Emission Current Fluctuation Research Articles

Field emission characteristics of iridium oxide tips

An important issue in field emission vacuum microelectronics is the stability of the field emitters with the residual ambient gas. Particularly important is that the field emitter tips made of refractory metals like molybdenum, niobium and tungsten are susceptible to oxidation. The corresponding metal oxides are insulating and adversely affect the emission current characteristic by increasing the width of the effective tunneling barrier. With this perspective, we studied iridium oxide field emitters to evaluate the characteristics of conductive oxide tips. We studied the field emission characteristics of iridium and thermally prepared iridium oxide field emitters using field emission microscopy and current–voltage measurements. We found that, upon oxidation, the voltage required to achieve the desired emission current desire dropped significantly. In addition, oxidation led to a decrease of emission current fluctuations. The development of stable conductive oxide field emitters should improve the performance of field emitter tips, especially under adverse vacuum conditions.

In situ imaging of field emission from individual carbon nanotubes and their structural damage

Field emission of individual carbon nanotubes was observed by in situ transmission electron microscopy. A fluctuation in emission current was due to a variation in distance between the nanotube tip and the counter electrode owing to a “head-shaking” effect of the nanotube during field emission. Strong field-induced structural damage of a nanotube occurs in two ways: a piece-by-piece and segment-by-segment pilling process of the graphitic layers, and a concentrical layer-by-layer stripping process. The former is believed owing to a strong electrostatic force, and the latter is likely due to heating produced by emission current that flowed through the most outer graphitic layers.

Diffusion of Potassium on the W(112) Plane Preadsorbed by Ni Atoms: Field Emission Current Fluctuations - Autocorrelation Study

Diffusion of Potassium on the W(112) Plane Preadsorbed by Ni Atoms: Field Emission Current Fluctuations - Autocorrelation Study

Electrophoresis deposition of carbon nanotubes for triode-type field emission display

A triode-type field emission display has been fabricated using carbon nanotube emitters. Purified single walled carbon nanotubes were selectively deposited onto a cathode electrode in a triode-type structure by an electrophoresis. Emission current was modulated with gate potentials of 100–300 V. A high brightness of 1000 cd/m2 with uniform emission was obtained at 900 V at the anode and 200 V at the gate. The fluctuation of emission current was found to be less than 5% in a fully sealed field emission display. Selective deposition of carbon nanotubes by electrophoresis shows high feasibility for triode-type field emission displays.

Growth of in situ CoSi2 layer by metalorganic chemical vapor deposition on Si tips and its field-emission properties

We prepared Si emitters coated with a metalorganic chemical vapor deposited CoSi2 layer to improve emission properties. The CoSi2 layer was grown in situ by reactive chemical vapor deposition of cyclopentadienyl dicarbonyl cobalt at 650 °C. The CoSi2 layer was conformally deposited on the Si emitter tips and had a twinned structure at the epitaxial CoSi2/Si interface in the partial region. The CoSi2-coated Si emitters showed an enhanced emission due to the increase in the number of emitting sites from the Fowler–Nordheim plot. The fluctuation of emission current was reduced by the CoSi2 coating. But the long-term stability was not much improved, which may be due to the decrease of the field enhancement factor and the number of emitting sites of the CoSi2-coated Si tip.

Determination of initial interface debonding in tungsten fibre reinforced epoxy composite using photon emission and electric current fluctuation

Photon emission from an interface and electric current fluctuation between fibre and matrix were studied using a tungsten fibre reinforced epoxy pullout specimen, to determine the initial interface debonding event. Direct observation of the interfacial debonding behaviour was carried out separately, for comparison with photon emission results and electric current measurements. Photon emission and electric current fluctuation were observed simultaneously, and the load at these events was nearly the same as that found at the onset of interface debonding by direct observation. Both techniques were found to be effective tools for determination of initial interface debonding, because the behaviours originated from a discharge at the interface which occurred just after the onset of debonding.

The influence of adatom diffusion on coverage and emission current fluctuations

In the present work, we have studied the influence of lateral interactions between adatoms (atoms adsorbed on a lattice–gas surface) on their surface mobility. In addition, we have investigated fluctuations of the adatom surface coverage and of the corresponding emission current. For this purpose, we have used the real space renormalization group (RSRG) method and the Monte Carlo (MC) simulation technique. We have evaluated the coverage and temperature dependences of the tracer, jump, and chemical diffusion coefficients, of the MSCFs and of the spectral density of emission current fluctuations. It is shown that lateral interactions between adatoms drastically change the behavior of these kinetic quantities especially at low temperatures when the system undergoes first (for attractive) or second (for repulsive ad–ad interactions). The agreement between RSRG and MC data is surprisingly good despite the fact that both methods constitute very different approaches.

A new lateral field emission device using chemical-mechanical polishing

A polysilicon lateral field emission device using chemical-mechanical polishing (CMP) is proposed and experimental results on the first prototype are reported. In this method, dry oxidation process determines the interelectrode gap. Thus, it is relatively easy to form electrode gaps with dimensions less than 1 μm. Also, the process allows for good uniformity and reproducibility in controlling the interelectrode gap. The turn-on voltage of the fabricated device with interelectrode gap of 3500 /spl Aring/ is as low as 5.4 V and the emission current is as high as 9 μA at 9.3 V. From the Fowler-Nordheim (FN) equation, field emitting area (/spl alpha/) and field enhancement factor (/spl beta/) are estimated to explain the low turn-on voltage and the high emission current. The emission current fluctuation is about /spl plusmn/4% for 25 min.

Noise characteristics of emission current from conductive diamond-like carbon thin films coating on cone shaped silicon field emitters

Electron emission properties and noise characteristics of emission current from the conductive diamond-like carbon (DLC) thin films, coated on cone shaped Si field emitters, were investigated. The effective work function of the emitters coated by DLC thin films was found to decrease as the conductivity of the DLC film increases. To coat the DLC film, the emission current fluctuation is decreased, but the fluctuation is not influenced by the conductivity of the DLC film. Flicker noise of the field emission current from these emitters was analyzed using fast Fourier transform. It was found that the noise power density of the DLC coated emitters is about 10 dB lower than that of Si field emitters and the flicker noise of the DLC coated field emitters is not influenced by the ambient pressure.

Analysis of bistable noise from microfabricated field emission cathodes

Field emission current fluctuations from microfabricated cathodes have been investigated. Time-correlated noise measurements and field emission electron microscope images indicate that the dominant current fluctuations are bistable in character and are emitted from a few localized sites on the cathode surface. Apertured bistable current transitions from these emission sites are often significantly larger than the percent change in total emitted current. Analysis of bistable pulse lengths has shown that the dwell time in a particular bistable emission state decays exponentially with time. Current autocorrelation measurements indicate that bistable noise at ⩽300 K is generated by adsorbates switching between emission states and not by adsorbate diffusion.

Silicon Field Emission Arrays Coated with CoSi2 Layer Grown by Reactive Chemical Vapor Deposition

ABSTRACTWe prepared Si emitters coated with an MOCVD CoSi2 layer to improve the emission properties. The CoSi2 layer was grown in situ by reactive chemical vapor deposition of cyclopentadienyl dicarbonyl cobalt at 650 °C. The CoSi2 layer was conformally coated on the Si emitter tips and had a twinned structure at the epitaxial CoSi2/Si interface. The CoSi2-coated Si emitters showed an enhanced emission due to the increase of the number of emitting site from Fowler-Nordheim plot. The fluctuation of emission current was reduced by CoSi2 coating. But the long-term stability was not much improved.

Improvement of field‐emission properties by formation of Nb‐silicide layer on silicon‐tip FEAs

Abstract— Metal silicide on silicon‐tip field‐emission arrays (FEAs) seems to be a promising way to improve the performance of the silicon‐tip FEAs. The niobium‐silicide layer was formed on a silicon surface. The Nb‐silicide FEAs were prepared by a silicidation process. The formation of the Nb‐silicide layer on a silicon surface was confirmed by using X‐ray diffractometry (XRD). The current‐voltage characteristics and the current fluctuation were measured under an ultra‐high‐vacuum environment using a Kiethley SMU 237 meter. The turn‐on voltage of silicon‐tip FEAs was decreased from 64 to 47 V by the formation of the Nb‐silicide layer on silicon tips, and the emission current fluctuation (2%) was more stable than that of conventional silicon‐tip FEAs.

Electron ejection from MgO thin films by low energy noble gas ions: Energy dependence and initial instability of the secondary electron emission coefficient

Low energy ion-induced secondary electron emission from the surface of thin (500–5000 Å) polycrystalline MgO films has been investigated with various noble gas ions at energies ranging from 45 to 300 eV. The dependence of secondary electron emission coefficient γi on the type and energy of ions is reported and interpreted in terms of electron ejection mechanisms. As-deposited MgO films showed an initial fluctuation in the secondary emission current, which upon annealing or after a certain ion bombardment time irreversibly disappeared.

Studies of field emission current from amorphous silicon deposited on a tungsten tip

Field electron emission from an amorphous silicon deposited tungsten tip has been studied. The current–voltage ( I– V) characteristics corresponding to the as-deposited and annealed states of the emitter were recorded. These characteristics showed semiconducting behaviour. Field emission current fluctuations from the two states were recorded. As-deposited tip shows more spikes in low-field region and a mixture of spikes and steps at higher fields. Fast Fourier Transform analysis of the current signal shows Lorentzian-type of power spectrum which is indicative of bistable traps in a-Si : H. Total emission current level remained almost constant for the entire duration of recording.

Diffusion of titanium on tungsten investigated by the current fluctuation method in FEM

Diffusion of titanium adsorbed on the (013) region of tungsten single microcrystal was investigated using the field emission current fluctuation method. The measurements were carried out for titanium layers chosen from the range about 0.2–2 monolayers in the temperature range 300–1500K. The autocorrelation function of the field emission current fluctuation was used to determine the diffusion coefficients and activation energy for surface diffusion of the adsorbate. A temperature range of 950–1450K was found where thermally activated diffusion occurred. The values of the activation energy depend on coverage and they change in the range of 0.84–1.13eV.

Improvement of field emission properties by formation of Nb‐silicide layer on silicon‐tip FEAs

AbstractMetal‐silicide on silicon‐tip field emission arrays (FEAs) seems to be a promising way to the performance of the silicon‐tip FEAs. The Nb(Niobium)‐silicide layer was formed on silicon surface. The Nb‐silicide FEAs was prepared by silicidation process. The formation of Nb‐silicide layer on silicon surface was confirmed by using X‐Ray Diffractometry(XRD). The current‐voltage characteristics and the current fluctuation were measured under the ultra high vacuum environment using a Kiethley SMU 237 meters. The turn‐on voltage of silicon‐tip FEAs was decreased from 64V to 47V by the formation of the Nb‐silicide layer on silicon‐tip and the emission current fluctuation (2%) was more stable than that of conventional silicon‐tip FEAs.

Electron emission from nitrogen-doped chemical vapour deposited diamond

We have used urea ((NH 2) 2CO) as a dopant and grown N-doped polycrystalline diamond using hot filament chemical vapor deposition (HFCVD) technique, and in addition, the mold-based technique is used in order to obtain the pyramidal-shape array structure. Both polycrystalline films and pyramidal-shape array are identified as diamond from the results of Auger electron spectroscopy (AES) and Raman spectroscopy. The nitrogen concentrations of the film are evaluated using Rutherford backscattering (RBS) technique and it is found to be about 10 20 cm −3. A turn-on field as low as 0.5 V/μm in the emission properties has been confirmed and the emission current fluctuations are discussed.

Experimental study of field emission characteristics as a function of the emitter to anode distance

It was obtained experimentally that the fluctuation of the field emission current was increased as the anode was approached to the emitter, under a low level of the vacuum condition. It is numerically solved that the number of generated gas molecules and ions by electron stimulated desorption on the anode surface come to the emitter surface. Under ultrahigh vacuum, the number was not so different for the distance. On the other hand, under low level vacuum condition, the number was increased largely as the anode approached the emitter. So the fluctuation can be increased when the anode approaches the emitter under low level vacuum condition.

Improvement of electron emission efficiency and stability by surface application of molybdenum silicide onto gated poly-Si field emitters

As an approach to improve electron field emission and its stability, molybdenum (Mo) silicide formation on n/sup +/ polycrystalline silicon (poly-Si) emitters has been investigated. Mo silicide was produced by direct metallurgical reaction, namely, deposition of Mo and subsequent rapid thermal annealing. The surface morphologies and emission properties of Mo-silicided poly-Si (Mo-polycide) emitters have been examined and compared with those of poly-Si emitters. While anode current of 0.1 /spl mu/A per tip could be obtained at the gate voltage of 82 V from poly-Si emitters, the same current level was measured at 72 V from Mo-polycide emitters. In addition, the application of Mo silicide onto poly-Si emitters reduced the emission current fluctuation considerably. These results show that the polycide emitters can have potential applications in vacuum microelectronics to obtain superior electron emission efficiency and stability.

Efficient surface-emitting cold cathodes based on electroluminescent porous silicon diodes

The porosity-modulation technique has been applied to improve the emission properties of the previously reported surface-emitting cold cathodes based on electroluminescent porous silicon (PS) diodes. It is demonstrated here that by introducing a modified structure into the PS layer, the emission efficiency is significantly improved. An extremely high efficiency of 12% has been obtained. A significant decrease in the emission current fluctuation and a consequent increase in the durability of the emission are also observed. These results are due to a regulated electric field distribution near the outer surface of the PS layer.