Nanotube Field Emitter Arrays Research Articles

Fabrication and properties of under-gated triode with CNT emitter for flat lamp

We investigated under-gate type carbon nanotube field emitter arrays (FEAs) for back light unit (BLU) in liquid crystal display (LCD). Gate oxide was formed by wet etching of ITO coated glass substrate instead of depositing SiO 2 on the glass substrate. Wet etching is easier and simpler than depositing and etching thick gate oxide to isolate the gate metal from cathode electrode in triode. To optimize the triode, we simulated the electric field distribution and electron trajectory in triode structures by the SIMION simulator. CNT emitters were formed using screen printing of photosensitive CNT paste. Field-emission characteristics of triode structure were measured. The maximum current density of 92.5 μA/cm 2 was when the gate and anode voltage was 95 and 2500 V, respectively, at the anode–cathode spacing of 1500 μm.

Robust and regenerable integrally gated carbon nanotube field emitter arrays

We have grown multiwalled carbon nanotubes by chemical-vapor deposition on two types of gated structures, one containing a silicon post, and another having an open aperture. A gate current to anode-current ratio of 2.5%, the lowest of any nanotube field emitter arrays was measured for the open aperture configuration. The silicon post structures produced 1-nA emission current at gate voltages below 20V and up to 1mA at 40V (from 0.5-mm2 area). The emission was relatively stable compared to other field emitter arrays and destructive arcing was not observed. The gate voltage needed to produce a given emission current was reduced by adsorbed water vapor and was unaffected by xenon. Emission in hydrogen at pressures near 10−4Torr also increased the emission current, and restored a large fraction of the original emission current to arrays degraded by operation in oxygen. Electron energy distributions broaden and shift to lower energies at higher emission current. The broadening can be explained by the potentials developed at the silicon-nanotube contacts, and at the nanotube-vacuum interface.

Fabrication of Flexible Carbon Nanotube Field Emitter Arrays by Direct Microwave Irradiation on Organic Polymer Substrate

Carbon nanotubes (CNTs) were directly synthesized on flexible polymer substrates without damage of polymer by microwave irradiation. Cobalt was used as the catalysts, and the synthesis was done in the atmospheric pressure with an acetylene carbon source. Only 5 s was required for the synthesis of well-graphitized CNTs. Field emission measurements revealed that this flexible CNT field emitter array has a great potential for the flexible field emission displays (FEDs).

Fabrication and field emission characteristics of high density carbon nanotube microarrays

High density carbon nanotube field emitter arrays (CNT-FEAs) with various multilayer cathode structures have been fabricated on Si utilizing conventional integrated circuit technology and microwave-heated chemical vapor deposition process. The CNT-FEAs were configured as triode emitters with 1-μm thermal SiO2 as the insulator and 400-nm Cr as the gate, and compared per the resulting morphologies, Raman spectra, and field emission characteristics. It was found that the Ni∕Cr∕Si cathode structure is the best fit for selective growth of CNTs in gate holes. In particular, a CNT-FEA fabricated on Ni(60nm)∕Cr(80nm)∕Si cathode structure has yielded excellent emission characteristics, with low turn-on and threshold fields, being, respectively, at 0.45 and 3.7V∕μm. This triode CNT device also exhibited a uniform image of high brightness(∼1800cd∕m2) on a green-phosphor coated idium-tin-oxide glass and a relatively stable emission current, being tested at a constant anode voltage of 1000 and 900 V, respectively.

Regeneration of gated carbon nanotube field emission

We report large increases in field emission current when operating carbon nanotubes in substantial pressures of hydrogen, especially when the nanotubes were contaminated. We have previously demonstrated two different configurations of integrally gated carbon nanotube field emitter arrays (cNTFEAs), CNTs grown inside microfabricated gate apertures with and without silicon posts. Salient features of these in situ grown microgated cNTFEAs include the absence of electrical arcing, low operating voltage, and enhancing effect of some residual ambient gases. Operating both configurations of cNTFEAs without special precleaning in greater than 10−5Torr hydrogen produced orders of magnitude enhancement in emission. For a cNTFEA intentionally degraded by oxygen, the operation in hydrogen resulted in a 340-fold increase in emission current at constant gate voltage. The results suggested a dependence on atomic hydrogen produced from the interaction between emission electrons and molecular hydrogen. The observed emission enhancement could be due to a surface dipole formation, hydrogen doping, or removal of oxygen-containing surface species.

Screen printed carbon nanotube field emitter array for lighting source application

We have investigated carbon nanotube (CNT)-field emitter array (FEA) for the application of lighting system like back light unit (BLU) in liquid crystal display (LCD). The photosensitive CNT paste was synthesized by mixing of multiwalled carbon nanotubes (MWNTs), spin on glass (SOG), organic vehicle, photosensitive monomers, photosensitive oligomers and photo initiators. Uniform CNT paste films were obtained by using backside exposure technique and emission properties of CNT paste were evaluated depending on variation in SOG content and firing conditions. Then we prepared line patterned CNT-FEAs using photolithography and measured their I–V characteristics and brightness.

Field-emission characteristics from carbon nanotube field emitter arrays grown on silicon emitters

The fluctuation of the emission current from carbon nanotube field emitter arrays (CNT FEAs) grown on silicon emitters was investigated as a function of total emission current and ambient pressure. The ratio of amplitude of short-term fluctuation ΔI and average emission current Iave strongly depended on Iave. The relationship ΔI/Iave∝Iave−1/2 was found. This relationship showed that the average emission current Iave is proportional to the number of active carbon nanotube emitters. The effect of vacuum pressure on the emission properties was examined by adjusting the pumping speed of the turbomolecular pump. The emission current at fixed voltage was affected by the adsorption of gas species and amounts.

Carbon nanotube field emitter arrays having an electron beam focusing structure

An electron beam focusing structure was incorporated into the gated field emitter arrays where the emitters were screen-printed carbon nanotubes. The focusing structure was comprised of 8-μm-thick bulky SiOx focus gate insulator and Cr focus gate, and exhibited negligible leakage between the gate and the focus gate. In current–voltage measurements, it is found that the anode current strongly depends on both the focus gate and the anode bias voltages. Electron beams were focused well at the anode with a slight overfocusing effect, which is due to the wide electron beam divergence from carbon nanotubes. A new focusing structure based on the simulation is proposed to overcome the overfocusing.

Direct growth of aligned carbon nanotube field emitter arrays onto plastic substrates

The direct growth of vertically aligned carbon nanotubes onto flexible plastic substrates using plasma-enhanced chemical vapor deposition is reported. We show that individual lines and dots of free-standing 20–50 nm diameter nanotubes can be grown onto chromium covered commercially available polyimide foil. The scalable deposition method allows large area coverage without degrading or bending the sensitive substrate material. Field emission measurements show a low turn-on field (3.2 V/μm) and a low threshold field (4.2 V/μm). The result establishes a method of flexible field emitter fabrication, which is well suited for display production and integration of nanotubes into plastic electronics.

Development of triode-type carbon nanotube field-emitter arrays with suppression of diode emission by forming electroplated Ni wall structure

Triode-type field-emitter arrays were developed by screen printing a photosensitive paste including single-walled carbon nanotubes. Ni wall structure (NWS) was electroplated to form a thick gate to suppress diode emission induced by strong electric strengths due to an anode potential and to focus electron beams to their destined color subpixels. It was observed in computer simulations, as well in experiments that the NWS with the optimum thickness was effective in reducing the diode emission and enhancing electron-beam focusing by modifying electrical potentials around the carbon nanotube emitters. Our fully sealed field-emission display panel using the field-emitter arrays with the NWS demonstrated full color moving images without serious diode emission and with satisfactory color separation.

High-current field emission from a vertically aligned carbon nanotube field emitter array

Arrays of vertically aligned carbon nanotubes (CNTs) were grown on a patterned sputtered cobalt film by chemical vapor deposition from ethylenediamine at 900 °C. Each square array comprises a moderate density of nanotubes with an average height of 90 μm covering a total area of 3.6×10−3 cm2. Field emission measurements were carried out on individual arrays at pressures below 10−8 mbar. The spacing between the anode and the top of the CNT array is 935 μm and a total current of 2 mA could be obtained at 2.5 kV. A Fowler–Nordheim plot of the I–V data shows an unusually high field enhancement factor at lower fields. At an average field strength of 1.925 V/μm, the corresponding emission current density is 130 mA/cm2. This emission current was found to be very stable, with short-term fluctuations (5 Hz measurement bandwidth) of no more than ±1.5%, while the current drifted less than 1.5% over a test period of 20 h.

Patterned selective growth of carbon nanotubes and large field emission from vertically well-aligned carbon nanotube field emitter arrays

We have grown well-aligned carbon nanotube arrays by thermal chemical vapor deposition at 800 °C on Fe nanoparticles deposited by a pulsed laser on a porous Si substrate. We also attain a selective growth of carbon nanotubes on a patterned Fe film on Si substrates in terms of pulsed laser deposition and a liftoff patterning method. Field emission measurement has been made on the carbon nanotube (CNT)-cathode diode device at room temperature and in a vacuum chamber below 10−6 Torr. The distance between the CNT cathode and the anode is 60 μm and is kept through an insulating spacer of polyvinyl film. The measured field emitting area is 4.0×10−5 cm2. Our vertically well-aligned carbon nanotube field emitter arrays on the Si-wafer substrate emit a large current density as high as 80 mA/cm2 at 3 V/μm. The transmission electron microscope image shows that they are multiwalled and bamboolike structures and that the tips of some of the carbon nanotube emitters are open. The open tip structure of our CNTs and their good adhesion via Fe nanoparticles to the Si substrate are part of the reason why we can attain a large field emission current density within a low field.

Large field emission current density from well-aligned carbon nanotube field emitter arrays

We have grown well-aligned carbon nanotube arrays by thermal chemical vapor deposition at temperatures below 800°C on Fe nanoparticles deposited by a pulsed laser on a porous Si substrate. Porous Si substrates were prepared by the electrochemical etching of p-Si (1 0 0) wafers with resistivities of 3–6 Ω cm . These well-aligned carbon nanotube field emitter arrays are suitable for electron emission applications such as cold-cathode flat panel displays and vacuum microelectronic devices like microwave power amplifier tubes. Field emission characterization has been performed on the CNT-cathode diode device at room temperature and in a vacuum chamber below 10 −6 Torr. The anode is maintained at a distance of 60 μm from the carbon nanotube cathode arrays through an insulating spacer of polyvinyl film. The measured field emitting area is 4.0×10 −5 cm 2 . Our carbon nanotube field emitter arrays emit 1 mA/cm 2 at an electric field of 2 V/μm; they emit a large current density as high as 80 mA/cm 2 at 3 V/μm, which is orders of magnitude higher than any other results reported so far. The open tip structure of our carbon nanotubes and their good adhesion through Fe nanoparticles to the Si substrate are part of the reason why we can attain a large field emission current density within a low field. The field emitter arrays in our diode device are vertically well-aligned carbon nanotubes on the Si-wafer substrate.

Large Field Emission from Vertically Well-aligned Carbon Nanotubes

AbstractWe have grown well-aligned carbon nanotube arrays by thermal chemical vapor deposition at 800°C on Fe nanoparticles deposited by a pulsed laser on a porous Si substrate. Porous Si substrates were prepared by the electrochemical etching of p-Si(100) wafers with resistivities of 3 to 6 ωcm. These well-aligned carbon nanotube field emitter arrays are suitable for electron emission applications such as cold-cathode flat panel displays and vacuum microelectronic devices like microwave power amplifier tubes. Field emission characterization has been performed on the CNT-cathode diode device at room temperature and in a vacuum chamber below 10−6 Torr. The anode is maintained at a distance of 60[.proportional]m away from the carbon nanotube cathode arrays through an insulating spacer of polyvinyl film. The measured field emitting area is 4.0×10−5cm2. Our carbon nanotube field emitter arrays emit 1mA/cm2at the electric field, 2V/[.proportional]m. And they emit a large current density as high as 80mA/cm2 at 3V/[.proportional]m. The open tip structure of our carbon nanotubes and their good adhesion through Fe nanoparticles to the Si substrate are part of the reason why we can attain a large field emission current density within a low field. The field emitter arrays in our diode device are vertically well-aligned carbon nanotubes on the Si-wafer substrate.