A. Albrecht

Inkjet printing and photonic sintering of silver and copper oxide nanoparticles for ultra-low-cost conductive patterns

Printing technologies to produce conductive films and electronic devices are well established and employ only inexpensive materials and devices as well as rapid post-processing methods. In this work, silver nanoparticle and copper-oxide nanoparticle ink was printed using a consumer inkjet printer on a large variety of commercially available substrates. The print quality was assessed by various methods. Self-sintering of the silver ink led to sheet resistances of less than 400 mΩ □−1. Photonic sintering reduced the sheet resistance down to 55 mΩ □−1 within a few milliseconds, equivalent to 2.4 times that of bulk silver. Copper oxide ink was reduced by intense pulsed light and a sheet resistance of 335 mΩ □−1, or 4.5 times that of bulk copper, was obtained. The parameters for sintering were optimized for both inks to achieve low resistivities within a few seconds without damaging the substrates. The production process can be reduced to a few minutes and is fully roll-to-roll compatible, thus providing a quick and ultra-low-cost manufacturing method to produce conductive patterns for wiring, printed circuit boards, antennas, sensor electrodes, light emitting diodes, and solar cells.

Integration of a Thin Film PDMS-Based Capacitive Sensor for Tactile Sensing in an Electronic Skin

We present a capacitive force sensor based on a polydimethylsiloxane (PDMS) film integrated into a printed circuit board (PCB) on a flexible substrate whose layout is defined by inkjet printing. The influence of the dielectric thickness on the sensor behavior is presented. The thinner PDMS film of about 45 μm shows a sensitivity of up to 3 pF/N but poorer dynamic response. The dielectrics with thicknesses above 200 μm show a significantly reduced sensitivity. The best compromise between sensitivity and dynamic response is found for PDMS film of about 100 μm, showing about 1.1 pF/N and less than 15 s of recovery time. This film is integrated into a flexible PCBS including a microcontroller capable of evaluating the sensor. Interconnects of the circuit are defined by silver nanoparticles deposited by inkjet printing. The working principle of the circuit is demonstrated, proving that this simple approach can be used for artificial skin applications.

Solution processing of silver nanowires for transparent heaters and flexible electronics

We present the solution-based synthesis of silver nanowires (AgNWs) with an aspect ratio over 400 in a short growth time of 20 min. The addition of potassium chloride (KCl) during the growth regulates the supply of silver atoms and leads to an agglomerate-free and well-dispersed solution. Via a facile and scalable deposition technique, i.e. spray-coating, the AgNWs are deposited to transparent electrodes (TEs) on flexible or glass substrates. Without any post-treatment such as sintering that can harm the substrate, the films show a high transparency at a low sheet resistance. The TEs are characterized as transparent heaters in terms of their infrared, transient thermal and electrical properties up to a working temperature of 130 deg. C. For the use in flexible electronics, an AgNW-film on a polyvinyl chloride (PVC) substrate is tested under operation for 10,000 bending cycles and shows only a slight increase in resistance.

Wireless Chipless System for Humidity Sensing

This work describes a fully wireless sensory system where a chipless strategy is followed in the sensor part. Alternatively, to characterize only the sensing element, we present the response of the reader antenna when the sensing element is placed in its vicinity: changes in the parameter of interest are seen by the reader through inductive coupling, varying its frequency response. The sensing part consists of a LC circuit manufactured by printing techniques on a flexible substrate, whose electrical permittivity shows dependence with the moisture content. The measurement distance show significant differences in the frequency response: a change of 700 kHz is observed when the measurement is performed directly on the wireless chipless sensor between 20% and 80%RH, while this variation in frequency is reduced more than three times when measuring at the reader antenna with 5 mm distance between elements. Furthermore, we demonstrate the importance of the separation between reader and sensor to get a reliable measuring system.

In-Depth Study of Laser Diode Ablation of Kapton Polyimide for Flexible Conductive Substrates

This work presents a detailed study of the photothermal ablation of Kapton® polyimide by a laser diode targeting its electrical conductivity enhancement. Laser-treated samples were structurally characterized using Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), as well as Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy. The results show that the laser-assisted ablation constitutes a simple one-step and environmental friendly method to induce graphene-derived structures on the surface of polyimide films. The laser-modified surface was also electrically characterized through the Transmission Line Method (TLM) aiming at the improvement of the conductivity of the samples by tuning the laser power and the extraction of the contact resistance of the electrodes. Once the laser-ablation process is optimized, the samples increase their conductivity up to six orders of magnitude, being comparable to that of graphene obtained by chemical vapor deposition or by the reduction of graphene-oxide. Additionally, we show that the contact resistance can be decreased down to promising values of ∼2 Ω when using silver-based electrodes.

A Handwriting Method for Low-Cost Gas Sensors

In this study, we report on an automated method based on a handwritten technique for the fabrication of low-cost gas sensors based on carbon nanotube (CNT) networks. Taking advantage of the inherent low-cost, flexible, and uncomplicated characteristics of pen-based techniques and combining them with an automated robotic system allows for high-resolution patterns, high reproducibility, and relatively high throughput considering the limitations of parallel processing. To showcase this, gas sensors capable of sensing NH3, CO2, CO, and ethanol, as well as temperature and relative humidity, are fabricated and characterized displaying competitive performance in relation to previously reported devices. The presented process is compatible with a variety of solutions and inks and, as such, allows for an easy integration into existing printing and coating frameworks with the greatest advantage being the ease of creating prototypes because of the nonstringent material requirements.

Inkjet-printed patch antennas for wireless chip-to-chip communication on flexible substrates

Printed electronics become more and more relevant for applications in wearable electronics and sensors. Inkjet printing of silver nano-particles can be done at very low cost with a reasonably high precision and conductivity. In this paper, we investigate flexible patch antennas for wireless chip-to-chip communication scenarios, rapidly prototyped using an inkjet printing process. A patch antenna with a return loss of almost −20 dB at a resonance frequency of 2.09 GHz that agrees well with the conducted simulations is presented.

Fabrication, characterization and modeling of flexible electronic components based on CNT networks

In this contribution, we will present a modeling approach based on a stochastic algorithm that can generate non-rigid solid objects in a three-dimensional space, emulating with high fidelity the typical fabrication processes involved (i.e. spray-coating). A randomly generated set of tube segments and tube junctions is converted into a netlist and the overall electrical behavior is computed via a SPICE software. The theoretical results agree well with experimental data and provide valuable details on the operation mode of the fabricated devices. In addition, we will discuss the characteristics of CNT films prepared by scalable spray deposition as well as inkjet printing onto rigid and flexible substrates. The performance of a variety of devices (e.g. pressure, temperature and gas sensors; FETs) will be described.