Ag Nanoparticle Ink Research Articles

Automated Continuously-Manufacturing Line of All-Printed Organic TFT Array Flexible Film

In the printed electronics field, it has been needed to realize the manufacturing technologies for inventing mass production phase. We JAPERA, which was organized 2011 as a NEDO project to develop the manufacturing technologies of large area flexible printed electronics, established the automated and continuously operated manufacturing line for which produced the all-printed TFT array flexible film. We operated the offset printer, inkjet printer, screen printer, and slit-die coater. Specialized ink materials, for example Ag nano particle ink for gate electrode and source/drain electrode, highly purified polymer ink for gate insulator, and organic semiconductor ink for TFT active layer have been developed. We have been acquiring successful results of TFT array flexible film by high yield. The applications of our THT array flexible film for making a display device or a sensor device are presented.

The Characteristic Variations of Inkjet-Printed Silver Nanoparticle Ink During Furnace Sintering

In this work, an experiment on furnace thermal sintering with printed silver (Ag) nanoparticle ink was carried out. The Ag nanoparticle ink employed in this study has a particle size of around 50 nm and particles constitute 34 wt% of the ink. The Ag nanoparticle ink was printed by inkjet printing. A thermal sintering process in a furnace was conducted at temperatures of 150, 200, and 250 degrees C for 20 to 3000 seconds. After sintering, electrical conductivities and cross-sectional images were measured. The specific resistance and the cross-sectional area of the sintered ink decrease as the sintering temperature increases. The SEM images indicate that surface premelting caused sintering below the melting temperature of silver, 960 degrees C, which increased neck growth and lowered the electrical resistance. Lastly, the minimum specific resistance of 7.08 microOmgega x cm was obtained after sintering for 3000 s at 250 degrees C. This specific resistance value was 4.4 times larger than that of bulk silver.

A Development of Atmospheric Pressure Plasma Equipment and Its Applications for Treatment of Ag Films Formed from Nano-Particle Ink

We have developed an equipment of atmospheric pressure plasma with two microwave guide antennas, which have a discharge line with 41 slots. The antennas are set against a stage with a heater in a process chamber. A process gas, which is a 1 % H2 gas diluted by Ar gas and its flow rate is 20 standard litter per minute (slm), flows into the micro-wave guide and goes to a process chamber through each slots. A micro-wave is introduced to the micro-wave guide and the atmospheric pressure plasma grows at each slots. We obtained the electron density of 1×1015 cm−3 and the H radical density of 1×10−16 cm−3 at the slot on the condition of a 10 GHz, 1.5 kWatt, pulsed micro-wave with 2.5 pulsed voltage, 4 kHz pulsed frequency, and a duty ratio of 0.16. We applied this system to improve the quality of the spin-coated Ag firm formed from Ag nano-particle ink. This Ag film showed a resistivity of 32 μΩ cm after annealing on the condition of 180 °C for 30 minutes recommended by the maker (The bulk resistivity of Ag is 1.6 μΩ cm). In order to make the annealing time shorter, we studied the effect of atmospheric plasma treatment of Ag film. We obtained the Ag film of the 5.7 μΩ cm resistivity after the atmospheric pressure plasma treatment under 180 °C for 5 min.

Invisible metal-grid transparent electrode prepared by electrohydrodynamic (EHD) jet printing

Invisible Ag-grid transparent electrodes (TEs) were prepared by electrohydrodynamic (EHD) jet printing using Ag nano-particle inks. Ag-grid width less than 10 µm was achieved by the EHD jet printing, which was invisible to the naked eye. The Ag-grid line-to-line distance (pitch) was modulated in order to investigate the electrical and optical properties of the EHD jet-printed Ag-grid TEs. The decrease in the sheet resistance at the expense of the transmittance was observed as the Ag-grid pitch decreased. The figure of merit of Ag-grid TEs with various Ag-grid pitches was investigated in order to determine the optimum pitch condition for both electrical and optical properties. With the 150 µm Ag-grid pitch, the EHD jet-printed Ag-grid TE has the sheet resistance of 4.87 Ω sq−1 and the transmittance of 81.75% after annealing at 200 °C under near-infrared. Ag filling factor (FF) was defined to predict the electrical and optical properties of Ag-grid TEs. It was found that the measured electrical and optical properties were well simulated by the theoretical equations incorporating FF. The EHD jet-printed invisible Ag-grid TE with good electrical and optical properties implies its promising application to the printed optoelectronic devices.

Various metallic nano-sized patterns fabricated using an Ag ink printing technique

This paper presents a new simple metal patterning technique, which is based on soft nanoimprint lithography. By using this method with a commercial Ag nano particle ink, a nano-sized metal pattern was successfully fabricated. The problem of the residual layer of patterned Ag layer was minimized by controlling the concentration of the solution and the process conditions. By using this method, we could easily fabricate various patterns without reference to any shape. Furthermore, we fabricated an Ag mesh type pattern for the application of conducting transparent glass.

The Effect of Thermal Annealing on Pentacene Thin Film Transistor with Micro Contact Printing

We used micro contact printing (micro-CP) to fabricate inverted coplanar pentacene thin film transistors (TFTs) with 1-microm channels. The patterning of micro-scale source/drain electrodes without etch process was successfully achieved using Polydimethylsiloxane (PDMS) elastomer stamp. We used the Ag nano particle ink as an electrode material, and the sheet resistance and surface roughness of the Ag electrodes were effectively reduced with the 2-step thermal annealing on a hotplate, which improved the mobility, the on-off ratio, and the subthreshold slope (SS) of the pentacene TFTs. In addition, the device annealing on a hotplate in a N2 atmosphere for 30 sec can enhance the off-current and the mobility properties of OTFTs without damaging the pentacene thin films and increase the adhesion between pentacene and dielectric layer (SiO2), which was investigated with the pentacene films phase change of the XRD spectrum after device annealing.

Fire-Through Ag Contact Formation for Crystalline Si Solar Cells Using Single-Step Inkjet Printing

Inkjet-printed Ag metallization is a promising method of forming front-side contacts on Si solar cells due to its non-contact printing nature and fine grid resolution. However, conventional Ag inks are unable to punch through the SiN(x) anti-reflection coating (ARC) layer on emitter Si surfaces. In this study, a novel formulation of Ag ink is examined for the formation of fire-through contacts on a SiN(x)-coated Si substrate using the single-step printing of Ag ink, followed by rapid thermal annealing at 800 degrees C. In order to formulate Ag inks with fire-through contact formation capabilities, a liquid etching agent was first formulated by dissolving metal nitrates in an organic solvent and then mixing the resulting solution with a commercial Ag nanoparticle ink at various volume ratios. During the firing process, the dissolved metal nitrates decomposed into metal oxides and acted in a similar manner to the glass frit contained in Ag pastes for screen-printed Ag metallization. The newly formulated ink with a 1 wt% loading ratio of metal oxides to Ag formed finely distributed Ag crystallites on the Si substrate after firing at 800 degrees C for 1 min.

Microstructural characterization of electrically failed conductive traces printed from Ag nanoparticle inks

Conductive traces printed from nanoparticle loaded silver inks failed due to the application of excessive electrical current. A non-homogeneous microstructure was observed in the vicinity of the failed region consisting of sintered particles, grains and melted particles indicating a significant amount of heat was transferred to the conductive trace, in some cases, resulting in substrate damage. A simple physical model describing the failure mechanisms is proposed.

Ag 인쇄배선과 이종재료기판과의 접합계면

Ag metallic particles from nano-scale to submicron-scale are combined with organic solvent to provide fine circuits and interconnection. Ink-jet printing with Ag nano particle inks demonstrated the potentials of the new printed electronics technology. The bonding at the interface between the Ag wiring layer and the various substrates is very important. In this study, the details of interfaces in Ag wiring are investigated primarily by microstructure observation. By adjusting the materials and sintering conditions, nicely formed interfaces between Ag wiring and Cu, Au or organic substrates are achieved. In contrast, transmission electron microscope (TEM) image clearly shows interface debonding between Ag wiring and Sn substrate. Sn oxides are formed on the surface of the Sn plating. The formation of these is a root cause of the interface debonding.

Microstructural and Process Characterization of Conductive Traces Printed from Ag Particulate Inks.

Conductive inks are key enablers for the use of printing techniques in the fabrication of electronic systems. Focus on the understanding of aspects controlling the electrical performance of conductive ink is paramount. A comparison was made between microparticle Ag inks and an Ag nanoparticle ink. The microstructures resulting from thermal cure processes were characterized morphologically and also in terms of their effect on the resistivity of printed traces. For microparticle inks, the variability of resistivity measurements between samples as defined by coefficient of variation (CV) was greater than 0.1 when the resistivity was 10 to 50 times that of bulk Ag. When the resistivity was lower (~1.4 times that of bulk Ag) the CV of sample sets was less than 0.1. In the case of the nanoparticle ink, resistivity was found to decrease by a factor ranging from 1.2 to 1.5 after doubling the amount of layers printed prior to curing though it was expected to remain the same. Increasing the amount of layers printed also enhanced the sintering process.

A Novel Inkjet Printed Surface Enhanced Raman Spectroscopy (SERS) Substrate for the Detection of Toxic Heavy Metals

A novel surface enhanced Raman spectroscopy (SERS) substrate was successfully fabricated on a silicon (Si) wafer using a 400nm inkjet printed thin film of silver (Ag) nanoparticle ink, with 150nm particle size. The capability of the fabricated SERS substrate for detecting toxic heavy metals such as mercury sulfide (HgS), cadmium sulfide (CdS) and zinc oxide (ZnO) was demonstrated. The SERS based response of the printed substrate produced an enhanced Raman signal when compared to that of target molecules adsorbed on bare Si wafer. An amplification of the SERS intensity by an order of 3 to 5 times was observed for all test samples, due to the presence of hotspots between the metal nanoparticle aggregates. The responses demonstrated the feasibility of the novel SERS substrate to be used in applications for detection of toxic heavy metals.

Surface Morphology and Conductivity Study of Inkjet Printed Traces from Ag Nanoparticle Inks

Non-contact printing of conductive traces for electronic device fabrication is attractive due to its low cost, high resolution and high throughput characteristics. Inkjet printing of Ag nanoparticle inks followed by thermal or photonic sintering has the greatest potential for commercialization. In this process, the chemical and physical properties of the ink formulation and post print processing have significant impacts on the performance of the printed traces. In this paper, the effects of sintering methods and process conditions on the surface morphology and conductivity of the fabricated Ag traces are discussed.

Fabrication of an organic field effect transistor using nano imprinting of Ag inks and semiconducting polymers

A simple and cheap procedure for flexible electronics fabrication was demonstrated by imprinting metallic nanoparticles (NPs) on flexible substrates. Silver NPs with an average diameter of 10 nm were prepared via an improved chemical approach and Ag Np ink was produced in α-terpineol with a concentration up to 15%. Silver micro/nanostructures with a dimension varying from nanometres to microns were produced on a flexible substrate (polyimide) by imprinting the as-prepared silver ink. The fine fluidic properties of an Ag NP/α-terpineol solution and low melting temperatures of silver nanoparticles render a low pressure and low temperature procedure, which is well suited for flexible electronics fabrication. The effects of sintering and mechanical bending on the conductivity of imprinted silver contacts were also investigated. Large area organic field effect transistors (OFET) on flexible substrates were fabricated using an imprinted silver electrode and semiconducting polymer. The OFET with silver electrodes imprinted from our prepared oleic acid stabilized Ag nanoparticle ink show an ideal ohmic contact; therefore, the OFET exhibit high performance (Ion/Ioff ratio: 1 × 103; mobility: 0.071 cm2 V−1 s−1).

Individually Dispersed Nanoparticles formed by Gas Evaporation Method and their Applications

Individually dispersed Au, Ag, Cu and ITO nanoparticle ink are formed by using the industrial scale modified gas evaporation method where formed particles are covered with an organic surfactant just after their formation. The average diameters of these particles are less than 10 nm. These nanoparticle inks are called Nanometalink and suitable for ink-jet printing. Ink-jet printing using Nanometalinks are expected to substitute a patterning process using sputtering and photolithography. The inner structures of the cured films are much dependent on curing conditions such as a curing temperature, a temperature profile and a curing atmosphere which affect the resistivities and the mechanical strengths of the films. An Ag Nanometalink film low temperature curing type which is heat treated at 150°C and 180°C, 200°C for 60min with a thickness of 1 μm has a resistivity of 15μΩ·cm, 4 μΩ·cm, and 3μΩ·cm respectively. The adhesion strengths are improved by adding Cu nanoparticles to Ag Nanometalink in the case of high temperature (over 350 C) curing process and by coating resins on a substrate in the case of low temperature curing process.The ITO film which is heat treated at 230°C for 60 min with a thickness of 240 nm has a specific electric resistance of 0.0055Ω·cm and transparency of 95% at 550nm. Other inks properties and application examples are also going to be presented.

Aerosol flow through a long micro-capillary: collimated aerosol beam

A micro-capillary system capable of generating a focused collimated aerosol beam (CAB) is demonstrated both theoretically and experimentally. The approach is based on a manifestation of the Saffman force where high velocity (∼100 m/s) aerosol particles, flowing through a micro-capillary (d ∼ 100 μm and l ∼ 1 cm), migrate perpendicular to the centerline of the capillary. Upon exiting the micro-capillary system, the particles maintain momentum, and when the aerosol is comprised of solid-in-liquid dispersions such as Ag nanoparticle ink, the CAB approach enables printing of advanced materials features with linewidth ≤ 10 μm.

Individually Dispersed Nanoparticle Ink for Film Formation using Ink-jet

Individually dispersed Au, Ag, Cu, Pd and ITO nanoparticle inks are formed by using the modified gas evaporation method (gas condensation) where formed particles are covered with an organic surfactant just after their formation. The particles formed by the gas evaporation method are alkaline and sulfur impurity free and have a narrow size distribution. The average diameters of these particles are less than 10 nm and the particles are stably dispersed in Toluene or Tetradecane or Decalin with a solid content of 70wt% for Au, 60wt% for Ag and Cu, 50wt% for Pd and 40wt% for ITO respectively. These nanoparticle inks are suitable for ink-jet printing. Ink-jet printing using nanoparticle ink is expected to substitute patterning processes using sputtering and photolithography. An Ag nanoparticle ink film(low temp.curing type) which is heat treated at 150C for 2hr with a thickness of 300nm has a specific electric resistance of 6μΩcm. An ITO nanoparticle ink film which is heat treated at 230C for 70 min with a thickness of 160 nm has a specific electric resistance of 0.02 Ocm and transparency of 95% at 550nm.