Asaad Essa Alzawwad
ID#214303
High Constant Dielectrics
Introduction
A dielectric is a non-conducting material which has the unique ability of
preventing electrical conduction but is at the same time capable of absorbing electric
charge. Indeed, it will carry on absorbing charge until its saturation capacity is
reached, whereupon, if its power source is still connected and still trying to pour more
electricity into it, it will rupture and a path will be created through it for current to
discharge. This phenomenon, called dielectric breakdown is most certainly to be
avoided for it renders the solid material useless thereafter. If, however, before it
ruptures the charge accumulated within the dielectric rises toward its saturation point
and reaches a level of voltage higher than the voltage of the charging circuit, then the
dielectric’s voltage will discharge itself (just like a short circuit - very violently) back
through the power source.(s1)
An important property of a dielectric is its ability to support an electrostatic field
while dissipating minimal energy in the form of heat. The lower the dielectric loss
(the proportion of energy lost as heat), the more effective is a dielectric material.
Another consideration is the dielectric constant, the extent to which a substance
concentrates the electrostatic lines of flux. Substances with a low dielectric constant
include a perfect vacuum, dry air, and most pure, dry gases such as helium and
nitrogen. Materials with moderate dielectric constants include ceramics, distilled
water, paper, mica, polyethylene, and glass. Metal oxides, in general, have high
dielectric constants. (s2) In this paper we are concerned with the high dielectric
constants material.
The dielectric constant of a material is related to the polarizability. When the atoms or
molecules of a dielectric are placed in an external electric field, the nuclei are pushed
with the field resulting in an increased positive charge on one side while the electron
clouds are pulled against it resulting in an increased negative charge on the other side.
This process is known as polarization and a dielectric material in such a state is said to
be polarized (s3). the polarization of the medium produces an electric field opposing
the field of the charges on the plate (s11)
Asaad Essa Alzawwad
ID#214303
Applications
High dielectric constant materials find numerous technological applications.
In the case of memory devices based on capacitive components, such as static and
dynamic random access memories (s4) (capacitors in general). Another use of
dielectrics is in the artificial muscles (s5).
All or must of these applications depend on making the dielectric material as a thin
films because the polarization of a region is defined as the dipole moment per unit
p
volume P 
, where the electric dipole moment of anything -- is defined as the
V
product of charge and separation p = q r from the calculation of the units we can see
that it depends on the separation. (For electric dipole moment with the SI unit of
coulombs times meters (C.m) and for the polarization it is C.m/m3 =C/m2.)(s3)
Application to perform thin films
There are some methods to perform thin films. In this paper I’ll mansion three
of them the Atomic Layer Deposition (ALD), the Chemical Vapor Deposition (CVD)
and the sol-gel deposition.
The ALD method:
ALD is a vapor deposition process based on sequential self-terminating
surface reactions where the precursors are injected separately in pulses added to a
flowing carrier gas separated by a purge of excess precursor vapor. Each pulse and
purge sequence constitutes an ALD half-cycle. Ideally, each half-cycle results in one
additional atomic monolayer of material and then the reaction stops even if more
precursor vapor arrives at the surface. This self-terminating character results in ALD’s
uniformity and precise thickness control. (s6) for more details see (s7).
the figure is from (s12)
Asaad Essa Alzawwad
ID#214303
The CVD method:
The technique generally involves forming a material from a hot reactive gas mix
which condenses onto a controlled surface (or substrate). In contrast to high pressure
and high temperature crystal synthesis, the CVD technique is generally - though not
always - performed at below atmospheric pressure and used to grow microns-thick
coatings onto surfaces of a few square centimetres. Development of CVD technology
over the last decade has led to the growth of millimetres-thick, self-supporting layers
over larger areas. Most often used to grow high purity semiconductor device
structures, the CVD technique is nowadays frequently used in industry to grow high
purity polycrystalline raw materials previously only synthesised as thin films in
research laboratory processes.(s10)
Sol-gel Deposition method:
A sol is a dispersion of the solid particles (~ 0.1-1 m) in a liquid where only the
Brownian motions suspend the particles. A gel is a state where both liquid and solid
are dispersed in each other, which presents a solid network containing liquid
components. The sol-gel coating process usually consists of 4 steps:
(1) The desired colloidal particles once dispersed in a liquid to form a sol.
(2) The deposition of sol solution produces the coatings on the substrates by spraying,
dipping or spinning.
(3) The particles in sol are polymerized through the removal of the stabilizing
components and produce a gel in a state of a continuous network.
(4) The final heat treatments pyrolyze the remaining organic or inorganic components
and form an amorphous or crystalline coating (s9)