WSi2 Research Articles

Enhanced performance of 19 single gate MOSFET with high permittivity dielectric material

<p><span>In this research, the performance of the 19 nm single gate MOSFET is enhanced through the implementation of the high permittivity dielectric material. The MOSFET scaling trends necessities in device dimensions can be satisfied through the implementation of the high-K dielectric materials in place of the SiO2. Therefore, the 19 nm n-channel MOSFET device with different High-K dielectric materials are implemented and its performance improvement has also been analysed. Virtual fabrication is exercised through ATHENA module from Silvaco TCAD tool. Meanwhile, the device characteristic was utilized by using an ATLAS module. The aforementioned materials have also been simulated and compared with the conventional gate oxide SiO2 for the same structure. At the end, the results have proved that Titanium oxide (TiO2) device is the best dielectric material with a combination of metal gate Tungsten Silicides (WSix). The drive current (ION) of this device (WSix/TiO2) is 587.6 µA/um at 0.534 V of threshold voltage (VTH) as opposed to the targeted 0.530 V predicted, as well as a relatively low IOFF that is obtained at 1.92 pA/µm. This ION value meets the minimum requirement predicted by International Technology Roadmap for Semiconductor (ITRS) 2013 prediction for low performance <br /> (LP) technology. </span></p>

Exploration of stable stoichiometries, ground-state structures, and mechanical properties of the W–Si system

Refractory tungsten silicides have been identified as typical high-temperature structural materials with excellent mechanical and thermal properties in various industrial applications. Here, we show the first extensive crystal structures search of W–Si system over a wide range of stoichiometries at ambient condition, using first-principles swarm intelligence structure search methods. Besides the well-known W5Si3 and WSi2, three novel and unexpected stoichiometries of W2Si, WSi, and W3Si4 with tetragonal ground-state structures were firstly uncovered and suggested to be experimentally synthesizable according to the convex hull calculations. It is found that the high silicon content benefits the formation of the puckered double W–Si zigzag covalent chains in WmSin, resulting in the enhanced resistance to shear deformation related to the macroscopic hardness. Results on the ideal tensile and shear strengths calculations indicated that the failure modes in the studied WmSin are mainly dominated by the shear type along the (110)[11‾0]directions. Further analysis of atomic shear deformation demonstrates that the collapse of Si–W building blocks is responsible for the lattice stability and achievable mechanical strength of WmSin.

Minimum leakage current optimization on 22 nm SOI NMOS device with HfO2/WSix/Graphene gate structure using Taguchi method.

To acquire the optimal value of the performance parameter, a bilayer graphene with silicon on insulator (SOI) was enhanced and analyzed on 22 nm NMOS device. The device is made of Hafnium Dioxide (HfO2) as a high-k material whereas Tungsten Silicide (WSix) as a metal gate. The Silvaco software ATHENA and ATLAS modules were applied to simulate the fabrication process of virtual devices and to verify the device’s electrical properties accordingly. The Taguchi L9 orthogonal array method was then used to enhance the device process parameters minimum leakage current (ILEAK) according to the International Technology Roadmap Semiconductor (ITRS) specification of 100nA/μm maximum range. The result from smaller-the-better (STB) for ILEAK is then reviewed by the percentage affecting the process parameter. The simulation result shows that the halo tilting angle is the most dominant factor for ILEAK optimization process. The optimized results indicate excellent device performance with ILEAK = 9.29746 nA/µm which is far lower than the prediction.

The mechanism of elastic and electronic properties of Tungsten Silicide (5/3) with vacancy defect from the first-principles calculations

The development prospects of transition metal silicon-based materials have received considerable attention. Tungsten-based silicides are one of the most important silicon-based high-temperature materials. Here, the mechanism of elastic and electronic properties of Tungsten Silicide (5/3) with vacancy defects was further studied using the first-principles approach. The vacancy formation enthalpy, elastic constants, elastic moduli, brittle/ductile behavior, hardness and electronic structure of the perfect W5Si3 and W5Si3 with vacancies were calculated and discussed, respectively. The result demonstrates that W5Si3 with W vacancies exhibit the better stability than W5Si3 with Si vacancies. Vacancy defects weaken the mechanical strength for the perfect W5Si3. The removal of the Si atoms makes W5Si3 with vacancies exhibit the better ductility than the parent W5Si3. The electronic structures explain the mechanism for structural stability and mechanics properties of W5Si3 by vacancy defects.

III-V photonic integrated circuit with waveguide-coupled light-emitting diodes and WSi superconducting single-photon detectors

We demonstrate cryogenic, all on-chip, single-photon-level photonic integrated circuits on a III-V platform with waveguide-coupled quantum-well sources and tungsten silicide superconducting nanowire single-photon detectors. We have measured the dark count rates below 10−3 counts/s and have reduced the cross talk to an adjacent waveguide by 30 dB.

A Stochastic SPICE Model for Superconducting Nanowire Single Photon Detectors and Other Nanowire Devices.

Superconducting nanowire devices, such as the superconducting nanowire single photon detector (SNSPD) or nanocryotron, have a time-dependent stochasticity that depends on the current flowing through them. When modeling complex circuits made of several such devices (for instance, an array of SNSPDs), the ability to include this randomness can be important for predicting unwanted effects and interactions within the circuit. We present a modification of the model described by Berggren et al. that allows for the inclusion of this stochasticity into the nanowire device model. We then verify the model against experiment using a tungsten silicide SNSPD, and show that the modified model replicates the stochasticity of the physical device.

Promising Superconducting Materials for Highly Sensitive Detectors of the Infrared and Terahertz Ranges

Modern technologies of photonics, astrophysics, medicine and security systems have a demand for development of new types of sensitive detectors and/or optimization of existing ones. As an example, a strong demand exists for improvement of the characteristics of highly sensitive detectors based on superconducting materials. One way to optimize the performance of such detectors is to select a suitable superconducting material. This is due to the fact that the technical characteristics of devices are determined by relaxation mechanisms of nonequilibrium processes that occur in the material upon absorption of electromagnetic radiation. In this paper, we focused on the study of the relaxation of nonequilibrium processes in superconducting materials such as highly boron-doped polycrystalline diamond films, highly disordered titanium nitride (TiN) films and ultrathin amorphous tungsten silicide films (WSi). The experimental data allowed us to determine the temperature dependence of the inelastic relaxation time in the studied materials. These results can help us to evaluate the applicability of these materials for the different types of superconducting detectors.

W/TaC/SiC sandwich stack for high temperature applications

High-temperature stability of the tungsten/tantalum carbide/silicon carbide (W/TaC/SiC) system was examined and compared to the tungsten/silicon carbide (W/SiC) system. Interfacial reactions, surface morphology, and roughness evolutions on thermal annealing at 1000 °C were systematically investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). For the W/SiC system, WC, W2C and W5Si3 phases were observed due to severe chemical reaction after 24 h annealing, which led to an inhomogeneous surface structure with several large craters and small pores, thereby increasing surface roughness greatly. On the other hand, there was no tungsten silicide and/or carbide formation upon annealing with a TaC diffusion barrier. The surface structure remained nearly unchanged, and small changes in surface roughness with annealing time, which could be due to the growth of W grains, were noted. Furthermore, both the as-deposited and the 24 h annealed W/TaC/SiC samples presented an excellent interfacial bonding with a dense uniform interface. The results indicate that TaC is a promising diffusion barrier in the W/SiC system for high temperature applications.

The structure, mechanical and electronic properties of WSi2 from first-principles investigations

Tungsten disilicide (WSi2) is an attractive advanced functional material, which is regarded as the potential thermoelectric devices, energy storage system and aerospace etc. However, the correlation between structure and the related performances of WSi2 is not well understood. To solve those problems, we apply first-principles calculations to study crystal structure, electronic properties, elastic properties and electronic structure of four possible WSi2. We demonstrate the WSi2 with C54 TiS2-type orthorhombic structure (Fddd, No.70) is a dynamically stable. These results show that MoSi2-type C11b tetragonal structure is more thermodynamically stable than that of the other structures. Importantly, MoSi2-type C11b, TiSi2-type C49 and HfSi2-type C54 structures show electronic properties because of band overlap between the valence band and the conduction band near the Fermi level. However, NbSi2-type C40 structure shows a semiconductor property with a band gap of 0.049 eV. We further find that MoSi2-type C11b structure shows the strong shear deformation resistance and high elastic stiffness due to the pyramidal bonding state. WSi2 with TiSi2-type C54 structure exhibits better ductile in comparison to the other structures.

Room-temperature synthesis of tungsten silicide powders using various initial systems

The present study investigated the synthesis of tungsten silicide powders using ternary (WO3-Si-Mg and W-SiO2-Mg) and binary (W-Si) initial systems at room temperature via mechanochemical synthesis (MCS) and mechanical alloying (MA) processes. Milling time was used as a process parameter. Subsequently, undesired Mg-based phases were leached out using aqueous HCl solution. Compositional analyses of powders were conducted by using an X-ray diffractometer (XRD) and Fourier transform infrared spectrometer (FTIR). Microstructural observations of powders were performed by utilizing particle size analyzer (PSA), scanning (SEM) and transmission electron microscopes (TEM). Also, differential scanning calorimetry (DSC) analyses were carried out for the synthesized powders. While the reaction for tungsten silicide formation took place by MCS in WO3-Si-Mg system after 1 min and by MA in W-Si system after 15 h, it did not occur in W-SiO2-Mg system even after 15 h milling. WSi2, W5Si3 and W phases were found in WO3-Si-Mg system whereas only WSi2 formed in W-Si system. The ternary WO3-Si-Mg system resulted in SiO2 coated nanoparticles owning a mean size of 203 nm. WSi2 submicron particles with an average size of 688 nm were obtained in binary W-Si system. The experimental results showed a good consistency with the reaction mechanisms predicted by FactSage™ thermodynamic calculations.

Two reactant systems for self-propagating high-temperature synthesis of tungsten silicide

Tungsten silicide (WSi2) intermetallic was prepared via self-propagating high-temperature synthesis (SHS) from two reactant systems: one using scheelite (CaWO4-Si-Al) and the other pure oxides (CaO-WO3-Si-Al). The equilibrium compositions of the reactions were calculated by a standard Gibbs energy minimization. Reactant mixtures were high-energy milled for durations of 0.5, 2, 4, and 8 h and the effects of milling on the synthesized products were studied. The effects of the sand mold on the products were also studied. The phase constituents and microstructural morphologies of the products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray (EDS) capability. Intermetallic WSi2 was successfully synthesized from both systems. The system that contained the pure oxide (CaO-WO3-Si-Al) reactant gave a higher yield of WSi2 than the system that contained scheelite (CaWO4-Si-Al) but the yield from the CaWO4-Si-Al reactant system could be optimized by increasing the proportion of Si in the system. The sand mold helped the phase separation of the oxide slag and the intermetallic.

Improving Abrasive Wear Resistance for Steel Hardox 400 by Electro-Spark Deposition

The mechanical and tribological properties of the steel Hardox 400 after electro-spark deposition (ESD) using electrodes made of hard-alloy carbides T15K6 (79% WC + 15% TiC + 6% Co), WK6 (94% WC + 6% Co), and composite materials based on iron such as 12S2 (12% Ni + 2% Si + 15% Cr3C2 + 71% Fe), K4F (15% WK3 (97 WC + 3 Co) + 4% Cr3C2 + 1% V + 80% Fe), and tungsten disilicide WSi2 (76.6% W; 23.4% Si) have been studied. The energy parameters (the energy of pulsed discharges, the amplitude and repetition rate thereof) and technological parameters (the type of processing electrode motion, vibration or vibration/rotation) for the ESD process, as well as the electrode composition at which the highest quality surface layers with high wear resistance is observed, have been optimized. The effect of the energy and technological parameters of the ESD process exerted on the properties of the coatings obtained has been determined. The studies have shown that coatings of WC–TiC–Co and WC–Co applied onto steel Hardox 400 exhibit a twofold decrease in abrasive wear. At the same time, it has been found that the wear resistance of composite coatings is sufficiently affected by the application modes (up to a 2.5-fold decrease in the wear level), and the coatings made of composites 12S2 and K4F are competitive with respect to coatings made of hard alloys based on tungsten carbides.

Intermetallic WSi2–W5Si3 Alloy by Magnesiothermic SHS Reaction

Intermetallic tungsten silicide alloy WSi2–W5Si3 was successfully synthesized via magnesiothermic SHS reaction in the WO3–Si–Mg system. Equilibrium composition of combustion products was calculated by standard Gibbs energy minimization method and the combustion products were characterized by XRD, SEM, and EDX. The synthesized alloy had a density of 8.97 g/cm3 (96.4% of theoretical). The process can be readily recommended for practical implementation.

A kinetic-inductance-based superconducting memory element with shunting and sub-nanosecond write times

We present a kinetic-inductance-based superconducting memory element with non-destructive readout, femtojoule read and write energies, both read and write shunts, which is writeable with pulses shorter than 400 ps. The element utilizes both a high-kinetic-inductance layer made from tungsten silicide as well as a low-kinetic-inductance layer made from niobium. By using tungsten silicide—which has a long (20 ns) thermal time constant—and measuring bit error rates from 10 MHz to 1 GHz, we were able to verify that the thin-film elements could be operated at a data rate at least as fast as the material thermal time constant with a bit error ratio less than 10−6. We also analyze the margins of the device, and outline the characteristics by which a more efficient device may be designed.

Synthesis of WSi<sub>2</sub>-W<sub>5</sub>Si<sub>3</sub> Intermetallic Alloy via Self-Propagating High Temperature Synthesis

Intermetallic alloy of tungsten silicide (WSi2-W5Si3) was synthesized by self-propagating high temperature synthesis (SHS) from the reactant of tungsten oxide (WO3) and silicon lump (Si) using magnesium (Mg) as fuel. The standard Gibbs energy minimization method was used to calculate the equilibrium composition of the possible reacting species. The as-SHS products were characterized by X-ray diffraction (XRD) technique. The magnesiothermic reaction process successfully synthesized dense of WSi2-W5Si3intermetallic alloy. According to the experimental results, it can be proposed that the reaction also promotes the phase separation between alloy and oxide slag of the product.

Mechanical and dielectric properties of carbon fiber reinforced reaction bonded silicon nitride composites

Carbon fiber (Cf) reinforced reaction bonded silicon nitride (RBSN) composites with various amounts of fiber (5, 10, 15 and 20 vol %) are fabricated at 1400 °C using the direct nitridation method. The effect of Cf on the phase formation, microstructure evolution, mechanical and dielectric properties has been investigated. The XRD analysis using Rietveld refinement shows the presence of alpha and beta silicon nitride with a trace amount of tungsten disilicide. Microstructural analyses show the uniform dispersion of Cf in the RBSN matrix and the different toughening mechanisms operated in the composites. Mercury intrusion porosimetry results show unimodal to the multimodal distribution of pores with the increase in the quantity of Cf. The porosity of the composites varies from 30 to 38% with the addition of Cf. The addition of Cf has enhanced the fracture toughness of the composites only with 5 vol % Cf and the maximum toughness achieved is 2.5 MPa m1/2. There is no interface reaction on the Cf, which indicates the stability of fibers in the nitrogen atmosphere at 1400 °C. The dielectric performance of the composites in the X-band frequency range (8.2–12.4 GHz) is found to increase with Cf content.

Amplification of Absorption Induced by Localized Surface Plasmons in Superconducting Nanowire Single-Photon Detector

The absorption can be amplified by using tungsten silicide (WSi) and metallic nano-antennas, which is related with the detection efficiency of a superconducting nanowire single-photon detector based on surface plasmons. A metal slot sandwiched between two hydrogen silsequioxane (HSQ), WSi nanowire, and metallic fan nano-antennas are the elements of the proposed single-photon detector. The slot is also filled with HSQ and WSi nanowire is inserted in the top of the slot. Metallic fan nano-antennas are added no WSi nanowire and the all these elements are deposed on the sapphire substrate. Our results show that the absorption/the detection efficiency of our proposed structure is much larger than the one with the niobium nitride (NbN) nanowire. There is an optimal width of WSi nanowire and the distance between WSi nanowire and metallic nano-antennas for the absorption/the detection efficiency of the detector. Our structure provides suitable parameters for designing SNSPD in experiments.

Insight into the thermodynamic properties of tungsten disilicides

Thermodynamic properties play a crucial role in high-temperature materials. Although WSi2 is a promising high-temperature material, the thermodynamic properties of WSi2 are unknown. We apply the first-principles to investigate the melting-point, Debye temperature and heat capacity of WSi2. The calculated melting-point of the hexagonal C40 structure, tetragonal C11b structure and orthorhombic C54 structure is 2256 K, 2559 K and 1856K, respectively. The calculated Debye temperature of WSi2 follows the order of C40 > C11b > C54. The thermodynamic properties of WSi2 derive from the vibration of the Si and Si-Si bond. However, the calculated heat capacity of C54 structure is larger than that of other structures.

Ultra-sensitive mid-infrared emission spectrometer with sub-ns temporal resolution.

We evaluate the performance of a mid-infrared emission spectrometer operating at wavelengths between 1.5 and 6 μm based on an amorphous tungsten silicide (a-WSi) superconducting nanowire single-photon detector (SNSPD). We performed laser induced fluorescence spectroscopy of surface adsorbates with sub-monolayer sensitivity and sub-nanosecond temporal resolution. We discuss possible future improvements of the SNSPD-based infrared emission spectrometer and its potential applications in molecular science.

Nonbolometric bottleneck in electron-phonon relaxation in ultrathin WSi films

We developed the model of the internal phonon bottleneck to describe the energy exchange between the acoustically soft ultrathin metal film and acoustically rigid substrate. Discriminating phonons in the film into two groups, escaping and nonescaping, we show that electrons and nonescaping phonons may form a unified subsystem, which is cooled down only due to interactions with escaping phonons, either due to direct phonon conversion or indirect sequential interaction with an electronic system. Using an amplitude-modulated absorption of the sub-THz radiation technique, we studied electron-phonon relaxation in ultrathin disordered films of tungsten silicide. We found an experimental proof of the internal phonon bottleneck. The experiment and simulation based on the proposed model agree well, resulting in tau_{e-ph} = 140-190 ps at T_C = 3.4 K, supporting the results of earlier measurements by independent techniques.