Lawrence Livermore National Lab
Livermore, CA 94550
Menlo Park, CA 94025
Dept of Physics
North Carolina State Univ
Raleigh, NC 27695-8202
Phoenix Corp Research Lab
Mail Drop EL508
Tempe, AZ 85284
* Invited paper
SESSION C1/B3: JOINT SESSION:
1:30 PM *C1.1/B3.1
STATUS ON THE DEVELOPMENT OF FIELD EMISSION DISPLAY TECHNOLOGY.
Lawrence N. Dworsky , Motorola, Inc., Flat Panel Display Division, Tempe,
FIELD EMISSION DISPLAYS
Monday Afternoon, April 5, 1999
Metropolitan I (A)
Field emission displays are currently moving from prototypes
into products. An overview of the current state of the technology will
2:00 PM *C1.2/B3.2
PACKAGING OF FIELD EMISSION DISPLAYS . Jim Browning ,
Micron Display Technology, Boise, ID.
Alignment, assembly, and sealing of Field Emission Displays
are important aspects of the display technology. The materials issues surrounding
FEDs including spacers, seal temperatures, cathode compatability, and glass
frits make component integration a challenge. These issues will be discussed.
3:00 PM *C1.3/B3.3
COATINGS, GASES, AND THEIR EFFECTS ON SILICON FIELD EMITTER
ARRAYS. D. Temple and W. D. Palmer, MCNC, Electronic Technologies Division,
Research Triangle Park, NC.
In the range of vacuum electronic devices, flat panel
displays and microwave power amplifier tubes represent the extremes in
cathode performance requirements. But both applications stand to benefit
greatly from the incorporation of cold cathode technologies once the state
of the art can offer the repeatability and reliability available from thermionic
cathodes. The stability of the cathode emission over time and with exposure
to various ambient gases is particularly important. In the flat panel display,
variations in the emission current produce variations in the pixel brightness
across the display. In the microwave amplifier tube, noise and drift in
the emission current degrades the quality of the amplified signal. This
talk will give an overview of fabrication and electrical performance of
silicon field emitter arrays (FEAs) in the context of requirements for
field emission flat panel display and microwave power amplifier applications.
Both as-fabricated Si FEAs and FEAs incorporating thin coatings of various
materials will be discussed, and experimental data illustrating the cathode
performance will be presented. In particular, we will discuss stability
of emission current over extended periods of time in high vacuum conditions,
and changes in the emission current upon exposure to gaseous ambients at
varying pressure. This work has been supported in part by DARPA via ONR.
3:30 PM *C1.4/B3.4
NEW MATERIALS, STRUCTURES, AND APPLICATIONS FOR VACUUM
MICROELECTRONICS. Henry F. Gray , Naval Research Laboratory, Washington,
Whereas Thermionic Integrated Circuits (TICs) have been
based on thermionic emission of electrons, most, but not all, Vacuum Microelectronics
devices have been based on field emission from Field Emitter Arrays (FEAs).
FEAs have been made from a variety of materials in many different structures.
This talk will address a variety of different materials including silicon,
refractory metals, resistive materials, diamond and diamond-like materials,
compound semiconductors, carbon and carbon like materials including fullerene
tubules, defected dielectric materials, etc. in structures including vertically
oriented conical and pyramidal structures, multilayer thin-film-edges,
surface conducting emitters, etc. Applications will include Field Emitter
Displays (FEDs), RF power amplifiers, lasers, scientific instrumentation,
multibeam electron lithography, etc.
4:00 PM *C1.5/B3.5
CATHODE LIFETIME ISSUES IN FIELD EMISSION DISPLAYS. Robert
H. Reuss , Motorola, Inc., Flat Panel Display Division, Tempe, AZ.
Long device life is required for the successful commercialization
of field emission display technology. In this paper, an overview of cathode
lifetime issues in high voltage field emission displays will be presented.
4:30 PM C1.6/B3.6
FIELD EMISSION FROM POLYMER FILMS. I. Musa , W. Eccleston,
Liverpool Univ, Dept of Electrical Engineering and Electronics, Liverpool,
UNITED KINGDOM; G.A.J. Amaratunga, Cambridge Univ, Dept of Engineering,
Cambridge, UNITED KINGDOM.
We have reported (Nature, Sept. 1998) low threshold field
emission from conjuaged polymers: poly(3-alkylthiophene). The polymers
are spun or cast on the surface of a polished n++ Si slice and are p type
with an electron affinity of about 3 eV. Like most carbon materials the
film requires conditiong before which the field dependece of the current
is consistent with Fowler-Nordheim emission from the surface. The molecules
are probably not aligned to give high carrier mobility in the direction
of emission. After conditioning I
V1.8 close to V2 expected for space charge limited
current. There may be generation of a localised high density of traps caused
by high current densities associated with these films during the conditioning
process. There is evidence that some material is removed during the process.
Two mechanisms then seem to be possible, one associated with the presence
of field intensification at crater/void rim. The other is a process whereby
electrons are emitted form the lower sidewalls of the voids where the electron
concentration is, with SCLC, very high and the field is near to its maximum
value. The changes in emission current with time will be discussed on the
basis of trapping effects.
4:45 PM C1.7/B3.7
BAND-BENDING EFFECTS ON FIELD ELECTRON EMISSION FROM
N- AND P-TYPE SILICON GATED EMITTER TIPS. Takashi Matsukawa , Seigo Kanemaru,
Junji Itoh, Electrotechnical Laboratory, Tsukuba, Ibaraki, JAPAN; Kazuaki
Tokunaga, Tokai University, Hiratsuka, Kanagawa, JAPAN.
Field emission characteristics from n- and p-type silicon
gated emitter tips have been investigated in detail by means of experiments
and theoretical calculation of band-bending induced by surface states.
The single-tip emitters have been fabricated from n-type (4 -cm)
and p-type (0.6 -cm) silicon,
and their current-voltage (I-V) characteristics have been evaluated. The
field emission from the p-type emitter has been found to occur at lower
extraction voltage than that of the n-type emitter. As the theoretical
approach to the origin of the lower extraction voltage for the p-type emitter,
potential distribution in the emitter tip has been calculated by means
of device simulation. The surface state density at the Si emitter tip has
been assumed to be
cm-2eV-1, and doping concentration for n-
and p-type Si has been decided as
cm-3. In the p-type Si emitter, the surface states are
positively charged, and the potential for electrons falls down toward the
top of the emitter tip. Electrons in the inversion layer under the extraction
gate can be transferred to the tip top without a potential barrier. On
the other hand, the surface state of the n-type emitter tip are negatively
charged and forms a potential barrier against the electrons. This potential
barrier prevents electrons from reaching the top of the emitter tip. These
are the reason why the emission current of the n-type emitter is suppressed
lower than that of the p-type emitter.
SESSION C2/B4: JOINT SESSION:
8:30 AM *C2.1/B4.1
DIAMOND AND CARBON NANOTUBE FIELD EMITTERS: PROPERTIES
AND APPLICATIONS. Wei Zhu , Bell Labs, Lucent Technologies, Murray Hill,
FIELD EMISSION DEVICES AND DISPLAYS
Tuesday Morning, April 6, 1999
Metropolitan I (A)
I will describe the physical properties of both diamond
and carbon nanotube field emitters. Both emit electrons efficiently at
low electric fields and are capable of producing technologically meaningful
emission current densities. I will discuss our current understanding of
the emission mechanisms involved. I will also present data on the emission
stability and uniformity, both of which are essential for successful vacuum
9:00 AM C2.2/B4.2
ELECTRON FIELD EMISSION PROPERTIES OF SiC/Si HETEROSTRUCTURES
SYNTHESIZED BY HIGH DOSE CARBON IMPLANTATION INTO SILICON. Dihu Chen, S.P.
Wong , W.Y. Cheung, Chinese Univ of Hong Kong, Dept of Electronic Engineering
and Materials Science & Technology Research Centre, Shatin, N.T., HONG
KONG, CHINA; R.W.M. Kwok, Chinese Univ of Hong Kong, Dept of Chemistry
and Materials Science & Technology Research Centre, Shatin, N.T., HONG
We have recently reported that electron field emission
with a remarkably low turn-on field of 1V/m
can be achieved from planar SiC/Si heterostructures synthesized by high
dose carbon implantation into silicon under appropriate conditions [D.
Chen et al, Appl. Phys. Lett. 72 (1998) 1926.]. The good field emission
property was attributed to the formation of a thin surface stoichiometric
SiC layer and the formation of densely distributed small protrusions on
the surface. This technique is attractive for its compatibility with Si
technology and is promising for the fabrication of silicon-based flat emitter
arrays. In this work, we shall report more of our recent results on the
field emission properties from these structures prepared under various
implantation and annealing conditions. The carbon implantation was performed
using a metal vapor vacuum arc ion source. The chemical composition depth
profiles were determined from x-ray photoelectron spectroscopy. The surface
morphology was observed by atomic force microscopy. The work function of
the surface SiC layer was determined by ultraviolet photoelectron spectroscopy.
It was found that the good field emission property was mainly controlled
by the surface morphology which is highly correlated with the field enhancement
factor. Issues on the stability and uniformity of the emission will also
be discussed. This work is supported in part by the Research Grants Council
of Hong Kong (RGC reference number: CUHK 513/95E).
9:15 AM C2.3/B4.3
FIELD EMISSION ENERGY DISTRIBUTIONS AND CURRENT-VOLTAGE
CHARACTERISTICS OF SINGLE TIP GATED DIODES. John B. Bernhard , Ambrosio
A. Rouse, Edward D. Sosa, Bruce E. Gnade and David E. Golden, Univ N Texas,
Depts Physics and Materials Science, Denton, TX; Babu R. Chalamala, Motorola,
Flat Panel Display Division, Tempe, AZ; S. Aggarwal and R. Ramesh, Univ
Maryland, Dept Materials Science and Nuclear Engineering, College Park,
Field emission (FE) current-voltage characteristics and
simultaneous electron energy spectra have been obtained using single tip
gated diodes. The electron spectra are generated at each step of each current-voltage
characteristic using a low-cost compact simulated hemispherical energy
analyzer. A personal computer (PC) is used for data acquisition and control.
The PC is programmed using graphics based data acquisition software and
is connected to a CAMAC crate and a picoammeter through a GPIB interface.
The picoammeter measures the current leaving the tip and the FE electrons
are energy analyzed, detected and then processed in the CAMAC crate. The
CAMAC crate also sends control voltages to the gate anode and the energy
analyzer. This apparatus allows the simultaneously measurement of tip work
functions and Fowler-Nordheim tip shape parameters. Work function measurements
are compared to photoelectric work function measurements for molybdenum
and iridium oxide.
9:30 AM C2.4/B4.4
METAL BORIDE CATHODE MATERIALS FABRICATED BY SELECTIVE
AREA LASER INDUCED SOLUTION DEPOSITION. Zhenchen Zhong , Veronica Holmes,
Peter A. Dowben and David J. Sellmyer, University of Nebraska-Lincoln,
Center for Materials Research and Analysis and Department of Physics and
Astronomy, Lincoln, NE.
We have developed a novel technique for the selective
area deposition of rare earth hexaborides: laser-induced solution deposition
(LISD). This technique is both simple and efficient and combines many advantages
of both chemical vapor deposition and electrolytic deposition. The results
of LISD deposition show that the polycrystalline thin films of rare earth
hexaborides and sub-borides such as MB6, MB4, and
MB2 (M = Gd, La) are formed through the light initiated chemical
reaction of nido-decaborane (B10H14) and rare earth
chloride in solution. These films grow with a strong texture and morphology
that is dependent both on the selection of solvents and laser wavelengths
and power used in LISD. The application as cathode materials in DC plasma
display panels will be discussed.
10:15 AM *C2.5/B4.5
LIFETIME AND STABILITY OF CARBON COLD CATHODES. R.L.
Fink , L.H. Thuesen, Z. Li Tolt and Zvi Yaniv, Field Emission Picture Element
Technology, Inc. (FEPET, Inc.), Austin, TX.
We present the results of tests measuring the life of
carbon cold cathodes and determining what conditions limit the life of
the cathode. Cathode life and stability are important for a broad range
of applications. Cathodes were tested in vacuum chambers using different
gas environments as well as in sealed and gettered glass envelopes. We
measured emission current half-lives of 10,000 - 20,000 hours or more in
sealed display devices, depending on operating conditions. The presence
of a significant oxygen or water partial pressure degrades the life of
the cathode. After removing the gases the decay rate was restored to near
the original value. A similar partial pressure of hydrogen gas has little
or no effect on the life of the cathode. These results will be discussed
with respect to the various applications available for carbon cold cathodes.
10:45 AM C2.6/B4.6
UST TEMPERATURE DEPENDENCE ON THE ELECTRO-OPTICAL CHARACTERISTICS
OF AMORPHOUS CARBON ACTIVE LAYER THIN-FILM LIGHT-EMITTING DIODE. Woo Yeong
Cho, Samsung Electronics Co. Ltd, Kiheung, Kyungki-do, KOREA; Koeng Su
Lim , Dept of EE, KAIST, Taejon, KOREA.
The effects of ultrasound treatment (UST) at the various
temperatures on the electro-optical properties of amorphous carbon (a-C:H)
active layer thin-film light-emitting diode (TFLED) have been investigated.
The TFLED has a structure of glass/tin-oxide (SnO2)/p-c-Si:H
(2.3eV)/i-a-C:H (3.2eV)/n-c-Si:H (2.4eV)/Al.
For the USTs at the room temperature, the threshold voltages of the TFLED
were not changed, while the series resistance decreased. For the USTs above
the room temperature, both the threshold voltage and the series resistance
were reduced. With increasing the UST temperature, electroluminescence
(EL) intensity increases, the peak of the EL spectra moves to shorter wavelength
region and the full-width half-maximum decreases. These improvement of
electro-optical characteristics are due to the reduction of defect states
in the a-C:H active layer and at the p/i interface.
11:00 AM C2.7/B4.7
PROPERTIES OF ELECTRON EMITTING DIODE FABRICATED WITH
SINGLE-CRYSTALLINE DIAMOND. Toshimichi Ito , Masaki Nishimura, Osaka Univ,
Dept of Electrical Engineering, Suita, Osaka, JAPAN.
Highly efficient electron emitting diodes with a flat
emission surface have been fabricated using single-crystalline diamond
thin-films homoepitaxially grown on high-pressure synthesized (100) diamond.
The fabrication method employed includes suitable ion-implantation and
diamond regrowth processes. The emitters examined in the present study
contain a buried electrode and a hydrogenated diamond surface with negative
electron affinity. When a driving voltage ranging from 0.3 to 1.1 kV
was applied between the buried electrode and the hydrogenated surface,
highly efficient emission currents were measured. In the best case, the
almost same amount of the emission current as the driving current (or the
injection current) was observed although the emission stability was not
very good, meaning that the emission efficiency (= emission current / injection
current) reached 100 %. The efficiency thus observed was always found
to be almost independent of the amount of the current below 200 nA. Details
of the performance will be addressed in relation to defects in the diamond
 M. Nishimura, A. Hatta and T. Ito, Jpn. J. Appl.
Phys. Vol.37, L1011(1998).
 T. Ito, M. Nishimura and A. Hatta, Appl. Phys. Lett.,
(1998) in press.
11:15 AM C2.8/B4.8
THE POSSIBILITY OF FIELD EMITTER IMPROVEMENT BY MEANS
OF FULLERENE COVERAGE. Gennadi G. Sominski, Tatjana A. Tumareva , St. Petersburg
State Technical Univ, Dept of Physical Electronics, St. Petersburg, RUSSIA.
It is safely determined that carbon containing coverages
can be used for the decrease of working voltages of field emitters and
for the stabilization of their emission. The search of sufficiently simple
methods of pure carbon coverage creation and of new containing carbon materials
for the field emitter improvement represent now the special interest. The
fullerene coverage influence on the emission ability of tungsten field
emitter was studied in present work. The measurements were performed in
the field projector. The coverages of C60 molecules were deposited upon
the tungsten tip with top radius 1 micrometer. The deposited coverages
were exposed to the thermal treatment. The coverage structure and field
emitter characteristics were defined in the wide range of the fullerene
amounts on the tip surface in temperature interval between 300 and 1800
K. The preliminary deposited fullerene coverage was found to transform
to the well-known system W+C after the heat of fullerenes onto the tip
at 850-950 K. The subsequent deposition of the large enough fullerene coverage
on the prepared by this way system W+C made it possible to create the rough
coverage with the typical microtip radius about 100 Angstrom or less. The
emitter with this coverage secure stable emission current more than 100
mA at the static regime. These currents were registered at voltages that
were less (up to 30%) than in the case of pure tungsten emitter. Thus the
results of the present work show the possibility to create the pure carbon
coverages and stable effective emitters with rough surface by means of
fullerene deposition and thermal treatment. This work was supported by
the Russian Foundation for Basic Research (grant N97-02-16080).
11:30 AM C2.9/B4.9
ORIENTED CARBON NANOTUBE GROWTH FOR FIELD EMISSION APPLICATIONS.
Alexander N. Obraztsov , Igor Yu. Pavlovsky, Alexander P. Volkov, Dept.
of Physics, Moscow State University, Moscow, RUSSIA; Vladimir L. Kuznetsov,
Andrey L. Chuvilin, Boreskov Inst. of Catalysis, Novosibirsk, RUSSIA.
Oriented carbon nanotube films were grown using method
of chemical vapor deposition in hydrogen/methane plasma activated by glow
discharge. The film phase composition and structural features were studied
by Raman, SEM, TEM, and HREM techniques. Field emission properties of the
films were examined to obtain I-V characteristics and the field emission
sites distribution. The I-V curves in Fowler-Nordheim coordinates were
linear, that is typical for the field emission, with the threshold average
field about 1.5 V/m and the emission
current density up to 50 mA/cm2 at the field of 5 V/m.
The field emission properties of the carbon nanotube films were studied
at various temperatures ranging from 77K to 600K.
11:45 AM C2.10/B4.10
FIELD EMISSION PROPERTIES OF THIN MOLYBDENUM CARBIDE
AND DIAMOND FILMS DEPOSITED BY DIELECTROPHORESIS. Ambrosio A. Rouse , John
B. Bernhard, Edward D. Sosa and David E. Golden, Univ N Texas, Depts of
Physics & Materials Science, Denton, TX.
Molybdenum carbide and diamond films were deposited at
room temperature by dielectrophoresis on molybdenum foil and tips. The
films have been characterized using UPS, XPS, SEM. In addition field emission
current voltage characteristics and electron energy distribution measurements
have been made using the tips as part of a single aperture gated diode.
A VG ESCALAB system and Al x-rays (1481.8 eV) were used to determine the
presence of molybdenum carbide, molybdenum trioxide, molybdenum dioxide,
graphite and diamond as a function of annealing temperature and time at
constant temperature. Molybdenum trioxide is present after molybdenum carbide
deposition at room temperature on all samples and is found to be stable
as the temperature is raised, until it undergoes a phase transition to
molybdenum dioxide. Molybdenum dioxide also has a stable temperature range.
The surfaces undergo a third transition to molybdenum carbide with a significant
graphite content at about 1000 K. The molybdenum carbide films are stable
when heated at 1073 K for 4 hours. UPS data for these samples was obtained
at the different annealing temperatures and a number of photon energies
to determine photoelectric work functions for molybdenum trioxide, molybdenum
dioxide, molybdenum carbide and diamond. The VG ESCALAB system was used
measure Fowler-Nordheim current-voltage characteristics, photoelectric
work functions and field emission energy distributions for these materials.
SESSION C3: NOVEL FABRICATION AND MATERIALS FOR FIELD
1:30 PM *C3.1
SOME EXOTIC ASPECTS OF PHYSICS WITH MICROTIPS. R. Baptist
, CEA-LETI, Departement de Microtechnologies, Grenoble, FRANCE.
Tuesday Afternoon, April 6, 1999
Franciscan III (A)
Vacuum microelectronics is presently dominated by the
Display application ; other applications such as microwaves tubes, light
sources, pressure sensors and vacuum gauges are still in infancy and may
never emerge due to commercial reasons or due to the competition with other
technologies (solid state devices with wide band gap semiconductors, electro-luminescence
from organic material, other types of sensors).
Other applications of integrated field emission, somewhat
more exotic, have also been studied in various laboratories ; some ones
with success and other without. In this paper we will present some of the
tentative which were studied by our group in collaboration with other laboratories
to produce electron sources with particular properties. We will also try
to explain why experiments were or were not successful.
An (unsuccessful) tentative to produce spin polarised
electron beams with NiFe microtips was the first experiment. Although the
degree of polarisation was carefully checked with a Mott polarimeter, no
evidence of a spin polarisation was found .
The production of interferences with low energy electrons
was the second, mitigated experiment. To our sense, the result, although
positive, is incomplete because no entire interference field could be recorded
as is done currently in laboratories working on electron-holography with
macroscopic W tips.
The third, was the demonstrated feasibility of an optical
command for microtips. This feasibility was, however, not pursued to prove
the possibility of pulsing the electronic emission at very high frequency
Finally, we will report on the injection of low energy
electrons emitted by microtips immersed in liquid xenon (an environment
very different from vacuum). This type of experiments should enable a better
understanding of the electronic structure of liquids apart of having already
shown a strong generation of UV light .
 Collaboration with Ecole Polytechnique, Palaiseau.
 Collaboration of the Grenoble High Magnetic Field
Laboratory with CEA-LETI.
2:00 PM *C3.2
SYNTHESIS AND CHARACTERIZATION OF Si/Cs/O NANOCLUSTER
THIN FILMS WITH NEGATIVE ELECTRON AFFINITY. L.N. Dinh , W. McLean II, M.A.
Schildbach, M. Balooch, Lawrence Livermore National Laboratory, Livermore,
Patterned and unpatterned thin films of Si/Cs/O nanoclusters
have been synthesized by the technique of supersaturated thermal vaporization
of Si and Cs in an oxygen background gas. These films, which were deposited
onto conducting or semiconducting substrates, exhibit negative electron
affinity (NEA) as evidenced by ultraviolet photoemission spectroscopy (UPS).
Photo, secondary, and field electron emission properties of these nanocluster
films were investigated with photo-electron emission microscopy (PEEM),
field electron emission microscopy (FEEM), secondary electron microscopy
(SEM), and current-voltage measurements. Flat cathodes covered with thin
films of Si/Cs/O nanoclusters exhibited high current outputs and lower
turn-on fields (<8.7 V/mm) than most NEA diamond surfaces and gated
Si or Mo tip arrays. The films' NEA is unaffected by air exposure and is
stable to high temperature annealing (550 C). The electron emission property
of the NEA nanocluster films can be best explained by a sub-band gap abundant
surface state nanocluster model. A field emission display unit with a simple
diode structure containing a flat cathode coated with a thin film of Si/Cs/O
nanoclusters has also been built to demonstrate the potential application
of this material in cold cathode electron emitting devices, particularly
field emission flat panel displays.
2:30 PM C3.3
DESIGN AND FABRICATION OF A InP/CdS/LaS
COLD CATHODE. M. Cahay , A. Malhotra, Y. Modukuru, H. Tang, W. Bresser,
P. Boolchand, University of Cincinnati, Dept of Electrical Engineering,
Cincinnati, OH; P. Mumford, Air Force Research Laboratory, Sensors Directorate,
WPAFB, Dayton, OH; W. Friz, Multi Area Research in Science (MARS) Consultants,
We will describe our recent efforts to develop a InP/CdS/LaS
cold cathode. The main elements of the cathode are: (1) a wide bandgap
semiconductor slab (CdS, Cadmium Sulfide) sandwiched between a heavily
doped semiconductor (n++ - InP) that supplied
electrons at a sufficient rate into the conduction band of CdS and
a thin semimetallic film (LaS). The latter provides Negative Electron
Affinity to the CdS surface. We analyze various physical phenomena
affecting the operation of the proposed cathode including: dynamical work
function shift, current crowding and self-heating effects, and the importance
of space-charge effects as a function of the anode to cathode spacing.
We show that the cold cathode has the following advantages: (1) low voltage
( < 20 V) operation, (2) emission current densities of several
100 A/cm2, and (3) large power efficiencies. We
will report on some experimental results including the growth of bulk LaS
samples and the characterization of CdS thin films grown by Molecular
Beam Epitaxy on InP substrates.
3:15 PM *C3.4
SECONDARY ELECTRON EMISSION STUDIES OF DIAMOND AND GaN
MATERIALS. J.E. Yater , A. Shih and D.S. Katzer, Naval Research Laboratory,
Wide bandgap materials such as diamond and group III-nitrides
have attracted recent interest as potential cold electron emitters due
to the low or negative electron affinity reported at specific surfaces.
While electron emission has been demonstrated from several of these materials,
it is important to understand the emission process and the factors that
determine the emitted electron intensity, energy and angular spread, and
emitter robustness. In this study, we use secondary electron emission spectroscopy
to examine the transport and emission of low-energy electrons in several
wide bandgap materials. In particular, we compare the secondary emission
properties of C(100) and C(111) samples in order to examine the effect
of crystallographic orientation on the emission characteristics. Very high
yields are obtained from negative-electron-affinity surfaces of both samples,
indicating that low-energy electrons are transported and emitted very efficiently
at both surfaces. Although the angular spread of the emission is not determined
in our study, the energy distribution of the emitted electrons is found
to be sharply peaked at low energy for both samples. However, the energy
distributions measured from the C(111) surfaces are broader and reveal
structure in the energy gap of the diamond. The different emission processes
at the C(100) and C(111) surfaces, as indicated by the energy distribution
data, may account for the broad energy distributions observed previously
from polycrystalline CVD diamond samples. Finally, we examine secondary
emission measurements from GaN and AlGaN films grown by MBE. The secondary
emission is not as strong as from the diamond samples, and the measurements
reveal the impact of interface and surface barriers on the emission process.
3:45 PM C3.5
ANODIC ALUMINA - MATERIAL FOR HIGH ASPECT RATIO TECHNOLOGY.
Alexander Govyadinov and Ivan Grigorishin, Vacuum Microelectronics Lab
of Institute of Electronics, Belarus National Academy of Sciences, Minsk,
Anodic aluminium oxide films formed by electrochemical
oxidation of aluminium are a promising material for vacuum microelectronics
and microtechnology. The anodic alumina (AA) films have a unique self-ordered
regular cellular-porous structure. The parallel pores extend through all
thickness of the AA. It gives opportunity to perform deep etch process
on AA analogous anisotropic wet etching. A simple wet etchants were used
for that purpose. It was shown that deep AA etching had rectangle profile
with features size less 2 um and aspect ratio up to 30. The rectangle profiles
based on aluminium supported and free (separated from aluminium sheet)
AA films with thickness in a range from 1 um up to 150 um have been realised.
The AA technology based on combination of AA growing and etching, lithography,
thin solid films deposition and high temperature treatment have been elaborated.
It has permited to form freestanding 3-D microstructures. A number of applications
of this AA technology for vacuum integrated circuits, microchannel plates,
soft X-ray windows, gas sensors, precision apertures and high transparency
grids for electron microscopy, etc. has been demonstrated. Wide prospects
of anodic alumina deep etch technology for vacuum microelectronics and
microtechnology has been shown. The elaborated AA technology can become
a cheap alternation of LIGA process.
4:00 PM C3.6
OPTIMUM THICKNESS OF ALUMINUM NITRIDE COATINGS ON ELECTRON
EMITTERS. Donghun Kang , Gregory J. Wojak, Dan E. Jonsen, Ed Preble, Jerry
J. Cuomo and John J. Hren, Department of Material Science and Engineering,
NC State University, Raleigh, NC; Victor V. Zhirnov, Semiconductor Research
Corporation, Research Triangle Park, NC.
It was shown recently that the emission properties of
wide band gap coatings depend on the coating thickness. Until now, however,
this effect was studied only in relation to emission threshold voltage,
i.e. emission in the low-current region, and not for coatings thicker than
100 nanometers. We present here results about the thickness effect of magnetron
sputtered AlN coatings on Mo tips ranging from a few nanometers to 1 micron
in thickness. All changes in the emissivity were referenced to uncoated
tips. Three parameters were chosen for characterization: threshold voltage
Vth, maximum current Imax, and high-current
transconductance Imax/Vmax. For very
thin coatings (2 nanometers), an increase in emission threshold voltage
was observed. This result was explained as being due to the formation of
an AlN dipole on the Mo surface with an orientation which increases the
local work function (nitrogen terminated surface). A further increase in
the coating thickness results in a decrease of Vth below
that of the original Mo emitter, with Vth reaching a
minimum at a thickness of 20 nanometers. This result is consistent with
the model of internal field emission and the decrease in emission current
is associated with the appearance of bulk properties of AlN (e.g. band
gap, electron affinity, dielectric constant, etc.) as a certain minimum
thickness is achieved. A further increase in coating thickness beyond 20
nanometers results in an increase in Vth. This effect
has been observed earlier for diamond, AlN, and c-BN coatings, and it is
most likely due to electron transport limitations in the poorly conductive
dielectric coatings. Maximum current limits of AlN based emitters were
studied for the first time. The value of high current transconductance
Imax/Vmax is proposed as a figure of
merit for characterization of the practical efficiency of AlN cathodes.
4:15 PM C3.7 INCREASING THE EMISSION EFFICIENCY
OF A FORMED MIM STRUCTURE. Sergei V. Kalistratov , Pavel E. Troyan and
Alexander A. Zhigalski, Tomsk State University of Control Systems and Radioelectronics,
Physical Electronics Dept, Tomsk, RUSSIA.
The classic formed MIM-structure works at voltages in
the range from 0 to 15 V and has the N-type circulating current versus
volage characteristic. The values of the emission efficiency coefficient
(EEC) lie within the limits of 1-5*10-3 in a pumping system and about x*10-4
in a sealed lamp . The MIM-cathode with these characteristics also have
a short lifetime, therefore its practical usage is limited.
We conducted an investigation of possibility of the EEC
increasing in formed MIM-structures. The authors of  pointed to the
absence of influence of lower electrode material on properties and characteristics
of MIM-structures. It was observed the fact of influence of electrode properties
of the lower electrode possessing surface resistance and representing insular
metal film of Mo. At the same time with the replacement of the lower metal
electrode by a resistive layer resulted in a change in working conditions
of MIM-cathode. The work voltage needed to operate such structures were
about 120-140 V. We observed several stages of work of this new investigation
1. Electrical forming under voltages about 25-30 V.
2. Combined process: repeated breakdown of the structure
and electrical forming continuation at Up=70-100 V.
3. Termination of the combined process. The value of
the circulating current (Ic) had a minimum level. The volume of the emission
current (Ie) was out of record device sensitivity.
4. As the applied voltage reached about 120-140 V the
emission current has been recorded. After some time (from several seconds
to several minutes) has elapsed the value of Ie increased in ten and more
times without any external changes in electric circuit parameters. The
range of EEC values for the obtained samples was from 0.5 to 5%. The output
of samples with increased EEC was from 10% to 20%. The EEC value of these
samples variate from 0.1-0.5% to 5% standing at the last from few to dozens
of minutes in succession. The total working time of samples with EEC >
1% laid in the range from 0.5 to 3 hours.
We made a supposition that in this investigation object,
which can be called new in comparison to formed MIM-structures, the emission
centers can be nano-clearances  between upper and lower electrodes making
as a result of sparring breakdown thin film structure. One fact in favor
of this point of view, in our opinion, is that the samples worked after
the breakdown and the gradual increase in the emission current when required
voltage was reached, which we connect with adsorption of a conducting phase
from surrounding atmosphere in the mentioned clearance.
1. Dearnaley G., Stoneham A., Morgan D., UFN-1974.-T.112-N1-
2. V.M. Mordvincev, B.L. Levin. The model of nano-MIM-diod
with carbon active condition with percolation in insulating slot. Microelectronics
1998 tom 27, N4, c.265-274.
4:30 PM LATE NEWS NOVEL EMITTERS
SESSION C4/B7: JOINT POSTER SESSION:
PREPARATION OF ULTRASHARP DIAMOND TIP EMITTERS BY ION
BEAM ETCHING. A.N. Stepanova, E.I. Givargizov and L.V. Bormatova, Institute
of Crystallography RAS, Moscow, RUSSIA; E.S. Mashkova and A.V. Molchanov,
Institute of Nuclear Physics, Moscow, RUSSIA.
Tuesday Evening, April 6, 1999
Metropolitan Ballroom (A)
Ion-beam milling was used for sharpening of diamond coatings
on ends of silicon tips. The sharpened diamond tips were used as field-emission
electron cathodes. I-V characteristics of the electron emitters were measured.
An effect of conditioning of the emitters was observed: after the emitters
worked during at least several hours, their currents increased for several
orders of magnitude and became stabilized.
PREPARATION OF STM/AFM PROBES OF SPECIAL SHAPE WITH DIAMOND
TIPS. E.I. Givargizov , L.N. Obolenskaya, A.N. Stepanova, and M.E. Givargizov,
Institute of Crystallography, Russian Academy of Sciences, Moscow, RUSSIA;
and I.W. Rangelow, University of Kassel, Kassel, GERMANY.
For investigations in submicron grooves with vertical
walls, typical of microelectronic technologies, and of objects with coarse
surfaces such as biological macromolecules special STM/AFM probes with
cylindrical or prismatic upper parts of probes are necessary. Such probes
have been prepared by growing/sharpening of single-crystalline whiskers.
To improve their robustness, the probes were coated with sharpened crystaline
A GATE CURRENT SUPPRESSED LATERAL FEAS INTEGRATED WITH
TFTS. Moo-Sup Lim , Cheol-Min Park and Min-Koo Han, Seoul Nat'l Univ.,
School of Electrical Engineering, Seoul, KOREA.
It is well known that the stability of field emission
current and the efficiency of control gate are key problems to real applications.
There are many researches to improve the stability and uniformity of field
emission current using the active device such as Field-Effect- Transistors
(FETs). However, most of them have four terminals and the fabrication process
becomes complicated due to the additional process of the integration of
FETs and FEAs. We have reported the three terminal lateral FEAs integrated
with TFTs without additional process steps. But the gate current of
the previous device is relatively large due to the fact that there is a
current path to the metal on the active layer. In this paper, we propose
new method to suppress the gate current. The details of fabrication steps
are in Ref. . Lower insulator layer including 500nm thick nitride and
50nm thick oxide was deposited on Si wafer. 100nm thick amorphous Si was
deposited and selective n+ doping is performed. Upper insulator layer including
50nm thick oxide, 100nm thick nitride was deposited. Tip patterning was
performed and upper insulator layer, poly-Si layer and oxide were etched
with anisotropic dry etching and then the poly-Si layer was over-etched
intentionally in order to make micro-cavity. It should be noted that the
region of cathode is n+ doping poly-Si, and that of tip is undoped poly-Si.
The oxidation was performed to sharpen the poly-Si tip, and isolates an
anode and a cathode. The thermal oxide was removed by BOE etchant. Then,
we deposited oxide using e-beam evaporation instead of deposition of molybdenum.
Al was deposited sequentially. Finally an electrical interconnection was
then fabricated in proper locations by employing mask steps. The proposed
device has three terminals and stable anode current. And, the gate current
of the device is negligible because insulator isolates gate electrode from
active layer. Reference  M.S. Lim, C.M. Park, M.H. Han, and Y.I. Choi,
A New Lateral Field Emitter Arrays inherently integrated with thin film
transistor, MRS spring meeting, 1998
THE INFLUENCE OF THE BASE ELECTRODE MATERIAL ON THE OPERATION
OF A FORMED MIM STRUCTURE. Sergei V. Kalistratov and Pavel E. Troyan, Tomsk
State University of Control Systems and Radioelectronics, Physical Electronics
Dept, Tomsk, RUSSIA.
An investigation of resistance layer In2O3
influence on the work of metal-insulator-metal structure was made. This
structure was exposed to electric forming, after which the circulating
current versus voltage characteristics exhibited a section with the N-type
negative resistance, electron emission and electroluminiscense . The
thickness of insulating layer and upper electrode are 30-40 nm and 10-20
All investigators note the absence of influence of the
base electrode material on electric properties of a formed MIM-structure
with different materials of insulating layer (SiOx, SiN4,
Al2O3, Ta2O5, etc.) and the
top electrode (Al, Ni, Mo, etc.) .
Our research showed that properties of the structure
In2O3-SiOx-Me (Al, Ni) strongly
depend on material, thickness and the resistance of the base electrode.
The result of replacement of metal base electrode by a In2O3
layer having surface resistance value about 50 Om/Ø and thickness
value about 100 nm is a significant change in the I-V characteristic which
consists in gradual smoothing of the N-type one and its complete transformation
into a characteristic which obeys the Ohm law.
We found out this effect to depend on the polarity of
the applied voltage. This effect became five times more rapid with the
reversed polarity. The change in the formed MIM-structure I-V is schematically
presented on picture 1 (reverse polarity: - - on top, + - on base electrode).
In some cases an effect of momentary restoring the N-type characteristic
is observed, which consists in conversion of the Ohm characteristic to
the N-type one (duration of this effect is about several minutes) and reverse
conversion. This gives us the possibility to talk about the origin of the
conducting crosspiece being responsible for the effects shown in figure
We think the building material for these crosspieces
can be In atoms formed as a result of interaction positive charging In
ions receiving because of In2O3 film decomposition
when a formed channel and conductivity electrons are created.
1. Dearnaley G., Stoneham A., Morgan D., UFN-1974.-T.112-N1-
2. Cold cathodes. Under edition M.I. Elinson. M., Sov.
radio, 1974, 336p.
NANOSCALE FIELD EMISSION STRUCTURES OF ULTRA-HIGH PACKING
DENSITY. Nikolai I. Tatarenko , Scientific Research Institute of Precision
Devices, Microelectronics Department, Moscow, RUSSIA.
Novel nanoscale field emission structures (NFESs) have
been fabricated and tested in vacuum and in air at atmospheric pressure.
The process of fabricating these structures is described. The nanoscale-tip
field emission system was formed on a glass substrate and consisted of
a titanium layer with regular nanoscale cylinder-like titanium pillars
of about 70 nm height, (3810) nm diameter
and packing density = 3.7x
1010 tips/cm2, which were incorporated into cylinder-shaped
through nanochannels of a dielectric layer of a porous anodic alumina.
Very small overall dimensions of tip emitters and opening diameters (188)
nm in a dielectric layer with the gained ultra-high packing density contributed
to reducing the potential required for field emission to units of volts.
While studying the I-V characteristics of such NFESs in air at atmospheric
pressure in a thin-film two-electrode device with a 150 nm in-between electrode
distance at the operation voltage of 2.7 V, average densities of field
emission currents of about 50 mA/cm2 have been observed. The
regular titanium tip array without a dielectric layer of a porous anodic
alumina (after its removing by a chemical way) in the conventional vacuum
system with a simple diode configuration with an in-between electrode distance
of 300 m at the pressure of residual
gasses of 2x10-3 Pa has been also tested. These tests showed
that the threshold field emission of such structures took place when the
electric-field intensity in a vacuum in-between electrode gap gained about
The Fowler-Nordheim plots associated with the observed
voltage-current traces for NEFSs tested both in vacuum and in air at atmospheric
pressure in a thin-film two-electrode device confirmed the field emission
character of such structures.
FIELD ELECTRON EMISSION CHARACTERISTCS OF DIAMOND AFTER
SURFACE TREATMENT. Wang Weibiao , Jin Changchun, Yuan Guang, Yin Xiuhua,
Zhao Haifeng, Fan Xiwu, Changchun Institute of Physics, Chinese Academy
of Sciences, Changchun, CHINA; Ji Hong, Department of Physics, Jilin University,
Diamond cold cathodes are made using diamond grit powder
which was synthesized from graphite by high pressure method. Diamond grit
is treated with Cs-salt and annealed in H2 at 1000C
and then mixed with AgO-base inorgranic conductive paste. The mixture of
diamond and inorgranic conductive paste is coated onto a Mo substrate.
The micture becomes a diamond coductive ceramic after heat treatment at
temperatures above 300C. Field
emission characteristics are measured in a high vacuum chamber at a pressure
of 10-5 Pa. ITO glass plate is used as an anode. The distance
between the anode and the cathode is 120 m.
The experimental results show that the turn-on voltage of diamond conductive
ceramic is about 400. Results also show that diamond conductive ceramic
has better emission ability and stable till about 3x10-2 Pa.
DIODE AND TRIODE CATHODOLUMINESCENT DEVICE PROTOTYPES
FOR BACK LIGHT APPLICATIONS. Alexander N. Obraztsov , Igor Yu. Pavlovsky,
Alexander P. Volkov, Department of Physics, Moscow State University, Moscow,
Diode and triode cathodoluminescent device prototypes
were fabricated with use of carbon thin film field emission cathodes. The
film cathodes were obtained by using techniques of chemical vapor deposition
in hydrogen/methane plasma activated by glow discharge. I-V characteristics,
brightness, power efficiency, and time dependence of the lamp parameters
were studied. We found that, for a diode type of device, the I-V curves
in Fowler-Nordheim coordinates were linear, that is typical for the field
emission, with the threshold average field about 1.5 V/um. The lamp brightness
and power efficiency were found to depend on a kind of used phosphors and
reached the values of 700 Cd/sq.m and 15%, correspondingly. Thikness of
the different types of sealed lamp prototypes was 3 to 10 mm that allows
their use as a back light source.
SUBSTRATE SENSITIVITY OF THE DEPOSITION RATE AND MATERIAL
PROPERTIES OF RF-PECVD AMORPHOUS CARBON. Shashi Paul , F.J. Clough, Emerging
Technologies Research Centre, Department of Electrical and Electronic Engineering,
De Montfort University, Leicester, UNITED KINGDOM.
Amorphous hydrogenated carbon (a-C:H), deposited by the
rf-plasma enhanced chemical vapour deposition (PECVD) technique, is a promising
material for flat panel display metal-semiconductor-metal (MSM) switches
and interlayer dielectric applications . The properties of PECVD a-C:H
have been shown to be sensitive to the substrate on which the thin film
is deposited. For MSM and interlayer dielectric applications this effect
may result in significant variations in the operating performance of the
material. This paper presents a detailed investigation of this effect and
examines the resulting issues for optimised a-C:H manufacture. Test structures
have been prepared by thermally evaporating thin films of Al, Cr and Cu,
through a shadow mask, on to c-Si and C7059 substrates. The shadow mask
defines thin metal strips and pads (with a range of dimensions) on the
substrate surface. Control substrates, with a continuous metal coating,
were also prepared without the shadow mask. Thin films of a-C:H were then
deposited at room temperature by rf-PECVD from CH4/He gas mixtures
over a range of growth conditions . A top contact was then formed by
the thermal evaporation of Al through a second shadow mask. Our investigation
shows that the choice of substrate (c-Si or C7059), and the existence and
geometrical dimensions of any metallic pattern on the substrate surface,
can result in significant spatial variations in the deposition rate and
material properties of rf-PECVD a-C:H thin films. The observed effects
can be attributed to potential variations across the metal patterned substrates
which influence the `local' dc self-bias. This leads to spatial variations
in the growth conditions and hence material properties. The nature of the
substrate and any overlying metallisation pattern are therefore important
considerations which can greatly influence the behaviour of a-C:H films
incorporated as an interlayer dielectric or as a semiconductor in MSM switches.
S. Egret, J. Robertson, W.I. Milne and F.J. Clough, Diamond and Related
Materials, 6 (1997) 879. K.J. Clay, S.P. Speakman, N.A. Morrison, N.
Tomozieu, W.I. Milne, and A. Kapoor, Diamond and Related Materials, 7 (1998)
FABRICATION OF PLANAR DIAMOND ELECTRON EMITTERS FOR FLAT
PANEL DISPLAYS. Hideki Kawamura , Shinichiro Kato, Tetsuro Maki, Takeshi
Kobayashi, Osaka Univ, Graduate School of Engineering Science, Osaka, JAPAN.
This work is on planar diamond electron emitters, which
are expected to realize large screen flat panel displays and low voltage
operation owing to its structural and material merit. This device is composed
of chemical vapor deposited (CVD) diamond particles selectively deposited
on a pair of patterned Pt film separated by several micrometers each other.
By applying voltage to a pair of Pt film, electrons are emitted from diamond
particles into vacuum and flow into the other side. In this study, planar
diamond electron emitters were fabricated for the first time and electron-emission
properties were closely investigated. Emitted current was observed above
150 V. If part of this current is drawn to the anode placed above the device,
whole the device will work as a cathode equipped with a controlling electrode.
The electron-emission properties of continuous polycrystalline diamond
film were also measured for comparison, and the mechanisms of the electron-emission
were discussed. The effective work function of continuous film was lower
than that of isolated particles. In case of continuous films, electrons
are emitted through electronic states induced by some kinds of defects,
which results in lower work function. On the other hand, in case of planar
electron-emitters using isolated particles, it was suggested that electrons
were emitted from near valence-band maximum. As the electron emission from
isolated particles is not affected by uncertain factor in inter-grain boundaries,
this device is also interesting from a scientific point of view.
CHANGES OF CONTACT POTENTIAL DIFFERENCE INDUCED BY FRICTIONAL
DAMAGE IN ULTRA-HIGH VACUUM. Lulu Zhang , Keiji Nakayama, Mechanical Engineering
Laboratory, Plasticity and Forming Division, Tsukuba, JAPAN.
Frictional electrification has been found to be important
in many areas. In the early 1950s, Harper proposed an electron transfer
mechanism, which is proportional to the contact potential difference of
the metals, to explain the contact charging of metals to metals. If it
were possible to identify the frictional electrification phenomena with
near atomic resolution, then a deeper understanding of this process might
obtain. In this study, we carried out the scratch test by using Ultra-High
Vacuum Atomic Force Microscope (UHV-AFM) and measured in-situ the contact
potential differences before and after scratch by means of the Kelvin probe
Force Microscope (KFM). By using KFM and Non-Contact AFM, we measured both
the contact potential difference and the topographic image simultaneously
without contacting the sample surface. In the AFM scratch test, we used
Si and metal deposited Si cantilevers as scratch tool and used the same
one to obtain the images. Si(111) wafers, which were deposited by metal,
were used as samples. The scratch loads were in the order of N
and speed was about 0.45 m/s.
The in-situ measurements show the changes in both topographic image and
contact potential difference after the scratch. In the topographic images,
scratch track and metal transfer from the cantilever to the surface were
observed. The contact potential difference images showed clear change between
the area with and without the scratch.
TOWARDS SUPRAMOLECULAR HYBRID MATERIALS FROM NANODIAMOND.
Peter I. Belobrov , Inst of Biophysics SB RAS, Krasnoyarsk, RUSSIA; Sergey
K. Gordeev, Central Research Inst of Materials, St. Petersburg, RUSSIA;
Olivier M. Kuettel, Louis Schlapbach, Univ of Fribourg, Fribourg, SWITZERLAND.
Synthesis-by-design of advanced hybrid materials from
nanodiamond (Nd) and its supramolecular aggregates in a solutions based
on the approach to molecular associates of coordinately saturated compounds
offered on a supermolecule (Ubermolekule) introduced by Wolf and developed
by Lehn. After transformation of carbon of explosive substances into Nd
we use chosen from detonation soot and purified Nd. Nanodiamond contains
carbon (main part of which contains in a diamond phase), hydrogen, nitrogen,
oxygen, the doping additives, metal impurity (iron, calcium etc.) and different
functional groups on a surface. Therefore an adequate definition of Nd
is supermolecule. As up to 5 nm Nd is more stable then graphite, i.e. the
phase of supramolecular hydride of diamond is most stable, as Nd is good
precursor for synthetic routes of organic-inorganic hybrids. Except for
hydrides at explosion and purification are always formed as well oxides.
The functionalization of this carbon supermolecule with diamond-like core
was made. All surface functional groups were modified by Cl, CH3
etc. The properties of Nd in microemulsions and in nanoporous carbon composites
synthesized in confined volumes have been describe. The stripped Nd was
prepared too by hydrogen plasma etching and electrophoretic deposition
of the one on silicon substrate. Field emission, XPS, UPS, Raman and X-ray
measured the physical characteristics. We plan to analyze sp3-sp2-sp
relation of Nd, to compare with other carbon scaffolding and to discuss
prospect of Nd supermolecule for carbon electronics and hydrogen storage.
We will compare the field electron emission and semiconductor properties
of porous nanocomposites as new organic-inorganic hybrid materials from
SESSION C5: CARBON AND DIAMOND FIELD EMITTERS
8:30 AM *C5.1
KINETIC ENERGY AND SPATIAL CHARACTERIZATION OF FIELD
EMISSION FROM WIDE BANDGAP MATERIALS. B.B. Pate , Washington State University,
Physics Department, Pullman, WA.
Wednesday Morning, April 7, 1999
Franciscan III (A)
A number of mechanisms have been put forward to clarify
the characteristics of field emission from both natural single crystal
and CVD diamond films. Fundamental understanding of the field emission
properties of diamond is incomplete. In this paper, we examine electronic
state origin and related characteristics of field emission from synthetically
produced thin film diamond materials using the technique of simultaneous
field emission and photoemission (FEPES). FEPES is achieved by placement
of a grounded grid about 100m above
the diamond surface. The electrostatic potential of the diamond cathode
is set to several kV (negative) simultaneous with a routine He I photo-emission
measurements. The utility of this technique includes the ability to directly
reference the field emission initial state energy to electron binding energies
at the surface as determined by He I photoemission. In the case of a natural
semiconducting (p-type) single crystal polished diamond flat we find that
the valence band is the origin of electron field emission at an applied
(macroscopic) field of 16 V/ m.
FEPES linewidth analysis finds a local field of ca. 2kV/ m.
FEPES measurements from synthetic N-doped diamond (from K. Okano) have
found a decrease in the required applied field together with a change of
the field emission initial state energy from the valence band edge to the
Fermi level, indicating that metallic states at the surface dominate field
emission. The spatial distribution of emission can be examined using an
imaging electron spectrometer. In a variety of materials studied, field
emission is found to be localized. Spectroscopic examination finds that
the field emission current instabilities are characterized by time varying
resistive voltage drops through the bulk of the WBS. Measurement of UPS
spectra under field emission conditions are shown to be useful to determine
cathode surface potential, and the spatial variation of the cathode surface
9:00 AM C5.2
ELECTRON FIELD EMISSION FROM UNDOPED AND DOPED DLC FILMS.
Volodimir G. Litovchenko , Anatoli A. Evtukh, Nikolai I. Klyui, Institute
of Semiconductor Physics, Kiev, UKRAINE; Andrei G. Chakhovskoi*, University
of California, Electrical and Computer Engineering Dept., Davis, CA; Thomas
E. Felter**, Lawrence Livermore National Laboratory, Livermore, CA.
In this presentation the electron field emission and electrical
conductivity of the undoped and nitroged doped DLC films have been investigated.
Undoped and nitrogen doped DLC films were grown by PE CVD method from CH4:H2
and CH4:H2:N2 mixtures, correspondingly.
During nitrogen doped DLC films deposition the nitrogen content in gas
mixture was varied within the range from 0 to 45.
In-situ the gas-phase doping allowed us to deposit DLC films with different
content nitrogen in them. DLC films were deposited under three different
levels of gas pressure in chamber: 0.2, 0.6 and 0.8 Torr. The measurement
of emission current from samples was perforrned in the vacuum system which
could be pumped to a stable pressure of 10-6 Torr. The emission
current was measured in the diode structure. The emitter-anode spacing
L was constant and equal to 20 m.
The current - voltage characteristics of the Si field electron emission
arrays covered with undoped and nitrogen doped DLC films show that at the
beginning the threshold voltage (Vth) remarkably increases
with nitrogen content growth, then the decreasing of Vth
is observed and finally Vth increases. Corresponding
Fowler-Nordheim (F-N) plots follow F-N tunneling over a wide field range.
The F-N plots were used for determination of the work functions, threshold
voltage, field enhancement factors, effective emission areas. The effective
work function on refractive index dependences of nitrogen doped and undoped
DLC films are nonmonotonous with minimum for both undoped and nitrogen
doped DLC films. For the qualitative explanation of experimental results
we base on the model of DLC film as a diamond-like (sp3 - bonds)
matrix with graphite-like inclusions in it.
9:15 AM C5.3
TETRAHEDRAL AMORPHOUS CARBON FILM FOR ELECTRON FIELD
EMISSION APPLICATION. L.K. Cheah , X. Shi, Ion Beam Processing Lab, School
of Electrical and Electronic Engineering, Nanyang Technological University,
The fact that carbon field emission cathodes can be produced
with varying degrees of sp3, sp2 and sp1 hybridizations means that these
films can be tuned for particular applications. It also means that these
films can be produced with a whole gamut of different properties resulting
in the difficulties to propose a single model to explain the observed electron
emission at low electric fields. The tetrahedral amorphous carbon (ta-C)
thin films deposited using a filtered cathodic vacuum arc (FCVA) system
has been shown to have different degrees of sp3 and sp2 and surface morphology
by varying the carbon ion energy, deposition rate and substrate temperature.
The field emission properties of the ta-C films were measured, i.e. field
emission current density versus applied electric field and field emission
spots projected from a tin oxide coated glass. The field emission properties
of the ta-C films are influenced by the microstructure. In addition, the
electron field emission properties of the ta-C films have been shown to
improve as a result of surface treatment with H, O and Ar ions. The surface
treatment transforms the mirror-smooth samples into the films with visible
nano-scale regions or protrusions formed on the surface within the slightly
receded network. Thus, we concluded that the front surface and the microstructure
of the ta-C films play an important role in the utilization of carbon films
for field emission application.
9:30 AM C5.4
MICROSTRUCTURES, OPTICAL AND ELECTRON EMISSION PROPERTIES
OF TETRAHEDRAL AMORPHOUS CARBON SYNTHESIZED BY FILTERED ARC DEPOSITION.
Y.H. Yu , Z.Y. Chen, J.P. Zhao, X. Wang, Ion Beam Laboratory, Shanghai
Institute of Metallurgy, Chinese Academy of Science, Shanghai, CHINA; N.Z.
Lou, S.P. Wong, I.H. Wilson, Department of Electronic Engineering, The
Chinese University of Hong Kong, Hong Kong, CHINA.
A new kind of carbon materials-tetrahedral amorphous carbon
(ta-C) films has received much attention in recent years. ta-C films have
been found to be amorphous and contain up tp 90% sp3-bonded C. This kind
of film is semiconducting, exhibits photoconductivity and has an optical
band gap 2.0-2.5eV, and is potentially useful as a stable wide-band-gap
semiconductor. In this work, tetrahedral amorphous carbon (ta-C) films
have been prepared by filtered arc depostion (FAD) technique. The surface
morphology, defect, microstructure of ta-C films are investigated by atomic
force microscopy (AFM), high-resolution transmittance electron microscopy
(HRTEM), and slow positron annihilation (SPA). Results show that the surface
ta-C films is smooth and compactive, electron emission properties are affacted
by deposition processes. Optical properties of ta-C films are studied and
a new optical method has been developed to determined the ratio of sp3
and sp2 in the films. The method is based on the simulation of the infrared
reflection spectrum by applying the Bruggeman effective medium approximation
(EMA). By the simulation of infrared reflection spectra with the established
model, the volume fraction of sp3 bonds is obtained, which is in good agreement
with the value obtained by the electron energy loss spectroscopy (EELS).
10:15 AM C5.5
ANALYSIS OF HIGH-CURRENT YIELD OF DIAMOND-BASED FIELD
EMITTERS FOR MICROWAVE VACUUM MICROELECTRONICS. Victor V. Zhirnov , Semiconductor
Research Corporation, Research Triangle Park, NC; C. Lizzul Rinne, Gregory
J. Wojak, J.J. Cuomo, John J. Hren, North Carolina State University, Dept
of Materials Science and Engineering, Raleigh, NC.
For microwave vacuum electronic devices, the most important
parameters for cathodes are to provide high maximum currents and integral
current densities. This work is the first attempt to summarize results
of high-current experiments with diamond-coated cathodes, to provide analysis
and recommendations for material properties, and to design an electron
source. Experimental results cover several cathode designs (single tips,
array of tips, and planar cathodes), and various diamond/carbon coatings
(CVD diamond, HPHT diamond, nanodiamond, and laser-ablated carbon). It
was found that the maximum current, Imax, varied significantly as
different coating materials were used. Imax was also found to be
a function of the coating thickness, d. The experimental dependencies
of Imax(d) and Imax/Vmax(d) for different diamond and carbon
materials were studied for the first time. It was found that for a single
emission site (or single-tip emitter), diamond coatings enhance the maximum
current by about two orders of magnitude. For large area (1 cm2)
arrays, the maximum current was about 2-7 times the maximum current of
an un-coated cathode, depending on the parameters of the coating. The possible
physics controlling the current limitation will be explored. There are
two main mechanisms controlling the current limitation: overheating of
the emission site due to heat dissipation at high local current densities,
and environmental effects (ion bombardment, arcing, etc.). Differences
in maximum emission currents can be partly explained by the various thermal
conductivities of the diamond and carbon coatings. This assumption was
used to obtain relative estimates of the thermal conductivity for the different
coating materials. The integral thermal conductivity depends on structural
material properties such as porosity, crystal size, and phase composition.
The results of a model developed for simulating maximum current operation
of a cathode will be presented. The model is based on cathode parameters
such as emission site density, thermal conductivity, thickness of the coating,
and random variations in the local field enhancement. Various methods to
increase the total current yield from diamond-based cathodes will also
10:30 AM C5.6
DEFECT AND RAMAN SPECTROSCOPY OF CHEMICAL VAPOR DEPOSITION
GROWN DIAMOND FILMS. J.M. Perez , R.E. Stallcup II, I.A. Akwani, Univ of
North Texas, Dept of Physics, Denton, TX.
We characterize the spatial distribution of unoccupied
defects in chemical vapor deposition grown polycrystalline diamond films
using two-photon spectroscopy and Raman spectroscopy. Photons of energy
2.4 eV, 2.5 eV, 2.7 eV and other energies from an argon ion laser are focussed
on a 10 micron location of the sample and used to excite electrons from
unoccupied defect states to vacuum. The emitted electrons are collected
with high efficiency using a microchannel plate detector. The number of
emitted electrons per incident photon is used as a measure of the defect
density at the location. Raman spectroscopy is simultaneously performed
at the location to determine the morphology and diamond versus graphite
content. For a given location, the defect density is compared with the
morphology and diamond versus graphite content. The results are compared
with the field emission properties.
10:45 AM C5.7
FIELD EMISSION FROM CARBON CARBON FILMS DEPOSITED BY
VHF CVD ON DIFFERENT SUBSTRATES. A.I. Kosarev , A.S. Abramov, A.J. Vinogradov,
M.V. Shutov, A.F. Ioffe Phys-Techn. Inst., St. Petersburg, RUSSIA; T.E.
Felter, Lawrence Livermore National Laboratory, CA; A.N. Andronov, S.V.
Robozerov, Technical University, St. Petersburg, RUSSIA.
As previously demonstrated, non diamond carbon (NDC) films
deposited at low temperatures (200-300 C)on silicon tips reduced threshold
field value of field emission. In this paper we will present the results
of study of field emission from flat NDC films prepared by VHF CVD. Effect
of different metals of back contact and of film thickness on electron emission
were observed. Emission measurements were performed in diode configuration
in vacuum at about 10-10 Torr. NDC films were deposited on ceramic
and on c-Si substrates coated by metall layers of Ti, Cu, Ni and Pt. The
metals were deposited by sputtering. Correlation of work function of back
contact metal and emission characteristics has been observed. Model of
field emission from metall-NDC film structure will be discussed.
11:00 AM C5.8
VERY LOW THRESHOLD FIELD EMISSION FROM NANO-CRYSTALLINE
DIAMOND FILMS GROWN BY HOT FILAMENT CVD PROCESS. B.S. Satyanarayana , X.L.
Peng*, J. Robertson, W.I. Milne & T.W. Clyne*, Department of Engineering,
Cambridge University, Cambridge, UNITED KINGDOM; *Department of Material
Science, Cambridge University, Cambridge, UNITED KINGDOM.
There is a great interest in field assisted electron emission
from diamond. The main attraction being its electro -negativity in addition
to its properties like the thermal stability, mechanical hardness and chemical
inertness. All forms of Diamond including crystalline, poly - crystalline,
doped diamond, nano diamond etc have been studied. Generally low threshold
field emission has been reported for doped diamond films grown by various
process. Here we report very low threshold field emission from undoped
discontinuous diamond films grown by the hot filament CVD process. The
diamond films were grown by the hot filament chemical vapour deposition
[HFCVD] process using methane and hydrogen as source gases. First the effect
of the crystal size were studied. It was observed that the threshold field
decreases from 19 V/m for 1 m
sized crystal diamond film to 0.5 V/m
for about 0.1 0.2 m
sized crystal diamond film. The threshold field is defined as that field
at which an emission current density of 1 A/cm2
is obtained. Next the effects of temperature [775C
- 975 C] and methane concentration
[0.5 to 3
CH4 / H2] were studied, trying to grow similar thin
discontinuous/defective or nano-crystalline films under all conditions.
With change in temperature it was observed that a low threshold field of
nearly 1 V/m was obtained for samples
grown at 975 and 825C.
Hence the effect of methane concentration variation was studied at 825 C.
It was observed that with increase in methane concentration from 1
to 3 the threshold field increased
from 0.5 V/m to 1.25 V/m.
However there was also a corresponding increase in current density and
emission site density. The varying morphological properties are compared
using the SEM.
11:15 AM C5.9
BAND-GAP STRUCTURE AND ELECTRON EMISSION PROPERTY OF
CHEMICAL VAPOR DEPOSITED DIAMOND FILMS. J. Liu , D.Y.T. Chiu, D.C. Morton
and W.H. Chang, Army Research Laboratory, Sensors and Electron Devices
Directorate, AMSRL-SE-EO, Adelphi, MD.
Diamond has been regarded as an ideal material of high-current-
density cold cathode for vacuum microelectronics devices over the years.
Diamond films synthesized using chemical vapor deposition (CVD) are able
to yield large current density at low electric field. Theoretical investigations
concluded that the emission could come from the surface and defects states
near the conduction band. Quasiballistic electron transport through band-gap
states was proposed to be the mechanism for sustaining the emission current.
It is widely accepted that the distribution of impurity bands and band-gap
states caused by defects and impurities in the CVD diamond. However, no
direct experimental measurement was performed or reported for such bands
and band-gap states and the resultant electron emission behavior. Using
visible to vacuum ultra-violet (VUV) photoluminescence spectroscopy, we
investigated the structure of the band gap and possible impurity states
of intrinsic, doped, and amorphous CVD diamond films. Natural diamond crystals
were used as reference for the measurement. Experiments revealed that in
doped and high-defect diamond films band-gap states are distributed very
closely to the conduction band and extended deep into the band gap. Such
band-gap structure resulted in a low-field electron emission. Amorphous
diamond, with a narrower band gap, showed no significant behavior in electron
11:30 AM C5.10
ELECTRON EMISSION FROM NEA DIAMOND: EXCITON TRANSPORT
STUDIES. W. Chang, B.B. Pate , Washington State University, Physics Department,
Photoelectron emission is a powerful spectroscopy for
the study of the electronic structure of solids and surfaces. UV photoelectron
emission studies of negative electron affinity (NEA) diamond recently discovered
electron emission from the breakup of bound electron-hole pairs (Mott-Wannier
excitons) at the diamond surface. In that work Spicer's three-step model
(absorption, transport, escape) identified the key role of exciton transport.
In this paper, we demonstrate that the observed exciton diffusion length
is intrinsic; that is, governed by phonon scattering events. Measurements
of photoelectron quantum yield (emitted electrons per incident photon)
versus excitation photon energy from natural type IIb diamond (aspolished
NEA (111) surface) were made at temperatures from 86 to 295 K. Note that
the electron yield decreases significantly as the temperature is increased
for a fixed photon energy. Moreover, the characteristic oscillatory structures
of the yield as a function of photon energy gradually vanishes as the temperature
is lowered. Assuming that intrinsic phonon-mediated exciton dissociation
(ionization) and recombination dominate the exciton lifetime and diffusion
coefficient we are able to reproduce the observed temperature dependence
of the quantum photoelectron yield. Consistent with numerical simulations,
we find that the disappearance of the photoyield oscillations at low temperature
result from the decrease of available acoustic phonons of sufficient wavelength
to dissociate (ionize) the excitons. A detailed physical model will be
11:45 AM LATE NEWS CARBON EMITTERS
SESSION C6: THEORY AND MODELING OF ELECTRON FIELD
1:30 PM *C6.1
SPACE CHARGE EFFECTS IN VACUUM MICROELECTRONICS. Ivor
Brodie , SRI International, Menlo Park, CA.
Wednesday Afternoon, April 7, 1999
Franciscan III (A)
In thermionic vacuum devices the use of space charge limited
flow of the electron current has the following desirable properties.It
enables the anode current to be virtually independent of the current the
emitter is capable of delivering, it smooths out spatial variations in
the emission from the cathode surface, and it substantially reduces (by
a factor of 10 to 1000) the current fluctuation noise (both flicker and
shot).The field emission sources used in vacuum microelectronics require
by their very nature that there is a very high electric field at the emitting
surface and this introduces problems for producing space charge limited
flow along subsequent portions of the electron path between the electron
source and the anode if similar desirable effects are to be obtained. In
this paper I explore on a theoretical basis how space charge limited flow
may be obtained from both a single gated micro-field emission source and
from planar arrays of large numbers of such sources.
2:00 PM C6.2
NUMERICAL SIMULATION OF THE TUNNELING CURRENT AND BALLISTIC
ELECTRON EFFECTS IN FIELD EMISSION DEVICES. L.R.C. Fonseca , R. Ramprasad,
P. von Allmen, Motorola Flat Panel Display Division, Tempe, AZ.
Due to the high performance sensitivity of field emission
devices on system parameters, realistic models are highly desirable. In
the present study we consider the effects of tunneling, quickly changing
potentials, and ballistic electron motion on the anode current and on the
width of the electron beam for a two-dimensional system. Despite the quantitative
limitations imposed by the lower dimensionality of the model, our qualitative
results offer useful insights. To accurately calculate the electric field
in typical field emission devices containing elements ranging from the
nanometer to the millimeter scale, we have chosen the boundary element
method which avoids solving the problem on a grid, thus allowing greater
flexibility. Our emission model evaluates the current density at the cathode
surface from the tunneling transmission coefficient, which is calculated
from the solution of the one-dimensional Schrödinger equation using
a potential barrier that includes the effect of image charges. Electrons
are emitted stochastically from the cathode with a velocity and angle (measured
from the normal to the surface) following the tunneling distribution function.
For very sharp tips the electric field changes from its surface value over
a very short distance away from the surface, which may be comparable to
the tunneling distance. We have compared the effect of a position-dependent
versus a constant field approach on the current density. Once emitted
at a rate following a Poisson distribution, we propagate electrons ballistically
through the device. We have compared the effect of the electrons lateral
kinetic energy and emission angle distribution on the electron beam width
at the anode with a pure electrostatic approach, which assumes that the
electrons exactly follow the electric field lines, and in particular are
emitted perpendicular to the surface.
2:15 PM C6.3
ANALYSIS OF MEASURED I(V) RELATIONS FOR ELECTRON EMISSION
FROM INSULATING DIAMOND FILMS ON VARIOUS SI SUBSTRATES. K.L. Jensen , Naval
Research Laboratory, Washington, DC; A. Goehl, G. Mueller, Fachbereich
Physik, Universitaet Wuppertal, Wuppertal, GERMANY.
Field emission from diamond microfabricated structures
hold promise for high power applications, in which the operating environment
is known to be deleterious to other cold-cathode candidates. In addition,
the surface/vacuum interface may have a negligible energy barrier, so electron
emission into vacuum should be more easily accomplished. Emission measurements
from insulating diamond on p- and n-doped Si substrates suggest that the
substrate-diamond interface plays a dominant role in the electron emission
of a diamond film . In particular, Fowler Nordheim plots of the current-voltage
relationship for diamond films on lightly n- and p- and on highly p-doped
Si substrates display convexity at low currents, analogous to the findings
of a heuristic model of internal field emission based on ad hoc modifications
to a WKB analysis of the potential at the substrate-diamond interface .
In this work, we shall present a substantially revised analysis of the
internal field emission problem, directed towards analyzing and understanding
the low voltage regime of the aforementioned data. Experimentally, the
data was taken from diamond samples approximately 8 µm thick and
grown in a microwave plasma-assisted CVD setup. Repeatable and characteristic
I(V) behavior was obtained from the samples. Theoretically, we shall develop
a more rigorous WKB analysis of the interface barrier and a current vs.
applied field model based on parameters ascertained from the data. Theoretical
current-applied field simulations and predictions shall be described and
related to experiment. We endeavor to show that the deviation from Fowler
Nordheim behaviour is explicable in terms of the nature of the interface
barrier.  A. Gö hl, et al.,, Local field emission features of oriented
diamond films on various silicon substrates. Tech. Digest of the 11th IVMC
(July 12-24, 1998, Asheville, NC) p200.  K. L. Jensen, et al., Advanced
emitters for next generation rf amplifiers, JVSTB16, 2038 (1998).
2:30 PM C6.4
MODELS OF INSTABILITIES IN FIELD EMISSION. V.M. Anikin
, A.F. Golubentsev.
The analytical Markov models are suggested for the description
of the stochastic dynamics of some physical parameters (e.g. current, number
of emission sites, work function) of field emission sources. These models
give relationships between emission statistical theoretical and applied
characteristics (autocorrelation functions, spectra, microparameters of
models and reliability parameters). We introduce the range of working states
of FEA and the probabilistic characteristics of lifetime, ``ageing'', failures
and other reliability parameters of FEA's reliability in the context of
various models of the ``drift''(decay) of emission from FEA. Some linear
and nonlinear (with random parameters) are presented.
3:15 PM *C6.5
MATERIALS ISSUES IN INVERSE NOTTINGHAM EFFECT COOLING.
R.F. Greene , R. Tsu, U. of N. Carolina at Charlotte, NC; J.J. Cuomo, N.
Carolina State University, Raleigh, NC.
Field emission from metal emitters produces excess ``Nottingham
heat'', with emission coming from states slightly below the Fermi-level
EF. We proposed  that field emission from p-type semiconductors
with low work function WF would be strongly cooling,
with cooling power and efficiency significantly greater for this inverse
Nottingham Effect (INE) than, e.g., for thermoelectrics. Strong INE cooling
power from strongly doped p-type semiconductors occurs if emission from
the conduction band CB dominates, while EF remains near
the valence band edge. Then, heat of transport w
energy gap, i.e. much higher than for Peltier. Cooling efficiency figure
of merit (FOM) in solid state coolers is explicitly restricted by the thermal
heat leak between cold and warm junctions, hence by the Wiedemann-Franz
ratio. In INE cooling, the vacuum electron path has zero heat leak, immediately
doubling the FOM. Since heat flux density is w times the electric current
density, the latter must be optimized, posing three materials issues: The
p-doping must be heavy so that the conduction band edge remains well above
EF despite field penetration. The semiconductor surface
recombination velocity must be high to prevent exhaustion of the CB states,
indicating direct-gap emitters. Third, lowering WF, e.g.,
by cesiation, favors CB emission. Ridge emitters should be used to maximize
emission area. Retarding-potential collection can minimize electron bombardment
heating of the collector. An INE cooler for spot-cooling Si or III-V chips
using integral (etched) porous -Si  micro-heat pipes for produce ``spot-cooling''
of chips is described.
1. R.F. Greene, 1997 DARPA Thermal Management Workshops
2. R. Tsu, 1994 Porous Silicon Workshop, UNC-Charlotte,
3:45 PM C6.6
DIRECT IMAGING OF BIAS DEPENDENT p-n JUNCTION BY SCANNING
CAPACITANCE MICROSCOPY. Chaiin Im , G. H. Buh, C. J. Kang, S. Lee, C. K.
Kim, Y. Kuk, National Creative Research Initatives, Center for Science
in Nanometer Scale, Seoul National Unversity, Dep. of Phyics, Seoul, KOREA.
With downsizing of feature sizes in very large scale integration
(VLSI), nanometer scale characterization of electrical devices become important.
Especially the characterization under the operating condition has drawn
much attention to understand the mechanism of their degradation and breakdown.
We directly observed the movement of a p-n junction with the applied bias
for the first time. Since the local C-V spectroscopy by scanning capacitance
microscopy (SCM) is determined by the carrier density at the location the
location of the p-n junction can be estimated. In order to control the
width of the depletion layer a DC bias voltage was applied to the n-type
region while a small modulation AC voltage was added to the grounded p-type
region in order to increase the sensitivity. At zero DC bias condition,
SCM image clearly showed static built-in depletion region. The depletion
region extends with the applied voltage in reverse bias condition and shrinks
in forward bias case. Therefore the bias dependent change of depletion
width could be imaged directly. An 1-D depletion approximation model was
given to explain the bias dependent depletion width quantitatively. By
comparing the experimental results with the 2D device simulation it was
suggested that the SCM result can be used to aid the device simulation.
4:00 PM C6.7
POTENTIAL DISTRIBUTION AT CLEAVED INSULATING SOLID SURFACE
IN ULTRAHIGH VACUUM. Keiji Nakayama , Lulu Zhang, Mechanical Engineering
Laboratory, Tsukuba, JAPAN.
To have a knowledge on charging mechanism at newly formed
insulating solid surfaces, potential distribution on cleaved insulating
solid surface has been investigated in ultrahigh vacuum. Insulating solids
such as MgO single crystals were cleaved in ultrahigh vacuum of 10-8 Pa.
Then the surface potential and topography at the fresh cleaved surface
were measured simultaneously in the UHV using Kelvin force microscope (KFM)
and non-contact atomic force microscope (NC-AFM), respectively. A Silicon
cantilever tip coated with metal was used. For measuring surface potential,
alternating voltage with the frequency of 2 kHz was applied. For MgO sigle
crystal, (100) surface was cleaved. The measured KFM images on the MgO
showed some distribution patterns of surface potential on the cleaved surface,
while AFM images showed step lines on them. The distribution of the potential
was investigated in connection to those of the steps. The results showed
that the potential distribution corresponded to those of the step distributions
where charging was low. On the other hand, where charging was high, the
correspondence was not seen because too intense surface charging was generated
over the surfaces including the terraces and ledges. The cleaved surface
morphologies were investigated also using surface analytical tools such
as micro-X-ray diffraction method.
4:15 PM C6.8
NUMERICAL SIMULATION OF ELECTRON FIELD EMISSION FROM
SILICON WEDGE MICROCATHODE. V.A. Fedirko and S.V. Polyakov, Joint Center
for Mathematical Modelling of Moscow State Univ of Technology ``Stankin''
and Institute for Mathematical Modelling RAS, Moscow, RUSSIA.
We report on the results of the numerical simulation of
electron field emission from a silicon wedge microcathode. Hot electron
effects in semiconductor are accurately taken into account in the framework
of 2D quasi-hydrodynamic approach. Electric field and tunneling current
density at the emitting surface are calculated and used as boundary conditions
for the quasi-hydrodynamic set of equations in semiconductor. An original
finite difference scheme with alternating mesh is used which guarantee
the conservatism and weak monotony of the solution.
Two dimensional distributions of the electron density
and the electron temperature near the emitting surface, as well as electric
field and current density distributions are calculated and analyzed. The
results of 1D and 2D modelling are compared.
Electron heating drastically change electron dynamics
in the semiconductor and strongly affects the emitting characteristics.
It may also dramatically influence the stability of the tip. It is shown
that 2D modelling is essential for adequate simulation of field emission
from a wedge microcathode.
4:30 PM LATE NEWS THEORY AND MODELING