Sebastian Wünscher

Roll‐to‐Roll Compatible Sintering of Inkjet Printed Features by Photonic and Microwave Exposure: From Non‐Conductive Ink to 40% Bulk Silver Conductivity in Less Than 15 Seconds

A combination of photonic and microwave flash exposure is used to sinter inkjet printed silver nanoparticles. This approach leads to conductive features on polymer substrates in short times that are compatible with roll-to-roll production. The sequential process of sintering the as-printed features revealed a final conductivity of 40% of bulk silver, in less than 15 seconds.

Progress of alternative sintering approaches of inkjet-printed metal inks and their application for manufacturing of flexible electronic devices

Well-defined high resolution structures with excellent electrical conductivities are key components of almost every electronic device. Producing these by printing metal based conductive inks on polymer foils represents an important step forward towards the manufacturing of plastic electronic products on an industrial scale. The development of fast, efficient and inexpensive post-deposition sintering technologies for these materials is an important processing step to make this approach commercially viable. This review discusses the advances in alternative sintering approaches for conductive, metal containing inks, which can be processed by inkjet-printing processes. Each sintering approach is examined regarding its mechanism, its compatibility with commonly used materials in the field of flexible electronics, its compatibility with high-throughput manufacturing processes and its applicability to the production of flexible electronic devices.

Localized atmospheric plasma sintering of inkjet printed silver nanoparticles

Atmospheric pressure argon plasma sintering of silver nanoparticle inks was investigated to improve the plasma sintering process in terms of sintering speed, substrate friendliness and technical complexity. Sintering times were reduced to several seconds while achieving similar conductivity values of above 10% compared to bulk silver. Sintering can be carried out under ambient conditions at specific locations without exposing the entire substrate. Plasma sintering at atmospheric pressure exhibits the capability to be used in roll-to-roll production processes.

Inkjet printed paper based frequency selective surfaces and skin mounted RFID tags: the interrelation between silver nanoparticle ink, paper substrate and low temperature sintering technique

Inkjet printing of functional frequency selective surfaces (FSS) and radio frequency identification (RFID) tags on commercial paper substrates using silver nanoparticle inks sintered using low temperature thermal, plasma and photonic techniques is reported. Printed and sintered FSS devices demonstrate performances which achieve wireless communication requirements having a forward transmission scattering parameter, S21, depth greater than -20 dB at 13 GHz. Printed and plasma sintered RFID tags on transfer paper, which are capable of being mounted on skin, improved read distances compared to previously reported single layer transfer RFID tags fabricated by conventional thermal sintering. This journal is cop. The Royal Society of Chemistry 2015.

Towards single-pass plasma sintering: temperature influence of atmospheric pressure plasma sintering of silver nanoparticle ink

A combination of atmospheric pressure plasma sintering (APPS) and a mild thermal treatment of less than 110 °C was investigated in order to reduce the sintering time of inkjet-printed silver nanoparticle inks. Cold as well as warm plasma sources revealed a resistivity down to 6 times of bulk silver within a single pass at a movement speed of 20 mm s−1, which equals a reduction of process time by a factor of at least five compared to previously reported plasma sintering techniques. The developed process was used to produce components for flexible electronics, like honeycomb grid structures and UHF RFID antennas on thermo-sensitive substrate materials. This approach represents a significant step towards a roll-to-roll (R2R) compatible technology.

Simulation and prediction of the thermal sintering behavior for a silver nanoparticle ink based on experimental input

In order to develop a prediction model for resistivity evolution during isothermal sintering, a commercial silver nanoparticle ink was characterized for its metal content, particle size and behavior upon heating. Electrical properties, mass loss behavior, grain size development and material densification were studied for thermal sintering at 175 °C. The correlation between mass loss, height loss of the resulting sintered structures, grain size and electrical resistivity was investigated to gain further understanding of the silver nanoparticle sintering process. The results of thermal sintering were used to calibrate a discrete element sintering model that provides microstructural properties with which the resistivity development at 150 and 200 °C was successfully predicted. The model was validated by experimental data obtained at these temperatures. A variation of particle size and particle size distribution in the simulations furthermore illustrate their influence on final resistivity showing that using small particles with a broad distribution are preferable for reducing the final resistivity of the inkjet-printed pattern.

Significant Factors in the Inkjet Manufacture of Frequency-Selective Surfaces

Additive fabrication of electromagnetic structures by inkjet printing technology is both cost effective and compatible with a wide range of environmentally friendly substrates, enabling the fabrication of frequency-selective surface (FSS) arrays with line dimensions less than 0.1 mm, which is difficult to achieve with conventional subtractive techniques. Several approaches, such as savings in ink by depositing it at the edges of dipole elements where the surface current tends to maximize, have been investigated in order to produce low-cost frequency-selective panels with acceptable level of isolation. The FSS transmission characteristics were improved by jetting multiple ink layers on the whole elements and at the edges. The electrical resistance of various arrays have been measured and analyzed and has been used to assess the performances of the FSS.