Kyungtae Kang

Ink-Jet Printing of Silver Conductive Tracks on Flexible Substrates

We have developed a conductive ink applicable to ink-jet printing to fabricate conductive lines on flexible substrates. Nano-sized silver particles with ∼21 nm diameter were used for the direct metal printing. Silver conductive ink was printed on polymer substrates for the application to flexible electronics. The printing conditions of pulse amplitude, head frequency, xy-stage moving velocity and substrate temperature were optimized to achieve smooth conductive track with high resolution. After heat-treatment at temperature of 100 ∼ 300°C for 30 min, the printed silver patterns exhibit metal-like appearance and high conductivity. The influence of the printing conditions on the microstructure and conductivity of the conductive track was investigated.

Periodic fuel supply to a micro-DMFC using a piezoelectric linear actuator

A reciprocating pump using a piezoelectric linear actuator is introduced as a fuel supply module for a direct methanol fuel cell (DMFC) stack. The results show that the key advantage of the pump with the linear actuator is its ability to operate at a low frequency, which enables high flow rectification performance. At the end of this study, the pump is applied to a DMFC system to demonstrate that the output voltage of a DMFC stack remains stable with time even when the pumping pressure oscillates periodically at frequencies of a few Hz. It is also demonstrated that the maximum output power of the stack exceeds 6 W with power consuming 3.5% of the stack power for the fuel pump.

Fabrication of organic light emitting display using inkjet printing technology

In this paper, we have investigated the characteristics of polymer inkjet printing and fabricated OLED(organic light emitting diode) display using inkjet printing technology. To control the wetting condition of the droplet to the substrate, UV/ozone treatment technique is used. To make the repeated pixels on a substrate, precise vision alignment and multi-layer printing is used. With the successive printing of PEDOT/PSS as a hole injection layer and MEH-PPV as a light emitting layer, we have successfully fabricated an OLED and demonstrated basic working of OLED.

Laser sintering of inkjet-printed silver nanoparticles on glass and PET substrates

Laser sintering of inkjet-printed silver nanoparicles was studied. Conducting lines were printed on glass and PET substrates of various thicknesses by a drop-n-demand (DOD) inkjet printer and silver nanoparticle ink. Selective sintering of the printed silver nanopartilces was then performed using laser beam to enhance electrical conductivity. Focused laser beam was irradiated normally to the silver layer printed on the transparent substrates with various beam intensity and various irradiation time. Conductivity and morphology of the laser sintered silver patterns were measured and compared with the results of oven-heated sintering. Temperature elevation by laser irradiation was also calculated based on laser beam intensity, irradiation time, surface reflectivity, and thermophysical property of a substrate to estimate enhancement of the electrical conductivity by laser sintering.

Fabrication of a paper-based analytical device for multiple colorimetric analysis via inkjet-printing and paper-cutting

We introduce a process for the fabrication of a paper-based analytical device (PAD) for multiple colorimetric analysis via paper- cutting and inkjet-printing. To create the selective flow channels, hydrophobic barriers were formed by using hydrophobic polyvinyl chloride tape-cutting and ultraviolet-curable resin printing. Multiple paper channels were isolated by the hydrophobic barriers on a single chip. An assay model was created from bovine serum albumin (BSA) and tetrabromophenol blue (TBPB) to verify the feasibility of the fabricated PAD. A multiple colorimetric analysis was demonstrated a reaction with different BSA concentrations after the TBPB regent was elaborately deposited onto the circular test spot areas by inkjet printing.

Laser sintering of the printed silver ink

Because flexible electronics have a weak characteristic in high temperature, the conductive ink including nano-metal particles is printed on flexible substrate by printing methods such as screen printing, inkjet printing, and R2R. Due to high electrical resistance of printed metal ink, the process to improve the property of electrical conductivity is needed. To improve the conductivity, the furnace curing is used after printing the ink on the substrate. But this process spends much time for curing. Therefore, flexible substrate or glass substrate can be damaged due to long exposed time. The curing by using a laser is utilized to minimize the damage of flexible substrate. In this work, the specific resistance of silver ink by using furnace curing at the temperature of 250 °C after 30 minutes is 3×10−8Ωm. The specific resistance of silver ink by the laser curing at the power of 5W from 5sec to 10 sec is 2. 38×10−8Ωm. Consequently, the curing time by using the laser is significantly smaller than that of the furnace curing.

A study on driving waveform of a piezoelectric inkjet print head

Inkjet printing technology with a drop-on-demand (DOD) inkjet head has been recognized as one of the versatile and low cost manufacturing tools in the electronics industry. However, general strategy to optimize jetting stability has not been understood well, because of the inherent complex multi-physics nature in inkjet phenomena. In this paper, an experimental approach has been adopted to attack this problem. Based on the driving voltage amplitude and duration as the main and controllable parameter, the jetting map of an OLED ink has been constructed and the effect of phase matching between pressure and surface waves at the nozzle tip has been discussed.

Characterization of Inkjet-Printed Silver Patterns for Application to Printed Circuit Board (PCB)

In this paper, we describe the analysis of inkjet-printed silver (Ag) patterns on epoxycoated substrates according to several reliability evaluation test method guidelines for conventional printed circuit boards (PCB). To prepare patterns for the reliability analysis, various regular test patterns were created by Ag inkjet printing on flame retardant 4 (FR4) and polyimide (PI) substrates coated with epoxy for each test method. We coated the substrates with an epoxy primer layer to control the surface energy during printing of the patterns. The contact angle of the ink to the coated epoxy primer was 69˚, and its surface energy was 18.6 mJ/m². Also, the substrate temperature was set at 70℃. We were able to obtain continuous line patterns by inkjet printing with a droplet spacing of 60 ㎛. The reliability evaluation tests included the dielectric withstanding voltage, adhesive strength, thermal shock, pressure cooker, bending, uniformity of line-width and spacing, and high-frequency transmission loss tests.

Laser Sintering of Inkjet-Printed Silver Lines on Glass and PET Substrates

In this study, the laser sintering of inkjet-printed silver lines was evaluated. Silver-nanoparticle ink and a drop-ondemand (DOD) inkjet printer were used for printing on glass and polyethylene terephthalate (PET) substrates with various thicknesses. To sinter the printed silver nanoparticles, the silver layer printed on the transparent substrates was irradiated by focused CW laser beams that were incident normal to the substrates; the irradiation was carried out for various beam intensities and for various irradiation times. The electrical conductivity of the laser-sintered silver patterns was measured and compared with the conductivity of silver patterns sintered by using an oven. The increase in the temperature caused by laser irradiation was also calculated on the basis of the laser beam intensity, irradiation time, surface reflectivity, and thermophysical property of the substrate in order to estimate the increase in the electrical conductivity caused by laser sintering.

Electrical sintering of inkjet-printed silver electrode for c-Si solar cells

Electrical sintering of the front electrode for crystalline silicon solar cells was performed applying a constant DC current to the printed lines. Conducting lines were printed on glass substrate by a drop-on-demand (DOD) inkjet printer and silver nanoparticle ink. Specific resistance and microstructure of sintered silver lines and were measured with varying DC current. To find the relation between temperatue increase with changing applied cuurent and specific resistance, temperature elevation was also calculated. Sintering process finished within a few milliseconds. Increasing applied DC current, specific resistance decreased and grain size increased after sintering. Achieved minimum specific resistance is approximately 1.7 times higher than specific resistance of the bulk silver.