Byeongju Kim

Direct printing of aligned carbon nanotube patterns for high-performance thin film devices

The aligned assembly of carbon nanotubes (CNTs) on substrate presents a significant bottleneck in the fabrication of high-performance thin film devices. Here, we report a direct printing method to prepare laterally aligned thick CNT patterns over large surface regions. In this method, CNT forests were grown selectively on specific regions of one substrate, and the forest patterns were transferred on another SiO2 substrate in a laterally aligned formation while keeping their original shapes. The degree of alignment was characterized via electrical measurement and polarized Raman spectroscopy. Furthermore, we demonstrated high-performance field-effect transistors and gas sensors using our method.

Highly selective and sensitive detection of neurotransmitters using receptor-modified single-walled carbon nanotube sensors

We present receptor-modified carbon nanotube sensors for the highly selective and sensitive detection of acetylcholine (ACh), one kind of neurotransmitter. Here, we successfully expressed the M1 muscarinic acetylcholine receptor (M1 mAChR), a family of G protein-coupled receptors (GPCRs), in E. coli and coated single-walled carbon nanotube (swCNT)-field effect transistors (FETs) with lipid membrane including the receptor, enabling highly selective and sensitive ACh detection. Using this sensor, we could detect ACh at 100 pM concentration. Moreover, we showed that this sensor could selectively detect ACh among other neurotransmitters. This is the first demonstration of the real-time detection of ACh using specific binding between ACh and M1 mAChR, and it may lead to breakthroughs for various applications such as disease diagnosis and drug screening.

An Analytic Current–Voltage Equation for Top-Contact Organic Thin Film Transistors Including the Effects of Variable Series Resistance

An analytic current?voltage (I?V) equation for top-contact organic thin film transistors (OTFTs) is derived by analyzing the channel and the overlap region separately. From the analysis on the overlap region, the series resistance of OTFTs is found to be a function of the gate voltage due to the sheet resistance change of the accumulation layer. Using the derived I?V equation, the characteristics of both the channel and the overlap region are well-explained. The I?V equation is verified with fabricated top-contact OTFTs and metal?insulator?semiconductor (MIS) capacitors, and the predicted I?V characteristics from the equation agree well with the measurements. Also, the ratio of the series resistance to the total resistance of the device is up to 60% which shows significant influence of the series resistance on top-contact OTFT performance.

Nanoneedle transistor-based sensors for the selective detection of intracellular calcium ions.

We developed a nanoneedle transistor-based sensor (NTS) for the selective detection of calcium ions inside a living cell. In this work, a single-walled carbon nanotube-based field effect transistor (swCNT-FET) was first fabricated at the end of a glass nanopipette and functionalized with Fluo-4-AM probe dye. The selective binding of calcium ions onto the dye molecules altered the charge state of the dye molecules, resulting in the change of the source-drain current of the swCNT-FET as well as the fluorescence intensity from the dye. We demonstrated the electrical and fluorescence detection of the concentration change of intracellular calcium ions inside a HeLa cell using the NTS.

Electrically Stable Organic Thin-Film Transistors and Circuits Using Organic/Inorganic Double-Layer Insulator

Pentacene-based organic thin-film transistors (OTFTs) and organic circuits are fabricated using a plasma-enhanced chemical vapor deposition (PECVD) SiO2/cross-linked poly(vinyl alcohol) (PVA) double-layer insulator. A considerable reduction in hysteresis is achieved by optimizing the double-layer insulator thickness. The main mechanism of a low hysteresis is attributed to the balance of the injected electrons and induced holes at the interface. The fabricated devices have several advantages including low hysteresis characteristics and a stable performance. On the basis of the proposed OTFTs, an electrically stable organic inverter and a buffer working at a frequency as high as 1 kHz are fabricated.

Uniform patterning of sub-50-nm-scale Au nanostructures on insulating solid substrate via dip-pen nanolithography.

We report a direct deposition strategy for sub-50-nm-scale uniform Au patterns on virtually any general insulating substrate via dip-pen nanolithography (DPN). In that process, HAuCl(4) molecules were deposited onto bare insulating substrates via a molecular diffusion process, in the absence of electrochemical reactions. Subsequently, the generated HAuCl(4) molecular patterns were decomposed to leave Au-only patterns using a thermal annealing process. Uniform Au patterns with a mean diameter of 47.9 +/- 3.1 nm were achieved after the annealing process. The strategy allowed us to generate Au patterns on virtually any general insulating substrate (e.g., SiO(2), Al(2)O(3), polyimide, etc) without the need for surface functionalization or additional electrode structures. This versatile and reliable patterning method is expected to be useful in the future development of various novel industrial applications (e.g., mask or nanocircuit repair, nanosensors, etc.).

A novel gated transmission line method for organic thin film transistors

Gated transmission line method (gated TLM) has been widely used to analyze the series resistance (Rsd) of organic thin film transistors (OTFTs). However, for organic thin film transistors (OTFTs), usually the crossing points at the second quadrant do not meet at one point, so it is hard to determine the coefficients. On the highly doped silicon substrate, 35 nm-thick thermal oxide and 10 nm-thick dilute PMMA make the insulator.

Considerations on the C-V Characteristics of Pentacene Metal-Insulator-Semiconductor Capacitors

C-V characteristics of pentacene MIS capacitors are obtained with various measurement conditions. High measuring frequency can decrease the measured capacitance due to the slow response of holes. When thick semiconductor is used, accurate C-V characteristics can not be obtained due to the resistance of bulk semiconductor. Bias stress makes positive or negative flat band voltage shift, also complicate accurate C-V measurement. Therefore, to obtain reliable C- V characteristics of organic MIS capacitors, these properties should be considered.

Temporal Noise Analysis and its Reduction Method in CMOS Imager Readout Circuit

Bong Chan Kim, Jongwook Jeon, and Hyungcheol Shin Inter-university Semiconductor Research Center(ISRC) and School of Electrical Engineering, Seoul National University, San 56-1, Shinlim-dong, Kwanak-gu, Seoul 151-742, Korea Phone: +82-2-880-7282, e-mail: bchan11@snu.ac.kr

Performance Improvement of OTFTs using Double Layer Insulator

Organic thin-film transistors (OTFTs) with improved performance are fabricated using SiO2-cross-linked PVA double layer insulator. The improved field- effect mobility, on-current, off-current, on/off ratio, and subthreshold slope are 0.12 cm2/V-sec, 9.2times10-6 Aring, 2times10-12 Aring, 4.6times106, and 0.4 V/dec, respectively. In addition, a negligible threshold voltage shift is observed in the device. The performance improvements are attributed to good leakage characteristic of SiO2 and high-k characteristic of cross- linked PVA. Based on the proposed OTFTs, an organic inverter working as high as 1 kHz is implemented.