Wim Deferme

Silicone Devices: A Scalable DIY Approach for Fabricating Self-Contained Multi-Layered Soft Circuits using Microfluidics

We present a scalable Do-It-Yourself (DIY) fabrication workflow for prototyping highly stretchable yet robust devices using a CO2 laser cutter, which we call Silicone Devices. Silicone Devices are self-contained and thus embed components for input, output, processing, and power. Our approach scales to arbitrary complex devices as it supports techniques to make multi-layered stretchable circuits and buried VIAs. Additionally, high-frequency signals are supported as our circuits consist of liquid metal and are therefore highly conductive and durable. To enable makers and interaction designers to prototype a wide variety of Silicone Devices, we also contribute a stretchable sensor toolkit, consisting of touch, proximity, sliding, pressure, and strain sensors. We demonstrate the versatility and novel opportunities of our technique by prototyping various samples and exploring their use cases. Strain tests report on the reliability of our circuits and preliminary user feedback reports on the user-experience of our workflow by non-engineers.

Links Between Heathland Fungal Biomass Mineralization, Melanization, and Hydrophobicity

Comprehending the decomposition process is crucial for our understanding of the mechanisms of carbon (C) sequestration in soils. The decomposition of plant biomass has been extensively studied. It revealed that extrinsic biomass properties that restrict its access to decomposers influence decomposition more than intrinsic ones that are only related to its chemical structure. Fungal biomass has been much less investigated, even though it contributes to a large extent to soil organic matter, and is characterized by specific biochemical properties. In this study, we investigated the extent to which decomposition of heathland fungal biomass was affected by its hydrophobicity (extrinsic property) and melanin content (intrinsic property). We hypothesized that, as for plant biomass, hydrophobicity would have a greater impact on decomposition than melanin content. Mineralization was determined as the mineralization of soil organic carbon (SOC) into CO2 by headspace GC/MS after inoculation by a heathland soil microbial community. Results show that decomposition was not affected by hydrophobicity, but was negatively correlated with melanin content. We argue that it may indicate that either melanin content is both an intrinsic and extrinsic property, or that some soil decomposers evolved the ability to use surfactants to access to hydrophobic biomass. In the latter case, biomass hydrophobicity should not be considered as a crucial extrinsic factor. We also explored the ecology of decomposition, melanin content, and hydrophobicity, among heathland soil fungal guilds. Ascomycete black yeasts had the highest melanin content, and hyaline Basidiomycete yeasts the lowest. Hydrophobicity was an all-or-nothing trait, with most isolates being hydrophobic.

Ultrasonically spray coated silver layers from designed precursor inks for flexible electronics

Integration of electronic circuit components onto flexible materials such as plastic foils, paper and textiles is a key challenge for the development of future smart applications. Therefore, conductive metal features need to be deposited on temperature sensitive substrates in a fast and straightforward way. The feasibility of these emerging (nano-) electronic technologies depends on the availability of well-designed deposition techniques and on novel functional metal inks. As ultrasonic spray coating (USSC) is one of the most promising techniques to meet the above requirements, innovative metal organic decomposition (MOD) inks are designed to deposit silver features on plastic foils. Various amine ligands were screened and their influence on the ink stability and the characteristics of the resulting metal depositions were evaluated to determine the optimal formulation. Eventually, silver layers with excellent performance in terms of conductivity (15% bulk silver conductivity), stability, morphology and adhesion could be obtained, while operating in a very low temperature window of 70 °C-120 °C. Moreover, the optimal deposition conditions were determined via an in-depth analysis of the ultrasonically sprayed silver layers. Applying these tailored MOD inks, the USSC technique enabled smooth, semi-transparent silver layers with a tunable thickness on large areas without time-consuming additional sintering steps after deposition. Therefore, this novel combination of nanoparticle-free Ag-inks and the USSC process holds promise for high throughput deposition of highly conductive silver features on heat sensitive substrates and even 3D objects.

Head-On Immobilization of DNA Fragments on CVD-Diamond Layers

Synthetic diamond is regarded as a promising material for biosensors: it forms a stable platform for genetic assays and its biocompatibility opens the possibility for in vivo sensing. In this study the use of a thymidine linker for covalent DNA attachment was evaluated. Contact angle measurements provided a qualitative test of the initially oxidized surface. X-ray photoemission spectroscopy was used for further analysis of the oxides and for monitoring the effect of subsequent chemical treatments. The presence of FITC-labelled DNA was confirmed by confocal fluorescence microscopy. Enzyme linked immunosorbent assays indicated that this DNA was merely adsorbed on the diamond surface instead of covalently bound.

Printing Smart Designs of Light Emitting Devices with Maintained Textile Properties

To maintain typical textile properties, smart designs of light emitting devices are printed directly onto textile substrates. A first approach shows improved designs for alternating current powder electroluminescence (ACPEL) devices. A configuration with the following build-up, starting from the textile substrate, was applied using the screen printing technique: silver (10 µm)/barium titanate (10 µm)/zinc-oxide (10 µm) and poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (10 µm). Textile properties such as flexibility, drapability and air permeability are preserved by implementing a pixel-like design of the printed layers. Another route is the application of organic light emitting devices (OLEDs) fabricated out of following layers, also starting from the textile substrate: polyurethane or acrylate (10–20 µm) as smoothing layer/silver (200 nm)/poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (35 nm)/super yellow (80 nm)/calcium/aluminum (12/17 nm). Their very thin nm-range layer thickness, preserving the flexibility and drapability of the substrate, and their low working voltage, makes these devices the possible future in light-emitting wearables.

Fabrication Approaches to Interconnect Based Devices for Stretchable Electronics: A Review

Stretchable electronics promise to naturalize the way that we are surrounded by and interact with our devices. Sensors that can stretch and bend furthermore have become increasingly relevant as the technology behind them matures rapidly from lab-based workflows to industrially applicable production principles. Regardless of the specific materials used, creating stretchable conductors involves either the implementation of strain reliefs through insightful geometric patterning, the dispersion of stiff conductive filler in an elastomeric matrix, or the employment of intrinsically stretchable conductive materials. These basic principles however have spawned a myriad of materials systems wherein future application engineers need to find their way. This paper reports a literature study on the spectrum of different approaches towards stretchable electronics, discusses standardization of characteristic tests together with their reports and estimates matureness for industry. Patterned copper foils that are embedded in elastomeric sheets, which are closest to conventional electronic circuits processing, make up one end of the spectrum. Furthest from industry are the more recent circuits based on intrinsically stretchable liquid metals. These show extremely promising results, however, as a technology, liquid metal is not mature enough to be adapted. Printing makes up the transition between both ends, and is also well established on an industrial level, but traditionally not linked to creating electronics. Even though a certain level of maturity was found amongst the approaches that are reviewed herein, industrial adaptation for consumer electronics remains unpredictable without a designated break-through commercial application.

Steering the Properties of MoOx Hole Transporting Layers in OPVs and OLEDs: Interface Morphology vs. Electronic Structure

The identification, fine-tuning, and process optimization of appropriate hole transporting layers (HTLs) for organic solar cells is indispensable for the production of efficient and sustainable functional devices. In this study, the optimization of a solution-processed molybdenum oxide (MoOx) layer fabricated from a combustion precursor is carried out via the introduction of zirconium and tin additives. The evaluation of the output characteristics of both organic photovoltaic (OPV) and organic light emitting diode (OLED) devices demonstrates the beneficial influence upon the addition of the Zr and Sn ions compared to the generic MoOx precursor. A dopant effect in which the heteroatoms and the molybdenum oxide form a chemical identity with fundamentally different structural properties could not be observed, as the additives do not affect the molybdenum oxide composition or electronic band structure. An improved surface roughness due to a reduced crystallinity was found to be a key parameter leading to the superior performance of the devices employing modified HTLs.

Eco-friendly spray coating of organic solar cells through water-based nanoparticles ink (Presentation Recording)

Ultrasonic spray coating is currently proven to be a reliable, flexible and cost efficient fabrication method for printed electronics [1-2]. Ultrasonic nozzles are by design especially well-suited to deposit nano-suspension dispersions. Due to the ultrasonic vibration of the nozzle, droplets having a median diameter of 20 μm are created in a homogeneous droplet cloud and directed towards the substrate. When one prepares an ink having the right wetting properties, thin and homogeneous layers, fully covering the surface, can be achieved. Together with conjugated polymer nanoparticles (NPs), emerging as a new class of nanomaterials, [3] it opens possibilities towards eco-friendly roll-to-roll processing of state-of-the-art organic bulk heterojunction solar cells. A ultrasonic spray coater was used to print the conjugated polymer NP layers under different conditions. A first optimization of the spray coater settings (flow rate, spray speed and temperature) and the ink formulation (water and co-solvent mixture and NP content) was performed for polystyrene particles dissolved in a water-ethanol mixture. As a next step, the low bandgap donor polymer poly[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophene-diyl] (PCDTBT) [4] and the fullerene acceptor phenyl-C71-butyric acid methyl ester (PCBM[70]) were combined in a water-based blend NP dispersion which was prepared using the mini-emulsion technique. [5,6] Optical Microscopy, profilometry and Scanning Electron Microscopy (SEM) are performed to study the roughness, surface structure, thickness and coverage of the spray coated layers. Finally the printed NP layers are integrated in organic bulk heterojunction solar cells and compared to spin coated reference devices.

Microwave annealing as fast alternative for hotplate annealing of poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate)

Poly(3,4-ethylenedioxythiophene): poly(styrene-sulfonate) (PEDOT:PSS) is used in a variety of organic based electronic devices and requires a time consuming thermal annealing step after deposition, to remove solvents and increase the conductivity. In order to speed-up this process, microwave annealing is investigated as post-deposition treatment of PEDOT:PSS thin films. In order to assess the feasibility of this annealing technique a comparative study between microwave annealing and conventional hotplate annealing is performed. PEDOT:PSS films treated with both techniques were characterized and compared by their morphology and their sheet resistance. In order to confirm the assumption that microwave annealing is the faster technique, the annealing times for both techniques where measured. No difference in the thin film morphology was observed for microwave annealed compared to the hotplate annealed samples. The measurements of the sheet resistance show that at sufficient low power setting of the microwave, e.g.: 150W, the sheet resistance of the microwave annealed PEDOT:PSS films are comparable to those annealed using the hotplate technique while decreasing the annealing time by 6 times. These results show that microwave annealing is a feasible fast annealing technique for PEDOT:PSS thin films and can therefor reduce the total processing time of organic and PEDOT:PSS based electronic applications.

Towards fully spray coated organic light emitting devices

Pi-conjugated polymer light emitting devices have the potential to be the next generation of solid state lighting. In order to achieve this goal, a low cost, efficient and large area production process is essential. Polymer based light emitting devices are generally deposited using techniques based on solution processing e.g.: spin coating, ink jet printing. These techniques are not well suited for cost-effective, high throughput, large area mass production of these organic devices. Ultrasonic spray deposition however, is a deposition technique that is fast, efficient and roll to roll compatible which can be easily scaled up for the production of large area polymer light emitting devices (PLEDs). This deposition technique has already successfully been employed to produce organic photovoltaic devices (OPV)1. Recently the electron blocking layer PEDOT:PSS2 and metal top contact3 have been successfully spray coated as part of the organic photovoltaic device stack. In this study, the effects of ultrasonic spray deposition of polymer light emitting devices are investigated. For the first time – to our knowledge -, spray coating of the active layer in PLED is demonstrated. Different solvents are tested to achieve the best possible spray-able dispersion. The active layer morphology is characterized and optimized to produce uniform films with optimal thickness. Furthermore these ultrasonic spray coated films are incorporated in the polymer light emitting device stack to investigate the device characteristics and efficiency. Our results show that after careful optimization of the active layer, ultrasonic spray coating is prime candidate as deposition technique for mass production of PLEDs.