Tae-Jun Ha

Waterproof Electronic-Bandage with Tunable Sensitivity for Wearable Strain Sensors

We demonstrate high-performance wearable electronic-bandage (E-bandage) based on carbon nanotube (CNT)/silver nanoparticle (AgNP) composites covered with flexible media of fluoropolymer-coated polydimethylsiloxane (PDMS) films. The E-bandage can be used for motion-related sensors by directly attaching them to human skin, which achieves a fast and accurate electric response with high sensitivity according to the bending and stretching movements that induce changes in the conductivity. This advance in the E-bandage is realized as a result of the sensitivity that can be achieved by controlling the concentration of AgNPs in CNT pastes and by modifying the device architecture. The fluoropolymer encapsulation with hydrophobic surface characteristics allows for the E-bandage to operate in water and protects it from physical and chemical contact with the daily life conditions of the human skin. The reliability and scalability of the E-bandage as well as the compatibility with conventional microfabrication allow new possibilities to integrate flexible human-interactive nanoelectronics into mobile health-care monitoring systems combined with Internet of things (IoTs).

High-Performance Single-Walled Carbon Nanotube-Based Thin-Film Transistors by Reducing Charge Transfer

We demonstrate high-performance single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) using the simple and robust method of an interacting fluoropolymer encapsulation with thermal annealing in vacuum to reduce the charge transfer. With an optimized combination of the fabrication process and the device configuration, drop-casted SWCNT-TFTs exhibit a field-effect mobility of ~18 cm2/V · s in the linear regime, an ON-OFF-current ratio of ~106, a threshold voltage of around 0 V, and a subthreshold swing of 97 mV/decade, which is among the best results that have been achieved in 2-D random networks of the SWCNTs. We also investigate the instability characteristics in the SWCNT-TFTs encapsulated with fluoropolymer during the prolonged electrical bias-stress. Interestingly, the drop in drain current of the SWCNT-TFTs was partially recovered with a second phenomenon that increases the drain current after a certain time. The hydrophobic surface that the fluoropolymer film possesses, reduced the chemical interaction of charge carriers with the hydroxyl (-OH) functional groups which act as defects in the SWCNT-TFTs.

Functionalized Carbon Nanotube Sensors for the Detection of Sub-ppm Nitric Oxide Gas

In this paper, we demonstrate the highly sensitive carbon nanotube (CNT) sensors for the detection of sub-ppm nitric oxide (NO) gas operating at room temperature. Such achievement can be realized by functionalizing CNT thin films with amine-based polymers through a solution-process technology at low temperature. In addition to high sensitivity, functionalized CNT sensors exhibit high selectivity towards NO gas, which is an effective and practical factor for health-care monitoring nano-electronics. We also investigated the effect of a post-cleaning treatment on the sensing performance of functionalized CNT thin films for sub-ppm NO gas sensors. We believe that this work can open-up new routes to realize high performance human-interactive electronics for respiratory diseases detection in exhaled air.

Characteristics of Low-Temperature Solution-Processed Boron Nitride Thin Films for Flexible Nanoelectronics

In this study, we demonstrate the characteristics of high quality boron nitride (BN) thin films for high performance 2 dimensional nanoelectronics. Such thin films were deposited using solution-pro ...

Hybrid Graphene/Fluoropolymer Field-Effect Transistors With Improved Device Performance

We demonstrate high-performance field-effect transistors consisting of hybrid graphene/fluoropolymer films by investigating the molecular interaction with strong carbon-fluorine dipoles and hydrophobic surface characteristics. A simple and reproducible solution-coating method on a chemical vapor deposition grown monolayer graphene was employed with fluoropolymer, amorphous CYTOP, and polycrystalline poly(vinylidene fluoride-co-trifluoroethylene) as an interacting layer. All of the key device metrics, including field-effect mobility, Dirac voltage, residual carrier concentration, ON-OFF current ratio, and electron-hole transport symmetry, were substantially improved. Significantly, the Dirac voltage shifted in both directions toward zero, regardless of its initial positions of the Dirac voltage after molecular encapsulation with fluoropolymers. We also demonstrate the improved stability of hybrid graphene/fluoropolymer films that possesses a hydrophobic surface through repelling hydroxyl (-OH) functional groups from the graphene surface.