Coating Terms
A
Abrasion – The process of scraping or wearing away a surface by friction
Abrasive Wear – Wear caused by the rubbing or scraping of particles across the surface of a substrate
Adhesion – Physical bonding between two surfaces of different materials. In terms of coatings, adhesion refers to the strength of the bond between the coating and the substrate
Adhesion Test – A test to give an indication of the adhesion. There are many types of adhesion tests including: breath, indentation, non-destructive, scratch, and tape
Adhesive Wear – Wear due to localized bonding between contacting solid surfaces leading to material transfer between the two surfaces or the loss from either surface.
Alloy – A homogeneous mixture of 2 or more metals
Alumina – Any of several forms of aluminum oxide (Al2O3).
Aluminum Titanium Nitride (AlTiN) – A wear resistant coating used in a wide variety of applications
Amorphous Diamond Like Carbon (ALDC) – An amorphous carbon material with mostly sp3 bonding that exhibits many of the desirable properties of diamond and graphite
Ampere (A) – The basic unit of electrical current. One ampere is equal to a flow of one coulomb per second, or a flow of 6.28 × 1018 electrons per second
Angle of Incidence – The angle of impingement of the depositing flux as measured from the normal to the surface
Angstrom (Å) – A unit of length equal to 10-10 meters, or 0.1 nanometer
Antireflection coating – A film structure designed to reduce reflection over a region of the light spectrum (commonly referred to as “AR”)
Architectural glass – In the context of coating, usually refers to glass coated with a low-emissivity substance that reflects radiant infrared energy, encouraging radiant heat to remain on the same side of the glass from which it originated, while letting visible light pass. This results in more efficient windows because radiant heat originating from indoors in winter is reflected back inside, while infrared heat radiation from the sun during summer is reflected away, keeping it cooler inside.
Argon – An inert (noble) gas commonly used in sputtering. Used because of its relative inexpense and
Aspect ratio – The ratio of the depth to the width of a feature. Aspect ratios factor significantly in the selection of a coating process.
B
Batch – A group of objects that can be coated at the same time in the same coating chamber
Band-pass filters – Optical coatings that allow a band of specific wavelengths to pass through while others are reflected or absorbed
Barrier film – A layer used to reduce the diffusion into a surface or through a film
Basecoat – A film that is applied to a surface in order to create suitable conditions (e.g. adhesion) for another layer to be applied
Bias sputtering – Sputter deposition in which a bias (electrical potential) is applied to the substrate in order to accelerate ions to the surface in the deposition.
Box coater– a type of deposition system in the form of a flat sided box
Bunny suit – Body covering that is typically used in a clean room environment
C
Calibration – To determine the absolute value of an instrument by comparison to a standard, done in a specified manner under specified conditions
Cathode – The negative electrode to which the target material to be evaporated is fixed. It often refers to the source or target in everyday usage
Cathodic Arc Deposition – A vacuum arc PVD coating process that generates the ions used for coating by forming an electrical discharge that is sustained primarily on the electrons and ions that originate from the cathodes used to produce the arc. The high ionization rate makes it a good general purpose coating process
Chemical Vapor Deposition (CVD) – The deposition of a coating by means of a chemical reaction in gases. This process can be done in atmosphere or vacuum. Because this is a chemical bond, the bond strength is very high. Due to the high processing temperature (1000+°C), there are limitations of material and tolerances
Chromium Carbide (CrC) – A coating with good resistance to chipping and cracking. Chromium carbide (CrC) has a slightly higher micro-hardness than chromium nitride (CrN)
Chromium Nitride (CrN) – A coating with good resistance to chipping and cracking
Class III medical device – An FDA classification for medical devices that support or sustain human life, are of substantial importance in preventing impairment of human health, or which present a potential, unreasonable risk of illness or injury. Class III devices have the most stringent regulatory controls. Examples of Class III devices: replacement heart valves, silicone gel-filled breast implants, and implanted cerebella stimulators
Code of Federal Regulations (CFR)/FDA 21 CFR Part 820 – Quality System Regulation (QSR) outlines Current Good Manufacturing Practice (CGMP) regulations that govern the methods used in, and the facilities and controls used for, the design, manufacture, packaging, labeling, storage, installation, and servicing of all finished devices intended for human use. These requirements are meant to ensure that medical devices are safe and effective. Medical device manufacturers undergo FDA inspections to ensure FDA 21 CFR Part 820 compliance
Coefficient of Friction – An empirical measurement which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient value is obtained by dividing the force necessary to move one body over another at a constant speed by the weight of the body. The coefficient of friction depends on the materials used; rougher surfaces tend to have higher effective values. Coefficients of friction range from near zero to greater than one
Cohesion – The molecular force between particles within a body or substance that acts to unite them. In the realm of thin film coating, it refers to the stability of the coating matrix
Columnar Morphology – In the area of thin films, this refers to the morphology that develops with thickness due to the development of surface roughness due to preferential film deposition on high points on the surface. The columnar morphology resembles stacked posts, and the columns are not single grains
Conditioning, target – Degassing and removal of surface contamination from the target material before a deposition process begins
Contamination – Materials in the vacuum system that interfere with either the deposition process or the properties of the coating
Contract coater – A firm that will coat items for a customer under a contract. Contrasted with an “in-house” coater.
Corrosion – production of an undesirable compound or surface effect due to a reaction between a material and the ambient environment. There are many types of corrosion, for example: chemical, electrochemical, and galvanic
Craze – Cracks in a coating or surface due to stress
Cryopump– A vacuum pump that captures vapors and gases by condensing them on a cold surface
Cut-off wavelength – The maximum wavelength at which a coating will allow radiation to pass
Cycle – the entire process from loading the batch and pump down of the chamber to coating, cooling and unloading
E
Electro-optical property – A property of a film, such as optical transmission or color, that is affected by electric fields
EMI Shielding – Metallic coatings applied to prevent electromagnetic interference (radiation) from affecting electronic components
Energy-dispersive X-ray spectroscopy (EDX) – An analytical technique used for the elemental analysis or chemical characterization of a sample
Epitaxial Growth – (as used in film formation) the growth of one crystal on another such that the growth of the deposited crystal is determined by the crystalline orientation of the underlying surface.
Ellipsometry – a powerful technique to measure changes in properties of transparent or semitransparent thin films. Applications include the accurate thickness measurement, identification of materials and thin layers, and the characterization of surfaces. Ellipsometry relies on the fact that the reflection at a dielectric interface depends on the polarization of the light, while the transmission of light through a transparent layer changes the phase of the incoming wave depending on the refractive index of the material. The measurements of the film’s thickness, index, and absorption contain vital information because they are a very sensitive indicator of changes in film stoichiometry or contamination.
Ellipsometer – A measurement tool used to perform Ellipsometry. An ellipsometer can be used to measure layers as thin as 1 nm up to layers which are several microns thick. The instrument measures the change in polarization between the incident and reflected beam from a sample surface.
F
Filtered Arc – A deposition process in which macroparticle contaminants are filtered out.
Fixture – the structure that holds substrates during the deposition process. There are many types of fixturing, and they are an important part of applying a good coating
FTIR (Fourier transform infrared analysis) – Infrared spectroscopy technique which is used to obtain an infrared spectrum of absorption, emission, photoconductivity or Raman scattering of a solid, liquid or gas
G
Galling – Surface damage due to adhesion and fracturing of surfaces in contact.
Gate Valve – a mechancical sealing valve where the motion of the sealing plat is mostly parallel to the plane of the seal.
Good Manufacturing Practice (GMP) / Quality System Regulation (QS) – GMP (also referred to as the Quality System Regulation) requirements are defined in 21 CFR 820. A quality system is required for the design, manufacture, packaging, labeling, storage, installation, and servicing of finished medical devices intended for commercial distribution in the United States. The QS Regulation covers: quality management and organization, device design, buildings, equipment, purchase and handling of components, production and process controls, packaging and labeling control, device evaluation, distribution, installation, complaint handling, servicing, records. The QS Regulation is similar to ISO 9001:1994, with added particular requirements from the FDA
Grain Boundary – the boundary between two crystalline regions that have different grain orientations
H
Hard Coating – a coating that extends the life of a tool or component.
Hardness – The resistance of a surface to deformation, usually measured by resistance to indentation or abrasion. Hardness does not have an absolute scale. There are many different types of hardness tests, each with its own scale, including Brinell, Knoop, Leeb, Rockwell and Vickers
High Vacuum – A gas pressure in which there is no significant amount of gaseous contamination that will affect the deposition process or the properties of the deposit film
I
Index of Refraction (Refractive Index) – A measure of the extent to which a substance slows down light waves passing through it. The index of refraction of a substance is equal to the ratio of the velocity of light in a vacuum to its speed in that substance. Its value determines the extent to which light is refracted when entering or leaving the substance.
Inert gas – A gas that does not chemically react with surfaces under processing conditions
Infrared Spectrum – Electromagnetic radiation in the wavelength range of 0.78-300 microns
Insulator – A material with a low electrical conductivity
Interface – the region of contact between two materials
Interphase Material –The material that is formed by diffusion, reaction or co-deposition at the interface between the film and the substrate. The properties of this material greatly affect the adhesion of coatings
Ion – an atom or molecule that has an excess (negative) or deficiency (positive) of electrons
Ion Beam Deposition – A method that uses a vacuum process to deposit a coating. An electron beam evaporates the source material in order to generate positively charged ions. The coating is deposited by the positively charged ions being attracted to the negative charge given to substrate
M
Magnetron Sputtering – A method used to deposit PVD coatings in which the source/target has particles extracted from it by the introduction to its surface of energized atomic-sized particles. These particles are ejected towards the substrate.
Mask – A physical cover that prevents deposition on an area of the substrate
Mean Free Path – The average distance that a molecule travels between collisions with other molecules
Micro-hardness – A measure of the hardness of a material on a microscopic scale. A precision indenter is forced into the surface a material, usually under a light load. The impression length and test load are used to calculate a hardness value. These values are useful indicators of a materials properties.
Micron (µm) – One millionth of a meter; also called a micrometer.10-6 meter, 103 nanometer, 104 Angstroms; written as 1 micron, .001 mm., or 1µm.
Multi-Layer Coating – A coating consisting of two or more component layers of two or more different materials. These coatings are designed to provide complimentary effects on substrates
N
Nanometer (nm) – A unit of length equal to 10-9 meters or 10 Angstroms
Nano-indentation hardness test – Indentation of a surface using a very light load to measure the hardness of a coating
Nano-Layer Coating – A coating that consists of a hundreds of very thin layers. They are fractions of a micron in thickness, and measured in nanometers
O
Optical coating – a coating applied to improve various optical properties of a material. Depending on the coating and substrate employed, the transmission or reflection of different wavelengths of light from a surface can be modified
P
PECVD (Plasma Enhanced Chemical Vapor Deposition) – This is a low temperature (under 200°C) process of standard CVD. In the case of PECVD the gas reaction is carried out through an RF power source. Sometimes referred to as Plasma activated CVD or Plasma assisted CVD (PACVD)
Physical Vapor Deposition (PVD) – the deposition of coatings via the physical process of vaporizing target material in a vacuum chamber. The process involves the generation of positively charged ions through various methods. Reactive gases are introduced into the chamber to create various compounds. The positively charged ions are attracted to a negative bias given to the substrates. This attraction results in a dense thin-film layer with an extremely strong physical bond to the substrate. A vacuum chamber is necessary to avoid reaction of the vaporized material with air. PVD is a relatively low temperature (400°C) process
Pinhole – A small hole in a coating due to incomplete coverage during deposition
Pin-on-disc test – A test to assess the tribological performance of thin films. This test uses a tribometers consisting of stationary “pin” under an applied load in contact with a rotating disc. The pin can have any shape to simulate a specific contact, but spherical tips are often used to simplify the contact geometry. As the sample rotates or slides, the resulting frictional forces acting between the pin and the sample are measured by very small deflections of the lever. Wear coefficients for both the sample and material are calculated from the volume of the material lost.
Plasma – A gas that contains an appreciable number of electrons and ions such that it is electrically conductive. A plasma is a collection of electrons (negative charge) and ions (positively charged particles). Plasmas are common in neon signs, the light being generated from the electrons and ions recombining with each other. Different gases release differing amounts of energy when the electrons and ions recombine. This difference in energy manifests itself as different colors (an Argon discharge is lavender/blue, Nitrogen is pinkish-purple, Oxygen is white-blue).
Plasma-Assisted CVD (PaCVD) – Also known as Plasma-Enhanced CVD (PeCVD), this is a CVD process where a plasma is used to assist in the decomposition and reaction of the chemical vapor precursor, thereby allowing the deposition to be performed at a significantly lower temperature than when using thermal processes alone.
R
Refractive Index – The ratio of the velocity light in vacuum to the velocity of light in a material. Also the sine of the angle-of-incidence of the light beam to the sine of the angle of refraction of the light
S
Salt Fog – ASTM B-117 test procedure that simulates the corrosive environment caused by road salt and marine spray
Scanning electron microscopy(SEM) – The scanning electron microscope (SEM) is an instrument that creates images at magnifications ranging from 20 -100,000 times by focusing and rastering a high energy beam of electrons onto the surface of a sample. The resulting signals from the interaction of the incident electrons with the sample’s surface are then detected
Scratch adhesion test – A test to determine the critical load for delamination (adhesion) of a coating. The scratch test works using a precision stage that moves a diamond stylus across the surface under constant, incremental or progressive force. At a certain critical load the coating will start to fail. The method also allows the wear properties and failure modes of the coating to be evaluated. This test is quantitative and allows precise comparison between samples.
Sheet Resistivity – The resistance from side to side of a square area of a film expressed in Ohms-per-square.
Silicon Carbide Coating (SiC) –The high micro-hardness of silicon carbide (SiC) coating provides a wear-resistant layer to tooling. Silicon carbide is generally used in conjunction with a dry-film lubricant coating
Source – device which holds the target material and which incorporates the trigger, magnets, body and cooling. The source is sometimes generally referred to as the cathode
sp2 – Carbon atoms bonded similar to graphite (trigonal structuring – graphite)
sp3 – Carbon atoms bonded similarly to natural diamond (tetrahedral structuring – diamond)
Sputtering – Ejection of particles from a surface by momentum transfer from an energetic atomic-sized particle impinging on the surface
Stack – A multilayer film structure used to obtain desired properties
Steered Arc – A cathodic ar where the arc is moved over the surface under the influence of a magnetic field
Stoichiometry – The numerical ratio of atoms in a compound
Stoichiometric Compound – A compound material which has the correct atomic ratios for all lattice sites to be occupied for the specific phase of the material
Substrate – The material, work piece, or substance on which a coating is deposited
Surface Engineering – Changing the properties of a surface to meet requirements. There are a variety of methods to achieve this, including coatings
T
Taber abrasion test – A test to evaluate the resistance of optical coatings to abrasion by contact with a rough surface (Tabor eraser) or contact with moving sand. Analysis is performed through a combination of visual inspection, profilometry of wear track, and scatter/haze measurements. (ASTM F735, Military Specification 48497 and 43511)
Tape Test – A pass/fail test of adhesion in which an adhesive tape is applied to a film surface, then rapidly pulled from it
Target – The material to be evaporated. The target is incorporated into the source and is sometimes referred to as the source or cathode
Target conditioning – Sputtering a target to remove natural contamination layers (such as oxides) prior to the deposition process
Target Poisoning – Reaction of the surface of a sputtering target either with reactive gas being used for deposition or with a contaminant gas. The reaction causes a change in the deposition process
Titanium Aluminum Nitride (TiAlN) – A wear resistant coating similar to AlTiN, but it is more ductile due to the higher percentage of titanium
Titanium Carbide (TiC) – A very hard coating that has excellent resistance to abrasion
Titanium CarboNitride (TiCN) – A coating with very high hardness with excellent resistance to abrasion
Titanium Nitride (TiN) – A very good general purpose coating that is widely used throughout the industry. It generally has high hardness and can be deposited in a variety of multi-layer coatings
Torr – A unit of pressure, being the pressure necessary to support a column of mercury one millimeter high at 0° C and standard gravity, equal to 1333.2 microbars or 1/760 of a standard atmosphere. The term is standard in measuring the level of vacuum in PVD coating chambers
Tribology – Term coined by David Tabor from the Greek word “tribos,” meaning rubbing. The science and technology of interacting surfaces in relative motions, and of associated subjects such as lubrication, friction, and wear.
Tribological Coating – Coatings designed to reduce friction and wear on contacting surfaces that move relative to each other (bearings, cams, gears, etc.)
V
Vacuum – Pressure in a container that is less than the ambient pressure outside the container
Vacuum, high – A gas pressure generally taken as below about 10 -5 Torr
Vickers test (HV) – A test to measure micro-indentation hardness test. It utilizes a 136° diamond pyramid indenter (Vickers) and variable loads, enabling the use of one hardness scale for all ranges of hardness. It is the most commonly used scale when measuring the hardness of thin film coatings
W
Wear – The removal of material by friction between materials in moving contact
Witness coupon – A substrate that is not a part of the production batch but is used for characterization of the coating after deposition
Z
Zirconium Nitride (ZrN) – A coating with good general purpose wear resistance. It is recommended for iron and non-ferrous materials such as aluminum, brass, copper, and titanium