Photo-Sintered Silver Thin Films by a High-Power UV-LED Module for Flexible Electronic Applications

In recent printed electronics technology, a photo-sintering technique using intense pulsed light (IPL) source has attracted attention, instead of conventional a thermal sintering process with long time and high temperature. The key principle of the photo-sintering process is the selective heating of a thin film with large light absorption coefficients, while a transparent substrate does not heat by the IPL source. Most research on photo-sintering has used a xenon flash lamp as a light source. However, the xenon flash lamp requires instantaneous high power and is unsuitable for large area applications. In this work, we developed a new photo-sintering system using a high-power ultraviolet light emitting diode (UV-LED) module. A LED light source has many merits such as low power consumption and potential large-scale application. The silver nanoparticles ink was inkjet-printed on a polyethylene terephthalate (PET) and photo-sintered by the UV-LED module with the wavelength of 365 and 385 nm. The electrical resistivity as low as 5.44 × 10−6 Ω·cm (just about three times compared to value of bulk silver) was achieved at optimized photo-sintering conditions (wavelength of 365 nm and light intensity of 300 mW/cm2).

Invisible and Flexible Printed Sensors Based on ITO Nanoparticle Ink for Security Applications

Here, we propose a method to create a transparent security system based on printed conductive indium tin oxide (ITO)—the most widely used transparent conducting oxide material integrated into the devices with high transparency. Commonly used solution-processed ITO annealing methods are utilizing temperatures which are limiting the use of flexible polymeric substrates. Our method combines inkjet printing on flexible temperature-stable colorless polyimide (CPI) substrate with fast flash lamp annealing (FLA). In this study, millisecond pulses of visible light from a xenon lamp induce rapid heating of the ITO films up to 650°C through the light-absorbing additional layer of a colored organic dye onto printed ITO, whereas the CPI bulk never exceeds the melting point. Fabricated flexible ITO patterns on CPI film processed with the flash lamp annealing through the dye layer exhibit a transmittance of up to 85% at the wavelength of 550 nm and sheet resistance of 520 Ω/sq for a 70 nm layer thickness. With the proposed technology of our demonstrator realization—transparent glass/window or any other object such as a curved door lock can be used for integrating a touch-enabled transparent security access system, which would be completely invisible.