Metal Organic Decomposition Ink Research Articles

Anomalous Temperature Effect on the Deposition Morphology in Reactive Inkjet Printing

Reactive inkjet (RIJ) printing represents an important approach for printed electronics. Different from the traditional inkjet printing of colloidal inks with nanosized metal particles, RIJ prints the solution of metal organic compound, that is, metal‐organic decomposition (MOD) ink, and reduces it to the pure metal during the post‐treatment to form conductive electrodes. Successful RIJ printing of MOD inks has been demonstrated; however, the fundamental understanding of droplet deposition involved in RIJ printing is lacking. Herein, the effect of substrate temperature and nozzle temperature during inkjet printing of copper MOD ink on the deposition morphology is investigated. It exhibits distinct behaviors in the deposition morphology at elevated temperatures when compared with the ones at room temperature. The different deposition morphology of the copper ink at various temperatures is attributed to the generation of a localized seeding layer which attracts the copper ions to deposit. In addition, the copper MOD ink printing is compared with a silver MOD ink. The different deposition morphology between the copper ink and silver ink is due to the solvent system. Understanding the deposition mechanism for reactive inks provides valuable information and guidance in the fabrication of printed functional devices using particle‐free reactive inks.

Laser-Assisted Photo-Thermal Reaction for Ultrafast Synthesis of Single-Walled Carbon Nanotube/Copper Nanoparticles Hybrid Films as Flexible Electrodes.

The hybridization of single-walled carbon nanotubes (SWCNTs) and Cu nanoparticles offers a promising strategy for creating highly conductive and mechanically stable fillers for flexible printed electronics. In this study, we report the ultrafast synthesis of SWCNT/Cu hybrid nanostructures and the fabrication of flexible electrodes under ambient conditions through a laser-induced photo-thermal reaction. Thermal energy generated from the nonradiative relaxation of the π-plasmon resonance of SWCNTs was utilized to reduce the Cu-complex (known as a metal-organic decomposition ink) into Cu nanoparticles. We systematically investigated the effects of SWCNT concentration and output laser power on the structural and electrical properties of the SWCNT/Cu hybrid electrodes. The SWCNT/Cu electrodes achieved a minimum electrical resistivity of 46 μohm·cm, comparable to that of the metal-based printed electrodes. Mechanical bending tests demonstrated that the SWCNT/Cu electrodes were highly stable and durable, with no significant deformation observed even after 1000 bending cycles. Additionally, the electrodes showed rapid temperature increases and stable Joule heating performance, reaching temperatures of nearly 80 °C at an applied voltage of less than 3.5 V.

The Influence of Ink Chemistry on the Microstructure Evolution and GHz RF Response of Printed Ag Transmission Lines.

High-frequency transmission is limited to the skin depth in metals. Because poor conductivity cannot be compensated for by increasing the conductor thickness as with DC, optimal transport properties are prerequisites for radio frequency (RF) use. Structural and chemical analyses of transmission lines printed using a traditional ink consisting of Ag nanoflakes in a dispersing phase revealed that optimized thermal treatments yielded thorough burnout of the binder, significant grain growth, elimination of the pore volume, and electrical responses that were comparable to values obtained for thermally evaporated, fully dense Ag controls. Specifically, a low DC resistivity of 2.3 μΩ·cm (1.4× bulk Ag) and RF transmission coefficients of 0.87 and 0.75 at 5 GHz and 10 GHz, respectively, were measured in the nanoflake Ag prints. Conversely, in transmission lines printed from a metal-organic decomposition ink, residual chemical contamination impeded diffusion and densification, yielding greater porosity, small grains that are pinned, and a degraded RF response. Reasonably good porosity approximations were obtained from a model based on percolation theory. The results indicate that contaminants at interfaces and pore surfaces impede diffusion, pore elimination, and full densification, and further, alter carrier dynamics and degrade RF response.

Unlocking the True Power of Additive Manufacturing for EMI Shielding

Miniaturization trends in electronic packaging led to reduced spacing of individual packages on the printed circuit boards and thus increased the overall electromagnetic interference (EMI) levels within a device. State-of-the-art conformal coatings as EMI shielding layers are typically applied via sputter technology and offer design limitations with respect to coating selectivity on individual positions of the overall package. Our new technology of additively Ag layer application via inkjet printing overcomes today’s design limitations and is key enabler for next generations packaging designs. In this study, we compare the shielding effectiveness (S.E.) on specifically designed transmission line emitter samples coated with state-of-the-art sputtered conformal layers against silver coatings applied via inkjet printing of particle free metal organic decomposition inks to evaluate the new technology for its potential on package level shielding performance. Mechanical and electrical characterization of the silver coatings indicate appropriate tools to specify layer characteristics and ensure S.E. of 40 dB or higher at frequencies of 800 MHz and higher. The suitability of our well-tailored silver coatings to match typical S.E. requirements is shown with even much thinner layer thickness as compared to state-of-the-art coatings.

Revealing The Morphology of Ink and Aerosol Jet Printed Palladium-Silver Alloys Fabricated from Metal Organic Decomposition Inks.

Palladium films hold signicance due to their remarkable affinity for hydrogen diffusion, rendering them valauble for the seperation and purification of hydrogen in membrane reactors. However, palladium is expensive, and its films can become brittle after only a few cycles of hydrogen separation. Alloying with silver has been shown to overcome the problem of palladium embrittlement. Palladium-silver films have been produced via several methods but all have drawbacks, such as difficulties controlling the alloy composition. This study explores two promising jet printing methods: Inkjet and Aerosoljet. Both methods offer potential advantages such as direct patterning, which reduces waste, enables thin film production, and allows for the control of alloy composition. For the first time, palladium-silver alloys have been produced via inkjet printing using a palladium-silver metal organic decomposition (MOD) ink, which alloys at a temperature of 300°C with nitrogen. Similarly, this study also demonstrates a pioneering approach for Aerosol Jet printing, showing the potential of a novel room-temperature method, for the deposition of palladium-silver MOD inks. This low temperature approach is considered an important development as palladium-silver MOD inks are originally designed for deposition on heated substrates.

Effects of copper metal organic decomposition ink on properties of single-walled carbon nanotube based flexible transparent electrodes

The effects of copper metal organic decomposition (Cu MOD) ink on the electrical and mechanical properties of SWCNT-based flexible transparent electrodes were investigated. In particular, we designed and demonstrated Cu MOD ink as bonding agents between oxidized SWCNT (Ox-SWCNT) and the polyethylene terephthalate (PET) substrate. PET substrates were surface-treated via plasma etching, and ultraviolet/ozone (UV/O3) treatment was conducted for enhancing the dispersion of SWCNTs. Subsequently, spray coating of numerous times with Ox-SWCNT dispersion and once with Cu MOD ink was applied to the PET substrates at low temperatures. In this way, a robust, flexible, and transparent Ox-SWCNT/Cu@PET composite electrode was fabricated. The as-prepared Ox-SWCNT/Cu@PET composite electrode exhibited good properties, with a sheet resistance of 483.9 Ω/sq and transmittance of 82.1%. Even after 10000 bending cycles and 100 peel-off times, the resistance was only increased by factors of 1.07 and 1.12, respectively, confirming good mechanical robustness. In addition, the electrode exhibited excellent environmental stability; its electrical resistance was only increased by a factor of 1.35 after subjected to harsh environmental conditions (85 °C, 85% relative humidity) for 48 h. These results indicate that the Ox-SWCNT/Cu@PET composite electrodes are promising for wide application as FTCEs.

Formulating nickel metal organic decomposition ink with low sintering temperature and high conductivity for ink jet printing applications

Formulating nickel metal organic decomposition ink with low sintering temperature and high conductivity for ink jet printing applications

Room Temperature Electronic Functionalization of Thermally Sensitive Substrates by Inkjet Printing of a Reactive Silver‐Based MOD Ink

AbstractThe developments in inkjet printing technology and the printed electronics industry in the past two decades have provided cost‐effective, environment‐friendly, and reliable alternates to traditional methods of fabricating electrical devices. However, most commercial metallic inks require high sintering temperatures to form desired functional patterns, which limits the applications of printed electronics in scenarios that require electrical devices on thermally sensitive substrates, like biomaterials or bio‐synthetic composite materials. This study provides the synthetic route of a novel silver‐based metal organic decomposition (MOD) ink which is used to form highly conductive silver films on the thermally sensitive skin‐inspired silk/epoxy composite substrates by directly inkjet printing with accurate pattern control, whilst self‐decomposing and sintering at room temperature. The fabricated silver patterns on the thermally sensitive silk/epoxy composite substrate are highly conductive with conductivity of 4.65 × 104 S m−1. These silver patterns also show impressive malleability as bulk silver films, which can be further developed into motion sensors for wearable devices or medical applications. Our strategy provides a general platform for electronic functionalization without temperature constraints. The particle‐free, reactive silver‐precursor, and lower sintering temperature of the ink also widen the choices of substrates, as exemplified herein with outstanding printing quality and high electrical conductivity (1.20 × 106 S m−1) also achieve on paper.

Facile synthesis of metal organic decomposition Al-doped ZnO ink for inkjet printing and fabrication of highly transparent conductive film

In this paper, a MOD (Metal organic decomposition) Al doped ZnO (AZO) ink was directly used for inkjet printing transparent and conductive AZO films. The ink was synthesized by using zinc acetate dihydrate and aluminum nitrate nonahydrate as precursor, 1,2-diaminopropane as a complexing agent, ethyl alcohol as solution, ethyl cellulose as addition agent. The thermal decomposition behavior of the MOD ink was investigated. The various MOD AZO inks were inkjet printed and heated at different temperatures for different times. The films were studied by X-ray diffraction, scanning electron microscopy, resistivity measurements and ultraviolet–visible spectroscopy. The results demonstrated that 0.2 M AZO (2 at%) film heated at 250 °C for 120 min showed highly preferential growth along the c-axis, uniform microstructure with a resistivity of 0.03 Ω cm and high transmittance more than 90% in the visible range of the spectrum with an optical band gap at 3.326 eV.

Laser-based, direct formation of thin copper–nickel alloy films with low thermal coefficient of resistivity

The growing market of printed electronics requires the development of new materials and processing technologies that enable the design of smart wearables, integrated sensors, and next-generation electronics. Against the backdrop of increasing material scarcity, these approaches must be resource-conserving and, at the same time, competitive with conventional technologies. As an alternative to nanoparticle-based inks currently used in printed electronics, another technology has been emerging in the last years that utilizes metal organic decomposition (MOD) inks, which are easy to fabricate and have a long shelf life. In this study, a method is presented that allows the direct formation of thin copper-nickel alloy films from a MOD ink. These alloys are preferably used for sensors like strain gauges as they exhibit a low thermal coefficient of resistivity (TCR). 250 nm thin alloy films are coated on glass substrates and thermally functionalized. In a conventional hot plate heat treatment under a nitrogen atmosphere, 10.2% bulk conductivity for a Cu55Ni45 alloy with a TCR of 8.3 × 10−5 K−1 is reached. X-ray diffraction analysis indicates the formation of a mixed crystal composed of nickel and copper atoms. A laser-based functionalization process is developed that allows the processing of Cu55Ni45 alloy films under ambient conditions without the formation of copper or nickel oxides. Laser-functionalized films exhibit 5.3% of the conductivity of bulk material. This study shows that metal alloy films can be fabricated directly from amine-based MOD inks.

Direct Laser Interference Ink Printing Using Copper Metal-Organic Decomposition Ink for Nanofabrication.

In this study, we developed an effective and rapid process for nanoscale ink printing, direct laser interference ink printing (DLIIP), which involves the photothermal reaction of a copper-based metal–organic decomposition ink. A periodically lined copper pattern with a width of 500 nm was printed on a 240 μm-wide line at a fabrication speed of 17 mm/s under an ambient environment and without any pre- or post-processing steps. This pattern had a resistivity of 3.5 μΩ∙cm, and it was found to exhibit a low oxidation state that was twice as high as that of bulk copper. These results demonstrate the feasibility of DLIIP for nanoscale copper printing with fine electrical characteristics.

A nickel metal-organic-decomposition ink of nickel-ethanolamine complex leading to highly conductive nickel patterns for printed electronic applications

Conductive inks are key materials for the wide application of printed electronics. A metal-organic-decomposition (MOD) ink of nickel was prepared via a simple and high-yield complexation reaction pathway between nickel formate dihydrate and ethanolamine in a mixed solvent containing ethanol and ethylene glycol. The well-designed non-particulate ink shows long-term storage stability. The decomposition process of the ink and the microstructure evolution of the spin-coated films during sintering were investigated. The observed increase in conductivity can be ascribed to the establishment of a continuous conductive path between particles due to sintering and particle growth and more thorough removal of residual organics after increasing the sintering temperature from 300 to 400 °C. A low resistivity of 20.6 µΩ cm (3.0 times that of bulk nickel) was obtained. The inkjet printing performance of the Ni MOD ink was demonstrated. Our systematic work provides a fundamental understanding of the synthesis scenario of nickel organic decomposition ink. The good inkjet-printing performance and excellent conductivity of Ni MOD ink provide a wide range of possibilities for its broader applications in the field of printed electronics.

Flexible and ultra-thin silver films with superior electromagnetic interference shielding performance via spin-coating silver metal–organic decomposition inks

Flexible and ultra-thin silver films for high-performance electromagnetic interference shielding were fabricated by thermal decomposition of metal–organic decomposition inks.

MODs vs. NPs: Vying for the Future of Printed Electronics.

This Minireview compares two distinct ink types, namely metal‐organic decomposition (MOD) and nanoparticle (NP) formulations, for use in the printing of some of the most conductive elements: silver, copper and aluminium. Printing of highly conductive features has found purpose across a broad array of electronics and as processing times and temperatures reduce, the avenues of application expand to low‐cost flexible substrates, materials for wearable devices and beyond. Printing techniques such as screen, aerosol jet and inkjet printing are scalable, solution‐based processes that historically have employed NP formulations to achieve low resistivity coatings printed at high resolution. Since the turn of the century, the rise in MOD inks has vastly extended the range of potentially applicable compounds that can be printed, whilst simultaneously addressing shelf life and sintering issues. A brief introduction to the field and requirements of an ink will be presented followed by a detailed discussion of a wide array of synthetic routes to both MOD and NP inks. Unindustrialized materials will be discussed, with the challenges and outlook considered for the market leaders: silver and copper, in comparison with the emerging field of aluminium inks.

Study of Inkjet-Printed Silver Films Based on Nanoparticles and Metal-Organic Decomposition Inks with Different Curing Methods.

Currently, inkjet printing conductive films have attracted more and more attention in the field of electronic device. Here, the inkjet-printed silver thin films based on nanoparticles (NP) ink and metal-organic decomposition (MOD) ink were cured by the UV curing method and heat curing method. We not only compared the electrical resistivity and adhesion strength of two types of silver films, but also studied the effect of different curing methods on silver films. The silver films based on NP ink had good adhesion strength with a lowest electrical resistivity of 3.7 × 10−8 Ω·m. However, the silver film based on MOD ink had terrible adhesion strength with a lowest electrical resistivity of 2 × 10−8 Ω·m. Furthermore, we found a simple way to improve the terrible adhesion strength of silver films based on MOD ink and tried to figure out the mechanisms. This work offers a further understanding of the different performances of two types of silver films with different curing methods.

Effectiveness of Ligand Denticity-Dependent Oxidation Protection in Copper MOD Inks.

The recent cost-driven transition from silver- to copper-based inks for printing on flexible substrates is connected with new key challenges. Given the high oxidation sensitivity of copper inks before, during, and after the curing process, the conductivity and thereby the device performance can be affected. Strategies to limit or even avoid this drawback include the development of metal organic decomposition (MOD) inks with selected "protective" ligands. In this study, the influence of the ligand on the oxide formation during the ink decomposition process is described using a wide variety of in situ characterization techniques. It is demonstrated that bidentate ligands provide an improved oxidation barrier, although the copper preservation mechanism has its limits: oxygen can interfere in every reduction pathway depending on the curing duration and atmospheric conditions. The generated insights can be applied in the further evolution toward ambient-curable copper MOD inks.

Metal−Organic Decomposition Ink for Printed Electronics

AbstractPrinted electronics is a rapidly expanding research field because of its incomparable economic efficiency. While various types of inks are employed in the printing of electronics, metal–organic decomposition (MOD) ink is an interesting type of ink worth paying attention to. MOD ink consists of metals in their ionic state and the advantages include simple preparation, long shelf life, high jetting stability, and low temperature processing. Additionally, the ease of large‐scale fabrication through industrial scale printing processes makes MOD ink ideal for printed electronics. To improve the conductivity, morphology, and variety of the conductive substance resulting from MOD ink, recent research has focused on the variation of the ink composition, printing techniques, and sintering methods. Here, the conventional methods of preparation and processing of MOD ink are introduced, followed by discussion of various research efforts to date. Furthermore, applications and their examples including but not limited to conventional conductive patterning are presented.

Laser sintering process optimization of microstrip antenna fabricated by inkjet printing with silver-based MOD ink

Inkjet printing has been widely used for the manufacturing of patch antennas, circuit boards, biochemical sensors, frequency selection surfaces and other electronic devices. As an essential process, laser sintering is of great significance to the inkjet printing, which can enable the printed patterns to possess very good conductivity. The laser sintering process for the MOD (Metal Organic Decomposition) ink is investigated in this manuscript. First of all, the laser sintering simulation of the MOD ink is carried out based on COMSOL Multiphysics and change mechanism of the sintering temperature under different process parameters is revealed. Then, sintering experiments and process optimization are conducted on the self-developed platform, and the sintering quality differences are comparatively analyzed by measuring the widths, conductivities and thicknesses of the printed silver lines. Finally, a microstrip antenna is fabricated based on the optimized process and the performance of the manufactured antenna satisfies the use requirements. The simulation results are highly consistent with the experimental results, and both of them have verified the feasibility, reliability and effectiveness of the optimized sintering process.

Effect of processing parameters on laser sintering of silver MOD inks for inkjet printing

Sintering is essential for inkjet printing and laser sintering is a promising sintering technology. In this study, the effect of laser sintering processing parameters on the sintering quality of silver content metal-organic-decomposition (MOD) inks is studied. A novel mathematic model is developed to reveal the temperature evolutions in MOD inks and the substrates during laser sintering. In the novel model, the change of thermal conductivity of MOD inks is taken into consideration for the first time to improve simulation accuracy. The simulation results agree well with the experiments, showing the advantages of the mathematic model. The surface morphology of the sintered MOD inks are also observed through experiments. The simulation and experimental results show that the laser sintering processing parameters have significant effects on the sintering quality. With authors’ optimised laser sintering processing parameters, the printed pattern can be sufficiently sintered and its electronic conductivity can reach 1.56 × 10–7 S/m. Thus, a sintering optimisation strategy is proposed based on the results. Finally, a microstrip antenna is fabricated with the optimised sintering strategy. The performance of the antenna agree well with the simulation results, indicating authors’ optimising strategy is useful for industrial production.

Understanding the Importance of Cu(I) Intermediates in Self-Reducing Molecular Inks for Flexible Electronics.

Fast and scalable low-temperature deposition of microscale metallic features is of utmost importance for the development of future flexible smart applications including sensors, wireless communication, and wearables. Recently, a new class of metal-organic decomposition (MOD) copper inks was developed, consisting of self-reducing copper formate containing amine complexes. From these novel inks, copper metal features with outstanding electrical conductivity (±105 S cm-1) are deposited at a temperature of 150 °C or less, which is well below the reduction temperature of orthorhombic α-copper formate (around 225 °C). However, the underlying principle of this reaction mechanism and the relationship between the corresponding temperature shift and the amine coordination are still under debate. The current study provides a full explanation for the shift in reduction temperatures via in situ characterization. The results clearly indicate that the structural resemblance and stability of the Cu(II) starting compound and the occurring Cu(I) intermediate during the in situ reduction are the two main variables that rationalize the temperature shift. As such, the thermal compatibility of copper MOD inks with conventional plastic substrates such as polyethylene terephthalate can be explained, based on metal-organic complex properties.