Andrei G. Chakhovskoi

Fabrication of Y3Al5O12:Eu thin films and powders for field emission display applications

Abstract Thin films of Y 3 Al 5 O 12 :Eu (YAG) were spin coated on different substrates from sols. The precursor solution was made from organic precursors by combining stoichiometric ratios of Y(III) iso-propoxide, Al(tri Sec-butoxide) and Eu(III) acetyl acetonate. Sol-gel derived thin films and powders are non-crystalline. Powder samples calcined at 650 °C for 5 h show the characteristic X-ray diffraction pattern for the YAG phase. Similarly, the thin film samples annealed at 600 °C for 5 h also show YAG phase in the XRD. The emission spectra were measured for both the powder and thin-film samples. Scanning electron microscopy for the powder samples show that the particles are reasonably crystallized with a particle size of 5 μm. The spectral response and out gassing characteristic of the new, low voltage YAG thin films mainly used for application in the field emission flat panel displays are also measured. The cathodoluminescent materials were tested with electron beam excitation at currents of up to 50 μA within the 3000–8000 V range (medium voltage range). The spectral coordinates with minimal optimization as compared with industrially manufactured P22 phosphors at low voltage operation are reasonable.

Phosphor challenge for field-emission flat-panel displays

The requirements of low-energy excitation combined with practical constraints of commercial supply and other issues, mandate the use of readily available commercial CRT phosphors, such as ZnS and Y2O3-based P22, for first-generation field-emission flat-panel displays. The use of these phosphors at low (e.g., ⩽2–4 kV) excitation energies places considerable problems with brightness, efficacy, spectral response, long-term reliability, screen manufacture and materials synthesis, surface conditioning and outgassing protection, and low-cost manufacturing. The tradeoffs imposed by using phosphors designed for optimum performance in the 15–30 kV range at the low voltages employed by field-emission displays are presented and discussed.

Phosphor selection constraints in application of gated field-emission microcathodes to flat panel displays

The major issues and tradeoffs surrounding phosphor selection for field‐emission flat panel displays are identified. The two main classes of commercially available phosphors applicable to flat panel displays are contrasted, and the major physical, electrical, chemical and optical factors effecting phosphor selection are discussed. The implications of screen layering designs and cathode materials are described as they relate to phosphor characteristics. Resolution requirements for displays severely limits the maximum anode voltage, which in turn forces specific phosphor choices. Possible solutions to these limitations are explored.

Reticulated vitreous carbon field emission cathodes for light source applications

Reticulated vitreous carbon (RVC) is demonstrated as a viable field emission electron source for cathodoluminescent lamps. The high void volume and porous structure of RVC help create a large number of natural emission sites on the surface. Emission centers are formed by the sharp edges of the carbon struts, which result from simple machining of the macroscopic open-pore material. Additional surface treatment of the emitters in vacuum or in open air helps to increase the extracted current and reduce the current fluctuations. Electron emission has been evaluated in the 10 to 500 μA range, in 10−6 to 10−8 Torr vacuum ambient. Extended lifetime tests were carried out for over 5000 h in sealed glass prototype devices utilizing commercial cathodoluminescent phosphors. Brightness levels exceeding 10 000 cd/m2 were achieved for diode and triode configurations. The low cost of manufacturing, along with chemical and mechanical robustness, make RVC a viable material for electron-beam vacuum device applications such...

Characterization of novel powder and thin film RGB phosphors for field emission display application

The spectral response, brightness, and outgassing characteristics of new, low-voltage phosphors for application in field emission flat panel displays, are presented. The tested phosphor materials include combustion synthesized powders and thin films prepared by rf diode or magnetron sputtering, laser ablation, and molecular beam epitaxy. These cathodoluminescent materials are tested with e-beam excitation at currents up to 50 μA within the 200–2000 V (e.g., “low-voltage”) and 3–8 kV (e.g., “medium-voltage”) ranges. The spectral coordinates are compared to commercial low-voltage phosphors. Phosphor outgassing, as a function of time, is measured with a residual gas analyzer at fixed 50 μA beam current in the low-voltage range. We find that levels of outgassing stabilize to low values after the first few hours of excitation. The desorption rates measured for powder phosphor layers with different thicknesses are compared to desorption from thin films.

Efficiency of cathodoluminescent phosphors for a field-emission light source application

The efficiency of major types of cathodoluminescent phosphors has been investigated at high-brightness (up to 30 000 cd/m2) operational conditions using thermionic electron source. The accelerating voltage was varied from 4 to 14 kV and electron beam current density was independently varied from 2 to 50 μA/cm2. Under those conditions both thermal quenching and current saturation of the phosphors were observed. Due to combined influence of those factors, it was found that the best way to characterize the phosphor is plotting the efficiency (in lm/W) versus the specific power density (in mW/cm2) graph. The resulting plots show the integrated influence of current loading and elevated temperature on the phosphor efficiency. The best efficiencies at 200 mW/cm2 and 10 kV were measured for a green color phosphor −55 lm/W, for a blue one—10 lm/W, and for a red—13 lm/W.

Ion-beam morphological conditioning of carbon field emission cathode surfaces

Square-cm samples of bulk graphite, reticulated vitreous carbon, and paste graphite film have been evaluated for field-emission properties both before and after surface modification using a novel Ar-ion flood bombardment method. The Ar-ion treatment results in a change in surface morphology of the emission cathode which physically resembles results of emission treatments using lasers or other heat sources, as well as results obtained using current or voltage stress treatment methods. Emission properties become more uniform, exhibit less noise, and, in the best cases, match results seen from carbon nanotubes or ultra-nanocrystalline diamond cathodes. The results demonstrate a method for obtaining large total currents at optimal extraction voltages, from large-area, low-cost cathodes. This method is useful for applications, such as field-emission lamps and x-ray tubes, which do not require nanofabricated cathode structures.

Effects of vacuum conditions on low frequency noise in silicon field emission devices

The effects of pressure on emission current noise have been studied. Field emission currents from 50×50 arrays and single emitter silicon devices were observed over a range of pressures. The current fluctuations were analyzed in both the time and frequency domain. Signal to noise ratios between 0.9 and 6.9 were observed and appear to be more dependent on operation time and current than on pressures. At higher pressures, emission currents are reduced and the current is cut off completely above a threshold pressure which is somewhere in the 10 s of Torr. Plasmas were observed in the mTorr range. The total current from a 50×50 tip array was measured to be only one order of magnitude greater than that for a single tip, suggesting that only 4–10 of the emitters in the array were functional. Spectral density coefficients of low frequency measurements range from 1.37 to 1.81. Some pressure dependence is suggested in the lower pressure ranges. The single emitter exhibited burst noise with a cutoff frequency of ab...

Cathodoluminescent Field Emission Flat Panel Display Prototype Built Using Arrays of Diamond-Coated Silicon Tips

Vacuum-sealed field-emission non-addressable flat panel display prototypes are manufactured and tested. The single-color 50×45×3 mm displays with emissive area 17×17 mm use ungated diode configuration based on arrays of diamond-coated silicon tips. Brightness of 100–200 candelas per square meter is achieved at 1500 volts.

Thin Film Energy‐Controlled Variable Color Cathodoluminescent Screens

A new technique for obtaining energy-variable multicolor cathodoluminescent display screens is presented. This technique employs radio frequency ion plasma sputtering of one thin-film phosphor material over a dissimilar phosphor substrate. The technique employed differs from the old Penetron screen in that the substrate and the secondary phosphor layer are single-crystal materials. This results in higher resolution and allows the use of lower energy beam excitation. The experiments presented use Y 2 0 3 :Eu (red) deposited on a Y 3 Al 5 0 12 -Tb,Ce (green) substrate with excitation in the low killovolt range. The method demonstrated, however, is extendable to a full red-green-blue triplet composed of a wide variety of materials. The screens are particularly applicable to small, low-power formats, such as avionics and instrumentation displays.