Chang-Ki Baek

Pohang University of Science and Technology, Antō, North Gyeongsang, South Korea

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Publications (53)84.18 Total impact

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    ABSTRACT: The electronic and photoconductive characteristics of CdTe nanowire based field effect transistors were studied systematically. The electrical characterization of a single CdTe nanowire FET verifies p-type behavior. The CdTe NW FETs respond to visible-near infrared (400-800 nm) incident light with a fast, reversible and stable response characterized by a high responsivity (81 AW-1), photoconductive gain (~2.5×104%) and reasonable response and decay times (0.7 s and 1 s, respectively). These results substantiate the potential of CdTe nanowire-based photodetectors in optoelectronics applications.
    Physical Chemistry Chemical Physics 09/2014; · 4.20 Impact Factor
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    ABSTRACT: Vertical gate-all-around (GAA) junctionless nanowire transistors (JNTs) with different diameters and underlap lengths are investigated using three-dimensional device simulations. The source-side diameter determines the on-current and drain-induced barrier lowering characteristics, whereas the drain-side diameter controls the band-to-band tunneling current during off-state conditions. The JNTs with short drain-side underlap lengths decrease the source/drain series resistance but increase the off-current values, especially due to large band-gap narrowing effects at the drain extension region. Proper device design of vertical GAA JNTs considering the device structure and underlap is needed to improve both on/off and short channel characteristics.
    Applied Physics Letters 09/2014; 105(10):102105-102105-4. · 3.79 Impact Factor
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    ABSTRACT: The interest in biologically sensitive field effect transistors (BioFETs) is growing explosively due to their potential as biosensors in biomedical, environmental monitoring and security applications. Recently, adoption of silicon nanowires in BioFETs has enabled enhancement of sensitivity, device miniaturization, decreasing power consumption and emerging applications such as the 3D cell probe. In this review, we describe the device physics and operation of the silicon nanowire BioFETs along with recent advances in the field. The silicon nanowire BioFETs are basically the same as the conventional field-effect transistors (FETs) with the exceptions of nanowire channel instead of thin film and a liquid gate instead of the conventional gate. Therefore, the silicon device physics is important to understand the operation of the BioFETs. Herein, physical characteristics of the silicon nanowire FETs are described and the operational principles of the BioFETs are classified according to the number of gates and the analysis domain of the measured signal. Even the bottom-up process has merits on low-cost fabrication; the top-down process technique is highlighted here due to its reliability and reproducibility. Finally, recent advances in the silicon nanowire BioFETs in the literature are described and key features for commercialization are discussed.
    Journal of Nanoscience and Nanotechnology 01/2014; 14(1):273-87. · 1.15 Impact Factor
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    ABSTRACT: The low-frequency noise (LFN) of a p-type nanowire FET (p-NWFET) was characterized and compared with that of an n-type NWFET (n-NWFET) in terms of dominant noise source and its location in the channel region. An inverse proportional dependence of the noise level on channel diameter was observed in the p-NWFET but not in the n-NWFET. The LFN was observed to be mainly generated by Hooge mobility fluctuation in the p-NWFET. Under a switched biasing condition, p-NWFET showed no substantial LFN reduction (in contrast to the n-NWFET), indicating that the carrier number fluctuation was insignificant. This was due to the compressive stress induced by embedded SiGe with heavier transverse effective hole mobility.
    IEEE Electron Device Letters 01/2014; 35(7):702-704. · 2.79 Impact Factor
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    ABSTRACT: We investigate the effect of single grain boundary (SGB) with arbitrary angles on the threshold voltage ( (V_{rm {th}}) ) variation in sub-50-nm polysilicon (poly-Si) channel devices using 3-D simulation. An SGB in the poly-Si channel causes changes in potential barrier profile resulting in the variation of (V_{rm {th}}) . As the planar devices scale down to 20-nm, oblique SGB can significantly increase the whole potential barrier profile and cause large (V_{rm {th}}) variation. However, due to superior gate controllability, the gate-all-around devices show relatively small increase of the conduction energy band, and thus mitigate the (V_{rm {th}}) variation even in 20-nm poly-Si channel.
    IEEE Transactions on Electron Devices 01/2014; 61(8):2705-2710. · 2.06 Impact Factor
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    ABSTRACT: A compact scaling length model for tapered Tri-gate fin field-effect transistors (FinFETs) is presented based on a 3-D simulation and an analytic potential model. Short-channel effects (SCEs) of rectangular FinFETs can be controlled by designing the fin width, fin height, and gate length to satisfy scaling theory. Tapered FinFETs have a fin top width shorter than the fin bottom width, and they show a different dependence of subthreshold behaviors and SCEs compared to rectangular FinFETs. The proposed scaling length model for tapered FinFETs, expressed as a function of fin bottom width, fin height, and tapering angle, is presented based on the 3-D Poisson's equation and a non-Cartesian mesh. The dependence of the subthreshold behaviors of tapered FinFETs calculated with the proposed model is compared with that of rectangular FinFETs. We found that longer fin bottom widths and fin heights of tapered FinFETs can be designed by applying the proposed scaling length model for the scaling parameter.
    IEEE Transactions on Electron Devices 09/2013; 60(9):2721-2727. · 2.06 Impact Factor
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    ABSTRACT: We report on the electrical stability of Si-nanowire biologically sensitive field-effect transistors (BioFETs) fabricated using conventional microfabrication technique, with an embedded Ag/AgCl pseudo-reference electrode (pRE) formed by an electrochemical method. The open-circuit potential (OCP) characteristics between the pRE and a commercial reference electrode have been measured in order to evaluate the influence of the pRE potential on the device performance. In a pH sensing mode, the fabricated pRE follows the applied potential accurately with a small offset value of below 6 mV for pH in the range of 4 to 10. The BioFET was also used for the detection of alpha fetoprotein (AFP) with a detection limit of 10 pg mL−1 and the corresponding OCP fluctuation of the pRE was less than 1.5 mV, independent of the AFP concentrations. These results suggest that the Si-NW BioFETs with the embedded Ag/AgCl pRE are very promising for reliable biosensing applications.
    RSC Advances 05/2013; 3(21):7963-7969. · 3.71 Impact Factor
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    ABSTRACT: In this paper, a simple but accurate model is presented to analyze source/drain (S/D) series resistance in trigate fin field-effect transistors, particularly on triangular or pentagonal rather than rectangular epitaxy. The model includes the contribution of spreading, sheet, and contact resistances. Although the spreading and sheet resistances are evaluated modifying standard models, the contact resistance is newly modeled using equivalent models of lossy transmission lines and transformations of 3-D to 2-D geometry. Compared with series resistance extracted from 3-D numerical simulations, the model shows excellent agreement, even when the S/D geometry, silicide contact resistivity, and S/D doping concentration are varied. We find that the series resistance is influenced more by contact surface area than by carrier path from the S/D extension to the silicide contact. To meet the series resistance targeted in the semiconductor roadmap, both materials and geometry will need to be optimized, i.e., lowering the silicide contact resistivity and keeping high doping concentration as well as maximizing the contact surface area, respectively.
    IEEE Transactions on Electron Devices 04/2013; 60(4):1302-1309. · 2.06 Impact Factor
  • Solid-State Electronics 02/2013; · 1.48 Impact Factor
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    ABSTRACT: The conventional source/drain series resistance (Rsd) extraction method is not applicable to nanowire field effect transistors (NWFETs), as NWFETs have fluctuating characteristics in Id and there is insufficient physical modeling. In this letter, we propose a modified Rsd extraction method that uses an optimized Id equation and a threshold voltage (Vth) extraction procedure for NWFETs. The Id equation is modified for the geometry of the NWFET, and Vth is obtained from the linear Y-function that can be observed in NWFETs because of volume inversion. A necessary assumption for this procedure is experimentally confirmed using the Y-function, and equations that fit the measured data perform well; this justifies the validity of applying the modified Id equations to NWFETs. Therefore, Rsd is perfectly extracted in all NWFETs and it is observed to be dependent on the channel diameter (dNW) when normalized by dNW, indicating that the extension resistance is the dominant component in the total Rsd.
    IEEE Electron Device Letters 01/2013; 34(7):828-830. · 2.79 Impact Factor
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    ABSTRACT: Ion-sensitive field-effect transistors (ISFETs) with a honeycomb nanowire (HCNW) structure have been fabricated on a silicon-on-insulator wafer. The HCNW ISFET shows lower threshold voltage, lower subthreshold swing, higher drain current, and lower variability than the conventional nanowire device. Improved electrical characteristics are mainly due to the increased effective channel width and enhanced current drivability. The HCNW structure also exhibits improved current sensitivity in its pH response. These results suggest that the HCNW structure is promising for enhancing device performance and realizing sensors with high sensitivity.
    IEEE Electron Device Letters 01/2013; 34(8):1059-1061. · 2.79 Impact Factor
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    ABSTRACT: The decomposition of In2Se3 nanowire phase change memory devices during current-driving operation was investigated. The devices were subjected to thermal/electrical stress with current density and electric field during the reset operation at 0.24–0.38 MA/cm2 and 5.3–6.4 kV/cm, respectively. After multiple operation cycles, a change in morphology and composition of the In2Se3 nanowire was observed and led to the device failure. The transmission electron microscopy and energy dispersive analysis indicate that electromigration causes the catastrophic failure by void formation where In atoms migrate toward the cathode and Se atoms migrate toward the anode depending on their electronegativities.
    Applied Physics Letters 01/2013; 103(23):233504-233504-4. · 3.79 Impact Factor
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    ABSTRACT: The low-frequency noise in the silicon nanowire field-effect transistor (SNWFET) is characterized using SNWFETs with different channel diameters dNW. The current density and the simulation result indicate that the volume inversion as manifested by the spatial charge distribution is enhanced in smaller dNW. The measured noise data are discussed based on the number and correlated mobility fluctuation model. It is shown that the low-frequency noise decreases in smaller dNW. This dNW-dependent noise behavior is clarified in terms of the effective oxide trap density and the fraction of inversion charges near the Si-SiO2 interface.
    IEEE Electron Device Letters 10/2012; 33(10):1348-1350. · 2.79 Impact Factor
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    ABSTRACT: This letter proposes simple guidelines to design nanoscale fin-based multigate field-effect transistors (FinFETs) for radio frequency (RF)/analog applications in terms of fin height and fin spacing. Geometry-dependent capacitive and resistive parasitics are evaluated using analytic models and are included in a small-signal circuit. It is found that reducing the fin-spacing-to-fin-height ratio of FinFETs, as long as it is compatible with the process integration, is desirable for improving RF performance. This is because the current-gain cutoff frequency and the maximum oscillation frequency are affected by decreasing parasitic capacitance more than by increasing series resistance.
    IEEE Electron Device Letters 09/2012; 33(9):1234-1236. · 2.79 Impact Factor
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    ABSTRACT: We performed 3D simulations to demonstrate structural effects in sub-20 nm gate-all-around silicon nanowire field effect transistors having asymmetric channel width along the channel direction. We analyzed the differences in the electrical and physical properties for various slopes of the channel width in asymmetric silicon nanowire field effect transistors (SNWFETs) and compared them to symmetrical SNWFETs with uniform channel width. In the same manner, the effects of the individual doping concentration at the source and drain also have been investigated. For various structural conditions, the current and switching characteristics are seriously affected. The differences attributed to the doping levels and geometric conditions are due to the electric field and electron density profile.
    Journal of Applied Physics 08/2012; 112(3). · 2.21 Impact Factor
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    ABSTRACT: We propose an asymmetric radial structure developed via simulation that improves the optical and electrical characteristics of silicon nanowire (SiNW) solar cells. This nanostructure is designed by shrinking the bottom core diameter and holding the top core diameter fixed in the SiNW, which results in a total reflection of the incident light in the outer wall of the shell due to the difference in the refractive index. The reflection enhances light trapping and concentration, which results in a 10 times higher optical generation rate and greater optical absorption in the high energy regime as compared with the fundamental symmetric radial structure. Further, we found that the efficiency is increased by over 10% when the bottom core diameter is decreased. The proposed structure has great potential to effectively improve the efficiency in concert with optimizing the design parameters.
    Journal of Applied Physics 04/2012; 111(7). · 2.21 Impact Factor
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    ABSTRACT: We propose an asymmetric structure using simulation to improve the electrical characteristics of the solar cell. This structure is designed by shrinking the bottom core diameter in radial structure. It causes the total reflection of the incident light in the outer wall and the light concentration in the bottom core. Consequently, an asymmetric solar cell (ASC) shows the increase in current density and cell efficiency (CE), which is 10 % higher than those of a symmetric solar cell (SSC). By increasing doping concentration of the shell and applying light trapping techniques i.e. anti-reflective coating and back-surface-field, the ASC showed high CE compared with the SSC. This novel structure offers an opportunity for effectively improving the CE.
    Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE; 01/2012
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    ABSTRACT: In this paper, the characteristics of the silicon nanowire (SiNW) based solar cells and biologically modified field-effect transistor (BioFET) are presented and discussed. The pH responses of the BioFETs clearly showed a sensitivity of 40 mV/pH. Also, the lateral shifts of transfer ID-VG curves were observed, depending on the pH value of the solution. Moreover the signal to noise ratio and sensing limit were evaluated, using the low frequency noise data. The solar cells showed higher light absorption and power convergence efficiency (PCE), compared with thin film solar cells. The various structural parameters of the solar cell have been optimized with the use of TCAD simulation and the 15 % improvement of PCE was achieved by adjusting the cell length.
    Solid-State and Integrated Circuit Technology (ICSICT), 2012 IEEE 11th International Conference on; 01/2012
  • Source
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    ABSTRACT: We have fabricated Si nanowire (SiNW) based ion-sensitive field effect transistors (ISFETs) for biosensing applications. The ability to prepare a large number of sensors on a wafer, the use of standard silicon microfabrication techniques resulting in cost savings, and potential high sensitivity are significant advantages in favor of nanoscale SiNW ISFETs. The SiNW ISFETs with embedded Ag/AgCl reference electrode were fabricated on a standard silicon-on-insulator wafer using electron-beam lithography and conventional semiconductor processing technology. The current-voltage characteristics show an n-type FET behavior with a relatively high on/off current ratio, reasonable sub-threshold swing value, and low gate-leakage current. The pH responses of the ISFETs with different pH solutions were characterized at room temperature which showed a clear lateral shift of the drain current vs. gate voltage curve with a change in the pH value of the solution and a sensitivity of 40 mV pH(-1). The low frequency noise characteristics were investigated to evaluate the signal to noise ratio and sensing limit of the devices.
    The Analyst 12/2011; 136(23):5012-6. · 4.23 Impact Factor
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    ABSTRACT: We study quasi-ballistic transport in nanoscale high-κ/metal gate nMOSFETs based on radio-frequency (RF) S -parameter analysis. An RF S -parameter-based simple experimental methodology is used for direct extraction of device parameters (i.e., L <sub>eff</sub>, R <sub>sd</sub>, and C <sub>inv</sub>) and the effective carrier velocity v<sub>eff</sub> from the targeted short-channel devices. Furthermore, an analytical top-of-the-barrier model, which self-consistently solves the Schrödinger-Poisson equations, is used to determine the ballistic carrier velocity v <sub>inj</sub> at the top of the barrier near the source. Based on the results of the experimental extraction and analytical calculations, backscattering coefficient r <sub>sat</sub> and ballistic ratio BR <sub>sat</sub> are calculated to assess the degree of the transport ballisticity for nMOSFETs. It is found that conventional high-κ/metal gate nMOSFETs will approach a ballistic limit at an effective gate length L <sub>eff</sub> of approximately 7 nm.
    IEEE Electron Device Letters 12/2011; · 2.79 Impact Factor

Publication Stats

50 Citations
84.18 Total Impact Points

Institutions

  • 2011–2013
    • Pohang University of Science and Technology
      • Department of Electronic and Electrical Engineering
      Antō, North Gyeongsang, South Korea
  • 2009
    • Chungnam National University
      • Department of Electronic Engineering
      Daiden, Daejeon, South Korea
  • 2007–2009
    • Korea Institute for Advanced Study
      Sŏul, Seoul, South Korea
  • 2006–2008
    • Seoul National University
      • • School of Electrical Engineering and Computer Sciences
      • • School of Computer Science and Engineering
      • • Department of Electrical and Computer Engineering
      Seoul, Seoul, South Korea