Thomas Otto

Enhancement of the thermoelectric properties of PEDOT:PSS thin films by post-treatment

In this work, the thermoelectric (TE) properties of poly(3,4-ethylenedioxylthiophene):poly(styrene sulfonate) (PEDOT:PSS) thin films at room temperature are studied. Different methods have been applied for tuning the TE properties: 1st addition of polar solvent, dimethyl sulfoxide (DMSO), into the PEDOT:PSS solution; 2nd post-treatment of thin films with a mixture of DMSO and ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4). It is verified that DMSO post-treatment is more efficient than DMSO addition in improving the electrical conductivity with a trivial change in the Seebeck coefficient. The power factor is increased up to 30.1 μW mK−2 for the film with DMSO post-treatment, while the optimized power factor by DMSO addition is 18.2 μW mK−2. It is shown that both DMSO addition and post-treatment induce morphological changes: an interconnected network of elongated PEDOT grains is generated, leading to higher electrical conductivity. In contrast, for those films post-treated in the presence of EMIMBF4, an interconnected network of short and circular PEDOT grains with increased polaron density is created, resulting in the improvement in the Seebeck coefficient and a concomitant compromise in the electrical conductivity. An optimized power factor of 38.46 μW mK−2 is achieved at 50 vol% of EMIMBF4, which is the highest reported so far for PEDOT:PSS thin films to our knowledge. Assuming a thermal conductivity of 0.17 W mK−1, the corresponding ZT is 0.068 at 300 K. These results demonstrate that post-treatment is a promising approach to enhance the TE properties of PEDOT:PSS thin films. Furthermore, ionic liquid, EMIMBF4, shows the potential for tuning the TE properties of PEDOT:PSS thin films via a more environmentally benign process.

Chemical post-treatment and thermoelectric properties of poly(3,4-ethylenedioxylthiophene):poly(styrenesulfonate) thin films

We report on the modification of the thermoelectric properties of poly(3,4-ethylenedioxylthiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films by means of a simple post treatment of the solid thin films realized by drop-coating. We show that the organic polar solvents, dimethyl sulfoxide and ethylene glycol as secondary dopants for PEDOT:PSS, only affect the film morphology for which a high electrical conductivity is observed. In contrast, ethanolamine (MEA) and ammonia solutions are reduction agents that improve the density of PEDOT chains in the reduced forms (polaron and neutral states), resulting in the trade-off between Seebeck coefficient and electrical conductivity. Furthermore, we show that the nature of amines determines the reduction degree: the nitrogen lone pair electrons in MEA are easier to be donated than those in ammonia solution and will therefore neutralize the PEDOT chains.

Modelling and simulation for dielectric constant of aerogel

Abstract Aerogel exhibits several attractive features as an interconnect dielectric in ULSI, because of its ultralow dielectric constant ( ϵ eff =1∼4.2), high dielectric strength, and good gapfill capabilities. In this paper, a uniformly distributed pore structure model which shows a significant improvement compared with parallel and serial models is presented to simulate the ϵ eff of aerogel. An empirical relation between the ϵ eff of aerogel and its porosity is obtained. At the same time, the effect of porosity, pore shape, pore size, pore-size distribution and pore distribution on the ϵ eff of aerogel is determined. It is found that the porosity is a major factor which affects ϵ eff .

Closed-form formulae for frequency-dependent 3-D interconnect inductance

Based on numerical results obtained from solutions to integral equations, other numerical results and theoretical considerations, a set of three-dimensional close-form formulae is presented for approximate calculation of frequency- dependent interconnect inductance. Extensive verifications reveal that the accuracy obtained by these close-form formulae is better than 5% for a wide range of parameters.

A novel dual-detector micro-spectrometer

Infrared analysis is a well-established tool for measuring composition and purity of various materials in industrial-, medical- and environmental applications. Traditional spectrometers, for example Fourier Transform Infrared (FTIR) Instruments are mainly designed for laboratory use and are generally, too large, heavy, costly and delicate to handle for remote applications. With important advances in the miniaturization, ruggedness and cost efficiency we have designed and created a new type of a micromirror spectrometer that can operate in harsh temperature and vibrating environments This device is ideally suited for environmental monitoring, chemical and biological applications as well as detection of biological warfare agents and sensing in important security locations In order to realize such compact, portable and field-deployable spectrometers we have applied MOEMS technology. Thus our novel dual detector micro mirror system is composed of a scanning micro mirror combined with a diffraction grating and other essential optical components in order to miniaturize the basic modular set-up. Especially it periodically disperses polychromatic radiation into its spectral components, which are measured by a combination of a visible (VIS) and near infrared (NIR) single element detector. By means of integrated preamplifiers high-precise measurements over a wide dynamic wavelength range are possible. In addition the spectrometer, including the radiation source, detectors and electronics can be coupled to a minimum-volume liquid or gas-flow cell. Furthermore a SMA connector as a fiber optical input allows easy attachment of fiber based probes. By utilizing rapid prototyping techniques, where all components are directly integrated, the micro mirror spectrometer is manufactured for the 700-1700 nm spectral range. In this work the advanced optical design and integration of the electronic interface will be reviewed. Furthermore we will demonstrate the performance of the system and present characteristic measurement results. Finally advanced packaging issues and test results of the device will be discussed.

Fabrication of micro-optical components by high-precision embossing

Optical components, such as miniature spectrometer gratings working in the infrared range for environmental monitoring or physical analytics, contribute appeciably to the price of Micro Electro Opto Mechanical Systems (MOEMS). These optical components could be a part of a miniature functional package produced with an alternative fabrication technology based on cold forming metals. The cost-efficient fabrication of these components, for example by implementation of forming technology, appears promising. With this technology, high quality embossing of optical structures for high precision requirements in a batch process is possible. In this way the system costs can be reduced. In this paper aluminum forming by cold embossed grating for the fabrication of gratings was investigated. Experiments with different geometries of the embossed grating were carried out. The quality of the embossed structures is primarily determined by the precision and surface quality of the die. Therefore we used a single crystalline silicon tool made by etching as a die. Quality criteria for the review of the formed optical grating were the geometry of surfaces and the surface roughness as well as optical properties of the total structure.

Process and equipment simulation of dry silicon etching in the absence of ion bombardment

Abstract The dependence of the etch rate uniformity across the wafer on the reactor design and various process parameters was investigated for the reactive ion etching (RIE) of silicon using pure sulphur hexafluoride (SF 6 ). The experiments were carried out in two different single wafer reactors without ion bombardment to determine the chemical component of the etch rate. The influence of pressure, gas flow, rf power, and loading on the radial course of the etch rate was measured and compared with the respective results of numerical simulation. The commercially available PHOENICS-CVD simulation tool was used for the solution of the fluid dynamic transport equations after some adaptations for its application to etching. A simple chemical model is proposed for the description of gas phase and surface plasma reactions, respectively. The values of the reaction rate parameters were fitted from the experimental data. The simulation represents the main experimental trends and can be applied to process and equipment optimization.

Integration of an Optical Ring Resonator Biosensor into a Self-Contained Microfluidic Cartridge with Active, Single-Shot Micropumps

While there have been huge advances in the field of biosensors during the last decade, their integration into a microfluidic environment avoiding external tubing and pumping is still neglected. Herein, we show a new microfluidic design that integrates multiple reservoirs for reagent storage and single-use electrochemical pumps for time-controlled delivery of the liquids. The cartridge has been tested and validated with a silicon nitride-based photonic biosensor incorporating multiple optical ring resonators as sensing elements and an immunoassay as a potential target application. Based on experimental results obtained with a demonstration model, subcomponents were designed and existing protocols were adapted. The newly-designed microfluidic cartridges and photonic sensors were separately characterized on a technical basis and performed well. Afterwards, the sensor was functionalized for a protein detection. The microfluidic cartridge was loaded with the necessary assay reagents. The integrated pumps were programmed to drive the single process steps of an immunoassay. The prototype worked selectively, but only with a low sensitivity. Further work must be carried out to optimize biofunctionalization of the optical ring resonators and to have a more suitable flow velocity progression to enhance the system’s reproducibility.

Principle and Applications of a new MOEMS-Spectrometer

Near Infrared (NIR) spectroscopy has developed to an important and useful analysis method over the past years. The existence of compact, portable devices offers a lot of applications possibilities, even in harsh environments. Compact devices, mostly based on detector arrays, are quite costly caused by the expensive Indium Gallium Arsenide (InGaAs) detector arrays. By using MOEMS the set-up can be realised much more efficiently. With an adapted optical set-up detector arrays can be replaced by single element detectors. We have realised a new miniaturised spectrometer based on a scanning micro mirror. The mirror is combined with a diffraction grating and other optical components. It periodically disperses the polychromatic radiation into its spectral components. The radiation is measured by an InGaAs-single element detector, which can be thermoelectrically cooled depending on the application. The radiation coupling is possible either directly or by using fiber optics. It allows an easy attachment of substance samples for reflectance measurements as well as attenuated total reflection (ATR) probes, cuvette holders and flow cells. Lowest noise preamplifiers enable high-precise measurements over a wide dynamic range. With a spectral range of 1000 - 2100 nm and a spectral resolution of approx. 12 nm the device is able to fulfill various requirements. Applications for food stuff industry; clinical chemistry and identification of polymers were tested and will be discussed. Furthermore we will show the advanced optical and mechanical design. In addition advanced performance issues and reliability test results of the device will be reviewed.

Ferroelectric P(VDF-TrFE) as a large-scale piezoelectric sensor in a table-tennis racquet

Piezoelectric poly(vinylidene fluoride — trifluoroethylene) copolymer is embedded as a functional material in a table-tennis racquet. Together with the developed electronics, this piezoelectric sensor is able to monitor the position where the ball contacts the racquet. In order to build up the device, conventional circuit boards with adapted electrode structures are used as substrates for the piezoelectric table-tennis racquet. This leads to challenges because such substrates are usually not flat in the micrometer range as well as the heights of copper electrodes cause irregularities in the final surface topology. Here, the adaptation of the circuit boards, the processing and polarization of the piezoelectric polymer layer, the designed electronics for signal detection and the properties of the table tennis racquet are discussed.