Supercapacitors for the Next Generation

Supercapacitors are presently applied in various devices and have the potential to be used in many fields in the future. For example, the use of supercapacitors is currently limited not only to automobiles, buses, and trucks, which have been electrified recently, but also to railways and aircraft. We believe that these devices are the most suitable physical batteries for absorbing regenerative energy produced during motor regeneration; thus, further research and development in this direction is expected in the future

A new SiC/HfB2 based micro hotplate for metal oxide gassensors

Abstract Solzbacher, Florian A new SiC/HfB2 based modular concept of micro hotplates for metal oxide gassensors Im Rahmen dieser Arbeit wurde ein neuer SiC/HfB2-basierter Mikroheizer mit niedrigster Leistungsaufnahme für die Anwendung in Metalloxid-Gassensoren entwickelt und demonstriert. Erstmals wurden Siliziumkarbid (SiC) und Hafniumdiborid (HfB2) als Werkstoffe für einen Mikroheizer eingesetzt. Durch geringe Modifikation der Herstellungsprozesse lässt sich der Heizer so variieren, dass der Einsatz sowohl für den automobilen Anwendungsbereich (12V- 24V) als auch für tragbare Geräte (1V-2V) für eine Vielzahl unterschiedlicher Messgase möglich ist. Es ist der erste Mikroheizer für Gassensoren überhaupt, der den Batteriebetrieb bei nur 1-2 V erlaubt. Der modulare Fertigungsansatz ermöglicht die Reduzierung der Entwicklungs- und Fertigungskosten für die unterschiedlichen Anwendungsbereiche. Aus der Marktentwicklung in der Sensorik, den industriellen Anforderungen und den zu den Metalloxid-Gassensoren im Wettbewerb stehenden alternativen Technologien ergeben sich das Anforderungsprofil des Sensors. Die Wahl der Materialien spielt eine Schlüsselrolle für die Heizereigenschaften. Der Mikroheizer besteht aus einer 1 (m dicken, an 150 (m langen und 10 bis 40 (m breiten Stegen aufgehängten Membran mit Außenmaßen von 100 (m x 100 (m. Alternativ kommen eine HfB2 - Dünnfilm-Widerstandsheizung oder ein dotierter SiC-Heizer zum Einsatz. Mit Leistungsaufnahmen von 32 mW werden Temperaturen von 600°C erreicht, was einer Effizienz von ca. 19 K/mW entspricht. Die verwendeten hexagonalen Strukturen ermöglichen dichtes Packen der Sensoren in Arrays bei hoher mechanischer Stabilität. Erste NO2 Sensoren mit gassensitiver In2O3 Schicht konnten gezeigt werden.A new SiC/HfB2-based micro hotplate with ultra low power consumption for the application in metal oxide micro gas sensors is developed and demonstrated. For the first time, silicon carbide (SiC) and Hafniumdiboride (HfB2) are used as materials for a micro hotplate structure. Using only slight modifications of the fabrication process, the device can be used either for automotive applications with operating voltages of 12V-24V or for battery operated handheld detectors with operating voltages of 1V-2V for a variety of different gases. It is the first micro hotplate device ever designed to work for low battery voltages of 1V-2V. The modular approach towards the processing allows easy modification for a variety of application fields and thus also reduces market entrance barriers. Based on the market development of micro sensors, the industrial requirements, and competing metal oxide gas sensors using alternative technologies, technical specifications for the hotplate as well as the state of the art's limits are determined. The new material choice plays a key role in the device properties. The micro hotplate consists of a 100 ?m x 100 ?m membrane supported by thin beams of 1 ?m thickness, 150 ?m length and 10 to 40 ?m width. Alternatively, an HfB2 ? thin film resistive heater or a doped SiC heater are used. Temperatures of 600°C are achieved using a power consumption of only 32 mW resulting in a thermal heater efficiency of ~19 K/mW. The hexagonal geometry allows close packing of the hotplates in array structures with high mechanical strength. NO2 sensors with gas sensitive In2O3 layer are presented

A micromachined zipping variable capacitor

Micro-electro-mechanical systems (MEMS) have become ubiquitous in recent years and are found in a wide range of consumer products. At present, MEMS technology for radio-frequency (RF) applications is maturing steadily, and significant improvements have been demonstrated over solid-state components. A wide range of RF MEMS varactors have been fabricated in the last fifteen years. Despite demonstrating tuning ranges and quality factors that far surpass solid-state varactors, certain challenges remain. Firstly, it is difficult to scale up capacitance values while preserving a small device footprint. Secondly, many highly-tunable MEMS varactors include complex designs or process flows. In this dissertation, a new micromachined zipping variable capacitor suitable for application at 0.1 to 5 GHz is reported. The varactor features a tapered cantilever that zips incrementally onto a dielectric surface when actuated electrostatically by a pulldown electrode. Shaping the cantilever using a width function allows stable actuation and continuous capacitance tuning. Compared to existing MEMS varactors, this device has a simple design that can be implemented using a straightforward process flow. In addition, the zipping varactor is particularly suited for incorporating a highpermittivity dielectric, allowing the capacitance values and tuning range to be scaled up. This is important for portable consumer electronics where a small device footprint is attractive. Three different modelling approaches have been developed for zipping varactor design. A repeatable fabrication process has also been developed for varactors with a silicon dioxide dielectric. In proof-of-concept devices, the highest continuous tuning range is 400% (24 to 121 fF) and the measured quality factors are 123 and 69 (0.1 and 0.7 pF capacitance, respectively) at 2 GHz. The varactors have a compact design and fit within an area of 500 by 100 μm

A micromachined zipping variable capacitor

Micro-electro-mechanical systems (MEMS) have become ubiquitous in recent years and are found in a wide range of consumer products. At present, MEMS technology for radio-frequency (RF) applications is maturing steadily, and significant improvements have been demonstrated over solid-state components.A wide range of RF MEMS varactors have been fabricated in the last fifteen years. Despite demonstrating tuning ranges and quality factors that far surpass solid-state varactors, certain challenges remain. Firstly, it is difficult to scale up capacitance values while preserving a small device footprint. Secondly, many highly-tunable MEMS varactors include complex designs or process flows.In this dissertation, a new micromachined zipping variable capacitor suitable for application at 0.1 to 5 GHz is reported. The varactor features a tapered cantilever that zips incrementally onto a dielectric surface when actuated electrostatically by a pulldown electrode. Shaping the cantilever using a width function allows stable actuation and continuous capacitance tuning. Compared to existing MEMS varactors, this device has a simple design that can be implemented using a straightforward process flow. In addition, the zipping varactor is particularly suited for incorporating a highpermittivity dielectric, allowing the capacitance values and tuning range to be scaled up. This is important for portable consumer electronics where a small device footprint is attractive.Three different modelling approaches have been developed for zipping varactor design. A repeatable fabrication process has also been developed for varactors with a silicon dioxide dielectric. In proof-of-concept devices, the highest continuous tuning range is 400% (24 to 121 fF) and the measured quality factors are 123 and 69 (0.1 and 0.7 pF capacitance, respectively) at 2 GHz. The varactors have a compact design and fit within an area of 500 by 100 µm

Surface Generated Acoustic Wave Biosensors for the Detection of Pathogens: A Review

This review presents a deep insight into the Surface Generated Acoustic Wave (SGAW) technology for biosensing applications, based on more than 40 years of technological and scientific developments. In the last 20 years, SGAWs have been attracting the attention of the biochemical scientific community, due to the fact that some of these devices - Shear Horizontal Surface Acoustic Wave (SH-SAW), Surface Transverse Wave (STW), Love Wave (LW), Flexural Plate Wave (FPW), Shear Horizontal Acoustic Plate Mode (SH-APM) and Layered Guided Acoustic Plate Mode (LG-APM) - have demonstrated a high sensitivity in the detection of biorelevant molecules in liquid media. In addition, complementary efforts to improve the sensing films have been done during these years. All these developments have been made with the aim of achieving, in a future, a highly sensitive, low cost, small size, multi-channel, portable, reliable and commercially established SGAW biosensor. A setup with these features could significantly contribute to future developments in the health, food and environmental industries. The second purpose of this work is to describe the state-of-the-art of SGAW biosensors for the detection of pathogens, being this topic an issue of extremely importance for the human health. Finally, the review discuses the commercial availability, trends and future challenges of the SGAW biosensors for such applications

Capacitive sensing for monitoring of microfluidic protocols using nanolitre dispensing and acoustic mixing

The development of protocols for bio/chemical reaction requires alternate dispensing and mixing steps. Whilst most microfluidic systems use the opening of additional parts of the channel to allow the ingress of fixed volumes of fluid, this requires knowledge of the protocol before the design of the chip. Our approach of using a microfluidic valve to regulate the flow into an initially empty cavity allows for on-chip protocol development and refinement. Mixing is provided by way of surface acoustic wave excitation; this high-frequency vibration causes steady-state streaming flows. We show that capacitive sensing can be used to measure fluid levels, even if multiple fluid types are used, such that nanolitre dispensing accuracy is achieved. Also, the capacitive readout can be used to establish mixing quality and to monitor temperature fluctuations. These capabilities allow for protocols to be conducted without optical assessment, and so will allow for multiplexing, such that reactions could be conducted, simultaneously, in multiple chambers across a chip

Direct and Non-Invasive Monitoring of Battery Internal State Via Novel GMI-IDT Magnetic Sensor

Efficient battery management systems (BMSs) in rechargeable battery-based systems require precise measurements of various battery parameters including state of charge (SOC), state of health (SOH) and charge capacity. Presently, SOC, charge capacity and SOH can only be indirectly inferred from long-term measurement of current, open circuit voltage (OCV), and temperature using multiple sensors. These techniques can only give an approximation of SOC and often require knowledge of the recent battery history to prevent excessive inaccuracy.To improve the performance of the BMS, an alternative method of monitoring the internal state of Li-ion batteries is presented here. Theoretical analysis of Li-ion batteries has indicated that the concentration of active lithium ions in the cathode is directly related to the magnetic susceptibility of the electrode materials. While charging/discharging, due to the change in the oxidation and/or spin state of metal atoms, the magnetic moment in the cathode varies. This indicates the potential for directly probing the internal state of the Li-ion batteries during charging/discharging by monitoring the changes in magnetic susceptibility via an appropriately designed magnetic sensor. In this research, a highly sensitive micromagnetic sensor design is investigated consisting of a single interdigital transducer (IDT) shunt-loaded with a magnetically sensitive Giant Magnetoimpedance (GMI) microwire. This design takes advantage of the coupling of the impedance characteristics of the GMI microwire to the IDT transduction process. The initial GMI-IDT sensor design is further developed and modified to maximize sensitivity and linearity. The sensor can detect magnetic field in the range of 900 nT and minute changes less than 1 μT when operated at or near its peak sensitivity. In addition, an appropriate procedure for preconditioning the GMI wire is developed to achieve sensor repeatability. Furthermore, using the identified optimum geometry of the experimental setup, the proposed sensor is implemented in monitoring the internal state of two types of Li-ion cells used in electric vehicles (EVs). The initial characterization results confirm that the GMI-IDT sensor can be used to directly monitor the charge capacity of the investigated Li-ion batteries. Other possible applications also include energy storage for renewable energy sources, and portable electronic devices

DEVELOPMENT OF IONIC CONDUCTIVE CELLULOSE MAT BY SOLUTION BLOW SPINNING AND LASER-INDUCED GRAPHENE FROM PINEAPPLE NANOCELLULOSE FOR USE IN FLEXIBLE ELECTRONIC DEVICES

In the face of environmental issues and aiming at electronic devices of rapid production at low cost, this doctoral thesis proposed two new and innovative approaches to obtain substrates, dielectrics, and electrodes from a single biopolymer: cellulose. In a first moment, a simple approach to produce low-cost flexible ionic conductive cellulose mats (ICCMs) using solution blow spinning (SB-Spinning) is reported. The electrochemical properties of the ICCMs were adjusted through infiltration with alkali hydroxides (LiOH, NaOH, or KOH), which enabled of ICCMs application as dielectric and substrate in oxide-based field effect transistors (FETs) and pencil-drawn resistorloaded inverters. The FETs showed good electrical performance under operating voltage <2.5 V, which was strictly associated with the type of alkali ion incorporated, presenting satisfactory performance for the ICCM infiltrated with K+ ion. The inverters with K+ ions also presented good dynamic performance, with a gain close to 2. Regarding the cellulose-based electrodes, a second innovative approach is reported to synthetize laser-induced graphene (LIG) structures from carboxymethyl cellulose (CMC)-based ink containing LIG obtained from cellulose nanocrystals (CNCs) extracted from pineapple leaf fibers (PALFs). To prove this concept, zinc oxide ultraviolet (ZnO UV) sensors were designed varying the amount of LIG from CNCs. Sensor obtained from LIG written directly on paper substrate were also performed. The ZnO UV sensors designed with CMC-based ink showed responsivity 40-fold higher than that of paper direct-written LIG, as well as excellent electrical performance under flexion. These findings may open new promising possibilities for low-consumption wearable electronics, allowing the use of concepts such as the "Internet of Things" and opening the possibility of generating 100% organic cellulose-produced electronic devices.Frente às questões ambientais e visando dispositivos eletrônicos de rápida produção e baixo custo, este projeto de pesquisa de doutorado propôs duas abordagens inovadoras para a obtenção de substratos, materiais dielétricos e eletrodos a partir de um único biopolímero: a celulose. Em um primeiro momento relata-se uma abordagem simples para produzir mantas condutoras iônicas de celulose (ICCM) flexíveis aplicando fiação por sopro em solução (SB-Spinning) seguido da infiltração com hidróxidos alcalinos (LiOH, NaOH ou KOH), permitindo sua aplicação como dielétrico e substrato em transistores e inversores com resistor desenhado a lápis. Os transistores exibiram um bom desempenho sob tensão de operação abaixo de 2,5 V, apresentando desempenho satisfatório para as mantas infiltradas com K+, além do inversor apresentar um ganho próximo de dois. Visando também eletrodos oriundos da celulose, este projeto relatou uma abordagem inovadora para sintetizar grafeno induzido por laser (LIG) a partir de tinta à base de carboximetilcelulose (CMC) contendo LIG obtido de nanocristais de celulose (CNCs) do abacaxi. Como prova de conceito, sensores de ZnO UV foram projetados variando a quantidade de LIG dos CNCs na tinta a base de CMC, assim como sensores obtidos por escrita direta de LIG em substrato de papel. Os sensores de ZnO UV flexíveis formulados com tinta apresentaram responsividade 40 vezes maior que os sensores contendo LIG direto do papel. Essas descobertas podem inaugurar uma nova Era na geração de eletrônicos vestíveis de baixo consumo, permitindo conceitos como "Internet das Coisas", e abrindo a possibilidade de dispositivos 100% orgânicos oriundos da celulose