Thin Film Technology And Its Applications Engineering Essay

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Advance technology and physics have developed this phenomenon of thin film technology. Thin film technology refers to a layer of materials starting from fractions of a nanometer which are also known as monolayer heading till several micrometers of thickness. This science plays an important role in the integrated passive devices (IPD). It is based on three pillars: fabrication, characterization and applications. This technology was developed to fulfill the needs of IC world. Some of the important fields where thin film technology is used are microelectronics, optical communication, coatings, conservation and generation of energy and telecommunication.

Thin film technology and its applications

With a growth rate of 17.7%, thin film industry has reached till $18.5 million dollar by 2010. This number is a sign of good Average annual growth rate (AAGR). The Chemical industry too accounts more than 72% of market captured by plating chemicals. Raw materials required for physical processes were reported a $ 2 Billion market and is expanding too. (bbc, 2010).The most common application of thin films is the mirror. In order to form a reflective index there is a thin film sheet applied to it. Very thin films of nanometer thickness are more comely used for two way mirrors. Generally the performance of optical coating /AR coatings is judged by its refractive indices and the multi layer coats. In case of computer memory, there are 2 types in which thin film optical coating is done i.e. ferromagnetic and ferroelectric. Thin film technology today is also used in making medicines, ceramics and even renewable batteries like solar cells.

The Process

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From the figure we can understand the process in a very simpler manner. The gas/solid/liquid is first exposed to the metal which is to de coated and bombarded with laser energy. Due to this action there is decomposition of atoms, molecules etc from the gases and starts depositing on the surface of metal. The thin film deposition is an act of depositing thin film of coating material onto the bed of to be coated metal.

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Fig 1 (sciencedirect)

The thin film deposition is an act of depositing thin film of coating material onto the bed of to be coated metal. The deposition technique controls the thickness of the coating within nanometers. The deposition technique is majorly divided into 2 types physical and chemical decomposition. Physical decomposition requires thermal evaporators, electron beam evaporator, molecule beam epitaxy,sputtering, pulsed laser depoistion, cathodic arc deposition, Electrohydrodyanamic deposition. Whereas in case of chemical decomposition the process is as follows:Application

Thin film technology related to integrated passive devices (IPDs) is picking up market since 2009. IPD was originally devised to replace heavy passive components. Now it is also used for RF, high brightness LED silicon sub mounts and mixing devices. Basically it is finding its place wherever size of the equipment is required to be reduced. Figure below shows the development process.

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Fig 2 (sciencedirect)

Thin film technology related to integrated passive devices (IPDs) is picking up market since 2009. IPD was originally devised to replace heavy passive components. Now it is also used for RF, high brightness LED silicon sub mounts and mixing devices. Basically it is finding its place wherever size of the equipment is required to be reduced. Figure below shows the development process. All printed memory platform is apt for its standalone applications in toys and online enabled cards and games. Thin film also integrates with logic, sensors, batteries and display for making RFID tags. Other areas were thin film technology is used are supply chain management and automation, authentication and brand protection. The independent research and analyst firms have claimed that IDTechEx that the potential market of Printed Electronics will be $50 billion by 2019. (ASA)C:\Users\user\Downloads\thin flim\I-Micronews - ADVANCED PACKAGING Is it time for thin-film IPDs ..._files\ASE Glass IPD product development.jpg

Examination of Optical coating (Anti reflection)

Thin film coatings are used to control the reflection and transmission of light. This is done with the help of optical interference. One of the applications of thin film technology is Anti reflection type of optical coating. This is one of the most used and most popular applications of this technology. Anti Reflective coating is applied to the surface of the lenses and other optical gadgets to reduce reflection. It is used to improve the efficiency of telescopes, binoculars, specks, camera lens etc. There are several coatings of transparent thin films having contrasting refractive index. In order to produce destructive interferences in the beams layer thickness is chosen. The color effects appear at oblique angles due to the change in wavelength and incident angles because of exposure. Wavelengths are predefined as per the requirement but better efficiency is achieved only when there is a wide range of frequencies, typically a choice of IR, UV.

Why is Anti Reflection coating so popular?

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With the advent of light passing through the desired glass approximately 4% will be definitely reflected at every interface. This combines transmission of only 92% of the incident light. The throughput of the surface increases by the application of AR coating. Not only this but the damages due to reflections travelling in backward direction through the surface which are often called as Ghost images. Most of the low light systems, the systems which contain multiple transmitting optical elements predominantly use Anti reflection.

Theory

The two main causes of optical effect are called as thin film and thick film effects. The thick film effect arises because of the difference in the refraction index between the above layers and bottom of the coating. It does not depend upon the thickness of coating rather it should be much thicker than a wavelength of light. Whereas the thin film coating depends on the thickness of the film, the wavelength of light. Thin film coating depends on the angle of light striking the coated surface.

Reflection

When a ray of light moves from one medium to other, there are some portion of light which travels back between the two media. The power of reflection depends on refractive indices of the two media as well as the angle of the surface to the beam of light. This value is calculated by Fresnel equations

R = \left( \frac{n_0 - n_S}{n_0 + n_S} \right) ^2

The intensity of light reflected is Reflection coefficient/reflectance (R), where n0 and nS are the refractive indices of the first and second media, respectively. This value of R varies from 0 (no reflection) to 1 (total reflection) and presented in percentage.

Rayleigh's film

In order to reduce the reflectivity, a thin film (such as tarnish) on the surface of glass. This effect can be explained by bombarding a thin layer of material with refractive index n1 between the air (index n0) and the glass (index nS). This optimum value is given by geometric mean of the two surrounding indices:n_1 = \sqrt{n_0 n_S}.

Working

The transmission properties of an optical coating depend on the following factors:

The wavelength of the used light

The refractive index of coating

The substrate's index of refraction

The coating thickness

The incident angle of the light

It is designed in such a way that the beam reflected at the upper and lower boundary of the thin film should be a linear angle (180 degree). When the destructive interference between two reflected beams occurs, they cancel both the beams before they leave the surface. In order to produce cancellation, the optical thickness of the coating must be an odd digit of one forth wavelengths. Below is the equation which is used for determining the refractive index which is required to complete the cancellation of two beams. (edmundoptics)http://www.edmundoptics.com/images/articles/lineart21.jpg

formula

nf is the index of refraction of the thin film

n0 is the index of refraction of air (or the incident material)

ns is the index of refraction of the substrate

Friction and wear coatings

The friction between 2 sliding surfaces and the related wear depends mainly on the contacting materials, load, lubricant formulations, and the lubrication times. Deposition if thin film low friction coating is evaluated for valvetrain friction reduction. The recent development in deposition of carbon films and maintaining quality has raised several investigations.

It is important to understand that wear progresses fairly linearly following a rapid initial increase some cases of coating. The important observation is the rate at which wearing number ends the test. The wear results shows that the wear of thin film coating decreases drastically if compared to surface in contact with a cast iron camshaft. The robustness of coated surfaces is determined. (stle, 2012)

Quantum well structures

In optical coating, AlGaN/GaN/ AlGaN quantum well (QW) is a form of potential well. When the minimum of the conduction band corresponds to the maximum of valence band it is known as quantum well. These structures can be flourished by molecular beam epitaxy or metal orgaic chemical vapor deposition. At the same time the layer thickness of the layer below the monolayer should also be considered. Figure below shows the quantum well.

Photovoltaic devices

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Due to the growth in demand of renewable energy resources, there is growth in production of photovoltaic cells. It is defined as process of generating electrical power by converting solar energy into electricity. This is done with the help of semiconductors that have the photovoltaic effect. Solar cells are generated because of such photovoltaic devices. Materials like monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium gallium selenide/sulfide are for the production of photovoltaic devices.

    Most solar cells are based on slabs of semiconductor material (often silicon). They are made up of controlled doping (impurity addition) such that light is strongly absorbed into a diode structure - and the built-in electric field within the diode structure is strong enough to separate the photo-generated electron-hole pairs so that light is converted into electricity. In this figure the light comes in from the top and is absorbed in the semiconducting material (either the n-type or the p-type part of the structure). After absorption the photo-generated electrons are moved toward the top contact which is a thin finger electrode (red arrows) and holes are conducted downwards (green arrows). The top contact draws current out from a narrow strip of the top of the cell. The top contact has to be narrow so as the light does not penetrate through metal and so any metal-covered-area represents some amount of lost efficiencyhttp://www.solar.rutgers.edu/Basics_files/image002.jpghttp://www.solar.rutgers.edu/Basics_files/image004.jpg

This figure shows a solar cell

These features are important:

The band gap (Eg) of the primary absorbing material 

The impurity concentration in the p-type and n-type regions 

The crystal quality of the material (solar.rtgers)

Giant magneto resistance devices for magnetic recording heads

The very first and commercially largest of giant magneto resistance is used in the spin valve giant spin valve giant magnetoresistive sensor to read back information stored on hard disk drives. The effect is observed as a significant change in the electrical resistance depending on whether the magnetization of adjacent ferromagnetic layers are in a parallel or an antiparallel alignment. To develop the spin valve GMR sensor a deeper understanding of GMR itself was needed, as well as the use of strong interlayer coupling and improvements in antiferromagnets.

Magnetoresistance is dependence of the electrical resistance of the sample on the strength of external magnetic field. Numerically, it is characterized by the value

\delta_H = \frac{R(0)-R(H)}{R(H)},

There are various types of GMR namely; Films non interacting material, Inverse GMR effect.

The figure sideways shows the schematic representation of recording done through GMR sensor. As technology grew it was discovered that GMR can be used for reading stored information from hard drive. Earlier it was not a success but later with the invention of anisotropic magnetoresistance (AMR) it was possible to read back the information.

AMR technology is to change the resistance in a ferromagnetic conductor when there is change in the angle between the current direction and magnetization. This is because of the spin orbit scattering.

Spintronics which is a recently recognized field helped GMR to cope up and useful for the applications like recording. Because of this technology GMR and tunneling successful GMR and tunneling magnetoresistance (TMR) readback sensors used in hard disk drives. . Between the years 2000 and 2006 virtually all hard disk drives used the technology and more than 5 billion GMR spin valves have been produced. (cospa, 2008)

Conclusion

From the above study it is clear that thin film technology is now extensively growing in electronic market. Its applications have made technology more easier, lighter and cheaper too. The most popular use is photovoltaic cells used for solar energy generation. The physics behind the thin film is based on the quantum well technique and is developing into new forms such as GMR devices which to is used for IPD devices.