High dielectric constant SU8 composite photoresist for embedded capacitors

A novel, photodefinable, high dielectric constant (high‐k) nanocomposite material was developed for embedded capacitor applications. It consists of SU8 as the polymer matrix and barium titanate (BT) nanoparticles as the filler. The UV absorption characteristics of BT nanoparticles were studied with a UV‐Vis spectrophotometer. The effects of BT nanoparticle size, filler loading, and UV irradiation dose on SU8 photopolymerization were systematically investigated. The dielectric properties of the photodefined SU8 nanocomposites were characterized. Embedded capacitors using the novel high dielectric constant SU8 composite photoresist were demonstrated on a flexible polyimide substrate by the UV lithography method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1523–1528, 2007     

Polystyrene-based carbon spheres as electrode for electrochemical capacitors

A series of carbon spheres with various porous texture parameters were prepared from polystyrene-based macroreticular resin spheres by carbonization and activation. The as-prepared carbon spheres had a maximum specific surface area of 996 m² g^?1, total pore volume of 1.34 cm³ g^?1 and average pore size of 5.39 nm. Moreover, these carbon spheres showed a mesopore size distributed mainly in about 40 nm. A high specific capacitance of 153 F g^?1 for carbon sphere by carbonization, 164 F g^?1 for carbon sphere by activation for 1 h and 182 F g^?1 for carbon sphere by activation for 2 h can be obtained. Moreover, a specific energy between 2.3 and 5.1 Wh kg^?1 for these carbon spheres can be obtained in 6 mol L^?1 KOH electrolyte.     

Determination of glass transition temperature from dielectric analysis for a series of epoxide oligomers

Dielectric properties have been investigated for a bisphenol-A type epoxide oligomer, whose weight average molecular weight (M?_w) was 9454. The dielectric α-relaxation of the oligomer was found to be governed by the Havriliak–Negami equation as well as the same series of oligomers with smaller M?_ws (388≦M?_w ≦ 3903). The dielectric relaxation times (τ)s for the oligomers with different M?_ws (1396 ≦ M?_w ≦ 9454) can be expressed by the Williams–Landel–Ferry (WLF) equation as a function of the glass transition temperature (T_g) at fixed temperatures from 70 to 100°C. The finding indicates that the T_g of the epoxide oligomer is calculated from the τ through the WLF equation, providing the relation between T_g and τ. The same type of WLF equation was also successfully applied to describe the T_g, dependence of the practical dielectric relaxation time (τ_p), which was obtained from the peak of the dielectric loss vs. frequency curve. The τ_p can be calculated more easily than the τ, based on the Havriliak–Negami equation, not only in the measurement of epoxide oligomer, but also in that of the reactive epoxy resin systems during curing. The T_g of an epoxy–aromatic amine system, which was determined from the τ_p nondestructively detected in the dielectric cure monitoring, was consistent with the T_g experimentally measured by differential scanning calorimetry (DSC).     

Graphene nanosheets as electrode material for electric double-layer capacitors

Graphene nanosheets (GNSs) with narrow mesopore distribution around 4 nm were mass-produced from natural graphite via the oxidation and rapid heating processes. The effects of oxidant addition on the morphology, structure and electrochemical performance of GNSs as electrode materials for electric double-layer capacitor (EDLC) were systematically investigated. The electrochemical properties of EDLC were influenced by the specific surface area, pore characteristics, layer stacking and oxygen-containing functional group contents of electrode materials. Deeper oxidation makes graphite possess both higher specific surface area and more graphene edges, which are favorable for the enhancement of capacitive performance of EDLC. The electrodes with freestanding graphene nanosheets prepared by coating method exhibited good rate capability and reversibility at high scan rates (to 250 mV s⁻¹) in electrochemical performances. GNS electrode with specific surface area of 524 m² g⁻¹ maintained a stable specific capacitance of 150 F g⁻¹ under specific current of 0.1 A g⁻¹ for 500 cycles of charge/discharge.     

Inkjet-printed thin film radio-frequency capacitors based on sol-gel derived alumina dielectric ink

There has been significant interest in printing radio frequency passives, however the dissipation factor of printed dielectric materials has limited the quality factor achievable. Al₂O₃ is one of the best and widely implemented dielectrics for RF passive electronics. The ability to spatially pattern high quality Al₂O₃ thin films using, for example, inkjet printing would tremendously simplify the incumbent fabrication processes – significantly reducing cost and allowing for the development of large area electronics. To-date, particle based Al₂O₃ inks have been explored as dielectrics, although several drawbacks including nozzle clogging and grain boundary formation in the films hinder progress. In this work, a particle free Al₂O₃ ink is developed and demonstrated in RF capacitors. Fluid and jetting properties are explored, along with control of ink spreading and coffee ring suppression. The liquid ink is heated to 400 °C decomposing to smooth Al₂O₃ films ~120 nm thick, with roughness of <2 nm. Metal-insulator-metal capacitors, show high capacitance density >450 pF/mm², and quality factors of ~200. The devices have high break down voltages, >25 V, with extremely low leakage currents, <2×10⁻⁹ A/cm² at 1 MV/cm. The capacitors compare well with similar Al₂O₃ devices fabricated by atomic layer deposition.     

Impact of fatigue behavior on energy storage performance in dielectric thin-film capacitors

The polarization hysteresis loops and the dynamics of domain switching in ferroelectric Pb(Zr_0.52Ti_0.48)O₃ (PZT), antiferroelectric PbZrO₃ (PZ) and relaxor-ferroelectric Pb_0.9La_0.1(Zr_0.52Ti_0.48)O₃ (PLZT) thin films deposited on Pt/Ti/SiO₂/Si substrates were investigated under various bipolar electric fields during repetitive switching cycles. Fatigue behavior was observed in PZT thin films and was accelerated at higher bipolar electric fields. Degradation of energy storage performance observed in PZ thin films corresponds to the appearance of a ferroelectric state just under a high bipolar electric field, which could be related to the nonuniform strain buildup in some regions within bulk PZ. Meanwhile, PLZT thin films demonstrated fatigue-free in both polarization and energy storage performance and independent bipolar electric fields, which are probably related to the highly dynamic polar nanodomains. More importantly, PLZT thin films also exhibited excellent recoverable energy-storage density and energy efficiency, extracted from the polarization hysteresis loops, making them promising dielectric capacitors for energy-storage applications.     

High energy storage and ultrafast discharge in NaNbO3-based lead-free dielectric capacitors via a relaxor strategy

Dielectric capacitors with decent energy storage and fast charge-discharge performances are essential in advanced pulsed power systems. In this study, novel ceramics (1-x)NaNbO₃-xBi(Ni_2/3Nb_1/3)O₃(xBNN, x = 0.05, 0.1, 0.15 and 0.20) with high energy storage capability, large power density and ultrafast discharge speed were designed and prepared. The impedance analysis proves that the introducing an appropriate amount of Bi(Ni_0·5Nb_0.5)O₃ boosts the insulation ability, thus obtaining a high breakdown strength (E_b) of 440 kV/cm in xBNN ceramics. A high energy storage density (W_total) of 4.09 J/cm³, recoverable energy storage density (W_rec) of 3.31 J/cm³, and efficiency (η) of 80.9% were attained in the 0.15BNN ceramics. Furthermore, frequency and temperature stability (fluctuations of W_rec ≤ 0.4% over 5–100 Hz and W_rec ≤ 12.3% over 20–120 °C) were also observed. The 0.15BNN ceramics exhibited a large power density (19 MW/cm³) and ultrafast discharge time (~37 ns) over the range of ambient temperature to 120 °C. These enhanced performances may be attributed to the improved breakdown strength and relaxor behavior through the incorporation of BNN. In conclusion, these findings indicate that 0.15BNN ceramics may serve as promising materials for pulsed power systems.     

Copper-doped mesoporous activated carbons as electrode material for electrochemical capacitors

Cu-doped activated carbon composites were prepared from phenolic resins by a doping method. The structure and specific capacitance of Cu-doped activated carbon composites were investigated using nitrogen gas adsorption and constant current cycling (CCC) methods. The pore size distributions of activated carbon-Cu series indicated that the doped Cu had no drastic effect on the structure of ACs. The percentage of copper in the composite electrode was less than 1 wt. %. It was found that the AC-Cu series had higher capacitance than that of activated carbons; even though their BET surface area was not larger than that of the AC ones. The Cu-doped activated carbon composite prepared by activating at 800 °C for 2 h had high capacitance (120 F g⁻¹) which was more than 25% than that of the ACs. XRD and TEM showed that copper existed in the form of oxidation state and the diameter of particles was under 100 nm.     

Improvement of the physicochemical properties of dielectric glass

The paper contains the results of research on methods of improving the physicochemical properties of dielectric glass by applying protective strengthening coatings and magnetic treatment of a glass drop, as well as the parameters of coating application and fixation.     

Lead-free multilayer ceramic capacitors with ultra-wide temperature dielectric stability based on multifaceted modification

The rapid development of high technology—such as space exploration and electric vehicles—urgently requires ultra-wide temperature multilayer ceramic capacitors (UWT MLCCs) to achieve reliable operation of electronic circuits in harsh environments. However, simultaneously achieving high dielectric permittivity, low dielectric loss, and ultrahigh thermal stability has been a major challenge for practical dielectric ceramics. The co-firing matching of the internal electrode and the dielectric ceramic is also an important factor that affects the reliability of UWT MLCCs. Herein, through multifaceted modification—i.e., composition design related to the modulation of the local polar nanoregions (PNRs) and optimizing device sintering in the context of the compatibility of the heterogeneous interface—these concerns have been well-addressed. A new lead-free dielectric system (1-x) (0.56Na_0.5Bi_0.5TiO₃-0.14K_0.5Bi_0.5TiO₃-0.3NaNbO₃)-xCaZrO₃ (NKBTNN-xCZ) dominated by P4bm PNRs was designed and corresponding UWT MLCCs with reliable Pt internal electrode interface bonding were fabricated by optimizing the sintering temperature. A record-high dielectric permittivity (ε_r = 839 ± 15 %) and low dielectric loss (tanδ ≤0.02) was achieved over an ultra-wide temperature range from -70 °C to 337 °C for NKBTNN-0.063CZ UWT MLCCs. This work suggests that multifaceted modification should be generalized for construction of high-performance UWT MLCCs.     

Zeolite coated interdigital capacitors as a new type of gas sensor

The adsorption of a gas influences the dielectric constant of zeolites. This property is used as the sensitive component of a gas sensor.

Planar interdigital capacitors were coated with thin films of zeolites. When gas molecules are adsorbed, the dielectric constant of the zeolite is altered, which causes a change in the capacitance of the interdigital capacitor. This change is strongly dependent on the concentration of adsorbate in the gas phase.     

Pre-imidized photoimageable polyimide as a dielectric for high density multichip modules

Issues relating to the fabrication of complex multichip modules were investigated from a manufacturability perspective. The use of a preimidized photosensitive polyimide reduces the number of processing steps, thus making it a desirable dielectric material. Factors influencing the polyimide resolution, stress, and feature profile were studied both by experimentation and modeling. Thermal cure cycles for polyimide baking were optimized for solvent resistance, polyimide mechanical properties, and process throughput. Studies were also done on polyimide interactions with metal depositions, including adhesion and polyimide surface damage. Results of this research are shown as embodied in a fabricated 1.4 Gbit/s optical transceiver multichip module.     

Motion of segment dislocations as a model for glass relaxation

Summary The meander model of polymer melts assumes nearly parallel packing of molecular chains and therefore invites to describe shear deformation processes by dislocation motion in analogy to metals. Examination of the glass relaxation data for 12 amorphous polymers leads to reasonable values for the energy and the Burgers vector of segment dislocations which are also consistent with thermal properties of the glass transition.Presented at the Third International Seminar on Polymer Physics Molecular Mobility and Energy Transfer in Polymer Systems, High Tatra, CSSR, April 1982     

Localization of dielectric breakdown defects in multilayer ceramic capacitors using 3D X-ray imaging

In this article, a non-destructive method using 3D X-ray imaging to find dielectric breakdown defects in multilayer ceramic capacitors (MLCCs) aged by high temperature and high voltage in an accelerated test is presented. In total, 64 aged samples were investigated using 2D X-ray imaging and half of them were further analysed with 3D X-ray imaging. Miniscule dielectric breakdown defects located in the MLCC active region are extremely difficult to identify solely using cross-section analysis or 2D X-ray imaging. In this study, the information provided by the 3D X-ray analysis was used to localize the defects for cross-section analysis. Cross-section analysis was performed to verify the dielectric breakdowns and their locations. 3D X-ray imaging is an effective method for detecting dielectric breakdown defects in MLCCs due to its short analysis time and high accuracy. This further facilitates failure analysis processes by providing the required grinding depth in cross-section analysis procedures.