Fabrication Of Capacitors Research Articles

Organic electrolytes for graphene-based supercapacitor: Liquid, gel or solid

The electrolyte is an important and decisive factor in battery, capacitor and supercapacitor fabrication. Here we report how electrolyte’s provenance and structure effect on the electro-optical properties of the graphene-based supercapacitor. The three organic electrolytes were synthesized: liquid electrolyte, which on the basis of propylene carbonate (PC), gel electrolyte – polyvinyl alcohol (PVA) and solid electrolyte – polyvinylidene fluoride (PVDF). As an application, we demonstrate an optical modulator using supercapacitor structure built by graphene electrodes and prepared electrolytes. All organic electrolyte-based supercapacitors potentiate optical modulation of graphene electrodes over a broad range of wavelengths, under ambient conditions. We reveal higher capacitance (78μF/cm2) for a supercapacitor with gel electrolyte during various bias voltages. We represent the increasing of light transmission at 3 times using solid electrolyte, in comparison with liquid and gel electrolytes and illustrate the supercapacitor possibility with gel electrolyte to operate under negative voltage. Consequently, we suggest applying of solid electrolyte as a more appropriate electrolyte for fabrication of graphene-based supercapacitor. We anticipate that using of solid electrolyte allows us to get desired electro-optical properties, minimize the size of the device and vary it shape.

Hermetic capacitive pressure sensors for biomedical applications

Purpose This paper aims to purpose the new design and fabrication scheme of Touch Mode Capacitive Pressure Sensor (TMCPS), which can be used in a wireless integrated resistor, inductor and capacitor circuit for monitoring pressure in biomedical applications. Design/methodology/approach This study focuses on the design, simulation and fabrication of dynamic capacitors, based on surface micromachining using polysilicon or aluminum films as the top electrode, both structural materials are capped with a 1.5 μm-thick polyimide film. Findings The design of microstructures using a composite model fits perfectly the preset mechanical behavior. After the full fabrication, the dynamic capacitors show complete mechanical flexibility and stability. Originality/value The novelty of the method presented in this study includes two important aspects: first, the capacitors are designed as a planar cavity within a rigid frame, where two walls contain channels which allow for the etching of the sacrificial material. Second, the electromechanical structures are designed using a composite model that includes a polyimide film capping for a precise pressure sensing, which also protects the internal cavity and, at the same time, provides full biocompatibility.

Biomass-Derived Electrode for Next Generation Lithium-Ion Capacitors.

We report the fabrication of a carbon-based high energy density Li-ion hybrid electrochemical capacitor (Li-HEC) from low cost and eco-friendly materials. High surface area (2448±20 m(2) g(-1) ) activated carbon (AC) is derived from the environmentally threatening plant, Prosopis juliflora, and used as the positive electrode in a Li-HEC assembly. Natural graphite is employed as negative electrode and electrochemically pre-lithiated prior to the Li-HEC fabrication. The Li-HEC delivers a specific energy of 162.3 Wh kg(-1) and exhibits excellent cyclability (i.e., ∼79 % of initial capacity is retained after 7000 cycles). The superior electrochemical performance of Li-HEC benefits from the tube-like unique structural features of the AC. Also, the presence of a graphitic nanocarbon network improves the ion transport, and the formed micro- and meso-porous network acts as reservoir for the accommodation of charge carriers.

Fabrication and investigation of three-dimensional ferroelectric capacitors for the application of FeRAM

Ferroelectric capacitors made by lead zirconate titanate (PZT) thin films and iridium electrodes are fabricated on three-dimensional structures and their properties are investigated. The iridium films are grown by Plasma Enhanced MOCVD at 300°C, while the PZT films are deposited by thermal MOCVD at different process temperatures between 450°C and 550°C. The step coverage and composition uniformity of the PZT films on trench holes and lines are investigated. Phase separation of PZT films has been observed on both 3D and planar structures. No clear dependences of the crystallization and composition of PZT on 3D structure topography have been found. STEM EDX line scans show a uniform Zr/(Zr+Ti) concentration ratio along the 3D profile but the variation of the Pb/(Zr+Ti) concentration ratio is large because of the phase separation. 3D ferroelectric capacitors show good ferroelectric properties but have much higher leakage currents than 2D ferroelectric capacitors. Nevertheless, during cycling tests the degradation of the remnant polarization between 2D and 3D capacitors is similar after 109 switching cycles. In addition, the sidewalls and bottoms of the 3D structures seem to have comparable remnant polarizations with the horizontal top surfaces.

Electrothermal actuation of vanadium dioxide for tunable capacitors and microwave filters with integrated microheaters

We report the fabrication, modeling and characterization of novel microwave tunable capacitors based on the metal-insulator transition (MIT) of Vanadium Dioxide (VO2) as a future replacement solution for microelectromechanical capacitive switches. We present the advantages of VO2-based capacitors over alternative technologies for microwave reconfigurable electronics in terms of ease of integration, design and performance at high frequency. We show the potential of the proposed devices for RF reconfigurable electronics by fabricating a tunable bandstop filter (22.5–19.8GHz) with insertion loss <2dB up to 40GHz. We propose an alternative method for actuation of the VO2 active regions by employing integrated microheaters and we study their effect on the filter performance by electrothermal and electromagnetic simulations.

Direct electrocaloric measurement of 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 films using scanning thermal microscopy

We show that scanning thermal microscopy can measure reversible electrocaloric (EC) effects in &amp;lt;40 μm-thick ceramic films of the relaxor ferroelectric 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3, with the substrate present. We recorded roughly the same non-adiabatic temperature change (±0.23 K) for a thinner film that was driven harder than a thicker film (±31 V μm−1 across 13 μm versus ±11 V μm−1 across 38 μm), because the thicker film lay relatively closer to the substantially larger adiabatic values that we predicted by thermodynamic analysis of electrical data. Film preparation was compatible with the fabrication of EC multilayer capacitors, and therefore our measurement method may be exploited for rapid characterisation of candidate films for cooling applications.

High energy Li-ion capacitors with conversion type Mn3O4particulates anchored to few layer graphene as the negative electrode

We report the fabrication of high energy Li-ion capacitors (LICs) using conversion type Mn3O4octahedrons anchored to few layer graphene (Mn3O4-G) as the negative electrode with activated carbon (AC) as the positive one.

Activated Carbon from Bio-wastes of Durian Fruits as Active Material for Electrodes of Electric Double-layer Capacitors

In this study, bio-wastes from durian fruits such as seeds and shells have been used as precursor materials to prepare activated carbon (AC). While the applicability of a one-step method of impregnation-activation has been investigated for the activation of durian shells, a two-step method of carbonization-impregnation-activation has been tried for the durian seeds. Durian shells based AC (DSh-AC) was found to have a BET surface area () of 2004 m2 g-1 and the durian seeds based AC (DS-AC) had of 1176 m2 g-1. A new approach to electrical double-layer capacitor (EDLC) fabrication has been attempted to avoid the use of polymer binders and organic solvents in the electrodes by coating the electrode material directly on the separator. Instead of coating onto metal current collector, the AC was coated on a glass microfiber filter which was used as the separator to form the electrode. As an electrode material in the EDLC, DSh-AC performed well with a specific capacitance () between 72 and 82 F g-1 whereas the DS-AC showed lower values of between 64 and 70 F g-1. The reasonable good results indicate that the simple approach of device fabrication can also produce EDLCs with satisfactory performance parameters.

Electrostatically assisted fabrication of silver–dielectric core/shell nanoparticles thin film capacitor with uniform metal nanoparticle distribution and controlled spacing

An electrostatically-assisted strategy for fabrication of thin film composite capacitors with controllable dielectric constant (k) has been developed. The capacitor is composed of metal–dielectric core/shell nanoparticle (silver/silica, Ag@SiO2) multilayer films, and a backfilling polymer. Compared with the simple metal particle-polymer mixtures where the metal nanoparticles (NP) are randomly dispersed in the polymer matrix, the metal volume fraction in our capacitor was significantly increased, owing to the densely packed NP multilayers formed by the electrostatically assisted assembly process. Moreover, the insulating layer of silica shell provides a potential barrier that reduces the tunneling current between neighboring Ag cores, endowing the core/shell nanocomposites with a stable and relatively high dielectric constant (k) and low dielectric loss (D). Our work also shows that the thickness of the SiO2 shell plays a dominant role in controlling the dielectric properties of the nanocomposites. Control over metal NP separation distance was realized not only by variation the shell thickness of the core/shell NPs but also by introducing a high k nanoparticle, barium strontium titanate (BST) of relatively smaller size (∼8nm) compared to 80–160nm of the core/shell Ag@SiO2 NPs. The BST assemble between the Ag@SiO2 and fill the void space between the closely packed core/shell NPs leading to significant enhancement of the dielectric constant. This electrostatically assisted assembly method is promising for generating multilayer films of a large variety of NPs over large areas at low cost.

Tube-like carbon for Li-ion capacitors derived from the environmentally undesirable plant: Prosopis juliflora

This work describes the fabrication of high-energy Li-ion hybrid electrochemical capacitors (Li-HEC) from the environmentally threatening and invasive Prosopis juliflora. The carbon derived from this acts as the positive electrode active material in organic medium. High-surface-area carbon was obtained from P. juliflora and activated using KOH at various concentrations and temperatures. Of the tested ratios, 1:2 (carbon: KOH) treated at 900 °C (KC21-900) yielded a high specific surface area (2410 m2 g−1) and specific capacitance (∼161 F g−1). Then, a Li-HEC was fabricated with a homemade insertion-type Li4Ti5O12 negative electrode, delivering a maximum energy density of ∼80 W h kg−1. In addition, the prepared Li-HEC had excellent cycleability (10000 cycles) and good capacity retention characteristics.

Fabrication and Characteristics of High Capacitance Al Thin Films Capacitor Using a Polymer Inhibitor Bath in Electroless Plating Process.

An aluminum (Al) thin film capacitor was fabricated for a high capacitance capacitor using electrochemical etching, barrier-type anodizing, and electroless Ni-P plating. In this study, we focused on the bottom-up filling of Ni-P electrodes on Al2O3/Al with etched tunnels. The Al tunnel pits were irregularly distributed on the Al foil, diameters were in the range of about 0.5~1 μm, the depth of the tunnel pits was approximately 35~40 μm, and the complex structure was made full filled hard metal. To control the plating rate, the experiment was performed by adding polyethyleneimine (PEI, C2H5N), a high molecular substance. PEI forms a cross-link at the etching tunnel inlet, playing the role of delaying the inlet plating. When the PEI solution bath was used after activation, the Ni-P layer was deposited selectively on the bottoms of the tunnels. The characteristics were analyzed by adding the PEI addition quantity rate of 100~600 mg/L into the DI water. The capacitance of the Ni-P/Al2O3 (650~700 nm)/Al film was measured at 1 kHz using an impedance/gain phase analyzer. For the plane film without etch tunnels the capacitance was 12.5 nF/cm2 and for the etch film with Ni-P bottom-up filling the capacitance was 92 nF/cm2. These results illustrate a remarkable maximization of capacitance for thin film metal capacitors.

Macroporous carbon from human hair: A journey towards the fabrication of high energy Li-ion capacitors

Human hair is a cheap and easily available source of carbon to be used as high performance electrode for electrochemical energy storage devices. In the present work, human hair is pre-treated and then activated using NaOH before being employed as electrode. The resulted activated carbon (ACHH) exhibits a high specific surface area of 1116m2g−1 which is one of the pre-requisite for it to be used as an electrode for supercapacitor applications. ACHH delivered a specific capacitance of ∼115Fg−1 at a current density of 100mAg−1 in single electrode configuration with Li in the presence of organic medium. This result was followed by the fabrication of symmetric supercapacitor and delivered an energy density of 19.2Whkg−1. The energy density has been further improved by introducing an insertion type electrode, Li4Ti5O12 in Li-ion hybrid electrochemical capacitor (Li-HEC) assembly. The combined battery-supercapacitor type reactions in Li-HEC recorded the maximum energy density of 23Whkg−1. An excellent cycleability is noted for both symmetric and Li-HEC in an organic medium.

Wafer level high-density trench capacitors by using a two-step trench-filling process

This paper reports on the design, fabrication and electrical characterization of high-density SIS trench capacitors by using a two-step deposition process for fast-filling the deep trenches. LPCVD silicon nitride is employed as the dielectric material to provide high efficiency deposition in the high aspect ratio trenches. The capacitance density in trench capacitors with 25 nm thick Si3N4 is characterized as high as 57.8 nF/mm2, while the breakdown voltage in trench capacitors with 35 nm thick Si3N4 is recorded to be as high as 14.5 V. Furthermore, the capacitances are measured over an applied voltage range from ź5 to 5 V, showing a small voltage-dependence of 1.2 and 0.6 % Vź1 for the 25 and 35 nm thick Si3N4 trench capacitor, respectively. The leakage currents are measured and the current transport mechanisms are analyzed. The ESR and ESL of the capacitors with 25 and 35 nm thick Si3N4 are very small, as low as 35---65 mΩ and 0.2---0.28 pH for 0.04 mm2 electrode surface.

XPS depth profiling and leakage properties of anodized titania dielectrics and their application in high-density capacitors

The chemical structure and electrical properties of anodized titania are investigated for their application as conformal ultra-thin dielectrics on high surface area titanium electrodes. The chemical structure is studied by XPS depth profiling for the first time along with the role of anodization conditions on dielectric thickness, leakage current, and capacitance densities. Different leakage current models were used to identify the defect mechanisms in the titania film formed at different voltages. EDS and structural SEM studies were performed to investigate the morphology and structure of the titania films. This research also demonstrates the fabrication and characterization of high-density capacitors using high surface area titanium metal electrodes, conformal high K, and thin-film dielectric of titania. High-permittivity and thin-film titania dielectric was grown on high surface area titanium anodes using anodization, while conducting polymer was used as the cathode. The fabricated capacitor showed 7.15 µF cm−2 at 100 kHz which corresponded to 7.5X enhancement in surface area compared to planar thin-film capacitors. This is the first demonstration of high-density capacitors using high surface area titanium anodes along with high-permittivity and thin-film titania as the dielectric.

Design and fabrication of wafer level suspended high Q MIM capacitors for RF integrated passive devices

A novel silicon-based suspended MIM capacitor fabrication technique combining thin-film and bulk silicon etching technologies with high-quality factor is presented. The influence of low resistive silicon on the parasitics of integrated capacitors is analyzed by EM simulation. The suspended structure is achieved and optimized by a two-step back-etching process. The Q factor of the 3.3 pF suspended MIM capacitor at 2 GHz is about 79 % larger than the non-suspended one and the Qmax is increased from 46.8 to 61.9, respectively. And a ten-element ź equivalent model including electrode and substrate parasitics as well as dielectric loss is used to fit the suspended MIM capacitors well up to 10 GHz, demonstrating that the suspended MIM capacitors exhibit both lower substrate loss and lower parasitic capacitance of the substrate.

Composition-Microstructure-Property Relationships in BaTiO&lt;sub&gt;3&lt;/sub&gt; with Mg Addition

Rising worldwide demands for energy encourages development of high-efficiency energy storage and capacitor components. Main requirements for dielectric materials employed in fabrication of high energy density capacitors include high dielectric constant, high dielectric breakdown strength, and low dielectric loss. Owing to its high dielectric constant and low dielectric loss [1], barium titanate is among common capacitor materials. Tailoring of dielectric properties of barium titanate can be achieved through controlled chemical composition, microstructure, and crystal structure. Synthesis and processing techniques, as well as doping of barium titanate, can be key factors to control the composition and structure, which consequently contribute to enhancement of dielectric constant in the material.

The Device-Perimeter Dependency in the Transient Current of a Metal-Insulator-Metal-Insulator-Semiconductor Capacitor with Anodic Oxide Films

Capacitors are commonly used in semiconductor devices like gate capacitors of transistors, memory cells of dynamic random access memory (DRAM), and so on. In this work, a capacitor with electrochemically grown thin oxide films was fabricated as shown in figure 1. The Al2O3/Al/AlSixOy/SiO2 stack structure was formed by anodization as shown in figure 2. First, the SiO2 layer was formed by anodizing the surface of a p-type Si wafer as shown in figure 2(a). Next, a thin Al film was thermally deposited. Then, the Al2O3 layer was formed by partially anodizing the surface of the Al film as shown in figure 2(b). The sample was then annealed at 380°C in N2 ambient for 10 min, and an AlSixOy layer was formed between Al and SiO2. Three square device patterns, 150×150μm2 (sample D1), 300×300μm2 (sample D2), and 600×600μm2 (sample D3), of the Al electrodes were fabricated by thermal deposition and lithography. Figure 3 shows the gate current per device-area and per device-perimeter versus the gate voltage of the capacitor. Note that the currents merge at negative voltages in (a) while they merge at the saturation region in (b). It tells that the current flows uniformly across the whole area of the device at negative voltages while it flows along the device edge at the voltages in current saturation region due to the fringing field effect, which coincides with the results in the previous studies [1]. Figure 4 shows the read currents of the capacitor at 0.1 V versus time after various negative and positive voltage pulses. The inset in (a) is the schematic diagram of the write and read processes settings. (b) is the read currents in (a) divided by the device perimeter. Note that the negative read currents merge in (a) while the positive read currents merge in (b). The charge in the sandwiched Al layer and the read current can be written as Qg (t)=Qg (0)exp(–t/τ) (1) Ig (t)=d Qg (t)/dt=–(Qg (0)/τ)exp(–t/τ) (2) where Qg (t) is the stored charge at time t. τ is the time constant which is equal to RsCg . Rs is the total series resistance. Cg is the gate capacitance. The time constants extracted from figure 4 are all about 0.7 s. Qg (0) can be obtained by the write process as follows: Qg (0)≈Qg (–t 0)=∫(I write–I leak)dt (3) where I write is the write current, I leak is the leakage current during writing, and t 0 is the switching time from write to read. While the write voltage is positive, the electrons flow from substrate to the sandwiched Al layer along the device edge due to the fringing field effect. However, the electrons also leak from the sandwiched Al layer to metal gate along the edge due to the thin oxide, and therefore Qg (0) is nearly independent of the device dimension. Hence, Ig (t) is independent of the device dimension. While the write voltage is negative, the stored electrons in the sandwiched Al layer were depleted due to the high negative gate field. When read at 0.1 V, the electrons were injected into the sandwiched Al layer along the edge due to the fringing field effect, and therefore Qg (0) is dependent on the device perimeter. Hence, Ig (t) is proportional to the device perimeter. The device-perimeter dependency in the current characteristics of the capacitor mentioned in this work might be useful for IC circuit design. This work was supported by the Ministry of Science and Technology of Taiwan, ROC, under Contract No. NSC 102-2221-E-002-183-MY3 and MOST 103-2622-E-002-031. Figure Captions: Figure 1. (a) The TEM cross-section and (b) the EDX line-scanning component analysis of the capacitor. Figure 2. The schematic diagrams of (a) SiO2 anodization and (b) Al2O3 anodization processes for the capacitor fabrication. Figure 3. (a) The gate current per device area and (b) the gate current per device perimeter versus gate voltage characteristics. Sample D1, D2, and D3 are the devices with square patterns of 150×150μm2, 300×300μm2, and 600×600μm2. Figure 4. The currents read at 0.1 V versus time after the write processes. The inset in (a) shows the operation process. (b) is the read currents in (a) divided by the device perimeters.

Fabrication of Capacitor–Resistor Bank for Calibrating Commercial Capacitance and Tan $\delta $ Measuring Bridges

A capacitor–resistor combined bank to calibrate both the capacitance ratio and dissipation factor over the whole range for commercial capacitance and tan $\delta $ measuring bridges was fabricated. A fabricated secondary working standard for capacitance ratio calibration was realized by connecting double-shielded capacitors in parallel employing a substitution and build-up technique, while a secondary working standard for dissipation factor calibration was attained by connecting shielded capacitors in parallel with a shielded T-resistor network. The design of the capacitor–resistor bank and calibration results for the two commercial bridges are presented and compared with specifications provided by manufacturers including the measurement uncertainty.

Solid-State Reaction Assisted Synthesis of Co-Doped MnO2 Nano-Composite Materials for Supercapacitor

Electrochemical supercapacitors are charge–storage devices that have greater power density and longer cycle life than batteries, and they possess higher energy density compared with conventional capacitors. Based on the different operation mechanisms, supercapacitors can be classified into two different categories: double-layer capacitors and pseudocapacitors [1,2]. Recently, relatively cheap oxide alternatives with similar characteristics have been developed to replace ruthenium oxide as electrode materials for use in pseudo-capacitors due to their low cost and no-toxicity. MnO2 has been used as one of the promising electrode materials for supercapacitor mainly because of its abundance in nature, low price, environment friendliness, wide charge/discharge potential range and large specific area [3]. In this work, a mechanically assisted solid-state reaction method was employed to prepare Co-doped MnO2 nanocomposites for supercapacitor electrode materials. It was found that the specific capacitance of 2.3 wt% Co doped MnO2 composite electrode was up to 340.1 F g-1 in 1.0 M KCl solution (Figure 1). Additionally, as prepared Co doped MnO2 composite electrode showed other desirable electrochemical properties, including good stable electrochemical properties, excellent reversibility and the long cycle life (Figure 2), demonstrating that it had potential advantages for the fabrication of electrochemical capacitor.

Fabrication of self-aligned, nanoscale, complex oxide varactors

Applications in ferroelectric random access memory and superparaelectric devices require the fabrication of ferroelectric capacitors at the nanoscale that exhibit extremely small leakage currents. To systematically study the material-size dependence of ferroelectric varactor performance, arrays of parallel-plate structures have been fabricated with nanoscale dielectric diameters. Electron beam lithography and inductively coupled plasma dry etching have been used to fabricate arrays of ferroelectric varactors using top electrodes as a self-aligned etch mask. Parallel-plate test structures using RF-sputtered Ba0.6Sr0.4TiO3 thin-films were used to optimize the fabrication process. Varactors with diameters down to 20 nm were successfully fabricated. Current-voltage (I-V) characteristics were measured to evaluate the significance of etch-damage and fabrication quality by ensuring low leakage currents through the structures.