Thick Capacitors Research Articles

Tough-Hydrogel Reinforced Low-Tortuosity Conductive Networks for Stretchable and High-Performance Supercapacitors.

All-solid-state supercapacitors are seeing emerging applications in flexible and stretchable electronics. Supercapacitors with high capacitance, high power density, simple form factor, and good mechanical robustness are highly desired, which demands electrode materials with high surface area, high mass loading, good conductivity, larger thickness, low tortuosity, and high toughness. However, it has been challenging to simultaneously realize them in a single material. By compositing a superficial layer of tough hydrogel on conductive and low tortuous foams, a thick capacitor electrode with large capacitance (5.25 F cm-2 ), high power density (41.28mW cm-2 ), and good mechanical robustness (ε= 140%, Γ= 1000 J m-2 ) is achieved. The tough hydrogel serves as both a load-bearing layer to maintain structural integrity during deformation and a permeable binder to allow interaction between the conductive electrode and electrolyte. It is shown that the tough hydrogel reinforcement is beneficial for both electrical and mechanical stability. With a simple design and facile fabrication, this strategy is generalizable for various conductive materials.

Periodic energy conversion in an electric-double-layer capacitor

Electrostatic conversion devices operate through periodic modulation of capacitance. Such devices have a wide range of configurations, involving either changes in permittivity, electrode-plate spacing or wetting area. The presented study examines, theoretically, a potential configuration of an electric-double-layer capacitor (EDLC)-based transducer, as it converts concentration and temperature oscillations into an electric alternating current. A constant voltage applied at the EDLC electrodes results in the formation of two opposite-sign EDLs, and an electric current is generated when ionic charges pass from one EDL to the other. In the examined configuration, this ionic charge transfer is induced by boundary modulation of temperature and/or concentration. To capture the oscillating dynamics of the ion distribution and ion flux, we solve the full set of Poisson-Nernst-Planck (PNP) equations coupled with the energy equation. We find that the transducer’s optimal conditions for conversion, for which the device’s frequency response is maximized, are governed by three main factors: low irreversible Joule heating, confined geometry, where the capacitor thickness is a close as possible to the EDL’s characteristic screening length, and, most importantly, ‘tuning’ the system to a resonance frequency dictated by the interplay between geometry and characteristic time scales for mass and heat diffusion.

All Silk-Screen Printed Polymer-Based Remotely Readable Temperature Sensor

In this paper, we present the fabrication and characterization results of a remotely readable flexible temperature sensor. The sensor has been fabricated with screen printing technology and it consists of a polymer-based capacitor (ASAHI CR18-KTI polymer paste) as a temperature sensitive component added to the antenna coil (ASAHI LS411-AW silver paste) for remote reading purposes. The resonance frequency of the sensor (i.e., the formed LC network) is measured as a function of temperature. The sensor has been characterized in the temperature range of 0 °C-70 °C and the total sensitivity over this range is ~9 kHz/°C. The sensor's normalized temperature response is independent from the polymer capacitor's thickness and the effective capacitor area, which enables reasonable performance despite fabrication process induced inaccuracies. Due to the inexact nature of the resonance peak measurement, a dataanalysis algorithm was developed to enhance the accuracy of the measurement method. In addition, the sensor response to the misaligned reader and the sensor self-heating effect, due to the inductive excitation voltage, are considered. Finally, the calibration of such a sensor is discussed.

X7R dielectric multilayer ceramic capacitors show good micro‐actuating properties with little hysteresis

The possibility of a kind of industrial-grade X7R type multilayer ceramic capacitor used as an actuator is studied. By applying a DC bias voltage, the ceramic capacitors exhibit a large converse piezoelectric effect which can be used for actuating applications. The experiments show that the capacitor's thickness changes rather linearly with a voltage applied on it. Three multilayer ceramic capacitors were selected to be studied. A hysteresis <1.8% and a nonlinearity <2.0% between the displacement and the driving voltage were observed for a 10 μF capacitor over a frequency range of 0.1–20 Hz and a temperature range of 15–35°C.

The Influences of Particle Sizes on the Dielectric Properties of PEI/(Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 Composites

In order to investigate the embedded capacitors with higher capacitance value in the future, two technologies of increasing the dielectric constant of filler and decreasing the thickness of capacitors can be combined to develop a best method. For that, the high dielectric constant of (Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 (BSTZ) ceramic powders with three different sizes (3 microm, 200 nm, and 100 nm) are used as the filler to mix with polyetherimide (PEI) to form the PEI/BSTZ composites. The dielectric constants and loss tangents of PEI/BSTZ composites with different contents of BSTZ ceramic powders are measured using the plate method. As the contents of BSTZ powders increase from 10 wt% to 70 wt%, the dielectric constants and loss tangents of PEI/BSTZ composites increase with the increase content of BSTZ ceramic powders, independent on the particle sizes. As the BSTZ content is less than and equal to 50 wt% and same loading ratio is used, the dielectric constants of PEI/200 nm-BSTZ and PEI/100 nm-BSTZ composites are large than those of PEI/3 microm-BSTZ composites. In this study, the Lichtenecker logarithmic mixing rule is also used to fit the measured results and predict the dielectric constants of PEI/BSTZ composites.

Laser Processing of 2-D and 3-D Structures for Tunable Embedded Capacitors

Material formulation, structuring, and modification are key to increasing the unit volume complexity and density of next generation electronic packaging products. Laser processing is finding an increasing number of applications in the fabrication of these advanced microelectronic devices. This is due, in part, to the ability to achieve highly localized treatment of materials with a spatial resolution of tens of microns. In addition, the process is data-driven, that is, patterns can be generated without the need for masking materials. In the present investigation, a variety of structures have been generated in polymer nanocomposites, nanoparticle films, and sol-gel thin films using a computer-controlled laser system. Specifically, micromachining technology has been used to produce both variable-thickness and discrete capacitors from a single sheet (layer) of capacitor material, such that both types of structures can be integrated into the same layer. In addition, the laser micromachining technology has been extended to design and develop new vertical multilayer embedded capacitors for high speed applications. High speed packages require thick dielectrics. Calculations show that multilayer vertical capacitors can be better than thick capacitors formed from a single layer. In general, multilayer embedded capacitors are fabricated by repeated lamination of resin-coated copper, or pre-preg with a capacitor core. This is a time consuming, lengthy process. As an alternative, we have deposited a single, thick capacitance layer, and subsequent laser micromachining has been used to form multiple parallel channels of a controlled depth. Metal deposition in the channels results in a multilayer embedded capacitor structure. Lasers micromaching can also provide various complex patterns such as 3-D spiral channels within a dielectric or magnetically active nanocomposite, subsequently filled with conducting materials to form inductors. This technique can be used to prepare inductors and capacitors in the same layer of nanocomposite material. Hence, the technique can be used to generate multi-functional structures for tunable device applications.

INNOVATION IN 1T1C FRAM TECHNOLOGIES FOR ULTRA HIGH RELIABLE MEGA DENSITY FRAM AND FUTURE HIGH DENSITY FRAM

ABSTRACT FRAM whose cell structure and operation is almost identical to DRAM, can ideally realize cell size and performance of DRAM. However, the density and performance of current FRAM still fall far behind those of DRAM. In this paper, innovative 1T1C FRAM technologies for ultra high reliable mega density FRAMs and future high density FRAMs are discussed. A novel electrode technology has been proved to guarantee 175°C, 10 years retention lifetime and more than 1E13 endurance lifetime of mega density 1T1C, COB FRAM with the cell size of 15F2 at 250 nm technology node. Furthermore, a cell size of 12F2 at 150 nm technology node has successfully been realized by developing innovative 200 nm thick capacitor stack technologies and novel capacitor etching technologies. Finally, critical issues of 3-D capacitor arising from 3-dimensional deposition, such as step coverage and film uniformity have been greatly improved by the modification of the MOCVD PZT feeding source and a newly introduced noble metal atomic layer deposition technology.

DC breakdown strength of polypropylene films: area dependence and statistical behavior

The DC breakdown strengths of 4-15 mum thick capacitor grade polypropylene (PP) films were determined. The measurements were performed with an automatic measurement system using five electrodes with areas between 0.045 and 9.3 cm2. Some samples were studied with larger electrodes. Samples were not aged but were measured as received. The measurements were performed in air at room temperature and typically 40-80 breakdowns per sample per electrode area were collected. The Weibull distribution parameters alpha and beta were fitted to the data. Depending on the electrode area and the film grade, the alpha-parameter values obtained were between 450 and 850 V/mum. The breakdown strength values showed decreasing area dependence with decreasing electrode area and the Weibull scaling law was not valid for the smallest electrode areas. The alpha-values for the large sample areas were extrapolated from the small area data by area and Weibull extrapolation. The area extrapolation overestimated the breakdown strength at 4 m2 by 40-50% whereas the Weibull extrapolation gave an accuracy of plusmn15%. The extrapolated breakdown strengths for the full-scale power capacitors deviated from the capacitor manufacturers test data. This indicated that different defect distributions were responsible for the breakdown strengths in the oil impregnated power capacitors than in the small dry film samples

Capacitance of InAs quantum dot arrays in a mean field approach

We present a mean field approach for an array of InAs quantum dots embedded in a capacitor. By assuming a thermodynamical equilibrium between the dots and the closer electrode, we derive the self-consistent equations for the mean dot occupation. The latter includes the Coulomb blockade for isolated dots and the capacitor feedback to the filling of the dots. By this means, we calculate the capacitance versus bias and obtain a satisfactory agreement with recent experimental findings. We succesfully interpret the increase of the splitting and the widths of the first two (S related) capacitance peaks with the capacitor thickness.

A Screen Printed Multilayer PZT Actuator with an Integrated Force Sensor

A thick film hybrid, combining a PZT (Pb0.97Nd002(Ti0.45Zr0.55)O3) low voltage multilayer micromovement actuator and a force sensor, has been realised using a specially developed double paste printing (DPP) method. The transducer structure is capable of working in pressure sensing applications where two clamped opposing surfaces are subjected to a static force loading. A decrease in capacitor voltage under static force conditions — a problem of the leakage current — was avoided by implementing a small force-inducing dynamic displacement (180 nm) multilayer (24 layers, layer thickness of 40 urn) actuator, vibrating at a frequency of 100 Hz, underneath of the force capacitor. The prototype transducer with the force capacitor thickness of 1.0 mm was able to measure static forces in the range of 0 to 10 N.

Switching, fatigue, and retention in ferroelectric Bi4Ti3O12 thin films

Thin films of bismuth titanate, Bi4Ti3O12, prepared by the metalorganic solution deposition technique and rapid thermally annealed at 700 °C for 20 s have shown good ferroelectric switching, fatigue, and retention characteristics. A switching time of 180 ns was measured for a 0.5 μm thick capacitor with an electrode area of 2.83×10−3 cm2. The switching degradation of the polarization state or fatigue was not significant, at least up to 1010 bipolar switching cycles. The films exhibited good memory retention characteristics after about 106 s.

Ferroelectric switching, memory retention and endurance properties of very thin PZT films

Successful ferroelectric polarization and domain switching have been demonstrated in thin leadzirconate-titanate (PZT) films, less than 500A, prepared by the sol-gel technique. 1 In this paper, the ferroelectric switching, memory retention and endurance properties of these thin films, ranging in thickness from 425A to 1500A with a Zr/Ti ratio of 50/50, were investigated. A remanent polarization of 27 μC/cm2 was observed on a 650A thick capacitor with a saturation voltage of 3 volts. A switching speed of 10.8 ns was measured for a 600A thick, 25 × 25 μm capacitor. A 1000A thick, 100 × 100 μm capacitor showed no data loss after 1650 hours of memory retention. The projected life for both 1000A and 650A thick, 40 × 40 μm capacitors is estimated to be longer than 1 × 1010 switching endurance cycles. Detailed measurements and experimental results will be described.

Properties and Life Performance of Silicon Monoxide Capacitors

In SiO capacitors, deposition rate and thickness interact in their effect on leakage resistance. Slow (2 Å/s) and fast (20 Å/s) deposited films in the 2000-Å thickness range exhibit almost a million-fold difference in leakage, while similar rates, for 10000-Å films, show only a thousand-fold difference. Dissipation factor and temperature coefficient of capacitance (TCC), under the same conditions, also show extreme variation: dissipation factor from 0.003 (slow films) to 0.075 (fast, thin films), and TCC from < 40 ppm/°C (slow films) to 5700 ppm/°C (fast, thin films). Life tests of SiO capacitors were conducted at 85°C for periods up to 14 000 hours. They included capacitors with a thick (about 10 000 Å) dielectric layer and ones with a thin (about 1000 Å) layer. The thicker ones were under a potential of 47 volts dc and the thinner ones 10 volts dc. In addition, a small group of thick capacitors were held at 125°C, 67 volts dc for a much shorter time, about 6000 hours. The test results for thick 85°C capacitors were that no permanent dielectric failures occurred during the test period and dielectric properties were unchanged from those at the start of the test. Among the 60 thin capacitors, four failures (on the same substrate) occurred during the final tenth of the life test period. Visual inspection indicated that aluminum electrode corrosion was responsible. Ten capacitors maintained at 125°C (only three under voltage stress) were in perfect condition at the conclusion of the test. Their capacitance had not changed significantly but the dissipation factor improved from 0.0075 to 0.0034 (average value of ten capacitors). The most significant finding regarding long-term instability is that aluminum electrodes often deteriorate, sometimes causing dielectric failure.