Jin Hwa Ryu

Rapid curing of solution-processed zinc oxide films by pulse-light annealing for thin-film transistor applications

In this study, a pulse-light annealing method is proposed for the rapid fabrication of solution-processed zinc oxide (ZnO) thinfilm transistors (TFTs). Transistors that were fabricated by the pulse-light annealing method, with the annealing being carried out at 90℃ for 15 s, exhibited a mobility of 0.05 cm2/Vs and an on/off current ratio of 106. Such electrical properties are quite close to those of devices that are thermally annealed at 165℃ for 40 min. X-ray photoelectron spectroscopy analysis of ZnO films showed that the activation energy required to form a Zn-O bond is entirely supplied within 15 s of pulse-light exposure. We conclude that the pulse-light annealing method is viable for rapidly curing solution-processable oxide semiconductors for TFT applications.

Silicone-Based Adhesives with Highly Tunable Adhesion Force for Skin-Contact Applications

A fundamental approach to fabricating silicone-based adhesives with highly tunable adhesion force for the skin-contact applications is presented. Liquid blends consisting of vinyl-multifunctional polydimethylsiloxane (V-PDMS), hydride-terminated PDMS (H-PDMS), and a tackifier composed of a silanol-terminated PDMS/MQ resin mixture and the MQ resin are used as the adhesive materials. The peel adhesion force of addition-cured adhesives on the skin is increased by increasing the H-PDMS molecular weights and the tackifier content, and decreasing the H-PDMS/V-PDMS ratio. There is an inverse relationship between the adhesion force and the Youngs modulus. The low-modulus adhesives with a low H-PDMS/V-PDMS ratio exhibit enhanced adhesion properties. The low-modulus adhesives with the high MQ resin content show significantly enhanced adhesion properties. These adhesives exhibit a wide range of modulus (2-499 kPa), and their adhesion force (0.04-5.38 N) is superior to commercially available soft silicone adhesives (0.82-2.79 N). The strong adhesives (>≈2 N) provide sufficient adhesion for fixing the flexible electrocardiogram (ECG) device to the skin in most daily activity. The human ECG signals are successfully recorded in real time. These results suggest that the silicone-based adhesives should be useful as an atraumatic adhesive for the skin-contact applications.

Integrated Flexible Electronic Devices Based on Passive Alignment for Physiological Measurement

This study proposes a simple method of fabricating flexible electronic devices using a metal template for passive alignment between chip components and an interconnect layer, which enabled efficient alignment with high accuracy. An electrocardiogram (ECG) sensor was fabricated using 20 µm thick polyimide (PI) film as a flexible substrate to demonstrate the feasibility of the proposed method. The interconnect layer was fabricated by a two-step photolithography process and evaporation. After applying solder paste, the metal template was placed on top of the interconnect layer. The metal template had rectangular holes at the same position as the chip components on the interconnect layer. Rectangular hole sizes were designed to account for alignment tolerance of the chips. Passive alignment was performed by simply inserting the components in the holes of the template, which resulted in accurate alignment with positional tolerance of less than 10 µm based on the structural design, suggesting that our method can efficiently perform chip mounting with precision. Furthermore, a fabricated flexible ECG sensor was easily attachable to the curved skin surface and able to measure ECG signals from a human subject. These results suggest that the proposed method can be used to fabricate epidermal sensors, which are mounted on the skin to measure various physiological signals.

Integrated optical refractometer based on bend waveguide with air trench structure

This study proposed a novel optical sensor based on a refractometer integrating a bend waveguide and a trench structure. The optical sensor is a planar lightwave circuit (PLC) device involving a bend waveguide with maximum optical loss. A trench structure was aligned with the partially exposed core layer’s sidewall of the bend waveguide, providing a quantitative measurement condition. The insertion losses of the proposed 1 x 2 single-mode optical splitter-type sensor were 4.38 dB and 8.67 dB for the reference waveguide and sensing waveguide, respectively, at a wavelength of 1,550 nm. The optical loss of the sensing waveguide depends on the change in the refractive index of the material in contact with the trench, but the reference waveguide had stable optical propagating characteristic regardless of the variations of the refractive index.

Design of integrated refractive index sensor based on bend waveguide with a trench structure

This study proposes a novel optical sensor structure based on a refractometer integrating a bend waveguide and an air trench. The optical sensor consists of a U-bend waveguide connecting four C-bends and a trench structure to expose the partial core layer. The U-bend waveguide consists of one C-bend with the maximum optical loss and three C-bend with minimum losses. A trench provides a quantitative measurement environment, and is aligned with the sidewall of a C-bend having the maximum loss. The intensity of the output power is dependent on the change of refractive index of the measured material.