Performance of capacitors under DC bias at liquid nitrogen temperature

Several commercially available capacitors were evaluated at the liquid nitrogen temperature (77 K). Our primary interest was their performance under a bias voltage when used as DC link capacitors in cryogenic power electronics. In general, the performance of polymer capacitors and certain ceramic capacitors is almost independent of the temperature, DC bias, and frequency. On the other hand, ceramic capacitors based on high dielectric constant materials showed a strong dependence on the boundary conditions. Aluminum electrolytic capacitors showed a dramatic decrease of capacitance at 77 K, possibly due to the electrolyte being frozen and therefore losing its conductivity.     

PLL jitter reduction by utilizing a ferroelectric capacitor as a VCO timing element

Ferroelectric capacitors have steadily been integrated into semiconductor processes due to their potential as storage elements within memory devices. Polarization reversal within ferroelectric capacitors creates a high nonlinear dielectric constant along with a hysteresis profile. Due to these attributes, a phase-locked loop (PLL), when based on a ferroelectric capacitor, has the advantage of reduced cycle-to-cycle jitter. PLLs based on ferroelectric capacitors represent a new research area for reduction of oscillator jitter.     

Polarization-switching D/A converter

This paper describes a novel digital-to-analog (D/A) conversion technique, which uses the analog quantity polarization as a D/A conversion medium. It can be implemented by CMOS capacitors or by ferroelectric capacitors, which exhibit strong nonlinearity in charge versus voltage behavior. Because a ferroelectric material inherently has spontaneous polarization and generally has a large dielectric constant, the effective capacitance of a ferroelectric capacitor is much larger than that of a CMOS capacitor of the same size. This ensures less influence of bottom-electrode parasitic capacitance on a ferroelectric capacitor. Furthermore, a data converter based on ferroelectric capacitors possesses the potential nonvolatile memory function owing to ferroelectric hysteresis. Along with the architecture proposed for polarization-switching digital-to-analog converter (PDAC), its circuit implementation is introduced. Described is implementation of two 9-bit bipolar PDACs: one is based on CMOS capacitors and the other on off-chip ferroelectric capacitors. Experimental results are presented for the performance of these two prototypes.     

Ferroelectric Thin-Film Capacitors and Piezoelectric Switches for Mobile Communication Applications

Thin-film ferroelectric capacitors have been integrated with resistors and active functions such as ESD protection into small, miniaturized modules, which enable a board space saving of up to 80%. With the optimum materials and processes, integrated capacitors with capacitance densities of up to 100 nF/mm>² for stacked capacitors combined with breakdown voltages of 90 V have been achieved. The integration of these high-density capacitors with extremely high breakdown voltage is a major accomplishment in the world of passive components and has not yet been reported for any other passive integration technology. Furthermore, thin-film tunable capacitors based on barium strontium titanate with high tuning range and high quality factor at 1 GHz have been demonstrated. Finally, piezoelectric thin films for piezoelectric switches with high switching speed have been realized.     

1/f noise of electrolytic capacitors as a reliability indicator

The electrical noise of capacitors and the relationship between typical imperfections in capacitors and their excess noise are described. It was assumed that a noisy capacitor is a poor-quality one. Investigations were aimed at the determination of a correlation between the inherent noise of capacitors and their reliability (time to failure) and also at the determination of an indicator to predict reliability. Investigations (noise measurements and reliability tests) were carried out on two samples of aluminium electrolytic capacitors. The method of reliability prediction for electrolytic capacitors based on their low-frequency noise is described. For reliability prediction the noise intensity G at a frequency of 2 Hz was used as a reliability indicator. It was found that the evaluated correlation coefficients between the noise parameter G and the time to failure, t, are statistically significant. It is concluded that it is possible to predict the lifetime of aluminium electrolytic capacitors on the basis of their 1/f noise. © 1998 John Wiley & Sons, Ltd.     

Capacitors with nonlinear characteristics based on stabilized zirconia with built-in gold nanoparticles

It is shown that capacitors based on stabilized zirconia with gold nanoparticles exhibit nonlinear properties: the admittance of these capacitors depends on the amplitude of the control voltage, test-signal frequency, and temperature. The nonlinearity is due to electron capture by traps generated during nanoparticle formation. The possibility of determining the trap parameters by measuring the capacitor admittance has been established.     

Reliability Assessment of Metallized Film Capacitors using Reduced Degradation Test Sample

Metallized film capacitor is a type of product with a long lifetime and high reliability. It is difficult to assess the lifetime and reliability using the traditional statistical inference method which is based on the large number of testing data. This paper presents a new testing methodology, called T‐performance degradation test, by dividing the test process into several stages. In each stage, the sample size of working capacitors under test decreases stage by stage until the test lasts enough time with few survival capacitors. Leveraging the T‐performance degradation data, this paper further presents a reliability assessment model to predict the lifetime of the high‐performance capacitors. Finally, the reliability assessment model is demonstrated on a type of high‐performance metallized film capacitors used in the energy module of the laser facility. Copyright © 2012 John Wiley & Sons, Ltd.     

GaN based high temperature strain gauges

Gallium Nitride based electronic devices have several unique properties such as robustness to high temperature, and both strong spontaneous and piezoelectric polarization fields. The polarization effects of Gallium Nitride are stable at high temperatures; therefore, it is an ideal material to fabricate high temperature strain gauges. In this work we have fabricated metal-insulator-semiconductor(MIS) capacitors to be used as a high temperature strain gauge. GaN based MIS capacitors were fabricated and tested both at room and high temperature. The gauge factor was measured to be 75 at room temperature. AlGaN/GaN heterostructures were also used to make MIS capacitors for testing at both room and high temperature. The gauge factors were measured on these devices to be 575 at room temperature, and 361 at 400 °C.     

Tunable microwave filters with controlled ferroelectric capacitors

Microwave microstrip resonators and filters controlled by ferroelectric capacitors have been simulated and experimentally studied. Control at room temperature and under cryogenic conditions has been ensured by capacitors based on BSTO and STO films, respectively. Cooled devices based on YBa₂Cu₃O_7-δ high-temperature superconducting films have been fabricated. The developed filters are efficiently tuned by applying a control voltage, are small, and have a low level of introduced losses.     

A multi-objective GRASP procedure for reactive power compensation planning

A multi-objective approach based on the GRASP (Greedy Randomized Adaptive Search Procedure) meta-heuristic is proposed to provide decision support in the problem of locating and sizing capacitors for reactive power compensation in electrical radial distribution networks. The installation of capacitors (local sources of reactive power) in the network is aimed at correcting the power factor to improve the quality of service, particularly the network voltage profile, and reduce energy losses and power peak. The mathematical model explicitly considers two conflicting objective functions: the minimization of the network active losses and the minimization of the capacitor installation cost. An algorithmic approach based on GRASP is presented for the characterization of the non-dominated solution set.     

MnOx基电化学电容器的研究进展

电化学电容器是近年来出现的一种介于常规电容器和充电电池之间的新型储能元件,具有功率密度大、能量密度高、极好的循环可逆性、循环寿命长等特点.由于MnOx具有资源广泛、价格低廉、电化学窗口较宽、良好的电化学性能和环境友善等特点,近年来引起研究工作者的极大兴趣.系统介绍了近年来国内外对MnOx基电化学电容器的研究进展,包括MnOx基材料的制备方法、材料的改性以及电化学性能的研究等.     

Capacitively-Coupled SQUID Bias for Time Division Multiplexing

The multiplexing scheme presented in this paper is part of the readout chain of the QUBIC instrument devoted to cosmic microwave background polarization observations. It is based on time domain multiplexing using superconducting quantum interference devices (SQUIDs) to read out a large array of superconducting bolometers. The originality of the multiplexer presented here lies in the use of capacitors for the SQUID addressing. Capacitive coupling allows us to bias many SQUIDs in parallel (in a 2D topology), with low crosstalk and low power dissipation of the cryogenic front-end readout. However, capacitors in series with the SQUID require a modification of the addressing strategy. This paper presents a bias reversal technique adopted to sequentially address the SQUIDs through capacitors using a cryogenic SiGe integrated circuit. We further present the different limitations of this technique and how to choose the proper capacitance for a given multiplexing frequency and current source compliance.     

Effect of UV radiation on slow relaxation processes in ferroelectric thin-film capacitors

The influence of UV radiation with wavelengths of about λ = 340 nm and power within 0.001–0.15 mW on the suppression of slow relaxation of residual polarization in ferroelectric capacitors based on thin (Ba,Sr)TiO₃ (BSTO) films in a paraelectric state has been studied. Experimental data on the behavior of capacitance relaxation time and conduction current in ferroelectric capacitors under the action of UV radiation are presented. A mechanism of relaxation with a characteristic time on the order of 1 s is found that is not affected by UV radiation.     

Characterization of the Properties of Barium–Strontium Titanate Films and Controlled Elements Based on Them in the Frequency Range of 1–60 GHz

Technical Physics Letters - The electrical properties of barium–strontium titanate films and tunable capacitors based on them are studied in a wide frequency range. The dielectric losses in...     

Developments in ferroelectric ceramics for capacitor applications

A brief overview of the materials and processes for making ceramic capacitors based on BaTiO₃ and relaxor ferroelectric compositions is presented with special emphasis on more recent developments.     

The commutation quality factor of electrically controlled microwave device components

Various circuit components based on electrically controlled capacitors can be compared using an integral criterion, called the commutation quality factor and determined by the efficiency of capacitance tuning and the losses in the control device. The value of commutation quality factor is independent of the physical nature of controlled components, which ensures objective comparative analysis of the efficiency of electrically tunable capacitive components operating in the microwave frequency range: p-i-n diodes, microelectromechanical switches, diodes with variable p-n junction capacitance (varactors), and ferroelectric capacitors.     

Counterfeit capacitors in the supply chain

Counterfeit electronic components have become a significant concern in the electronic parts supply chain. Original equipment manufacturers in particular are concerned about counterfeit components as there have been several recent reports of counterfeit parts entering the supply chain of the US military. This paper presents a case study of multilayer ceramic capacitors for use in a printed circuit assembly in an electronic system on a military aircraft. The capacitors failed during a high temperature screening test. Upon failure analysis it was revealed that the capacitors were not made to the correct specifications and were suspected to be counterfeit and not the authentic military grade capacitors manufactured by Kemet. Further investigation revealed that the suspect multilayered ceramic capacitors had entered into the electronics parts supply chain and were sold as authentic Kemet capacitors that met the higher military-specified requirements. The manufacturing and distribution of the counterfeit capacitors were traced to locations where, according to Kemet, its authentic capacitors are neither manufactured nor distributed.     

Solid-state AC breaker with parallel switched capacitor circuits for microgrid system

ABSTRACT

In this paper, a novel solid-state AC breaker, based on double-paralleled switched capacitors controlled with complementary pulse width modulation technique, is proposed for transition of microgrid due to its advantages of low di/dt stress to power devices and controllable resistance features. The circuit topology of the breaker is based on parallel switched capacitors, its operating and control theory are analyzed in detail to show its advantage in theory. The equivalent impedance of proposed parallel switched capacitor circuits is up to the switching frequencies, and the proposed switch is suitable for seamless transition between the island mode and grid-connected mode to reduce the current shock by changing the switching frequencies. Simulation and experimental results verify the effectiveness and feasibility of the new AC breaker.     

New Fused-Silica-Dielectric 10-and 100-pF Capacitors and a System for Their Measurement

New instruments have been designed to bring to standards laboratories the improved accuracy of capacitor calibrations developed by the National Bureau of Standards. The new 10-and 100-pF reference standard capacitors, based upon an NBS design, use a fused-silica dielectric with gold electrodes to provide the time and voltage stability required for calibrations to parts in 107. To maintain the capacitor temperature constant to within 0.01 °C, one model of the capacitors is designed for use in an oil bath, the other model is fitted with a new, stable, thermostatically controlled air bath. The system to measure these capacitors with a precision of parts in 108 consists of a bridge, detector, and oscillator. For these special measurements and for the general calibration of a wide range of capacitors, the new transformer-ratio-arm bridge has 12 capacitance decades and a range of 10 MAF-10-7 pF, and five conductance decades and a range of 103110-10 tmho. The new phasesensitive detector and power oscillator provide high sensitivity to bridge imbalance over the frequency range 10 Hz-100 kHz.     

Synthesis of copper-ferrous (CuFe) nanowires via electrochemical method and its investigations as a fluid sensor

The special behaviour of nanowires with respect to electrical conductivity makes them suitable for sensing application. In this paper, we present a copper-ferrous (CuFe) nanowires based sensor for detection of chemicals. CuFe nanowires were synthesized by template-assisted electrochemical method. By optimizing the deposition parameters, continuous nanowires on a copper substrate were synthesized. The morphological and structural studies of the synthesized CuFe nanowires were carried out using scanning electron microscope (SEM) and X-ray diffraction (XRD). Substrates containing CuFe nanowires were moulded to form a capacitor. Different chemicals were used as dielectric in the capacitor which showed that the capacitance was a nonlinear function of the dielectric constant of fluid unlike the linear relation shown by conventional capacitors. This unique property of the nanowires based capacitors may be utilized for developing fluid sensors with improved sensitivity.