Showing papers on "Equivalent series resistance published in 2015"

Bulk GaN flip-chip violet light-emitting diodes with optimized efficiency for high-power operation

Abstract: We report on violet-emitting III-nitride light-emitting diodes (LEDs) grown on bulk GaN substrates employing a flip-chip architecture. Device performance is optimized for operation at high current density and high temperature, by specific design consideration for the epitaxial layers, extraction efficiency, and electrical injection. The power conversion efficiency reaches a peak value of 84% at 85 °C and remains high at high current density, owing to low current-induced droop and low series resistance.

Screen printed passive components for flexible power electronics

Abstract: Additive and low-temperature printing processes enable the integration of diverse electronic devices, both power-supplying and power-consuming, on flexible substrates at low cost. Production of a complete electronic system from these devices, however, often requires power electronics to convert between the various operating voltages of the devices. Passive components-inductors, capacitors, and resistors-perform functions such as filtering, short-term energy storage, and voltage measurement, which are vital in power electronics and many other applications. In this paper, we present screen-printed inductors, capacitors, resistors and an RLC circuit on flexible plastic substrates, and report on the design process for minimization of inductor series resistance that enables their use in power electronics. Printed inductors and resistors are then incorporated into a step-up voltage regulator circuit. Organic light-emitting diodes and a flexible lithium ion battery are fabricated and the voltage regulator is used to power the diodes from the battery, demonstrating the potential of printed passive components to replace conventional surface-mount components in a DC-DC converter application.

Generalized Optoelectronic Model of Series-Connected Multijunction Solar Cells

Abstract: The emission of light from each junction in a series-connected multijunction solar cell both complicates and elucidates the understanding of its performance under arbitrary conditions. Bringing together many recent advances in this understanding, we present a general 1-D model to describe luminescent coupling that arises from both voltage-driven electroluminescence and voltage-independent photoluminescence in nonideal junctions that include effects such as Sah–Noyce–Shockley (SNS) recombination with n ≠ 2, Auger recombination, shunt resistance, reverse-bias breakdown, series resistance, and significant dark area losses. The individual junction voltages and currents are experimentally determined from measured optical and electrical inputs and outputs of the device within the context of the model to fit parameters that describe the devices performance under arbitrary input conditions. Techniques to experimentally fit the model are demonstrated for a four-junction inverted metamorphic solar cell, and the predictions of the model are compared with concentrator flash measurements.

Bipolar Ripple Cancellation Method to Achieve Single-Stage Electrolytic-Capacitor-Less High-Power LED Driver

Abstract: Conventional topologies for high-power LED drivers with high power factors (PFs) require large capacitances to limit the low frequency (100 or 120 Hz) LED current ripples. Electrolytic capacitors are commonly used because they are the only capacitors with sufficient energy density to accommodate high-power applications. However, the short life span of electrolytic capacitors significantly reduces the life span of the entire LED lighting fixture, which is undesirable. This paper proposes a bipolar (ac) ripple cancellation method with two different full-bridge power structures to cancel the low-frequency ac ripple in the LED current and minimize the output capacitance requirement, enabling the use of long-life film capacitors. Compared with the existing technologies, the proposed circuit achieves zero double-line-frequency current ripple through LED lamps and achieves a high PF and high efficiency. A 100-W (150 V/0.7 A) LED driver prototype was built which demonstrates that the proposed method can achieve the same double-line-frequency LED current ripple with only 44- $\mu \text{F}$ film capacitors, compared with the 4700- $\mu \text{F}$ electrolytic capacitors required in the conventional single-stage LED drivers. Meanwhile, the proposed prototype has achieved a peak power efficiency of 92.5%, benefiting from active clamp technology.

InGaN based micro light emitting diodes featuring a buried GaN tunnel junction

Abstract: GaN tunnel junctions (TJs) are grown by ammonia molecular beam epitaxy. High doping levels are achieved with a net acceptor concentration close to ∼1020 cm−3, thanks to the low growth temperature. This allows for the realization of p-n junctions with ultrathin depletion width enabling efficient interband tunneling. n-p-n structures featuring such a TJ exhibit low leakage current densities, e.g., <5 × 10−5 A cm−2 at reverse bias of 10 V. Under forward bias, the voltage is 3.3 V and 4.8 V for current densities of 20 A cm−2 and 2000 A cm−2, respectively. The specific series resistance of the whole device is 3.7 × 10−4 Ω cm2. Then micro-light emitting diodes (μ-LEDs) featuring buried TJs are fabricated. Excellent current confinement is demonstrated together with homogeneous electrical injection, as seen on electroluminescence mapping. Finally, the I-V characteristics of μ-LEDs with various diameters point out the role of the access resistance at the current aperture edge.

Experimental evaluation of capacitors for power buffering in single-phase power converters

Abstract: Single-phase inverters and rectifiers require the use of an energy buffer to absorb the twice-line-frequency power ripple present on the AC side. Historically this challenge has been addressed by the use of large electrolytic capacitors. However reliability constraints and the need for improved system performance have motivated designers to seek other capacitor technologies such as ceramic and metal film which are frequently used in conjunction with active filtering converters to reduce the volume of required capacitance. Active filtering converters cycle the capacitor voltage over a wide voltage range while maintaining a constant DC bus voltage. This large-swing operation is very different from that of most other filtering applications, and the data sheet parameters available for commercial capacitors may be ineffective or require special care for calculating characteristics such as efficiency and energy storage capability. This work presents an experimental setup for evaluating capacitor performance under a large voltage swing. Energy storage data for several capacitors in the 50 V to 450 V range from several manufacturers is included. The approach and findings of this paper can serve as an aid to power electronics designers for the selection and evaluation of capacitors in energy buffering applications.

A Current-Sensorless Online ESR and C Identification Method for Output Capacitor of Buck Converter

Abstract: As electrolytic capacitor is apt to fail in power circuits, it is very important to identify its electrical parameters, mainly the equivalent series resistance (ESR) and capacitance ( C ). A noninvasive online identification method of capacitor's ESR and C for continuous-conduction-mode (CCM) buck converter is proposed in this paper. Based on the ac component of capacitor voltage, the calculation model is founded. By sampling the pulse width modulation signal and output voltage, the method needs no current sensor and is effective for the CCM buck converter operating at different conditions. Implementation of the identification system is presented. The tests are carried out for different aged capacitors and ambient temperatures. The experimental results validate the effectiveness of the method.

A Method for Identification of the Equivalent Inductance and Resistance in the Plant Model of Current-Controlled Grid-Tied Converters

Abstract: Precise knowledge of the plant time constant $L/R$ is essential to perform a thorough analysis and design of the current control loop in voltage source converters (VSCs). From the perspective of the current controller dynamics in the low-frequency range, such plant time constant is also suitable for most cases in which an LCL filter is used. As the loop behavior can be significantly influenced by the VSC working conditions, the effects associated to converter losses should be included in the model, through an equivalent series resistance. In addition, the plant inductance may also present important uncertainties with respect to the value of the VSC L/LCL interface filter measured at rated conditions. Thus, in this paper, a method is presented to estimate both parameters of the plant time constant, i.e., the equivalent inductance and resistance in the plant model of current-controlled VSCs. The proposed technique is based on the evaluation of the closed-loop transient responses of both axes of the synchronous reference frame when a proportional-integral current controller is implemented. The method gives a set of resistance and inductance values that should be employed for a rigorous design of the current controllers. Experimental results validate the approach.

Silver Nanowire Transparent Conductive Electrodes for High-Efficiency III-Nitride Light-Emitting Diodes

Abstract: Silver nanowires (AgNWs) have been successfully demonstrated to function as next-generation transparent conductive electrodes (TCEs) in organic semiconductor devices owing to their figures of merit, including high optical transmittance, low sheet resistance, flexibility, and low-cost processing In this article, high-quality, solution-processed AgNWs with an excellent optical transmittance of 965% at 450 nm and a low sheet resistance of 117 Ω/sq were demonstrated as TCEs in inorganic III-nitride LEDs The transmission line model applied to the AgNW contact to p-GaN showed that near ohmic contact with a specific contact resistance of ~10(-3) Ωcm(2) was obtained The contact resistance had a strong bias-voltage (or current-density) dependence: namely, field-enhanced ohmic contact LEDs fabricated with AgNW electrodes exhibited a 56% reduction in series resistance, 565% brighter output power, a 675% reduction in efficiency droop, and a approximately 30% longer current spreading length compared to LEDs fabricated with reference TCEs In addition to the cost reduction, the observed improvements in device performance suggest that the AgNWs are promising for application as next-generation TCEs, to realise brighter, larger-area, cost-competitive inorganic III-nitride light emitters

Bilayer insulator tunnel barriers for graphene-based vertical hot-electron transistors

Abstract: Vertical graphene-based device concepts that rely on quantum mechanical tunneling are intensely being discussed in the literature for applications in electronics and optoelectronics. In this work, the carrier transport mechanisms in semiconductor–insulator–graphene (SIG) capacitors are investigated with respect to their suitability as electron emitters in vertical graphene base transistors (GBTs). Several dielectric materials as tunnel barriers are compared, including dielectric double layers. Using bilayer dielectrics, we experimentally demonstrate significant improvements in the electron injection current by promoting Fowler–Nordheim tunneling (FNT) and step tunneling (ST) while suppressing defect mediated carrier transport. High injected tunneling current densities approaching 103 A cm−2 (limited by series resistance), and excellent current–voltage nonlinearity and asymmetry are achieved using a 1 nm thick high quality dielectric, thulium silicate (TmSiO), as the first insulator layer, and titanium dioxide (TiO2) as a high electron affinity second layer insulator. We also confirm the feasibility and effectiveness of our approach in a full GBT structure which shows dramatic improvement in the collector on-state current density with respect to the previously reported GBTs. The device design and the fabrication scheme have been selected with future CMOS process compatibility in mind. This work proposes a bilayer tunnel barrier approach as a promising candidate to be used in high performance vertical graphene-based tunneling devices.

Deep level transient spectroscopy in III-Nitrides: Decreasing the effects of series resistance

Abstract: A modification of deep level transient spectroscopy which varies the measurement frequency from 10 kHz to 1 MHz and is based on commercially available inductance–capacitance–resistance meters and pulse generators was tested for GaN films and AlGaN/GaN high electron mobility transistor structures with various series resistances. It is demonstrated that the measured spectra at high and low frequency follow the well documented frequency dependences of the stationary capacitance and magnitude of the capacitance transient. Measurements at low frequency allow for accurate determination of the concentration of the traps and, in many cases, detect traps that cannot be observed in the high frequency measurements. This is particularly valuable in materials like GaN where series resistance effects can be significant.

Z-source Dc circuit breakers with coupled inductors

Abstract: This paper considers design details of the z-source breaker. Specifically, the effect of coupled inductors on the z-source breaker is studied. It is shown that the inductor weight can be reduced by 30% and the inductor volume can be reduced by about 25% when coupled inductors are used. Furthermore, the coupling plays a part in the commutation process meaning that the breaker can operate with one capacitor instead of two. These results mean that the major components of the z-source breaker can be greatly reduced. Simulations are carried out to verify the results.

Analysis and Equivalent-Circuit Model for CMOS On-Chip Multiple Coupled Inductors in the Millimeter-Wave Region

Abstract: A growing number of on-chip inductors have been applied in the millimeter-wave IC design. The coupling effects between them have a negative impact on the performance of the circuit and each on-chip inductor. In this paper, a new equivalent-circuit model and a parameter extraction method for multiple on-chip inductors in the millimeter-wave region are proposed. The impacts of coupling effects on every on-chip inductor are comprehensive considered in the proposed parameter extraction method. The characteristics of the multiple on-chip-coupled inductors are analyzed, modeled, and measured. The test structures were fabricated by 0.18- $\mu \text{m}$ and 90-nm CMOS processes. The inductances, quality factors, and S-parameters of the model agree well with the measured performance of on-chip-nested and side-by-side-coupled inductors over a wide frequency range from 10 MHz up to millimeter-wave frequency band.

Design and Characterization of Integrated Submillimeter-Wave Quasi-Vertical Schottky Diodes

Abstract: This work reports on a new approach to realizing vertically oriented Schottky diodes, with ohmic contact formed directly below the anode, that can be readily integrated into planar millimeter and submillimeter-wave circuits. The diode structure is based on backside processing and bonding of the diode epitaxy to a host, high-resistivity silicon substrate that supports both the vertical diode and its associated circuitry. A set of prototype diodes of different anode diameters are fabricated for characterization at both dc and (for the first time) submillimeter-wave frequencies (325–750 GHz) using micromachined on-wafer probes. Device equivalent circuit parameters extracted from these measurements are in good agreement with those expected from fundamental Schottky barrier diode theory and indicate the vertically oriented diodes yield series resistance values that are comparable to or lower than planar-oriented diodes of similar dimensions.

Self-oscillation up to 9 MHz based on voltage triggered switching in VO2/TiN point contact junctions

Abstract: We demonstrate self-sustaining electrical oscillations with frequency of MHz range based on out-of-plane voltage-triggered switching in VO2 thin films grown on conductive layers. VO2 films deposited by a reactive sputtering method at a low temperature of 250 °C on conductive TiN layers showed thermally induced out-of-plane insulator-metal transition with two orders of change in resistance. By applying dc voltage to the layered device in a point contact configuration, self-sustaining electrical oscillations were triggered and the highest frequency of 9 MHz was achieved. Dependence of the frequency on the film thickness, as well as on the source voltage and on the series resistance, was examined in order to clarify the oscillation mechanism and the factors that affect the frequency. The oscillation frequency, which is dominated by recovering time from metallic to insulating state, decreased with increasing film thickness, indicating that the resistance of VO2 film determines the time constant for the recove...

A Comprehensive Study on the Frequency-Dependent Electrical Characteristics of Sm 2 O 3 MOS Capacitors

Abstract: In this paper, we report comprehensive frequency-dependent electrical characterizations of samarium oxide (Sm2O3) MOS capacitors. The Sm2O3 crystal structure and phase identifications of the films were confirmed by X-ray diffractometry. The electrical characterizations were performed in the wide frequency ranges by the capacitance-voltage ( $C$ – $V$ ) and conductance-voltage ( $G/\omega $ – $V$ ) measurements at room temperature and series resistance effects were investigated following the correction of the measured $C$ – $V$ and G/ $\omega $ – $V$ characteristics. Significant changes have been observed in capacitance, especially in conductance curves following the corrections. Interestingly, the corrected conductance gives two distinct peaks in the corresponding depletion and inversion edge. The $G_{c}/\omega $ – $V$ characteristics in the low-frequency regions decrease with increasing in the frequency, in the high-frequency regions slightly increase with increasing in frequency. In addition, similar distinct behaviors have been observed for the calculated interface state density, diffusion, and barrier potential at low-high frequencies. The main reason of these behaviors can be attributed to the acceptor-/donor-like interface states and/or different relaxation time dependences of interface states. These results demonstrate that series resistance and interface states should be considered during the electrical characterization. Calculated interface density and barrier potential are suitable to use the Sm2O3 as a dielectric layer for MOS-based applications.

Bilayer Insulator Tunnel Barriers for Graphene-Based Vertical Hot-electron Transistors

Abstract: Vertical graphene-based device concepts that rely on quantum mechanical tunneling are intensely being discussed in literature for applications in electronics and optoelectronics. In this work, the carrier transport mechanisms in semiconductor-insulator-graphene (SIG) capacitors are investigated with respect to their suitability as the electron emitter in vertical graphene base transistors (GBTs). Several dielectric materials as tunnel barriers are compared, including dielectric double layers. Using bilayer dielectrics, we experimentally demonstrate significant improvements in the electron injection current by promoting Fowler-Nordheim tunneling (FNT) and step tunneling (ST) while suppressing defect mediated carrier transports. High injected tunneling current densities approaching 10$^3$ A/cm$^2$ (limited by series resistance), and excellent current-voltage nonlinearity and asymmetry are achieved using a 1 nm-thick high quality dielectric, thulium silicate (TmSiO), as the first insulator layer, and titanium dioxide (TiO$_2$) as a high electron affinity second layer insulator. We also confirm the feasibility and effectiveness of our approach in a full GBT structure which shows dramatic improvement in the collector on-state current density with respect to the previously reported GBTs. The device design and the fabrication scheme have been selected with future CMOS process compatibility in mind. This work proposes a bilayer tunnel barrier approach as a promising candidate to be used in high performance vertical graphene-based tunneling devices.

Quantifying interface states and bulk defects in high‐efficiency solution‐processed small‐molecule solar cells by impedance and capacitance characteristics

Abstract: The AC properties of high-efficiency (η = 8.01% under standard 100 mW/cm2 AM1.5 illumination) small-molecule bulk heterojunction (SM BHJ) solar cells (p-DTS(FBTTh2)2/PC70BM) at different DC biases and frequencies of small amplitude (±10 mV) AC signal in the dark at room temperature were investigated in details. We showed the presence of interface states at the heterojunction interface and determined their parameters from the analysis of spectral distributions of real and imaginary components of the measured impedance. The dielectric constant of BHJ eBHJ = 2.9 was determined from the geometrical capacitance of totally depleted BHJ layer. We explained quantitatively the effect of interface states and series resistance on the measured C-V characteristics of the SM BHJ solar cells at both low and high frequencies. The quantitative value of the density of defect states in the bulk N = 1.05 × 1016 cm−3 was determined from the high frequency C-V characteristic corrected by the effect of the series resistance. Copyright © 2015 John Wiley & Sons, Ltd.

Single transistor high linearity and wide dynamic range active inductor

Abstract: In this paper, an active inductor AI with high linearity and high dynamic range, including a minimum number of components, is presented. The AI is composed by a single transistor, and by a passive compensation network; the latter allows the control of the values of both the inductance and the series resistance.

Effects of post deposition annealing, interface states and series resistance on electrical characteristics of HfO 2 MOS capacitors

Abstract: The purposes of this paper are to investigate the post deposition annealing (PDA) effect on structural and electrical characterizations of HfO2 MOS capacitor and the frequency dependency of series resistance and interface states in this device. PDA processes on the HfO2 films deposited using RF magnetron sputtering system were performed in N2 ambient at 350, 550, 650, and 750 °C. The phase identifications and crystallization degrees of the HfO2 films were determined by using X-ray diffractometry. The grain size of the films was varied from 4.5 to 15.23 with increasing in PDA temperature. The HfO2 MOS capacitors were fabricated using the as-deposited and annealed films for electrical characterization. C–V and G/ω–V measurements were performed at 1 MHz frequency. The C–V characteristics of the MOS capacitor fabricated with film annealed at 550 °C show a better behaviour in terms of the high dielectric constant and low effective oxide charge compared to others. For this device, C–V and G/ω–V measurements were performed in different frequencies ranging from 10 kHz to 1 MHz at room temperature. Obtained results show that series resistance and interface states strongly influence the C–V and G/ω–V behaviour of the MOS capacitor.

InGaAs axial-junction nanowire-array solar cells

Abstract: Axial p–i–n junction nanowire (NW) solar cells (SCs) with a position-controlled GaAs-based NW array were fabricated by selective-area metal organic vapor phase epitaxy (SA-MOVPE). The measured electron-beam-induced current (EBIC) signals showed the formation of an axial p–i–n junction, which confirms power generation under sunlight illumination. The series resistance of the NW SCs is much higher than that of conventional planar SCs based on Si or other III–V compound semiconductors. The main difficulty concerning the fabrication of these NW SCs is the degradation of series resistance between the GaAs-based NWs and the indium–tin oxide (ITO) deposited as a transparent electrode. The series resistance of the fabricated GaAs-based NW SCs was reduced by introducing a tin doping contact layer between the ITO and the NW array, which is formed by pulse doping. As a result of this improved structure, the fabricated SCs exhibited an open-circuit voltage of 0.544 V, a short-circuit current of 18.2 mA/cm2, and a fill factor of 0.721 for an overall conversion efficiency of 7.14% under AM1.5G illumination. The series resistance of the SCs could be decreased to 0.132 Ωcm2, which is one order of magnitude lower than that of the SC without a highly doped contact layer. This reduced series resistance indicates that nanostructure SCs with transparent electrodes and multijunction NW SCs with high efficiencies can be fabricated on a commercial basis in the near future.

Ordered multiphase polymer nanocomposites for high-performance solid-state supercapacitors

Abstract: Multilayered ordered nanostructures were fabricated by assembling in-situ grown polyaniline nanowire arrays with graphene oxide nanosheets. As-fabricated nanostructure was subsequently impregnated with the (H3PO4–Nafion)/polyvinyl alcohol solution to create a multiphase composite, which was used as a solid-state supercapacitor where graphene oxide/polyaniline nanowires served as electrode and (H3PO4–Nafion)/polyvinyl alcohol served as solid electrolyte. The ordered polyaniline (PANI) nanostructures facilitated the charge transfer and resulted in the specific capacitance of 83 F/g even if the discharge current was 5 A/g. The efficient charge transportation and electrode–electrolyte interaction resulted in small equivalent series resistance as low as 5.83 Ω, and thus outstanding electrochemical performance. The charge transfer resistance was much smaller than other commonly used solid-state electrolyte and almost negligible. As a result only 7% capacitance loss was found when the frequency increased from 100 to 1000 Hz. The energy density was as high as 26.5 Wh/kg while the power density was ∼3600 W/kg. The energy storage performance was also very stable since 82% specific capacitance was maintained after 1000 cycles.

Rate and cycle performances of supercapacitors with different electrode thickness using non-aqueous electrolyte

Abstract: Activated carbons (AC) powder was coated onto Al current collectors with different thickness (∼30 and ∼80 μm) for use as electrodes of supercapacitors. The relationship between the electrode thickness and the specific capacitance of the supercapacitor cells using a non-aqueous electrolyte was investigated under different charge–discharge current density and for charge–discharge cycling at constant current density. Two types of microporous AC powders of which specific surface areas were 1454 and 2587 m 2 /g were deposited using a binary binder composed of styrene-butadiene rubber and sodium carboxymethyl cellulose. The rate stability of the specific capacitance was shown to be independent of the electrode thickness, and thinner electrodes could maintain higher specific capacitance regardless of the AC type. Thicker electrodes allowed a larger increase in equivalent series resistance with cycling, decreasing the voltage allocated to the formation of the electrical double-layer and thus reducing the specific capacitance. Microscopic surface observation showed that the thicker electrodes exhibited voids resulting from reduced adhesion among AC particles. The reduced adhesion and the electrolyte decomposition in the thicker electrodes were likely to be connected to their performance deterioration.

Investigation of negative dielectric constant in Au/1 % graphene (GP) doped-Ca1.9Pr0.1Co4Ox/n-Si structures at forward biases using impedance spectroscopy analysis

Abstract: The dielectric properties of Au/(1 % graphene doped-Ca1.9Pr0.1Co4Ox)/n-Si structures were investigated by the impedance spectroscopy method including capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements in the frequency range of 10–2 MHz at room temperature. The experimental results show that the real and imaginary parts of dielectric constant (e′, e′′) and electric modulus (M′ and M′′), and ac electrical conductivity (σ ac ) are a strong functions of frequency and voltage, both. Negative dielectric constant behavior was observed at sufficiently high forward bias voltages at low frequencies and it was attributed to the interfacial polarization, interface traps and series resistance. e′ decreases with increasing frequency at sufficiently high biases whereas e′′ increases. Since interfacial polarization and interface states, both, can follow the ac external signal easily at low frequencies, there occurs a contribution to the measured capacitance and conductance. The negative values of e′ correspond to maximum value of e′′. Such contrary behavior in the e′ and e′′ appears as an abnormality when compared to the conventional behavior metal–semiconductor structures with and without interfacial layer. Experimental results confirmed that the dielectric properties of these structures are quite sensitive to the frequency and applied bias voltage, both, especially at low frequencies and high voltages because of density distribution of interface states and interfacial polarization.