Fabrication Of Capacitors Research Articles

(Invited) Nanoengineered Thermoelectric Energy Devices for IoT Sensing Applications

Flexible thermoelectric micro power generators have been developed for wearable devices such as body area network. Also in order to store the generated power, a solid state micro-supercapacitor using a thin film composed of graphene nanowall are developed. The flexible thermoelectric micro power generator is fabricated by electrochemical deposition of Bi2Te3 and Sb2Te3, which is embedded by PDMS as shown in Fig. 1 (1). A power generation of 4 μW/cm2 are demonstrated from human body temperature. In order to improve the power generation performance, nanocomposites processes of Bi2Te3 are developed. In this method, nanomaterials such as metal nanoparticles and carbon nanomaterials are included in the film by a co-electrodeposition method (Fig. 2). For the fabrication of the solid state micro super capacitor, plasma-enhanced chemical vapor deposition is used to deposit graphene nanowall on a spiral-shaped silicon electrode pattern, as shown in Fig. 3. On the graphene nanowall Ru oxide or Ni oxide is deposited for electrochemical charge storage layer. Areal energy density of ~15 μWh/cm2 and areal power density of ~2.49 mW/cm2 are achieved (2). References (1) T. N. Huu, T. Nguyen, and T. Ono, "Fabrication of π-type flexible thermoelectric generators using an electrochemical deposition method for thermal energy harvesting applications at room temperature" Journal of Micromechanics and Microengineering 27, (2017) 125006. (2) J. Li, M. Zhu, Z. An, Z. Wang, M. Toda, T. Ono, Constructing in-chip micro-supercapacitors of 3D graphene nanowall/ruthenium oxides electrode through silicon-based microfabrication technique, Journal of Power Sources 401, (2018) 204-212. Figure 1

Hydrothermal synthesis of transition metal sulfides/MWCNT nanocomposites for high-performance asymmetric electrochemical capacitors

Achieving both high energy and power densities for electrochemical capacitors is always one of the greatest scientific and societal challenges. Owing to the outstanding electrochemical performances of transition metal sulfides, especially high theoretical capacities and wide potential windows, they have drawn extensive attention as promising electrode materials for electrochemical capacitors recently. Herein, the Ni–S/MWCNT composite as positive electrode and the Ni–Fe–S/MWCNT composite as negative electrode have been prepared by a hydrothermal method. The Ni–S/MWCNT electrode shows a high specific capacity of 265.6 mAh g−1 at 1 A g−1 and an excellent rate performance, which are attributed to a larger BET surface area and faster charge transfer rate due to an introduction of MWCNTs compared to the pure Ni–S electrode. The Ni–Fe–S/MWCNT electrode also exhibits a good electrochemical performance due to its rich redox reaction and high total pore volume after the integration of MWCNTs. The fabricated Ni–S/MWCNT//Ni–Fe–S/MWCNT asymmetric electrochemical capacitor delivers a high cell potential of 1.7 V, a high energy density of 42.2 Wh kg−1 at a high power density of 3.7 kW kg−1 (even 19.1 Wh kg−1 at 11.9 kW kg−1), and a relatively good cycling stability. Our work may provide an alternative protocol for the fabrication of high-performance electrochemical capacitors.

A Gated Diode DRAM Cell for Improved Power and Speed

In this paper performance analysis of Gated diode based Dynamic Random Access Memory (GD-DRAM) cell is compare with capacitor based DRAM cell in terms of average power dissipation, propagation delay, read access time and write access time at 250nm technology. The GD-DRAM is also referred as capacitorless DRAM. This gated diode stored data in DRAM which is an alternative solution to capacitor. This gated diode DRAM shows cutback in leakage and access time as compared to capacitor based DRAM. A gated diode is formed by shorting two terminal of MOS transistor i.e. source and drain. When the voltage Vgs is higher than knee voltage Vth; then data get stored on it. Nowadays dynamic random access memory is highly attracting market as compared static RAM because of its high package density, low cost and small area. In this paper this gated diode also resolves the issue of fabrication of capacitor in conventional DRAM cell. The major problem associated with DRAM is power dissipation. The above cells were designed and simulated in Tanner EDA tool and their results were analyzed at 250μm technology. Here we investigated that gated diode based DRAM has superior performance in terms of read time, write time and average power dissipation.

Catechol-Based Capacitor for Redox-Linked Bioelectronics.

A common bioelectronics goal is to enable communication between biology and electronics, and success is critically dependent on the communication modality. When a biorelevant modality aligns with instrumentation capabilities, remarkable successes have been observed (e.g., electrodes provide a powerful tool to observe and actuate biology through its ion-based electrical modality). Emerging biological research demonstrates that redox is another biologically relevant modality, and recent research has shown that advanced electrochemical methods enable biodevice communication through this redox modality. Here, we briefly summarize the biological relevance of this redox modality and the use of redox mediators to enable access to this modality through electrochemical measurements. Next, we describe the fabrication of a catechol-chitosan redox capacitor that is redox-active but nonconducting and thus offers a unique set of molecular electronic properties that enhance access to redox-based information. Finally, we cite several recent studies that demonstrate the broad potential for this capacitor to access redox-based biological information. In summary, we envision the redox capacitor will become a vital component in the integrated circuitry of redox-linked bioelectronics.

Monolithic radio frequency SiNx self-rolled-up nanomembrane interdigital capacitor modeling and fabrication

Monolithic capacitors operating at radio frequencies (RF) serve as critical components in integrated circuits for wireless communication. Design and fabrication innovations for high capacitance density RF capacitors are highly desired for the miniaturization of RFIC chips. However, practical and simple solutions are limited by existing capabilities in three-dimensional (3D) structure construction and the effective configuration of electrodes. We report a unique route to achieve unprecedentedly high capacitance density at a high operating frequency through a capacitor configuration of 3D coil interdigital electrodes using planar semiconductor processing compatible materials and fabrication methods. A systematic mechanical-electrical design principle is demonstrated, and fabricated devices show a maximum 21.5 pF capacitance, which is 17.2× larger after rolling up. The corresponding capacitance density is as large as 371 pF mm−2, with resonant frequency of 1.5 GHz. The performance could be improved significantly by simply rolling up more turns with minimal change to the area footprint.

Fabrication and evaluation of an electrochemical double-layer capacitor with natural graphite electrodes and magnesium trifluoromethanesulfonate–based gel polymer electrolyte

Super capacitors have emerged as a promising substitute for batteries and conventional capacitors which have played a key role as energy storage devices. The continuous concerns over green and low-cost concepts have motivated the consideration of natural materials as they are non-toxic and low cost. On the other hand, the realization of the dangers of liquid electrolytes has promoted the attention on gel polymer electrolytes to be used for devices. The prime objective of the present study is fabricating an electrochemical double-layer capacitor (EDLC) which is a type of super capacitor make using natural graphite and a gel polymer electrolyte. The electrolyte having the composition 0.5 PVdF-Co-HFP:0.70 MgTF:1 EC:1 DEC showed an optimum room temperature conductivity of 3.45 × 10−3 S cm−1. It was purely an ionic conductor having improved amorphous nature. EDLCs were fabricated with two identical natural graphite electrodes. Evaluation of EDLC was carried out using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge test. The proposed electrode/electrolyte combination seemed to be suitable for the application in EDLCs. Specific capacitance values obtained are satisfactory to carry forward further investigations to improve performance.

Solid state MXene based electrostatic fractional capacitors

Here, we report the fabrication of electrostatic fractional capacitors based on two-dimensional Ti3C2 MXene/vinylidene fluoride–trifluoroethylene–chlorofluoroethylene terpolymer [P(VDF-TrFE-CFE)] composites. The bandwidth of MXene-based fractional capacitors varies between 200 kHz and 2 MHz, while the phase angle varies less than ±2°. Additionally, the constant phase angle of the MXene/P(VDF-TrFE-CFE) can be precisely tuned from −67° to −34° by varying the volume ratio of MXene nanosheets in the polymer matrix. The results presented in this work demonstrate the potential of MXene/P(VDF-TrFE-CFE) composites as solid-state electrostatic fractional capacitors.

Plasticized solid polymer electrolyte based on natural polymer blend incorporated with lithium perchlorate for electrical double-layer capacitor fabrication

A plasticized solid polymer electrolyte system is prepared using polymer blend of methyl cellulose–potato starch with lithium perchlorate (LiClO4) as dopant salt and glycerol as plasticizer. Transport properties of the electrolytes are investigated using electrical impedance spectroscopy (EIS). By applying a method proposed by Arof et al. which was found to be suitable for both Arrhenius and Vogel–Tammann–Fulcher (VTF) type of electrolytes, the number density (n), diffusion coefficient (D), and mobility (μ) of ions are found to be influenced by the concentration of glycerol. From ion and electron transference number analysis, it is verified that ions are the main charge carriers. Linear sweep voltammetry (LSV) verifies the suitability of the most conductive electrolyte to be employed in the carbon-based symmetric electrical double-layer capacitor (EDLC) fabrication. The EDLC has been tested using the galvanostatic charge–discharge and cyclic voltammetry (CV) techniques. The specific capacitance (Csp) of the electrode using CV at a sweep rate of 2 mV s−1 is found to be 61.58 F g−1. The EDLC has been tested for 1000 charge–discharge cycles with the highest Csp value of 28.04 F g−1.

Flexible Graphene/Carbon Nanotube Electrochemical Double-Layer Capacitors with Ultrahigh Areal Performance.

The fabrication of electrochemical double-layer capacitors (EDLCs) with high areal capacitance relies on the use of elevated mass loadings of highly porous active materials. Herein, we demonstrate a high-throughput manufacturing of graphene/carbon nanotubes hybrid EDLCs. The wet-jet milling (WJM) method is exploited to exfoliate the graphite into single-few-layer graphene flakes (WJM-G) in industrial volumes (production rate ca. 0.5 kg/day). Commercial single-/double-walled carbon nanotubes (SDWCNTs) are mixed with graphene flakes in order to act as spacers between the flakes during their film formation. The WJM-G/SDWCNTs films are obtained by one-step vacuum filtration of the material dispersions, resulting in self-standing, metal- and binder-free flexible EDLC electrodes with high active material mass loadings up to around 30 mg cm-2 . The corresponding symmetric WJM-G/SDWCNTs EDLCs exhibit electrode energy densities of 539 μWh cm-2 at 1.3 mW cm-2 and operating power densities up to 532 mW cm-2 (outperforming most of the reported EDLC technologies). The EDCLs show excellent cycling stability and outstanding flexibility even in highly folded states (up to 180°).

Design and Characterization of a Micro-Fabricated Graphene-Based MEMS Microphone

We fabricate a microelectromechanical systems (MEMS) microphone that incorporates a graphene-based membrane that vibrates in response to acoustic forcing. We employ a novel fabrication process, where a graphene/poly(methyl methacrylate) (PMMA) bilayer membrane is transferred over a cavity on a separate chip before being affixed to the surface of another chip containing an electrode, resulting in the fabrication of a moveable capacitor with a membrane-to-electrode gap of 8 $\mu \text{m}$ . The gap, which is less than half the size of other reported graphene membrane-based audio transducers, allows for the device to operate with the low-DC bias voltages of about 1 V and, when integrated with a custom-designed readout circuit, demonstrates a sensitivity to sound pressure between 0.1 and 10 mV/Pa across the range 100 Hz–20 kHz. As well as a sensitivity that is comparable with the previous work, the flat frequency response is stable when the sound pressure is varied between 70 and 80 dBSPL, with the sensitivity value not varying by more than 0.2 mV/Pa.

Optimization of Design Parameters and Operating Conditions of Electrochemical Capacitors for High Energy and Power Performances

Theoretical expressions for performance parameters of different electrochemical capacitors (ECs) were optimized by writing MATLAB scripts to solve them and also via MATLAB R2014a optimization tool box. Performance of different kind of ECs at given circumstances were compared through theoretical equations and simulation of various models subject to conditions of device components, using optimal coefficient associated to battery-kind material and constant associated to electrolyte material KBMopt and KEopt , as well as our symmetric electric double layer capacitor (EDLC) experimental data. Estimations of performance parameters were feasible and achievable once details of electrodes mass ratio, operating potential range ratio and specific capacitance of electrolyte are known. Performances of asymmetric EC with suitable electrode mass and operating potential range ratios using aqueous electrolytes, and that with suitable electrode mass and operating potential range ratios using organic electrolyte with appropriate operating potential range and specific capacitance were factors of 2.2 and 5.56, respectively, greater than those of symmetric EDLC and asymmetric EC using the same aqueous electrolyte, respectively. This enhancement came along with reduction in cell mass and volume. Also, storable and deliverable energies of asymmetric EC with suitable electrode mass and operating potential range ratios using proper organic electrolyte were factor of 12.9 greater than those of symmetric EDLC using aqueous electrolyte, with reduction in cell mass and volume. Storable energy, energy density and power density of asymmetric EDLC with suitable electrode mass and operating potential range ratios using proper organic electrolyte were factor of 5.56 higher than those of similar symmetric EDLC using aqueous electrolyte with reduction in cell mass and volume by a factor 1.77. Also, introduction of asymmetric EDLC with the same type of electrode, and suitable electrodes mass ratio, working potential range ratios and proper organic electrolyte enhanced performance of conventional symmetric EDLC using aqueous electrolyte with reduction in cell mass and volume. These results can obviously reduce number of experiments to determine optimum manufacturing state of EC, and also demonstrated that institution of asymmetric electrode and organic electrolyte was very successful in improving performance of EC with reduction in cell mass and volume. These results can as well be a guideline for design, fabrication and operation of electrochemical capacitor with outstanding storable energy, energy and power densities. Key words: Electrodes symmetry; Modelling and simulation; Performance parameters; Electrolytes type; Working potential range; Asymmetric capacitors.

All Coconut Sprout Sodium Ion Hybrid Capacitor

Electrochemical Energy storage systems play a vital role in many applications like electronics, automotive, aerospace, smart electric grids etc. There are mainly two types of energy storage systems known as batteries and supercapacitors. The first one offers high energy density, and the later one is well known for its power density. Hybrid ion capacitor (HIC) is a new class of energy storage device, a combination of battery and supercapacitor1. Commonly anode part in HIC is taken from a battery, and the cathode part will be from a capacitor and in principle, the duo offers intermediate energy and power density in comparison with batteries and supercapacitors2 3. Sodium based hybrid capacitors are extensively explored today due to large abundance and low cost of sodium4. Here in we report for the first-time, fabrication of a hybrid sodium ion capacitor, in which the cathode, anode and separator are derived from a single precursor called coconut sprout (CS). Graphene-like carbon derived from CS, employed as an intercalating anode, provides a specific capacity of 181.09 mAhg- 1. High surface area (BET surface area of 2000 m2g-1) ion adsorption cathode part obtained by KOH activation of CS delivers a capacity of 90.15 mAhg- 1. Combination of CS derived anode, cathode and separator give rise to a capacitor works in a potential window of 1.5 -4.0V. The all sprout capacitor could deliver an energy density of 88.12 Whkg-1 at power density 273.26 Wkg-1 and energy density of 25.07 Whkg-1 at power density 7078 Wkg-1. This green, all sprout hybrid capacitor retained 65% of its initial capacity after 5000 cycles, while cycled at a current density of 1Ag-1. The spongy sprout separator showed excellent chemical and mechanical stability even after 10000 cycles of charge and discharge. Though the performance is not outstanding, low cost single precursor, facile synthesis route, minimal environmental impact of the device makes it a promising candidate among eco-friendly electrochemical systems. Reference (1) Amatucci, G. G.; Badway, F.; Du Pasquier, A.; Zheng, T. An Asymmetric Hybrid Nonaqueous Energy Storage Cell. J. Electrochem. Soc. 2001, 148 (8), A930. (2) Ding, J.; Wang, H.; Li, Z.; Cui, K.; Karpuzov, D.; Tan, X.; Kohandehghan, A.; Mitlin, D. Peanut Shell Hybrid Sodium Ion Capacitor with Extreme Energy-Power Rivals Lithium Ion Capacitors. Energy Environ. Sci. 2015, 8 (3), 941–955. (3) Sivakkumar, S. R.; Pandolfo, A. G. Evaluation of Lithium-Ion Capacitors Assembled with Pre-Lithiated Graphite Anode and Activated Carbon Cathode. Electrochim. Acta 2012, 65, 280–287. (4) Ding, J.; Hu, W.; Paek, E.; Mitlin, D. Review of Hybrid Ion Capacitors : From Aqueous to Lithium to Sodium. Chem. Rev. 2018, 118, 6457–6498.

Optimization of LC sensor enabling wireless passive intracranial pressure monitoring

With the increasingly widespread researches of wireless passive sensing technology based on LC sensors in the field of intracranial pressure (ICP) monitoring and other biomedical applications, the importance of sensor optimization has become increasingly prominent. This paper presents an optimization method of LC sensor enabling wireless passive ICP monitoring. The LC sensor is a resonant tank formed by a pressure-sensitive capacitor and a fixed inductor. The parameters of the capacitor and the inductor are optimized based on four optimization criteria: maximizing sensitivity, setting anodic bonding voltage less than pull-in voltage, maximizing quality factor and setting an upper limit of resonant frequency. Among them, the pull-in voltage is a critical value when pull-in effect occurs during anodic bonding, a key step in the process of capacitor fabrication. To analytically calculate the pull-in voltage, a pull-in effect model is built, and its effectiveness is verified by simulation and experiment. Based on the above-mentioned optimization criteria, the LC sensor is optimized, fabricated and characterized. The experimental results show that the optimized sensor achieves competitive sensitivity, quality factor and resonant frequency compared with the previous reports, and illustrate the effectiveness of the optimization method enabling ICP monitoring.

Fabrication of graphene-based electrochemical capacitors through reactive inverse matrix assisted pulsed laser evaporation

Electrodes constituted by nitrogen-doped reduced graphene oxide (NrGO) in combination with NiO nanostructures were fabricated by means of reactive inverse matrix assisted pulsed laser evaporation technique. The structure-composition of the electrode composites was tailored by laser-inducing chemical reactions of graphene oxide (GO) flakes with different precursor molecules (citric acid, ascorbic acid and imidazole) during GO deposition. Structural characterizations reveal the formation of wrinkles and nanoholes in the NrGO sheets, besides their coating with NiO nanostructures. Compositional studies disclose that imidazole precursor promotes the synthesis of NrGO with the largest degree of reduction and nitrogen doping (mainly with graphitic and pyridinic N). Electrochemical analyses of the obtained electrodes reveal that NiO nanostructures increase surface charge storage processes (double layer – pseudocapacitive) over diffusive ones, being the imidazole-based electrodes the ones exhibiting the best performance (up to 114 F cm−3 at 10 mV s−1). Symmetric and asymmetric electrochemical capacitors were also fabricated showing excellent robustness over 10,000 charge-discharge cycles at high specific currents.

Nitrogen-doped CNT on CNT hybrid fiber as a current collector for high-performance Li-ion capacitors

In this work, we describe a scalable synthesis process of binder-free, nitrogen-doped carbon nanotubes (CNTs) on CNT fibers combining a solvothermal process with chemical vapor deposition (CVD). Li4Ti5O12 was selected as an example active material to evaluate the performance of the obtained current collector electrode, which achieved 100% capacity retention after 1000 cycles at a 15C rate and a stable specific capacity of 144 mAhg−1 at 5C. We also report here the fabrication of an asymmetrical hybrid capacitor that exhibited a maximum specific energy of 0.296 mWhcm−2/0.019 Whcm−3/68 Whkg−1 at a specific power of 0.172 mWcm−2/0.011 Wcm−3/126 Wkg-1. It maintained specific capacitance of 0.0779 mWhcm−2/0.005 Whcm−3/17 Whkg−1 at a high specific power of 57.05 mWcm−2/3.719 Wcm−3/12,500 Wkg-1. The device exhibited a very stable cycling performance, retaining 100% of its specific energy after 2000 cycles at 4 Ag-1 current density. The increase in specific power, energy and cycling performance was attributed to the porous network afforded by the nitrogen-doped CNTs and their strong binding with the active material Li4Ti5O12. The porous network enabled fast Li-ion diffusion paths while the pristine CNT allowed for fast electron transfer all in a fiber format, making it attractive as an electrode for wearable energy storage devices.

A label-free aptamer-based nanogap capacitive biosensor with greatly diminished electrode polarization effects.

A significant impediment to the use of impedance spectroscopy in bio-sensing is the electrode polarization effect that arises from the movement of free ions to the electrode-solution interface, forming an electrical double layer (EDL). The EDL screens the dielectric response of the bulk and its large capacitance dominates the signal response at low frequency, masking information particularly relevant for biological samples, such as molecular conformation changes and DNA hybridization. The fabrication of nanogap capacitors with electrode separation less than the EDL thickness can significantly reduce electrode polarization effects and provide enormous improvement in sensitivity due to better matching of the sensing volume with the size of the target entities. We report on the fabrication of a horizontal thin-film nanogap capacitive sensor with electrode separation of 40 nm that shows almost no electrode polarization effects when measured with water and ionic buffer solutions, thereby allowing direct quantification of their relative permittivity at low frequencies. Surface modification of the electrodes with thiol-functionalized single strand DNA aptamers transforms the device into a label-free biosensor with high sensitivity and selectivity towards the detection of a specific protein. Using this approach, we have developed a biosensor for the detection of human alpha thrombin. In addition, we also examine frequency dependent permittivity measurements on high ionic strength solutions contained within the nanogap and discuss how these support recent experimental observations of large Debye lengths. A large shift in the Debye relaxation frequency to lower frequency is also found, which is consistent with water molecules being in a rigid-like state, possibly indicating the formation of an ordered "ice-like" phase. Altogether, this work highlights the need for better understanding of fluids in confined, nanoscale geometries, from which important new applications in sensing may arise.

Doping effect of SrZrO3 on KNLN ceramics structure and their dielectric properties

In this work, lead-free systems; ([Formula: see text]) (K[Formula: see text]Na[Formula: see text]Li0.07) NbO3–[Formula: see text]SrZrO3 ([Formula: see text], 0.005, 0.050, 0.095 and 0.14) were synthesized by the conventional solid-state reaction technique. XRD, SEM, densification parameter as well as dielectric parameters of the obtained KNLN ceramics were investigated. XRD analysis showed the formation of orthorhombic perovskite structure in all investigated specimens. SrZrO3 (SZ) inhibited the grain growth and increased the distribution of grains uniformly in the microstructure. In addition, SZ changed the crystalline system of KNLN ceramics abnormally. As a consequence, the permittivity, dielectric loss as well as AC conductivity decreased remarkably. The ceramics of [Formula: see text] are characterized by low conductivity (10[Formula: see text][Formula: see text]S/cm), low dielectric loss (0.005) and relatively high permittivity (34). They can be useful for the electrical capacitors fabrication and filtering out noise from signals in resonant circuits. At frequencies lower than 105[Formula: see text]Hz, DC conductivity and separation of the charges at the interfaces were found to dominate the electrical behavior of ceramics, whereas at higher frequencies, a faster or dipole polarization may become more dominated. A broad peak has been observed in the imaginary part of electric modulus revealing to the non-Debye dielectric relaxation behavior. Quantum mechanical tunneling (QMT) was found to be the most suitable to characterize the electrical conduction mechanism in the ceramic compounds.

Large-Area All-Carbon Nanocapacitors from Graphene and Carbon Nanomembranes

We report on the fabrication of large-area all-carbon capacitors (ACCs) composed of multilayer stacks of carbon nanomembranes as dielectrics sandwiched between two carbon-based conducting electrodes. Carbon nanomembranes (CNMs) are prepared from aromatic self-assembled monolayers of phenylthiol homologues via electron irradiation. Two types of carbon-based electrode materials, (1) trilayer graphene made by chemical vapor deposition and mechanical stacking and (2) pyrolyzed graphitic carbon made by pyrolysis of cross-linked aromatic molecules, have been employed for this study. The capacitor area is defined by the width of electrode ribbons, and the separation between two electrodes is tuned by the number of CNM layers. Working ACCs with an area of up to 1200 μm2 were successfully fabricated by a combination of bottom-up molecular self-assembly and top-down lithographic approaches. Then ACCs were characterized by Raman spectroscopy, helium ion microscopy, and impedance spectroscopy. A dielectric constant of 3.5 and an average capacitance density of 0.3 μF/cm2 were derived from the obtained capacitances. A dielectric strength of 3.2 MV/cm was determined for CNMs embedded in graphene electrodes with the interfacial capacitance being taken into account. These results show the potential of carbon nanomembranes to be used as dielectric components in next-generation environment-friendly carbon-based energy storage devices.

Direct writing of anodic oxides for plastic electronics

Metal oxide thin films for soft and flexible electronics require low cost, room temperature fabrication, and structuring processes. We here introduce an anodic printing process to realize the essential building blocks of electronic circuitry, including resistors, capacitors, field-effect transistors, diodes, rectifiers, and memristors directly on imperceptible plastic substrates. Largely independent on surface properties, we achieve high-quality, few nanometer thin dielectric and semiconducting films even on rough substrates via localized anodisation of valve metals using a scanning droplet cell microscope. We demonstrate printing-like fabrication of 3D multilayer solid-state capacitors with a record-high areal capacity of 4 µF cm−2. Applicable to the whole class of valve metals and their alloys, our method provides a versatile fabrication technique for the circuits that empower the flexible and stretchable electronics of tomorrow.

Fabrication of high-energy hybrid capacitors by using carbon-sulfur composite as promising cathodes

The full realization of the high energy density concept in current hybrid capacitors is still a challenge due to the huge difference in specific capacity and reaction kinetics of the commonly used cathode and anode materials. Herein, for the first time, the carbon-sulfur composite is proposed as the high-capacity cathode for hybrid capacitors to achieve a high energy density. The as-prepared carbon-sulfur composite delivers a high specific capacity of 212.2 mAh g−1 (424.4 F g−1) at 4 A g−1, which is much higher than that of the pure carbon cathode. Additionally, the kinetics gap between cathode and anode is narrowed by using carbon-sulfur composite as the cathode. As a result, the carbon-sulfur composite based hybrid capacitor delivers a high energy density of 258.4 Wh kg−1 at 995 W kg−1. Even at high power density of 17350 W kg−1, the energy density can still remain 125.3 Wh kg−1. This study provides an alternative approach for designing hybrid capacitors with both high energy and power density by using carbon-sulfur composite as the cathode, and also paves a way to extend the application of sulfur to a new field for taking its advantages of high-capacity, environmental friendliness, low-cost.