Jeong-Soo Lee

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

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Publications (53)104.39 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: Abstract A radio frequency plasma enhanced chemical vapor deposition system was used for the successful growth of thin vertical carbon nanowalls, also known as vertical graphene, on various substrates. Transmission electron microscopy studies confirmed the presence of vertical graphene walls, which are tapered, typically consisting of 10 layers at the base tapering off to 2 or 3 layers at the top. The sides of the walls are facetted at quantized angles of 30° and the facetted sides are usually seamless. Growth occurs at the top open edge which is not facetted. Hydrogen induced etching allows for nucleation of branch walls apparently involving a carbon onion-like structure at the root base. Characterization by a superconducting quantum interference device showed magnetic hysteresis loops and weak ferromagnetic responses from the samples at room temperature and below. Temperature dependence of the magnetization revealed a magnetic phase transition around T = 50 K highlighting the coexistence of antiferromagnetic interactions as well as ferromagnetic order.
    Carbon 06/2014; 72. · 5.87 Impact Factor
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    ABSTRACT: The resistance stability and thermal resistance of phase change memory devices using ∼40 nm diameter Ga-doped In2O3 nanowires (Ga:In2O3 NW) with different Ga-doping concentrations have been investigated. The estimated resistance stability (R(t)/R 0 ratio) improves with higher Ga concentration and is dependent on annealing temperature. The extracted thermal resistance (Rth ) increases with higher Ga-concentration and thus the power consumption can be reduced by ∼90% for the 11.5% Ga:In2O3 NW, compared to the 2.1% Ga:In2O3 NW. The excellent characteristics of Ga-doped In2O3 nanowire devices offer an avenue to develop low power and reliable phase change random access memory applications.
    Applied Physics Letters 03/2014; 104(10):103510. · 3.79 Impact Factor
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    ABSTRACT: Phase change random access memory (PCRAM) devices are usually constructed using tellurium based compounds, but efforts to seek other materials providing desirable memory characteristics have continued. We have fabricated PCRAM devices using Ga-doped In2O3 nanowires with three different Ga compositions (Ga/(In+Ga) atomic ratio: 2.1%, 11.5% and 13.0%), and investigated their phase switching properties. The nanowires (∼40 nm in diameter) can be repeatedly switched between crystalline and amorphous phases, and Ga concentration-dependent memory switching behavior in the nanowires was observed with ultra-fast set/reset rates of 80 ns/20 ns, which are faster than for other competitive phase change materials. The observations of fast set/reset rates and two distinct states with a difference in resistance of two to three orders of magnitude appear promising for nonvolatile information storage. Moreover, we found that increasing the Ga concentration can reduce the power consumption and resistance drift; however, too high a level of Ga doping may cause difficulty in achieving the phase transition.
    Nanotechnology 01/2014; 25(5):055205. · 3.84 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: Electrical phase transition characteristics of self-assembled In2Se3 nanowire-based phase-change random access memory are presented. Through repeatable phase switching behavior in In2Se3 nanowire, we explored critical device parameters, such as set/reset programming voltage, extremely high resistance ratio (~107), power consumption, thermal resistance by Fourier's law, resistance drift coefficient by power law, etc. Size-dependent properties were observed: a systematic reduction in set/reset voltage and programming power, increase in thermal resistance of amorphous/crystalline phases and decrease in resistance drift coefficient at reset state, all scaling down the nanowire diameter. Such investigations provide an opportunity to develop highly-scalable and thermally efficient nonvolatile memory architecture in the future.
    The 13th IEEE International Conference on Nanotechnology, Beijing; 08/2013
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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. · 2.56 Impact Factor
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    ABSTRACT: The electrical characteristics of nonvolatile In2Se3 nanowire phase change memory are reported. Size-dependent memory switching behavior was observed in nanowires of varying diameters and the reduction in set/reset threshold voltage was as low as 3.45 V/6.25 V for a 60 nm nanowire, which is promising for highly scalable nanowire memory applications. Also, size-dependent thermal resistance of In2Se3 nanowire memory cells was estimated with values as high as 5.86×1013 and 1.04×106 K/W for a 60 nm nanowire memory cell in amorphous and crystalline phases, respectively. Such high thermal resistances are beneficial for improvement of thermal efficiency and thus reduction in programming power consumption based on Fourier's law. The evaluation of thermal resistance provides an avenue to develop thermally efficient memory cell architecture.
    Journal of Applied Physics 04/2013; 113(16). · 2.21 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
  • Source
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    ABSTRACT: Bandgap engineering of single-crystalline alloy Cd(x)Zn(1-x)Te (0 ≤ x ≤ 1) nanowires is achieved successfully through control of growth temperature and a two zone source system in a vapor-liquid-solid process. Extensive characterization using electron microscopy, Raman spectroscopy and photoluminescence shows highly crystalline alloy nanowires with precise tuning of the bandgap. It is well known that bulk Cd(x)Zn(1-x)Te is popular for construction of radiation detectors and availability of a nanowire form of this material would help to improve detection sensitivity and miniaturization. This is a step forward towards the accomplishment of tunable and predetermined bandgap emissions for various applications.
    Nanoscale 01/2013; · 6.23 Impact Factor
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    ABSTRACT: This work investigates the effect of Hfin on the device and circuit characteristics, and discusses the design aspects for the SoC integration such as 6T-SRAM and 2-stage OPAMPs. Table summarizes the device- and circuit-level assessment using the FinFETs and the planar FETs. Even though the gate control of FinFETs is better than of the planar FETs, further attention should be paid to design Hfin of the FinFETs. SoC blocks such as SRAMs require both high density and low power, so the minimum Lgate will restrict designing Hfin. On the other hand, the analog/RF applications prefer long Lgate to achieve high output resistance for better performance, so we may raise the Hfin without losing the gate control capability. Multiple Hfin design may be good choice for the sub-22-nm SoC integration because Hfin may affect the power, density, and the design convenience.
    VLSI Technology, Systems, and Applications (VLSI-TSA), 2013 International Symposium on; 01/2013
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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 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: The thermal conductivity of individual ZnTe nanowires (NWs) was measured using a suspended micro-bridge device with built-in resistance thermometers. A collection of NWs with different diameters were measured, and strong size-dependent thermal conductivity was observed in these NWs. Compared to bulk ZnTe, NWs with diameters of 280 and 107 nm showed approximately three and ten times reduction in thermal conductivity, respectively. Such a reduction can be attributed to phonon-surface scattering. The contact thermal resistance and the intrinsic thermal conductivities of the nanowires were obtained through a combination of experiments and molecular dynamic simulations. The obtained thermal conductivities agree well with theoretical predictions.
    Journal of Applied Physics 01/2013; 114(13):134314-134314-7. · 2.21 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 dc performance and low-frequency (LF) noise behaviors after hot-carrier (HC)-induced stress were compared for a junctionless nanowire transistor (JNT) and an inversion-mode nanowire transistor (INT). Less dc degradation was found in the JNT than in the INT. Due to the low lateral peak electric field (E-field) and electrons traveling through the center of the nanowire, the LF noise increment after HC-induced stress in the JNT is much lower than that in the INT. Furthermore, due to the higher lateral peak E-field located under the gate and the conduction path that occurs near the surface, the LF noise of the INT is very sensitive to HC stress.
    IEEE Electron Device Letters 11/2012; 33(11):1538-1540. · 2.79 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
  • N R Das, M W Shinwari, M J Deen, Jeong-Soo Lee
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    ABSTRACT: In this paper, the energy states of electrons in a silicon nanowire are analytically calculated in the presence of a surface potential and an electric field, as in a nanowire field-effect transistor. The calculations are done for both partial and complete volume inversion and accumulation biasing conditions. Computations are performed for the 〈100〉 and 〈110〉 orientations of the silicon nanowire. The results show the effects of the surface potential, the electric field and the transverse dimensions of the nanowire on the electron energies and wavefunctions. Depending on the combinations of the surface potential and electric field, the energy level can increase, decrease or remain constant as the thickness of the nanowire increases. It is also observed that higher surface potentials can significantly change the energy states due to the increase of volume inversion/accumulation.
    Nanotechnology 09/2012; 23(41):415201. · 3.84 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: ZnTe nanowires, grown by a vapor–liquid–solid technique are p-type and show a very high intrinsic resistivity. Enhancement of the nanowire conductivity was investigated by vacuum annealing, doping and Joule heating. The current–voltage (I–V) characteristics were measured in all cases and electrical parameters such as resistivity, carrier concentration and mobility were computed from the I–V curves. An improvement of five orders of magnitude in the electrical conductivity was seen after thermal annealing and Joule heating, comparable to the enhancement in conductivity obtained by doping.
    Chemical Physics Letters 08/2012; 543:117–120. · 2.15 Impact Factor

Publication Stats

20 Citations
136 Downloads
2k Views
104.39 Total Impact Points

Institutions

  • 1996–2014
    • Pohang University of Science and Technology
      • Department of Electronic and Electrical Engineering
      Geijitsu, North Gyeongsang, South Korea
  • 2012
    • University of Calcutta
      • Institute of Radio Physics and Electronics
      Kolkata, Bengal, India