Jung Su Kang

Carbon Nanotube Electron Emitter for X-ray Imaging

The carbon nanotube field emitter array was grown on silicon substrate through a resist-assisted patterning (RAP) process. The shape of the carbon nanotube array is elliptical with 2.0 × 0.5 mm2 for an isotropic focal spot size at anode target. The field emission properties with triode electrodes show a gate turn-on field of 3 V/µm at an anode emission current of 0.1 mA. The author demonstrated the X-ray source with triode electrode structure utilizing the carbon nanotube emitter, and the transmitted X-ray image was of high resolution.

Highly stable carbon nanotube cathode for electron beam application

The authors fabricated an optimized electron beam (e-beam) with a carbon nanotube (CNT) cathode and triode configuration. CNT emitters grown with a resist-assisted patterning process were used as an electron source. The gate mesh was aligned with the CNT emitter islands for a lower leakage current, resulting in a higher electron emission current and transmission ratio. Additionally, the width between CNT islands and the pitch between CNTs were optimized to enhance the electric field at the tip of the CNT emitters. With the optimized e-beam module, consisting of a CNT cathode and gate mesh, CNT pitch of 30 μm, dot size of 3 μm, line width of 210 μm, and gate mesh width of 75 μm, the emission current showed an increase of 165 times and operated for more than 500 h with DC driving. The optimized e-beam can be a building block for vacuum nanoelectronic devices.

Electron extraction electrode for a high-performance electron beam from carbon nanotube cold cathodes

The effect of an electron extraction electrode on electron emission for a high-performance electron beam was studied using vertically aligned carbon nanotube emitters as a cold cathode. For the lower electron emission regime (anode current less than 1 mA), the gate electrode structure and materials used had little effect on the electron emission current. However, at the higher electron emission regime (anode current higher than 1 mA), the gate electrode materials and structure do begin to deviate from an ideal Fowler–Nordheim plot by the thermal and electrostatic load on the gate electrode, especially for the small cathode area. The gate mesh bends upward under a higher current load, which then increases the gate leakage current. The upward bending in the gate mesh electrode could reduce the effective electric field by increasing the gate to cathode distance, resulting in saturation of the electron emission current. For higher electron emission currents on the anode, a gate electrode comprising a lower th...

Fabrication of miniature carbon nanotube electron beam module for x-ray tube application

We fabricated miniature electron beam module by using carbon nanotube electron emitters for x-ray tube application. The x-ray tubes with the beam module were fabricated with glass envelop and vacuum sealed. The miniature electron beam module was designed to achieve more than 90 % of electron transmission ratio through gate electrode with higher than 3 mA of anode current. The x-ray tube shows micro focused focal spot size and enough flux for dental imaging.

High-performance carbon-nanotube-based cold cathode electron beam with low-thermal-expansion gate electrode

The emission of a high-performance electron beam via a carbon nanotube cold cathode requires a higher electron transmission through the gate electrode. The transmittance of electrons through the gate mesh electrode strongly depends on the gate electrode structure and material properties. Therefore, thermal expansion of the gate electrode induced by the thermal load owing to the gate leakage current is a significant hurdle to be overcome. Using a high-thermal-expansion gate electrode comprised of SUS304 grid mesh, electron emission was brought to saturation when the mesh was bent upward, which was the result of a reduction of the effective electric field under the grid mesh. To mitigate the effect of this bending, a Mo grid mesh material possessing low thermal expansion introduced. The Mo grid material properties of low linear temperature expansion coefficient, high tensile strength, and low resistivity are necessary. With this grid mesh improvement, the electron emission current increased to ten times that of the SUS304 mesh grid.The emission of a high-performance electron beam via a carbon nanotube cold cathode requires a higher electron transmission through the gate electrode. The transmittance of electrons through the gate mesh electrode strongly depends on the gate electrode structure and material properties. Therefore, thermal expansion of the gate electrode induced by the thermal load owing to the gate leakage current is a significant hurdle to be overcome. Using a high-thermal-expansion gate electrode comprised of SUS304 grid mesh, electron emission was brought to saturation when the mesh was bent upward, which was the result of a reduction of the effective electric field under the grid mesh. To mitigate the effect of this bending, a Mo grid mesh material possessing low thermal expansion introduced. The Mo grid material properties of low linear temperature expansion coefficient, high tensile strength, and low resistivity are necessary. With this grid mesh improvement, the electron emission current increased to ten times tha...

Deep-ultraviolet light source with a carbon nanotube cold-cathode electron beam

Deep-ultraviolet (UV) light is widely used in many industries including medicine because it has sufficient energy to kill viruses and bacteria. However, deep UV with a wavelength of 254 nm can damage human cells, so it is necessary to develop a deep-UV light source with a shorter wavelength to minimize the damage to human cells while still killing viruses. The authors used a carbon nanotube-based cold-cathode electron beam (C-beam) and wide-bandgap anode to fabricate a deep-UV light source with an emission wavelength below 250 nm. The anode was fabricated by annealing ZnO ink on a Si wafer; deep UV with a wavelength of 247 nm and full width at half maximum of 23 nm was obtained. In the case of C-beam irradiation of an anode fabricated on a quartz substrate, deep UV with wavelengths of 208, 226, and 244 nm was generated through excitation with a beam energy of 7 kV and beam currents of 0.3 and 0.5 mA.Deep-ultraviolet (UV) light is widely used in many industries including medicine because it has sufficient energy to kill viruses and bacteria. However, deep UV with a wavelength of 254 nm can damage human cells, so it is necessary to develop a deep-UV light source with a shorter wavelength to minimize the damage to human cells while still killing viruses. The authors used a carbon nanotube-based cold-cathode electron beam (C-beam) and wide-bandgap anode to fabricate a deep-UV light source with an emission wavelength below 250 nm. The anode was fabricated by annealing ZnO ink on a Si wafer; deep UV with a wavelength of 247 nm and full width at half maximum of 23 nm was obtained. In the case of C-beam irradiation of an anode fabricated on a quartz substrate, deep UV with wavelengths of 208, 226, and 244 nm was generated through excitation with a beam energy of 7 kV and beam currents of 0.3 and 0.5 mA.

Fabrication of a compact glass-sealed x-ray tube with carbon nanotube cold cathode for high-resolution imaging

A glass-sealed x-ray tube with field emission electron sources has been fabricated using carbon nanotubes (CNTs) grown on a silicon substrate by direct current plasma-enhanced chemical vapor deposition. Here, the authors report on the fabrication of CNT-based emitters, the field emission characteristics of these emitters, and the properties of the glass-sealed x-ray tube. The field emission produced a current of 5 mA with an electron transmission rate of 91.1% in a high-vacuum chamber. The glass-sealed x-ray tube had a conventional design and comprised a reflection anode, an evaporation getter, and a vacuum-sealed glass tube without additional focusing electrode requirements for ease of commercialization. Using this x-ray tube, the authors obtained x-ray images of objects, including a human finger and a commercial universal serial bus (USB) flash drive. The x-ray image allowed a 100 μm metal wire to be distinguished in the USB flash drive. The x-ray images were obtained at a dose rate of 1944 mrad/h, whic...

High performance glass sealed x-ray tube with CNT cold cathode electron beam (C-beam)

We fabricated field emission electron sources and applied for the glass sealed x-ray tube for medical imaging devices. The x-ray tube consists of an electron beam with a patterned grown CNT emitters with RAP process. Those electron beam shows higher electron emission current and transmittance after glass seal. With the x-ray tube, we success to measure medical image with finger and high resolution PCBs. The fabricated x-ray tube shows electron transmission ratio (>90%) and current (>3 mA).

Fabrication of highly stable electron beams with CNT cold cathode

We fabricated a high performance electron beam for the vacuum electronic devices with carbon nanotube (CNT) cathode. For the vacuum electronic devices application, a structure of cold cathode should be highly adhere on cathode substrate and endure a resistive heating during electron emission. For fabrication of stable electron beam, we optimized the CNT emitters and the triode structure. The structural properties of CNT emitters could be enhanced with functional coating on CNT surfaces. In this study, we developed silicon functional coating technique on CNT emitters and enhanced and stable electron emission with the coating.

Deep UV light source with CNT cold cathode electron beam (C-beam)

We developed deep UV generation techniques with home-made wide bandgap anode and carbon nanotube (CNT) based cold cathode electron beam (C-beam). The wide bandgap anodes excited with high performance C-beam. The fabrication process for anodes were developed and optimized for high performance deep UV generation. Also, the performance of C-beams optimized. With the optimized C-beam and anode, we could obtain deep UV with wavelength of 208, 226 and 244 nm. The deep-UV light sources could make new era of UV lighting technologies and industries.