강대환 교수

A one-dimensional heat conduction model is developed for a phase change random access memory device with an 8F2 memory cell structure (F=0.15 μm). The required current level for a reset operation, which corresponds to the phase switching from a crystalline (“1” state) to an amorphous phase (“0” state) of Ge2Sb2Te5, was investigated by calculating one-dimensional temperature profiles for the memory cell structure. It is revealed that a reset operation is not achieved at the current level (2 mA) r

Fluctuations (or drifts) in switching voltages such as programming set/reset voltages and threshold voltage pose serious obstacles to the reliable operation of electrical phase change memory devices. Using a phase change memory device having a GeSb2Te4 phase change material and TiN electrode, these fluctuations are demonstrated to result from device resistances varying with programming cycles. Fluctuating resistances appear to stem primarily from large contact resistances at the interface betwee

The electrical switching behaviors of an offset-type phase change memory device with a highly resistive TiON layer were investigated, where the TiON layer (7 nm thick) was formed at a 70 nm wide contact between Ge 1 Sb 2 Te 4 and TiN layers. Reversible transitions between crystalline (set) and amorphous (reset) phases were found to occur at relatively lower reset and set voltages, as compared with a device having no TiON layer. These results hold a high promise for a low-power operation of a pha

The spike-timing dependent plasticity (STDP) of biological synapses, which is known to be a function of the formulated Hebbian learning rule of human cognition, learning and memory abilities, was emulated with two-phase change memory (2-PCM) cells built with 39 nm technology. For this, we designed a novel time-modulated voltage (TMV) scheme for changing the conductance of 2-PCM cells, that could produce both long-term potentiation (LTP) and long-term depression (LTD) by applying variable (decrea

The power-coupling mode was changed from a capacitively coupled (E-mode) to an inductively coupled (H-mode) with an increase of rf input power in an immersed-coil-type inductively coupled Ar discharge at 1 mTorr. It was identified that the bimodal-shaped ion energy distribution (IED) of the capacitively coupled discharge was dominant below 100 W (E-mode), while the single peak due to the inductively coupled discharge became dominant above 250 W (H-mode). In addition, it was possible to quantitat

The aim of this study is to prepare pH- and redox-sensitive nanoparticles for doxorubicin (DOX) delivery against DOX-resistant HuCC-T1 human cholangiocarcinoma (CCA) cells. For this purpose, L-histidine methyl ester (HIS) was attached to chitosan oligosaccharide (COS) via dithiodipropionic acid (abbreviated as ChitoHISss). DOX-incorporated nanoparticles of ChitoHISss conjugates were fabricated by a dialysis procedure. DOX-resistant HuCC-T1 cells were prepared by repetitive exposure of HuCC-T1 ce

We experimentally demonstrate that the crystallization process of Ge-Sb-Te crystallites during the set operation in non-volatile phase change memory commences after threshold switching event. It is also shown that the nucleation and growth rates have opposite behaviors with the increase of set operation power: the incubation time in nucleation stage can be minimized at higher power, whereas the percolation time in growth stage is smaller at lower power. Based on these results, we introduce a two

The amorphous hydrogenated carbon (a-C:H) films were deposited on (100) silicon substrates using a divergent Ar+CH4 electron cyclotron resonance plasma. During the deposition sequence, the rf bias was applied to the substrate to increase the ion bombardment energy. The results of the microhardness test and the Raman spectroscopy revealed that these films showed abrupt changes in the mechanical properties and in the bonding characteristics from polymerlike to diamondlike when the rf substrate bia

The effects of the aluminum nitride coating thickness on molybdenum emitter tips were investigated by an in situ I–V measurement technique inside a typical magnetron sputtering system. AlN was deposited on Mo tips using a dc-modulated 1 kW power source at 200 °C. Each I/V measurement was carried out immediately following a 15 s AlN deposition. Significantly improved field emission was observed as well as a strong emission thickness dependence, which we attribute to the influence of space charge.

We synthesized a block copolymer composed of dextran and methoxy poly(ethylene glycol) (mPEG). To accomplish this, the end group of dextran was modified by reductive amination. The aminated dextran (Dextran‐NH 2 ) showed the intrinsic peaks of both dextran at 3~5.5 ppm and hexamethylene diamine at 1~2.6 ppm at 1 H nuclear magnetic resonance (NMR) spectrum. The amino end group of dextran was conjugated with mPEG to make the block copolymer consisting of dextran/mPEG (abbreviated as DexPEG). The s

The aim of this study is to fabricate nanophotosensitizers composed of methoxy poly(ethylene glycol) (mPEG), chlorin e6 (Ce6), and phenylboronic acid pinacol ester (PBAP) with diselenide linkages for reactive oxygen species (ROS)-sensitive photodynamic therapy (PDT) of cervical cancer cells. To fabricate nanophotosensitizers, Ce6 was conjugated with mPEG via selenocystamine linkage and then remaining carboxylic acid groups of Ce6 was attached to PBAP (mPEGseseCe6PBAP conjugates). Nanophotosensit