A Study on Fabrication of Nano Electrolytic Powders Used in Capacitors

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

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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: [email protected]

mailto:[email protected]



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



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



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



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



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



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).



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



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



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



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



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



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



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.

A Study on Fabrication of Nano Electrolytic Powders Used in Capacitors

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