Chang-Ki Baek

Pohang University of Science and Technology | POSTECH · Department of Convergence IT Engineering

Silicon photodiodes are widely used in applications that require the measurement of the intensity, colour and position of visible light. Silicon is an attractive material for these systems owing to its low cost, low noise, and easy on-chip integration with read-out electronics. However, silicon cannot effectively be used to detect near-infrared (NI...

Three-terminal (3-T) thyristor random-access memory is explored for a next-generation high-density nanoscale vertical cross-point array. The effects of standby voltages on the device are thoroughly investigated in terms of gate–cathode voltage ( V GC,ST ) and anode–cathode voltage ( V AC,ST ) in the standby state for superior data retention charact...

We demonstrate a near-infrared (NIR) photodiode (PD) by using a wave-shaped sidewall silicon nanopillars (WS-SiNPs) structure. The designed WS sidewall nanostructure increases the horizontal component of incident light and induces multiple whispering-gallery modes with low-quality factor, which increases the light absorption path. Thus, the WS-SiNP...

A memory device includes at least one semiconductor layer having a double PN junction ,and an anode and a cathode which simultaneously contact the semiconductor layer, wherein a junction between the semiconductor layer and the anode is a Schottky junction ,and a junction between the semiconductor layer and the cathode is an Ohmic junction. In addit...

We propose a new drain-extended FinFET (DeFinFET) that can improve the intrinsic gain (gm/gds) and the electrical safe operating area (SOA). This structure features a novel utilization of the drain potential by using a floating poly (FP) and split high-k material (HK) on the drain and drift regions. This method effectively controls the potential dr...

We have designed a tunneling source follower (TSF) for image sensors that achieves high voltage gain (Av) and low 1/f noise simultaneously. The TSF is composed of N-P-N-N, especially the p-doped grounded area, which serves to amplify the insufficient tunneling current, allowing the source follower (SF) to utilize band-to-band tunneling (BTBT). Comp...

Dynamic random-access memory (DRAM) has been scaled down to meet high-density, high-speed, and low-power memory requirements. However, conventional DRAM has limitations in achieving memory reliability, especially sufficient capacitance to distinguish memory states. While there have been attempts to enhance capacitor technology, these solutions incr...

We have proposed leaky integrate-and-fire (LIF) neuron having low-energy consumption and tunable functionality without external circuit components. Our LIF neuron has a simple configuration consisting of only three components: one bandgap-engineered resistive switching transistor (BE-RST), one capacitor, and one resistor. Here, the crucial point is...

Neuromorphic technologies typically employ a point neuron model, neglecting the spatiotemporal nature of neuronal computation. Dendritic morphology and synaptic organization are structurally tailored for spatiotemporal information processing, such as visual perception. Here we report a neuromorphic computational model that integrates synaptic organ...

We demonstrate a highly biomimetic spiking neuron capable of fast and energy-efficient neuronal oscillation dynamics. Our simple neuron circuit is constructed using silicon–germanium heterojunction based bipolar transistors (HBTs) with nanowire structure. The HBT has a hysteresis window with steep switching characteristics and high current margin i...

We have designed a tunneling source follower (TSF) for image sensors that achieves high voltage gain (Av) and low 1/f noise simultaneously. The TSF is composed of N-P-N-N, especially the p-doped grounded area, which serves to amplify the insufficient tunneling current, allowing the source follower (SF) to utilize band-to-band tunneling (BTBT). Comp...

Dynamic random-access memory (DRAM) has been scaled down to meet high-density, high-speed, and low-power memory requirements. However, conventional DRAM has limitations in achieving memory reliability, especially sufficient capacitance to distinguish memory states. While there have been attempts to enhance capacitor technology, these solutions incr...

We demonstrate Three-Terminal Thyristor Random Access Memory (3T TRAM) on a monolithic silicon-CMOS-photonic platform. The gate contact plays an important role in controlling dynamic memory characteristics and optimized design can lead to non-volatile characteristics.

Chemical sensors are an essential part of modern society to ensure safety, from preventing pollution to saving lives. Especially, the demand for real-time monitoring of hydrogen fluoride (HF) increases continuously due to its high toxicity, contrary to its wide use in industries. In addition, compact size and low cost are favorable to utilize the s...

The simple structure, low power consumption, and small form factor have made surface acoustic wave (SAW) devices essential to mobile communication as RF filters. For instance, the latest 5G smartphones are equipped with almost 100 acoustic wave filters to select a specific frequency band and increase communication capacity. On the arrival of the ne...

A drain-extended (DE) FinFET with a dual material gate (DMG) and a high-k field plate (FP), named DF-DeFF, is proposed for high-voltage RF applications. The FP induces the charge variation in the drain extension, which appears as either the extended depletion in the gate-off state or the electron accumulation in the gate-on state. Along with the FP...

Immunotherapy using CAR-T cells is a new paradigm technology for cancer treatment. To avoid severe side effects and tumor escape variants observed for conventional CAR-T cells approach, adaptor CAR technologies are under development, where intermediate target modules redirect immune cells against cancer. In this work, silicon nanowire field effect...

Three-terminal (3-T) thyristor random-access memory is explored for a next generation high-density nanoscale vertical cross-point array. The effects of standby voltages on the device are thoroughly investigated in terms of gate-cathode voltage ( V GC,ST ) and anode- cathode voltage ( V AC,ST ) in the standby state for superior data retention charac...

Three-terminal (3-T) thyristor random-access memory is explored for a next generation high-density nanoscale vertical cross-point array. The effects of standby voltages on the device are thoroughly investigated in terms of gate-cathode voltage ( V GC,ST ) and anode- cathode voltage ( V AC,ST ) in the standby state for superior data retention charac...

Silicon nanowires (SiNWs) have attracted attention as promising high efficiency thermoelectric materials by significantly improving the thermoelectric efficiency of silicon. Here, we have fabricated cobalt silicide/silicon heterostructure on both ends of nanowires using self-aligned silicide (salicide) process. By forming cobalt silicide (CoSi2) la...

Two-terminal (2-T) thyristor random access memory (TRAM) based on nanoscale cross-point vertical array is investigated in terms of lengths and doping concentrations of storage regions for long data retention time (Tret). For high device scalability and low program voltage (VP), lengths of the storage regions are determined by the sum of depletion w...

Small molecules with no or little charge are considered to have minimal impact on signals measured by field effect transistor (FET) sensors. This fact typically excludes steroids from the family of analytes, detected by FETs. We present a portable multiplexed platform based on an array of nanowire sensors for label-free monitoring of daytime levels...

[Full text: https://rdcu.be/b4ovR] Neuromorphic architectures merge learning and memory functions within a single unit cell and in a neuron-like fashion. Research in the field has been mainly focused on the plasticity of artificial synapses. However, the intrinsic plasticity of the neuronal membrane is also important in the implementation of neurom...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

We report the reduction of thermal conductivity and phonon mean-free-path below the Casimir limit originated by phonon backscattering in silicon nanowires with scallop shaped surface modulation. The scallop surface modulation with a period of 55–110 nm on 200 nm diameter nanowires was created using top-down deep-reactive-ion-etching. The measured t...

Using calculations from first principles, the site disorder between Ga and Zn of crystalline InGaZnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> is shown to play key roles in its unique transport properties. The analysis based on Density Functional Theory reveals that the various types of s...

In the above-maned article [ibid., vol. 10, no. 2, pp. 475– 479, Mar. 2020], the author Kihyun Kim's affiliation is modified from "the Future IT Innovation Laboratory, Department of Creative IT Engineering, Pohang University of Science and Technology, Pohang 37673, South Korea (kihyun.kim@postech.ac.kr)." to "Division of Electronic Engineering, Jeo...

Despite the recent progress in the synthesis of crystalline boronate ester covalent organic frameworks (BECOFs) in powder and thin‐film through solvothermal method and on‐solid‐surface synthesis, respectively, their applications in electronics, remain less explored due to the challenges in thin‐film processability and device integration associated...

A drain-extended (De) FinFET (DeFinFET) with a high-k dielectric field plate is proposed for high-voltage (HV) system-on-chip (SoC) applications at 10-nm CMOS technology nodes. Conventional DeFinFETs without the dielectric field plate and DeFinFETs with SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlin...

Despite the recent progress in the synthesis of crystalline boronate ester covalent organic frameworks (BECOFs) in powder and thin‐film through solvothermal method and on‐solid‐surface synthesis, respectively, their applications in electronics, remain less explored due to the challenges in thin‐film processability and device integration associated...

Polycrystalline (poly) lanthanum fluoride (LaF3) Electrolyte-Insulator-Semiconductor (EIS) sensors can serve as a promising portable sensor platform for monitoring fluoride ion (F⁻) concentration due to their small size, fast response and simple fabrication method. The key to successful implementation is to consider and understand the effects of th...

Silicon nanowires (SiNWs) are promising structures with excellent photovoltaic properties for low-cost, high-efficiency solar cells and have the potential to overcome the limits of bulk silicon solar cells. There is still a need to enhance light absorption in SiNWs without increasing the surface area. Here, we introduce a novel design, hourglass-sh...

We propose a hybrid device substituting the software synapse in artificial neural networks with an individual hardware transistor unit. The unit merges a silicon nanowire semiconductor channel with a metal-ion doped solgel film as hybrid gate of the transistor. The film, amorphous and transparent, shows a memristive property due to ion redistributi...

A silicon-based laser is a critical component in the realization of full silicon (Si) photonic integrated circuits due to advantages in cost-competitive integration with the mature digital technology. The poor optical gain stemming from the indirect energy band structure of Si, however, has been a hurdle to realize this goal. An efficient Si nanoca...

Thermoelectric modules based on silicon nanowires (Si-NWs) have recently attracted significant attention as they show improved thermoelectric efficiency due to a decrease in thermal conductivity. Here, we adopt a top-down fabrication method to dramatically reduce the thermal conductivity of vertical Si-NWs. The thermal conductivity of vertical Si-N...

Zinc oxide nanowire (ZnO NW) gas sensor with single Schottky contact is capable of sensitive detection of gas molecules. In this study, we investigate the effect of design factors such as nanowire defect density, diameter, and length on the gas sensitivity using 3-D numerical simulation. The sensor with lower defect density or smaller NW diameter e...

Electrolyte-insulator-semiconductor (EIS) sensor is commonly considered for chemical and biosensing applications due to its small size and simple fabrication method. Here, we demonstrate a fluoride-sensitive EIS sensor using thermally-deposited polycrystalline lanthanum fluoride (poly LaF3) film as sensing membrane, which is cheaper than single-cry...

Miniaturized and cost-efficient methods aiming at high throughput analysis of microbes is of

We demonstrate high responsivity in a polysilicon (Poly-Si) near-infrared photodetector by reducing the adverse effects of grain boundaries. The presence of grain boundaries is a serious problem in polysilicon since they act as traps and degrade the electrical characteristics. However, the relation between grain boundaries and photodetector perform...

DC characteristics of n-type SiGe heterojunction nanowire tunneling field-effect transistors (TFETs) adopting a core-shell structure are investigated using 3-D numerical simulation. Different mole fractions between the core and the shell regions induce strain effects along the nanowire, which modulate the energy bandgap and thus the dc performance...

Miniaturized and cost-efficient methods aiming at high throughput analysis of microbes is of great importance for the surveillance and control of infectious diseases and the related issue of antimicrobial resistance. Here we demonstrate a miniature nanosensor chip based on a honeycomb-patterned silicon nanowire field effect transistor (FET) capable...

We report the first observation of negative photoconductance (NPC) in n- and p-doped Si nanowire field-effect transistors (FETs) and demonstrate the strong influence of doping concentrations on the nonconventional optical switching of the devices. Furthermore, we show that the NPC of Si nanowire FETs is dependent on the wavelength of visible light...

Nano-helical array of p-NiO/n-SnO2 p-n junctions with well-defined and highly-gas-accessible hetero-interfaces is presented for designable and highly selective gas sensors. The gas sensor having the nanoscale p-n junction sensing layer with a top-and-bottom electrodes configuration was fabricated by conventional photolithography and oblique-angle d...

Invited talk

Silicon is the most widely used material for various applications, such as electronic devices, solar cells, and micro-electro-mechanical-systems due to abundant reserves and low cost. Nevertheless, it has not considered as thermoelectric material because of its relatively low thermoelectric efficiency due to high thermal conductivity of 120 W/m∙K....

A study of responsivity on photodetector with Poly-Si layer deposited by LPCVD according to doping concentration.

Invited talk

We demonstrate the direct biosensing of the Ebola VP40 matrix protein, using a memristor mode of a liquid-integrated nanodevice, based on a large array of honeycomb-shaped silicon nanowires. To shed more light on the principle of biodetection using memristors, we engineered the opening of the current-minima voltage gap VGAP by involving the third g...

Tunneling field-effect transistor (TFET) is one of the promising alternatives to substitute the conventional MOSFETs for ultra-low power applications. TFETs can attain the subthreshold swing (SS) below 60 mV/dec for a few orders of drain currents by following band-to-band tunneling instead of thermionic emission transport. However, it is difficult...

DC characteristics of polysilicon nanowire tunneling field-effect transistors (poly-Si NW TFETs) are investigated when a single grain boundary (SGB) existed in the channel region. Poly-Si NW TFETs are analyzed using 3-D numerical simulations in terms of different location and size of the SGB. As the SGB is closer to the source/channel junction, lon...

Wavelength-selective absorption phenomena of silicon-based vertical nanowire (NW) photodetectors (PDs) are investigated using 3-D numerical simulations. The difference in the refractive indexes between silicon NW and its surrounding material induces diameter-dependent waveguide effects at several specific wavelengths for asymmetric as well as symme...

Inversion-mode (IM) and depletion-mode (DM) ion-sensitive field effect transistors (ISFETs) are investigated in terms of dc characteristics, pH response and low-frequency noise (LFN) characteristics. The dc characteristics show a low threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">...

Thermal conductivity is one of the most important indicators for evaluating the performance of thermoelectric devices. Thermal conductivity of bulk materials can be measured by flash flash method and flat plate heat flow method, and there are already commercially available products. On the other hand, thermal conductivity measurement of thin film m...

DC/AC performance and the variations due to single interface trap of the nanowire FETs were investigated in the 7-nm technology node using fully-calibrated TCAD simulation. Shorter junction gradient and greater diameter reduced RC delay without short channel degradations. Spacer with smaller dielectric constants decreased parasitic and gate capacit...

We propose three-terminal core-shell (CS) silicon vertical nanowire tunneling field-effect transistors (TFETs), which can be fabricated by conventional CMOS technology. CS TFETs show lower subthreshold swing (SS) and higher on-state current than conventional TFETs through their high surface-to-volume ratio, which increases carrier-tunneling region...

Optimization of operation conditions for biosensing is investigated for the doped silicon nanowire channel transistor sensors. Sensors with phosphorus doped honeycomb nanowire channel are fabricated on 8-inch wafer using conventional CMOS technology. From the low frequency noise (LFN) characteristics, the noise equivalent gate voltage fluctuation i...

Process-induced variations of 10-nm node n-type FinFETs considering middle-of-line parasitics were investigated in terms of dc/ac performances using fully calibrated TCAD simulations. Variations of positive fixed oxide charge density at shallow trench isolation interface and source/drain (S/D) height influenced off-state and on-state performance va...

Vertical Si nanowire (NW) structure is applicable to a variety of applications such as field-effect transistors (FETs), photodetectors (PDs), and nonvolatile memory because of its high surface-to-volume ratio and quantum effects. Among these, statistical variability study of NWFETs induced by random dopant fluctuation and electrical/optical propert...

Random dopant fluctuation effects of gate-all-around Si nanowire field-effect transistors (FETs) are investigated in terms of different diameters and junction gradients. The nanowire FETs with smaller diameters or shorter junction gradients increase relative variations of the drain currents and the mismatch of the drain currents between source-drai...

In this brief, we systematically investigated the effects of fin pitch (FP) and fin height ( $H_{textrm {fin}}$ ) on parasitic resistances and capacitances to achieve the best $RC$ delay, which is an adequate metric of the ac behavior of FinFETs, for Si bulk n/pFinFETs in system-on-a-chip applications. The $RC$ delays were directly extracted from t...

DC/AC characteristics of Si bulk FinFETs including middle-of-line levels are precisely investigated using well-calibrated 3-D device simulations for system-on-chip applications. Scaling the fin widths down to 5 nm effectively enhances gate-to-channel controllability and improves delay, but a dramatic increase in band-to-band tunneling currents from...

Gas sensors based on metal-oxide-semiconductor transistor with the polysilicon gate replaced by a gas sensitive thin film have been around for over 50 years. These are not suitable for the emerging mobile and wearable sensor platforms due to operating voltages and powers far exceeding the supply capability of batteries. Here we present a novel appr...

Effects of single grain boundary (SGB) and random interface traps (RITs) on the electrical characteristics of the macaroni structure in sub-30 nm poly-silicon (poly-Si) channel devices are analyzed using 3D simulation. The macaroni structure can mitigate the adverse effects of SGB on the electrical variations compared to the conventional structure....