Low-firing and temperature stability regulation of tri-rutile MgTa_(2)O_(6)microwave dielectric ceramics

A glass frit containing Li_(2)O-MgO-ZnO-B_(2)O_(3)-SiO_(2)component was used to explore the low-temperature sintering behaviors and microwave dielectric characteristics of tri-rutile MgTa_(2)O_(6)ceramics in this study.The good low-firing effects are presented due to the high matching relevance between Li_(2)O-MgO-ZnO-B_(2)O_(3)-SiO_(2)glass and MgTa_(2)O_(6)ceramics.The pure tri-rutile MgTa_(2)O_(6)structure remains unchanged,and high sintering compactness can also be achieved at 1150℃.We found that the Li_(2)O-MgO-ZnO-B_(2)O_(3)-SiO_(2)glass not only greatly improves the low-temperature sintering characteristics of MgTa_(2)O_(6)ceramics but also maintains a high(quality factor(Q)×resonance frequency(f))value while still improving the temperature stability.Typically,great microwave dielectric characteristics when added with 2wt%Li_(2)O-MgO-ZnO-B_(2)O_(3)-SiO_(2)glass can be achieved at 1150℃:dielectric constant,ε_(r)=26.1;Q×f=34267 GHz;temperature coefficient of resonance frequency,τ_(f)=-8.7×10^(-6)/℃.

Solvent-free fabrication of broadband WS2 photodetectors on paper

Paper-based devices have attracted extensive attention due to the growing demand for disposable flexible electronics.Herein,we integrate semiconducting devices on cellulose paper substrate through a simple abrasion technique that yields high-performance photodetectors.A solvent-free WS_(2) film deposited on paper favors an effective electron-hole separation and hampers recombination.The as-prepared paper-based WS2 photodetectors exhibit a sensitive photoresponse over a wide spectral range spanning from ultraviolet(365 nm)to near-infrared(940 nm).Their responsivity value reaches up to~270 mA W^(−1) at 35 V under a power density of 35 mW cm^(−2).A high performance photodetector was achieved by controlling the environmental exposure as the ambient oxygen molecules were found to decrease the photoresponse and stability of the WS_(2) photodetector.Furthermore,we have built a spectrometer using such a paperbased WS_(2) device as the photodetecting component to illustrate its potential application.The present work could promote the development of cost-effective disposable photodetection devices.

Synergically enhanced piezocatalysis performance of eco-friendly(K_(0.52)Na_(0.48))NbO_(3) through ferroelectric polarization and defects

Piezocatalysis has attracted unprecedented research interest as a newly emerging catalysis technology.However,the inherent insulating property of ferroelectric materials ultimately leads to the poor vibration-electricity conversion ability.Herein,this work reports the(K_(0.52)Na_(0.48))NbO_(3) ferroelectric ceramics(KNNFCx),for which the FeCo modification strategy is proposed.The substitution of the moderate amount of FeCo(x=0.015)at Nb site not only optimizes ferroelectricity but also produces beneficial defects,notably increasing Rhodamine B water purification efficiency to 95%.The pinning effect of monovalent oxygen vacancies on ferroelectric domains is responsible for the excellent ferroelectric polarization of KNNFC0.015 through the generation of an internal field to promote charge carriers separation and reduce nonradiative recombination.Importantly,the accompanying electron carriers can easily move to the material surface and participate in redox reactions because they have low activation energy.Therefore,ferroelectric polarization and defects play synergetic roles in enhancing piezocatalytic performance.

Optical and electrical anisotropy regulation engineering of low-dimensional materials toward polarized detection and imaging applications

Polarized-sensitive image sensors are a kind of photodetector with great development potential due to their enhanced ability to detect and identify the target objects from the aspect of spatial,spectral and polarized information.Recently,low-dimensional anisotropic materials with inherent anisotropic properties,ultrathin thickness,tunable bandgap and feasible integration with complementary metal oxide semiconductor(CMOS)fabrication processes have attracted great interest for their facilitation of polarized photodetector devices miniaturization.Maximizing the polarized detection performance of low-dimensional materials to satisfy realistic needs stimulates the exploration of modulation of anisotropic properties.In this review,we comprehensively introduce the latest research progress in modulating the optical and optoelectronic anisotropy characteristics of low-dimensional materials.The strategy of anisotropy regulation through crystal structure engineering and coupling system is discussed emphatically.Then,the latest progress in image recognition applications using anisotropic low-dimensional materials is reviewed in detail.Finally,we summarize the challenge and propose future opportunities in the practical application of polarized-sensitive imaging photodetectors based on low-dimensional anisotropic materials.

Trimetallic synergistic optimization of 0D NiCoFe-P QDs anchoring on 2D porous carbon for efficient electrocatalysis and high-energy supercapacitor

Developing multi-functional and low-cost noble-metal-free catalysts such as transition metal phosphides(TMPs)to replace noble-metal is of practical significance for energy conversion and storage.However,the low-durability and the agglomeration phenomenon during the electrochemical process limit their practical applications.Herein,using metal–organic frameworks(MOFs)as the precursor and a combined strategy of gradient temperature calcination and thermal phosphorization,a 0D/2D heterostructure of NiCoFe-P quantum dots(QDs)anchored on porous carbon was successfully developed as highly efficient electrode materials for overall water splitting and supercapacitors.Owing to this distinctive 0D/2D heterostructure and the synergistic effect of multi-metallic TMPs,the NiCoFe-P/C exhibits excellent electrocatalytic activity and durability of HER(87 mV at 10 mA cm^(-2))and OER(257 mV at 100 mA cm^(-2))in the KOH electrolyte.When NiCoFe-P/C is used as the two electrodes of electrolyzed water,only 1.55 V can drive the current density to 10 m A cm^(-2).At the same time,our NiCoFe-P/C possessed extraordinary property for charge storage.In particular,an ultra-high energy density of 100.8 Wh kg^(-1) was achieved at a power density of 900.0 W kg^(-1) for our assembled hybrid supercapacitor device NiCoFe-P/C(2:1)//activated carbon(AC).This work may open a potential way for the design of 0D/2D hybrid multifunctional nanomaterials based on TMPs QDs.

Preparation and infrared emissivities of alkali metal doped ZnO powders

Alkali metal(Li, Na, K) doped ZnO powders were synthesized by solid-state reaction at different calcination temperatures and holding time. Effects of holding time and K sources on the infrared emissivity of ZnO were investigated. The structure and surface morphologies of samples were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM). The UV-Vis absorption and infrared emissivities were investigated by a UV-Vis spectrophotometer and an infrared emissometer, respectively. XRD patterns confirm the wurtzite structure of the as prepared samples with single phase. Smooth grain surfaces are detected in all doped ZnO samples, while ZnO:Li and ZnO:Na present the aggregation of grains. The redshifts in the optical band-gap are observed in K-, Na-, and Li-doped ZnO with the values 3.150, 3.144, and 3.142 eV. Due to better crystalline quality, ZnO:K shows a lower emissivity than others. The emissivity of K-doped ZnO decreases to the minimum value(0.804), at 1200 °C and holding 2 h. Compared with KNO3 as K source, K2CO3 doped ZnO has lower emissivities.

Improvement of the off-state breakdown voltage with field plate and low-density drain in AlGaN/GaN high-electron mobility transistors

We present an AlGaN/GaN high-electron mobility transistor（HEMT） device with both field plate（FP） and lowdensity drain（LDD）. The LDD is realized by the injection of negatively charged fluorine（F-） ions under low power in the space between the gate and the drain electrodes. With a small-size FP and a LDD length equal to only 31% of the gate-drain spacing, the device effectively modifies the electric field distribution and achieves a breakdown voltage enhancement up to two times when compared with a device with only FP.

Mechanism of improving forward and reverse blocking voltages in AlGaN/GaN HEMTs by using Schottky drain

In this paper, we demonstrate that a Schottky drain can improve the forward and reverse blocking voltages （BVs） simultaneously in A1GaN/GaN high-electron mobility transistors （HEMTs）. The mechanism of improving the two BVs is investigated by analysing the leakage current components and by software simulation. The forward BV increases from 72 V to 149 V due to the good Schottky contact morphology. During the reverse bias, the buffer leakage in the Ohmic- drain HEMT increases significantly with the increase of the negative drain bias. For the Schottky-drain HEMT, the buffer leakage is suppressed effectively by the formation of the depletion region at the drain terminal. As a result, the reverse BV is enhanced from -5 V to -49 V by using a Schottky drain. Experiments and the simulation indicate that a Schottky drain is desirable for power electronic applications.

Fabrications and characterizations of high performance 1.2 kV,3.3 kV, and 5.0 kV class 4H–SiC power SBDs

In this paper, 1.2 kV, 3.3 kV, and 5.0 kV class 4H-SiC power Schottky barrier diodes （SBDs） are fabricated with three N-type drift layer thickness values of 10 μm, 30μm, and 50 μm, respectively. The avalanche breakdown capabilities, static and transient characteristics of the fabricated devices are measured in detail and compared with the theoretical pre- dictions. It is found that the experimental results match well with the theoretical calculation results and are very close to the 4H-SiC theoretical limit line. The best achieved breakdown voltages （BVs） of the diodes on the 10 p.m, 30 m, and 50 -tm epilayers are 1400 V, 3320 V, and 5200 V, respectively. Differential specific-on resistances （Ron-sp） are 2.1 m--cm2, 7.34 mO. cm2, and 30.3 m-. cm2, respectively.

Interface and border trapping effects in normally-off Al2O3/AlGaN/GaN MOS-HEMTs with different post-etch surface treatments

Trapping effect in normally-off Al2O3/AlGaN/GaN metal–oxide–semiconductor (MOS) high-electron-mobility transistors (MOS-HEMTs) with post-etch surface treatment was studied in this paper. Diffusion-controlled interface oxidation treatment and wet etch process were adopted to improve the interface quality of MOS-HEMTs. With capacitance–voltage (C–V) measurement, the density of interface and border traps were calculated to be 1.13 × 10^12 cm^−2 and 6.35 × 10^12 cm^−2, effectively reduced by 27% and 14% compared to controlled devices, respectively. Furthermore, the state density distribution of border traps with large activation energy was analyzed using photo-assisted C–V measurement. It is found that irradiation of monochromatic light results in negative shift of C–V curves, which indicates the electron emission process from border traps. The experimental results reveals that the major border traps have an activation energy about 3.29 eV and the change of post-etch surface treatment process has little effect on this major activation energy.

Effect of NO annealing on charge traps in oxide insulator and transition layer for 4H-SiC metal–oxide–semiconductor devices

The effect of nitric oxide（NO） annealing on charge traps in the oxide insulator and transition layer in n-type4H–Si C metal–oxide–semiconductor（MOS） devices has been investigated using the time-dependent bias stress（TDBS）,capacitance–voltage（C–V）,and secondary ion mass spectroscopy（SIMS）.It is revealed that two main categories of charge traps,near interface oxide traps（Nniot） and oxide traps（Not）,have different responses to the TDBS and C–V characteristics in NO-annealed and Ar-annealed samples.The Nniotare mainly responsible for the hysteresis occurring in the bidirectional C–V characteristics,which are very close to the semiconductor interface and can readily exchange charges with the inner semiconductor.However,Not is mainly responsible for the TDBS induced C–V shifts.Electrons tunneling into the Not are hardly released quickly when suffering TDBS,resulting in the problem of the threshold voltage stability.Compared with the Ar-annealed sample,Nniotcan be significantly suppressed by the NO annealing,but there is little improvement of Not.SIMS results demonstrate that the Nniotare distributed within the transition layer,which correlated with the existence of the excess silicon.During the NO annealing process,the excess Si atoms incorporate into nitrogen in the transition layer,allowing better relaxation of the interface strain and effectively reducing the width of the transition layer and the density of Nniot.

The coupling effect of air-bridges on broadband spiral inductors in SiC-based MMIC technology

The coupling effect of air-bridges on broadband spiral inductors in SiC-based MMIC technology has been investigated deeply. The fabricated 1-nH spiral inductor on SiC substrate demonstrates a self-resonant frequency of 51.6 GHz, with a peak Q-fact of 12.14 at 22.1 GHz. From the S-parameters measurements, the exponential decay phenomenon is observed for L, Q-factor, and SRF with the air-bridge height decreasing, and an analytic expression is concluded to exactly fit the measured data which can be used to predict the performance of the spiral inductor. All the coefficients in the formula have specific meaning. By means of establishing the lumped model, the parasitic coupling capacitance of the air-bridge has been extracted and presents the exponential decay with the air-bridge heights decreasing which indicates that this capacitor is directly related to the coupling effect of the air-bridge. Through the electromagnetic field distribution simulation, the details of the electric field around the air-bridge have been presented which demonstrate the formation and the variation principles of the coupling effect.

Fabrication and characterization of the normally-off N-channel lateral 4H–SiC metal–oxide–semiconductor field-effect transistors

In this paper, the normally-off N-channel lateral 4H-SiC metal-oxide-semiconductor field-effect transistors （MOSF- FETs） have been fabricated and characterized. A sandwich- （nitridation-oxidation-nitridation） type process was used to grow the gate dielectric film to obtain high channel mobility. The interface properties of 4H-SiC/SiO2 were examined by the measurement of HF l-V, G-V, and C-V over a range of frequencies. The ideal C-V curve with little hysteresis and the frequency dispersion were observed. As a result, the interface state density near the conduction band edge of 4H-SiC was reduced to 2 x 1011 eV-l.cm-2, the breakdown field of the grown oxides was about 9.8 MV/cm, the median peak field- effect mobility is about 32.5 cm2.V-1 .s-1, and the maximum peak field-effect mobility of 38 cm2-V-1 .s-1 was achieved in fabricated lateral 4H-SiC MOSFFETs.

Effects of electrical stress on the characteristics and defect behaviors in GaN-based near-ultraviolet light emitting diodes

The degradation mechanism of GaN-based near-ultraviolet(NUV,320-400 nm)light emitting diodes(LEDs)with low-indium content under electrical stress is studied from the aspect of defects.A decrease in the optical power and an increase in the leakage current are observed after electrical stress.The defect behaviors are characterized using deep level transient spectroscopy(DLTS)measurement under different filling pulse widths.After stress,the concentration of defects with the energy level of 0.47-0.56 eV increases,accompanied by decrease in the concentration of 0.72-0.84 eV defects.Combing the defect energy level with the increased yellow luminescence in photoluminescence spectra,the device degradation can be attributed to the activation of the gallium vacancy and oxygen related complex defect along dislocation,which was previously passivated with hydrogen.This study reveals the evolution process of defects under electrical stress and their spatial location,laying a foundation for manufacture of GaN-based NUV LEDs with high reliability.

Effects of Low-Damage Plasma Treatment on the Channel 2DEG and Device Characteristics of AlGaN/GaN HEMTs

We investigate the effects of remote nitride-based plasma treatment on the channel carrier and device characteristics of AlGaN/GaN high electron mobility transistors(HEMTs).A 200W NH3/N2 remote plasma causes little degeneration of carrier mobility and an increase in electron density due to surface alteration,which results in a decrease in sheet resistance and an increase in output current by 20–30%.Improved current slump,suppressed gate leakage current,and improved Schottky contact properties are also achieved by using low-damage nitride-based plasma treatment.It is found that NH3/N2 remote plasma treatment is a promising technique for GaN-based HEMTs to modulate the surface conditions and channel properties.

Improved RF power performance of InAlN/GaN HEMT by optimizing rapid thermal annealing process for high-performance low-voltage terminal applications

Improved radio-frequency(RF)power performance of InAlN/GaN high electron mobility transistor(HEMT)is achieved by optimizing the rapid thermal annealing(RTA)process for high-performance low-voltage terminal applications.By optimizing the RTA temperature and time,the optimal annealing condition is found to enable low parasitic resistance and thus a high-performance device.Besides,compared with the non-optimized RTA HEMT,the optimized one demonstrates smoother ohmic metal surface morphology and better heterojunction quality including the less degraded heterojunction sheet resistance and clearer heterojunction interfaces as well as negligible material out-diffusion from the barrier to the channel and buffer.Benefiting from the lowered parasitic resistance,improved maximum output current density of 2279 mA·mm^(-1)and higher peak extrinsic transconductance of 526 mS·mm^(-1)are obtained for the optimized RTA HEMT.In addition,due to the superior heterojunction quality,the optimized HEMT shows reduced off-state leakage current of 7×10^(-3)mA·mm^(-1)and suppressed current collapse of only 4%,compared with those of 1×10^(-1)mA·mm^(-1)and 15%for the non-optimized one.At 8 GHz and V_(DS)of 6 V,a significantly improved power-added efficiency of 62%and output power density of 0.71 W·mm^(-1)are achieved for the optimized HEMT,as the result of the improvement in output current,knee voltage,off-state leakage current,and current collapse,which reveals the tremendous advantage of the optimized RTA HEMT in high-performance low-voltage terminal applications.

Low-resistance ohmic contacts on InAlN/GaN heterostructures with MOCVD-regrown n+-InGaN and mask-free regrowth process

This paper studied the low-resistance ohmic contacts on InAlN/GaN with metal–organic chemical vapor deposition(MOCVD)regrowth technique.The 150-nm regrown n-InGaN exhibits a low sheet resistance of 31Ω/□,resulting in an extremely low contact resistance of 0.102Ω·mm between n^(+)-InGaN and InAlN/GaN channels.Mask-free regrowth process was also used to significantly improve the sheet resistance of InAlN/GaN with MOCVD regrown ohmic contacts.Then,the diffusion mechanism between n^(+)-InGaN and InAlN during regrowth process was investigated with electrical and structural characterizations,which could benefit the further process optimization.

Phase field modeling of ferroelastic variant switching in yttria-stabilized t'zirconia with strain gradient elasticity and interface tension

The 6–8 wt%yttria-stabilized zirconia with a tetragonal structure(t’-YSZ)is extensively employed in thermal barrier coatings.The exceptional fracture toughness of t’-YSZ can be attributed to its distinctive ferroelastic toughening mechanism.Microstructure and interface tension play a critical role in ferroelastic variant switching at the micro-and nano-scale.This paper presents an original thermodynamically consistent phase field(PF)theory for analyzing ferroelastic variant switching at the micro-and nano-scale of t’-YSZ.The theory incorporates strain gradient elasticity using higher-order elastic energy and interface tension tensor via geometric nonlinearity to represent biaxial tension resulting from interface energy.Subsequently,a mixed-type formulation is employed to implement the higher-order theory through the finite element method.For an interface in equilibrium,the effects of strain gradient elasticity result in a more uniform distribution of stresses,whereas the presence of interface tension tensor significantly amplifies the stress magnitude at the interface.The introduction of an interface tension tensor increases the maximum value of stress at the interface by a factor of 4 to 10.The nucleation and evolution of variants at a pre-existing crack tip in a mono-phase t’-YSZ have also been studied.The strain gradient elasticity is capable of capturing the size effect of ferroelastic variant switching associated with microstructures in experiments.Specifically,when the grain size approaches that of the specimen,the critical load required for variant switching at the crack tip increases,resulting in greater dissipation of elastic energy during ferroelastic variant switching.Moreover,the interface tension accelerates the evolution of variants.The presented framework exhibits significant potential in modeling ferroelastic variant switching at the micro-and nano-scale.

Optimization of ferroelectricity and endurance of hafnium zirconium oxide thin films by controlling element inhomogeneity

Ferroelectric thin films based on HfO_(2) have garnered increasing attention worldwide,primarily due to their remarkable compatibility with silicon and scalability,in contrast to traditional perovskite-structured ferroelectric materials.Nonetheless,significant challenges remain in their widespread commercial utilization,particularly concerning their notable wake-up effect and limited endurance.To address these challenges,we propose a novel strategy involving the inhomogeneous distribution of Hf/Zr elements within thin films and explore its effects on the ferroelectricity and endurance of Hf_(0.5)Zr_(0.5)O_(2) thin films.Through techniques such as grazing incidence X-ray diffraction,transmission electron microscopy,and piezoresponse force microscopy,we investigated the structural characteristics and domain switching behaviors of these materials.The experimental results indicate that the inhomogeneous distribution of Hf/Zr contributes to improving the frequency stability and endurance while maintaining a large remnant polarization in Hf_(0.5)Zr_(0.5)O_(2) ferroelectric thin films.By adjusting the distribution of Zr/Hf within the Hf_(0.5)Zr_(0.5)O_(2) thin films,significant enhancements in the remnant polarization(2P_(r)>35μC/cm2)and endurance(>109)along with a reduced coercive voltage can be achieved.Additionally,the fabricated ferroelectric thin films also exhibit high dielectric tunability(≥26%)under a low operating voltage of 2.5 V,whether in the wake-up state or not.This study offers a promising approach to optimize both the ferroelectricity and endurance of HfO_(2)-based thin films.

Defects‑Rich Heterostructures Trigger Strong Polarization Coupling in Sulfides/Carbon Composites with Robust Electromagnetic Wave Absorption

Defects-rich heterointerfaces integrated with adjustable crystalline phases and atom vacancies,as well as veiled dielectric-responsive character,are instrumental in electromagnetic dissipation.Conventional methods,however,constrain their delicate constructions.Herein,an innovative alternative is proposed:carrageenan-assistant cations-regulated(CACR)strategy,which induces a series of sulfides nanoparticles rooted in situ on the surface of carbon matrix.This unique configuration originates from strategic vacancy formation energy of sulfides and strong sulfides-carbon support interaction,benefiting the delicate construction of defects-rich heterostructures in M_(x)S_(y)/carbon composites(M-CAs).Impressively,these generated sulfur vacancies are firstly found to strengthen electron accumulation/consumption ability at heterointerfaces and,simultaneously,induct local asymmetry of electronic structure to evoke large dipole moment,ultimately leading to polarization coupling,i.e.,defect-type interfacial polarization.Such“Janus effect”(Janus effect means versatility,as in the Greek two-headed Janus)of interfacial sulfur vacancies is intuitively confirmed by both theoretical and experimental investigations for the first time.Consequently,the sulfur vacancies-rich heterostructured Co/Ni-CAs displays broad absorption bandwidth of 6.76 GHz at only 1.8 mm,compared to sulfur vacancies-free CAs without any dielectric response.Harnessing defects-rich heterostructures,this one-pot CACR strategy may steer the design and development of advanced nanomaterials,boosting functionality across diverse application domains beyond electromagnetic response.