Jo-won Lee

Carbon nanotube electron emitters with a gated structure using backside exposure processes

We have fabricated fully vacuum-sealed 5 in. diagonal carbon nanotube field-emission displays of a gated structure with reliable electron emission characteristics. Single-walled carbon nanotube tips were implemented into the gate structure using self-aligned backside exposure of photosensitive carbon nanotube paste. An onset gate electrode voltage for emission was about 60 V and the luminance as high as 510 cd/m2 was exhibited under an application of 100 V and 1.5 kV to gate electrode and anode, respectively.

Ultrahigh-density nanotransistors by using selectively grown vertical carbon nanotubes

A type of carbon nanotube transistors, which would be suitable for large-scale integration, has been fabricated from vertically aligned carbon nanotubes. We fabricated highly ordered carbon nanotubes, which are selectively grown on the patterned aluminum oxide nanotemplates. Each device element is formed on a vertical carbon nanotube attached to a bottom (source) and upper (drain) electrodes and a gate electrode, which is electrostatically switchable. The transistors can be integrated in large arrays with the potential for tera-level density (2×1011/cm2). The vertical carbon nanotube transistor shows ON/OFF switching operation at 30 K.

Carbon-nanotube-based nonvolatile memory with oxide–nitride–oxide film and nanoscale channel

We have fabricated a single-wall carbon-nanotube (CNT)-based nonvolatile memory device using SiO2–Si3N4–SiO2 (ONO) layers as a storage node. The memory device is composed of a top gate structure with a channel width of a few nanometers and the ONO layer embedded between CNT and gate electrode. When the bias voltage between the CNT and gate electrode increases to 4 V, charges are tunneled out from CNT surfaces and captured to the traps in the ONO layers. Stored charges on the trap sites make the threshold voltage shift of 60 mV and is independent of charging time, suggesting that the ONO has traps with a quasiquantized energy state. The quantized state is related to the localized high electric field associated with CNT channel. The CNT-field-effect transistor with an ONO storage node could be used for an ultrahigh-density nonvolatile memory.We have fabricated a single-wall carbon-nanotube (CNT)-based nonvolatile memory device using SiO2–Si3N4–SiO2 (ONO) layers as a storage node. The memory device is composed of a top gate structure with a channel width of a few nanometers and the ONO layer embedded between CNT and gate electrode. When the bias voltage between the CNT and gate electrode increases to 4 V, charges are tunneled out from CNT surfaces and captured to the traps in the ONO layers. Stored charges on the trap sites make the threshold voltage shift of 60 mV and is independent of charging time, suggesting that the ONO has traps with a quasiquantized energy state. The quantized state is related to the localized high electric field associated with CNT channel. The CNT-field-effect transistor with an ONO storage node could be used for an ultrahigh-density nonvolatile memory.

A new low voltage fast SONOS memory with high-k dielectric

Abstract The comparison of simulated write/erase characteristics of silicon–oxide–nitride–oxide–silicon (SONOS) nonvolatile memory with different oxides SiO 2 , Al 2 O 3 and ZrO 2 as a top dielectric was made. We demonstrate, that an application of high- k dielectrics allows to decrease the write/erase programming voltage amplitude or programming time from 1 ms to 10 μs. The ZrO 2 suppresses parasitic electron injection from polysilicon gate. Also the design of SONOS memory based on high- k dielectrics is promising for terabit scale using hot carriers injection EEPROM and DRAM memory.

Synthesis, Properties, and Applications of 2-D Materials: A Comprehensive Review

Recent advances in atomically thin two-dimensional (2-D) materials have led to a variety of promising future technologies for post-CMOS nanoelectronics and energy generation. This review is an attempt to thoroughly illustrate the current status and future prospects for 2-D materials other than graphene (e.g., BN nanosheets, MoS2, NbSe2, WS2, etc.), which have already been contemplated for both low-end and high-end technological applications. An overview of the different synthesis techniques for 2-D materials is presented here, with an exploration of the potential for developing methods of controllable large scale synthesis. Furthermore, we summarize the underlying theories which correlate the structural and physical properties of 2-D materials with their state-of-the-art applications. Finally, we show that utilizing the unprecedented properties arising from these materials would lead to innovative devices. Such devices would significantly reduce both device dimensions and power consumption, as necessary for the creation of tomorrows sustainable technology.

Performance of microstrip bandpass filters using high‐Tc superconducting YBa2Cu3O7−δ thin films on LaAlO3

We have fabricated a microstrip three‐pole bandpass filter with a fractional bandwidth of 5% at a center frequency of 10.5 GHz utilizing laser ablated high‐ Tc superconducting YBa2Cu3O7−δ thin films on LaAlO3 substrates. Microwave performance of the filter was carried out as a function of temperature. The filter exhibited low insertion losses of about 0.077 and 0.304 dB at 20 and 77 K, respectively. More than 15 dB in return losses was obtained at the same temperatures. Intermodulation distortion measurements were performed to evaluate power‐handling capacity of the filter, which results from the nonlinear effects of surface resistance. Third‐order intercept points were 68 dBm at 20 K and 58 dBm at 77 K. The nonlinear performance in the passband was also measured using a group delay method. The superconducting filter was compared with an equivalent gold filter which showed the insertion loss of more than 3.5 dB at 77 K.

Interleukin-18 as an efficient marker for remission and follow-up in patients with inactive adult-onset Still’s disease

Objectives: Diagnosis of adult-onset Still’s disease (AOSD) is difficult because of a lack of pathognomonic findings and markers. The aim of this study was to investigate the efficacy of interleukin (IL)-18 and free IL-18 in the diagnosis and follow-up of patients with AOSD. Method: Levels of inflammatory cytokines, IL-18, IL-18 binding protein (IL-18BP), and free IL-18 were compared in 80 AOSD patients and 90 controls. The AOSD patients were divided into active and inactive groups according to disease activity, and the inactive patients were subdivided into a remission subgroup and a low disease activity subgroup. We compared erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), ferritin, IL-18, and free IL-18 as disease activity markers in the AOSD patients. Serial serum levels of activity markers were measured in 52 of the 80 AOSD patients at 3- to 6-month intervals. Results:There were significantly higher levels of IL-18 and free IL-18 in the AOSD patients than in the controls. IL-18 and free IL-18 were significantly higher in the active group than the inactive group (p < 0.001 for all). Unlike other activity markers, IL-18 and free IL-18 levels in the low disease activity subgroup were significantly higher than those in the remission subgroup within the inactive group (p = 0.004 and 0.005, respectively). During serial follow-up, ferritin and IL-18 showed a significant decrease in the responder and remission subgroup. Conclusions: IL-18 might be an efficient marker for diagnosis and follow-up of AOSD and might also be a useful predictor of remission, especially in clinically inactive patients.

39.2: The Full‐Color Video Images with Uniquely‐Gated Carbon Nano‐tube Field Emission Displays

Thick-film printing processes have been applied for preparing a carbon nanotube field emission display (c-FED), which has a strong cost advantage for large-size flat panel display. For practical display applications, two types of the gated cathode structure named the normal-gate cathode and the under-gate cathode have been developed and improved. The normal-gate and the under-gate cathode structures have the driving voltages of ±35 V and ±65 V, respectively. The 5″ c-FED panel with the normal-gate cathode and the 7″ c-FED panel with the under-gate cathode were successfully implemented and excellent full-color video images were obtained.

Tunability and loss tangent of ferroelectric films in superconducting resonator

Using a high-temperature superconducting resonator, measurements of the dielectric properties of ferroelectric films at microwave frequency ( GHz) are performed. The variation in dielectric constant, , of film under the influence of an applied dc voltage, , at liquid-nitrogen temperature affects the value of the capacitance, C, and loss tangent, , of the ferroelectric capacitor. In order to evaluate the values of C and of the capacitor, we used the resonator which has a planar ferroelectric capacitor in the break of the microstrip line. The couplings of each microwave input and output port are designed in the resonator, including the bias circuits of the zero-field points. ferroelectric capacitors with values of the capacitance of about 0.5 pF and less than 0.01 successfully control the tunability of the resonance frequency in the resonator with a factor of .

Improvement of carrier mobility of top-gated SiC epitaxial graphene transistors using a PVA dielectric buffer layer

The effects of treatment with polyvinyl alcohol (PVA) and a dielectric film of HfO(2) on the properties of SiC based epitaxial graphene have been explored and analyzed. We have characterized the carrier mobility of graphene on Si-face and C-face SiC with a layer of HfO(2), with or without an initial PVA treatment on the device active layer. Epitaxial graphene grown on the C-face displays a higher mobility than a film grown on the silicon face. Also, the mobility in the presence of the PVA treatment with HfO(2) dielectric layer has been improved, compared with the mobility after deposition of only gate dielectric: ∼20% in C-face graphene and ∼90% in Si-face graphene. This is a major improvement over the degradation normally observed with dielectric/graphene systems.