Jung-hyun Lee

Improvement of CBRAM Resistance Window by Scaling Down Electrode Size in Pure-GeTe Film

TaN-pure-GeTe-Cu bipolar switching devices which can be adaptable to semiconductor processes were fabricated as a function of top-electrode sizes (0.2, 0.4, 10, and 50 mum). The on/off resistance change ratio increased highly with decreasing electrode size. In particular, the on/off resistance change ratio was about 103 when the electrode size was scaled down to 200 nm. We obtained the characteristics of conductive bridging memory cell using pure-GeTe film without any doping of Cu or Ag; we also determined the reason for the enhancement of the on/off resistance change ratio when scaling down the electrode size.

A symmetric metamaterial element-based RF biosensor for rapid and label-free detection

A symmetric metamaterial element-based RF biosensing scheme is experimentally demonstrated by detecting biomolecular binding between a prostate-specific antigen (PSA) and its antibody. The metamaterial element in a high-impedance microstrip line shows an intrinsic S21 resonance having a Q-factor of 55. The frequency shift with PSA concentration, i.e., 100 ng/ml, 10 ng/ml, and 1 ng/ml, is observed and the changes are Δf ≈ 20 MHz, 10 MHz, and 5 MHz, respectively. The proposed biosensor offers advantages of label-free detection, a simple and direct scheme, and cost-efficient fabrication.

Asymmetric split-ring resonator-based biosensor for detection of label-free stress biomarkers

In this paper, an asymmetric split-ring resonator, metamaterial element, is presented as a biosensing transducer for detection of highly sensitive and label-free stress biomarkers. In particular, the two biomarkers, cortisol and α-amylase, are used for evaluating the sensitivity of the proposed biosensor. In case of cortisol detection, the competitive reaction between cortisol-bovine serum albumin and free cortisol is employed, while alpha-amylase is directly detected by its antigen-antibody reaction. From the experimental results, we find that the limit of detection and sensitivity of the proposed sensing device are about 1 ng/ml and 1.155 MHz/ng ml−1, respectively.

Low temperature crystallization of high permittivity Ta oxide using an Nb oxide thin film for metal/insulator/metal capacitors in dynamic random access memory applications

(Ta1−xNbx)2O5 as the dielectric for metal/insulator/metal capacitors with Ru electrodes were investigated. Deposition was performed by ALD using tantalum ethoxide, niobium ethoxide, and ozone as source materials. The high-κ dielectric layer was synthesized from a binary layer (Ta2O5∕Nb2O5) with self-diffusion of the seed layer, Nb2O5. The seed layer becomes effective at a thickness of over 60 A. The dielectric deposited with 60 A Nb2O5 crystallized at 575 °C, the lowest processing temperature required to achieve good step-coverage (86%) for future generation dynamic random access memory. A capacitance density of about 23.0fF∕μm2 was observed for seed layers of 20 and 35 A. Capacitors with a Nb2O5 seed layer of 60 A achieved a capacitance density as high as 44.2fF∕μm2. The reason for this disparity is that the thicker insulator crystallizes at a post-annealing temperature of 575 °C. The leakage current measured at 1 V was moderately low, near 1×10−7A∕cm2.

A robust digital timing recovery with asymmetry compensator for high speed optical drive systems

This paper presents a new four-sampled zero crossing asymmetry compensation algorithm for high-speed DVD/CD applications. Simulations show 34% improvement of jitter performances, 50% reduction of compensation time and 2.0 dB gain of bit error rate (BER) compared with other algorithms. Simultaneously, a new digital timing recovery scheme for the optical drive system is presented. By comparative simulations using DVD patterns with marginal input conditions, the proposed timing recovery algorithm shows enhanced performances in jitter variance and SNR margin by 4 times and 3 dB respectively.

Advanced PRML data detector for high density recording

An advanced PRML data recovery system is presented for a high-density recording. The system consists of three major hardware units, which are DC offset compensator, adaptive equalizer, and Viterbi detector with level adaptation scheme. The experiment based on an improved PRML scheme and FPGA hardware realization shows highly reliable performance of data detection up to 35GB recording density. The SER experiment result for 35GB shows that the detector using the proposed PRML yields a result to meet the SER limit of 4.0x10-3 with a margin of 0.45° for tangential and 0.55° for radial tilt. And the base SER marks 7.0x10-5 when there is no tangential and radial tilt error.

Comprehensive chromosome analysis of blastocysts before implantation using array CGH

BackgroundChromosomal abnormalities are common in embryos produced in vitro and cause implantation failure, miscarriage, and serious medical problems in infants. Because preimplantation genetic screening (PGS) is increasingly being used to detect aneuploidy in embryos with the purpose of improving implantation rates after IVF (in vitro fertilization), we aimed to validate the usefulness of array CGH for the preimplantation genetic screening (PGS) of embryos at the blastocyst stage of development.ResultsA total of 150 blastocysts were biopsied from couples undergoing IVF and analyzed using array CGH. We found that 54.5% (73/134) of the blastocysts were euploid embryos, whereas 45.5% of the embryos (61/134) had chromosomal abnormalities. Multiple chromosome abnormality was most frequently observed (34.4%), and dual aneuploidy was observed in 26.2% of the embryos. Monosomy (21.3%) appeared more frequently than trisomy (18%).ConclusionChromosomal microarray analysis provided clinically significant cytogenetic information regarding the frequency and variety of chromosomal abnormalities observed in embryos at the blastocyst stage, suggesting that this is a useful tool for comprehensive aneuploidy screening in IVF.

Highly Conductive and Transparent Poly(3,4-ethylenedioxythiophene):p-Toluene Sulfonate Films as a Flexible Organic Electrode

Highly transparent and conductive poly(3,4-ethylenedioxythiophene):p-toluene sulfonate (PEDOT:PTS) films were prepared by gas-phase polymerization using the chemical vapor deposition (CVD) technique for flexible organic electrodes. These conductive PEDOT:PTS films have a high transparency (up to 80%), and possess a very low sheet resistance of a 100 Ω/ (up to 2500 S cm-1) at 150 nm thickness. Their sheet resistance attained 27 Ω/ at 350 nm thickness with O2 plasma doping. The 1–3 mm pitched pattern can also be easily formed by plasma etching and/or the selective exposure technique of O2 plasma. This electrode film has a higher transmittance than an amorphous indium–tin oxide (a-ITO) electrode film with thickness under 120 nm, and their conductivities were comparable with the a-ITO layer. We report on the fabrication and characterization of a flexible organic light-emitting diode (OELD) using PEDOT:PTS for the electrodes. The device is demonstrated to exhibit light emission and a brightness level up to 1800 cd/m2 at 25 V.

Multibit memories using a structure of SiO2/partially oxidized amorphous Si∕HfO2

Memory capacitors with a structure of SiO2/partially oxidized amorphous Si (a-Si)/HfO2 have been prepared by sequential processes: atomic layer deposition (ALD) of 6nm a-Si on 3.5nm SiO2, thermal oxidation at 900°C, and another ALD of 12nm HfO2. The memory devices offer hybrid type of charge memory: the interface states of partially oxidized a-Si∕SiO2 tend to act as hole traps, resulting in a negative shift of flatband voltage in capacitance-voltage (C-V) curve, and the partially oxidized a-Si∕HfO2 interface has dominantly electron-trap centers, leading to a positive voltage shift. By this hybrid effect, the memory window in C-V curve is observed to be enlarged enough to realize four-level (2bit) memories, which is demonstrated through measurements of program/erase speeds and charge-loss rates.

Preparation of Pb(ZrxTi1 - x)O3 Films on Trench Structure for High-Density Ferroelectric Random Access Memory

The growth characteristics of Pb(ZrxTi1 - x)O3 thin films on three-dimensional (3D) electrodes were investigated for the application to high-density ferroelectric random access memory (FeRAM) devices. PZT films have been grown on Ir coated trench structures having aspect ratio of 1.2 by liquid delivery-metal organic chemical vapor deposition (LD-MOCVD). Atomic layer deposited (ALD) Ir electrode showed good step coverage and electrical properties. MOCVD PZT films showed step coverage of 90% at the deposition temperature of 500°C, while it is decreased to 63% at 550°C. Compositional non-uniformity of PZT along the sidewall was greatly affected by the types of the metal organic sources.