Inkjet-printed Silver Nanoparticle Ink Research Articles

Systematic Investigation of Novel, Controlled Low-Temperature Sintering Processes for Inkjet Printed Silver Nanoparticle Ink.

Functional inks enable manufacturing of flexible electronic devices by means of printing technology. Silver nanoparticle (Ag NP) ink is widely used for printing conductive components. A sintering process is required to obtain sufficient conductivity. Thermal sintering is the most commonly used method, but the heat must be carefully applied to avoid damaging low-temperature substrates such as polymer films. In this work, two alternative sintering methods, damp heat sintering and water sintering are systematically investigated for inkjet-printed Ag tracks on polymer substrates. Both methods allow sintering polyvinyl pyrrolidone (PVP) capped Ag NPs at 85°C. In this way, the resistance is significantly reduced to only 1.7 times that of the samples on polyimide sintered in an oven at 250°C. The microstructure of sintered Ag NPs is analyzed. Taking the states of the capping layer under different conditions into account, the explanation of the sintering mechanism of Ag NPs at low temperatures is presented. Overall, both damp heat sintering and water sintering are viable options for achieving high conductivity of printed Ag tracks. They can broaden the range of substrates available for flexible electronic device fabrication while mitigating substrate damage risks. The choice between them depends on the specific application and the substrateused.

Hybrid additive manufacture: Surface finishing methods for improving conductivity of inkjet printed tracks on non-planar substrates fabricated using fused deposition modeling

This study investigates the impact of the surface quality of 3D printed non-planar surfaces on the conductivity of an inkjet-printed silver nano-particle ink, in the context of fused deposition modeling; a type of additive manufacture (3D pritnting). It was observed that the as-printed surface finish resulted in continuity breaks together with reduced and overall poor batch consistency of conductivity (SDbatch = 16.51 mS/mm). Therefore, to pave the way for high density, consistent and repeatable electronic tracks, the surface finish of as-printed 3D printed parts must be improved. To mitigate this, several finishing methods were investigated, CNC machining, non-planar nozzle ironing and the technique of burnishing with a custom-made heated tool. Of all the investigated finishing techniques, burnishing was identified as the most effective solution that ensured a high and consistent conductivity across the surface for subsequently printed nanoparticle tracks (SDbatch = 2.88 mS/mm). The combination of non-planar burnishing and non-planar printed electronics is key to unlocking the possibility of completely embedded 3D electronics and sensors in 3D printed objects and components.

Multi-parameter paper sensor fabricated by inkjet-printed silver nanoparticle ink and PEDOT:PSS

This work presents the evaluation of a multiparametric sensing device on paper fabricated by inkjet printing, for applications such as smart packaging-labeling and disposable biosensors where biocompatibility and low cost are key factors. The device is able to measure simultaneously relative humidity, temperature and compressive and tensile bending. Commercial silver nanoparticle ink and PEDOT:PSS were printed onto inkjet photo glossy paper using a drop-on-demand inkjet printer forming an interdigitated electrode array and a meander shaped micro-ribbon. Humidity measurements revealed that sensor response, which is effectively expressed by the relationship between paper substrate resistance and relative humidity was similar for both materials utilized as electrodes. Temperature coefficients of resistance (TCR) were extracted for Ag-nanoparticle and PEDOT:PSS - based temperature sensors respectively in the range of 25–45 °C. The bending tests indicated that both materials exhibited similar trend in tensile bending, with resistance increasing in a linear manner up to a maximum tensile length of 900 μm. Ag-nanoparticle ink outperformed PEDOT:PSS ink in terms of repeatability, sensitivity and hysteresis. In compressive bending measurements Ag-nanoparticle and PEDOT:PSS gauge factors exhibited similar gauge factor of opposite sign.

Selective laser sintering of inkjet-printed silver nanoparticle inks on paper substrates to achieve highly conductive patterns

Development of cost-effective and environmentally friendly manufacturing methods will enable important advances for the production of large-scale flexible electronics. Laser processing has shown to be a promising candidate that offers a fast and non-destructive way to produce highly conductive patterns on flexible substrates such as plastics. However, an emerging option with a lower environmental impact is instead the use of cellulose-based flexible substrates, such as paper. In this work we investigate the use of laser sintering of silver nanoparticle inks, which were inkjet-printed on three different types of paper. Patterns with a high conductivity could be manufactured where a special care was taken to prevent the substrates from damage by the intense laser light. We found that the best results was obtained for a photopaper, with a conductivity of 1.63 ∗ 107 S/m corresponding to nearly 26% of the bulk silver conductivity. In addition, we demonstrate laser sintering to fabricate a fully functional near field communication tag printed on a photopaper. Our results can have an important bearing for the development of cost-effective and environmentally friendly production methods for flexible electronics on a large scale.

Thermal conductivity estimation of inkjet-printed silver nanoparticle ink during continuous wave laser sintering

We determined the thermal conductivity of silver nanoparticle ink during laser sintering by applying the Wiedemann–Franz law to two-dimensional heat conduction equations. Ink with 34wt% silver (Ag) nanoparticles with an average size of approximately 50nm was printed on Eagle-XG (Samsung–Corning) glass substrate by inkjet printing. Inkjet-printed patterns were irradiated with a 532nm continuous wave laser at various laser intensities. To obtain a transient thermal conductivity trace of the ink during the laser sintering process, in-situ electrical resistance data were measured to estimate the thermal conductivity of the inkjet-printed ink using the Wiedemann–Franz law. Two-dimensional heat conduction equations were iteratively solved to obtain transient temperature information about the sintered ink. As the laser sintering temperature increased, the surface morphology of the sintered ink affected the thermal conductivity of the laser-sintered ink. Thermal conductivity of the laser-sintered Ag nanoparticle ink was estimated by considering the thermal conductivity of the air confined in pores.

Roll-to-roll infrared (IR) drying and sintering of an inkjet-printed silver nanoparticle ink within 1 second

The scheme shows the experimental setup of roll-to-roll infrared drying and sintering of inkjet-printed silver layers on flexible polymer substrates.

Correction: Roll-to-roll infrared (IR) drying and sintering of an inkjet-printed silver nanoparticle ink within 1 second

Correction for ‘Roll-to-roll infrared (IR) drying and sintering of an inkjet-printed silver nanoparticle ink within 1 second’ by Enrico Sowade et al., J. Mater. Chem. C, 2015, DOI: 10.1039/c5tc02291f.

Evaporation-free inverted organic photovoltaics using a mixture of silver nanoparticle ink formulations for solution-processed top electrodes

We report an investigation of inkjet-printed silver (Ag) nanoparticle inks combined with a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) formulation for solution-processed top electrodes in inverted organic photovoltaics (OPVs) employing the poly(3-hexylthiopehene):phenyl-C61-butyric acid methyl ester material system. We propose a suitable mixture of Ag nanoparticle inks to control the printability and electrical conductivity of the solution-processed top electrode. Based on the proposed solution-processed hole-selective contact, a power conversion efficiency in the range of 3% is reported for evaporation-free inverted OPVs.

Transient variation of a cross-sectional area of inkjet-printed silver nanoparticle ink during furnace sintering

Abstract In this work, the transient variation of a cross-sectional area of inkjet-printed silver nanoparticle ink was monitored as a function of temperature. The ink was composed of 34 wt% silver nanoparticles with an average grain size of 50 nm. In order to determine the relationship between shrinkage and electrical properties, the cross-sectional area and specific resistance change were measured with various sintering temperatures and times. The samples were sintered at 150, 200, and 250 °C for 60, 120, 300, 600, 1200, and 3000 s. The cross-sectional profile was investigated in order to calculate the cross-sectional area of the ink using a surface profiler. To examine the mass transfer in a conductive line with various sintering temperatures and times, the surface morphology was investigated via field-emission scanning electron microscopy. As the temperature increased, the shrinkage ratio of the ink's cross-sectional area increased. By investigating the relationship between specific resistance and shrinkage, the sintering mechanisms can be determined.

Alternative sintering methods compared to conventional thermal sintering for inkjet printed silver nanoparticle ink

In this contribution several alternative sintering methods are compared to traditional thermal sintering as high temperature and long process time of thermal sintering are increasing the costs of inkjet-printing and preventing the use of this technology in large scale manufacturing. Alternative sintering techniques are evaluated based on the electrical and mechanical performance they enable on inkjet-printed structures as well as their potential feasibility for large scale manufacturing. Photonic sintering was identified as the most promising alternative to thermal sintering.

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.

Integrated circuits using fully solution-processed organic TFT devices with printed silver electrodes

We have demonstrated fully solution-processed inverter, NAND and NOR circuits using pseudo-CMOS logic and p-type organic TFT devices with printed electrodes that were fabricated using ink-jet printed silver nanoparticle inks at low temperatures. In order to optimize the gate electrode profiles, we thoroughly assessed the surface wettability of the silver nanoparticle inks. The pseudo-CMOS inverter circuit exhibited exceptional switching characteristics with a high signal gain of 34 at a supply voltage of 20V. The NAND and NOR circuits also exhibited excellent logic characteristics, whereby the switching voltage was approximately VDD/2 with a high noise margin and short delay time of 12.5ms.

The Effect of Temperature on the Electrical Properties of Inkjet-Printed Silver Nanoparticle Ink During Electrical Sintering

In this work, the thermal behavior of ink-jet-printed nanoparticle ink during electrical sintering was demonstrated. The ink consisting of silver nanoparticles approximately 50 nm in size and 34 wt% was used. Constant currents of 0.11, 0.22, and 0.31 A were applied to Joule-heat the inkjet-printed silver nanoparticles. During the sintering process, in-situ voltage and current measurements were taken to calculate the heat source and thermal conductivity. In order to estimate the temperature during the electrical sintering process, numerical modeling of the two-dimensional heat conduction equation was adopted. Thermal conductivity was obtained from the in-situ electrical conductivity measurement and coupled to the numerical model using the Wiedemann Franz law. From these numerical modeling results, the relationship between the specific resistance of the ink and the temperature was determined. During the electrical sintering process, the specific resistance of the ink was strongly related to the sintering temperature. The specific resistance of the ink decreases as the process temperature rises.

Effect of temperature on electrical conductance of inkjet-printed silver nanoparticle ink during continuous wave laser sintering

To determine the effect of temperature on the specific electrical conductance of inkjet-printed ink during continuous wave laser sintering, the temperature of the sintered ink was estimated. The ink, which contained 34wt.% silver nanoparticles with an average size of approximately 50nm, was inkjet-printed onto a liquid crystal display glass substrate. The printed ink was irradiated with a 532nm continuous wave laser for 60s with various laser intensities. During laser irradiation, the in-situ electrical conductance of the sintered ink was measured to estimate the transient thermal conductivity of the ink. The electrical conductance and thermal conductivity of the ink was coupled to obtain the transient temperature by applying the Wiedemann–Franz law to a two-dimensional transient heat conduction equation. The electrical conductance of laser-sintered ink was highly dependent on the sintering temperature of the ink.

Effect of laser-induced temperature field on the characteristics of laser-sintered silver nanoparticle ink

Laser sintering of metal nanoparticles is a key technology for high-performance printed electronics fabricated on heat-sensitive substrates such as glass or plastic. Although laser-sintered electronic devices have been successfully fabricated, the role of the induced temperature field in the laser sintering process has not been reported thus far. In this work, the effect of temperature on the laser sintering process is described for the first time using a two-dimensional transient heat conduction equation for inkjet-printed silver nanoparticle ink. The in situ electrical resistance was measured to estimate the transient thermal conductivity and hence the temperature of the sintered ink during the laser sintering process. To verify the estimated laser sintering temperature, the morphology of furnace-sintered silver nanoparticle ink was compared with that of laser-sintered ink. The electrical characteristics and surface morphology of laser-sintered ink are found to be related to the process temperature.

Oven Sintering Process Optimization for Inkjet-Printed Ag Nanoparticle Ink

This paper focuses on optimizing the oven sintering time and temperature for inkjet-printed silver nanoparticle ink on a polyimide substrate. Two basic aspects in fabricating conductor structures in printable electronics are conductivity and adhesion between the ink and the substrate material. Conductivity evolution during oven sintering is monitored with real-time resistance measurements at five different temperatures. Based on conductivity results, adhesion is evaluated at several time points at three temperatures. The higher the sintering temperature, the faster the structures reach their maximum conductivity values. The lowest conductor resistivity values are below 4 μΩ· cm. However, at each sintering temperature, it takes longer to reach the best adhesion values. In this paper, we aim to better understand oven sintering of silver nanoparticles and determine the best oven sintering conditions (temperature, time) for our particular ink-substrate combination. The results can be used to further define optimum sintering conditions for printed nanoparticle inks on polymer substrates.

Low Temperature Chemical Post-Treatment of Inkjet Printed Nano-Particle Silver Inks

Inkjet printing of electrically conducting tracks often faces the requirement to restrict the temperature/time range of postprocesses in order to allow a wider choice of substrate materials. Thermal oven curing of inkjet printed silver nano-particle inks typically requires temperatures well above 100 °C for several minutes, while laser-based thermal treatment uses higher peak temperatures during shorter periods.A ‘chemical’ post-treatment with halogenides in a ‘semi-dry’ process, which was performed at room temperature or slightly elevated temperatures, was demonstrated to efficiently cure inkjet printed silver nano-particle inks, and to produce electrical conductivities close to that of pure silver. The tests were conducted on several coated paper grades and the chemical post-treatment appears especially well suited for applications in paper-based packaging, where electrical devices add functionality or ‘intelligence’ to packaging.