Yoichiro Neo

Fabrication of a Field Emitter Array with a Built-in Einzel Lens

A field emitter array (FEA) with four stacked gate electrodes, that is, FEA with a built-in einzel lens, was fabricated using an etch-back technique. In our method, gate hole opening is a self-aligned process; therefore, the axes of electrode holes are well aligned without precise lithography. Emitter tip opening is also a unique process: the tip opening is usually carried out using buffered hydrofluoric (BHF) acid to prevent tip damage. However, in the case of the FEA with a multistacked electrode, BHF etching produces a long undercut under the electrode, particularly under the upper electrode. In our process, the upper lens electrode is used as a photolithography mask when etching silicon dioxide in order to prevent excess undercut. In this paper, the details of fabrication are described.

Resonant Fowler–Nordheim tunneling emission from metal-oxide-semiconductor cathodes

A metal-oxide-semiconductor tunneling cathode was fabricated with an ultrathin oxide layer and an abrupt interface between the oxide layer and the polycrystalline Si gate electrode. The emission current shows periodic deviations on the Fowler–Nordheim plot estimated by the Wentzel–Kramers–Brillouin (WKB) approximation. The peaks in the oscillations are confirmed to arise from the resonant effect of electron tunneling by comparing the experimental results with the theoretical calculations. This article describes the first experiment of resonant tunneling emission.

Experiments of highly emissive metal–oxide–semiconductor electron tunneling cathode

An effective mean‐free path of hot electrons in the conduction band of SiO2 in a Si‐gate metal–oxide–semiconductor (MOS) electron tunneling cathode was measured and found to be about 0.7 nm. Following these observations, we proposed and fabricated a depletion gate MOS electron tunneling cathode. The highest transfer ratio of 13.3% was achieved in the cathode at the low emission current level, which was considerably higher than that of tunneling cathodes studied in the past. However, the ratio decreased drastically at high current due to the hole injection into the depletion region from the gate.

Emission and focusing characteristics of volcano-structured double-gated field emitter arrays

Volcano-structured double-gated field emitter arrays (VDG-FEAs) with different focusing electrode height have been fabricated and the focusing characteristics for each VDG-FEAs were evaluated in detail. The authors experimentally proved that lowering the focusing electrode was very effective to keep a high emission current and successfully removed the electric field relaxation at the tip during the focusing operation. The anode current of about 1.9μA was maintained for the VDG-FEA with the height of the focusing electrode relative to the extraction electrode, hf=−470nm, even in applying 5V to the focusing electrode, and the current was 84.4 times larger, compared with the sample with hf=220nm under the same focusing condition. It was found that the emitted electrons returned back to the extraction electrode by the potential barrier caused by the low focusing potential below 3V in every sample.

Electronic transport properties of Cs-encapsulated single-walled carbon nanotubes created by plasma ion irradiation

The electronic transport properties of Cs-encapsulated single-walled carbon nanotubes (Cs@SWNTs), which are created by a plasma ion irradiation method, are experimentally investigated at both room and low temperatures by fabricating field-effect transistor devices with these modified SWNTs. It is found that Cs@SWNTs exhibit air stable n-type transport characteristics at room temperature, where Cs atoms function as an electron donor. Moreover, Coulomb oscillations are observed under a low temperature, which is derived from the electronic structure modulated mainly by the encapsulated Cs atoms.

Field emission characteristics of a graphite nanoneedle cathode and its application to scanning electron microscopy

A high-brightness electron beam of more than 1011Asr−1m−2 was achieved from a graphite nanoneedle cathode, which was fabricated by simple hydrogen plasma etching of a graphite rod. A field emission was obtained at a high residual pressure of 10−6Torr. The performance of this cold cathode was demonstrated by the fabrication of a scanning electron microscope, which was operated at a high residual pressure of 10−5–10−6Torr. The brightness of this cathode offers a convenient field electron emission source that does not require a massive ultrahigh vacuum system.

Study of Carbon-Nanotube Web Thermoacoustic Loud Speakers

Thermoacoustic carbon nanotube (CNT) speakers were fabricated using CNT webs spun from a multiwalled carbon nanotube (MWNT) array of 0.8–1.6 mm height. The generated sound pressure level (SPL) showed a linear relationship with frequency over a wide range from 10 Hz to 40 kHz with a slope of 6 dB/octave. In addition to this, significantly broad and flat SPLs were obtained in the ultrasonic region, ranging from 40 to 100 kHz. The distance from the speaker to the microphone was 0.5 m. The high SPL is due to the good heat radiation property of the MWNT web. Herein, we showed an acoustical property for the MWNT web thermoacoustic speaker from the viewpoint of the structural web morphology. The role of heat radiation behavior and the effects of the length of individual MWNTs are discussed.

Electron Optical Properties of Microcolumn with Field Emitter

We present the electron optical properties of a newly designed microcolumn. The microcolumn consists of an objective lens and an electron gun, which is composed of a microscale field emitter and a condenser lens. An acceleration lens was used as the objective lens. Each component was optimized to maximize its own function while minimizing its impact on the functions of the other components. The current–voltage characteristics of each electrode were evaluated. The current variation characteristics of each electrode indicated that each optimized structure could be used to control the electron beam. The objective lens could also focus the electron beam to a diameter of approximately 40 µm at a working distance of 2 mm and 400× magnification when no acceleration electric field was applied between the microcolumn and the anode.

Fabrication of Volcano-Structured Double-Gate Field Emitter Array by Etch-Back Technique

Volcano-structured double-gate field emitter arrays (VDG-FEAs) were fabricated using the etch-back technique. The fabrication process of the VDG-FEA is simple, and the height (hf) of the focusing electrode relative to the extraction gate electrode is easily adjusted by varying the etch-back time without high-resolution lithography. We have fabricated two types of VDG-FEAs with hf = +220 and 0 nm. The focusing characteristic is controlled by tuning hf. The decrease of the anode current is reduced for the VDG-FEA with lower hf under focusing condition producing the same beam spot size.

Improvement of the emission current from a cesiated metal-oxide-semiconductor cathode

We have reduced the work function of the gate electrode of a metal-oxide-semiconductor tunneling cathode by cesiation. After cesiation, there was a considerable increase in the emission current and a large number of electrons were detected at energies lower than the original vacuum level of the poly-Si gate electrode. These results indicate that almost all the tunneling electrons have energies lower than the original vacuum level of the gate electrode, and that after cesiation electrons initially prevented from being emitted by the original vacuum level were emitted, because of the reduced work function due to cesiation.