HOME

TheInfoList




A thin film is a layer of material ranging from fractions of a
nanometer file:EM Spectrum Properties edit.svg, 330px, Different lengths as in respect to the Electromagnetic spectrum, measured by the Metre and its derived scales. The nanometre is often used to express dimensions on an atomic scale and mostly in the Mo ...
(
monolayerA monolayer is a single, closely packed layer of atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objec ...
) to several
micrometerMicrometer can mean: * Micrometer (device) A micrometer, sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw widely used for Accuracy and precision, accurate measurement of components in mechanical engineeri ...
s in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many applications. A familiar example is the household
mirror A mirror is an object that reflects an image An image (from la, imago) is an artifact that depicts visual perception Visual perception is the ability to interpret the surrounding environment Environment most often refers t ...

mirror
, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of
silvering Silvering is the chemical A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimat ...

silvering
was once commonly used to produce mirrors, while more recently the metal layer is deposited using techniques such as
sputtering In physics, sputtering is a phenomenon in which microscopic particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object to which can be ascribe ...

sputtering
. Advances in thin film deposition techniques during the 20th century have enabled a wide range of technological breakthroughs in areas such as magnetic recording media, electronic semiconductor devices,
Integrated passive devicesIntegrated Passive Devices (IPD's) ''"or Integrated Passive Components (IPC's) or Embedded Passive Components"'' are electronic components where resistor A resistor is a passive two-terminal electrical component that implements electrical res ...
,
LEDs A light-emitting diode (LED) is a that emits light when flows through it. s in the semiconductor recombine with s, releasing energy in the form of s. The color of the light (corresponding to the energy of the photons) is determined b ...
,
optical coating An optical coating is one or more thin layers of material deposited on an optical component such as a lens A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a ...
s (such as
antireflective An antireflective or anti-reflection (AR) coating is a type of optical coating An optical coating is one or more thin layers of material deposited on an optical component such as a lens A lens is a transmissive optical device that focuse ...
coatings), hard coatings on cutting tools, and for both energy generation (e.g.
thin-film solar cell A thin-film solar cell is a second generation solar cell that is made by depositing one or more thin layers, or thin film (TF) of photovoltaic material on a substrate, such as glass, plastic or metal. Thin-film solar cells are commercially us ...
s) and storage ( thin-film batteries). It is also being applied to pharmaceuticals, via
thin-film drug delivery Thin-film drug delivery uses a dissolving film or oral drug strip to administer drugs via absorption in the mouth (buccally or sublingual Sublingual ( abbreviated SL), from the Latin Latin (, or , ) is a classical language belonging to the I ...
. A stack of thin films is called a multilayer. In addition to their applied interest, thin films play an important role in the development and study of materials with new and unique properties. Examples include multiferroic materials, and
superlattice A superlattice is a periodic structure of layers of two (or more) materials. Typically, the thickness of one layer is several nanometers. It can also refer to a lower-dimensional structure such as an array of quantum dots or quantum wires. Disco ...

superlattice
s that allow the study of quantum phenomena.


Deposition

The act of applying a thin film to a surface is ''thin-film deposition'' – any technique for depositing a thin film of material onto a
substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached **Substrate (locomotion), the surface over which an organism loco ...
or onto previously deposited layers. "Thin" is a relative term, but most deposition techniques control layer thickness within a few tens of
nanometre file:EM Spectrum Properties edit.svg, 330px, Different lengths as in respect to the Electromagnetic spectrum, measured by the Metre and its derived scales. The nanometre is often used to express dimensions on an atomic scale and mostly in the Mo ...
s.
Molecular beam epitaxy Molecular-beam epitaxy (MBE) is an epitaxy Epitaxy refers to a type of crystal growth or material deposition in which new crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) ...

Molecular beam epitaxy
, the Langmuir–Blodgett method,
atomic layer deposition Atomic layer deposition (ALD) is a thin-film deposition A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometre, micrometers in thickness. The controlled synthesis of materials as thin films (a ...
and
molecular layer depositionMolecular layer deposition (MLD) is a vapour phase thin film deposition technique based on self-limiting surface reactions carried out in a sequential manner. Essentially, MLD resembles the well established technique of atomic layer deposition (ALD) ...
allow a single layer of
atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of ato ...

atom
s or molecules to be deposited at a time. It is useful in the manufacture of
optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually describes t ...

optics
(for
reflective Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light Light or visible ligh ...
,
anti-reflective coating An antireflective or anti-reflection (AR) coating is a type of optical coating An optical coating is one or more thin layers of material deposited on an optical component such as a lens A lens is a transmissive optical device that focuse ...
s or
self-cleaning glassSelf-cleaning glass is a specific type of glass Glass is a non- crystalline, often transparency and translucency, transparent amorphous solid, that has widespread practical, technological, and decorative use in, for example, window panes, tablew ...
, for instance),
electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons The electron is a subatomic particle In physical sciences, subatomic particles are smaller than ...
(layers of
insulator Insulator may refer to: * Insulator (electricity), a substance that resists electricity ** Pin insulator, a device that isolates a wire from a physical support such as a pin on a utility pole ** Strain insulator, a device that is designed to work i ...
s,
semiconductor A semiconductor material has an electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric curre ...
s, and
conductor Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble like, for example, an orchestra. * Conductor (album), ''Conductor'' (album), an album by indie rock band The Comas * Conduction, a type of ...
s form
integrated circuits An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuit 200px, A circuit built on a printed circuit board (PCB). An electronic circuit is composed of indiv ...

integrated circuits
),
packaging Packaging is the science Science () is a systematic enterprise that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe."... modern science is a disco ...

packaging
(i.e., aluminium-coated PET film), and in
contemporary art Contemporary art is the art Art is a diverse range of (products of) human activities Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and ...

contemporary art
(see the work of Larry Bell). Similar processes are sometimes used where thickness is not important: for instance, the purification of copper by
electroplating Electroplating is a general name for processes that produce a metal coating on a solid substrate through the redox, reduction of cations of that metal by means of a direct current, direct electric current. The part to be coated acts as the cathode ...
, and the deposition of
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

silicon
and enriched
uranium Uranium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

uranium
by a CVD-like process after gas-phase processing. Deposition techniques fall into two broad categories, depending on whether the process is primarily
chemical A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which ...

chemical
or
physical Physical may refer to: *Physical examination, a regular overall check-up with a doctor *Physical (album), ''Physical'' (album), a 1981 album by Olivia Newton-John **Physical (Olivia Newton-John song), "Physical" (Olivia Newton-John song) *Physical ( ...

physical
.


Chemical deposition

Here, a fluid
precursor Precursor or Precursors may refer to: *Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of unre ...
undergoes a chemical change at a solid surface, leaving a solid layer. An everyday example is the formation of soot on a cool object when it is placed inside a flame. Since the fluid surrounds the solid object, deposition happens on every surface, with little regard to direction; thin films from chemical deposition techniques tend to be '' conformal'', rather than ''directional''. Chemical deposition is further categorized by the phase of the precursor:
Plating Plating is a surface covering in which a metal is deposited on a conductive surface. Plating has been done for hundreds of years; it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve ...

Plating
relies on liquid precursors, often a solution of water with a salt of the metal to be deposited. Some plating processes are driven entirely by
reagent A reagent is a substance or compound added to a system to cause a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter ...
s in the solution (usually for
noble metal In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo duri ...
s), but by far the most commercially important process is
electroplating Electroplating is a general name for processes that produce a metal coating on a solid substrate through the redox, reduction of cations of that metal by means of a direct current, direct electric current. The part to be coated acts as the cathode ...
. In semiconductor manufacturing, an advanced form of electroplating known as electrochemical deposition is now used to create the copper conductive wires in advanced chips, replacing the chemical and physical deposition processes used to previous chip generations for aluminum wires Chemical solution deposition (CSD) or
chemical bath deposition Chemical bath deposition (CBD), or chemical solution deposition (CSD), is a method to deposit thin films and nanomaterials * Nanomaterials describe, in principle, materials of which a single unit small sized (in at least one dimension) between ...
(CBD) uses a liquid precursor, usually a solution of
organometallic Organometallic chemistry is the study of organometallic compounds, chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any subst ...
powders dissolved in an organic solvent. This is a relatively inexpensive, simple thin-film process that produces stoichiometrically accurate crystalline phases. This technique is also known as the sol-gel method because the 'sol' (or solution) gradually evolves towards the formation of a gel-like diphasic system. The Langmuir–Blodgett method uses molecules floating on top of an aqueous subphase. The packing density of molecules is controlled, and the packed monolayer is transferred on a solid substrate by controlled withdrawal of the solid substrate from the subphase. This allows creating thin films of various molecules such as nanoparticles, polymers and lipids with controlled particle packing density and layer thickness.
Spin coating Spin coating is a procedure used to deposit uniform thin film A thin film is a layer of material ranging from fractions of a nanometer The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol ...
or spin casting, uses a liquid precursor, or sol-gel precursor deposited onto a smooth, flat substrate which is subsequently spun at a high velocity to centrifugally spread the solution over the substrate. The speed at which the solution is spun and the
viscosity The viscosity of a fluid In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, ...

viscosity
of the sol determine the ultimate thickness of the deposited film. Repeated depositions can be carried out to increase the thickness of films as desired. Thermal treatment is often carried out in order to crystallize the amorphous spin coated film. Such crystalline films can exhibit certain preferred orientations after crystallization on single
crystal A crystal or crystalline solid is a solid Solid is one of the four fundamental states of matter (the others being liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformatio ...

crystal
substrates.
Dip coating image:Dip coating.svg, A schematic of the continuous dip coating process. Roll of coarse cloth Cloth Bath Liquid material Rollers Oven Scrapers Excess liquid falls back A coating remains on the fabric cloth. Dip coating is an industrial ...
is similar to spin coating in that a liquid precursor or sol-gel precursor is deposited on a substrate, but in this case the substrate is completely submerged in the solution and then withdrawn under controlled conditions. By controlling the withdrawal speed, the evaporation conditions (principally the humidity, temperature) and the volatility/viscosity of the solvent, the film thickness, homogeneity and nanoscopic morphology are controlled. There are two evaporation regimes: the capillary zone at very low withdrawal speeds, and the draining zone at faster evaporation speeds.
Chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition Vacuum deposition is a family of processes used to deposit layers of material atom-by-atom or molecule-by-molecule on a solid surface. These processes operate at pressures well below atmo ...
(CVD) generally uses a gas-phase precursor, often a
halide A halide is a binary phase, of which one part is a halogen atom and the other part is an chemical element, element or radical (chemistry), radical that is less electronegative (or more electropositive) than the halogen, to make a, e.g., fluoride, ...
or
hydride In chemistry, a hydride is formally the anion of hydrogen, H−. The term is applied loosely. At one extreme, all chemical compound, compounds containing covalent bond, covalently bound H atoms are called hydrides: water (H2O) is a hydride of o ...

hydride
of the element to be deposited. In the case of
MOCVD Metalorganic vapour-phase epitaxy (MOVPE), also known as organometallic vapour-phase epitaxy (OMVPE) or metalorganic chemical vapour deposition (MOCVD), is a chemical vapour deposition method used to produce single- or polycrystalline thin films. ...
, an
organometallic Organometallic chemistry is the study of organometallic compounds, chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any subst ...
gas is used. Commercial techniques often use very low pressures of precursor gas. Plasma enhanced CVD (PECVD) uses an ionized vapor, or
plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral) or heliotrope, a mineral aggregate * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood plasma ...
, as a precursor. Unlike the soot example above, commercial PECVD relies on electromagnetic means (electric current,
microwave Microwave is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space a ...

microwave
excitation), rather than a chemical-reaction, to produce a plasma.
Atomic layer deposition Atomic layer deposition (ALD) is a thin-film deposition A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometre, micrometers in thickness. The controlled synthesis of materials as thin films (a ...
(ALD), and its sister technique
molecular layer depositionMolecular layer deposition (MLD) is a vapour phase thin film deposition technique based on self-limiting surface reactions carried out in a sequential manner. Essentially, MLD resembles the well established technique of atomic layer deposition (ALD) ...
(MLD), uses gaseous precursor to deposit conformal thin films one layer at a time. The process is split up into two half reactions, run in sequence and repeated for each layer, in order to ensure total layer saturation before beginning the next layer. Therefore, one reactant is deposited first, and then the second reactant is deposited, during which a chemical reaction occurs on the substrate, forming the desired composition. As a result of the stepwise, the process is slower than CVD, however it can be run at low temperatures, unlike CVD.


Physical deposition

Physical deposition uses mechanical, electromechanical or thermodynamic means to produce a thin film of solid. An everyday example is the formation of
frost Frost is a thin layer of ice Ice is water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is ...

frost
. Since most engineering materials are held together by relatively high energies, and chemical reactions are not used to store these energies, commercial physical deposition systems tend to require a low-pressure vapor environment to function properly; most can be classified as
physical vapor deposition Physical vapor deposition (PVD), sometimes (especially in single-crystal A single-crystal, or monocrystalline, solid Solid is one of the four fundamental states of matter (the others being liquid, gas and plasma). The molecules ...
(PVD). The material to be deposited is placed in an
energetic
energetic
,
entropic
entropic
environment, so that particles of material escape its surface. Facing this source is a cooler surface which draws energy from these particles as they arrive, allowing them to form a solid layer. The whole system is kept in a vacuum deposition chamber, to allow the particles to travel as freely as possible. Since particles tend to follow a straight path, films deposited by physical means are commonly ''directional'', rather than ''conformal''. Examples of physical deposition include: A thermal
evaporator An evaporator is a device in a process used to turn the liquid form of a chemical substance such as water into its gaseous-form/vapor. The liquid is evaporated, or vaporized, into a gas form of the targeted substance in that process. Uses One ki ...
that uses an electric resistance heater to melt the material and raise its vapor pressure to a useful range. This is done in a high vacuum, both to allow the vapor to reach the substrate without reacting with or
scattering Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light Light or visible light is electromagnetic radiation within the portion of the electromagnetic ...

scattering
against other gas-phase atoms in the chamber, and reduce the incorporation of impurities from the residual gas in the vacuum chamber. Obviously, only materials with a much higher
vapor pressure Vapor pressure (or vapour pressure in British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial cod ...

vapor pressure
than the
heating element A heating element converts electrical energy into heat through the process of Joule heating Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current An electric current ...
can be deposited without contamination of the film.
Molecular beam epitaxy Molecular-beam epitaxy (MBE) is an epitaxy Epitaxy refers to a type of crystal growth or material deposition in which new crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) ...

Molecular beam epitaxy
is a particularly sophisticated form of thermal evaporation. An electron beam evaporator fires a high-energy beam from an
electron gun An electron gun (also called electron emitter) is an electrical component in some vacuum tube A vacuum tube, an electron tube, valve (British usage) or tube (North America), is a device that controls electric current flow in a high vacuum b ...

electron gun
to boil a small spot of material; since the heating is not uniform, lower
vapor pressure Vapor pressure (or vapour pressure in British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial cod ...

vapor pressure
materials can be deposited. The beam is usually bent through an angle of 270° in order to ensure that the gun filament is not directly exposed to the evaporant flux. Typical deposition rates for electron beam evaporation range from 1 to 10 nanometres per second. In
molecular beam epitaxy Molecular-beam epitaxy (MBE) is an epitaxy Epitaxy refers to a type of crystal growth or material deposition in which new crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) ...

molecular beam epitaxy
(MBE), slow streams of an element can be directed at the substrate, so that material deposits one atomic layer at a time. Compounds such as
gallium arsenide Gallium Gallium is a chemical element with the Symbol (chemistry), symbol Ga and atomic number 31. Discovered by France, French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in boron group, group 13 of the periodic ta ...

gallium arsenide
are usually deposited by repeatedly applying a layer of one element (i.e.,
gallium Gallium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elemen ...

gallium
), then a layer of the other (i.e.,
arsenic Arsenic is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same num ...

arsenic
), so that the process is chemical, as well as physical; this is known also as
atomic layer deposition Atomic layer deposition (ALD) is a thin-film deposition A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometre, micrometers in thickness. The controlled synthesis of materials as thin films (a ...
. If the precursors in use are organic, then the technique is called
molecular layer depositionMolecular layer deposition (MLD) is a vapour phase thin film deposition technique based on self-limiting surface reactions carried out in a sequential manner. Essentially, MLD resembles the well established technique of atomic layer deposition (ALD) ...
. The beam of material can be generated by either physical means (that is, by a
furnace A furnace is a structure in which heat is produced with the help of combustion. Furnace may also refer to: Appliances Buildings * Furnace (house heating) A furnace (American English), referred to as a heater or boiler in British English, is ...

furnace
) or by a chemical reaction ( chemical beam epitaxy).
Sputtering In physics, sputtering is a phenomenon in which microscopic particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object to which can be ascri ...

Sputtering
relies on a plasma (usually a
noble gas The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that m ...
, such as
argon Argon is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

argon
) to knock material from a "target" a few atoms at a time. The target can be kept at a relatively low temperature, since the process is not one of evaporation, making this one of the most flexible deposition techniques. It is especially useful for compounds or mixtures, where different components would otherwise tend to evaporate at different rates. Note, sputtering's step coverage is more or less conformal. It is also widely used in optical media. The manufacturing of all formats of CD, DVD, and BD are done with the help of this technique. It is a fast technique and also it provides a good thickness control. Presently, nitrogen and oxygen gases are also being used in sputtering. Pulsed laser deposition systems work by an
ablation Ablation is removal or destruction of material from an object by vaporization, chipping, or other erosion, erosive processes. Examples of ablative materials are described below, and include spacecraft material for ascent and atmospheric reentry, ...
process. Pulses of focused
laser A laser is a device that emits light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as h ...

laser
light vaporize the surface of the target material and convert it to plasma; this plasma usually reverts to a gas before it reaches the substrate.
Cathodic arc depositionCathodic arc deposition or Arc-PVD is a physical vapor deposition technique in which an electric arc is used to vaporize material from a cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. T ...
(arc-PVD) which is a kind of
ion beam deposition {{Use dmy dates, date=December 2017 Ion beam deposition (IBD) is a process of applying materials to a target through the application of an ion beam. Ion beam deposition setup with mass separator An ion beam deposition apparatus typically consist ...
where an electrical arc is created that literally blasts ions from the cathode. The arc has an extremely high
power density Power density is the amount of power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal t ...
resulting in a high level of
ionization Ionization or ionisation is the process by which an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday ...
(30–100%), multiply charged ions, neutral particles, clusters and macro-particles (droplets). If a reactive gas is introduced during the evaporation process, dissociation,
ionization Ionization or ionisation is the process by which an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday ...
and
excitation Excitation or Excitement may refer to: * Excitation (magnetic), provided with an electrical generator or alternator * Electron excitation, the transfer of an electron to a higher atomic orbital * Stimulation or excitation or excitement, the action o ...
can occur during interaction with the ion flux and a compound film will be deposited. Electrohydrodynamic deposition (electrospray deposition) is a relatively new process of thin-film deposition. The liquid to be deposited, either in the form of nanoparticle solution or simply a solution, is fed to a small capillary nozzle (usually metallic) which is connected to a high voltage. The substrate on which the film has to be deposited is connected to ground. Through the influence of electric field, the liquid coming out of the
nozzle A nozzle is a device designed to control the direction or characteristics of a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. Fluids are a ...

nozzle
takes a conical shape (
Taylor cone A Taylor cone refers to the cone observed in electrospinning image of electrospun polycaprolactone fibers. . Electrospinning is a fiber production method that uses electric force to draw charged threads of polymer solutions or polymer A poly ...

Taylor cone
) and at the apex of the cone a thin jet emanates which disintegrates into very fine and small positively charged droplets under the influence of Rayleigh charge limit. The droplets keep getting smaller and smaller and ultimately get deposited on the substrate as a uniform thin layer.


Growth modes

Frank–van der Merwe growth ("layer-by-layer"). In this growth mode the adsorbate-surface and adsorbate-adsorbate interactions are balanced. This type of growth requires lattice matching, and hence considered an "ideal" growth mechanism. Stranski–Krastanov growth ("joint islands" or "layer-plus-island"). In this growth mode the adsorbate-surface interactions are stronger than adsorbate-adsorbate interactions. Volmer–Weber ("isolated islands"). In this growth mode the adsorbate-adsorbate interactions are stronger than adsorbate-surface interactions, hence "islands" are formed right away.


Epitaxy

A subset of thin-film deposition processes and applications is focused on the so-called epitaxial growth of materials, the deposition of crystalline thin films that grow following the crystalline structure of the substrate. The term epitaxy comes from the Greek roots epi (ἐπί), meaning "above", and taxis (τάξις), meaning "an ordered manner". It can be translated as "arranging upon". The term homoepitaxy refers to the specific case in which a film of the same material is grown on a crystalline substrate. This technology is used, for instance, to grow a film which is more pure than the substrate, has a lower density of defects, and to fabricate layers having different doping levels. Heteroepitaxy refers to the case in which the film being deposited is different from the substrate. Techniques used for epitaxial growth of thin films include
molecular beam epitaxy Molecular-beam epitaxy (MBE) is an epitaxy Epitaxy refers to a type of crystal growth or material deposition in which new crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) ...

molecular beam epitaxy
,
chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition Vacuum deposition is a family of processes used to deposit layers of material atom-by-atom or molecule-by-molecule on a solid surface. These processes operate at pressures well below atmo ...
, and pulsed laser deposition.


Stress and strain

Thin films may be biaxially loaded via stresses originated from their interface with a substrate. Epitaxial thin films may experience stresses from misfit strains between the coherent
lattices
lattices
of the film and substrate. Thermal stress is common in thin films grown at elevated temperatures due to differences in thermal expansion coefficients with the substrate. Differences in interfacial energy and the growth and coalescence of
grains A grain is a small, hard, dry seed A seed is an embryonic ''Embryonic'' is the twelfth studio album by experimental rock band the Flaming Lips released on October 13, 2009, on Warner Bros. Records, Warner Bros. The band's first double albu ...

grains
contribute to intrinsic stress in thin films. These intrinsic stresses can be a function of film thickness. These stresses may be tensile or compressive and can cause
cracking
cracking
or
buckling In structural engineering Structural engineering is a sub-discipline of in which s are trained to design the 'bones and muscles' that create the form and shape of man-made structures. also must understand and calculate the , strength, and ...
among other forms of stress relaxation. In epitaxial films, initially deposited atomic layers may have coherent lattice planes with the substrate. However, past a critical thickness misfit dislocations will form leading to relaxation of stresses in the film.


Measuring stress and strain

The stresses in Films deposited on flat substrates such as
wafers A wafer is a crisp, often sweet, very thin, flat, light and dry cookie A cookie is a Baked goods, baked or cooked snack or Dessert, dessert that is typically small, flat and sweet. It usually contains flour, sugar, egg, and some type of Cook ...
can be measured by measuring the
curvature In mathematics Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained (geometry), and quantities an ...

curvature
of the wafer because of strain by the film. Lasers are reflected off the wafer in a grid pattern and distortions in the grid are used to calculate the curvature. Strain in thin films can also be measured by
x-ray diffraction X-ray crystallography (XRC) is the experimental science determining the atomic and molecular structure of a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a ...

x-ray diffraction
or by milling a section of the film via
focused ion beam Focused ion beam, also known as FIB, is a technique used particularly in the semiconductor industry, materials science and increasingly in the biological field for site-specific analysis, deposition, and ablation of materials. A FIB setup is a s ...
and the relaxation observed via
scanning electron microscopy A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that ...
.


Strain engineering

Stress and relaxation of stresses in films can influence the materials properties of the film, such as mass transport in
microelectronics Microelectronics is a subfield of electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons The electron is a subatomic particle In physica ...
applications. Therefore precautions are taken to either mitigate or produce such stresses; for example a buffer layer may be deposited between the substrate and film. Strain engineering is also used to produce various
phase Phase or phases may refer to: Science * State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter) In the physical sciences, a phase is a region of space (a thermodynamic system A thermodynamic system is a ...
and domain structures in thin films such as in the domain structure of the ferroelectric
Lead Zirconate Titanate Lead zirconate titanate is an with the (0≤''x''≤1). Also called lead zirconium titanate, it is a ceramic material that shows a marked , meaning that the compound changes shape when an electric field is applied. It is used in a number of ...
(PZT).


Applications


Decorative coatings

The usage of thin films for decorative coatings probably represents their oldest application. This encompasses ca. 100 nm thin gold leaves that were already used in ancient India more than 5000 years ago. It may also be understood as any form of painting, although this kind of work is generally considered as an arts craft rather than an engineering or scientific discipline. Today, thin-film materials of variable thickness and high
refractive index In optics Optics is the branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or ...

refractive index
like
titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s a ...
are often applied for decorative coatings on glass for instance, causing a rainbow-color appearance like oil on water. In addition, intransparent gold-colored surfaces may either be prepared by sputtering of gold or
titanium nitride Titanium nitride (TiN; sometimes known as Tinite) is an extremely hard ceramic material, often used as a coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface properties. Applied as a thin coating ...
.


Optical coatings

These layers serve in both reflective and
refractive In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior throu ...

refractive
systems. Large-area (reflective)
mirror A mirror is an object that reflects an image An image (from la, imago) is an artifact that depicts visual perception Visual perception is the ability to interpret the surrounding environment Environment most often refers t ...

mirror
s became available during the 19th century and were produced by sputtering of metallic silver or aluminum on glass. Refractive lenses for optical instruments like cameras and microscopes typically exhibit aberrations, i.e. non-ideal refractive behavior. While large sets of lenses had to be lined up along the optical path previously, nowadays, the coating of optical lenses with transparent multilayers of titanium dioxide,
silicon nitride Silicon nitride is a chemical compound of the elements silicon and nitrogen. is the most thermodynamically stable of the silicon nitrides. Hence, is the most commercially important of the silicon nitrides when referring to the term "silicon nitr ...
or silicon oxide etc. may correct these aberrations. A well-known example for the progress in optical systems by thin-film technology is represented by the only a few mm wide lens in smart phone cameras. Other examples are given by anti-reflection coatings on eyeglasses or
solar panels A solar cell panel, solar electric panel, photo-voltaic (PV) module or just solar panel is an assembly of photo-voltaic cells mounted in a framework for installation. Solar panels use sunlight Sunlight is a portion of the given off by ...

solar panels
.


Protective coatings

Thin films are often deposited to protect an underlying work piece from external influences. The protection may operate by minimizing the contact with the exterior medium in order to reduce the diffusion from the medium to the work piece or vice versa. For instance, plastic lemonade bottles are frequently coated by anti-diffusion layers to avoid the out-diffusion of CO2, into which carbonic acid decomposes that was introduced into the beverage under high pressure. Another example is represented by thin
TiN Tin is a with the Sn (from la, ) and  50. Tin is a silvery-colored metal that characteristically has a faint yellow hue. Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent ...
films in separating electrically conducting aluminum lines from the embedding insulator SiO2 in order to suppress the formation of Al2O3. Often, thin films serve as protection against abrasion between mechanically moving parts. Examples for the latter application are
diamond-like carbon Diamond-like carbon (DLC) is a class of amorphous carbon material that displays some of the typical properties of diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic ...
(DLC) layers used in car engines or thin films made of nanocomposites.


Electrically operating coatings

Thin layers from elemental metals like copper, aluminum, gold or silver etc. and alloys have found numerous applications in electrical devices. Due to their high
electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current An electric current is a stream of charged particle In p ...
they are able to transport electrical currents or supply voltages. Thin metal layers serve in conventional electrical system, for instance, as Cu layers on
printed circuit boards A printed circuit board (PCB) mechanically supports and electrically connects electrical Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a ...
, as the outer ground conductor in
coaxial cable Coaxial cable, or coax (pronounced ) is a type of consisting of an inner surrounded by a concentric conducting , with the two separated by a ( material); many coaxial cables also have a protective outer sheath or jacket. The term ' refers t ...
s and various other forms like sensors etc. A major field of application became their use in
integrated passive devicesIntegrated Passive Devices (IPD's) ''"or Integrated Passive Components (IPC's) or Embedded Passive Components"'' are electronic components where resistor A resistor is a passive two-terminal electrical component that implements electrical res ...
and
integrated circuits An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuit 200px, A circuit built on a printed circuit board (PCB). An electronic circuit is composed of indiv ...

integrated circuits
, where the electrical network among active and passive devices like
transistors file:MOSFET Structure.png, upright=1.4, Metal-oxide-semiconductor field-effect transistor (MOSFET), showing Metal gate, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A ...
and capacitors etc. is built up from thin Al or Cu layers. These layers dispose of thicknesses in the range of a few 100 nm up to a few µm, and they are often embedded into a few nm thin
titanium nitride Titanium nitride (TiN; sometimes known as Tinite) is an extremely hard ceramic material, often used as a coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface properties. Applied as a thin coating ...
layers in order to block a chemical reaction with the surrounding dielectric like SiO2. The figure shows a micrograph of a laterally structured TiN/Al/TiN metal stack in a microelectronic chip.
HeterostructureA heterojunction is an interface that occurs between two layers or regions of dissimilar semiconductor A semiconductor material has an Electrical resistivity and conductivity, electrical conductivity value falling between that of a Electrical con ...
s of
gallium nitride Gallium nitride () is a binary boron group, III/nitrogen group, V direct bandgap semiconductor commonly used in blue light-emitting diodes since the 1990s. The compound (chemistry), compound is a very hard material that has a Wurtzite crystal st ...
and similar
semiconductor A semiconductor material has an electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric curre ...
s can lead to electrons being bound to a sub-nanometric layer, effectively behaving as a
two-dimensional electron gas A two-dimensional electron gas (2DEG) is a scientific model Scientific modelling is a scientific activity, the aim of which is to make a particular part or feature of the world easier to understand, define, quantify, visualize, or simulate ...
. Quantum effects in such thin films can significantly enhance
electron mobility In solid-state physics Solid-state physics is the study of rigid matter, or solids, through methods such as quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state ...
as compared to that of a bulk crystal, which is employed in high-electron-mobility transistors.


Biosensors and plasmonic devices

Noble metal In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo duri ...
thin films are used in structures such as
surface plasmon resonance Surface plasmon resonance (SPR) is the resonant oscillation of conduction electrons at the interface between negative and positive permittivity material stimulated by incident light. SPR is the basis of many standard tools for measuring adsorption ...
(SPR) sensors.
Surface plasmon polariton Surface plasmon polaritons (SPPs) are electromagnetic waves that travel along a metal–dielectric or metal–air interface, practically in the infrared or visible spectrum, visible-frequency. The term "surface plasmon polariton" explains that the ...
s are surface waves in the optical regime that propagate in between metal-dielectric interfaces; in Kretschmann-Raether configuration for the SPR sensors, a prism is coated with a metallic film through evaporation. Due to the poor adhesive characteristics of metallic films,
germanium Germanium is a chemical element with the Symbol (chemistry), symbol Ge and atomic number 32. It is a lustrous, hard-brittle, grayish-white metalloid in the carbon group, chemically similar to its group neighbors silicon and tin. Pure germanium i ...

germanium
,
titanium Titanium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical ele ...

titanium
or
chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

chromium
films are used as intermediate layers to promote stronger adhesion. Metallic thin films are also used in plasmonic waveguide designs.


Thin-film photovoltaic cells

Thin-film technologies are also being developed as a means of substantially reducing the cost of
solar cells A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived b ...

solar cells
. The rationale for this is
thin-film solar cell A thin-film solar cell is a second generation solar cell that is made by depositing one or more thin layers, or thin film (TF) of photovoltaic material on a substrate, such as glass, plastic or metal. Thin-film solar cells are commercially us ...
s are cheaper to manufacture owing to their reduced material costs, energy costs, handling costs and capital costs. This is especially represented in the use of
printed electronics Printed electronics is a set of printing Printing is a process for mass reproducing text and images An Synthetic aperture radar, SAR radar imaging, radar image acquired by the SIR-C/X-SAR radar on board the Space Shuttle Endeavour s ...
(
roll-to-roll In the field of electronic devices, roll-to-roll processing, also known as web processing, reel-to-reel processing or R2R, is the process of creating electronic devices on a roll of flexible plastic, metal foil, or flexible glass. In other fields ...
) processes. Other thin-film technologies, that are still in an early stage of ongoing research or with limited commercial availability, are often classified as emerging or third generation photovoltaic cells and include,
organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or ...
, dye-sensitized, and polymer solar cells, as well as
quantum dot Quantum dots (QDs) are semiconductor particles a few nanometres in size, having optical and electronic properties that differ from larger particles due to quantum mechanics. They are a central topic in nanotechnology Nanotechnology, also ...
, copper zinc tin sulfide,
nanocrystal A ''nanocrystal'' is a material particle having at least one dimension smaller than 100 nanometres, based on quantum dots (a nanoparticle) and composed of atoms An atom is the smallest unit of ordinary matter that forms a chemical element ...
and
perovskite solar cell A perovskite solar cell (PSC) is a type of solar cell A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light Light or visible light is electromagnetic radiation within the portion of the electromag ...
s.


Thin-film batteries

Thin-film printing technology is being used to apply solid-state
lithium polymer A lithium polymer battery, or more correctly lithium-ion polymer battery (abbreviated as LiPo, LIP, Li-poly, lithium-poly and others), is a rechargeable battery A rechargeable battery, storage battery, or secondary cell, (or archaically acc ...
s to a variety of substrates to create unique batteries for specialized applications. Thin-film batteries can be deposited directly onto chips or chip packages in any shape or size. Flexible batteries can be made by printing onto plastic, thin metal foil, or paper.


Thin-film bulk acoustic wave resonators (TFBARs/FBARs)

For miniaturising and more precise control of resonance frequency of piezoelectric crystals thin-film bulk acoustic resonators TFBARs/FBARs are developed for oscillators, telecommunication filters and duplexers, and sensor applications.


See also

*
Coating A coating is a covering that is applied to the surface of an object, usually referred to as the Substrate (materials science), substrate. The purpose of applying the coating may be decorative, functional, or both. Paints and lacquers are coating ...
* Dual-polarisation interferometry *Ellipsometry *Hydrogenography *Kelvin probe force microscope *Langmuir–Blodgett film *Layer by layer *Microfabrication *Organic LED *Sarfus *Thin-film interference *Thin-film optics *Thin-film solar cell *Thin-film bulk acoustic resonator


References


Further reading

;Textbooks * * * ;Historical * {{Authority control Artificial materials Materials science Nanotechnology Thin films,