Kyung-hyun Kim

A Carbon Nanotube Synapse with Dynamic Logic and Learning

A carbon nanotube (CNT) synapse emulates a biological synapse with its dynamic logic, learning, and memory functions induced by the interactions between CNTs and hydrogen ions in an electrochemical cell. A circuit of CNT synapses operates with extremely low-energy consumption and could potentially emulate the functions of the neuronal network.

Intense pulsed light induced platinum-gold alloy formation on carbon nanotubes for non-enzymatic glucose detection

We demonstrated a novel method for the formation of alloy nano-islands on carbon nanotube (CNT). The two metal layers (Pt, Au) were sputtered on CNTs and the intense pulsed light (IPL) was irradiated on the metal layers. The absorbed light provides enough energy for the diffusion mixing between Pt and Au, forming Pt-Au alloy phase. While the alloy is being formed by the IPL irradiation, the metal layers are broken into nano-islands on CNT due to the surface energy minimization between the metal layers and CNT. The surface characterizations of the Pt-Au/CNT were performed with X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectroscopy. Different compositions of alloy nanoparticles were obtained by adjusting the deposition thicknesses of Pt and Au on CNT. Pt50Au50/CNT electrode showed the highest glucose oxidation current peak among Pt, Pt70Au30, Pt50Au50, Pt30Au70, and Au/CNT electrodes while the electroactive surface areas of them are kept to be similar (average surface area=7.00 cm2, coefficient of variation=0.06). The amperometric response of Pt50Au50/CNT electrode to the glucose concentrations showed a wide linear range up to 24.44 mM with a high detection sensitivity of 10.71 μA mM(-1) cm(-2). Reproducibility and long-term stability of the Pt-Au/CNT electrode were also proven in the experiments.

Delamination Growth in Angle-Ply Laminated Composites

Delamination, a frequently observed failure mode in composite laminate, is a key issue in structural design and integrity consideration. In this paper, the stability of delamination crack is investigated for angle-ply laminates subjected to uniform displacement and ther mal loading. Due to the complexities of the problem, a quasi three-dimensional finite ele ment method is used to obtain strain energy release rate. The effect of parameters, such as temperature drop, loading type, stacking sequence, laminate width and laminate thick ness will be considered. Also, the effect of delamination crack on the tensile strength of angle-ply laminate for small fiber orientation is evaluated by using a rule of mixtures and energy release rate concept in classical fracture mechanics. Finally, failure mode and ten sile strength are predicted and compared with known experimental data to assess the pre diction accuracy of the delamination growth model.

Analog neuromorphic module based on carbon nanotube synapses.

We report an analog neuromorphic module composed of p-type carbon nanotube (CNT) synapses and an integrate-and-fire (I&F) circuit. The CNT synapse has a field-effect transistor structure with a random CNT network as its channel and an aluminum oxide dielectric layer implanted with indium ions as its gate. A positive voltage pulse (spike) applied on the gate attracts electrons into the defect sites of the gate dielectric layer, and the trapped electrons are gradually released after the pulse is removed. The electrons modify the hole concentration and induce a dynamic postsynaptic current in the CNT channel. Multiple input spikes induce excitatory or inhibitory postsynaptic currents via excitatory or inhibitory CNT synapses, which flow toward an I&F circuit to trigger output spikes. The dynamic transfer function between the input and output spikes of the neuromorphic module is analyzed. The module could potentially be scaled up to emulate biological neural networks and their functions.

A modular expandable tactile sensor using flexible polymer

In this paper, we have proposed and demonstrated a modular expandable tactile sensor using PDMS elastomer. A sensor module consists of 16 /spl times/ 16 tactile cells with 1 mm spatial resolution, similar to that of human skin, and interconnection lines for expandability. Tactile response of a cell has been measured with a force gauge. Initial capacitance of each cell is about 180 fF. The fabricated cell shows a sensitivity of 3%/mN within the full scale range of 40 mN (250 kPa). Four tactile modules have been successfully attached by using ACP to demonstrate expandability. Various tactile images have been successfully captured by one sensor module as well as the expanded 32 /spl times/ 32 modular array sensors.

Nonvolatile Analog Memory Transistor Based on Carbon Nanotubes and C60 Molecules

A nonvolatile analog memory transistor is demonstrated by integrating C60 molecules as charge storage molecules in the transistor gate, and carbon nanotubes (CNTs) in the transistor channel. The currents through the CNT channel can be tuned quantitatively and reversibly to analog values by controlling the number of electrons trapped in the C60 molecules. After tuning, the electrons trapped in the C60 molecules in the gate, and the current through the CNT channel, can be preserved in a nonvolatile manner, indicating the characteristics of the nonvolatile analog memory.

CHAMPS (chemical-mechanical planarization simulator)

Simulation of chemical-mechanical polishing is important because the chip-level planarity and wafer-level uniformity dependent on many dynamic factors are difficult to control. CHAMPS (chemical mechanical planarization simulator) has been developed for predicting and optimizing the thickness distribution after the CMP process using the chip level pattern density and an elastic spring model including equipment parameters. In this work, the results of CMP simulation are shown to agree well with the measured data. This simulator can be used to optimize CMP process conditions and to generate design rules for filling dummy patterns which are used to improve planarity and uniformity.

Highly manufacturable 1 Gb NAND flash using 0.12 /spl mu/m process technology

An 1 Gb NAND flash memory has been successfully developed by integrating new technologies, inverse narrow-width effect (INWE) suppression scheme, 32-cell NAND flash combined with the scaling-down of tunnel oxide, inter-poly ONO, and gate poly re-oxidation. It is implemented using KrF photolithography along with a resolution enhancing technique, the planarized surface by etch-back and CMP processes, highly selective contact etching and nonoverlapped dual damascene metallization. Thus, for the first time, a 1 Gb NAND flash memory with mass-producible chip size of 132 mm/sup 2/, lower Vcc operation below 1.8 V and lower power consumption, has been obtained.

A miniaturized low-power wireless remote environmental monitoring system using microfabricated electrochemical sensing electrodes

In this paper we report a miniaturized low-power wireless remote environmental monitoring system. This system has been developed for the on-site monitoring of water pollution by heavy metal ions. The system is composed of an electrochemical sensor module using microfabricated electrodes for detecting heavy-metal contamination in sample water; a custom potentiostat module (including readout circuitry, analog-to-digital converter and microcontroller); and an RF module for sending detected signals to a base station through wireless communication.

Functionalized Carbon Nanotube Networks with Field‐Tunable Bandgaps

IO N The energy bandgap is an intrinsic property of semiconductors that plays a central role in modern device physics and technology. A tunable bandgap would be highly desirable because it would allow great fl exibility in applications. The carbon nanotubes (CNTs) have been considered as the material for the future nanoscale devices and circuits, but their applications are limited by their dispersed bandgaps. In this work, we demonstrate the realization of the fl exibly tunable CNT bandgaps controlled by electric fi elds in a fi eld-tinable transistor, which could lead to novel nanoelectronic and nanophotonic applications such as fi eld programmable logic, neuromorphic, and photovoltaic devices. The remarkable properties of carbon nanotubes (CNTs) have earned them intensive researches in nano-electronics and nano-optoelectronics, but their applications are still limited by their dispersed bandgaps. [ 1 ] Numerous efforts have been taken to modify the CNT bandgaps by synthetic conditions, [ 2–4 ] postsynthesis differentiation, [ 5 , 6 ] passing high currents, [ 7 ] applying mechanical strain, [ 8 ] plasma etching, [ 9 ] light irradiation, [ 10 ] and chemical functionalization. [ 11–16 ] However, it is impossible to completely eliminate the bandgap variations due to their intrinsic structural disparity. In this communication we report the realization of the fl exibly tunable bandgaps controlled by in situ electric fi elds in a fi eld-tunable transistor. An electrochemical cell with a polymer electrolyte is integrated in the transistor gate, and the CNT functionalization can be electrochemically tuned by gate voltages, which modifi es CNT bandgaps continuously and reversibly to nonvolatile values between 0 and 3.2 eV. The fi eld-tunable bandgaps could lead to novel nanoelectronic and nanophotonic applications such as fi eld programmable, [ 17 ]