Search

Millimeter wave components, such as circulators and isolators, frequently use magnetic fields to break symmetry of the signal propagation and provide unidirectional signal transmission. While effective, these components have not seen the level of miniaturization of other millimeter wave components, primarily due to the discrete nature of the magnets used in the components. Using circulators in the 40-50 GHz range as a motivating application, requirements arise for the deposited films, namely immunity to eddy currents, sufficient magnetization to act as self-biasing magnets, and out-of-plane orientation of the self-biasing field. Based on these required properties, hexaferrite materials are selected for their strong magnetocrystalline anisotropy (MCA) and low conductance. The difficulty of integrating these components monolithically with monolithic microwave integrated circuits (MMIC) originates from the incompatibility of crystal structure with standard semiconductor materials and process conditions. Additive manufacturing using a composite of strontium hexaferrite (SrFe12O19) particles and photoresist has been chosen as a method to overcome the difficulties of integrating hexaferrite material to semiconductor substrates. Due to their large internal anisotropy field, the particles of strontium hexaferrite tend to rotate to the field direction instead of changing magnetization direction under application of an external magnetic field (less than the anisotropy field). We have developed a method for 3D printing composites of high strontium hexaferrite concentration (up to 20% by volume) in a liquid photoresist, SU8. Rotation of hexaferrite particles in polymer matrix and thus magnetic anisotropy has been demonstrated in the composite, which is subsequently cured to hold the physical position and orientation of the particles. The anisotropy of the self-biasing field provided by the films has been experimentally characterized, and a ferromagnetic resonance (FMR) frequency ~43 GHz has been observed. We have also characterized the viscosity of the particle-laden polymer at different particle concentrations. 3D printing of this composite with poling will make it possible to directly print magnetic components that require out-of-plane anisotropic magnetization.

Magnetic circuit components have long been the largest and most difficult components to miniaturize. Printed circuit board (PCB) fabrication methods cannot achieve small diameter, high aspect-ratio vias for high winding turn numbers to achieve high inductance, and microelectronics methods cannot achieve the high-quality and thick ferrite core materials. In this paper, we present an alternative breakthrough method of printed circuit fabrication to significantly reduce the effective via diameter for embedded magnetic devices, boosting the inductance per unit area. To reduce the effective via diameter, high-density via plugs are ex-situ fabricated and shaped, and then embedded into PCB substrate in the same process as standard magnetic core embedding. The structure of the plug is such that precise placement within the substrate, or alignment to the plug with the winding pattern, is not necessary. Devices presented in this paper use via plugs with an effective diameter of 40 μm and a theoretically unlimited aspect ratio, though refinements in the plug fabrication process are expected to reduce the via diameter down to 10μm. The process is experimentally demonstrated with a 14-turn racetrack shaped transformer; novel diagnostic methods using magneto-optic garnet films to image current paths are also demonstrated.

Ammonium dihydrogen phosphate (ADP) single crystals along with the incorporated 0.5 and 1% L-lysine, an organic molecule which possesses a good nonlinear response, were grown with the vision to meet the requirements of the optoelectronic industry. The inclusion of the L-lysine molecule in the crystal was confirmed by the XRD and EDX. The experiment not only confirms the inclusion level of the impurity but also the capability of the amino acid molecule to bond hydrogen within the crystal facet. A minor decrease in lattice parameters was reported for all ADP: L-lysine crystals compared with pure ADP. The structures of the grown crystals were identified as tetragonal with the space group I42d by the single-crystal XRD analysis. Vibrational signatures and functional groups were confirmed using FTIR spectroscopy. The thermal stability and decomposition temperatures of 0.5 and 1% L-lysine-added crystals were measured by TG/DTA and found to be 203 °C and 207 °C, respectively. The UV–visible transmission spectra prove a higher transparency for doped crystals as compared to pure crystals; therefore, these doped crystals can be considered the best option for the frequency doubling process in a broad range of visible and near-IR spectra. The improved hardness of the doped crystals was confirmed by the Vickers hardness data. The nonlinear optical (NLO) behaviour investigated using a second-harmonic generation (SHG) technique, indicating an efficient quadratic nonlinear coefficient of ADP: Lysine crystals at a 1064 nm initial wavelength, shows about 1.5-fold higher efficiency compared with undoped ADP.

Power components such as High Electron Mobility Transistors (HEMTs) are used for high power and high frequency applications. These tend to overheat and destroy their packaging and connections to the wire bondings. This paper presents planar micro-thermoelectric sensors (μTESs) developed to measure partial heat flow dissipated by the HEMTs to avoid the HEMTs from reaching critical temperatures. These sensors use the same active materials as well as the same fabrication process as the HEMTs, enabling them to be fabricated simultaneously for a simple integration. The HEMTs’ active layers consist in AlGaN/GaN heterostructures resulting in the formation of a 2D Electron Gas (2DEG) at the interface. Tension factors of 47 mV/(K.mm2) were obtained with these sensors and heat flows of 0.2 W to 7 W were measured.

Radiative cooling without energy consumption and environmental pollution holds great promise as the next-generation cooling technology. To date, daytime radiative cooling performance is still slightly low, especially in humid areas. In this work, we demonstrated that nanoporous polyethylene (Nano PE) film can improve solar reflectivity from 96% to 99%, thus boosting radiative cooling performance. Moreover, the experimental results in humid areas indicate that Nano PE films can improve radiative cooling performance by ∼76% in a clear day and 120% in a day with few clouds. Additionally, compared with ordinary PE films, thin Nano PE films have significantly higher weather fastness and mechanical strength. More importantly, nano PE films can scatter part of visible light, thus suppressing the generation of light pollution in practical applications. Lastly, the modeling results reveal that with Nano PE films, more than 95% of China's areas can achieve daytime cooling performance. Our work can boost the development of radiative cooling technology with a very low cost.

Transparan İletken Oksit (TCO) ince filmler günümüzde güneş pilleri, LED’ler, lazerler gibi optoelektronik cihazlarda sıklıkla kullanılmaktadır. Bu kontakların kullanımı cihazların verimliliğini doğrudam etkilemektedir. Bu çalışmanın amacı heteroeklemli güneş hücrelerinin (HJSCs) (n+) a-Si:H yüzünde ve yüksek elektron hareketliliği olan tranzistörlerde (HEMT) kullanmak üzere atomik katman kaplama (ALD) tekniği kullanarak alüminyum katkılı çinko oksit (AZO) üretmek ve optimize etmektir. Bu çalışmada büyütme sıcaklığı ve alüminyum katkılama oranının ALD’de büyütülmüş AZO’nun yapısal, elektriksel ve optik özelliklerine etkisi çalışılmıştır.Sonuçlar göstermiştir ki filmler görünür bölgede %80-90 arasında ışık geçirgenliğine, düşük elektriksel rezistansa (2.04x10-3 ohm.cm) ve 5.25 cm2/V.s değerinde mobiliteye sahiptir., Transparent Conductive Oxide (TCO) films are widely used in optoelectronic devices, such as solar cells, LEDs, and Lasers. Utilization of these contacts directly affects the device efficiencies. Purpose of this study is to produce and optimize properties of Aluminum doped Zinc Oxide (AZO) using a vapor phase technique, Atomic Layer Deposition (ALD) for (n+) a-Si:H surface of silicon Heterojunction Solar Cells (HJSCs) and High Electron Mobility Transistor (HEMT) applications. This study is focused on the effect of the deposition temperature and aluminum atomic concentration on structural, electrical and optical properties of ALD grown AZO ohmic contact films. The results show that as-deposited films have 80-90% transmittance in the visible spectra, low resistance (2.04x10-3 ohm.cm) and mobility value of 5.25 cm2/V.s.

У статті пропонується експериментально дослідити гофрований конічний випромінювач з метою підтвердження теоретичних розрахунків р Г  коефіцієнта відбивання електромагнітного поля від розкриву досліджуваного гофрованого конічного випромінювача. Дослідження ґрунтуються на впливі електромагнітних полів на фізико-хімічні процеси в біологічних об’єктах. Теоретичні дослідження показали, що для промислового використання необхідний випромінювач з діапазоном частот 30-31 ГГц і діаметром не більше 30 мм, який повинен забезпечити ширину діаграми направленнності в межах 24-30 мм. Для дослідження використовувався виготовлений конічний гофрований опромінювач довжина якого від розкриття до фазового центру дорівнює 21 мм. Діаметр випромінюючого розкриву дорівнює 25 мм. Основні геометричні параметри гофри: h= 2,5 мм, с = 1,25 мм, b= 1,25 мм. Для живлення розглянутого випромінювача використовується перехід з прямокутного хвилеводу перетином 7,2 × 3,4 мм на круглий діаметром 7 мм. Вимірювання проводились на частоті 30 ГГц. Оскільки модуль коефіцієнта відбиття від випромінювача повинен бути близький до нуля, то для точних вимірювань необхідно використовувати метод рефлектометра.

The pulsed current has been proposed to achieve fast charging and extend the lifetime of lithium-ion (Li-ion) batteries. However, the optimal condition of the pulsed current is still inconclusive in previous studies. This article experimentally investigated the effect of the low-frequency positive pulsed current (PPC) charging on the lifetime and charging performance of Li-ion batteries. A two-stage degradation model of Li-ion batteries is developed to determine the inhibitory effect of the PPC on degradation mechanisms at different aging stages. Moreover, the changes in the internal resistance (IR) and the incremental capacity (IC) curve are provided to thoroughly explore the effects of the PPC on the degradation of Li-ion batteries. Compared with the traditional constant current (CC) charging, the lifetime, maximum rising temperature, and energy efficiency of the Li-ion batteries that were cycled by the PPC charging are improved by 81.6%, 60.5%, and 9.1%, respectively, after 1000 cycles. Therefore, low-frequency PPC charging should be considered as a promising charging strategy for Li-ion batteries.

High light-harvesting efficiency and low interfacial charge transfer loss are essential for the fabrication of high-efficiency quantum dot-based solar cells (QDSCs). Increasing the thickness of mesoporous TiO2 films can improve the loading of pre-synthesized QDs on the film and enhance the absorbance of photoanode, but commonly accompanied by the increase in the unfavorable charge recombination due to prolonged electron transmission paths. Herein, we systematically studied the influence of the balance between QD loading and TiO2 film thickness on the performance of QDSCs. It is found that the relative thin photoanode prepared by the cationic surfactant-assisted multiple deposition procedure has achieved a high QD loading which is comparable to that of the thick photoanode commonly used. Under AM 1.5G illumination, Zn–Cu–In–Se and Zn–Cu–In–S based QDSCs with optimized 11.8 μm photoanodes show the PCE of 10.03% and 8.53%, respectively, which are comparable to the corresponding highest PCE of Zn–Cu–In–Se and Zn–Cu–In–S QDSCs (9.74% and 8.75%) with over 25.0 μm photoanodes. Similarly, an impressive PCE of 6.14% was obtained for the CdSe based QDSCs with a 4.1 μm photoanode, which is slightly lower than the best PCE (7.05%) of reference CdSe QDSCs with 18.1 μm photoanode.

A general high-efficiency time-modulated module and harmonic beam scanning time-modulated array (TMA) are proposed and investigated in this paper. By introducing the periodically controlled phased-shifters, a significant improvement on theoretical overall efficiency and transmitted bandwidth can be realized in harmonic beam scanning. Then equivalent cascade structure of the general modulation module is proposed for RF circuit simplification and practicability in actual applications. Theoretical derivation and simulation results show that increased efficiency, 100% feeding network efficiency and theoretical overall efficiency tending to 100% without consideration of insertion loss, can be achieved with the increase the phase-shifter states when only a single sideband is utilized. Compared to the existing state-of-the-art harmonic beam scanning TMAs, the proposed TMA exhibits a much higher overall efficiency while keeps a similar hardware complexity. Additionally, with acceptable increase of circuit complexity less than existing works, similar level of the wide transmission bandwidth can also be achieved. To experimentally verify the feasibility of the proposed general design, a 4-bit time-modulated module with reconfigurable states and the corresponding 8-element harmonic beam scanning TMA are fabricated and tested. The experiments on signal transmission and harmonic beam scanning demonstrate the effectiveness of power loss reduction and improvement in transmitted bandwidth with the increase of modulation phase states.

This paper presents performance of gallium arsenide (GaAs) light emitting diode (GaAsLED) for wireless systems such as mobile communication system. Due to the fact mobile communication systems require effective signal transmission it is possible to aid with quantum photonic devices such as light emitting diodes at the transmitting ends which can provide effective and efficient photons transmission from one base station (BS) to another base station through the optical link under ground surface. At the receiving end the photons in the form of light are fed into a photodetector for further information processing as electrical signals. Simulation results portray the current-voltage characteristics of quantum photonic device namely GaAs LED for various scenarios. Further, the bit error rate performance analysis of GaAsLED cellular system is analysed in indoor and outdoor fading channels. The obtained results could be used for the implementation of 5G systems in mobile wireless systems.

Eutectic gallium indium (E-GaIn) alloy based liquid metal is considered to be a promising material for manufacturing interconnects in stretchable electronics based applications due to its high electrical conductivity and inherent mechanical deformability. The current work demonstrates an easy and single step method of fabricating micron-sized (the width of ~ 200 μm) highly conducting stretchable interconnects by stencil printing of E-GaIn on stretchable polydimethylsiloxane (PDMS) substrate. The obtained stretchable pattern showed excellent electrical and mechanical property by exhibiting a low average resistance value of ~ 6.5 O even at elongation up to 50%. Moreover, it showed superior stability against stretching cycles with just ± 0.12 Ω of variation in resistance. A commercial light emitting diode was mounted on the patterns and illuminated to describe the role of interconnects in a realistic circuit.

The transparent relaxor ferroelectric ceramics of the system lanthanum modified lead magnesium niobate (PLMN-13PT) have been investigated for a variety of electro-optic, properties; good electro-optic switching times and modest half-wave voltages. In this work, the dependence of microstructural, structural, dielectrical, optical, and electro-optical properties in function of Rare Earth (RE = Tm3+, Nd3+, Yb3+, Er3+ and Ho3+) has been reported. PLMN-13PT:RE with excellent properties were obtained, highlighting the electrical, optical, and electrooptical properties, suitable for the fabrication of multifunctional devices. The most prominent or important feature is the largest quadratic Electro-optic coefficient achieved ((9.37 ± 0.39) × 10−16 m2/V2) corresponding to PLMN-13PT:Ho transparent ceramics. This result in addition to the electrical and photoluminescence properties becomes a promising alternative to building multifunctional devices.

In this work comparative analysis of the effect of various active materials and use of photonic crystal in active layer of organic photodetector in the wavelength range between 400 nm and 700 nm is described. The active organic material used in the photodetector is PH3T: PCBM. The various materials used for the analysis of absorbance and transmittance between the active layer are nc_ZnO organic material and Al2O3, GaAs and silicon nitride (Si3N4) semiconductor materials. The maximum absorbance reported in this work are 80.0969%, 80.0451%, 75.4784%, 80.8878%, 76.8223% for without PC on nc_ZnO organic layer, with nc_ZnO PC on nc_ZnO layer, Al2O3, GaAs and silicon nitride (Si3N4) semiconductor materials with PC. The absorption is almost flat between 70% and 80% for without PC and for with PC having materials nc_ZnO, Al2O3 and GaAs between the wavelength range 450 nm to 630 nm. We have achieved an improvement in the absorption at wavelength ranging from 630 nm to 700 nm by using PC with nc_ZnO organic material.

The current manuscript introduces a dielectric regulated charge plasma based Triple metal Gate Tunnel Field Effect Transistor (CPB-TG-TFET) biological sensor. In which a nano-cavity is introduced below the gate and source electrode to detect the biological molecules like amino acids (AAs), protein, etc. The proposed P + and N + regions are contrived depending upon the electrode’s work function on the device’s silicon body. The effects of metal electrode work function modulation, gate electrode length variation and gate oxide thickness variation are analyzed for improving band-to-band tunneling efficiency at the source- channel transition. The proposed structure shows noticeable sensitivity results for neutral and charged biomolecules. The sensitivity of the neutral biomolecules having higher dielectric constant(Kp) is observed higher; the surface potential sensitivity of the Gelatin (Kp = 14) is estimated as 3 . × 10 10 which is 13% and 35% higher than the sensitivity of Keratin (Kp = 10) and Bacteriophage T7 (Kp = 5) respectively at the cavity length of 30 nm.

In this paper a recess gate AlGaN/GaN HEMT on beta gallium oxide (BGO) is designed and analysed using Silvaco ATLAS TCAD software. The DC and RF performance of the device is compared with a schottky gate AlGaN/GaN HEMT on BGO substrate. For optimizing the gate recess depth, three variations with recess depths 6 nm, 12 nm and 20 nm is also simulated. A highest transconductance of 0.4 mS/ µm is observed for recess gate AlGaN/GaN HEMT on BGO substrate with a recess gate depth of 20 nm with a decrease in current density. The radio frequency performance is also highest for the recess gate AlGaN/GaN HEMT with recess gate depth of 20 nm. The device exhibited a maximum oscillation frequency of 2.6 THZ which is highest till reported.

One of the most important industrial applications of lasers is the treatment of materials. In this work pulsed Nd:YAG laser of wavelength (1064 nm) was used to precipitate the prepared solution of CuO nanoparticles in the form of thin films using energies (300, 400, 500 and 600 mJ) at a distance (10 cm) and for an irradiation period (20 s) for each energy. The optical properties of the material were examined, which include transmittance, absorbance and some other optical constants, in addition to calculating the optical energy gap and knowing the effect of increasing the laser energy on its values.

Functional nanomaterials possess exceptional multi-physical (e.g., mechanical, electrical and optical) properties compared with their bulk counterparts. To facilitate both synthesis and device applications of these nanomaterials, it is highly desired to characterize their multi-physical properties with high accuracy and efficiency. The nanomanipulation techniques under scanning electron microscopy (SEM) has enabled the testing of mechanical and electrical properties of various nanomaterials. However, the seamless integration of mechanical, electrical, and optical testing techniques into an SEM for triple-field-coupled characterization of single nanostructures is still unexplored. In this work, we report the first SEM-based nanomanipulation system for high-resolution mechano-optoelectronic testing of single semiconductor InGaN/GaN nanowires (NWs). A custom-made optical measurement setup was integrated onto a four-probe nanomanipulator inside an SEM, with two optical microfibers actuated by the nanoma-nipulator for NW excitation and emission measurement. A conductive tungsten nanoprobe and a conductive atomic force microscopy (AFM) cantilever probe were integrated onto the nanomanipulator for electrical nanoprobing of single NWs for electroluminescence (EL) measurement. The AFM probe also served as a force sensor for quantifying the contact force applied to the NW during nanoprobing. Using this unique system, we examined, for the first time, the effect of mechanical compression applied to an InGaN/GaN NW on its optoelectronic properties.

CdSe, Cu2Se and CdSe:Cu2Se nanocrystal (NC) thin films were synthesized using vacuum deposition technique. The open aperture Z-scan measurements carried out using 7 ns pulses at 532 nm revealed that the CdSe and Cu2Se samples exhibited saturable absorption (SA) at 30 µJ. A nonlinear optical switching from saturable absorption (SA) to reverse saturable absorption (RSA) is observed by increasing the laser input intensity.

Semiconductor Quantum Dots have unique properties, such as the quantum size effect that provide the breakthrough in optoelectronic devices. The small effective mass of electron and hole open-up an avenue of wide bandgap tunability in InAs Quantum Dots (QDs), making them an attractive material for solar cell application. Therein, 4x4 Luttinger Kohn Hamiltonian method is used to calculate the absorption co-efficient of epitaxially grown InAs QDs. Further, we studied the size-dependent absorption co-efficient and the barrier material model of InAs QDs capping with InP and GaAs. Our theoretical simulation predicts the efficiency of InAs/GaAs and InAs/InP system in the intrinsic layer of p-i-n structure solar cells.

The effect of planar photonic crystal on CZTS/CdS solar cell is systematically investigated. The reflective properties of PhC ARC which consists of the periodic stack of ZnO and HfO2 with two numbers of periods having quarter wavelength thickness are analyzed. Similarly, the DBR having periodic stacks of HfO2 and ZnO dielectric layers with four numbers of periods having half wavelength thickness in CZTS/CdS solar cells are explored. Moreover, the results of the photovoltaic properties of CZTS/CdS solar cells are also analyzed. The outcome of the findings obtained from the computation using the transfer matrix method are very well agreeable with the recent literature. The planar (ZnO /HfO2)2 PhC ARC and (ZnO/HfO2)4 DBR has been expected to provide significant improvement in the performance of CZTS/CdS solar cells.

Graphitic-carbon nitride has displayed a splendid future in cutting–edge optoelectronic gadgets, because of exceptional and promising physicochemical properties. In the course of recent years, lot of examination witnessed tremendous advancement in graphitic-carbon nitride as photocatalyst. In this work, graphitic-carbon nitride thin film was fabricated using cost-effective doctor-blade method. The structural, optical and electrical properties of the graphitic-carbon nitride thin film are investigated. Structural and morphological characterization result affirms the development of graphitic-carbon nitride thin film. Optical properties of graphitic-carbon nitride thin film are done by UV–Visible spectroscopy and photoluminescence measurements. The wide absorbance range, reduction in bandgap (1.88 eV) and the presence of luminescence center obviously indicate the future of graphitic-carbon nitride thin film in the optoelectronic application. Hall Effect measurement result reveals n-type conductivity and shows the carrier concentration value of −1.42X 1018 cm−3.

Microstrip silicon detectors are one of the key trackers in particle physics experiment like LHC at CERN. There is a continuous need to improve upon various parameters of detectors like breakdown voltage, leakage current, full depletion voltage, post radiation hardness, charge collection efficiency and low thermal budget. We have introduced new doping less silicon microstrip detector for the very first time and investigated the various parameter of the detector. We have studied and compared the results of doped and dopingless charge plasma silicon microstrip detector. Our study shows improvement in Preradiation breakdown voltage of 2200 V with leakage current of 5.2 pA/um in dopingless charge plasma microstrip detector as compared to 1500 V of breakdown voltage with leakage current of 6.5pA/um as in the case of doped silicon microstrip detector.

In this study, three samples of GaN/AlInN/AlN/Al2O3 high electron mobility (HEMT) structures are investigated with high resolution X-ray diffraction (HR-XRD) technique. Peak positions and peak broadenings are used in calculations, gained from rocking curves. Structural quality is determined from symmetric and asymmetric peak planes. Mosaic defects such as treadening dilocations (TDs), tilt and twist angles, lateral and vertical crystallite lengths are determined by using Williamson Hall (WH) method. In addition to these, surface morphology is also investigated by atomic force microscopy (AFM). It is noticed that crystal quality of epitaxial layers decrease in the order of samples C, B and A. Al compositions for samples A, B and C are found as %87.4, %86.6 and %86.4, respectively by using Vegard’s law.

The fast and high response detection of neurotoxic H2S is of great importance for the environment. In this paper, directly electrospinning technology on the ceramic tube is developed to improve the response of H2S detector based on superlong SnO2 fibers. The submillimeter continuous fibers are deposited directly on ceramic tubes by in-situ electrospinning method and can keep morphology of fibers during calcination. By employing this technology, CuO-doped SnO2 fiber H2S detectors are fabricated, and 10% atom CuO-doped SnO2 H2S detector shows the highest response of 40 toward 1 ​ppm ​H2S at 150 ​°C while the response is only 3.6 for the H2S detector prepared in traditional route. In addition, the in-situ electrospinning H2S detectors show faster response and recovery compared to the H2S detectors fabricated by the conventional way. The high and fast response of H2S detectors based on in-situ electrospinning can be ascribed to the continuous fiber structure and CuO modification. The present in-situ electrospinning technology may provide a new strategy for the development of other gas-detectors and bio-detectors with fast and high response.

In this paper, series-connection of SiC MOSFETs has been attempted with the help of an active gate driving (AGD) technique. The gate currents of SiC MOSFETs are actively controlled in such a way that several devices can switch fast (within 50ns) even in the presence of a moderate amount of gate pulse delay mismatch and jitter in the gate pulse. This enables the AGD's to share gate pulse signal information among each other. Such a feature can reduce the cost of the net solution by reducing the number of optical cables required for the gate pulse transmission. In addition to this, the AGD is designed in such a way that fast switching can be achieved even in the presence of moderate parasitic inductance in the layout. The proposed AGD technique is experimentally verified in a double pulse test (DPT) setup with two and four switching devices in series using 32A, 1kV CREE SiC MOSFETs. The experimental results show a turn-on, turn-off switching times of 45ns, 34ns respectively at 35A load current. The AGD has also shown 47% reduction in the turn-off switching losses compared to the passive gate driving technique.

A gallium nitride (GaN)-based resonant step-up converter is proposed for the application in the satellite electric propulsion (EP) system. This converter consists of a full-bridge inverter, a resonant tank and a multi-stage Cockcroft-Walton (CW) voltage multiplier to provide a high gain. Additionally, the air-core transformer is introduced due to the megahertz switching frequency allowed by the GaN device. Thus, the limited magnetizing inductance of transformer and the remarkable junction capacitance of diode have to be carefully considered in the resonant tank design, especially after considering that this converter normally operates at the light load in the EP system. In this work, the 4-order LCLC resonant converter is investigated. The recommended parameter selection for the 4-order resonant tank is also provided. A 1.2-MHz, 23-V/2.5-kV, and 6-W prototype is demonstrated. It achieves a low harmonics distortion and a low power loss with the zero voltage switching (ZVS).

This paper demonstrates the developments toward a high performance monolithic wheeled structure horizontal dual-axis (pitch (X-axis) and roll (Y-axis)) microelectromechanical system (MEMS) gyroscope based on off-plane coupling suppression silicon gratings. Gyroscopes have been fabricated with a silicon-on-glass fabrication process with vacuum-sealed in a metal packaging. The featured gyroscope operates in split-mode with the bandwidths of two axes devices both ~70Hz. By unitizing two individual active restraining control loops that adjust the quadrature amplitude via differentially biasing the silicon gratings in real-time, the off-plane mechanical couplings of the two sense modes are significantly reduced by ~95 and ~30 times, which enables ~25-fold and ~56-fold improvements in the bias instability for a typical dual-axis device. Tactical-grade performances are achieved for both the X-axis and Y-axis gyroscopes with angle random walk (ARW) of 0.02 deg/h and 0.045 deg/h along with in-run bias instability (BI) of 0.26 deg/h and 0.65 deg/h respectively without any temperature compensation. The current preliminary results show great potential to achieve navigation grade precision by employing the mode-matching technique in the future. The use of silicon gratings for out-of-plane coupling reduction also provides an effective way to build a high performance planar monolithic chip inertial measurement unit (IMU).

An interesting phenomenon was found that fluorophore was introduced into ionic liquid (IL) to magnify fluorescence signal via the thermally activated delayed fluorescence process; thus up to 15 fold enhancements were achieved. Hence, we reported a succinct enhanced luminescence strategy to reduce single-triplet energy split by the tunability of ILs. This strategy could be extended to more kinds of ILs by the virtue of a preliminary DFT calculation screening. Moreover, the optical feature of IL sensor made it a promising candidate as a gas fluorescence sensor.

Evaluating the robustness of power semiconductor devices is key for their adoption into power electronics applications. Recent static acceleration tests have revealed that SiC MOSFETs can safely operate for thousands of hours at a blocking voltage higher than the rated voltage and near the avalanche boundary. This work evaluates the high-bias robustness of SiC MOSFETs under continuous, hard-switched, turn-off stresses with a dc-bias higher than the device rated voltage. Under this high-bias switching condition, SiC MOSFETs show degradation in merely tens of hours at 25°C and tens of minutes at 100°C. Two independent degradation and failure mechanisms are unveiled, one present in the gate-oxide and the other in the bulk-semiconductor regions, featured by the increase in gate leakage current and drain leakage current, respectively. The second degradation mechanism has not been previously reported in the literature; it is found to be related to the electron hopping along the defects in semiconductors generated in the switching tests. The comparison with the static acceleration tests reveals that both degradation mechanisms correlate to the high-bias switching transients rather than the high-bias blocking states. These results suggest the insufficient robustness of SiC MOSFETs under high-bias, hard switching conditions and the significance of using switching-based tests to evaluate the device robustness.

Dynamic avalanche (DA) phenomena and current filament (CF) formation are two extreme conditions observed in high-power devices, setting the maximum limit on turn-on/off current capability and di/dt in Silicon-based bipolar devices. The properties of the Silicon Carbide (SiC) material enable devices with increased resilience for DA and CF compared to Si counterparts, and thus the SOA limits may be extended. In this study, the limit of DA and CF in SiC-based semiconductor structures are investigated by numerical TCAD simulations, for different current levels, di/dt, and temperatures for high-voltage devices (e.g., 20 kV class). DA is first indicated for di/dt beyond 105 kA/μs for current densities in the range of 50–1000 A/cm2, at 448 K. Similarly, stray inductance induced avalanche conditions are initiated above 33 kA/μs, while CF is initiated for di/dt starting from 83 kA/μs for current densities in the range of 8.3 kA/cm2. Moreover, the effects of the stray inductance in the main circuit loop are studied which may cause critical voltage transients during certain operating conditions. The outcome of the study may be useful to determine safe-operating-area limits and to be used as input for power electronic converter design as well as gate driver design for high-power electronic systems.

In this work, we demonstrate the realization of L-Shaped Schottky Barrier FET as a biosensing device with improved sensitivity. The proposed device uses dual material gate with work functions of 4.2 eV (Al) and 4.8 eV (Cu) and Hafnium Oxide (HfO2) as the gate dielectric. In order to detect the biomolecule, a nano-gap cavity is created in the vertical gate (Gate1) by etching out the oxide. The electrical characteristics of biomolecules such as dielectric constant and charge density modulate the Schottky Barrier width, which in turn, changes the drive current of the device. Various sensitivity parameters have been thoroughly investigated at VDS = VGS = 0.5V and a comparative analysis with the conventional device has been performed. The results so obtained reveal that ION sensitivity of the proposed device is much better for both neutral as well as charged biomolecules (maximum of 21x for neutral, at K=12; 20x for charged biomolecules at ρ=-5x1010cm-2, at K=12). Besides this, the ION/IOFF sensitivity, transconductance (gm) sensitivity and selectivity show similar improvements. Further, the proposed device shows better sensitivity performance at low as well as at higher temperatures as compared to the state-of-the-art biosensing devices.

The goal of this paper is to advance the understanding of the impact of hard switching on the dynamic performance of GaN-based HEMTs. To this aim, we developed a fast (10 V/ns) on-wafer system for testing devices in hard switching. The system has been used to study the reliability of several WG = 2 mm p-type GaN HEMTs with different LGD or buffer properties. First, we show that by optimizing the drain node capacitance, we can speed-up the hard-switching transition to a few ns, even on-wafer level. Second, repeating the experiment by using multiple frequencies, from 1 kHz to 100 kHz, we demonstrate that, in real-world applications, cumulative turn-on stress has a much stronger effect on RON compared to off-state stress. Third, by comparing the results on identical devices having shorter LGD, we pinpoint hot electrons as the main mechanism in the device degradation, ruling out the contribution of self-heating. Finally, by comparing three wafers with different processing conditions (different passivation, different buffer) we suggest that trapping phenomena related to hot electrons happen in ns time scale and that the properties of the buffer can significantly impact the dynamic performance of the devices in hard switching.

Junction temperature fluctuation is the main cause of failure of power devices including silicon carbide (SiC) MOSFETs, and active junction temperature control is an effective way to improve their reliability. Most existing methods of active junction temperature control rarely consider the system efficiency and the complexity of hardware implementation, which limits their applications. This paper proposes an active junction temperature control method for SiC MOSFETs based on a resistor-less gate driver, which consists of two auxiliary MOSFETs with adjustable gate-source voltages. Hence, the switching loss of the SiC MOSFET can be continuously and accurately adjusted to mitigate the efficiency suffer with the junction temperature control. The power loss model of SiC MOSFETs with the proposed gate driver was established. The design principle of the junction temperature controller is introduced. The experimental results show that the junction temperature fluctuation is reduced by 24.1%, and that the lifetime of the SiC MOSFET is prolonged by 3.92 times via using the proposed junction temperature control method. The energy loss of the prototypical inverter is decreased by 4.15% over the whole testing period. The experiment was conducted with SiC MOSFETs, and the proposed method is also suitable for other Sibased semiconductor devices.

In this work, the influences of P-well design and turn-off gate-to-source bias on the surge robustness of SiC MOSFET’s body diode are studied. Devices with high and low P-well doping concentration designs are stressed with surge current pulses when gate-to-source is biased with 0V or -5 V. The gate-to-source bias is found to have effects on the surge capability of the low P-well doping designed device. In the case of 0 V bias, the channel is prone to turning on and acquires a higher surge capability than the devices under the -5 V. On the other hand, the surge capability of high P-well doping designed device is found less influenced by the gate-to-source bias. Furthermore, threshold voltage instability after repetitive surge pulses is also investigated. The device with low P-well doping shows better threshold stability due to its lower interface trap density. Based on the results above, a design methodology is proposed from the view of device mechanism and operation condition. Relatively low P-well doping design and negative gate bias are recommended for SiC MOSFET, as they can improve the single pulse surge robustness of body diode and minimize the threshold voltage instability in repetitive surge pulse events.

The near-infrared (NIR) persistent luminescence materials (PLMs) can remain long-lasting luminescence after removal of the excitation light, which permits bioimaging with high sensitivity owing to the absence of background fluorescence interference from in situ excitation. Recently, the NIR PLMs have aroused intensive research interest in bioimaging. However, the optimal excitation wavelength of current NIR PLMs is located in the ultraviolet region with shallow tissue penetration, making it difficult to activate effectively in vivo, and seriously hindering their further application in bioimaging. Herein, we report a novel kind of Cr3+ ions and Y3+ ions co-doped NIR PLM, Zn1.3Ga1.4Sn0.3O4:Cr3+,Y3+ (ZGSCY), which emits NIR persistent luminescence at 696 nm. Compared with Zn1.3Ga1.4Sn0.3O4:Cr3+ (ZGSC) excited by the light with a wavelength in the biological window (>650 nm), after being co-doped with Y3+ ions, the NIR persistent luminescence performance of ZGSCY is significantly improved because of the increase of trap concentration in the matrix. In addition, we synthesized ZGSCY nanoparticles (NPs) by the combustion method, which exhibit excellent optical properties after being excited by the light with a wavelength in the biological window. After surface modification with PEG, the ZGSCY NPs present low cytotoxicity. Notably, due to the co-doping of Y3+ ions, the signal-to-noise ratio (SNR) of ZGSCY NPs in vivo imaging is about 1.8 times higher than that of the ZGSC NPs. Furthermore, the rechargeable in vivo imaging and passive tumor-targeted imaging are successfully achieved by activating with a light-emitting diode (LED, 659 nm) after intravenous injection of ZGSCY. Thus, this kind of NIR PLM with high excitation efficiency performance in the biological window is expected to promote its biomedical application in deep tissues.

Multiplexing circuits in pixelated PET detectors are being studied with the goal of minimizing the degradation of detector performance. The purpose of this study was to develop a diode-based symmetric charge division (SCD) circuit with reducing the crosstalk caused by the leakage currents of adjacent channels connected in rows and columns. Four different SCD circuits (diode-based SCD with grounding path, diode-based SCD, resistor-based SCD with grounding path and resistor-based SCD) were constructed and their performance was evaluated and compared after being combined with a PET detector consisting of LYSO crystals optically coupled with SiPM. The diode-based SCD circuit with grounding path achieved a crosstalk ratio, energy resolution, coincidence timing resolution (CTR) and mean peak to valley ratio of 0.02, 14.3%, 0.5 ns and 27.9: 1, respectively; the diode-based SCD circuit achieved 0.03, 15.9%, 0.7 ns and 19.4: 1, respectively; the resistor-based SCD circuit with grounding path achieved 0.04, 14.5%, 0.9 ns and 19.4: 1, respectively; the resistorbased SCD circuit achieved 0.05, 17.8%, 1.8 ns and 17.7: 1, respectively. These results indicate that the proposed SCD has the potential to improve not only the crosstalk but also the energy linearity, energy resolution, and coincidence timing resolution characteristics in PET detectors.

Low quality (Q) factor is often the limiting factor for high performance carbon nanotube (CNT) resonators. The most commonly used approach to enhance the Q factor of CNTs is to reduce/eliminate the intrinsic defects. Herein, we show surprisingly that hole defects of suitable size and position are able to enhance the Q factor of CNT, which strongly contradicts to the common notion that the presence of defects promote intrinsic dissipation via defects dissipation. By analyzing the strain distribution, we find that such abnormal enhancement in Q factor of defected CNT originates from a coupling competition mechanism between the atomic mismatch around defected atoms and the thermoelastic damping. Although the presence of holes will introduce an additional defect dissipation source, suitable holes are capable of reducing the energy dissipation arisen from the thermoelastic damping, through changing the spatial strain field of defected CNT. This coupling competition mechanism provides a new route for designing high performance CNT resonators via defects engineering.

Background: Nanowires (NWs) have received extensive attention as the candidate materials for transparent conductive films (TCFs) in recent years. To date, the aligned nanowire (NW)- based TCFs with the same arrangement direction have shown superior characteristics to their random counterparts in applications. Objective: To fully develop the potential of NW TCFs in devices and provide inspiration for the development of subsequent NW alignment processes, this review summarizes state-of-the-art alignment techniques and emphasizes their mechanisms in detail from multiple perspectives. Methods: According to the mechanism of NW alignment, this review divides these techniques into seven categories, i.e., the assisted assembly of fluid flow, meniscus, pressure, template, electromagnetic field, contact and strain, and analyzes the characteristics of these techniques. Moreover, by briefly enumerating the applications of aligned NW films in solar cells, organic light-emitting diodes, and touch screens, the superiority of aligned NW films over random NW films is also addressed. Results: Contact-assisted assembly exhibits the best arrangement effect, reaching a 98.6% alignment degree within ±1°. Under the same conditions, shorter NWs show better alignment in several cases. The combination of various assembly techniques is also an effective means to improve the alignment effect. Conclusion: There is still room for improvement in the precise control of NW position, density, and orientation in a simple, efficient and compatible process. Therefore, follow-up research work is needed to conquer these problems. Moreover, a process that can realize NWs’ alignment and film patterning simultaneously is also a desirable scheme for fabricating personalized devices.

Background: Al is the promising candidate for deep UV and longer wavelength range plasmonic applications. But it is difficult to have the pure aluminium nanostructure as it is easily oxidized, forming a thin layer of Al2O3. In this paper, we have evaluated the field enhancement of oxide layer on metallic shell (Al-Al2O3 and Au-Al2O3) for single and dimer core-shell configuration and showed potential of the oxide layer in SERS. Methods: The Finite Difference Time Domain (FDTD) has been used to evaluate the LSPR and field enhancement of single and dimer Al-Al2O3 and Au- Al2O3 nanostructure. Results: The results exhibit the tunable plasmon resonance on varying the inner and outer radii of the Al2O3 shell. A redshift and decrease in enhancement were observed as shell thickness increases, whereas on increasing the core size, the enhancement increases in the case of Au-Al2O3 and decreases in Al- Al2O3 due to quadrupole contribution. But on comparing the Au-Al2O3 with Al-Al2O3 for the same particle size, Al-Al2O3 shows larger enhancement because Au has to compete with its interband transition. Conclusion: By optimizing the thickness of the shell and core size, it can be concluded that an ultrathin shell of Al2O3 can give higher enhancement. With Al as a core metal, the enhancement increases as compared to Au-Al2O3. Since a single Al-Al2O3 nanoshell has shown a huge enhancement we have considered the multimer configuration of two identical nanoshells. Due to coupling between two nanoshells a huge increase in enhancement factor ~1012 was observed for Al-Al2O3 dimer nanoshell in the UV region.

A 650-V/84-m normally-off GaN/SiC cascode device is demonstrated with systematic static and dynamic characterizations. The cascode device features a low voltage enhancement-mode (E-mode) GaN-HEMT to enable normally-off gate control, and a 650 V normally-on SiC JFET provides the high-voltage blocking capability. The GaN/SiC cascode device exhibits many application-desired behaviors, including reverse conduction capability, avalanche breakdown capability, thermally stable threshold voltage, low input/output capacitances, no dynamic RON degradation, and negligible dynamic VTH shift. In addition, a customized double-pulse test board is built to evaluate the switching performance of this cascode device and other 650-V SiC-based power devices. This cascode device adopting low-voltage GaN HEMT has low QGRON and exhibits excellent switching performance. The switching losses (EON and EOFF) are much smaller than that of 650-V Si/SiC cascode device and comparable to that of the state-of-the-art 650-V SiC MOSFETs.