubled conduction and valence band offsets. These offsets create energy barriers and potential wells that contribute to the bistable behavior. Photo-impedance spectroscopic measurements were conducted on the device under blue light, demonstrating its ability to function as a light-power tunable microwave resonator and MOS capacitor. In the absence of light, negative capacitance (NC) effects were observed above a driving frequency of 1.07 GHz. As the device was exposed to light and the light power increased, the frequency range of NC effects shifted to higher driving frequencies. Furthermore, the range of NC effects became narrower with increasing light power, indicating a more limited frequency range for the manifestation of negative capacitance. In addition, Si/SeO2/SiO2 microwaves resonators displayed high cutoff frequency exceeding 0.10 THz at driving frequency of 1.07 GHz in the dark. The driving frequency also shifted toward larger values as light power is increased indicating the ability to optically control the cutoff frequency range and value. The high response of the capacitance, conductance, cutoff frequency spectra and the dependence of capacitance–voltage characteristics on incident light power nominate the device as microwave resonators and MOS electro-optic devices suitable for 5G/6G communication technology.

Sol–gel synthesis, electromagnetic properties and microwave absorption behavior of strontium Co2Z hexaferrites

Owing to the special planar structure and very high resistivity, [Formula: see text]-type hexaferrites possess the high initial permeability and cut-off frequency, indicating great application potential in high-frequency devices. Strontium Co2Z hexaferrites (Sr3Co2Fe[Formula: see text]O[Formula: see text]) were successfully prepared by the sol–gel method and calcined at the different temperatures from [Formula: see text]C to [Formula: see text]C. The influence of the calcined temperatures on the microstructure, phase structures, magnetic properties and microwave absorption behavior of all samples was investigated in detail. All results indicated that strontium hexaferrites go through the [Formula: see text]-, [Formula: see text]-, [Formula: see text]-, and [Formula: see text]-phase transformation process from [Formula: see text]C to [Formula: see text]C, and S-1200 (calcined at [Formula: see text]C) is confirmed to be Co2Z-type hexaferrites. S-1200 showed the highest imaginary permeability while the imaginary permittivity of all samples is close to zero, indicating the excellent microwave adsorption behavior of strontium Co2Z hexaferrites. The reflection loss results indicate that S-1200 exhibits the best microwave absorption performance with the RL value of −32.4 dB for 4.0 mm thickness at 4.72 GHz, according to the impedance matching and quarter-wavelength theory.

An application for the earthquake spectral and source parameters and prediction using adaptive neuro fuzzy inference system and machine learning

Parameters related to earthquake origins can be broken down into two broad classes: source location and source dimension. Scientists use distance curves versus average slowness to approximate the epicentre of an earthquake. The shape of curves is the complex function to the epicentral distance, the geological structures of Earth, and the path taken by seismic waves. Brune’s model for source is fitted to the measured seismic wave’s displacement spectrum in order to estimate the source’s size by optimising spectral parameters. The use of ANFIS to determine earthquake magnitude has the potential to significantly alter the playing field. ANFIS can learn like a person using only the data that has already been collected, which improves predictions without requiring elaborate infrastructure. For this investigation’s FIS development, we used a machine with Python 3x running on a core i5 from the 11th generation and an NVIDIA GEFORCE RTX 3050ti GPU processor. Moreover, the research demonstrates that presuming a large number of inputs to the membership function is not necessarily the best option. The quality of inferences generated from data might vary greatly depending on how that data is organised. Subtractive clustering, which does not necessitate any type of normalisation, can be used for prediction of earthquakes magnitude with a high degree of accuracy. This study has the potential to improve our ability to foresee quakes larger than magnitude 5. A solution is not promised to the practitioner, but the research is expected to lead in the right direction. Using Brune’s source model and high cut-off frequency factor, this article suggests using machine learning techniques and a Brune Based Application (BBA) in Python. Application accept input in the Sesame American Standard Code for Information Interchange Format (SAF). An application calculates the spectral level of low frequency displacement (Ω0), the corner frequency at which spectrum decays with a rate of 2(fc), the cut-off frequency at which spectrum again decays (fmax), and the rate of decay above fmax on its own (N). Seismic moment, stress drop, source dimension, etc. have all been estimated using spectral characteristics, and scaling laws. As with the maximum frequency, fmax, its origin can be determined through careful experimentation and study. At some sites, the moment magnitude was 4.7 0.09, and the seismic moment was in the order of (107 0.19) 1023. (dyne.cm). The stress reduction is 76.3 11.5 (bars) and the source-radius is (850.0 38.0) (m). The ANFIS method predicted pretty accurately as the residuals were distributed uniformly near to the centrelines. The ANFIS approach made fairly accurate predictions, as evidenced by the fact that the residuals were distributed consistently close to the centerlines. The R2, RMSE, and MAE indices demonstrate that the ANFIS accuracy level is superior to that of the ANN.

Simulation of a multichannel vacuum transistor with high cut-off frequency

A multichannel vertical vacuum transistor based on the Fowler–Nordheim tunneling emission mechanism was proposed and numerically investigated. The multichannel structure was demonstrated to be effective in enhancing the drain current when compared to the traditional single-channel structure with the same device size. For example, transconductance increased from 0.42 mS of the single-channel structure to 0.86 mS of the four-channel structure. In addition, when the vacuum channel number increases, the size of a single channel decreases correspondingly, leading to a reduction in electric field intensity on the electron emission surface. Thus, the off-state current dramatically reduced by two orders of magnitude reaching10−15 A according to the simulated results. In other words, the ON/OFF drain current ratio of the multichannel structure is significantly enhanced. Furthermore, the simulation results indicate that the cut-off frequency of the multichannel device is 33% higher than that of the traditional single-channel one reaching 0.19 THz.

Reduction of Corner Effect in ZG-ES-TFET for Improved Electrical Performance and its Reliability Analysis in the Presence of Traps

In this paper, various electrical parameters of a Z-shaped gate elevated source TFET (ZG-ES-TFET) in the presence of interface traps are investigated. The placement of Z-shaped gate across the elevated source region enhances the line tunneling in both horizontal and vertical direction, which eventually increases the device ON-current. Moreover, the L-shaped pocket placed above the elevated source region increases the rate of carriers tunneling into the channel region and improves the drain current in ZG-ES-TFET. In addition to this, the optimization of channel portion below the source region limits the corner effects, suppress the OFF-state leakage and which in turn leads to achieve high switching ratio in the proposed ZG-ES-TFET. Simulation results revels that ZG-ES-TFET shown improvement in switching ratio (ION/IOFF) and ON-current (ION) by an order of ∼2 and ∼1 as when compared to conventional LTFET. Thereafter, improvement in the carrier’s tunneling rate at source-channel (S-C) interface shows a significant enhancement in the transconductance (∼76.4 μs μm−1) of ZG-ES-TFET. It further helps to achieve a high cut-off frequency and Gain-Bandwidth-Product (GBW) of ∼6.9 GHz and ∼1.3 GHz, respectively. In reliability concern, the transfer characteristics of the proposed ZG-ES-TFET found to be less sensitive towards the presence of interface traps and temperature variations.

High cut-off frequency and low magnetic loss of Bi3+-Cr3+ co-substitution NiCuZn ferrite for chip inductors applications

With the rapid growth of high-frequency chip inductors, there is an urgent demand for NiCuZn ferrite that exhibits low magnetic loss and high cut-off frequency. To enhance its electromagnetic features, this study investigates the doping of Bi3+-Cr3 + ions into NiCuZn ferrite. The research examines the effects of different Cr3+ concentrations on the electric and magnetic properties, as well as the crystal structure of NiCuZn ferrites. The results showed that using a low sintering temperature of 925℃ can obtain NiCuZn ferrite with high population density and uniform microstructure. The inclusion of Cr3+ causes the lattice parameter to decrease, with a preference for octahedral B-sites. Furthermore, the saturation magnetization declines as the concentration of Cr3+ increases, according to the results of the magnetic hysteresis loops. The permittivity measurements demonstrate that the addition of Cr3+ ions can enhance permittivity and reduce dielectric loss. Lastly, NiCuZn ferrite co-doped with 0.30 wt% Bi2O3 and x = 0.15 of Cr3+ ions had appropriate saturation magnetization (∼57.05 emu/g) and coercivity (∼0.680 kA/m), meanwhile exhibited the highest dielectric constant (∼12.32 @ 1 MHz) and cut-off frequency (218 MHz), the lowest permeability loss tangent (0.0036@1 MHz) and imaginary part of the permittivity (0.54@1 MHz), making it a suitable for high-frequency chip inductors.

Analysis of III-V material-based dual source T-channel junction-less TFET with metal implant for improved DC and RF performance

In this paper, two III-V material-based junctionless tunnel FET devices, D-1 and D-2, are proposed. The proposed device D-1 has a low bandgap (GaSb-based) dual source and a higher bandgap (GaAs-based) T-channel junctionless, and the proposed device D-2 has the same architecture as D-1 in addition to a metal strip implant in the gate oxide near both source regions. Due to junctionless architecture, the proposed D-1 and D-2 eliminate random dopant fluctuations (RDF), remove the need for high thermal budgeting, and give better performance with less variability. The wide bandgap (GaAs) T-channel and the drain region formed far from the gate fully suppress the ambipolarity for both the proposed D-1 and D-2. The low-bandgap GaSb material in the source improves the ON current for D-1 and D-2. Compared to the conventional junctionless TFET (JL-TFET), the proposed D-2 (even at a lower bias of 0.5 V) improves the ON current by 1.7 times and the ION/IOFF ratio by 216.66 times, with a much-reduced average subthreshold swing value of 32.7 mV/dec compared to 70 mV/dec of the conventional JL-TFET. Furthermore, the proposed D-2 also provides much improved RF performance with a higher transconductance (gm) of 147.8 μs, higher cut-off frequency (fT) of 32.26 GHz, a higher gain-bandwidth product (GBW) of 3.52 GHz, higher transconductance-frequency product (TFP) of 286 GHz, and a lower transit time (τ) of 5 × 10–12 s. Furthermore, we analyze various linearity parameters such as gm2, gm3, VIP2, VIP3, IIP3, and IMD3 for both D-1 and D-2, and our findings indicate that D-2 exhibits improved linearity performance.

Highly Efficient Zero-Dimensional Cuprous Halides Hybrids for Pulsed X-Ray Detection and 3D Reconstruction Imaging

Zero-dimensional organic-inorganic metal halides have shown various applications in X-ray detection. However, the mechanism of energy distribution (direct and indirect detection interactions) needs further clarification, and real application reliability (pulsed X-ray and 3D imaging) requires further study. Herein, we designed and synthesized a representative MHs, TBACuI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (TBA <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> : tetrabutylammonium cation). Experimental and theoretical analyses demonstrate that the energy of luminescent excitons and conducting carriers will not be readily interconverted. Also, the X-ray specific response was achieved, and high sensitivity (>45000 μCGy <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), low shot noise (1.68×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> nAHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1/2</sup> ), and superior stability (long time and high energy irradiation or immersion in water) were obtained. Importantly, the device has a high cutoff frequency (>140 Hz) for pulsed X-rays, meeting the needs of medical dynamic imaging (10 Hz). Additionally, the demonstration of 3D reconstruction imaging with direct detectors was achieved.

A phase transition approach to elucidate the propagation of shear waves in viscoelastic materials

In the field of acoustics, a medium has traditionally been considered a liquid if shear waves cannot propagate. For more complex liquids, such as those containing polymer chains or surfactant aggregates, this definition begins to be unclear. By adopting a rheological model-independent approach, this work investigated by means of dynamic elastography, the liquid–solid phase transitions in viscoelastic liquid media. When the storage shear modulus G′ dominated the loss shear modulus G″, a minimal shear wave attenuation frequency region was defined and the medium was considered solid. When G″ dominated G′, the shear waves were strongly attenuated and the medium was considered liquid. The investigated medium, an aqueous solution of xanthan gum, behaved as a bandpass filter with transition bands, showing liquid–solid–liquid behavior from low to high frequency. During these transitions bands, shear waves still propagated but highly attenuated. The limiting values where shear waves were no longer observed were identified as the low and high cutoff frequencies. Finally, the ability of various rheological models to predict the phase transition frequencies and describe the dispersion curves was tested. A three-element rheological model, the Jeffreys model, was required to accurately fit the experimental response of the medium at different concentrations over the entire frequency range. Shear wave propagation methods can overcome the technical limitations of traditional rheometry and explore higher frequencies, rarely investigated in viscoelastic liquids.

Large-Area GeSe Realized Using Pulsed Laser Deposition for Ultralow-Noise and Ultrafast Broadband Phototransistors.

Here, we report on the comprehensive growth, characterization, and optoelectronic application of large-area, two-dimensional germanium selenide (GeSe) layers prepared using the pulsed laser deposition (PLD) technique. Back-gated phototransistors based on few-layered 2D GeSe have been fabricated on a SiO2/Si substrate for ultrafast, low noise, and broadband light detection, showing spectral functionalities over a broad wavelength range of 0.4-1.5 μm. The broadband detection capabilities of the device have been attributed to the self-assembled GeOx/GeSe heterostructure and sub-bandgap absorption in GeSe. Besides a high photoresponsivity of 25 AW-1, the GeSe phototransistor displayed a high external quantum efficiency of the order of 6.14 × 103%, a maximum specific detectivity of 4.16 × 1010 Jones, and an ultralow noise equivalent power of 0.09 pW/Hz1/2. The detector has an ultrafast response/recovery time of 3.2/14.9 μs and can show photoresponse up to a high cut-off frequency of 150 kHz. These promising device parameters exhibited by PLD-grown GeSe layers-based detectors make it a favorable choice against present-day mainstream van der Waals semiconductors with limited scalability and optoelectronic compatibility in the visible-to-infrared spectral range.

High frequency single crystalline diamond MOSFET with high temperature (300 °C) ALD grown Al2O3 dielectric

In this paper, hydrogen terminated metal oxide semiconductor field effect transistors (MOSFETs) having a sub-micron gate length were fabricated on a single crystalline diamond sample using the 300 °C ALD grown Al2O3 as gate dielectric and passivation layer. The device shows a maximum output current density of 942 mA/mm and a lowest on-resistance of 6.2 Ω·mm at a VGS of −3 V. A maximum transconductance of 284 mS/mm was achieved. In addition, a high cut-off frequency of 41.3 GHz and a maximum oscillation frequency of 80.6 GHz were achieved. These are the highest values among the reported H-diamond MOSFETs with high temperature (>200 °C) grown dielectrics. The hole mobility is estimated to be 138 cm2/Vs at VGS = -3 V. The high carrier mobility contributes to the achievement of the high output current density. These results demonstrate that the high temperature grown Al2O3 dielectric has also a great potential to be used in high frequency H-diamond MOSFETs.

Optical micro-elastography with magnetic excitation for high frequency rheological characterization of soft media

The propagation of shear waves in elastography at high frequency (>3 kHz) in viscoelastic media has not been extensively studied due to the high attenuation and technical limitations of current techniques. An optical micro-elastography (OME) technique using magnetic excitation for generating and tracking high frequency shear waves with enough spatial and temporal resolution was proposed. Ultrasonics shear waves (above 20 kHz) were generated and observed in polyacrylamide samples. A cutoff frequency, from where the waves no longer propagate, was observed to vary depending on the mechanical properties of the samples. The ability of the Kelvin–Voigt (KV) model to explain the high cutoff frequency was investigated. Two alternative measurement techniques, Dynamic Mechanical Analysis (DMA) and Shear Wave Elastography (SWE), were used to complete the whole frequency range of the velocity dispersion curve while avoid capturing guided waves in the low frequency range (<3 kHz). The combination of the three measurement techniques provided rheology information from quasi-static to ultrasonic frequency range. A key observation was that the full frequency range of the dispersion curve was necessary if one wanted to infer accurate physical parameters from the rheological model. By comparing the low frequency range with the high frequency range, the relative errors for the viscosity parameter could reach 60 % and they could be higher with higher dispersive behavior. The high cutoff frequency may be predicted in materials that follow a KV model over their entire measurable frequency range. The mechanical characterization of cell culture media could benefit from the proposed OME technique.

Non-wearable pulse rate measurement system using laser Doppler flowmetry with algorithm to eliminate body motion artifacts for masked palm civet (Parguma larvata) during husbandry training

Husbandry training (HT) shapes specific actions of animals to facilitate healthcare or animal research. The challenge of HT is that learning the specific actions requires zoo-keepers to grasp the stress states of animals. Here we suggest a non-wearable pulse rate measurement system to help zoo-keepers. The pulse rate indicates the stress state. By using laser Doppler flowmetry with an algorithm to eliminate body motion artifacts, it is possible to measure pulse rates. In the algorithm, the cutoff frequency is an important parameter. This paper reports the relationship between the cutoff frequency and the blood flow signal. We applied 100 Hz, 12 kHz and 15 kHz cutoff frequencies and compared blood flow signals. The results indicated that the appropriate cutoff frequency can vary depending on the magnitude of body motion artifacts. When there are few body motion artifacts, a low cutoff frequency is suitable. Otherwise, a high cutoff frequency is preferred.

Extremely high frequency Schottky diodes based on single GaN nanowires

Gallium nitride (GaN) is one of the most promising materials for high-frequency devices owing to its prominent material properties. We report on the fabrication and study of a series of Schottky diodes in the ground-signal-ground topology based on individual GaN nanowires. The electrical characterization of I–V curves demonstrated relatively high ideality factor value (about 6–9) in comparison to the planar Au/GaN diodes that can be attributed to the nanowire geometry. The effective barrier height in the studied structures was defined in the range of 0.25–0.4 eV. The small-signal frequency analysis was employed to study the dependency of the scattering parameters in the broad range from 0.1 to 40 GHz. The approximation fitting of the experimental data indicated the record high cutoff frequency of about 165.8 GHz.

Tunable magnetocrystalline anisotropy and high-frequency magnetic properties of Y2(Co1−xFex)17 and their composites

Rare-earth transition-metal (R-T) intermetallic compounds are emerging as competitive candidates for novel microwave absorption materials (MAMs) since they show high magnetization and tunable easy magnetization directions (EMDs). In this work, Y2(Co1−xFex)17 (0 ≤ x ≤ 0.3) compounds with the Th2Ni17 hexagonal structure were prepared with the purpose of tuning the EMDs. As x increases, the EMDs of the Y2(Co1−xFex)17 compounds change from the ab-plane (0 ≤ x &amp;lt; 0.0329) to the cone (0.0329 ≤ x ≤ 0.038) and then to the c-axis direction (0.038 &amp;lt; x ≤ 0.3). Furthermore, it was found that the extremely high cutoff frequencies of the uniaxial anisotropy materials give them considerably potential for microwave absorption applications above 10 GHz, despite their relatively low initial permeability compared to the planar anisotropic materials. By studying the high-frequency properties of Y2(Co1−xFex)17/paraffin composites, it is noted that uniaxial anisotropy compounds with x = 0.1 and x = 0.3 can possess higher permeability above 10 GHz as compared to both planar anisotropy and conical anisotropy compounds (x &amp;lt; 0.1) due to their high cutoff frequencies arising from large magnetocrystalline anisotropy fields. This can improve the impedance matching and thus lead to a better microwave absorption performance in the range of 10 to 40 GHz for materials with uniaxial anisotropy. Among all the compositions, the Y2(Co0.9Fe0.1)17/paraffin composite exhibits a minimum reflection loss (RL) of −50 dB at 6 GHz with a thickness of 2.5 mm and a wide qualified bandwidth (QB, RL &amp;lt; −10 dB) of 9.6 GHz at a center frequency of 30.3 GHz with a thickness of 0.6 mm, thus making it a promising candidate for MAMs above 10 GHz.

The microwave absorption properties of soft magnetic materials in frequency up to 40 GHz

With the continuous development of communication technology, the microwave frequency used has been extended to 24∼30 GHz or even higher. Thus, for the research on microwave absorption materials, the commonly used 2∼18 GHz frequency range might no longer be enough. More studies of microwave absorption properties in a higher frequency band are necessary. In this work, we report the microwave absorption properties of several soft magnetic composites in frequency up to 40 GHz. Magnetic materials such as iron, Y2Fe16Si, Ce2Fe17N3−δ, and La2Fe4Co10B micron powders which display excellent microwave absorption properties in 2∼18 GHz, are investigated. Within 2∼40 GHz, the reflection loss (RL) of iron/paraffin, Y2Fe16Si/paraffin, Ce2Fe17N3−δ/paraffin and La2Fe4Co10B/paraffin composites could reach −46.2 dB, −71.4 dB, −49.1 dB, and −40.1 dB, respectively. Moreover, their effective absorption bandwidth (RL &amp;lt; −10 dB) could reach 16.9 GHz, 8.53 GHz, 10.08 GHz, and 8.03 GHz, respectively. Though the measurements are extended to 40 GHz, the absorption properties of these composites become weak when the frequency rises to around 40 GHz, which is restricted by the cutoff frequencies of the materials. The measured data shows that these soft magnetic composites are good candidates for high-frequency microwave absorption materials, while exploring magnetic materials with further higher cutoff frequencies may result in better performance.

Simulation of High Breakdown Voltage, Improved Current Collapse Suppression, and Enhanced Frequency Response AlGaN/GaN HEMT Using A Double Floating Field Plate

In this paper, DC, transient, and RF performances among AlGaN/GaN HEMTs with a no field plate structure (basic), a conventional gate field plate structure (GFP), and a double floating field plate structure (2FFP) were studied by utilizing SILVACO ATLAS 2D device technology computer-aided design (TCAD). The peak electric fields under the gate in drain-side can be alleviated effectively in 2FFP devices, compared with basic and GFP devices, which promotes the breakdown voltage (BV) and suppresses the current collapse phenomenon. As a result, the ON-resistance increase caused by the current collapse phenomena is dramatically suppressed in 2FFP ~19.9% compared with GFP ~49.8% when a 1 ms duration pre-stress was applied with Vds = 300 V in the OFF-state. Because of the discontinuous FP structure, more electric field peaks appear at the edge of the FFP stacks, which leads to a higher BV of ~454.4 V compared to the GFP ~394.3 V and the basic devices ~57.6 V. Moreover, the 2FFP structure performs lower a parasitic capacitance of Cgs = 1.03 pF and Cgd = 0.13 pF than those of the GFP structure (i.e., Cgs = 1.89 pF and Cgd = 0.18 pF). Lower parasitic capacitances lead to a much higher cut-off frequency (ft) of 46 GHz and a maximum oscillation frequency (fmax) of 130 GHz than those of the GFP structure (i.e., ft = 27 GHz and fmax = 93 GHz). These results illustrate the superiority of the 2FFP structure for RF GaN HEMT and open up enormous opportunities for integrated RF GaN devices.

Nanocrystalline Mn-doped Ni–Cu ferrites with a high cut-off frequency and initial permeability: Suitable for advanced electronic devices and biomedical applications

The microstructural and electromagnetic properties of Mn-doped Ni0.50-xMnxCu0.50Fe2O4 (x = 0.0, 0.10, 0.20, 0.30, 0.40) magnetic nanoparticles are studied. Compositions are produced by the combustion method, and samples prepared from these powders are sintered at different sintering temperatures. The Rietveld refinement of X-ray diffraction (XRD) data confirmed that all compositions have cubic spinel structures with an Fd-3m space group. The average crystallite size is within 8–65 nm measured by different methods. The porosity of the surface, average grain diameter, and grain distribution are measured using optical micrographs. The high cut-off frequency of 10 MHz is observed in the initial permeability as a function of frequency plots. The maximum Curie temperature of 855 K is found for the x = 0 sample. The maximum relative quality factor (2636) and lowest relative loss factor (0.04) are found for x = 0.4. The initial permeability as a function of frequency is also measured at liquid nitrogen temperature (77 K). The “law of approach to saturation (LAS)” is used for magnetization data and the highest saturation magnetization value 61 emu/g is obtained for x = 0.3. The "Jonscher universal power law" fitted the ac electrical conductivity with large dispersion at a higher frequency region and a small polaron hopping model is applicable in this case. The dielectric constant exhibit dispersive behavior at low frequency and follow Koop's as well as Maxwell-Wagner's two-layer models. At 100 Hz the maximum value of the dielectric constant is 2.8 × 105. Nyquist plot representation stated that the electrical conduction mechanism in these ferrites is mainly due to the influence of the grain and grain boundary effects. An electrical equivalent circuit is suggested to explain the impedance analysis. Electric modulus studies confirm the non-Debye type relaxation process of the compositions. Tuning all of the properties specifies that the synthesized magnetic nanoparticles may be an optimistic application for high-frequency electronic devices and biomedical applications.