Woo Young Choi

Bio: Woo Young Choi is an academic researcher from Sogang University. The author has contributed to research in topics: CMOS & Avalanche photodiode. The author has an hindex of 38, co-authored 495 publications receiving 6751 citations. Previous affiliations of Woo Young Choi include Seoul National University & University College of Engineering.

Tunneling Field-Effect Transistors (TFETs) With Subthreshold Swing (SS) Less Than 60 mV/dec

Abstract: We have demonstrated a 70-nm n-channel tunneling field-effect transistor (TFET) which has a subthreshold swing (SS) of 52.8 mV/dec at room temperature. It is the first experimental result that shows a sub-60-mV/dec SS in the silicon-based TFETs. Based on simulation results, the gate oxide and silicon-on-insulator layer thicknesses were scaled down to 2 and 70 nm, respectively. However, the ON/ OFF current ratio of the TFET was still lower than that of the MOSFET. In order to increase the on current further, the following approaches can be considered: reduction of effective gate oxide thickness, increase in the steepness of the gradient of the source to channel doping profile, and utilization of a lower bandgap channel material

Hetero-Gate-Dielectric Tunneling Field-Effect Transistors

Abstract: A tunneling field-effect transistor (TFET) is considered one of the most promising alternatives to a metal-oxide-semiconductor field-effect transistor due to its immunity to short-channel effects. However, TFETs have suffered from low on-current, severe ambipolar behavior, and gradual transition between on- and off -states. To address those issues, the authors have proposed hetero-gate-dielectric TFETs. The proposed device enhances on-current, suppresses ambipolar behavior, and makes abrupt on-off transition by replacing the source-side gate insulator with a high-k material, which induces a local minimum of the conduction band edge at the tunneling junction.

Demonstration of L-Shaped Tunnel Field-Effect Transistors

Abstract: An L-shaped tunnel FET (TFET), which features band-to-band tunneling (BTBT) perpendicular to the channel direction, is experimentally demonstrated for the first time. It is more scalable than other vertical-BTBT-based TFET designs and provides more than $1000\times $ higher ON-current ( $I_{{\mathrm{\scriptscriptstyle ON}}}$ ) than a conventional planar TFET with the same gate overdrive ( $V_{\mathrm{ov}}$ ) of 0.8 V, due to improved subthreshold swing ( $S$ ) and larger tunnel junction area. Its temperature dependence, constant $S$ , and nonlinear output characteristics are discussed.

Negative Capacitance in Organic/Ferroelectric Capacitor to Implement Steep Switching MOS Devices.

Abstract: Because of the “Boltzmann tyranny” (i.e., the nonscalability of thermal voltage), a certain minimum gate voltage in metal–oxide–semiconductor (MOS) devices is required for a 10-fold increase in drain-to-source current. The subthreshold slope (SS) in MOS devices is, at best, 60 mV/decade at 300 K. Negative capacitance in organic/ferroelectric materials is proposed in order to address this physical limitation in MOS technology. Here, we experimentally demonstrate the steep switching behavior of a MOS device—that is, SS ∼ 18 mV/decade (much less than 60 mV/decade) at 300 K—by taking advantage of negative capacitance in a MOS gate stack. This negative capacitance, originating from the dynamics of the stored energy in a phase transition of a ferroelectric material, can achieve the step-up conversion of internal voltage (i.e., internal voltage amplification in a MOS device). With the aid of a series-connected negative capacitor as an assistive device, the surface potential in the MOS device becomes higher than ...

All-optical signal up-conversion for radio-on-fiber applications using cross-gain modulation in semiconductor optical amplifiers

Abstract: The authors present a novel scheme of up-converting optical intermediate frequency (IF) signals with an optical local oscillator (LO) signal using cross-gain modulation in a semiconductor optical amplifier. This scheme provides high conversion efficiency and is independent of the incident light wavelength and polarization. It can be useful for radio-on-fiber transmission system applications in which one remote LO signal is provided for several wavelength-division-multiplexing IF signals.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Microwave photonics combines two worlds

Abstract: Microwave photonics, which brings together the worlds of radiofrequency engineering and optoelectronics, has attracted great interest from both the research community and the commercial sector over the past 30 years and is set to have a bright future. The technology makes it possible to have functions in microwave systems that are complex or even not directly possible in the radiofrequency domain and also creates new opportunities for telecommunication networks. Here we introduce the technology to the photonics community and summarize recent research and important applications.

Tunneling Field-Effect Transistors (TFETs) With Subthreshold Swing (SS) Less Than 60 mV/dec

Abstract: We have demonstrated a 70-nm n-channel tunneling field-effect transistor (TFET) which has a subthreshold swing (SS) of 52.8 mV/dec at room temperature. It is the first experimental result that shows a sub-60-mV/dec SS in the silicon-based TFETs. Based on simulation results, the gate oxide and silicon-on-insulator layer thicknesses were scaled down to 2 and 70 nm, respectively. However, the ON/ OFF current ratio of the TFET was still lower than that of the MOSFET. In order to increase the on current further, the following approaches can be considered: reduction of effective gate oxide thickness, increase in the steepness of the gradient of the source to channel doping profile, and utilization of a lower bandgap channel material

Low-Voltage Tunnel Transistors for Beyond CMOS Logic

Abstract: Steep subthreshold swing transistors based on interband tunneling are examined toward extending the performance of electronics systems. In particular, this review introduces and summarizes progress in the development of the tunnel field-effect transistors (TFETs) including its origin, current experimental and theoretical performance relative to the metal-oxide-semiconductor field-effect transistor (MOSFET), basic current-transport theory, design tradeoffs, and fundamental challenges. The promise of the TFET is in its ability to provide higher drive current than the MOSFET as supply voltages approach 0.1 V.