Reinhard R. Baumann

Argon plasma sintering of inkjet printed silver tracks on polymer substrates

An alternative and selective sintering method for the fabrication of conductive silver tracks on common polymer substrates is presented, by exposure to low-pressure argon plasma. Inkjet printing has been used to pattern a silver nanoparticle ink. This resulted in conductive features with a resistivity less than one order of magnitude higher than the bulk value of silver without affecting the polymer substrate. This process may be employed in the production of conductive features with low material usage on common polymer substrates in, for example, printed electronics.

Direct Intense Pulsed Light Sintering of Inkjet-Printed Copper Oxide Layers within Six Milliseconds

We demonstrate intense pulsed light (IPL) sintering of inkjet-printed CuO layers on a primer-coated porous PET substrate to convert the electrically insulating CuO into conductive Cu. With this approach, conductive layers are obtained in less than 1 s after the printing process. The IPL sintering was performed for high productivity with minimum duration and repetition of IPL irradiation to evaluate the effect of pulse number and energy output on the conductivity and morphology of the sintered Cu layers. Depending on the energy output, sheet resistances were measured as 0.355, 0.131, and 0.121 Ω·□(-1) by exposure energy of 5.48 (single pulse), 7.03 (double pulse), and 7.48 J·cm(-2) (triple pulse), respectively. In contrast, an excessive energy with relatively short pulse duration causes a delamination of the Cu layer. The lowest resistivity of about 55.4 nΩ·m (corresponds to about 30% conductivity of bulk Cu) was obtained by an IPL sintering process of 0.26 s after the printing, which was composed of 2 ms triple pulses with 10 Hz frequency.

Comparison of laser and intense pulsed light sintering (IPL) for inkjet-printed copper nanoparticle layers

In this contribution we discuss the sintering of an inkjet-printed copper nanoparticle ink based on electrical performance and microstructure analysis. Laser and intense pulsed light (IPL) sintering are employed in order to compare the different techniques and their feasibility for electronics manufacturing. A conductivity of more than 20% of that of bulk copper material has been obtained with both sintering methods. Laser and IPL sintering techniques are considered to be complementary techniques and are highly suitable in different application fields.

A Novel Wearable Electronic Nose for Healthcare Based on Flexible Printed Chemical Sensor Array

A novel wearable electronic nose for armpit odor analysis is proposed by using a low-cost chemical sensor array integrated in a ZigBee wireless communication system. We report the development of a carbon nanotubes (CNTs)/polymer sensor array based on inkjet printing technology. With this technique both composite-like layer and actual composite film of CNTs/polymer were prepared as sensing layers for the chemical sensor array. The sensor array can response to a variety of complex odors and is installed in a prototype of wearable e-nose for monitoring the axillary odor released from human body. The wearable e-nose allows the classification of different armpit odors and the amount of the volatiles released as a function of level of skin hygiene upon different activities.

Inkjet printing and low temperature sintering of CuO and CdS as functional electronic layers and Schottky diodes

Here we report on inkjet printing of a conductive amorphous copper oxide (CuO) ink and of semiconducting cadmium sulfide (CdS) quantum dots under ambient conditions and at low temperature to form functional thin films, which were used for the fabrication of Schottky diodes. Inkjet printed CuO features were sintered using a commercial photonic sintering tool in order to form the diode rectifying contacts. This was accomplished by using the tools proprietary high-intensity flash lamp at very short pulse durations, ensuring a low processing temperature that favors the usage of low-cost substrates. The photonic sintering method was also used for sintering CdS films, resulting in a more efficient removal of the organic moieties around the CdS nanoparticles than a wet chemical KOH treatment. The here reported process allows the deployment of a low-cost polyethylene terephthalate (PET) polymer foil as the substrate material. The initial results showed modest performance of the fabricated Schottky diode. Nevertheless, the general approaches demonstrate new routes for low temperature manufacturing methods for functional electronic layers based on accordingly developed functional materials utilising amorphous metal oxides and quantum dots.

Inkjet printing as a tool for the patterned deposition of octadecylsiloxane monolayers on silicon oxide surfaces

We present a case study about inkjet printing as a tool for molecular patterning of silicon oxide surfaces with hydrophobic functionality, mediated by n-octadecyltrichlorosilane (OTS) molecules. In contrast to state-of-the-art techniques such as micro contact printing or chemical immersion with subsequent lithography processes, piezo drop-on-demand inkjet printing does not depend on physical masters, which allows an effective direct-write patterning of rigid or flexible substrates and enables short run-lengths of the individual pattern. In this paper, we used mesithylene-based OTS inks, jetted them in droplets of 10 pL on a silicon oxide surface, evaluated the water contact angle of the patterned areas and fitted the results with Cassies law. For inks of 2.0 mM OTS concentration, we found that effective area coverages of 38% can be obtained. Our results hence show that contact times of the order of hundred milliseconds are sufficient to form a pattern of regions with OTS molecules adsorbed to the surface, representing at least a fragmented, inhomogeneous self-assembled OTS monolayer (OTS-SAM).

All-Inkjet-Printed Bottom-Gate Thin-Film Transistors Using UV Curable Dielectric for Well-Defined Source-Drain Electrodes

Technological restrictions of the inkjet printing technology for printed electronics can hinder its application potential, mainly due to the limited resolution and layer homogeneity in comparison to conventional manufacturing techniques for electronics. The manufacturing of active devices such as thin-film transistors with appropriate performance using printing technologies is still one of the current challenges towards industrial applications. This work demonstrates the application of an ultraviolet (UV) curable ink as insulating material for the gate dielectric. The advantage of the UV curable ink is its fast curing and the smooth surface enabling high resolution patterns on top of it. In this way, all-inkjet-printed organic thin-film transistors (OTFTs) were fabricated with silver electrodes, UV curable gate dielectric, and 6,13-bis(triisopropylsilylethynyl)pentacene for the active semiconductor layer. By fine tuning of processing parameters and pattern geometries, a stable channel length of about 10 μm was obtained in the bottom-gate configuration without the need of additional steps, suggesting a way to build low-cost all-inkjet-printed OTFTs with well-defined source-drain electrodes and fast UV curable dielectric without any additional steps. The inkjet-printed device is characterized by an electron mobility of 0.012 cm2 V−1 s−1 and on/off ratio of 103.

Polymer Microsieves Manufactured by Inkjet Technology

Liquid sessile drops can be used as sacrificial templates for the creation of pores in polymeric microsieves. Using inkjet printing, we deposit sessile drops of a water-based liquid onto a hydrophobic solid support and cover them with a thin liquid layer of a polymer solution in such a way that the sessile drops penetrate through the top interface of this layer. The liquid layer is solidified, and the sessile drops imprint their shape into it, acting as templates for the creation of pores. Finally, the polymer layer is separated from the substrate, and a freely suspended polymer microsieve is obtained.

Inkjet Printing of Colloidal Nanospheres: Engineering the Evaporation-Driven Self-Assembly Process to Form Defined Layer Morphologies

We report on inkjet printing of aqueous colloidal suspensions containing monodisperse silica and/or polystyrene nanosphere particles and a systematic study of the morphology of the deposits as a function of different parameters during inkjet printing and solvent evaporation. The colloidal suspensions act as a model ink for an understanding of layer formation processes and resulting morphologies in inkjet printing in general. We investigated the influence of the surface energy and the temperature of the substrate, the formulation of the suspensions, and the multi-pass printing aiming for layer stacks on the morphology of the deposits. We explain our findings with models of evaporation-driven self-assembly of the nanosphere particles in a liquid droplet and derive methods to direct the self-assembly processes into distinct one- and two-dimensional deposit morphologies.

All-inkjet printed organic transistors: Dielectric surface passivation techniques for improved operational stability and lifetime

Abstract We report about the use of a printed pentafluorothiophenol layer on top of the dielectric surface as a passivation coating to improve the operational stability of all-ink-jet printed transistors. Transistors with bottom-gate structure were fabricated using cross-linked poly-4-vinylphenol (c-PVP) as dielectric layer and an ink formulation of an amorphous triarylamine polymer as semiconductor. The resulting TFTs had low turn-on voltage (Vth