Ryoongbin Lee

Bio: Ryoongbin Lee is an academic researcher from Seoul National University. The author has contributed to research in topics: Field-effect transistor & Capacitance. The author has an hindex of 6, co-authored 26 publications receiving 106 citations.

Investigation of Electrical Characteristic Behavior Induced by Channel-Release Process in Stacked Nanosheet Gate-All-Around MOSFETs

Abstract: In this brief, several issues attributed to the channel-release process in vertically stacked-gate-all-around MOSFETs (GAAFETs) having various nanosheet (NS) widths were rigorously investigated. Because of the finite selectivity of SiGe (sacrificial layer) etchant to Si (channel layer), Si channel is likely to be thinned during the channel-release step which is one of the key processes in stacked-GAA FET fabrication. Consequently, the thickness of channel and the interchannel space becomes variable depending on the NS width, since the etch time must be determined by the widest channel within a wafer. It results in a channel width dependence of gate work function, gate-to-drain capacitance, and channel interfacial property as well as the electrostatic gate controllability. The electrical characteristic behavior of stacked-GAAFETs induced by these effects was thoroughly investigated through process-based 3-D technology computer-aided design (TCAD) device simulation along with a transmission electron microscopy (TEM) and an energy-dispersive spectroscopy (EDS) analyses. The results confirm that width-dependent effects should be taken into account when fabricating and compact modeling the stacked-GAAFETs with various NS widths which are required for logic and static random access memory (SRAM) applications.

Simulation of the effect of parasitic channel height on characteristics of stacked gate-all-around nanosheet FET

Abstract: By using technology computer aided design (TCAD) simulation, the aim of this paper is to investigate the effect of Si parasitic channel, which is placed under stacked nanosheet channels, on electrical characteristic of stacked nanosheet GAA FETs. We have controlled the parasitic channel height, and evaluated the effect on electrical performance of the device. Trade-off in performance of the nanosheet FET is observed: the increase in parasitic channel height results in improvement in subthreshold swing and on/off ratio, while the increase in capacitance brings worse RC delay and active power. The parasitic channel height control in devices with ground plane doping is also investigated.

Surface Ge-rich p-type SiGe channel tunnel field-effect transistor fabricated by local condensation technique

Abstract: In this study, tunnel field-effect transistor (TFET) which has surface Ge-rich SiGe nanowire as a channel has been demonstrated. There are improvements in terms of on-current and subthreshold swing (SS) comparing with control groups (constant Ge concentration SiGe TFET and Si TFET) fabricated by the same process flow except for the channel formation step. In order to obtain the concentration-graded SiGe channel, Ge condensation method which is a kind of oxidation is adopted. The rectangular shape of the channel becomes a rounded nanowire through the Ge condensation process. The TFET with the concentration-graded SiGe channel can improve drive current due to a smaller band gap at the Ge-condensed surface of the channel compared to Si or non-condensed SiGe channel TFET.

Investigation of Feasibility of Tunneling Field Effect Transistor (TFET) as Highly Sensitive and Multi-sensing Biosensors

Abstract: In this letter, we propose the use of tunneling field effect transistors (TFET) as a biosensor that detects bio-molecules on the gate oxide. In TFET sensors, the charges of target molecules accumulated at the surface of the gate oxide bend the energy band of p-i-n structure and thus tunneling current varies with the band bending. Sensing parameters of TFET sensors such as threshold voltage (Vt) shift and on-current (ID) change are extracted as a function of the charge variation. As a result, it is found that the performances of TFET sensors can surpass those of conventional FET (cFET) based sensors in terms of sensitivity. Furthermore, it is verified that the simultaneous sensing of two different target molecules in a TFET sensor can be performed by using the ambipolar behavior of TFET sensors. Consequently, it is revealed that two different molecules can be sensed simultaneously in a read-out circuit since the multi-sensing is carried out at equivalent current level by the ambipolar behavior.

Field-effect sensors – from pH sensing to biosensing: sensitivity enhancement using streptavidin–biotin as a model system

Abstract: Field-Effect Transistor sensors (FET-sensors) have been receiving increasing attention for biomolecular sensing over the last two decades due to their potential for ultra-high sensitivity sensing, label-free operation, cost reduction and miniaturisation. Whilst the commercial application of FET-sensors in pH sensing has been realised, their commercial application in biomolecular sensing (termed BioFETs) is hindered by poor understanding of how to optimise device design for highly reproducible operation and high sensitivity. In part, these problems stem from the highly interdisciplinary nature of the problems encountered in this field, in which knowledge of biomolecular-binding kinetics, surface chemistry, electrical double layer physics and electrical engineering is required. In this work, a quantitative analysis and critical review has been performed comparing literature FET-sensor data for pH-sensing with data for sensing of biomolecular streptavidin binding to surface-bound biotin systems. The aim is to provide the first systematic, quantitative comparison of BioFET results for a single biomolecular analyte, specifically streptavidin, which is the most commonly used model protein in biosensing experiments, and often used as an initial proof-of-concept for new biosensor designs. This novel quantitative and comparative analysis of the surface potential behaviour of a range of devices demonstrated a strong contrast between the trends observed in pH-sensing and those in biomolecule-sensing. Potential explanations are discussed in detail and surface-chemistry optimisation is shown to be a vital component in sensitivity-enhancement. Factors which can influence the response, yet which have not always been fully appreciated, are explored and practical suggestions are provided on how to improve experimental design.

Interface Engineering of Metal Oxide Semiconductors for Biosensing Applications

Abstract: In the last decade, there has been considerable development in the area of oxide semiconductors, owing to their superior electrical properties as compared to a-Si:H, and lower cost and better uniformity over large areas as compared to poly-Si. On the other hand, multi-functional sensing systems play a significant role in building a bridge across bio/electronic interface and require advanced thin-film transistors (TFT) as sensing components and signal processing circuits. High-performance oxide TFTs are constructed based on material design, advanced processing and device architecture and provide higher sensitivity when compared with other active thin-film transistor platforms. Their versatile configurations and integration with functional materials make oxide TFT the focal point of sensing systems, including wearable and implantable electronics.

Hybrid Silicon Nanowire Devices and Their Functional Diversity

Abstract: In the pool of nanostructured materials, silicon nanostructures are known as conventionally used building blocks of commercially available electronic devices. Their application areas span from miniaturized elements of devices and circuits to ultrasensitive biosensors for diagnostics. In this Review, the current trends in the developments of silicon nanowire-based devices are summarized, and their functionalities, novel architectures, and applications are discussed from the point of view of analog electronics, arisen from the ability of (bio)chemical gating of the carrier channel. Hybrid nanowire-based devices are introduced and described as systems decorated by, e.g., organic complexes (biomolecules, polymers, and organic films), aimed to substantially extend their functionality, compared to traditional systems. Their functional diversity is explored considering their architecture as well as areas of their applications, outlining several groups of devices that benefit from the coatings. The first group is the biosensors that are able to represent label-free assays thanks to the attached biological receptors. The second group is represented by devices for optoelectronics that acquire higher optical sensitivity or efficiency due to the specific photosensitive decoration of the nanowires. Finally, the so-called new bioinspired neuromorphic devices are shown, which are aimed to mimic the functions of the biological cells, e.g., neurons and synapses.

Bimetal-organic framework nanocomposite based point-of-care visual ratiometric fluorescence pH microsensor for strong acidity

Abstract: pH is of great importance in understanding physiological and pathologic processes. Abnormal gastric juice pH is an indicator of many gastric diseases such as peptic ulcer and gastric cancer. In this work, a nanocomposite 1-hydroxypyrene@ Co/Tb- dipicolinic acid metal-organic framework (1-OHP@Co/Tb-DPA MOF) was constructed as a ratiometric fluorescent pH sensor for strong acidity. The nanocomposite-based pH sensor was response-rapid (30 s), linearly responsive in the broad pH range of 0.3–7.8 (r > 0.95) and ultra-sensitive in the pH range of 0.3–5.0. Importantly, the nanocomposite-loaded fiber paper was prepared as a visual microsensor for point-of-care pH detection via ratiometric chromaticity, coupled with a homemade portable determination device. The paper-based visual microsensor is response-rapid and sensitive, long-term stable (at least 30 days), and suitable for pH assay of microvolume (as little as 5 μL) samples at pH 0.3–5.0. Both the nanocomposite-based ratiometric fluorescent sensor and the paper-based visual microsensor can accurately determine the pH of artificial gastric juices (relative error

An Accurate Analytical Current Model of Double-gate Heterojunction Tunneling FET

Abstract: A continuous accurate analytical drain current model considering the effect of the inversion charge is presented for the double-gate heterojunction tunneling FET. The band-to-band tunneling current is calculated analytically in terms of the integration with respect to the generation rate using a tangent line approximation method. The accuracy of the model is validated by comparing it with the TCAD simulation. The model, applied to the example of GaAsSb/InGaAs heterojunction, predicts the surface potential profiles, ${I}_{\mathsf {DS}}-{V}_{\mathsf {GS}}$ and ${I}_{\mathsf {DS}}-{V}_{\mathsf {DS}}$ characteristics accurately. Under different device parameters (gate oxide dielectric constant, gate oxide thickness, and heterojunction materials), the validity of the model is demonstrated by its agreement with the TCAD simulation.