Dongouk Kim

Experimental evidence of ballistic transport in cylindrical gate-all-around twin silicon nanowire metal-oxide-semiconductor field-effect transistors

We have investigated the electrical characteristics of cylindrical gate-all-around twin silicon nanowire metal-oxide-semiconductor field effect-transistors with 4nm radius and the gate length ranging from 22to408nm. We observed strong transconductance overshoot in the linear source-drain bias regime in the devices with channel length shorter than 46nm. The mean free path estimated from the slope of the zero-field one dimensional ballistic resistance measured as a function of device length was almost the same as this length.

Design of multi-functional dual hole patterned carbon nanotube composites with superhydrophobicity and durability

AbstractMost current research on nanocomposites has focused on their bulk attributes, i.e., electrical, microwave, thermal, and mechanical properties. In practical applications, surface properties such as robustness against environmental contamination are critical design considerations if intrinsic properties are to be maintained. The aim of this research is to combine the bulk properties of nanocomposites with the superhydrophobic surface properties provided by imprinting techniques to create a single multi-functional system with enhanced bulk properties. We report the development of a highly conductive superhydrophobic nanotube composite, which is directly superimposed with a durable dual hole pattern through imprinting techniques. The dual hole pattern avoids the use of high slenderness ratio structures resulting in a surface which is robust against physical damage. Its stable superhydrophobic properties were characterized both theoretically and experimentally. By incorporating high aspect ratio carbon nanotubes (CNTs), the dual patterned composites can also be effectively used for anti-icing and deicing applications where their superhydrophobic surface suppresses ice formation and their quick electric heating response at low voltage eliminates remaining frost. In addition, superior electromagnetic interference (EMI) shielding effectiveness (SE) was attained, with one of the highest values ever reported in the literature.

Suppression of Injection Voltage Disturbance for High-Frequency Square-Wave Injection Sensorless Drive With Regulation of Induced High-Frequency Current Ripple

In the square-wave voltage signal injection sensorless drive of the interior permanent-magnet synchronous machine, the injection voltage can be distorted by the inverter nonlinearity effects especially when the injection voltage is low. If that happens, a high-frequency (HF) current signal which contains the rotor position information could be also distorted, which directly leads to an error in the position estimation. This paper analyzes the effects of the inverter nonlinearity on injection voltage, on induced current ripple, and on the position estimation performance in sequence and proposes a voltage injection method to minimize the impact of the inverter nonlinearity by the regulation of the HF current ripple. By simulations and experiments, the performance of the proposed method has been verified. The experimental results show 19.7% reduction of position estimation error under 15% of rated voltage signal injection without increasing the current ripple at a certain operating condition. Moreover, the performance of position estimation is kept uniform regardless of the loading condition.

Anti-frost coatings containing carbon nanotube composite with reliable thermal cyclic property

One of the most important applications for superhydrophobic coatings is anti-frosting for safety and energy conservation. Safety concerns are especially critical in cold-climate regions where the daily temperature fluctuation is large. However, superhydrophobic coatings have not been studied in terms of their thermomechanical reliability. In this study, wetting characteristics and stress relaxation behavior were quantitatively investigated with multi-walled carbon nanotube (MWNT)–silicone composite films under thermal cycling conditions. It is concluded that an open structure with numerous nanopores among the fillers, constituting air pockets described as the “Cassie structure,” is of great importance not only for developing a films superhydrophobic nature but also for accommodation of thermal stress that results from a difference in coefficient of thermal expansion between the coating and the substrate. The amount of stress relaxation for a 30 vol% MWNT–silicone composite film with open structure reaches ∼80% of the value for its counterpart with a closed structure and no pores. A superhydrophobic MWNT–silicone composite film that can endure over 4000 thermal cycles (−30 °C to room temperature) is fabricated by controlling the composition and microstructure of the composite. In addition, the importance of the size and shape of the nanofillers in delaying nucleation and growth of frost on superhydrophobic coatings is also discussed.

Subthreshold Degradation of Gate-all-Around Silicon Nanowire Field-Effect Transistors: Effect of Interface Trap Charge

We measured and analyzed the subthreshold degradation of the gate-all-around (GAA) silicon nanowire field-effect transistors with the length of 300/500 nm and the radius of 5 nm. An analytical model incorporating the effect of interface traps quantitatively explained the measured subthreshold swing (SS) degradation. A simple electrostatic argument showed that the GAA device had smaller degradation of SS values than planar devices for the same interface trap densities.

Temperature Dependent Study of Random Telegraph Noise in Gate-All-Around PMOS Silicon Nanowire Field-Effect Transistors

We report the random telegraph noise observed in gate-all-around (GAA) PMOS silicon nanowire FETs (SNWFETs) with the radius of 5 nm, at various temperatures (s) down to 4.2 K. From the -dependence of the capture/emission time, we obtain the energy and the charging status of the trap states. The gate bias dependence and the -dependence of the scattering coefficient-mobility product extracted from the relative fluctuation amplitude of the drain current are consistent with the fact that the surface roughness scattering is dominant in GAA PMOS SNWFETs.

Observation of three-dimensional shell filling in cylindrical silicon nanowire single electron transistors

The authors have measured addition energy spectra from gate-all-around twin silicon nanowire single electron transistors (SETs) with the radius of 5nm and with circular cross sections. Nonmonotonically varying addition energies are observed and the authors interpret them as shell fillings of silicon nanowire quantum dots with three-dimensional harmonic confinement potentials. A 45nm long SET shows 2-1-2-1 filling behavior while a 38nm long SET exhibits 1-2-2-1 filling. These filling behaviors match with the calculated degeneracies of nanowires with different confinement strengths.

Suppression of injection voltage disturbance for High Frequency square-wave injection sensorless drive with regulation of induced High Frequency current ripple

In the square-wave voltage signal injection sensorless drive of the interior permanent-magnet synchronous machine, the injection voltage can be distorted by the inverter nonlinearity effects especially when the injection voltage is low. If that happens, a high-frequency (HF) current signal which contains the rotor position information could be also distorted, which directly leads to an error in the position estimation. This paper analyzes the effects of the inverter nonlinearity on injection voltage, on induced current ripple, and on the position estimation performance in sequence and proposes a voltage injection method to minimize the impact of the inverter nonlinearity by the regulation of the HF current ripple. By simulations and experiments, the performance of the proposed method has been verified. The experimental results show 19.7% reduction of position estimation error under 15% of rated voltage signal injection without increasing the current ripple at a certain operating condition. Moreover, the performance of position estimation is kept uniform regardless of the loading condition.

Carbon Nanotube Nanocomposite Having Segregated Network Structure for Wearable Thermotherapy Application

Multiwalled nanotube (MWNT)/silicone composites having segregated MWNT network and micro-void structure were developed for wearable thermotherapy application. The nano-composites could be quickly fabricated from instant evaporation of aqueous medium during spray coating process. Fast electric heating behavior (4.8 °C/s) was demonstrated, in comparison with that (1.4 °C/s) of conventional silicone rubber composites having no void. Long-term stability was also verified with thermal aging and thermal cycling tests up to 100 h.

Transport through single dopants in gate-all-around silicon nanowire MOSFETs (SNWFETs)

Temperature (T) dependent transport measurements of cylindrical shaped gate-all-around silicon nanowire MOSFETs (SNWFETs) were performed. Single electron tunneling behaviors were observed at 4.2 K and one of the devices exhibited anomalously strong current peak which survived even at room temperature. The observed peak was interpreted as an evidence of transport through single impurities in the channel.