Effect of Pulse and dc Formation on the Performance of One-Transistor and One-Resistor Resistance Random Access Memory Devices

We investigate the effect of the formation process under pulse and dc modes on the performance of one transistor and one resistor （1 T1R） resistance random access memory （RRAM） device. All the devices are operated under the same test conditions, except for the initial formation process with different modes. Based on the statistical results, the high resistance state （FIRS） under the dc forming mode shows a lower value with better distribution compared with that under the pulse mode. One of the possible reasons for such a phenomenon originates from different properties of conductive filament （CF） formed in the resistive switching layer under two different modes. For the dc forming mode, the formed filament is thought to be continuous, which is hard to be ruptured, resulting in a lower HRS. However, in the case of pulse forming, the filament is discontinuous where the transport mechanism is governed by hopping. The low resistance state （LRS） can be easily changed by removing a few trapping states from the conducting path. Hence, a higher FIRS is thus observed. However, the HRS resistance is highly dependent on the length of the gap opened. A slight variation of the gap length will cause wide dispersion of resistance.

Three-dimensional forward modeling of DC resistivity using the aggregation-based algebraic multigrid method

To speed up three-dimensional （3D） DC resistivity modeling, we present a new multigrid method, the aggregation-based algebraic multigrid method （AGMG）. We first discretize the differential equation of the secondary potential field with mixed boundary conditions by using a seven-point finite-difference method to obtain a large sparse system of linear equations. Then, we introduce the theory behind the pairwise aggregation algorithms for AGMG and use the conjugate-gradient method with the V-cycle AGMG preconditioner （AGMG-CG） to solve the linear equations. We use typical geoelectrical models to test the proposed AGMG-CG method and compare the results with analytical solutions and the 3DDCXH algorithm for 3D DC modeling （3DDCXH）. In addition, we apply the AGMG-CG method to different grid sizes and geoelectrical models and compare it to different iterative methods, such as ILU-BICGSTAB, ILU-GCR, and SSOR-CG. The AGMG-CG method yields nearly linearly decreasing errors, whereas the number of iterations increases slowly with increasing grid size. The AGMG-CG method is precise and converges fast, and thus can improve the computational efficiency in forward modeling of three-dimensional DC resistivity.

Forward modeling of marine DC resistivity method for a layered anisotropic earth

Since the ocean bottom is a sedimentary environment wherein stratification is well developed, the use of an anisotropic model is best for studying its geology. Beginning with Maxwell＇s equations for an anisotropic model, we introduce scalar potentials based on the divergence-free characteristic of the electric and magnetic （EM） fields. We then continue the EM fields down into the deep earth and upward into the seawater and couple them at the ocean bottom to the transmitting source. By studying both the DC apparent resistivity curves and their polar plots, we can resolve the anisotropy of the ocean bottom. Forward modeling of a high-resistivity thin layer in an anisotropic half-space demonstrates that the marine DC resistivity method in shallow water is very sensitive to the resistive reservoir but is not influenced by airwaves. As such, it is very suitable for oil and gas exploration in shallowwater areas but, to date, most modeling algorithms for studying marine DC resistivity are based on isotropic models. In this paper, we investigate one-dimensional anisotropic forward modeling for marine DC resistivity method, prove the algorithm to have high accuracy, and thus provide a theoretical basis for 2D and 3D forward modeling.

Detecting and monitoring of water inrush in tunnels and coal mines using direct current resistivity method:A review

Detecting, real-time monitoring and early warning of underground water-bearing structures are critically important issues in prevention and mitigation of water inrush hazards in underground engineering. Direct current （DC） resistivity method is a widely used method for routine detection, advanced detection and real-time monitoring of water-bearing structures, due to its high sensitivity to groundwater. In this study, the DC resistivity method applied to underground engineering is reviewed and discussed, including the observation mode, multiple inversions, and real-time monitoring. It is shown that a priori information constrained inversion is desirable to reduce the non-uniqueness of inversion, with which the accuracy of detection can be significantly improved. The focused resistivity method is prospective for advanced detection;with this method, the flanking interference can be reduced and the detection dis-tance is increased subsequently. The time-lapse resistivity inversion method is suitable for the regions with continuous conductivity changes, and it can be used to monitor water inrush in those regions. Based on above-mentioned features of various methods in terms of benefits and limitations, we propose a three-dimensional （3D） induced polarization method characterized with multi-electrode array, and introduce it into tunnels and mines combining with real-time monitoring with time-lapse inversion and cross-hole resistivity method. At last, the prospective applications of DC resistivity method are discussed as follows： （1） available advanced detection technology and instrument in tunnel excavated by tunnel boring machine （TBM）, （2） high-resolution detection method in holes, （3） four-dimensional （4D） monitoring technology for water inrush sources, and （4） estimation of water volume in water-bearing structures.

Geoelectrical survey over perched aquifers in the northern part of Upper Sakarya River Basin,Türkiye

In this study,a groundwater exploration survey was conducted using the DC Resistivity(DCR)method in a hydrogeological setting containing a perched aquifer.DCR data were gathered and an electrical tomography section was recovered using conventional four-electrode instruments with a Schlumberger array and a two-dimensional(2D)inversion scheme.The proposed scheme was tested over a synthetic threedimensional(3D)subsurface model before deploying it in a field situation.The proposed method indicated that gathering data with simple four-electrode instruments at stations along a line and 2D inversion of datasets at multiple stations can recover depth intervals of the studied aquifer in the hydrogeological setting even if it has a 3D structure.In this study,2D inversion of parallel profiles formed a pseudo-3D volume of the subsurface resistivity structures and mapped out multiple resistive(>25 ohm·m)bodies at shallow(between 50-100 m)and deep sections(>150 m).In general,the proposed method is convenient to encounter geological units that have limited vertical and spatial extensions in any direction and presents resistivity contrast from groundwater-bearing geologic materials.

Experimental Analysis on Influence of Temperature and Bolted Torque to DC Contact Resistance of Terminal Connector in UHV Valve Hall

The overheating problems of terminal connectors severely threaten the operation of ultra-high voltage projects and cause enormous losses of economy,so a higher currentcarrying reliability of the connectors has an important engineering significance with the development of transmission capacity.In this paper,a bivariate mathematical model of contact resistance as functions of temperature and tightening torque was deduced based on the large current temperature rise tests.To perform such analysis,four typical terminal connectors,namely:overlapping terminal of aluminum plates,overlapping terminal of copper plates,overlapping terminal of plates with clad layer and overlapping terminal of copper rod with aluminum clamp,were chosen for the experiments.The changing rules of DC resistance with different tightening torques and different currents were studied.Then the empirical formula of contact resistance was deduced.Finally,temperature calculations of different terminal connectors were realized to verify the effectiveness of the bivariate mathematical model.

Tuning structural,electrical,dielectric and magnetic properties of Mg-Cu-Co ferrites via dysprosium(Dy^(3+))doping

In current research work,Dy3+substituted Mg0.5Cu0.25Co0.25Fe2-xDyxO4(0.0≤x≤0.04 with the step interval of 0.01)soft ferrites were synthesized by the sol-gel auto combustion method.The prepared samples were characterized by the techniques using X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDS),Fourier transform infrared(FTIR)spectroscopy,curre nt-voltage(Ⅰ-Ⅴ)measurement,LCR meter,vibrating sample magnetometer(VSM)and Raman.XRD data reveal that the average crystallite size is 49.71 nm and the lattice constant is 0.83703 nm for sample x=0.03.The non-uniform grain growth was demonstrated by micrographs and impurity-free elemental composition was observed from EDX analysis.The DC resistivity has an increasing and decreasing trend in ferromagnetic and paramagnetic regions with an increase in temperature.Moreover,the high resistivity is observed with the order of 1010Ω·cm,and the activation energy is 0.944 eV for samples x=0.03.The dielectric parameters including dielectric constant,dielectric losses,and impedance gradually decrease with the increase in frequency from 8 Hz to 8 MHz.The minimum dielectric loss at high frequency is found for sample x=0.03.The coercivity(Hc)and saturation magnetization(Ms)are found in the ranges of 520.82-544.02 Oe and 20.5841-21.1473 emu/g,respectively.These observations confirm that dysprosium(x=0.03)doped MCC-soft ferrites may be applicable in transformer cores,microwave absorbance,and telecommunication devices.

Analysis of cerium substitution in Co-Sr based spinel ferrites for high frequency application

Spinel ferrites exhibit exceptional magnetic properties,making them a distinctive class of magnetic materials.The sol-gel technique was utilized for the synthesis of spinel ferrites with the chemical formula Co_(0.6)Sr_(0.4)Ce_(x)Fe_(2-x)O_(4). Following that,a comprehensive X-ray diffraction analysis unveiled the crystalline cubic structure of the synthesized materials.Through the utilization of the M-H loop approach,the ferromagnetic attributes of ferrites were assessed,and the assimilation of rare earth elements led to substantial enhancements in saturation magnetization,remanence,and coercivity.Spinel ferrites with a high concentration of rare earth elements have improved direct current resistivity and activation energy.The logarithm of a material's resistance increased from 5.29 to 8.12 Ω·cm as cerium is added.With a change in the amount of cerium,the activation energy goes up from 0.19 to 0.29.By changing the frequency from 5.5 to 9.5 GHz,the dielectric characteristics were determined.As the frequency goes up,the dielectric constant goes down.Spinel ferrites that have been made better in every way can be used in high-frequency applications.

2.5-D DC Resistivity Modeling Considering Flexibility and Accuracy

We highlighted the flexibility of using unstructured mesh together with the local refinement by a resistivity model with complicated topography. The effect of topography is emphasized. Based on this, we calculated a specific class of layered models and found that the accuracy is not always satisfactory by utilizing the standard approach. As an improvement, we employed the layered earth as the reference model to calculate the wavenumbers. The comparison demonstrates that the accuracy is considerably improved by using this enhanced approach.

Impact of La^(3+)substitution on electrical,magnetic,dielectric and optical properties of Ni_(0.7)Cu_(0.1)Zn_(0.2)LaxFe_(2-x)O_(4)(0

The oxalate co-precipitation method was used to synthesize the La3+substituted Ni-Cu-Zn(La-NCZ)nanoferrites having chemical composition Ni_(0.7)Cu_(0.1)Zn_(0.2)LaxFe_(2-x)O_(4)(x=0.015,0.025 and 0.035).DC resistivity study of nanoferrites shows both the conducting and semiconducting behaviour.The room temperature DC electrical resistivity of Ni-Cu-Zn(NCZ)nanoferrites decreases,whereas Curie temperature increases with increasing La^(3+)content.In the temperature range of 30-170℃nanoferrites show p-type semiconducting behavior except x=0.015;thereafter,they show n-type behaviour.The frequency dispersive initial permeability(μi)associated with its real and imaginary(μ’andμ")parts are attributed to the domain wall movement and magnetic spin resonant.Theμi,u’andμ"of La-NCZ nanoferrites are higher than those of pure NCZ nanoferrite.Dielectric constant(ε’),dielectric loss(ε")and AC resistivity(ρAC)of La-NCZ nanoferrites show normal dielectric behaviour.It is found thatε’of NCZ nanoferrites decreases with the increasing content of La3+ions.The bandgap energy of La-NCZ nanoferrites is achieved in the range 1.36-1.70 eV confirming the semiconducting nature of materials.

Influence of Ni substitution on structural,morphological,dielectric,magnetic and optical properties of Cu-Zn ferrite by double sintering sol–gel technique

Polycrystalline NiCuZn ferrite(Ni_(x)Cu_(0.3)Zn(0.7-x)Fe_(2)O_(4);x=0.2,0.3,0.4 and 0.5)were prepared through solgel auto combustion method applying double sintering technique.Structural,morphological,elemental analyses(EDS),Fourier-transform infrared spectroscopy(FTIR),Direct Current(DC)electrical resistivity,dielectric,magnetic and optical properties of prepared samples were analyzed.XRD profiles reveal the formation of simple cubic spinel structure without any traceable impurity.The average crystallite size lies within the range of 22–29 nm.Lattice parameter decreases with increasing Ni concentration.Room temperature DC resistivity was recorded from 6:39×10^(5)to 3:79×10^(5)Ωcm.Both dielectric constant(ε)and loss factor(tanδ)were decreased with increase of frequency while AC conductivity increases.FTIR absorption peak occurred at three different frequency ranges at 570-577 cm^(-1),1635-1662 cm^(-1)and 3439–3448 cm^(-1).Magnetic properties were investigated by using vibrating sample magnetometer(VSM).Decreasing trends were observed for saturation magnetization(Ms),magnetic coercivity(Hc)and remanant magnetization(Mr)with the increase of Ni content.Optical band gap(-2.70-2.79 eV)were calculated from diffuse reflectance data by using Kubelka–Munk function.

Structural,electrical and magnetic properties of cobalt ferrite with Nd^(3+) doping

A systematic study on the influence of Nd^(3+) substitution on structural,magnetic and electrical properties of cobalt ferrite nanopowders obtained by sol–gel auto-combustion routewas reported.The formation of spinel phasewas confirmed by X-ray diffraction(XRD)data,and percolation limit ofNd3?into the spinel lattice was also observed.Fourier transform infrared spectroscopy(FTIR)bands observed ≈580 and ≈390 cm^(-1 ) support the presence of Fe^(3+) at A andBsites in the spinel lattice.The variation in microstructure was investigated by scanning electronmicroscopy(SEM),and the average grain size varies from 5.3 to 3.3 lm.The substitution of Nd^(3+) significantly affects the formation of pores and grain size of cobalt ferrite.Room-temperature saturation magnetization and coercivity decrease from 60 to 30 mA·m^(2)·g^(-1) and 19.9–17.8 mT,respectively,with Nd^(3+) substitution increasing.These decreases in magnetic properties are explained based on the presence of non-magnetic nature of Nd^(3+) concentration and the dilution of super-exchange interaction in the spinel lattice.The room-temperature direct-current electrical resistivity increases with Nd^(3+) concentration increasing,which is due to the unavailability of Fe^(2+) at octahedral B sites.

REVISIT TO DIELECTRIC PROPERTIES OF FERRITE CERAMICS

Dielectric properties offerrite ceramics have been less reported than their magnetic properties.Ourrecent study indicated that ferrite ceramics with very low dielectric loss tangent can be developed byusing appropriate sintering aids,together with the optimization of other sintering parameters suchas sintering temperature and time duration.Among various candidates of sintering aids,Bi_(2)O_(3)isthe most promising one.It is important to find that the optimized concentration of sintering aid forfull densification is not sufficient to achieve lowest dielectric loss tangent.This short review was aimed to summarize the understanding in microstructural evolution,grain growth,densificationand dielectric properties offerrite ceramics as a function of sintering aid concentration and sinteringparameters,which could be used as a guidance to develop ferrite ceramics with low dielectric losstangents for various applications.