Intense pulsed light annealing of solution-based indium-gallium-zinc-oxide semiconductors with printed Ag source and drain electrodes for bottom gate thin film transistors.

In this study, an intense pulsed light (IPL) annealing process for a printed multi-layered indium-gallium-zinc-oxide (IGZO) and silver (Ag) electrode structure was developed for a high performance all-printed inorganic thin film transistor (TFT). Through a solution process using IGZO precursor and Ag ink, the bottom gate structure TFT was fabricated. The spin coating method was used to form the IGZO semiconductor layer on a heavily-doped silicon wafer covered with thermally grown silicon dioxide. The annealing process of the IGZO layer utilized an optimized IPL irradiation process. The Ag inks were printed on the IGZO layer by screen printing to form the source and drain (S/D) pattern. This S/D pattern was dried by near infrared radiation (NIR) and the dried S/D pattern was sintered with intense pulsed light by varying the irradiation energy. The performances of the all-printed TFT such as the field effect mobility and on-off ratio electrical transfer properties were measured by a parameter analyzer. The interfacial analysis including the contact resistance and cross-sectional microstructure analysis is essential because diffusion phenomenon can occur during the annealing and sintering process. Consequently, this TFT device showed noteworthy performance (field effect mobility: 7.96 cm2/V s, on/off ratio: 107). This is similar performance compared to a conventional TFT, which is expected to open a new path in the printed metal oxide-based TFT field.

Fabrication of solderable intense pulsed light sintered hybrid copper for flexible conductive electrodes.

Additively printed circuits provide advantages in reduced waste, rapid prototyping, and versatile flexible substrate choices relative to conventional circuit printing. Copper (Cu) based inks along with intense pulsed light (IPL) sintering can be used in additive circuit printing. However, IPL sintered Cu typically suffer from poor solderability due to high roughness and porosity. To address this, hybrid Cu ink which consists of Cu precursor/nanoparticle was formulated to seed Cu species and fill voids in the sintered structure. Nickel (Ni) electroplating was utilized to further improve surface solderability. Simulations were performed at various electroplating conditions and Cu cathode surface roughness using the multi-physics finite element method. By utilizing a mask during IPL sintering, conductivity was induced in exposed regions; this was utilized to achieve selective Ni-electroplating. Surface morphology and cross section analysis of the electrodes were observed through scanning electron microscopy and a 3D optical profilometer. Energy dispersive X-ray spectroscopy analysis was conducted to investigate changes in surface compositions. ASTM D3359 adhesion testing was performed to examine the adhesion between the electrode and substrate. Solder-electrode shear tests were investigated with a tensile tester to observe the shear strength between solder and electrodes. By utilizing Cu precursors and novel multifaceted approach of IPL sintering, a robust and solderable Ni electroplated conductive Cu printed electrode was achieved.

The surface plasmonic welding of silver nanowires via intense pulsed light irradiation combined with NIR for flexible transparent conductive films.

In this work, surface plasmonic welding of silver nanowires (AgNWs) by intense pulse light (IPL) combined with NIR was investigated. AgNWs were coated on a flexible PET (polyethylene terephthalate) substrate using a bar-coater. The coated AgNW films were welded at room temperature and under ambient conditions by white IPL from a xenon lamp, assisted with light from a UV-C (ultraviolet C) and NIR (near infra-red) lamp using an in-house multi-wavelength IPL welding system. In order to investigate the welding mechanism, in situ monitoring with a Wheatstone bridge electrical circuit was performed. The sheet resistance changes of AgNW films during the welding process were monitored under various IPL conditions (e.g. light energy and on-time) with and without UV-C and NIR light irradiation. The microstructure of the welded AgNW film and the interface between the AgNW film and the PET substrate were observed using a scanning electron microscope (SEM) and transmission electron microscope (TEM). COMSOL multi-physics simulations were conducted and compared with the in situ monitoring results to discuss the in-depth mechanism of the IPL welding of AgNWs and its dependence on the wavelength of light. From this study, the optimal IPL welding conditions and appropriate wavelength were suggested, and the optimized IPL welding process could produce AgNW film with a lower sheet resistance (45.2 Ω sq-1) and high transparency (96.65%) without damaging the PET substrate.

Selective Wavelength Plasmonic Flash Light Welding of Silver Nanowires for Transparent Electrodes with High Conductivity.

In this work, silver nanowires (AgNWs) printed on a polyethylene terephthalate substrate using a bar coater were welded via selective wavelength plasmonic flash light irradiation. To achieve high electrical conductivity and transparent characteristics, the wavelength of the flash white light was selectively chosen and irradiated by using high-pass, low-pass, and band-pass filters. The flash white light irradiation conditions such as on-time, off-time, and number of pulses were also optimized. The wavelength range (400-500 nm) corresponding to the plasmonic wavelength of the AgNW could efficiently weld the AgNW films and enhance its conductivity. To carry out in-depth study of the welding phenomena with respect to wavelength, a multiphysics COMSOL simulation was conducted. The welded AgNW films under selective plasmonic flash light welding conditions showed the lowest sheet resistance (51.275 Ω/sq) and noteworthy transmittance (95.3%). Finally, the AgNW film, which was welded by selective wavelength plasmonic flash light with optical filters, was successfully used to make a large area transparent heat film and dye-sensitized solar cells showing superior performances.

Intensive Plasmonic Flash Light Sintering of Copper Nanoinks Using a Band-Pass Light Filter for Highly Electrically Conductive Electrodes in Printed Electronics.

In this work, an intensive plasmonic flash light sintering technique was developed by using a band-pass light filter matching the plasmonic wavelength of the copper nanoparticles. The sintering characteristics, such as resistivity and microstructure, of the copper nanoink films were studied as a function of the range of the wavelength employed in the flash white light sintering. The flash white light irradiation conditions (e.g., wavelength range, irradiation energy, pulse number, on-time, and off-time) were optimized to obtain a high conductivity of the copper nanoink films without causing damage to the polyimide substrate. The wavelength range corresponding to the plasmonic wavelength of the copper nanoparticles could efficiently sinter the copper nanoink and enhance its conductivity. Ultimately, the sintered copper nanoink films under optimal light sintering conditions showed the lowest resistivity (6.97 µΩ·cm), which was only 4.1 times higher than that of bulk copper films (1.68 µΩ·cm).