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- 2018
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- University of Manchester
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Hydrothermal synthesis of quantum dots dispersed on conjugated polymer as an efficient electrodes for highly stable hybrid supercapacitors
摘要： Hydrothermal synthesis of graphene quantum dots (GQDs) composited with conjugated polymer were investigated the high specific capacitance and cyclic stability of supercapacitor. The situ chemical polymerization method was employed to synthesize the polypyrrole - graphene quantum dots (PPY-GQDs) composite at different concentrations of GQDs. The size, morphology and structural phase of the PPY- GQDs composites was studied by using Transmission Electron Microscope (TEM), Field Emission Scanning Electron Microscope (FESEM), Atomic Force Microscope (AFM) and X-ray diffractometry (XRD) techniques respectively. The optical and electrochemical measurements were carried out by using Ultraviolet-Visible (UV–Vis) Absorption spectroscopy, Photoluminescence Spectroscopy (PL) and electrochemical work station. The cyclic voltammetry (CV) results show enhanced current density and area of CV loop with increasing scan rate and the concentration of GQDs. The Supercapacitor was fabricated by two electrodes owns a high energy density 67.8 Wh/kg and 93 Wh/kg at a power density of 1210 W/kg and 1430 W/kg for PGC1 and PGC3 composites. The highest specific capacitance values 467.32 and 647.54F/g are achieved by PGC1 and PGC3 composite compare to pure PPY. The PPY-GQDs composites achieved excellent cycle stability until the 2000 cycle. Thus, it demonstrates that GQDs is playing a unique and important role in improving the performance of a hybrid supercapacitor device.
关键词： Electrochemical Impedance spectra,Graphene quantum dots,Specific capacitance,Supercapacitors,Polypyrrole
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE Conference on Power Electronics and Renewable Energy (CPERE) - Aswan City, Egypt (2019.10.23-2019.10.25)] 2019 IEEE Conference on Power Electronics and Renewable Energy (CPERE) - Common-Mode Voltage Analysis of Three-phase Quasi-Z Source Inverters for Transformerless Photovoltaic Systems
摘要： Reducing the capacitance of programmable capacitor arrays (PCAs), commonly used in analog integrated circuits, is necessary for low-energy applications. However, limited mismatch data are available for small capacitors. We report mismatch measurement for a 2-fF poly–insulator–poly (PIP) capacitor, which is the smallest reported PIP capacitor to the best of the authors’ knowledge. Instead of using complicated custom on-chip circuitry, direct mismatch measurement is demonstrated and veri?ed using Monte Carlo simulations and experimental measurements. Capacitive test structures composed of 9-bit PCAs are implemented in a low-cost 0.35-μm CMOS process. Measured data are compared to the mismatch of large PIP capacitors, theoretical models, and recently published data. Measurement results indicate an estimated average relative standard deviation of 0.43% for the 2-fF unit capacitor, which is better than the reported mismatch of metal–oxide–metal (MOM) fringing capacitors implemented in an advanced 32-nm CMOS process.
关键词： programmable capacitor array (PCA),Analog-to-digital converter (ADC),energy-ef?cient circuits,mismatch characterization,capacitance-to-digital converter (CDC),capacitor mismatch
更新于2025-09-23 15:21:01
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Polarization and charge carrier density coupling in epitaxial PbZr <sub/>0.2</sub> Ti <sub/>0.8</sub> O <sub/>3</sub> /ZnO heterostructures
摘要： The integration of ferroelectric materials with semiconductor heterostructures can greatly enhance the functionality of electronic devices, provided the ferroelectric material retains a significant part of its switchable polarization. This work reports polarization switching in epitaxial PbZr0.2Ti0.8O3/ZnO/GaN heterostructures grown on c-cut sapphire single-crystal substrates. The electrical measurements of PbZr0.2Ti0.8O3/ZnO ferroelectric/semiconductor capacitors reveal an unexpected difference between a counterclockwise ferroelectric hysteresis loop and a clockwise C-V loop. A non-linear hysteretic behavior of the capacitance is observed in the voltage range that is at least 3 times narrower than the range of ferroelectric polarization switching voltages. This difference can be explained by charge injection effects at the interface between ferroelectrics and semiconductors. The interaction between electric polarization and the electronic structure of the heterojunction leads to capacitance and charge carrier concentrations that are switchable by polarization of the ferroelectric layer. These findings are important for both fundamental and applied research of switchable and highly tunable ferroelectric/semiconductor heterostructures.
关键词： ferroelectric materials,polarization switching,charge injection effects,capacitance,semiconductor heterostructures
更新于2025-09-23 15:21:01
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Effects of postmetallization annealing on interface properties of Al <sub/>2</sub> O <sub/>3</sub> /GaN structures
摘要： In this study, we investigated the e?ects of postmetallization annealing (PMA) on the interface properties of GaN metal–oxide–semiconductor (MOS) structures using Al2O3 prepared by atomic layer deposition. Excellent capacitance–voltage (C–V ) characteristics without frequency dispersion were observed in the MOS sample after PMA in N2 ambient at 300–400 °C. The PMA sample showed state densities of only at most 4 ' 1010 cm%1 eV%1. A geometric phase analysis of transmission electron microscopy images after PMA revealed a uniform distribution of the lattice constant near the Al2O3/GaN interface, leading to the improved bond termination and bonding order con?guration along the interface.
关键词： atomic layer deposition,capacitance–voltage characteristics,Al2O3/GaN structures,interface properties,postmetallization annealing
更新于2025-09-23 15:21:01
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The Origin of Photoinduced Capacitance in Perovskite Solar Cells: Beyond Ionica??toa??Electronic Current Amplification
摘要： Photoinduced capacitances of perovskite solar cells exhibit peculiarities such as an apparently high capacitance and an inductive feature, so-called negative capacitance, which are not easily explained with typical carrier dynamics. Consequently, the origins of the photoinduced capacitances in perovskite solar cells have been intensively debated over the past several years. Here, the photoinduced capacitances of perovskite solar cells are analyzed by impedance spectroscopy. The analysis clarifies that the photoinduced capacitances of perovskite solar cells comprise several Debye relaxation-type capacitance components. Among these components, the photoinduced capacitance in the low-frequency range is attributed to ionic-to-electronic current amplification. However, the photoinduced capacitances in the middle- and high-frequency ranges originate from bipolar injection. The clear elucidation of the origins of the photoinduced capacitances in perovskite solar cells provides comprehensive insights for analyzing properties of perovskites in either the time or frequency domain.
关键词： perovskite solar cells,impedance spectroscopy,ionic to electronic response,negative capacitance
更新于2025-09-23 15:21:01
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Manganese doping stabilizes perovskite light-emitting diodes by reducing ion migration
摘要： Lead halide perovskite light-emitting diodes have recently emerged as high-performance devices. However, they degrade rapidly. This degradation has been attributed to the mixed ionic-electronic nature of these perovskites. Manganese doping increases the stability of perovskite light-emitting diodes, but the effects of manganese doping on ion migration are not well understood. We use impedance spectroscopy and transient ion-drift measurements to study the effect of manganese doping on ion migration in PEABr0.2Cs0.4MA0.6PbBr3 quasi-bulk 2D/3D perovskite light-emitting diodes. We find that manganese doping enhances the activation energy for ion migration two fold and reduces the diffusion coefficient. These changes in the behavior of mobile ions help to explain the improved stability in perovskite light-emitting diodes upon manganese doping and lead to a better understanding of the influence of passivating agents on ion migration and thus on the stability of the devices.
关键词： capacitance,perovskites,manganese,mobile ions,transient ion drift,impedance,light-emitting diodes
更新于2025-09-23 15:21:01
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[IEEE 2018 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) - Singapore (2018.7.16-2018.7.19)] 2018 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) - Nano C-V imaging of Semiconductor Devices with Scanning Microwave Impedance Microscopy
摘要： Two doped semiconductor samples are measured using probe-based Scanning Microwave Impedance Microscopy (sMIM). One is a plan-view polished CMOS image sensor and the other is a cross-section polished power device. Both samples are imaged with sMIM using two different approaches: the first using a dual pass method with dC/dV images acquired simultaneously with sMIM during the first pass in contact mode, and the second pass at a fixed offset from the surface. The second method uses a non-resonant mode where C-V are acquired at specific lateral locations. The C-V curves are used to determine polarity compared to dC/dV and also to distinguish p-n junctions, characterize doping concentration, and build images at constant DC values to discern subtle changes not evident in traditional SCM imaging.
关键词： Nano-C-V,SCM,Scanning Probe Microscopy,doping characterization,Scanning Microwave Impedance Microscopy,Scanning Capacitance Microscopy,sMIM
更新于2025-09-23 15:21:01
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A Wideband On-Chip Directional Coupler Using a Negative Capacitance Circuit
摘要： We propose a wideband lumped element directional coupler using lossy negative capacitance (NCAP). NCAP provides a broadband resonance effect combined with passive inductors and capacitors in a circuit, enabling the coupler to exhibit wideband directivity performance. In addition, a 3-dB loss in the NCAP enhanced the bandwidth at the expense of the transmission gain, which decreased by only 0.3 dB. The proposed coupler was implemented in the IBM 7RF 180-nm CMOS technology. The size of the core chip is 1180 μm × 570 μm. The designed NCAP provides a capacitance of ?13 pF using a supply voltage of 2.7 V and a current of 9.6 mA. The coupling was designed to be ?10 dB at the center frequency of 1 GHz. The bandwidth was de?ned by the frequency range, which exhibited a directivity of more than 30 dB. The S-parameter measurements showed an absolute bandwidth ranging from 0.86 to 1.12 GHz, and a fractional bandwidth of 26%. In the bandwidth, the coupling had a 0.5-dB variation, the transmission loss was smaller than 2.14 dB, and the noise ?gures were 1.8–2.5 dB.
关键词： Broadband resonance,wideband lumped element (LE) directional coupler,negative capacitance (NCAP)
更新于2025-09-23 15:21:01
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[IEEE 2018 IEEE AUTOTESTCON - National Harbor (Oxon Hill), MD, USA (2018.9.17-2018.9.20)] 2018 IEEE AUTOTESTCON - Spread Spectrum Time Domain Reflectometry for Complex Impedances: Application to PV Arrays
摘要： Spread spectrum time domain reflectometry (SSTDR) has previously been used for detection and location of intermittent faults on live electrical wiring. These intermittent faults can be open circuits, short circuits, or resistive changes, all of which preserve the original shape of the SSTDR correlated waveform. But things are very different when SSTDR encounters a complex impedance discontinuity such as a capacitor or inductor. In this case, the reflection is a function of frequency, changing the shape of the SSTDR signature. In this paper, we will show the SSTDR response to single capacitors and inductors. We will also explore how SSTDR responds to arrays of PV panels (which are capacitive) connected by wires. We will show both simulations and measurements. In some configurations, it is relatively easy to see faults, although algorithms are still under development. In other configurations, little change occurs, which makes it very difficult to create a system for testing for these faults.
关键词： Inductance,Complex impedances,Capacitance,Photovoltaic (PV) arrays,Spread spectrum time domain reflectometry (SSTDR)
更新于2025-09-23 15:21:01
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Structural, morphological and electrochemical properties of long alkoxy-functionalized polythiophene and TiO2 nanocomposites
摘要： High performance alkoxy-functionalized polythiophene (PM4EOT) and TiO2 nanocomposites were prepared via a facile in situ oxidative chemical polymerization of thiophene monomer. The morphology studied demonstrated that nanocomposites were of the core–shell structure with a particle size of approximately 30 nm and PM4EOT shell was of about 2–10 nm thickness. X-ray photoelectron spectroscopy (XPS) spectra proved that there was a new Ti–S interaction between the polymer and TiO2 surface. The supercapacitive behaviors of the nanocomposites investigated by cyclic voltammetry galvanostatic charge–discharge and AC impedance measurements demonstrated that the prepared PM4EOT/TiO2 nanocomposite [1:1 (weight ratio)] exhibits enhanced specific capacitance and cycling stability as compared to the two pristine components and various ratio contents. The specific capacitance of PM4EOT/TiO2 nanocomposite (1:1) was obtained up to 111 F/g at a current density of 0.5 A/g, which is much higher than that of the pure PM4EOT (45 F/g) and TiO2 (1.6 F/g). In addition, the energy density of 15.4 Wh kg?1 and the power density of 308 W kg?1 delivered by composite (1:1) capacitor were achieved at a current density of 0.5 A/g.
关键词： specific capacitance,TiO2 nanocomposites,supercapacitive behaviors,alkoxy-functionalized polythiophene,energy density
更新于2025-09-23 15:21:01