전극-절연막-용액 시스템의 전도현상의 이해 및 나노전기변색 소자로의 응용

학위논문(박사)--서울대학교 대학원 :자연과학대학 화학부,2019. 8. 정택동김지환.The conduction in the dielectric materials has been regarded as an important issue for electronic devices. Recently, the operating condition of devices that employing oxides has expanded to wet condition such as in batteries, energy conversion devices, and electrochemical field effect transistors. For enhanced device performance, a deeper understanding of its conduction and breakdown mechanism should be preceded. In this dissertation, therefore, the electrical and ionic conduction of oxide dielectrics in contact to the electrolyte is understood in the electrolyte/oxide/semiconductor system. Especially, the role of chemical species which are dissolved in the electrolyte is revealed, focusing on their effect on the physical and chemical nature of the oxide-electrolyte interface. Not only the basic principles of conduction in dielectric oxides but also a new application field of cation conductive oxide is suggested in this dissertation. When dielectrics or large bandgap semiconductors allow the introduction of ionic species from electrolyte to the matrix by means of the electrical potential applied on the underlying electrode, their optical properties are changed, which is called electrochromism. There are numerous studies regarding on electrochromism, however, the scope of application is limited because the wide color expression and the dynamic color tunability has not been achieved. To overcome these problems, the structure around the electrochromic oxide, WO3, is thoroughly designed for tunability in the visible regime. By employing nanometer-thick WO3 film in the structure, full-color tunable reflective- and transmissive- type devices are achieved with the advantages of reversibility and low energy consumption.산화물의 전기적 특성에 대한 이해는 전자소재 분야에서 중요한 이슈로 다루어졌다. 최근 들어 산화물이 전해질과 접한 상태에서 작동하도록 요구하는 시스템이 중요하게 연구되고 있다. 배터리, 전기촉매로 구성된 에너지 변환 장치, 전기화학적으로 제어되는 장효과 트랜지스터 (field effect transistor, FET) 등이 그것이다. 이와 같은 장치들의 성능 및 안정성을 개선하기 위해서는 전해질과 계면을 이루는 산화물의 전기적 특성을 깊이 있게 이해하는 것이 선행되어야 한다. 이에 본 학위논문에서는 전해질/산화막/도체로 구성된 시스템의 전도현상에 대해 다루었다. 전해질에 속한 화학종들이 시스템의 전도도 및 절연파괴에 미치는 영향에 대해 분석하였으며, 전해질/산화막 계면에서 일어나는 현상을 중심으로 이를 이해하였다. 양성자를 포함한 이온종 및 전기화학적 반응종의 역할과 그들간의 상호작용이 계면 및 산화막 내부의 전도 기작에 큰 영향을 끼침을 실험적으로 밝혔으며 이론적으로 현상을 설명하였다. 이러한 기초적인 시스템에 대한 이해뿐만 아니라 높은 이온 전도도를 갖는 산화박막이 활용된 새로운 개념의 전기변색소자에 대해서 학위논문을 통해 제안하였다. 큰 밴드갭을 가진 산화물이 외부의 이온을 머금게 되면 전기적 성질이 변함과 동시에 광학적 성질 역시 변한다. 이를 전기변색 현상이라 하는데, 전자종이, 지능형 창호 개발을 목적으로 연구되고 있다. 다양한 개념의 전기변색 소자가 제안되었으나 대부분이 단순히 명암 제어에 그치고 있으며 특정 색상을 표현하는 경우에도 색의 순도가 낮은 한계를 가지고 있다. 텅스텐 산화물(WO3)은 대표적인 전기변색물질로써 앞서 언급된 한계를 갖고 있다. 이에 본 연구에서는 WO3 주위에 효율적으로 설계된 나노구조체를 도입함으로써 이와 같은 한계를 극복할 수 있음을 보이고자 한다. 가시광선 대역에서 폭넓은 색 표현이 가능한 투과 및 반사형의 광소자가 구현되었으며 공진 파장 및 빛의 세기를 전기변색의 원리에 입각하여 제어할 수 있음을 보였다.1. Introduction …………………………………………………………10 2. Conduction of Dielectric Material in Contact to Electrolyte ……14 2.1. Introduction: Related issue on Charge Conduction of SiO2 and Si3N4 in Contact to Electrolyte ……………………………………………………14 2.2. Theoretical Background …………………………………………16 2.2.1. Conduction of thin dielectric film in solid state device ………16 2.2.2. Dielectric breakdown ………………………………………22 2.2.3. Electrolyte/oxide/semiconductor (EOS) system …24 2.3. Experimental Section ……………………………………………28 2.3.1. Materials ……………………………………………………28 2.3.2. Preparation of dielectric film-coated Si electrode ………………28 2.3.3. Protective layer coatings on Si/SiO2 ………………………28 2.3.4. Electrochemical characterization …………………………………..29 2.3.5. Theoretical calculation ……………………………………………30 2.4. Results ………………………………………………………………32 2.4.1. Electrochemical analysis of large-area dielectrics. Effect of unwanted damage and misunderstandings due to the inevitable defects ……….32 2.4.2. Methods for minimizing experimental deviation ………………36 2.4.3. General electrochemical behavior of defect-suppressed dielectrics in contact to solution ………………………………………………………39 2.4.4. Cation effect on dielectric breakdown characteristics: sodium intercalation and accelerated breakdown kinetics …………………………42 2.4.5. Electron scavenger effect on dielectric breakdown characteristics: non-destructive conducting pathway by electron scavenger……………………52 2.4.6. Postbreakdown phenomena …………………………………….58 2.5. Summary ………………………………………………………………65 3. Full-color-tunable Electrochromic Device Using Tungsten Trioxide Thin Film …………………………………………………………………68 3.1. Introduction: Electrochromic Device and Nanostructure for Better Optical Performance …………………………………………………68 3.2. Experimental Section ………………………………………71 3.2.1. Reagent and Appartus ……………………………………………71 3.2.2. Deposition of WO3 films ………………………………71 3.2.3. Preparing WO3 coated Si electrode for optical and electrochemical analysis …………………………………………………………………………72 3.2.4. Electrochemical analysis ……………………………………………72 3.2.5 Optical analysis ……………………………………………………73 3.2.6. Fabrication of reflective- and transmissive- type device ……73 3.3. Results and discussion ………………………………………75 3.3.1. Analysis on tungsten trioxide thin film …………………………75 3.3.2. Reflective type display using WO3 thin film ………………85 3.3.3. Transmissive type display using WO3-based thin film ……90 3.4. Summary ……………………………………………………………94 4. Conclusion ……………………………………………………………95 Reference ……………………………………………………………97Docto

Structural, Thermodynamic, and Electronic Properties of Mixed Ionic/Electronic Conductor Materials

Due to the mainstream CMOS technology facing a rapid approach to the fundamental downscaling limit, beyond CMOS technologies are under active investigation and development with the intention of revolutionizing and sustaining a wide range of applications including sensors, cryptography, neuromorphic and quantum computing, memory, and logic, among others. Resistive switching electronics, for example, are devices that can change their electrical resistance with an applied external field. Despite their simple metal-insulator-metal structure, resistive switching devices exhibit an intricate set of IV characteristics based on the chemical composition of the solid electrolyte that ranges from non-volatile bipolar and non-polar switching to volatile threshold switching (abrupt but reversible change in resistance). This rich variety of electrical responses offer new alternatives to traditional CMOS applications in the areas of RF-signal switching, relaxation oscillators, over-voltage protection, and notably, memory cells and two-terminal non-linear selector devices. With the aim of unraveling the physics behind two of such conduction mechanisms, filamentary and threshold, in electrochemical cells consisting solid mixed ionic-electronic conductor electrolytes, this work focused on using first-principles calculations to characterize the structural, thermodynamic, and electronic properties of copper-doped amorphous silicon dioxide and copper-doped germanium-based glassy chalcogenides. The Cu/a-SiO2 system is a promising candidate for resistive switching memory applications. The conduction mechanism in the low-resistance state is known to be filamentary, that is, a physical metallic filament bridges between the metallic electrodes through the amorphous silica. However, many fundamental materials processes that would aid the design and optimization of this devices, such the shape and size of stable metallic filaments, remain unknown. In the first part of this work, the morphology and diffusion of small copper clusters embedded in amorphous silicon dioxide were characterized by density functional theory calculations. The average formation energy of a single copper ion in the amorphous matrix is found to be 2.4 eV, about 50% lower than in the case of silicon dioxide in its cristobalite or quartz phases. The theoretical predictions show that copper clusters with an equiaxed morphology are always energetically favorable relative to the dissolved copper ions in a-SiO2; hence, stable clusters do not exhibit a critical size. The stochasticity in the atomistic structure of the amorphous silicon dioxide leads to a broad distribution activation energies for diffusion of copper in the matrix, ranging from 0.4 to 1.1 eV. Since ab initio molecular dynamics are prohibitively expensive to simulate the switching process in Cu/a-SiO2 electrochemical metallization cells, a multi-scale simulation approach based on electrochemical dynamics with implicit degrees of freedom and density functional theory was developed to study the electronic evolution during metallic filament formation cells. These simulations suggest that the electronic transport in the low-resistance configuration is attributed to copper derived states belonging to the filament bridging between electrodes. Interestingly, the participation of states derived from intrinsic defects in the amorphous SiO2 around the Fermi energy are negligible and do not contribute to conduction. Unlike the Cu/a-SiO2 system which only exhibits filamentary switching, copper-doped germanium-based glassy chalcogenides show filamentary or threshold type of conduction depending on the chemical composition of the glass and copper concentration. Ab initio molecular dynamics based on density functional theory is used to understand the atomistic origin of the electronic transport in these materials. The theoretical predictions show that glasses containing tellurium tend to favor the formation of copper clusters; hence, these materials exhibit filamentary conduction. Threshold conduction is predicted to be the transport mechanism for glassy sulfides and selenides due to the ability of copper to remain dissolved in the amorphous matrix even at high metal concentration. Furthermore, the charge carrier transport in sulfur and selenium glasses was found to be assisted by defective states derived from chalcogen atoms whose bonds exhibit a polar character. Finally, taking advantage of the van der Waals gap as intercalation sites and crystal order in molybdenum disulfide, a novel mixed ionic-electronic conductor material based on copper and silver intercalation of MoS2 is proposed. The theoretical predictions show that on average, the intercalation energy of copper into MoS2 is 1 eV, while intercalation of silver shows a strong dependence on concentration ranging from 2.2 to 0.75 eV for low and high concentrations, respectively. The activation energy for diffusion of copper and silver intercalated within the van der Waals gap of MoS2 is predicted to be 0.32 and 0.38 eV, respectively, comparable to other superionic conductors. Upon Cu and Ag intercalation, MoS2 undergoes a semiconductor-to-metal transition, where the in-plane and out-of-plane conductances are comparable and exhibit a linear dependence with metal concentration

Charging effects in niobium nanostructures

Three types of metallic nanostructures comprising niobium were investigated experimentally; in all three types, electric transport at very low temperatures was governed by Coulomb blockade effects. 1. Thin film strips of niobium could be tuned into resistor strips by an electrochemical anodisation process, using microfabricated masks and in situ resistance monitoring. These resistors showed a transition from superconducting to insulating behaviour with increasing sheet resistance, occurring at a value approximately equal to the quantum resistance for Cooper pairs, h/(4e^2). 2. Combining the anodisation technique with lateral size minimisation by shadow evaporation, devices in a single electron transistor-like configuration with two weak links and a small island between these were made. Direct evidence for the Coulomb blockade in the anodisation thinned niobium films was found when the transport characteristics could be modulated periodically by sweeping the voltage applied to a gate electrode placed on top of the structure. 3. Conventional single electron transistors with Al base electrodes, AlO_x barriers formed in situ by oxidation, and Nb top electrodes were made by angular evaporation. The output current noise of such a transistor was measured as a function of bias voltage, gate voltage, and temperature. The low frequency noise was found to be dominated by charge input noise. The dependence of the noise on the bias voltage is consistent with self-heating of the transistor activating the noise sources.Comment: PhD thesis, 177 pages, 42 figures (images downsampled

Biocompatible low-cost CMOS electrodes for neuronal interfaces, cell impedance and other biosensors

The adaptation of standard integrated circuit (IC) technology for biosensors in drug discovery pharmacology, neural interface systems, environmental sensors and electrophysiology requires electrodes to be electrochemically stable, biocompatible and affordable. Unfortunately, the ubiquitous IC technology, complementary metal oxide semiconductor (CMOS), does not meet the first of these requirements. For devices intended only for research, modification of CMOS by post-processing using cleanroom facilities has been achieved by others. However, to enable adoption of CMOS as a basis for commercial biosensors, the economies of scale of CMOS fabrication must be maintained by using only low-cost post-processing techniques. The scope of this work was to develop post-processing methods that meet the electrochemical and biocompatibility requirements but within the low-cost constraint. Several approaches were appraised with the two most promising designs taken forward for further investigation. Firstly, a process was developed whereby the corrodible aluminium is anodised to form nanoporous alumina and further processed to optimise its impedance. A second design included a noble metal in the alumina pores to enhance further the electrical characteristics of the electrode. Experiments demonstrated for the first time the ability to anodise CMOS metallisation to form the desired electrodes. Tests showed the electrode addressed the problems of corrosion and presented a surface that was biocompatible with the NG108-15 neuronal cell line. Difficulties in assessing the influence of alumina porosity led to the development of a novel cell adhesion assay that showed for the first time neuronal cells adhere preferentially to large pores rather than small pores or planar aluminium. It was also demonstrated that porosity can be manipulated at room temperature by modifying the anodising electrolyte with polyethylene glycol. CMOS ICs were designed as multiple electrode arrays and optimised for neuronal recordings. This utilised the design incorporating a noble metal deposited into the porous alumina. Deposition of platinum was only partially successful, with better results using gold. This provided an electrode surface suitable for electric cell-substrate impedance sensors (ECIS) and many other sensor applications. Further processing deposited platinum black to improve signal-to-noise ratio for neuronal recordings. The developed processes require no specialised semiconductor fabrication equipment and can process CMOS ICs on laboratory or factory bench tops in less than one hour. During the course of electrode development, new methods for biosensor packaging were assessed: firstly, a biocompatible polyethylene glycol mould process was developed for improved prototype assembly. Secondly, a commercial ‘partial encapsulation’ process (Quik-Pak, U.S.) was assessed for biocompatibility. Cell vitality tests showed both methods were biocompatible and therefore suitable for use in cell-based biosensors. The post-processed CMOS electrode arrays were demonstrated by successfully recording neuronal cell electrical activity (action potentials) and by ECIS with a human epithelial cell line (Caco2). It is evident that these developments may provide a missing link that can enable commercialisation of CMOS biosensors. Further work is being planned to demonstrate the technology in context for specific markets.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Biennial report ... / Leibniz-Institut für Oberflächenmodifizierung e.V.

damit Erscheinen eingestell

An integrated microelectronic device for biomolecular amplification and detection

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 133-154).The extraordinarily high sensitivity, large dynamic range and reproducibility of polymerase chain reaction (PCR) have made it one of the most widely used techniques for analyzing nucleic acids. As a result, considerable effort has been directed towards developing miniaturized systems for PCR, but most rely on off-chip optical detection modules that are difficult to miniaturize into a compact analytical system and fluorescent product markers that can require extensive effort to optimize. This thesis presents a robust and simple method for direct label-free PCR product quantification using a microelectronic sensor. The thesis covers the design, fabrication, and characterization of the sensing technique and its integration with PCR microfluidics into a monolithic detection platform. The sensor used in this thesis study is an electrolyte-insulator-silicon (EIS) device fabricated on planar silicon substrates. Based on electronic detection of layer-by-layer assembly of polyelectrolytes, the sensing technique can specifically quantify double-stranded DNA product in unprocessed samples and monitor the product concentration at various stages of PCR to generate readout analogous to that of a real-time fluorescent measurement.(cont.) Amplification is achieved with integrated metal resistive heaters, temperature sensors, and microfluidic valves. Direct electronic quantification of the product on-chip yields analog surface potential signals that can be converted to a digital true/false readout. A silicon field-effect sensor for direct detection of heparin by its intrinsic negative charge has also been developed. Detection of heparin and heparin-based drugs in buffer and serum has been studied, and a study demonstrating strong correlation between electronic heparin sensing measurements and those from a colorimetric assay for heparin-mediated anti-Xa activity has been performed.by Chih-Sheng Johnson Hou.Ph.D

Functional Oxide Thin Films and Nanostructures: Growth, Properties, and Applications

This Special Issue of Coatings is entitled “Functional Oxide Thin Films and Nanostructures: Growth, Properties, and Applications”. Recent materials nanotechnologies have created possibilities regarding the fabrication of oxide thin films at the nanometric level and other nanocomposites’ fabrication. In parallel, recent measurement technologies can characterize their unique properties arising from the limited regions of surfaces and interfaces. This Special Issue provides an opportunity to share surface-related science and engineering topics on oxide thin films and nanocomposites in an interactive and interdisciplinary manner. The ultimate goal is to elucidate the commonalities and differences between multilayer interfaces and nanocomposite grain boundaries. This Special Issue is as an effort to bridge the gap between materials science and the applications of oxide thin films and nanostructures. The topics covered in this Special Issue range from nanoparticles to thin films, heterostructures, and homojunctions and are related to various aspects of oxide materials’ preparation, characterization, and applications

Electrochemical noise limits of femtoampere-sensing, CMOS-integrated transimpedance amplifiers

Low-noise operational amplifiers are an important tool in the life sciences. Biosensor measurements typically rely on low-noise transimpedance amplifiers to record biological signals. Two different techniques were used to leverage the advantages of low-noise circuitry for bioelectronics. A CMOS-integrated system for measuring redox-active substrates using electrochemical read-out at very low noise levels is presented. The system incorporates 112 amplifier channels capable of current sensing with noise levels below 1 fArms in a 3.5-Hz bandwidth. The amplifier is externally connected to a gold microelectrode with a radius of 15 µm. The amplifier enables measurement of redox-couples such as potassium ferrocyanide/ferricyanide with concentrations down to 10 nM at current levels of only 300 fA. The electrochemical noise that sets the limits of detection is also measured and analyzed based on redox mass transfer equation and electrochemical impedance spectroscopy. Secondly, CMOS-integrated low noise junction field-effect transistors (JFETs) were developed in a standard 0.18-µm CMOS process. These JFETs reduce input referred flicker noise power by more than a factor of 10 when compared with equally sized n-channel MOS devices by eliminating oxide interfaces in contact with the channel. We show that this improvement in device performance translates into a factor-of-10 reduction in the input-referred noise of integrated CMOS operational amplifiers when JFET devices are used at the input