High Figure Of Merit Research Articles

High Aspect-Ratio Open Grating Fabry-Perot Resonator for High-Sensitivity Refractive Index Sensing

This paper presents a high aspect-ratio open grating Fabry-Perot resonator theoretically and experimentally for aqueous refractive index sensing with high figure of merit. Transmission line modelling and associated Smith charts are utilized to give a better intuitive understanding of the physical sensing mechanism. The analysis aids understanding of the relative contribution to refractive index changes both within the grating fingers and external to them. Measurements of refractive index are carried out with Kretschmann coupling configuration for both transverse magnetic (TM) and transverse electric (TE) polarization. The results show an improvement of 10- and 44-fold in figure of merit over conventional SPR for TM and TE, respectively. When the designed system is analyzed for sensitivity, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${{1}.{874}\times }{{{10}}}^{-{8}}{\textit {RIU}}$ </tex-math></inline-formula> is achieved with a single frame even without a reference channel for noise cancellation. With 794 frames averaging (approximately 1-second acquisition time), the sensitivity of the system can be further improved to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${{1}.{609}\times }{{{10}}}^{{-{9}}}{\textit {RIU}}$ </tex-math></inline-formula> . The simulations and experimental results demonstrate strong potential for biosensing applications, e.g., kinetic molecular binding, ultrasensitive refractive index sensing and photoacoustic detection.

Highly Q-factor refractive index sensor based on graphene stack

The perfect absorber with high figure of merit (FOM) and sensitivity for mid-infrared application is developed in this study. The structure contains a nanoaperture as a resonator and multi-layer hyperbolic metamaterial of graphene-SiN is place under the nanoaperture to increasing the absorption. The results show how the chemical potential of graphene can improve the absorbance. Finally, a coat of SiO2 is pinpointed over the nanoaperture for enhance the absorption and protecting the surface. The proposed aperture is designed symmetrically based on crossed shape to reduce the polarization effects on sensing. The Q-factor has increased sharply to 3000 for the final device by utilizing the hyperbolic material structure. The left-hand characteristic of the hyperbolic metamaterial provides a condition for concentrating the surface Plasmon’s at the interface of the gold layer with the substrate, leading to the reflection reduction to − 46 dB. This absorber is considered as an optical sensor for various materials under test (MUT) in the optical spectrum and it is simulated by FIT method as a time-domain technique. This sensor has a sensitivity of 400 nm/RIU and the FOM of 89000 RIU−1.

Enhancing the performances of V2O3 thin films as p-type transparent conducting oxides via compressive strain

The traditional strategy for transparent conducting oxides (TCOs) follows the path of chemical design by increasing carrier concentrations in insulators through deliberate doping to coordinate the exclusive properties of electrical conductivity with optical transparency. Despite the success of n-type TCOs, the developed p-type TCOs based on chemical design exhibit much lower performance than the n-type counterparts primarily constrained by the hole doping trouble. Recently, the correlated metal of a V2O3 thin film has been reported as high-performance p-type TCOs with high hole concentration (&amp;gt;1022 cm−3). In this paper, we propose an alternative approach of compressive strain in V2O3 thin films toward further increasing the carrier concentration and, consequently, enhancing the performance of p-type TCOs. The compressive strain of the V2O3 thin film is realized by the lattice mismatch between V2O3 and Al2O3. Interestingly, carrier concentrations in strained V2O3 thin films can be increased by several times exceeding 1023 cm−3, which directly correlates with the increase (decrease) in a1g (egπ) orbital occupation as verified by the Raman spectrum. Meanwhile, the screened plasma energy of a strained V2O3 thin film shifts to ∼1.6 eV, which is less than 1.75 eV to assure the opening of the transparency window in the visible region. As a result, strained V2O3 thin films exhibit enhanced performance as p-type TCOs with relatively high figure of merit. These results indicate that the structural modification can open up an effective approach for increasing the carrier concentration and enhancing the performance of p-type TCOs.

Electromagnetic multipolar quasi-bound states in the continuum for optical sensing

Optical sensing is of vital importance in many applications, which has received extensive attention in recent years. The pursuit of optical sensing mechanism with higher figure of merit (FOM) is very important for various sensing applications. Bound states in the continuum (BIC) with theoretical infinite Q factor is an ideal candidate to effectively improve the FOM of optical sensor. Herein, we propose and numerically demonstrate an optical refractive index sensor based on the electromagnetic multipolar quasi-BICs of all-dielectric metasurfaces. Based on the eigen-solution and excitation simulation, we find that magnetic dipole (MD) quasi-BIC is the best candidate for optical refractive index sensing among the electromagnetic multipolar quasi-BICs in the proposed all dielectric metasurface. The sensitivity (S) and the value of FOM for the optical refractive index sensor are 225.27 nm/RIU and 441762.93, respectively. It is anticipated that our results might shed new light on the optical refractive index sensing of high sensitivity and ultra-high FOM.

Performance assessment of a novel 4H–SiC junctionless planar power MOSFET towards improving electrical properties

In this paper, a novel 4H–SiC power MOSFET structure based on junctionless (JL) concept is proposed. The proposed device is investigated using accurate numerical models based on Atlas TCAD device simulator. It is revealed that the use of cost-effective junctionless structure can allow overcoming problems related to power MOSFET channel resistance, which results in a high figure of merit (FoM) (BV2/Ron,sp = 2676/5.78 = 1236) without the need of lowering the drift region resistance. In addition, the analyzed device based on JL aspect exhibits a good reliability at short-circuit conditions. Moreover, the device breakdown voltage, specific on resistance and drain current are studied in order to reveal and provide some insights regarding the impact of design dimensions on these electrical performances. Besides, the output and transfer characteristics are compared to those of the conventional counterpart, as well as the critical electric field at breakdown. It is found that the proposed structure pave the way for achieving enhanced derived current capability, while maintaining excellent breakdown characteristics. These significant results makes the proposed JL structure a promising candidate toward the design of high-performance and cost-effective 4H–SiC MOSFETs, which are highly suitable for power electronics applications.

An A0 mode Lamb-wave AlN resonator on SOI substrate with vertically arranged double-electrodes

In this paper, a novel vertically arranged double-electrodes A0 mode Lamb-wave AlN resonator on SOI substrate with a high electromechanical coupling coefficient and high figure of merit (FOM) is reported. The AlN resonator has a sandwich structure with aluminum and N-type doped silicon as electrode layers and a 500 nm thick AlN film as piezoelectric layer. The resonator has only two electrodes vertically arranged rather than horizontal interdigitated (IDT) electrodes which is common in conventional Lamb-wave resonators. The electrode gaps for the vertically arranged double-electrodes resonators are defined by AlN layer thickness rather than by photolithography for lateral field excitation resonators, which results in higher electric field strength and higher electromechanical coupling efficient (). Compared with conventional thickness field excitation (TFE) resonators with floating bottom electrodes, the vertically arranged double-electrodes resonators have higher electric field strength as the potential difference is larger between the top electrode and bottom electrode than that between the IDT electrodes and floating electrode. As a result, a higher electromechanical coupling coefficient is achieved. Furthermore, the resonant frequency of the vertically arranged double-electrodes resonator presented in this work can be defined by photolithography by controlling the width of the silicon layer. The of the vertically arranged double-electrodes resonator calculated from the measurement results of admittance versus frequency by numerically fitting with the Butterworth Van Dyke model shows an increase by 3.85 times, from 0.073% to 0.281% compared with conventional TFE resonators, and the FOM also increases by three times, from 2.66 to 7.99. This work provides a new structure to design future AlN Lamb-wave resonators on SOI substrate.

Antimonene, CNT and MoS2 Based SPR-Fiber-Optic Probe for Tuberculosis Detection

In this work, two–dimensional (2D) materials-based surface plasmon resonance assisted fiber sensor is designed to detect the tuberculosis (TB) disease. Transfer matrix method (TMM) that includes characteristic matrix is applied to compute the reflection coefficient and transmitted power of normal and tuberculosis infected sample. Probe design is made up of multimode fiber core, polymer clad, silver (Ag) as plasmonic metal, and 2D material and analyte. Three 2D materials such as carbon-nanotube (CNT), MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and antimonene are explored to detect TB infection. The impact of introducing the CNT, MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and antimonene on the output of sensor is discussed in detail. The maximum figure of merit (FOM) and sensitivity values with probe-1, probe-2, and probe-3 are 95.23 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , 88.23 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> and 117.64 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> and 15000 nm/RIU, 20,000 nm/RIU, 20,000 nm/RIU, respectively. Sensitivity and FOM increases with an increase in refractive index (RI) of the TB sample with probe 2 and probe 3 design. In the case of probe 1 employing MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as 2D material, sensitivity and FOM increase first, reaches a maximum, and then decrease with an increase in RI. The proposed 2D materials based SPR fiber sensor with probe-3 design provides high FOM and sensitivity value makes it suitable platform to detect TB in the range of 1.343 RIU- 1.351 RIU.

Study of optical and thermoelectric properties of double perovskites Cs2KTlX6 (X = Cl, Br, I) for solar cell and energy harvesting

The double perovskites have emerging optical properties and extensively studied solar cells and renewable energy. In this work, we have investigated the optical, electronic and transport properties of Cs2KTlX6 (X = Cl, Br, I) using density functional theory. The thermodynamic stability is determined from the calculation of enthalpy of formation and structural stability is probed by computing the tolerance factor. Energy-volume optimization graphs reveal that lattice constant increased (11.31–12.80 Å) and bulk modulus decreased (20.46–15.90 GPa) with the increasing size of halogens. The optical properties are computed using TB-mBJ which reveals direct bandgaps (3.10, 2.0, 0.96) eV for (Cl, Br, I). In addition, the dielectric constant, refractive index, and reflectivity has been discussed in detail in the energy range of 0–6 eV. The absorption bands are recorded in infrared, visible and ultraviolet regions for Cl, Br and I based DPs. The temperature and chemical potential dependent transport properties are computed using BoltzTrap code. The appropriate values of thermoelectric parameters with high figure of merit at room temperature show the potential of these DPs for thermoelectric applications.

Composition-dependent contact resistivity in an n-type Mg3SbxBi2−x thermoelectric single leg

In the current thermoelectric research framework, the material used to assemble a module is selected simply based on its transport properties while assuming that thermoelectric junction contact resistivity values are nearly constant for a specific material matrix, which raises concerns regarding incorrect material selection and thus deficient device performance. Here, by analyzing the thermoelectric performance of a series of Mg3.2SbxBi1.99−xTe0.01-based compounds, as well as their electrical contact resistivity across the Fe/Mg3.2SbxBi1.99−xTe0.01/Fe interface, we show that the contact resistivity in the n-type Mg3.2SbxBi2−x thermoelectric single leg is composition-dependent and then demonstrate that the high contact resistivity of a junction based on a material with even the highest figure of merit (zT) may considerably restrict performance at the device level. To overcome this dilemma, a multi-layered single leg design is proposed and investigated with the goal to reduce contact resistivity and thus maximize the conversion efficiency of thermoelectric devices.

Deep-UV Transparent Conducting Oxide La-Doped SrSnO3 with a High Figure of Merit.

Perovskite stannate SrSnO3 (SSO) is attracting attention as ultraviolet transparent conducting oxides (UV TCOs) due to its ultrawide band gap and high conductivity. Here, we investigate in detail the thickness-dependent electrical, structural, and optical properties of sequentially strain-relaxed La-doped SrSnO3 (SLSO) epitaxial thin films. We find that the SLSO films grow as an orthorhombic Pnma phase with a–a–c+ in the c+ direction under the tensile strain. With the strain relaxation, as the films become thicker, vertical grain boundaries are created and the orthorhombic phase becomes reoriented to all three possible orientations. Simultaneously, the conductance starts to deviate from the linear behavior with increasing film thickness. Through the analysis of thickness fringes in optical transmittance, we found that a 120 nm thick nominally 4% La-doped SrSnO3 film has a figure of merit (φTC = 2.65 × 10–3 Ω–1) at λ = 300 nm in the deep-UV region, which is the highest value among the well-known candidates for UV TCOs reported to date.

Dual‐Quasi Bound States in the Continuum Enabled Plasmonic Metasurfaces

AbstractLocalized surface plasmon resonances (LSPRs) in metallic nanostructures attract great attention for their potential applications such as highly sensitive optical sensors. However, the performance of LSPR sensors is strongly hampered by their low quality (Q) factors due to the intrinsic ohmic losses and far‐field radiation losses. Here, a kind of all‐metal metasurfaces that can achieve high‐Q and high figure of merit (FOM) resonances based on bound states in the continuum (BICs), is theoretically designed and experimentally demonstrated. The devices can simultaneously exhibit symmetry‐protected and Friedrich–Wintgen quasi‐BICs features at normal incidence, leading to higher Q‐factors than those solely inspired by single quasi‐BIC. Additionally, the constraint of symmetrical dielectric environment for common metasurfaces can be released by utilizing a metal substrate rather than a dielectric one. The proof‐of‐concept experiments demonstrate the high performances of such dual quasi‐BIC based plasmonic refractive index sensors with the Q‐factor of 145, the sensitivity of 657 nm RIU‐1, and the FOM of 109 RIU‐1. These findings may stimulate some promising applications, such as biosensing, optical lasing, and light absorption.

Design of a 1.29–1.61GHz LC-VCO with Improved Phase Noise and Figure-of-Merit (FoMT) for GPS and Satellite Navigation

This paper demonstrates a low-phase noise and high FoMT differential CMOS LC-VCO working at 1.29–1.61[Formula: see text]GHz. An RC filter tail current source is used in this design to reduce the second-harmonic oscillation phase noise. The VCO is implemented in 180[Formula: see text]nm process technology. The post-layout simulation results indicate that this proposed VCO operates faithfully in the 1.29–1.61[Formula: see text]GHz band with a frequency tuning range (FTR) of 320[Formula: see text]MHz. By using inversion mode N-MOSFET varactor, the designed VCO obtains 22.06% FTR. The phase noise of the VCO is [Formula: see text]130.21[Formula: see text]dBc/Hz at 1[Formula: see text]MHz offset frequency. It consumes 4.01[Formula: see text]mW average power from 1.3[Formula: see text]V supply. The cell area occupied by the design is [Formula: see text]. Figure-of-merit considering FTR (FoM[Formula: see text] is [Formula: see text]194.14[Formula: see text]dBc/Hz at 1[Formula: see text]MHz offset frequency, phase noise and average power consumption. The proposed VCO can be used for low-phase noise GPS and satellite navigation.

A moving window-based spatial assessment method for dynamic urban growth simulations

This study proposes a spatial evaluation method for urban growth simulation based on moving windows, where the metrics measured within each window are considered to be those of the central cell. We also applied the generalized additive model to identify the quantitative relationship between the urban growth drivers and the spatial assessment metrics. A case study in Jiaxing city shows that the single-number overall accuracies (OAs) are above 94% and the figure-of-merits (FOMs) are above 27% in both 2010 and 2015. Most regions of the study area yield very high OAs and low FOMs while the regions around the administration centres yield low OAs and high FOMs. The spatial method can well indicate the model’s effects on the urban simulations in different regions. The spatial assessment can report the assessment metrics of each cell to produce assessment maps as well as quantify the relationship between drivers and assessment metrics.

Enhanced optoelectronic properties of magnetron sputtered ITO/Ag/ITO multilayers by electro-annealing

Indium tin oxide/silver/indium tin oxide (ITO/Ag/ITO) multilayers have attracted much attention to fulfill the growing need for high-performance transparent conducting oxide electrodes. To make these transparent multilayers work better, electro-annealing, which is a method of self-heating by electric current, can be effective. Moreover, the effect of current on ITO/Ag/ITO multilayers should be investigated to make sure that electronic devices will be reliable over their lifetime. In this study, ITO/Ag/ITO multilayer electrodes with varying Ag thicknesses were grown by DC magnetron sputtering at room temperature. Structural, optical, and electrical properties of these multilayers were investigated before and after electro-annealing. Measurement results revealed that improved optical transmittance and sheet resistance can be obtained by the optimization of Ag thickness for the as-grown ITO/Ag/ITO layers. The highest figure of merit (FoM) value of 17.37 × 10−3 Ω−1 with optical transmittance of 85.15% in the visible region and sheet resistance of 11.54 Ω/□ was obtained for the Ag thickness of 16.5 nm for as-grown samples. The electro-annealing of as-grown ITO/Ag/ITO multilayers led to improved optical behavior of the multilayer structure over a wide spectral range, especially in the near-infrared range. Electro-annealing also provided an improvement in the crystallinity and sheet resistance of the electrodes. The improvement of the electrical and optical properties of the structure enabled a FoM of 23.07 × 10−3 Ω−1 with the optical transmittance of 86.80% in the visible region and sheet resistance of 10.52 Ω/□. The findings of this work provide proper knowledge of the properties of ITO/Ag/ITO multilayers under electrical current and suggest that the overall performance of the multilayers can be improved by the electro-annealing process.

Pressure and Thickness Dependence of Physical Properties of ZnO:Ga Thin Films by Radio Frequency Magnetron Sputtering

Indium-free transparent conducting oxide films have attracted extensive attention in the field of optoelectronics. Ga-doped ZnO (GZO) thin films are deposited by radio frequency magnetron sputtering on glass substrates at a temperature of 200 °C with ZnO:Ga2O3 (3 wt%). The structural, electrical, and optical properties of the GZO thin films were investigated in terms of deposition pressure and film thickness variations. X-ray diffraction analysis showed that all the prepared GZO films exhibited hexagonal wurtzite crystal structure with a (002) preferential orientation along the c-axis, regardless of pressure and thickness. The average visible transmittance (including the glass substrate) in a wavelength range of 400–700 nm decreased with increasing thickness but varied less with pressure. The highest average visible transmittance reached 88.4% at the thickness of 150 nm and the pressure of 5 mTorr. The optical band gap of the GZO films calculated using Tauc’s method was in the range of about 3.6–3.9 eV. The resistivity of GZO thin films decreased with decreasing deposition pressure and increasing film thickness, and the minimum resistivity obtained at 5 mTorr and 1000 nm was 3.36 × 10-4 Ω-cm. The maximum figure of merit (FOM) of 3.09 × 10-2 Ω-1 was achieved at 5 mTorr and 1000 nm. The superior optical and electrical properties and high FOM show that the prepared GZO thin films are suitable for transparent conducting films and optoelectronic devices.

Electronic structures and thermoelectric properties of heavily doped n-type ZrCoBi from first principles calculations

We present a theoretical investigation on the electronic structures and the thermoelectric properties of doped ZrCoBi half-Heusler compound using a combination of density functional theory calculations, semi classical Boltzmann transport theory and deformation potential theory. The effect of doping is described by a combination of rigid band approximation (RBA) and a model that explicitly includes the dopant atom within the lattice of ZrCoBi. The results demonstrate a high power factor with considerable n- and p-doping concentrations at high temperatures. Our findings further reveal that the electronic transport coefficients of ZrCo0.75M0.25Bi (M = Ni, Pd, Pt) are comparable because of their identical electronic structures. At 900 K, a high figure of merit (ZT) of ~ 0.35, ~ 0.38, and ~ 0.40 are obtained for ZrCo0.75Ni0.25Bi, ZrCo0.75Pd0.25Bi and ZrCo0.75Pt0.25Bi respectively.

±0.3V Bulk-Driven Fully Differential Buffer with High Figures of Merit

A high performance bulk-driven rail-to-rail fully differential buffer operating from ±0.3V supplies in 180 nm CMOS technology is reported. It has a differential–difference input stage and common mode feedback circuits implemented with no-tail, high CMRR bulk-driven pseudo-differential cells. It operates in subthreshold, has infinite input impedance, low output impedance (1.4 kΩ), 86.77 dB DC open-loop gain, 172.91 kHz bandwidth and 0.684 μW static power dissipation with a 50-pF load capacitance. The buffer has power efficient class AB operation, a small signal figure of merit FOMSS = 12.69 MHzpFμW−1, a large signal figure of merit FOMLS = 34.89 (V/μs) pFμW−1, CMRR = 102 dB, PSRR+ = 109 dB, PSRR− = 100 dB, 1.1 μV/√Hz input noise spectral density, 0.3 mVrms input noise and 3.5 mV input DC offset voltage.

DFT study of double perovskites Cs2AgBiX6 (X = Cl, Br): An alternative of hybrid perovskites

The double perovskites are promising materials for renewable energy to fulfil the challenges of energy requirements in the world. Therefore, in this article, the optical, thermoelectric, thermodynamic, and mechanical properties of Cs2AgBiX6 (X ​= ​Cl, Br) are addressed comprehensively by the DFT approach. The stabilities regarding structure, and thermodynamics are ensured by findings of tolerance factor, and formation energy. The mechanical stability and ductile nature has been confirmed from elastic constants, Passion's, and Pugh's rules. The hardness, Debye temperature, longitudinal and transverse velocities of sounds are also explained for thermodynamic behavior understanding. The band gap for Cs2AgBiCl6 is 2.76 ​eV, which reduces to 1.9 ​eV by changing Cl with Br due to pd-hybridization of anions and cations. The optical characteristics are elaborated by dielectric constants, absorption, refractive index, and reflectivity. The absorption in visible and ultraviolet regions make them significantly important for solar cells. The ultralow lattice thermal conductivity and high figure of merit have been computed due to large Seebeck coefficient and electrical conductivity.

D-Shaped Surface Plasmon Photonic Crystal Fiber Temperature Sensor

A D-shaped photonic crystal fiber (PCF) temperature sensor based on surface plasmon resonance (SPR) with high sensitivity and high figure of merit is presented in this paper. To enhance surface plasmon resonance, the gold film is deposited on the polished flat of D-shaped photonic crystal fiber. Ethanol and chloroform are employed as temperature-sensitive materials, which are placed on the outside of the fiber to detect temperature changes. When the phase-matching condition is met, the core mode couples with the surface plasma mode. The finite element method is used to perform all numerical simulations of sensor characteristics in the COMSOL software. The results show that the highest sensitivity of the sensor can reach 6.36 nm/°C and the maximum figure of merit (FOM) is 0.3440/°C in the range of −5 ~ 60 °C. To our knowledge, the achieved sensing characteristics are significantly better than those of the current PCF temperature sensors. Furthermore, excellent linearity with a polynomial fit R2 as high as 0.9981. The proposed sensor has exceptional performance in terms of temperature detection range, sensitivity, FOM, and fabrication, making it suitable for a wide variety of biochemical and medical applications.

A very high-resolution refractive index sensor based on hybrid topology of photonic crystal cavity and plasmonic nested split-ring resonator

In this paper, an optical refractive index (RI) sensor based on a photonic crystal and plasmonic (PhC-P) hybrid topology is designed. The sensor's structure is composed of nested circular metallic split-ring resonators (NCMSRR), which are embedded inside a hexagonal cavity in a rod-type photonic crystal (PhC) structure. The finite-difference time-domain (FDTD) method is used for the numerical simulation of the sensor. The obtained results show that by the cooperative coupling between the surface plasmon polaritons (SPP) induced by the NCMSRR and resonant PhC cavity modes, a hybrid PhC-P mode is created. The hybrid mode provides unique opportunities, not only for incrementing the sensitivity but also for obtaining a much higher figure of merit (FoM) compared to modes belonging to purely plasmonic or purely PhC sensors. The simulation results demonstrate a fairly high sensitivity of 1250 nm/RIU and an excellent FoM of 2083 RIU−1 when the proposed sensor is exposed to hazardous gases. These results show considerable improvement compared to the works published in the literature. Accordingly, the sensor proposed in this paper has tremendous potential to be used for high-sensitivity and high-resolution sensing applications at optical communication wavelengths.