Hyobong Ryu

A stretchable humidity sensor based on a wrinkled polyaniline nanostructure

A humidity sensor has received great interest in sensor fields because of their various applications. Especially, a stretchable humidity sensor which has mechanical stability has remained challenging issue in stretchable electronics. Here, we report a novel stretchable nanostructured polyaniline humidity sensor. The sensor was fabricated by simple fabrication methods such as pre-stretching process and self-assembly texturing process. The periodically wrinkled structure supported by microstructured elastomeric substrates provides an excellent stretchability. The micro-textured substrate was introduced for solving crack problem by Poisson effect as a stretchable sensor. The sensor maintains its humidity sensitivity well at the differed elongations. To the best our knowledge, this is the first report for a stretchable humidity sensor.

Fabrication and Calibration of pH Sensor Using Suspended CNT Nanosheet

In this research, the pH sensor was developed using CNT nanosheet with Nafion coating for the advanced medical sensor such as a blood gas analyzer. The CNT nanosheet was formed by dielectrophoresis and water-meniscus between cantilever-type electrodes. Then, the process of the heat annealing and the Nafion coating was conducted for reducing contact resistance and giving proton selectivity respectively. We measured the response of the pH sensor as the electrolyte-gated CNT-nanosheet field effect transistor. The sensor showed a linear current ratio in a similar range of the normal blood pH. A calibration method for decreasing of the response variation among sensors has also been introduced. Coefficient of variance of the pH sensor was decreased by applying the calibration method. A linear relation between the calibrated response of the sensors and pH variance was also obtained. Finally, the pH sensor with a high resolution was fabricated and we verify the feasibility of the sensor by applying the calibration method.

Advanced glass etching method exhibiting the controllable etch stop using metal etchant

The limitations of conventional glass etching methods are a bottleneck in the further development of glass as a substrate, which is critically important in micro- and nanoelectromechanical systems. In this paper, we describe a new wet etching method for Pyrex glass using a metal etchant. An aluminum pattern is deposited on the Pyrex and then subjected to thermal and electrostatically induced interdiffusion to form an aluminum-rich layer of controllable thickness in the glass, which can then be etched with an aluminum etchant. Because the underlying glass acts as an etch stop, no etching mask is required and the etching depth is effectively controlled by the electric field strength. This method can be used for fabricating glass nanochannels and nanodepth structures, and also in processes incompatible with hydrogen fluoride.

Fabrication of carbon nanotube bridge in V-groove channel using Dielectrophoresis

Since their discovery in 1991, Carbon nanotubes (CNTs) are known to have unique electrical, mechanical and thermal properties and have been used at many applications. For using at applications, the manipulation of the CNTs is very important. Recently, Dielectrophoresis has attracted much interest for CNTs alignment and deposition on a desirable location, but all the work have been done on plane electrodes. In this work, We propose a novel fabrication method of carbon nanotube bridge in V-groove channel using dielectrophoresis. Compared to the case using plane electrode, this method has several advantages. The electrodes in V-groove channel provide high and parallel electric field and eliminate nonspecific CNTs deposition so that efficiency of CNTs alignment increases. V-groove channel was fabricated on silicon wafer by TMAH bulk etching. The gold electrodes were deposited in V-groove channel. To prepare the SWNTs suspension, SWNTs were dispersed in DI water with 0.1 wt% sodium dodecyl sulfate by sonication. A drop of suspension was introduced onto the electrodes and ac voltage was applied. When SWNTs alignment on a electrodes in V-groove is compared with that on a plane electrodes, SWNTs were aligned to electric field direction and formed SWNTs bundle bridges cross V-groove channel. These carbon nanotube bridges have diameter of 0.5-2 mum and length of 5~20 mum. We think that this phenomenon was happened by 3D electric field in V-groove channel. Because these bridges had regular shape and wide contact areas, these bridges can have uniform electric properties and lower contact resistance, but the phenomenon need a further theoretically studies. SWNTs bridges can be used in various sensors. Because sensor bridges were away from surface, effects of surface reduced and signal to noise ratio increased. High surface areas of SWNTs bridges can improve sensitivity of sensors, and embedded SWNTs bridges in microchannel can be easily used at various microfluidic applications without additional work.

Evaluation of Electrospun TiO2/PVP/LiCl Nanofiber Array for Humidity Sensing

Abstract Recently, tremendous application utilizing electrospun nanofibers have been actively reported due to its several advantages, such ashigh surface to volume ratio, simple fabrication and high-throughput manufacturing. In this paper, we developed highly sensitive andconsistent nanofiber humidity sensor by electrospinning. The humidity sensor was fabricated by rapid electrospinning (~2 sec) TiO 2 /PVP/LiCl mixed solution on the micro-interdigitated electrode. In order to evaluate the humidity sensing performances, we measuredcurrent response using DC bias voltage under various relative humidity levels. The results show fast response / recovery time and mar-ginal hysteresis as well as long-term stability. In addition, with the aid of micro-interdigitated electrode, we can reduce a total resistanceof the sensor and increase the total reaction area of nanofibers across the electrodes resulting in high sensitivity and enhanced currentlevel. Therefore, we expect that the electrospun nanofiber array for humidity sensor can be feasible and promising for diverse humiditysensing application.