On-chip Power Sources Research Articles

Graphene/SiC composite porous electrodes for high-performance micro-supercapacitors

Micro-supercapacitor (MSC) electrodes prepared by chemical vapor deposition (CVD) possess high potential as on-chip integrated micro-power sources for future microdevices. In this study, porous graphene/SiC composite films are grown using laser CVD. A double-layer specific capacitance up to 219.3 mF/cm2 is achieved at 10 mV/s, which is 26 times higher than those of the electrodes prepared by CVD with the same energy storage mechanism reported in literatures. After 20000 charge-discharge cycles at room temperature (20 °C) and variable temperatures (0–60 °C), the electrode exhibits robust cycling stability with 99.9% and 109.6% capacitance retention, respectively. Subsequently, it is revealed that the abundance of graphene on the SiC porous skeleton plays a key role in promoting the capacitance enhancement. The strong structure of SiC as well as the strong adhesion between graphene and SiC guarantee the excellent cycling stability. Evidently, the preparation of graphene/SiC porous composite films as MSC electrodes is a highly promising route for fabricating high-performance and reliable on-chip power sources for future miniaturized devices.

All-Solid-State Thin Film Lithium/Lithium-Ion Microbatteries for Powering the Internet of Things.

As the world steps into the era of Internet of Things (IoT), numerous miniaturized electronic devices requiring autonomous micropower sources will be connected to the internet. All-solid-state thin-film lithium/lithium-ion microbatteries (TFBs) combining solid-state battery architecture and thin-film manufacturing are regarded as ideal on-chip power sources for IoT-enabled microelectronic devices. However, unlike commercialized lithium-ion batteries, TFBs are still in the immature state, and new advances in materials, manufacturing, and structure are required to improve their performance. In this review, the current status and existing challenges of TFBs for practical application in internet-connected devices for the IoT are discussed. Recent progress in thin-film deposition, electrode and electrolyte materials, interface modification, and 3D architecture design is comprehensively summarized and discussed, with emphasis on state-of-the-art strategies to improve the areal capacity and cycling stability of TFBs. Moreover, to be suitable power sources for IoT devices, the design of next-generation TFBs should consider multiple functionalities, including wide working temperature range, good flexibility, high transparency, and integration with energy-harvesting systems. Perspectives on designing practically accessible TFBs are provided, which may guide the future development of reliable power sources for IoT devices.

Area-selective atomic layer deposition of titanium oxide and nitride on vertically aligned carbon nanotubes patterned by Aerosol Jet Printing for 3D Microsupercapacitors

This article demonstrates novel fabrication of the first interdigital 3D microsupercapacitors (MSC) using area-selective atomic layer deposition (ASALD). A unique ASALD process was developed to selectively deposit pseudocapacitive titanium oxide and nitride layers on one or both interdigitated vertically aligned carbon nanotube (VACNT) electrodes to form asymmetric or symmetric 3D MSC devices. This work compliments and expands on our previously published article exploring ALD of thin conformal coatings of TiO2 and TiN on VACNTs for 3D MSCs. Further, we demonstrate the first use of Aerosol Jet Printing, a recently developed additive manufacturing technique, to enable ASALD patterning of 3D MSC devices by direct writing of PMMA inhibitors on and adjacent to relatively thick nanostructured electrodes. The synthesis, characterization, and performance evaluation of ASALD TiN-TiO2-VACNT 3D MSCs described herein provides a novel approach for manufacturing of new nanocomposite based electrochemical energy storage microdevices that could be integrated as an on-chip power source for portable electronics. Results indicated the symmetric ASALD TiN(100)-TiO2(100)-VACNT MSC (6.55 mF cm−2) exhibited nearly two orders of magnitude (94×) improvement in specific capacitance compared to the uncoated VACNT MSC (0.07 mF cm−2), significantly improving energy density (3.28 mWhr cm−2) while maintaining high power density (2.34 mW cm−2).

Ultrafast high-energy micro-supercapacitors based on open-shell polymer-graphene composites

Micro-supercapacitors are poised to serve as on-chip power sources for electronics. However, the challenge to simultaneously increase their power, energy, and lifetime demands new material combinations beyond current carbon-based systems. Here, we demonstrate that electro-deposition of an open-shell conjugated polymer with reduced graphene oxide achieves electrodes with capacitance up to 186 mF cm −2 (372 F cm −3 ). The extended delocalization within the open-shell polymer stabilizes redox states and facilitates a 3 V wide potential window, while the hierarchical electrode structure promotes ultrafast kinetics. The micro-supercapacitor shows a high power density of 227 mW cm −2 with an energy density of 10.5 μWh cm −2 and stability of 84% capacitance retention after 11,000 cycles. These attributes allow operation at 120 Hz for fast charging and alternating current (AC) line filtering applications, which may be suitable to replace bulky electrolytic capacitors or serve as high-endurance energy storage for wireless electronics. • A new class of open-shell conjugated polymer-based composite electrodes • Electrodes incorporating polymers with extended delocalization facilitating 3 V redox stability window • Ultrafast kinetics compatible with a typical AC line frequency of 60 Hz • Suitable replacement for bulky electrolytic capacitors, reducing volume by >10 times Micro-supercapacitors are promising for on-chip power sources. Yao et al. show that the electro-polymerization of an open-shell conjugated polymer with reduced graphene oxide enables hierarchical electrodes for micro-supercapacitors, simultaneously increasing their power, energy, and lifetime for wireless electronic applications.

Design and manufacture of high-performance microbatteries: lithium and beyond

The accelerated development of miniaturized and customized electronics has stimulated the demand for high-energy microbatteries (MBs) as on-chip power sources for autonomous state operations. However, commercial MBs with thin-film configurations exhibit insufficient energy and power density due to their limited active materials and sluggish ion diffusion kinetics. In order to simultaneously enhance electrochemical performance and maintain low-cost production, efforts have been devoted to constructing three-dimensional battery architectures. This review summarizes the state-of-the-art progress in designing and fabricating microelectrodes for microbattery assembly, including the top-down etching and bottom-up printing techniques, with a particular focus on elucidating the correlations between electrode structures, battery performance, and cost-effectiveness. More importantly, advancements in post-lithium batteries based on sodium, zinc and aluminum are also surveyed to offer alternative options with potentially higher energy densities and/or lower battery manufacturing costs. The applications of advanced MBs in on-chip microsystems and wearable electronics are also highlighted. Finally, conclusions and perspectives for the future development of MBs are proposed.

Graphitic Mesoporous Carbon Thin Film Prepared By Rapid Thermal Annealing for Micro-Supercapacitors

The miniaturization of electronic devices led to the advent of on-chip power sources with high energy and power density requirement. The development of such miniaturized energy devices further requires the preparation and/or processing of thin films (down to a few nanometers) of active material. Mesoporous carbon possessing both high porosity and conductivity are desired for such applications. However, obtaining thin films of mesoporous carbon on various substrates using commercially viable approaches requires further improvement and investigation. We have adapted rapid thermal annealing (RTA) as a novel approach to obtain mesoporous carbon. RTA enables rapid heating to temperatures up to 1200oC in just a few seconds and therefore provides a route for complete carbonization within a few minutes. Carbon precursor films comprised of brush block copolymers (BBCP) as sacrificial templates and phenol formaldehyde (PF) resin as a carbon source were prepared. In particular, the self-assembly of polydimethylsiloxane-b-polyethylene oxide (PDMS–b-PEO) BBCP and PF resin led to the formation of microphase-segregated film on various substrates including Si wafer, fused silica, and stainless steel. The PDMS domain in the BBCP fostered strong adhesion to the substrate even after annealing. RTA enabled complete carbonization of the precursor film within only 5 minutes, whereas conventional methods require approximately 500 minutes. Rapid processing at 1000oC resulted in the formation of mesoporous carbon with higher degree of graphitization, which is difficult to achieve with conventional carbonization method. The device prepared via RTA has a capacitance value of 7.0 mF/cm2 at 100mV/s, which is one of the highest values obtained for nanometer-thick carbon-based electrodes. These electrodes maintained a quasi-rectangular shape during the potential vs current scan, even at a scan rate of 20 V/s, which suggests that these materials are promising candidates for applications requiring very high-power density.The mesoporous carbon structure having high porosity and high conductivity can be further utilized as supports for the deposition of pseudo-capacitance materials to further boost the energy density of the device. Figure 1

Active microvalve driven by electro-conjugate fluid jet flow with a hydraulic power source on a chip

Powered microvalves are necessary for a variety of microfluidic applications such as on-demand droplet generators and droplet capture systems. Currently, a central challenge for these microvalve systems is the miniaturization of bulky power sources and control components, for example, air compressors, hydraulic pumps, solenoid valves, and regulators. In this paper, we propose a polydimethylsiloxane (PDMS)-based microvalve integrated with an on-chip power source, an electro-conjugate fluid (ECF) micropump. The assembled PDMS membrane of the device deforms and then blockades the port in the microchannel via fluidic pressure generated by the ECF micropump with the application of high DC voltage. Following finite element method simulations, we utilized 15 electrode pairs for the on-chip ECF micropump. By combining a MEMS process and the bonding process, we successfully realized the designed device and proceeded to evaluation of its performance characteristics. First, we evaluated the performance of the ECF micropump, which showed a maximum output pressure and a flow rate of 49.7 kPa, 87.3 mm3 s−1, respectively, at an applied voltage of 2.0 kV. Second, we found that the minimum sealing pressure of the microvalve was 10 kPa without any load condition. Third, we investigated the cracking pressures, which were 20 kPa and 50 kPa at the applied voltages of 1.5 kV and 2.0 kV to the ECF micropump, respectively. This study experimentally demonstrated the feasibility of the proposed microvalve device and its potential to be integrated into other microfluidic devices for precision control of liquid volumes.

Nitrogen and oxygen co-doped graphene quantum dots with high capacitance performance for micro-supercapacitors

The applications of carbon-based micro-supercapacitors (MSCs) based on the electrical double layer capacitance mechanism are usually limited by the extremely low specific capacitances and energy storage densities of carbon electrodes fabricated from less active, large-size carbon materials. As a promising alternative, high-activity N and O co-doped graphene quantum dots (N-O-GQDs) offer a combination of advantages, such as ultrasmall sizes, rich active sites, high hydrophilicity, and facile assembly into conductive carbon films. Here we report the facile electrophoresis construction of carbon-based MSCs for ultrahigh energy density storage using N-O-GQDs as the initial electrode material. The N-O-GQD MSCs show extremely high volumetric capacitances of 325 F cm−3 in H2SO4 due to their high pseudocapacitive activity, high loading density, and enhanced electrolyte wettingability ascribed to a large amount of doped nitrogen and oxygen functional groups. They deliver an ultrahigh volumetric energy density, superior to that of thin-film lithium batteries. Three connected all-solid-state N-O-GQD MSCs can light a red light--emitting diode. Furthermore, the pseudocapacitive MSCs maintain high power densities, and cycling stability owing to improvements in electrical conductivity and electrolyte penetration. The important results highlight the promising applications of high-activity nanographenes in on-chip power sources for driving diverse micro-devices.

All-solid-state high-energy planar hybrid micro-supercapacitors based on 2D VN nanosheets and Co(OH)2 nanoflowers

Planar micro-supercapacitors are recognized as one of the most competitive on-chip power sources for integrated electronics. However, most reported symmetric micro-supercapacitors suffer from low energy density. Herein, we demonstrate the facile mask-assisted fabrication of new-type all-solid-state planar hybrid micro-supercapacitors with high energy density, based on interdigital patterned films of porous vanadium nitride nanosheets as negative electrode and Co(OH)2 nanoflowers as positive electrode. The resultant planar hybrid micro-supercapacitors display high areal capacitance of 21 mF cm−2 and volumetric capacitance of 39.7 F cm−3 at 0.2 mA cm−2, and exhibit remarkable energy density of 12.4 mWh cm−3 and power density of 1750 mW cm−3, based on the whole device, outperforming most reported planar hybrid micro-supercapacitors and planar asymmetric micro-supercapacitors. Moreover, all-solid-state planar hybrid micro-supercapacitors show excellent cyclability with 84% capacitance retention after 10000 cycles, and exceptionally mechanical flexibility. Therefore, our proposed strategy for the simplified construction of planar hybrid micro-supercapacitors will offer numerous opportunities of utilizing graphene and other 2D nanosheets for high-energy microscale supercapacitors for electronics.

Disposable Wireless Immuno-Sensing Chips

A disposable immuno-sensor chip which is proposed for use in continuous health monitoring and for early diagnosis of infectious disease. On-chip high-power density wireless power sources and on-chip wireless data transfer technologies are developed to minimize chip production costs.

A primary battery-on-a-chip using monolayer graphene

We present here a bottom-up approach for realizing on-chip on-demand batteries starting out with chemical vapor deposition-grown graphene. Single graphene monolayers contacted by electrode lines on a silicon chip serve as electrodes. The anode and cathode are realized by electrodeposition of zinc and copper respectively onto graphene, leading to the realization of a miniature graphene-based Daniell cell on a chip. The electrolyte is housed partly in a gel and partly in liquid form in an on-chip enclosure molded using a 3d printer or made out of poly(dimethylsiloxane). The realized batteries provide a stable voltage (∼1.1 V) for many hours and exhibit capacities as high as 15 μAh, providing enough power to operate a pocket calculator. The realized batteries show promise for deployment as on-chip power sources for autonomous systems in lab-on-a-chip or biomedical applications.

Ultrasonic-electrodeposition of PtPd alloy nanoparticles on ionic liquid-functionalized graphene paper: towards a flexible and versatile nanohybrid electrode.

Here we fabricate a new type of flexible and versatile nanohybrid paper electrode by ultrasonic-electrodeposition of PtPd alloy nanoparticles on freestanding ionic liquid (IL)-functionalized graphene paper, and explore its multifunctional applications in electrochemical catalysis and sensing systems. The graphene-based paper materials demonstrate intrinsic flexibility, exceptional mechanical strength and high electrical conductivity, and therefore can serve as an ideal freestanding flexible electrode for electrochemical devices. Furthermore, the functionalization of graphene with IL (i.e., 1-butyl-3-methylimidazolium tetrafluoroborate) not only increases the electroactive surface area of a graphene-based nanohybrid paper electrode, but also improves the adhesion and dispersion of metal nanoparticles on the paper surface. These unique attributes, combined with the merits of an ultrasonic-electrodeposition method, lead to the formation of PtPd alloy nanoparticles on IL-graphene paper with high loading, uniform distribution, controlled morphology and favourable size. Consequently, the resultant nanohybrid paper electrode exhibits remarkable catalytic activity as well as excellent cycle stability and improved anti-poisoning ability towards electrooxidation of fuel molecules such as methanol and ethanol. Furthermore, for nonenzymatic electrochemical sensing of some specific biomarkers such as glucose and reactive oxygen species, the nanohybrid paper electrode shows high selectivity, sensitivity and biocompatibility in these bio-catalytic processes, and can be used for real-time tracking hydrogen peroxide secretion by living human cells. All these features demonstrate its promising application as a versatile nanohybrid electrode material in flexible and lightweight electrochemical energy conversion and biosensing systems such as bendable on-chip power sources, wearable/implantable detectors and in vivo micro-biosensors.

Rapid, simple and low cost fabrication of a microfluidic direct methanol fuel cell based on polydimethylsiloxane

In this paper a simple and rapid fabrication method for a microfluidic direct methanol fuel cell using polydimethylsiloxane (PDMS) as substrate is demonstrated. A gold layer on PDMS substrate as seed layer was obtained by chemical plating instead of conventional metal evaporation or sputtering. The morphology of the gold layer can be controlled by adjusting the ratio of curing agent to the PDMS monomer. The chemical properties of the gold films were examined. Then catalyst nanoparticles were grown on the films either by cyclic voltammetry or electrophoretic deposition. The microfluidic fuel cell was assembled by simple oxygen plasma bonding between two PDMS substrates. The cell operated at room temperature with a maximum power density around 6.28 mW cm−2. Such a fuel cell is low-cost and easy to construct, and is convenient to be integrated with other devices because of the viscosity of the PDMS. This work will facilitate the development of miniature on-chip power sources for portable electronic devices.

Operation of an Adiabatic Quantum-Flux-Parametron Gate Using an On-Chip AC Power Source

Adiabatic quantum-flux-parametron (AQFP) logic devices can operate under extremely low bit energy approaching the thermal limit by varying their potential energy adiabatically using ac bias currents. We have proposed an on-chip ac power source, which is composed of a Josephson relaxation oscillator and a superconducting LC resonator in order to drive AQFP circuits at 5 GHz or higher frequencies. We herein experimentally confirmed the correct switching operation of an AQFP gate at 4.94 GHz using the proposed on-chip ac power source. Furthermore, we confirmed that the ac power source can drive approximately 800 AQFP gates.

Design and demonstration of an on-chip AC power source for adiabatic quantum-flux-parametron logic

Adiabatic quantum-flux-parametron (AQFP) logic is a promising technology for use in future high-end computers because its bit energy can be potentially reduced to the order of thermal energy. AQFP gates are driven by an AC bias current, which changes their potential energy adiabatically. In the present paper, we propose an on-chip AC power source, which is composed of a Josephson relaxation oscillator and a superconducting resonator, to drive the AQFP gates. We designed and implemented the AC power source using a Nb Josephson integrated circuit process. We confirmed that the AC power source can generate a 4.4 GHz sinusoidal current from a DC bias current and that the output amplitude of the AC power source can be controlled by varying the DC bias current.

A precious-metal free micro fuel cell accumulator

In recent years, integrated fuel cell (FC) type primary and secondary batteries attracted a great deal of attention as integrated on-chip power sources due to their high theoretical power densities. Unfortunately, the costs of these devices have been rather high. This is partially due to the involved clean-room processes, but also due to the fact that these devices generally rely on expensive precious-metals such as Pd and Pt. Therefore we developed a novel integrated FC type accumulator that is based on non-precious-metals only. The key component of the presented accumulator is its alkaline polymer electrolyte membrane that allows not only the usage of a low-cost AB5 type hydrogen storage electrode, but also the usage of La0.6Ca0.4CoO3 as a precious-metal free bifunctional catalyst for the air-breathing electrode. Additionally the presented design requires only comparatively few cleanroom processes which further reduces the overall production costs. Although abdicating precious-metals, the presented accumulator shows an open circuit voltage of 0.81V and a maximum power density of 0.66mWcm−2 which is comparable or even superior to former precious-metal based cells.

On-Chip Fuel Cell: Micro Direct Methanol Fuel Cell of an Air-Breathing, Membraneless, and Monolithic Design

This paper proposes a novel design for a microfuel cell as an on-chip power source and demonstrates its fabrication and operation to prove the concept. Its simple design is important from the viewpoints of fabrication (e.g., replication), integration, and compatibility with other microdevices. In testing, the prototype cell was able to generate electric power (maximum: ca. 1.4 microW) on methanol without pumps under both neutral and acidic conditions. As for the size, the electrode part of the cell (two cathodes and one anode) is 400 microns in width and 6 mm in length. The evaluation demonstrated that the proposed design is a promising on-chip power source for miniature devices.

Rapid fabrication of microfluidic polymer electrolyte membrane fuel cell in PDMS by surface patterning of perfluorinated ion-exchange resin

In this paper we demonstrate a simple and rapid fabrication method for a microfluidic polymer electrolyte membrane (PEM) fuel cell using polydimethylsiloxane (PDMS), which has become the de facto standard material in BioMEMS. Instead of integrating a Nafion sheet film between two layers of a PDMS device in a traditional “sandwich format,” we pattern a perfluorinated ion-exchange resin such as a Nafion resin on a glass substrate using a reversibly bonded PDMS microchannel to generate an ion-selective membrane between the fuel-cell electrodes. After this patterning step, the assembly of the microfluidic fuel cell is accomplished by simple oxygen plasma bonding between the PDMS chip and the glass substrate. In an example implementation, the planar PEM microfluidic fuel cell generates an open circuit voltage of 600–800 mV and delivers a maximum current output of nearly 4 μA. To enhance the power output of the fuel cell we utilize self-assembled colloidal arrays as a support matrix for the Nafion resin. Such arrays allow us to increase the thickness of the ion-selective membrane to 20 μm and increase the current output by 166%. Our novel fabrication method enables rapid prototyping of microfluidic fuel cells to study various ion-exchange resins for the polymer electrolyte membrane. Our work will facilitate the development of miniature, implantable, on-chip power sources for biomedical applications.

Magnetically-driven biomimetic micro pumping using vortices

Planar micropumps utilizing vortices shed by an oscillating ferromagnetic bar are presented. The movement of the bar is induced by magnetic coupling with an external spinning magnet. Thus, energy transfer is achieved without physical contact or need of any on-chip power source. To create vortices inside the chip, the Reynolds number is locally increased with the oscillation of the bar. The utilization of the vortices as a tool for efficient transfer of energy is inspired by the behaviour of swimming animals and flying insects in nature. The pumps operate in two different scales (milli-scale and micro-scale) in order to take advantage of both. Experiments are presented characterizing the pumps and their flow patterns. The range of operation of the pumps is from 3 microl min(-1) to 600 microl min(-1), though smaller flow rates are also possible.

Disposable Smart Lab on a Chip for Point-of-Care Clinical Diagnostics

This paper presents the development of a disposable plastic biochip incorporating smart passive microfluidics with embedded on-chip power sources and integrated biosensor array for applications in clinical diagnostics and point-of-care testing. The fully integrated disposable biochip is capable of precise volume control with smart microfluidic manipulation without costly on-chip microfluidic components. The biochip has a unique power source using on-chip pressurized air reservoirs, for microfluidic manipulation, avoiding the need for complex microfluidic pumps. In addition, the disposable plastic biochip has successfully been tested for the measurements of partial oxygen concentration, glucose, and lactate level in human blood using an integrated biosensor array. This paper presents details of the smart passive microfluidic system, the on-chip power source, and the biosensor array together with a detailed discussion of the plastic micromachining techniques used for chip fabrication. A handheld analyzer capable of multiparameter detection of clinically relevant parameters has also been developed to detect the signals from the cartridge type disposable biochip. The handheld analyzer developed in this work is currently the smallest analyzer capable of multiparameter detection for point-of-care testing.