The temperature characteristic of the reading current of the NOR embedded flash memory with a 1.5T-per-cell structure is theoretically analyzed and experimentally verified. We verify that for a cell programmed with a “10” state, the reading current is either increasing, decreasing, or invariable with the temperature, depending on the reading overdrive voltage of the selected bitcell, or its programming strength essentially. By precisely controlling the programming strength and thus manipulating its temperature coefficient, we propose a new setting method for the reference cells, which is to program each of the reference cells to a charge state with a temperature coefficient closely tracking tail data cells, thereby solving the current coefficient mismatch and improving read window.
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A 4H-SiC trench gate metal–oxide–semiconductor field-effect transistor (UMOSFET) with semi-super-junction shielded structure (SS-UMOS) is proposed and compared with conventional trench MOSFET (CT-UMOS) in this work. The advantage of the proposed structure is given by comprehensive study of the mechanism of the local semi-super-junction structure at the bottom of the trench MOSFET. In particular, the influence of the bias condition of the p-pillar at the bottom of the trench on the static and dynamic performances of the device is compared and revealed. The on-resistance of SS-UMOS with grounded (G) and ungrounded (NG) p-pillar is reduced by 52% (G) and 71% (NG) compared to CT-UMOS, respectively. Additionally, gate oxide in the GSS-UMOS is fully protected by the p-shield layer as well as semi-super-junction structure under the trench and p-base regions. Thus, a reduced electric-field of 2 MV/cm can be achieved at the corner of the p-shield layer. However, the quasi-intrinsic protective layer cannot be formed in NGSS-UMOS due to the charge storage effect in the floating p-pillar, resulting in a large electric field of 2.7 MV/cm at the gate oxide layer. Moreover, the total switching loss of GSS-UMOS is 1.95 mJ/cm2 and is reduced by 18% compared with CT-UMOS. On the contrary, the NGSS-UMOS has the slowest overall switching speed due to the weakened shielding effect of the p-pillar and the largest gate-to-drain capacitance among the three. The proposed GSS-UMOS plays an important role in high-voltage and high-frequency applications, and will provide a valuable idea for device design and circuit applications.
Discrimination of dislocations is critical to the statistics of dislocation densities in 4H silicon carbide (4H-SiC), which are routinely used to evaluate the quality of 4H-SiC single crystals and homoepitaxial layers. In this work, we show that the inclination angles of the etch pits of molten-alkali etched 4H-SiC can be adopted to discriminate threading screw dislocations (TSDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) in 4H-SiC. In n-type 4H-SiC, the inclination angles of the etch pits of TSDs, TEDs and BPDs in molten-alkali etched 4H-SiC are in the ranges of 27°−35°, 8°−15° and 2°−4°, respectively. In semi-insulating 4H-SiC, the inclination angles of the etch pits of TSDs and TEDs are in the ranges of 31°−34° and 21°−24°, respectively. The inclination angles of dislocation-related etch pits are independent of the etching duration, which facilitates the discrimination and statistic of dislocations in 4H-SiC. More significantly, the inclination angle of a threading mixed dislocations (TMDs) is found to consist of characteristic angles of both TEDs and TSDs. This enables to distinguish TMDs from TSDs in 4H-SiC.
To solve the Flash-based FPGA in the manufacturing process, the ion implantation process will bring electrons into the floating gate of the P-channel Flash cell so that the Flash switch is in a weak conduction state, resulting in the Flash-based FPGA eigenstate current problem. In this paper, the mechanism of its generation is analyzed, and four methods are used including ultraviolet light erasing, high-temperature baking, X-ray irradiation, and circuit logic control. A comparison of these four methods can identify the circuit design by using circuit logic to control the path of the power supply that is the most suitable and reliable method to solve the Flash-based FPGA eigenstate current problem. By this method, the power-on current of 3.5 million Flash-based FPGA can be reduced to less than 0.3 A, and the chip can start normally. The function and performance of the chip can then be further tested and evaluated, which is one of the key technologies for developing Flash-based FPGA.
High-performance germanium (Ge) waveguide photodetectors are designed and fabricated utilizing the inductive-gain-peaking technique. With the appropriate integrated inductors, the 3-dB bandwidth of photodetectors is significantly improved owing to the inductive-gain-peaking effect without any compromises to the dark current and optical responsivity. Measured 3-dB bandwidth up to 75 GHz is realized and clear open eye diagrams at 64 Gbps are observed. In this work, the relationship between the frequency response and large signal transmission characteristics on the integrated inductors of Ge waveguide photodetectors is investigated, which indicates the high-speed performance of photodetectors using the inductive-gain-peaking technique.
In recent years, Janus two-dimensional (2D) materials have received extensive research interests because of their outstanding electronic, mechanical, electromechanical, and optoelectronic properties. In this work, we explore the structural, electromechanical, and optoelectronic properties of a novel hypothesized Janus InGaSSe monolayer by means of first-principles calculations. It is confirmed that the Janus InGaSSe monolayer indeed show extraordinary charge transport properties with intrinsic electron mobility of 48 139 cm2/(V·s) and hole mobility of 16 311 cm2/(V·s). Both uniaxial and biaxial strains can effectively tune its electronic property. Moreover, the Janus InGaSSe monolayer possesses excellent piezoelectric property along both in-plane and out-of-plane directions. The results of this work imply that the Janus InGaSSe monolayer is in fact an efficient photocatalyst candidate, and may provide useful guidelines for the discovery of other new 2D photocatalytic and piezoelectric materials.
In the present study, a simple method for the preparation of a luminescent flexible gallium doped zinc oxide (GZO)/polystyrene nanocomposite film was developed. The prepared GZO powder was characterized through different optical and structural techniques. The XRD study revealed the existence of a wurtzite structure with no extra oxide peaks. Elemental-mapping, EDX, FTIR and XPS analyses were used to confirm the presence of elements and the several groups present in the structure. Under excitations of UV, the prepared hybrid nanocomposite showed a strong cyan emission with narrow full width at half the maximum value (20 nm) that has not been reported before. X-ray and laser-induced luminescence results of the hybrid film revealed novel blue-green emission at room temperature. The prepared composite film showed a strong scintillation response to ionizing radiation. The strong emissions, very weak deep-level emissions, and low FWHM of composite indicate the desirable optical properties with low-density structural defects in the GZO composite structure. Therefore, the prepared hybrid film can be considered to be a suitable candidate for the fabrication of optoelectronic devices.
Silicon solar cells continue to dominate the market, due to the abundance of silicon and their acceptable efficiency. The heterojunction with intrinsic thin layer (HIT) structure is now the dominant technology. Increasing the efficiency of these cells could expand the development choices for HIT solar cells. We presented a detailed investigation of the emitter a-Si:H(n) layer of a p-type bifacial HIT solar cell in terms of characteristic parameters which include layer doping concentration, thickness, band gap width, electron affinity, hole mobility, and so on. Solar cell composition: (ZnO/nc-Si:H(n)/a-Si:H(i)/c-Si(p)/a-Si:H(i)/nc-Si:H(p)/ZnO). The results reveal optimal values for the investigated parameters, for which the highest computed efficiency is 26.45% when lighted from the top only and 21.21% when illuminated from the back only.
Potassium-ion batteries (PIBs) have been considered a promising candidate in the post-lithium-ion battery era. Till now, a large number of materials have been used as electrode materials for PIBs, among which vanadium oxides exhibit great potentiality. Vanadium oxides can provide multiple electron transfers during electrochemical reactions because vanadium possesses a variety of oxidation states. Meanwhile, their relatively low cost and superior material, structural, and physicochemical properties endow them with strong competitiveness. Although some inspiring research results were achieved, many issues and challenges remain to be further addressed. Herein, we systematically summarize the research progress of vanadium oxides for PIBs. Then, feasible improvement strategies for the material properties and electrochemical performance are introduced. Finally, the existing challenges and perspectives are discussed with a view to promoting the development of vanadium oxides and accelerating their practical applications.
Silicon nanomaterials have been of immense interest in the last several decades due to their remarkable optoelectronic responses, elemental abundance, and higher biocompatibility. Two-dimensional silicon is one of the new allotropes of silicon with compelling properties such as quantum-confined photoluminescence, high charge carrier mobilities, anisotropic electronic and magnetic response, and non-linear optical properties. This review summarizes recent advancements in the synthesis of two-dimensional silicon nanomaterials with various structures (silicene, silicane, and multilayered silicon), surface ligand engineering, and the corresponding optoelectronic applications.
The electronic structure and optical properties of bilayer germanene under different warpages are studied by the first-principles method of density functional theory. The effects of warpages on the electronic structure and optical properties of bilayer germanene are analyzed. The results of the electronic structure study show that the bottom of the conduction band of bilayer germanene moves to the lower energy direction with the increase of warpages at the K point, and the top of the valence band stays constant at the K point, and so the band gap decreases with the increase of warpage. When the warpage is 0.075 nm, the top of the valence band of bilayer germanene changes from K point to G point, and the bilayer germanene becomes an indirect band gap semiconductor. This is an effective means to modulate the conversion of bilayer germanene between direct band gap semiconductor and indirect band gap semiconductor by adjusting the band structure of bilayer germanene effectively. The study of optical properties shows that the effect of warpage on the optical properties of bilayer germanene is mainly distributed in the ultraviolet and visible regions, and the warpage can effectively regulate the electronic structure and optical properties of bilayer germanene. When the warpage is 0.069 nm, the first peak of dielectric function and extinction coefficient is the largest, and the energy corresponding to the absorption band edge is the smallest. Therefore, the electron utilization rate is the best when the warpage is 0.069 nm.
The atomic structure and surface chemistry of GaP/Si(100) heterostructure with different pre-layers grown by molecular beam epitaxy are studied. It is found that GaP epilayer with Ga-riched pre-layers on Si(100) substrate has regular surface morphology and stoichiometric abrupt heterointerfaces from atomic force microscopes (AFMs) and spherical aberration-corrected transmission electron microscopes (ACTEMs). The interfacial dynamics of GaP/Si(100) heterostructure is investigated by X-ray photoelectron spectroscopy (XPS) equipped with an Ar gas cluster ion beam, indicating that Ga pre-layers can lower the interface formation energy and the bond that is formed is more stable. These results suggest that Ga-riched pre-layers are more conducive to the GaP nucleation as well as the epitaxial growth of GaP material on Si(100) substrate.
In recent years, one-dimensional (1D) nanomaterials have raised researcher's interest because of their unique structural characteristic to generate and confine the optical signal and their promising prospects in photonic applications. In this review, we summarized the recent research advances on the spectroscopy and carrier dynamics of 1D nanostructures. First, the condensation and propagation of exciton–polaritons in nanowires (NWs) are introduced. Second, we discussed the properties of 1D photonic crystal (PC) and applications in photonic–plasmonic structures. Third, the observation of topological edge states in 1D topological structures is introduced. Finally, the perspective on the potential opportunities and remaining challenges of 1D nanomaterials is proposed.
Significant advancements in nanoscale material efficiency optimization have made it feasible to substantially adjust the thermoelectric transport characteristics of materials. Motivated by the prediction and enhanced understanding of the behavior of two-dimensional (2D) bilayers (BL) of zirconium diselenide (ZrSe2), hafnium diselenide (HfSe2), molybdenum diselenide (MoSe2), and tungsten diselenide (WSe2), we investigated the thermoelectric transport properties using information generated from experimental measurements to provide inputs to work with the functions of these materials and to determine the critical factor in the trade-off between thermoelectric materials. Based on the Boltzmann transport equation (BTE) and Barden-Shockley deformation potential (DP) theory, we carried out a series of investigative calculations related to the thermoelectric properties and characterization of these materials. The calculated dimensionless figure of merit (ZT) values of 2DBL-MSe2 (M = Zr, Hf, Mo, W) at room temperature were 3.007, 3.611, 1.287, and 1.353, respectively, with convenient electronic densities. In addition, the power factor is not critical in the trade-off between thermoelectric materials but it can indicate a good thermoelectric performance. Thus, the overall thermal conductivity and power factor must be considered to determine the preference of thermoelectric materials.
Silicon on glasses process is a common preparation method of micro-electro-mechanical system inertial devices, which can realize the processing of thick silicon structures. The paper proposes that the indium tin oxides (ITO) film can be severed as a deep silicon etching cut-off layer, for ITO is damaged less under the attack of fluoride ions. ITO has good electrical conductivity and can absorb fluoride ions for silicon etching, reducing the reflection of fluoride ions, thus reducing the foot effect. The removal and release of ITO adopt an acidic solution, which does not damage the silicon structure. Therefore, the selection of the sacrificial layer has an excellent effect on maintaining the shape of the MEMS structure size. This method is used in the preparation of MEMS accelerometers with a structure thickness of 100 μm and a feature size of 4 μm. The over-etching of the bottom of the silicon structure caused by the foot effect is negligible, and the difference between the simulated value and the designed value of the device characteristic frequency is less than 5%, indicating that ITO is excellent deep silicon etch stopper material.
Wavelength-tunable organic semiconductor lasers based on mechanically stretchable polydimethylsiloxane (PDMS) gratings were developed. The intrinsic stretchability of PDMS was explored to modulate the period of the distributed feedback gratings for fine tuning the lasing wavelength. Notably, elastic lasers based on three typical light-emitting molecules show comparable lasing threshold values analogous to rigid devices and a continuous wavelength tunability of about 10 nm by mechanical stretching. In addition, the stretchability provides a simple solution for dynamically tuning the lasing wavelength in a spectral range that is challenging to achieve for inorganic counterparts. Our work has provided a simple and efficient method of fabricating tunable organic lasers that depend on stretchable distributed feedback gratings, demonstrating a significant step in the advancement of flexible organic optoelectronic devices.
Two-dimensional materials have shown great application potential in high-performance electronic devices because they are ultrathin, have an ultra-large specific surface area, high carrier mobility, efficient channel current regulation, and extraordinary integration. In addition to graphene, other types of 2D nanomaterials have also been studied and applied in photodetectors, solar cells, energy storage devices, and so on. Bi2O2Se is an emerging 2D semiconductor material with very high electron mobility, modest bandgap, near-ideal subthreshold swing, and excellent thermal and chemical stability. Even in a monolayer structure, Bi2O2Se has still exhibited efficient light absorption. In this mini review, the latest main research progresses on the preparation methods, electric structure, and the optical, mechanical, and thermoelectric properties of Bi2O2Se are summarized. The wide rang of applications in electronics and photoelectronic devices are then reviewed. This review concludes with a discussion of the existing open questions/challenges and future prospects for Bi2O2Se.
Colloidal CdSe quantum dots (QDs) are promising materials for solar cells because of their simple preparation process and compatibility with flexible substrates. The QD radiative recombination lifetime has attracted enormous attention as it affects the probability of photogenerated charges leaving the QDs and being collected at the battery electrodes. However, the scaling law for the exciton radiative lifetime in CdSe QDs is still a puzzle. This article presents a novel explanation that reconciles this controversy. Our calculations agree with the experimental measurements of all three divergent trends in a broadened energy window. Further, we proved that the exciton radiative lifetime is a consequence of the thermal average of decays for all thermally accessible exciton states. Each of the contradictory size-dependent patterns reflects this trend in a specific size range. As the optical band gap increases, the radiative lifetime decreases in larger QDs, increases in smaller QDs, and is weakly dependent on size in the intermediate energy region. This study addresses the inconsistencies in the scaling law of the exciton lifetime and gives a unified interpretation over a widened framework. Moreover, it provides valuable guidance for carrier separation in the thin film solar cell of CdSe QDs.
We report on the synthesis of Sn-doped hematite nanoparticles (Sn-α-Fe2O3 NPs) by the hydrothermal method. The prepared Sn-α-Fe2O3 NPs had a highly pure and well crystalline rhombohedral phase with an average particle size of 41.4 nm. The optical properties of as-synthesized α-Fe2O3 NPs show a higher bandgap energy (2.40–2.57 eV) than that of pure bulk α-Fe2O3 (2.1 eV). By doping Sn into α-Fe2O3 NPs, the Sn-doped hematite was observed a redshift toward a long wavelength with increasing Sn concentration from 0% to 4.0%. The photocatalytic activity of Sn-doped α-Fe2O3 NPs was evaluated by Congo red (CR) dye degradation. The degradation efficiency of CR dye using Sn-α-Fe2O3 NPs catalyst is higher than that of pure α-Fe2O3 NPs. The highest degradation efficiency of CR dye was 97.8% using 2.5% Sn-doped α-Fe2O3 NPs catalyst under visible-light irradiation. These results suggest that the synthesized Sn-doped α-Fe2O3 nanoparticles might be a suitable approach to develop a photocatalytic degradation of toxic inorganic dye in wastewater.
We report the study of magnetic and transport properties of polycrystalline and single crystal Na(Zn,Mn)Sb, a new member of “111” type of diluted magnetic materials. The material crystallizes into Cu2Sb-type structure which is isostructural to “111” type Fe-based superconductors. With suitable carrier and spin doping, the Na(Zn,Mn)Sb establishes spin-glass ordering with freezing temperature (Tf) below 15 K. Despite lack of long-range ferromagnetic ordering, Na(Zn,Mn)Sb single crystal still shows sizeable anomalous Hall effect below Tf. Carrier concentration determined by Hall effect measurements is over 1019 cm–3. More significantly, we observe colossal negative magnetoresistance (MR ≡ [ρ(H) − ρ(0)]/ρ(0)) of –94% in the single crystal sample.
Chip-sized alkali atom vapor cells with high hermeticity are successfully fabricated through deep silicon etching and two anodic bonding processes. A self-built absorption spectrum testing system is used to test the absorption spectra of the rubidium atoms in alkali atom vapor cells. The influence of silicon cavity size, filling amount of rubidium atoms and temperature on the absorption spectra of rubidium atom vapor in the atom vapor cells are studied in depth through a theoretical analysis. This study provides a reference for the design and preparation of high quality chip-sized atom vapor cells.
Flexible humidity sensors are effective portable devices for human respiratory monitoring. However, the current preparation of sensitive materials need harsh terms and the small production output limits their practicability. Here, we report a synthesis method of single-crystal BiOBr nanosheets under room temperature and atmospheric pressure based on a sonochemical strategy. A flexible humidity sensor enabled by BiOBr nanosheets deliver efficient sensing performance, a high humidity sensitivity (Ig/I0 = 550%) with relative humidity from 40% to 100%, an excellent selectivity, and a detection response/recovery time of 11 and 6 s, respectively. The flexible humidity sensor shows a potential application value as a wearable monitoring device for respiratory disease prevention and health monitoring.
In this work, carbon fiber and polyaniline (CF|PANI) composites are prepared by using an electrochemical polymerization method. The morphology and composition characterization results show that the PANI nanospheres are successfully synthesized and coated on the CF uniformly. When the electrodeposition period is 300 cycles, the as-prepared CF|PANI electrode exhibits good specific capacitance of 231.63 F/g at 1 A/g, high performance of 98.14% retention rate from 0.5 to 20 A/g, and excellent cycle stability with only 0.96% capacity loss after 1000 cycles. This is ascribed to the internal resistance reduced significantly without binders, which helps to the CF|PANI electrode maintains high operating potential and pseudo-capacitance performance at high current density. The symmetrical supercapacitor based on two CF|PANI electrodes connecting by acidic PVA-H2SO4 gel electrolyte exhibits an energy density of 6.55 W·h/kg at a power density of 564.37 W/kg. Also, the asymmetric supercapacitor based on MoS2|MWCNTs and CF|PANI electrodes with neutral PVA-Na2SO4 gel electrolyte shows an energy density of 16.12 W·h/kg at a power density of 525.03 W/kg. These results indicate that the low internal resistance contributes to the high energy density of symmetrical supercapacitors and asymmetric supercapacitors at high current density and high power density, which is significant for its practical application.
Laser writing is a fast and efficient technology that can produce graphene with a high surface area, whereas laser-induced graphene (LIG) was widely used in both physics and chemical device application fields according to recent studies. It is very necessary to update these important progresses, which may provide a clue to consider the current challenges and the possible future directions. In this review, the basic principles of LIG fabrication were first briefly described for a deep understanding of the lasing process. Subsequently, we summarized the physical device applications of LIG and their advantages, including flexible electronics and energy harvesting. Then, chemical device applications were categorized into chemical sensors, supercapacitors, batteries, and electrocatalysis, and a detailed interpretation was provided. Finally, we present our vision of future developments and challenges in this exciting research field.
We present a series of Sm3+/Tb3+ co-doped CaMoO4 phosphors synthesized by an efficient method of microwave-assisted heating. The prepared CaMoO4 samples were characterized by X-ray diffraction, photoluminescence, and Commission Internationale de l’Elcairage (CIE) chromaticity diagram. The X-ray diffraction results confirmed that all of the synthesized CaMoO4 samples are crystallized in a pure tetragonal phase. The photoluminescence spectra significantly show both red- and green emission in the synthesized Sm3+/Tb3+ co-doped CaMoO4 phosphors. It is obvious that the variations in the intensity ratio of red/green emission depend on the molar ratio of Sm3+/Tb3+ co-doping and dominate the CIE color coordinates on the chromaticity diagram. The investigations evidence that the light-emitting region of Sm3+/Tb3+ co-doped CaMoO4 phosphors can be controlled by adjusting the molar ratio of Sm3+/Tb3+ ions, acting as advanced color-tunable phosphors for white-LEDs.
