Post on 21-Feb-2023
ISSN No. : 2394 – 174X, V – 1, I – 1, 2014 Journal Club for Electrical Engineering (JCEE)
Manuscript No: JCEE/REV/2014/10, Received On: 14/09/2014 , Accepted On : 25/09/2014, Published On: 10/11/2014
REVIEW ARTICLE
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A Study on Fabrication of Nano Electrolytic Powders Used in Capacitors
Ganesan J1, Prakash KS2, Gajendran S3, Karthik R4, Raguvelan R5, Selvaraj DE6, Priyan SS7, Sugumaran CP8, Kumar MR9, Joshi RM10, Kumar SD11
1Assistant Professor, Department of Electrical and Electronics Engineering, Sree Sowdambika College of Engineering, Aruppukottai, India
2,3,4,5 Department of Electronics and Communication Engineering, Sree Sowdambika College of Engineering, Aruppukottai, India
6,7 Assistant Professor, Department of Electrical and Electronics Engineering, Panimalar Engineering College, Chennai, India
8 Associate Professor, Division of High Voltage Engineering, College of Engineering, Guindy, Anna University, Chennai, India
9 Assistant Professor, Department of Electrical and Electronics Engineering, Dhanalakshmi Srinivasan College of Engineering and Technology, Mamallapuram, Chennai, India
10 Associate Professor, Department of Electrical and Electronics Engineering, Panimalar Engineering College, Chennai, India
11 Research Scholar, Department of Electrical and Electronics Engineering, St. Peter’s University, Avadi, Chennai, India
ABSTRACT In this paper, a wide literature survey was done on the various fabrication methods used for the manufacture of nano fillers used in electrical apparatuses. The important characteristics, advantages, disadvantages of the various fabrication methods used for the manufacture of nano fillers were discussed. The applications of the various fabrication methods used for the manufacture of nano fillers were also discussed. This paper would be helpful for the young scientist and engineers to study about the important fabrication methods used for the manufacture of nano fillers used in the electrical insulation system. This would motivate the young scientist for their research work to invent nano electrical and electronic apparatuses.
KEYWORDS
Fabrication methods, Metal organic vapour phase epitaxy (MOVPE), metal organic chemical vapour deposition (MOCVD), Molecular beam epitaxy (MBE)
INTRODUCTION
Capacitors were called as charge storage
devices. It will store the energy in the form
of electric field such as charges. The
capacitors were used in electrical and
electronics appliances. The performance of
the capacitors can be increased by using
nano technology. Hence the capacitors
were called as Nano Capacitors. In this
paper, an enhanced a wide literature survey
was done on the various fabrication
methods used for the manufacture of nano
Address for Correspondence: Ganesan J., Assistant Professor, Department of Electrical and Electronics Engineering, Sree Sowdambika College of Engineering, Aruppukottai, India. Email: powergrid4@gmail.com
A Study on Fabrication of Nano Electrolytic Powders Used in Capacitors
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electrolytic powders used in capacitors.
Nano technology plays an important role in
the improvement of the performance of the
electronic appliances. Hence the
fabrications of the nano electronic
appliances play a vital role in the design of
the electronic appliances. So, the
fabrication method of the different
electronic appliances was discussed with
utmost care. A special attention was given
to the fabrication of capacitors.
FABRICATION METHODS
Metal Organic Vapour Phase Epitaxy
Metal organic vapour phase epitaxy
(MOVPE), also known as organo metallic
vapour phase epitaxy (OMVPE) or metal
organic chemical vapour deposition
(MOCVD), was a chemical vapour
deposition method of epitaxial growth of
materials, especially compound
semiconductors, from the surface reaction
of organic compounds or metal organics
and hydrides containing the required
chemical elements. For example, indium
phosphide could be grown in a reactor on a
substrate by introducing Trimethylindium
((CH3)3In) and phosphine (PH3).
Formation of the epitaxial layer occurs by
final pyrolysis of the constituent chemicals
at the substrate surface [1-3]. In contrast to
molecular beam epitaxy (MBE) the growth
of crystals was by chemical reaction and not
physical deposition. This takes place not in
a vacuum, but from the gas phase at
moderate pressures (2 to 100 kPa). As such,
this technique was preferred for the
formation of devices incorporating
thermodynamically Meta stable alloys, and
it has become a major process in the
manufacture of optoelectronics. The
following figure 1 shows chemical reaction
of the Metal organic vapour phase epitaxy
process.
Fig. 1. chemical reaction of Metal organic vapour phase epitaxy process
Illustration Process
Reactor components
A reactor was a chamber made of a
material that does not react with the
chemicals being used. It must also
withstand high temperatures. This chamber
was composed by reactor walls, liner, a
susceptor, gas injection units, and
temperature control units. Usually, the
reactor walls were made from stainless steel
or quartz. To prevent overheating, cooling
water must be flowing through the channels
within the reactor walls [4-7]. Ceramic or
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special glasses, such as quartz, are often
used as the liner in the reactor chamber
between the reactor wall and the susceptor.
A substrate sits on a susceptor which was at
a controlled temperature.
The susceptor was made from a material
resistant to the metal organic compounds
used; graphite was sometimes used. For
growing nitrides and related materials, a
special coating on the graphite susceptor
was necessary to prevent corrosion by
ammonia (NH3) gas. In cold-wall CVD,
only the susceptor was heated, so gases do
not react before they reach the hot wafer
surface. In hot-wall CVD, the entire
chamber was heated. This may be
necessary for some gases to be pre-cracked
before reaching the wafer surface to allow
them to stick to the wafer.
Gas inlet and switching system
Gas was introduced via devices known as
‘bubblers’. In a bubbler a carrier gas
(usually nitrogen or hydrogen) is bubbled
through the metal organic liquid, which
picks up some metal organic vapour and
transports it to the reactor [8-9]. The
amount of metal organic vapour transported
depends on the rate of carrier gas flow and
the bubbler temperature, and in usually
controlled automatically and most
accurately by using a Piezo con type vapour
control system. Allowance must be made
for saturated vapours.
Pressure maintenance system
Gas Exhaust and cleaning System
Toxic waste products must be converted to
liquid or solid wastes for recycling
(preferably) or disposal. Ideally processes
will be designed to minimize the production
of waste products. The following figure 2
shows the Metal organic vapour phase
epitaxy process.
Fig. 2. Metal organic vapour phase epitaxy
process
MOCVD Apparatus
Organo metallic precursors
Semiconductors
Zinc selenide (ZnSe)
HgCdTe
ZnO
Zinc sulfide (ZnS)
Semiconductors
Si
Ge
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Environment, Health and Safety
As MOVPE has become well-established
production technology, there were equally
growing concerns associated with its
bearing on personnel and community
safety, environmental impact and
maximum quantities of hazardous materials
(such as gases and metal organics)
permissible in the device fabrication
operations. The safety as well as
responsible environmental care has become
major factors of paramount importance in
the MOVEPE- based crystal growth of
compound semiconductors.
Chemical Beam Epitaxy
Chemical beam epitaxy (CBE) forms an
important class of deposition techniques for
semiconductor layer systems, especially
III-V semiconductor systems. This form of
epitaxial growth was performed in an
ultrahigh vacuum system [10-12]. The
reactants are in the form of molecular
beams of reactive gases, typically as the
hydride or a metal organic. The term CBE
was often used interchangeably with metal-
organic molecular beam epitaxy
(MOMBE).
Basic Principles
Chemical Beam Epitaxy was first
demonstrated by W.T. Tsang in 1984. This
technique was then described as a hybrid of
metal-organic chemical a pour deposition
(MOCVD) and molecular beam epitaxy
(MBE) that exploited the advantages of
both the techniques. In this initial work, InP
and GaAs were grown using gaseous group
III and V alkyls.
Fig. 3. Basic process a) MOCVD, b) MBE,
and c) CBE
While group III elements were derived
from the pyrolysis of the alkyls on the
surface, the group V elements were
obtained from the decomposition of the
alkyls by bringing in contact with heated
Tantalum (Ta) or Molybdenum (Mo) at
950-1200 C. Typical pressure in the gas
reactor was between 102 Torr and 1 atm for
MOCVD. Here, the transport of gas occurs
by viscous flow and chemicals reach the
surface by diffusion. In contrast, gas
pressures of less than 10-4 Torr are used in
CBE. The gas transport now occurs as
molecular beam due to the much longer
mean-free paths, and the process evolves to
a chemical beam deposition [13- 15]. It was
also worth noting here that MBE employs
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atomic beams (such as aluminium (AL) and
Gallium (Ga) and molecular beams (such as
As4 and P4) that are evaporated at high
temperatures form solid elemental sources,
while the sources for CBE are in a pour
phase at room temperatures. The following
figure 3 shows the comparison of the
different processes in the growth chamber
for MOCVD, MBE and CBE.
Experimental Setup
A combination of turbo molecular and cryo
pumps are used in standard UHV growth
chambers. The chamber itself was
equipped with a liquid nitrogen cryo shield
and a rotatable crystal holder capable of
carrying more than one wafer. The crystal
holder was usually heated form the
backside to temperatures of 500 to 700 C.
Most setups also have RHEED equipment
for the in-situ monitoring of surface
superstructures on the growing surface and
for measuring growth rates, and mass
spectrometers for the analysis of the
molecular species in the beams and the
analysis of the residual gases. The gas inlet
system, which was one of the controlled
systems are used most commonly. The
materials flux was controlled by the input
pressures of the gas injection capillary. The
pressure inside the chamber can be
measured and controlled by a capacitance
manometer. The molecular beams of
gaseous source materials injectors or
effusion jets that ensure a homogeneous
beam profile [16-18]. For some starting
compounds, such as the hydrides that are
the group V starting material, the hydrides
have to be pre cracked into the injector.
This was usually done by thermally
decomposing with a heated metal or
filament.
Growth Kinetics
In order to better understand the growth
kinetics associated with CBE, it was
important to look at physical and chemical
processes associated with MBE and
MOCVD as well. Figure 4 depicts those.
The growth kinetics for these three
techniques differs in many ways. In
conventional gas source MBE, the growth
rate was determined by the arrival rate of
the group III atomic beams. The epitaxial
growth takes place as the group III atoms
impinge on the heated substrate surface,
migrates into the appropriate lattice sites
and then deposits near excess group V
dimmers or tetramers. It was worth noting
that no chemical reaction is involved at the
surface since the atoms are generated by
thermal evaporation from solid elemental
sources. In MOCVD, group III alkyls are
already partially dissociated in the gas
stream. These diffuse through a stagnant
boundary layer that exists over the heated
substrate, after which they dissociate into
the atomic group III elements. These atoms
then migrate to the appropriate lattice site
and deposit epitaxial by associating with a
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group V atom that was derived from the
thermal decomposition of the hydrides. The
growth rate here was usually limited by the
diffusion rate of the group III alkyls through
the boundary layer. Gas phase reactions
between the reactants have also been
observed in this process.
Fig. 4. Growth kinetics involved in a)
conventional MBE, b) MOCVD, and c)
CBE
In CBE processes, the hydrides are cracked
in a high temperature injector before they
reach the substrate. The temperatures are
typically 100-150C lower than they are in a
similar MOCVD or MOVPE. There was
also no boundary layer (such as the one in
MOCVD) and molecular collisions are
minimal due to the low pressure. The group
V alkyls are usually supplied in excess, and
the group III alkyl molecules impinge
directly onto the heated substrate as in
conventional MBE. The group III alkyl
molecule has two options when this
happens [19-21]. The first option was to
dissociate its three alkyl radicals by
acquiring thermal energy from the surface,
a leaving behind the elemental group III
atoms on the surface. The second option
was to re-evaporate partially or completely
un dissociated. Thus, the growth rate was
determined by the arrival rate of the group
III alkyls at a higher substrate temperature,
and by the surface pyrolysis rate at lower
temperatures
Compatibility with Device Fabrication
Selective Growth at Low Temperatures
Selective growth through dielectric
masking is readily achieved using CBE ad
compared to its parent techniques of MBE
and MOCVD. Selective growth was hard
to achieve using elemental source MBE
because group III atoms do not desorbs
readily after they were adsorbed. With
chemical sources, the reactions associated
with the growth rate are faster on the
semiconductor surface than on the
dielectric layer. No group III element can,
however, arrive at the dielectric surface in
CBE due to the absence of any gas phase
reactions. Also, it is easier for the
impinging group III metal organic
molecules to desorb in the absence of the
boundary layer. This makes it easier to
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perform selective epitaxy using CBE and at
lower temperatures, compared to MOCVD
or MOVPE.
P-Type Doping
It was observed that using TMGa for the
CBE of GaAs led to high p-type
background doping (1020 cm-3) due to
incorporated carbon. However, it was
found that using TEGa instead of TMGa led
to very clean GaAs with room temperature
hole concentrations between 1014 and 1016
cm-3. It has been demonstrated that the hole
concentrations can be adjusted between
1014and 1021 cm-3 by just adjusting the alkyl
beam pressure and the TMGa/TEGa ratio,
providing means for achieving high and
controllable p-type doping of GaAs. This
has been exploited for fabricating high
quality hetero junction bipolar transistors.
Advantages Over MBE
i. Easier multi wafer scale up: Substrate
rotation is required for uniformity in
thickness and conformity since MBE has
individual effusion cells for each element.
Large effusion cells and efficient heat
dissipation make multi wafer scale up more
difficult.
ii. Better for production environment: Instant
flux response due to precision electronic
control flow.
Absence of oval defects: these oval defects
generally arise from micro-droplets of Ga
or In spit out from high temperature
effusion cells. These defects vary in size
and density system-to-system and time-to-
time.
Advantages over MOCVD
1. Easy implementation of in-situ diagnostic
instruments such as RHEED.
2. Compatibility with other high vacuum thin-
film processing methods, such as metal
evaporation and ion implantation.
Shortcomings of CBE
1. More pumping required compared to
MOCVD.
2. Composition control can be difficult when
growing GaInAs. Incorporation of In from
TMIn is significantly larger than that for Ga
from TEGa at temperatures around 600 C.
3. High carbon incorporation for GaAIAs.
Molecular Beam Epitaxy
Molecular beam epitaxy (MBE) is one of
several methods of depositing single
crystals.
Fig. 5. Schematic drawing of a generic
MBE system
Molecular beam epitaxy takes place in high
vacuum or ultra-high vacuum (10-8 Pa).
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Figure 5 shows the simple sketch of the
main chamber in Molecular Beam Epitaxy
system.
The following figure 6 shows the
Simplified schematic of an MBE growth
chamber with in-situ RHEED.
Fig. 6. Simplified schematic of an MBE
growth chamber with in-situ RHEED
In solid-source MBE, elements such as
gallium and arsenic, in ultra-pure form, are
heated in separated quasi-Kundsen effusion
cells until they begin to slowly sublimate.
The gaseous elements then condense on the
wafer, where they may react with each
other. In the example of gallium and
arsenic, single-crystal gallium is formed.
The term “beam” means that evaporated
atoms do not interact with each other or
vacuum chamber gases until they reach the
wafer, due to the long mean free paths of
the atoms. During operation, reflection high
energy electron diffraction (RHEED) is
often used for monitoring the growth of the
crystal layers [22-24]. A computer controls
shutters in front of each furnace, allowing
precise control of the thickness of each
layer, down to a single layer of atoms. In
systems where the substrate needs to be
cooled, the ultra-high vacuum environment
within the growth chamber is maintained by
a system of cryo pumps, and cryo panels,
chilled using nitrogen or cold nitrogen gas
to a temperature close to 77 Kelvin (-196
degrees Celsius). Cryogenic temperatures
act as a sink for impurities in the vacuum,
so vacuum levels need to be several orders
of magnitude better to deposit films under
these conditions. In other systems, the
wafers on which the crystals are grown may
be mounted on a rotating platter which can
be heated to several hundred degrees
Celsius during operation. The following
figure 7 shows the Atomic growth level
controls.
Fig. 7. Atomic growth level controls
Molecular beam epitaxy is also used for the
deposition of some types of organic
semiconductors. In this case, molecules,
rather than atoms, are evaporated and
deposited onto the wafer. Other variations
include gas-source MBE, which resembles
chemical vapour deposition. Lately
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molecular beam epitaxy has been used to
deposit oxide materials for advanced
electronic, magnetic and optical
applications. For these purposes, MBE
systems have to be modified to incorporate
oxygen sources.
ATG Instability
The ATG (Asaro-Tiller-Grinfeld)
instability, also known as the Grinfeld
instability, is an elastic instability often
encountered during molecular beam
epitaxy. If there is a mismatch between the
lattice sizes of the growing film and the
supporting crystal, elastic energy will be
accumulated in the growing film. At some
critical height, the free energy of the film
can be lowered if the film breaks into
isolated islands, where the tension cab be
relaxed laterally. The critical height
depends on Young’s moduli, mismatch
size, and surface tensions [23-25]. Some
applications for this instability have been
researched, such as the self-assembly of
quantum dot. This community uses the
name of Stranski-Krastanov growth for
ATG.
Atomic Layer Epitaxy
The growth of thin films has had dramatic
impact on technological progress. Because
of the various properties and functions of
these films, their applications are limitless
especially in microelectronics. These layers
can act as superconductors,
semiconductors, conductors, insulators,
dielectric, or ferroelectrics. In
semiconductor devices, these layers can act
as active layers and dielectric, conducting,
or ion barrier layers. Depending on the type
of film material and its applications, various
deposition techniques may be employed.
For gas-phase deposition, these include
vacuum evaporation, reactive sputtering,
chemical vapor deposition (CVD),
especially metal organic CVD (MOCVD),
and molecular beam epitaxy (MBE).
Atomic layer deposition (ALD), originally
called Atomic layer epitaxy (ALE) or
Atomic Layer Chemical Vapour Deposition
(ALCVD), now more generally called
Atomic Layer Deposition (ALD), is a
specialized form of epitaxy that typically
deposit alternating mono layers of two
elements onto a substrate. The crystal
lattice structure is thin, uniform, and
aligned with the structure of the substrate.
The reactants are brought to the substrate as
alternating pulses with “dead” times in
between. ALE makes use of the fact that
the incoming material is bound strongly
until all sites available for chemisorptions
are occupied. The dead times are used to
flush the excess material. It is mostly used
in semiconductor fabrication to grow thin
films of thickness of the atomic order. ALD
refers to the method whereby film growth
occurs by exposing the substrate to its
starting materials alternately. It should be
noted that ALE is actually a sub-set of
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ALD, in which the grown film is epitaxial
to the substrate; however, the terms are
often used interchangeably. Although both
ALD and CVD use chemical (molecular)
precursors, the difference between the
techniques is that the former uses self-
limiting chemical reactions to control in a
very accurate way the thickness and
composition of the film deposited. In this
regard ALD can be considered as taking the
best of CVD and MBE.
Technique
The main trick used for this technique is the
use of a self-limiting chemical reaction to
control in a very accurate way the thickness
of the film deposited. This is very clever
because the reaction is very easy to set up
and it doesn’t require that many restrictions
over the reactants, allowing the use of a
wide range of materials. ALD introduces
two complementary precursors (e.g. Al
(CH3)3 and H2O) alternatively into the
reaction chamber.
Typically, one of the precursors will adsorb
onto the substrate surface until it saturates
the surface and further growth cannot occur
until the second precursor is introduced.
Thus the film thickness is controlled by the
number of precursor cycles rather than the
deposition time as is the case for
conventional CVD processes. ALD allows
for extremely precise control of film
thickness and uniformity.
Working Principle of ALE
The process behind the ALD process is a
simple one. The substrate (amorphous or
crystalline) is exposed to the first gaseous
precursor molecule (elemental vapor or
volatile compound of the element) in excess
and the temperature and gas flow is
adjusted so that only one monolayer of the
reactant is chemisorbed onto the surface.
The excess of the reactant, which is in the
gas phase on the surface, is then purged out
of the chamber with an inert gas pulse
before exposing the substrate to the other
reactant [23-25]. The second reactant then
chemisorbs and undergoes an exchange
reaction with the first reactant on the
substrate surface. This results in the
formation of a solid molecular film and a
gaseous side product that may then be
removed with an inert gas pulse. The
following Figure 8 shows the Schematic
representation of an ALD process.
Fig. 8. Schematic representation of an
ALD process
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The deposition may be defined as self-
limiting since one, and only one, monolayer
of the reactant species remains on the
surface after each exposure. In this case,
one complete cycle results in the deposition
of one monolayer of the compound on the
substrate. Repeating this cycle leads to a
controlled layer-by-layer growth. Thus the
film thickness is controlled by the number
of forebear cycles rather than the deposition
time, as is the case for a CVD processes.
This self-limiting behaviour is the
fundamental aspect of ALD and
understanding the underlying mechanism is
necessary for the future exploitation of
ALD.
One basic condition for a successful ALD
process is that the binding energy of a
monolayer chemisorbed on a surface is
higher than the binding energy of
subsequent layers on top of the formed
layer, where this reaction is controlled by
its own temperature. The temperature must
be kept low enough to keep the monolayer
on the surface until the reaction with the
second reactant occurs, but high enough to
re-evaporate or break the chemisorptions
bond. The control of a monolayer can
further be influenced with the input of extra
energy such as UV irradiation or laser
beams. The greater the difference between
the bond energy of a monolayer and the
bond energies of the subsequent layers, the
better the self-controlling characteristics of
the process. Basically, the ALD technique
depends on the difference between
chemisorptions and physic sorption. Physi
sorption involves the weak van der Waal's
forces, whereas chemi sorption involves the
formation of relatively strong chemical
bonds and requires some activation energy,
therefore it may be slow and not always
reversible. Above certain temperatures
chemi sorption dominates and it is at this
temperature ALD operates best. Also,
chemi sorption is the reason that the process
is self-controlling and insensitive to
pressure and substrate changes because
only one atomic or molecular layer can
absorb at the same time.
Equipment for The ALD Process
Equipment used in the ALD process may be
classified in terms of their working pressure
(vacuum, low pressure, atmospheric
pressure), method of pulsing the precursors
(moving substrate or valve sources) or
according to the types of sources [25].
Several system types are discussed. In a
typical moving substrate ALD growth
system link the substrate, located in the
recess part of the susceptor (material), is
continuously rotated and cuts through
streams of the gaseous precursors, in this
case, trimethylgallium [TMG, Ga(CH3)3]
and arsine (AsH3). These gaseous
precursors are introduced through separate
lines and the gases come in contact with the
substrate only when it revolves under the
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inlet tube. This cycle is repeated until the
required thickness of GaAs is achieved. The
exposure time to each of the gas streams is
about 0.3 s. The following figure 9 shows
the typical moving substrate ALD growth
system used to grow GaAs films.
Fig. 9. A typical moving substrate ALD
growth system used to grow Ga As films
ALD may be carried out in a vacuum
system using an ultra-high vacuum with a
movable substrate holder and gaseous
valving. In this manner it may be also
equipped with an in-situ LEED system for
the direct observation of surface atom
configurations and other systems such as
XPS, UPS, and AES for surface analysis.
A lateral flow system may also be
employed for successful ALE deposition.
This uses an inert gas flow for several
functions; it transports the reactants, it
prevents pump oil from entering the
reaction zone, it valves the sources and it
purges the deposition site between pulses.
Inert gas valving has many advantages as it
can be used at ultra-high temperatures
where mechanical valves may fail and it
does not corrode as mechanical valves
would in the presence of halides. This
method is based on the fact that as the inert
gas is flowing through the feeding tube
from the source to the reaction chamber, it
blocks the flow of the sources. Although in
this system the front end of the substrate
receives a higher flux density than the
down-stream end, a uniform growth rate
occurs as long as the saturation layer of the
mono-formation predominates. This lateral
flow system effectively utilizes the
saturation mechanism of a monolayer
formation obtained in ALE. Depending on
the properties of the precursors used, and on
the growth temperature, various growth
systems may be used for ALE.
Requirements for ALD Growth
Several parameters must be taken into
account in order to assure successful ALD
growth. These include the physical and
chemical properties of the source materials,
their pulsing into the reactor, their
interaction with the substrate and each
other, and the thermodynamics and
volatility of the film itself. Source
molecules used in ALD can be elemental or
an inorganic, organic, or organo metallic
compound. The chemical nature of the
precursor is insignificant as long as it
possesses the following properties. It must
be a gas or must volatilize at a reasonable
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temperature producing sufficient vapour
pressure. The vapour pressure must be high
enough to fill the substrate area so that the
monolayer chemi sorption can occur in a
reasonable length of time. Note that
prolonged exposure to the substrate can
cause the precursor to condense on the
surface hindering the growth. Chemical
interaction between the two precursors
prior to chemi sorption on the surface is also
undesired. This may be overcome by
purging the surface with an inert gas or
hydrogen between the pulses. The inert gas
not only separates the reactant pulses but
also cleans out the reaction area by
removing excess molecules. Also, the
source molecules should not decompose on
the substrate instead of chemisorbing. The
decomposition of the precursor leads to
uncontrolled growth of the film and this
defeats the purpose of ALD as it no longer
was self-controlled, layer-by-layer growth
and the quality of the film plummets. In
general, temperature remains the most
important parameter in the ALD process.
There exists a processing window for ideal
growth of mono layers. The temperature
behavior of the rate of growth in monolayer
units per cycle gives a first indication of the
limiting mechanisms of an ALD process. If
the temperature falls too low, the reactant
may condense or the energy of activation
required for the surface reaction may not be
attained. If the temperature is too high, then
the precursor may decompose or the
monolayer may evaporate resulting in poor
ALD growth. In the appropriate
temperature window, full monolayer
saturation occurs meaning that all bonding
sites are occupied and a growth rate of one
lattice unit per cycle is observed. If the
saturation density is below one, several
factors may contribute to this. These
include an oversized reactant molecule,
surface reconstruction, or the bond strength
of an adsorbed surface atom is higher when
the neighboring sites are unoccupied. Then
the lower saturation density may be
thermodynamically favored. It is known
that if the saturation density is above 1 then
the under composed precursor molecules
form the monolayer. Generally, ideal
growth occurs when the temperature is set
where the saturation density is one.
Advantages of ALD
Atomic layer deposition provides an easy
way to produce uniform, crystalline, high
quality thin films, especially to layered
structures such as super lattices and super
alloys.
It is controllable to an accuracy of a single
atomic layer.
It was possible to grow different thin films
by choosing suitable starting materials
among the thousands of available chemical
compounds. Provided that the
thermodynamics are favorable, relatively
easy task because the process was
A Study on Fabrication of Nano Electrolytic Powders Used in Capacitors
© All Rights Reserved by “Journals Club & Co.” 48
insensitive to small changes in temperature
and pressure due to its relatively large
processing window.
In which, final thickness of the film was
dependent only upon the number of
deposition cycles and the lattice constant of
the material can be reproduced and
controlled and independent of the partial
pressures of the precursors and growth
temperature. Under ideal conditions, the
uniformity and the reproducibility of the
films are excellent.
ALE also has the potential to grow very
abrupt hetero structures and very thin layers
and these properties are in demand for some
applications such as super lattices and
quantum wells.
CONCLUSIONS
In this paper, a wide literature survey was
done on the various fabrication methods
used for the fabrication of nano electrolytic
powders used in capacitors. The important
characteristics, advantages, disadvantages
of the various fabrication methods used for
the manufacture of nano electrolytic
powders used in capacitors were discussed.
The applications of the various fabrication
methods used for the manufacture of nano
electrolytic powders used in capacitors
were also discussed. This paper would be
helpful for the young scientist and
engineers to study about the important
fabrication methods used for the
manufacture of nano electrolytic powders.
This would motivate the young scientist for
their research work to invent nano
electrolytic powders used capacitors. Hence
these capacitors were also called as Nano
Capacitors.
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HOW TO CITE THIS ARTICLE
Ganesan, J., Prakash, K.S., Gajendran, S., Karthik, R., Raguvelan, R., Selvaraj, D.E., Priyan, S.S., Sugumaran, C.P., Kumar, M.R., Joshi, R.M., Kumar, S.D. (2014). A Study on Fabrication of Nano Electrolytic Powders Used in Capacitors. Journal Club for Electrical
Engineering (JCEE), 1(I), 35-51.