NanoPrint
Technologies is using the technology, processes, and expertise that
we have developed over 7 years to print electronics.
There
are three types of companies in the Printed Electronics (PE) market:
ink manufacturers, electronic component designers/manufacturers, and
printing companies. The companies who make ink and/or
design/manufacture electronic components do not have the technology
and expertise that it takes to print electronics at high speeds with
good quality. These companies may have prototype printers to test
concepts, but they rely on printing companies like us to do their
production printing.
PE is a
disruptive technology that promises to produce many new products and
applications that will take advantage of low cost, flexible, durable
electronic components that were not possible with traditional silicon
based electronics. It is estimated that over 50% of the PE market
will be made up of electronic products and applications that
currently do not exist.
Printed Electronics is the term for a
relatively new technology that defines the printing of electronics on
common media such as paper, plastic, and textile using standard
printing processes. This printing preferably utilizes common press
equipment in the graphics arts industry, such as screen
printing, flexography, gravure,
and offset
lithography. Instead of
printing graphic arts inks, families of electrically functional
electronic inks are used to print active devices, such as thin
film transistors. Printed
electronics is expected to facilitate widespread and very low-cost
electronics useful for applications not typically associated with
conventional (i.e., silicon-based) electronics, such as flexible
displays, smart
labels, animated posters, and
active clothing.
The term printed electronics is often used in
association with organic
electronics or plastic
electronics, where one or more
functional inks are composed of carbon-based compounds. While these
other terms refer to the material system, the process used to deposit
them can be either solution-based, vacuum-based, or some other
method. Printed electronics, in contrast, specifies the process, and
can utilize any solution-based material, including organic semiconductors, inorganic semiconductors, metallic conductors, nanoparticles, nanotubes,
etc.
Standards Development and Activities
Several printed electronics industry leaders have
established standards and roadmapping initiatives, which are intended to facilitate value
chain development (for sharing
of product specifications, characterization standards, etc.) This strategy of standards development mirrors the
historical development, market introduction, and wide spread
acceptance of silicon-based electronics over the past 50 years. As an
example of this development of standards for printed electronics, the Institute
of Electrical and Electronics Engineers (IEEE) [1] launched an initiative to develop standards to assist in the
development of the technology. To date, the IEEE
Standards Association has
published IEEE 1620-2004™ [2] and IEEE 1620.1-2006™ [3],
which will enable the continued maturity of printed electronics. In
addition, similar to the well-established International
Technology Roadmap for Semiconductors (ITRS) [4],
the International Electronics Manufacturing Initiative (iNEMI) [5] has published a roadmap for printed and organic
electronics.
Organic
electronics
Organic electronics, or plastic
electronics, is a branch of electronics that deals with conductive polymers,
or plastics.
It is called 'organic'
electronics because the molecules in the polymer are carbon-based,
like the molecules of living things. This is as opposed to traditional electronics which
relies on inorganic conductors such as copper or silicon.
In addition to organic Charge
transfer complexes,
technically, electrically conductive polymers are mainly derivatives
of polyacetylene black (the "simplest melanin").
Examples include PA (more specificially iodine-doped
trans-polyacetylene); polyaniline: PANI, when doped with a protonic
acid; and poly(dioctyl-bithiophene): PDOT.
For a history of the field, see "An Overview of the First
Half-Century of Molecular Electronics" by Noel S. Hush, Ann.
N.Y. Acad. Sci. 1006: 1–20 (2003).
Organic
semiconductor
An organic semiconductor is any organic
material that has semiconductor properties. A semiconductor is any compound whose electrical
conductivity is between that of typical metals and that of insulating
compounds. Both short chain (oligomers)
and long chain (polymers)
organic semiconductors are known. Examples of semiconducting
oligomers are: pentacene, anthracene and rubrene.
Examples of polymers are: poly(3-hexylthiophene), poly(p-phenylene
vinylene), F8BT, as well as
polyaectylene and its derivatives.
There are two major classes of organic
semiconductors, which overlap significantly: organic charge-transfer
complexes, and various "linear
backbone" polymers derived from polyacetylene,
such as polyacetylene itself, polypyrrole,
and polyaniline.
Charge-transfer complexes often exhibit similar conduction mechanisms
to inorganic semiconductors,
at least locally. This includes the presence of a hole and electron conduction layer and a band
gap. As with inorganic
amorphous semiconductors, tunneling, localized states, mobility
gaps, and phonon-assisted
hopping also contribute to conduction, particularly in
polyacetylenes. Like inorganic semiconductors, organic semiconductors
can be doped.
Highly doped organic semiconductors, for example Polyaniline (Ormecon) and PEDOT:PSS,
are also known as organic metals.
Several kinds of carriers mediate conductivity in
organic semiconductors. These include π-electrons and unpaired electrons. Almost all organic solids are insulators.
But when their constituent molecules have π-conjugate
systems, electrons can move via π-electron
cloud overlaps. Polycyclic aromatic
hydrocarbons and phthalocyanine salt crystals are examples of this type of organic semiconductor.
In charge
transfer complexes, even
unpaired electrons can stay stable for a long time, and are the
carriers. This type of semiconductor is also obtained by pairing an
electron donor molecule and an electron acceptor molecule.
Analogous rigid-backbone organic semiconductors are
now-used as active elements in optoelectronic devices such as organic
light-emitting diodes (OLED), organic
solar cells, organic
field effect transistors (OFET), electrochemical transistors and recently in biosensing
applications.
Organic semiconductors have many advantages, such as
easy fabrication, mechanical flexibility, and low cost. Melanin is a semiconducting polymer currently of high interest to researchers
in the field of organic
electronics in both its organic
and synthesized forms.
Conductive
polymer
A conductive polymer is an organic polymer semiconductor,
or an organic
semiconductor. Roughly, there
are two classes-- the Charge
transfer complexes and the
conductive polyacetylenes. The latter include polyacetylene itself as well as polypyrrole, polyaniline,
and their derivatives.
Most commercially produced organic polymers are electrical
insulators. Conductive organic
polymers often have extended delocalized
bonds (often composed of aromatic units). At least locally, these create a band structure similar to silicon,
but with localized states. When charge
carriers (from the addition or
removal of electrons)
are introduced into the conduction or valence bands (see below) the electrical
conductivity increases
dramatically. Technically almost all known conductive polymers are semiconductors due to the band structure and low electronic mobility. However,
so-called zero band
gap conductive polymers may
behave like metals.
The most notable difference between conductive polymers and inorganic semiconductors is the mobility,
which until very recently was dramatically lower in conductive
polymers than their inorganic counterparts, though recent advancements in molecular
self-assembly are closing that
gap.
Delocalization can be accomplished by forming a conjugated backbone of continuous overlapping orbitals.
For example, alternating single and double carbon-carbon bonds can form a continuous path of overlapping p
orbitals. In polyacetylene,
but not in most other conductive polymers, this creates degeneracy in the frontier molecular orbitals (the highest occupied and lowest
unoccupied orbitals named HOMO
and LUMO respectively). This
leads to the filled (electron containing) and unfilled bands (valence and conduction
bands respectively) resulting
in a semiconductor.
However, conductive polymers generally exhibit very
low conductivities. In fact, as with inorganic amorphous
semiconductors, conduction in
such relatively disordered materials is mostly a function of
"mobility
gaps" with phonon-assisted
hopping, polaron-assisted tunnelling,
etc. between localized states and not band gaps as in crystalline semiconductors.
In more ordered materials, it is not until an
electron is removed from the valence band (p-doping)
or added to the conduction band (n-doping,
which is far less common) does a conducting polymer become highly
conductive. Doping (p or n) generates charge
carriers which move in an electric
field. Positive charges (holes)
and negative charges (electrons)
move to opposite electrodes. This movement of charge is what is
actually responsible for electrical conductivity in crystalline
materials.
In contrast, typically "doping" in the
polyacetylene-derived conductive polymers involves actually oxidizing
the compound. Conductive organic polymers associated with a protic
solvent may also be "self-doped". Melanin is the classic example of both types of doping, being both an
oxidized polyacetylene and likewise commonly being hydrated.
Doping
In silicon semiconductors, a few of the silicon atoms
are replaced by electron rich (e.g., phosphorus)
or electron-poor (e.g. boron)
atoms to create n-type and p-type
semiconductors, respectively.
In contrast, there are two primary methods of doping a conductive
polymer, both through an oxidation-reduction (redox)
process. The first method, chemical doping, involves exposing a
polymer, such as melanin (typically a thin
film), to an oxidant (typically iodine or bromine)
or reductant (far less common, but typically involves alkali
metals). The second is electrochemical doping in which a polymer-coated, working electrode is suspended in an electrolyte solution in which the polymer is insoluble along with separate counter and reference electrodes. An electric potential
difference is created between
the electrodes which causes a charge (and the appropriate counter ion from the electrolyte)
to enter the polymer in the form of electron addition (n doping) or
removal (p doping). Polymers may also be self-doped, e.g., when
associated with a protonic solvent such as water or an alcohol.
The reason n doping is so much less common is that Earth's
atmosphere is oxygen-rich,
which creates an oxidizing environment. An electron-rich n doped polymer will react immediately
with elemental oxygen to de-dope (re-oxidize to the neutral state)
the polymer. Thus, chemical n doping has to be done in an environment
of inert gas (e.g., argon).
Electrochemical n doping is far less common in research, because it
is much more difficult to exclude oxygen from a solvent in a sealed flask;
therefore, although very useful, there are likely to be no
commercialized n doped conductive polymers.
Electroluminesence
Electroluminescence and photoconductivity in organic
compounds has been known since the early 1950's. However, the very
poor conductivity of such materials limited current flow and thus
light output. In contrast, the increased current flow through
conductive polymers and improvements in their efficiency has led to
the rapid development of practical polymer-based light emitting
devices (OLEDs)
and organic photovoltaic devices.
Properties
The biggest advantage of conductive polymers is their
processibility. Conductive polymers are also plastics (which are organic polymers) and therefore can combine the mechanical
properties (flexibility, toughness, malleability elasticity,
etc.) of plastics with the high electrical conductivities of a doped
conjugated polymer.
Physics
In
addition to "switching", an increase in conductivity can
also be accomplished in a field
effect transistor (organic FET
or OFET),
or by irradiation (originally-demonstrated in the 1960's [9]).
Strong coupling can also occur between electrons and phonons (mechanical oscillations such as heat vibrations, particles of sound)
since both are constrained to travel along the polymer backbone.
Applications of conducting polymers
Electroluminescence
(light emission) in organic compounds has been known since the early
1950's, when Bernanose and coworkers first produced
electroluminescence in crystalline thin films of acridine orange and
quinacrine. [10].
In 1960, researchers at Dow Chemical developed AC-driven
electroluminescent cells using doped anthracene. [11] and http://www.iitk.ac.in/scdt/doc/Organic%20Semiconductors.pdf).
In some cases, similar light
emission is observed when a voltage is applied to a thin layer of a conductive organic polymer film. The
increased conductivity of modern conductive polymers means enough
power can be put through the device at low voltages to generate
practical amounts of light. This has led to the development of flat
panel displays using OLEDs, solar
panels and optical amplifiers.
Back to Top
An electronic paper display is a specialized type of electronic
paper that combines the uses
and advantages of a computer
display and paper. Electronic
paper displays are extremely thin, use minimal amounts of power and
provide a high-contrast viewing surface like paper, but can be easily
updated like a monitor.[1]
Back to Top
An EPC RFID tag used for Wal-Mart
'Radio-frequency identification'('RFID')is an [Automated
identification and data capture|automatic identification]method,
relying on storing and remotely retrieving data using devices called
RFID tags or [transponder]s. An RFID tag is an object that can be
attached to or incorporated into a product,animal,or person for the
purpose of identification using radiowaves. Most RFID tags contain at
least two parts.
One
is an integrated circuit for storing and processing
information,modulating and demodulating a(RF)signal and perhaps other
specialized functions.
The
second is an antenna for receiving and transmitting the signal.A
technology called chipless RFID allows for discrete identification of
tags without an integrated circuit,thereby allowing tags to be
printed directly onto assets at lower cost than traditional tags.
The RFID tag can automatically be read from several meters away and
does not have to be in the line of sight of the reader. The current
thrust in RFID use is in supply chain management for large
enterprises.RFID increases the speed and accuracy with which
inventory can be tracked and managed thereby saving money for the
business.
History
of RFID tags
An
RFID tag used for electronic
toll collection
RFID tags
RFID tags come in three general varieties:passive, semi-passive (also known as battery-assisted), or active.Passive tags require no internal power source, whereas
semi-passive and active tags require a power source, usually a small
battery.
RFID in inventory systems
An advanced automatic identification technology such as the Auto-ID
system based on the Radio Frequency Identification (RFID) technology
has two values for inventory systems. First, the visibility provided
by this technology allows an accurate knowledge on the inventory
level by eliminating the discrepancy between inventory record and
physical inventory. Second, the RFID technology can prevent or reduce
the sources of errors. Benefits of using RFID include the reduction
of labour costs, the simplification of business processes and the
reduction of inventory inaccuracies.
RFID mandates
Wal-Mart and the United
States Department of Defense have published requirements that their vendors place RFID tags on all
shipments to improve supply
chain management Due to the
size of these two organizations, their RFID mandates impact thousands
of companies worldwide. The deadlines have been extended several
times because many vendors face significant difficulties implementing
RFID systems. In practice, the successful read rates currently run
only 80%, due to radio wave attenuation caused by the products and packaging. In time it is expected that
even small companies will be able to place RFID tags on their
outbound shipments.
Since January, 2005, Wal-Mart has required its top
100 suppliers to apply RFID labels to all shipments. To meet this
requirement, vendors use RFID printer/encoders to label cases and
pallets that require EPC tags for Wal-Mart.
These smart labels are produced by embedding RFID inlays inside the
label material, and then printing bar code and other visible
information on the surface of the label.
Replacing barcodes
RFID tags are often envisioned as a replacement for UPC or EAN barcodes, having a number of important advantages over the older
barcode technology. They may not ever completely replace barcodes,
due in part to their higher cost and in other part to the advantage
of more than one independent data source on the same object. The new EPC,
along with several other schemes, is widely available at reasonable
cost.
Back to Top
Photovoltaics,
or PV for short, is a solar
power technology that uses solar
cells or solar
photovoltaic arrays to convert
light from the sun directly into electricity.
Photovoltaics is also the field of study relating to this technology
and there are many research institutes devoted to work on
photovoltaics.[1][2] The manufacture of photovoltaic cells has expanded dramatically in
recent years.[3][4][5] Total nominal 'peak power' of installed solar PV arrays was around
3,700 MW as
of the end of 2005, a 42%
increase for the year,[6] and most of this consisted of grid-connected applications. Such
installations may be ground-mounted (and sometimes integrated with
farming and grazing)[7] or building integrated.[8] Financial incentives, such as preferential feed-in tariffs for
solar-generated electricity and net
metering, have supported solar
PV installations in many countries including Germany, Japan,
and the United
States.[9]
Environmental
impacts
Unlike fossil
fuel based technologies, solar
power does not lead to any harmful emissions during operation, but
the production of the panels leads to some amount of pollution. Also,
placement of photovoltaics affects the environment. If they are
located where photosynthesizing plants would normally grow, they
simply substitute one potentially renewable resource (biomass)
for another. It should be noted, however, that the biomass cycle
converts solar radiation energy to electrical energy with
significantly less efficiency than photovoltaic cells alone. However,
if they are placed on the sides of buildings (such as in Manchester)
or fences, or rooftops (as long as plants would not normally be
placed there), or in the desert they are purely additive to the
renewable power base.
Back to Top
Indium
tin oxide
Indium tin oxide (ITO, or tin-doped
indium oxide) is a mixture of indium(III)
oxide (In2O3)
and tin(IV)
oxide (SnO2),
typically 90% In2O3, 10% SnO2 by
weight. It is transparent and colorless in thin layers. In bulk form,
it is yellowish to grey.
Indium tin oxide's main feature is the combination of electrical
conductivity and optical
transparency. However, a
compromise has to be reached during film deposition, as high
concentration of charge
carriers will increase the
material's conductivity, but decrease its transparency.
Thin
films of indium tin oxide are
most commonly deposited on surfaces by electron
beam evaporation, physical
vapor deposition, or a range of sputter
deposition techniques.
Uses
ITO is mainly used to make transparent conductive
coatings for liquid
crystal displays, flat
panel displays, plasma
displays, touch
panels, electronic
ink applications, organic
light-emitting diodes, and solar
cells, and antistatic
coatings and EMI shieldings.
ITO is also used for various optical
coatings, most notably infrared-reflecting
coatings (hot
mirrors) for architectural,
automotive, and sodium
vapor lamp glasses. Other uses
include gas
sensors, antireflection
coatings, and Bragg
reflectors for VCSEL lasers.
ITO thin film strain
gauges can operate at
temperatures up to 1400 °C and can be used in harsh environments,
eg. gas
turbines, jet
engines, and rocket
engines [1]
Alternatives
Due to high cost and limited supply of indium, the
fragility and lack of flexibility of ITO layers, and the costly layer
deposition requiring vacuum, alternatives are being sought. Carbon
nanotube conductive coatings
are a prospective replacement. These coatings are being developed by Eikos and Unidym as a lower cost, more mechanically robust alternative to ITO. PEDOT and PEDOT:PSS are manufactured by AGFA and H.C.
Starck. PEDOT:PSS layers
are in use (though they degrade when exposed to ultraviolet radiation
and have other disadvantages). Other alternatives are eg. aluminium-doped zinc
oxide.
Back to Top
A 3.8cm (1.5in) OLED Screen
An organic light-emitting diode (OLED)
is any light-emitting
diode (LED) whose emissive electroluminescent layer comprises a film of organic
compounds. The layer usually
contains a polymer substance that allows suitable organic compounds to be deposited.
They are deposited in rows and columns onto a flat carrier by a
simple "printing" process. The resulting matrix of pixels can emit light of different colors.
Such systems can be used in television screens, computer
displays, portable system
screens, advertising, information and indication. OLEDs can also be
used in light sources for general space illumination, and large area
light-emitting elements. OLEDs typically emit less light per area
than inorganic solid-state based LEDs which are usually designed for
use as point light sources.
A great benefit of OLED displays over traditional liquid
crystal displays (LCDs) is that
OLEDs do not require a backlight to function. Thus they draw far less power and, when powered from a
battery, can operate longer on the same charge. OLED-based display
devices also can be more
effectively manufactured than LCDs and plasma displays. But
degradation of OLED materials has limited the use of these materials.
See Drawbacks.
OLED technology was also called Organic Electro-Luminescence (OEL),
before the term "OLED" became standard.
Working principle
An OLED is composed of an emissive layer, a
conductive layer, a substrate, and anode and cathode terminals. The layers are made of special organic polymer molecules
that conduct electricity. Their levels of conductivity range from
those of insulators to those of conductors, and so they are called organic
semiconductors.
OLED schematic -
1. Cathode (-), 2. Emissive Layer, 3. Emission of radiation, 4 .
Conductive Layer, 5. Anode (+)
A voltage is applied across the OLED such that the
anode is positive with respect to the cathode. This causes a current
of electrons to flow through the device from cathode to anode. Thus, the cathode
gives electrons to the emissive layer and the anode withdraws
electrons from the conductive layer; in other words, the anode gives electron
holes to the conductive layer.
Soon, the emissive layer becomes negatively charged,
while the conductive layer becomes rich in positively charged holes.
Electrostatic forces bring the electrons and the holes towards each
other and recombine. This happens closer to the emissive layer,
because in organic semiconductors holes are more mobile than
electrons, (unlike in inorganic semiconductors). The recombination
causes a drop in the energy levels of electrons, accompanied by an
emission of radiation whose frequency is in the visible
region. That is why this layer
is called emissive.
The device does not work when the anode is put at a negative
potential with respect to the cathode. In this condition, holes move
to the anode and electrons to the cathode, so they are moving away
from each other and do not recombine.
Indium
tin oxide is commonly used as
the anode material. It is transparent to visible light and has a high work
function which promotes
injection of holes into the polymer layer. Metals such as aluminium and calcium are often used for the cathode as they have low work functions which
promote injection of electrons into the polymer layer.[17]
Advantages
The
radically different manufacturing process of OLEDs lends itself to
many advantages over flat panel displays made with LCD technology.
Since OLEDs can be printed onto any suitable substrate using inkjet printer or even screen printing[18] technologies, they can theoretically have a significantly lower cost
than LCDs or plasma
displays. Printed OLEDs onto
flexible substrates opens the door to new applications such as
roll-up displays and displays embedded in clothing.
OLEDs enable a greater range of colors, brightness,
and viewing angle than LCDs, because OLED pixels directly emit light.
OLED pixel colors appear correct and unshifted, even as the viewing
angle approaches 90 degrees from normal. LCDs use a backlight and cannot show true black, while an "off" OLED element
produces no light and consumes no power. Energy is also wasted in
LCDs because they require polarizers which filter out about half of the light emitted by the backlight.
Additionally, color filters in color LCDs filter out two-thirds of
the light.
OLEDs
also have a faster response time than standard LCD screens. Whereas a
standard LCD has around 10ms response time, an OLED can have less
than 0.01ms response time. [19]
Drawbacks
The
biggest technical problem for OLEDs is the limited lifetime of the
organic materials. In particular, blue OLEDs typically have lifetimes
of around 5,000 hours when used for flat panel displays, which is
lower than typical lifetimes of LCD or Plasma technology. But recent experiments have shown that it is possible to
swap the chemical component for a phosphorescent one, if the subtle differences in energy transitions are accounted
for, resulting in lifetimes of up to 20,000 hours for blue PHOLEDs. [20]
The intrusion of water into displays can damage or destroy the
organic materials. Therefore, improved sealing processes are
important for practical manufacturing and may limit the longevity of
more flexible displays.
Commercial
development of the technology is also restrained by patents held by Eastman
Kodak and other firms,
requiring other companies to acquire a license.[citation
needed] In the past,
many display technologies have become widespread only once the
patents had expired; a classic example is aperture
grille Cathode
ray tube. [21]
Commercial uses
OLED
technology is used in commercial applications such as small screens
for mobile phones and portable digital
audio players (MP3 players),
car radios, digital
cameras and high-resolution
microdisplays for head-mounted
displays. Such portable
applications favor the high light output of OLEDs for readability in
sunlight, and their low power drain. Portable displays are also used
intermittently, so the lower lifespan of OLEDs is less important
here. Prototypes have been made of flexible and rollable displays
which use unique OLEDs characteristics. OLEDs have been found in most Motorola and Samsung color cell phones, as well as some Sony
Ericsson phones, notably the
Z610i, and some models of the Sony
Walkman. [27]
OLEDs can be used on Hight Resolution Holography (Volumetric Display)
Professor Orbit showed on 12 May of 2007,EXPO Lisbon the potential
application of these materials to reproduce 3-Dimensional Videos.
OLEDs
could also be used as solid-state light sources. OLED efficacies and
lifetime already exceed those of Incandescent
light bulbs, and OLEDs are
investigated worldwide as source for general illumination; an example
is the EU OLLA project[28].
eMagin Corporation is the only manufacturer of active
matrix OLED-on-silicon displays. These are currently being developed for the US military,
the medical field and the future of entertainment where an individual
can immerse themselves in a movie or a video game.
Back to Top
Integrated
circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and
input/output pads around the periphery
Microchips with
a transparent window, showing the integrated circuit inside. Note the
fine silver-colored wires that connect the integrated circuit to the
pins of the package.
A monolithic integrated circuit (also known as IC, microcircuit, microchip, silicon chip,
or chip) is a miniaturized electronic
circuit (consisting mainly of semiconductor
devices, as well as passive
components) that has been
manufactured in the surface of a thin substrate of semiconductor material.
A hybrid
integrated circuit is a
miniaturized electronic circuit constructed of individual
semiconductor devices, as well as passive components, bonded to a
substrate or circuit board.
Manufacture
Fabrication
Rendering
of a small standard
cell with three metal layers
(dielectric has been removed). The sand-colored structures are metal
interconnect, with the vertical pillars being contacts, typically
plugs of tungsten. The reddish structures are polysilicon gates, and
the solid at the bottom is the crystalline silicon bulk.
The semiconductors of the periodic
table of the chemical
elements were identified as the
most likely materials for a solid
state vacuum
tube by researchers like William
Shockley at Bell
Laboratories starting in the
1930s. Starting with copper
oxide, proceeding to germanium,
then silicon,
the materials were systematically studied in the 1940s and 1950s.
Today, silicon monocrystals are the main substrate used for integrated circuits (ICs) although some III-V
compounds of the periodic table such as gallium
arsenide are used for
specialised applications like LEDs, lasers, solar
cells and the highest-speed
integrated circuits. It took decades to perfect methods of creating crystals without defects in the crystalline
structure of the semiconducting
material.
Semiconductor ICs are fabricated in a layer process which includes these key
process steps:
-
Imaging
-
Deposition
-
Etching
The main process steps are supplemented by doping, cleaning and
planarisation steps.
Mono-crystal silicon wafers (or for special applications, silicon
on sapphire or gallium
arsenide wafers) are used as
the substrate. Photolithography is used to mark different areas of the substrate to be doped or to have polysilicon, insulators or metal (typically aluminium)
tracks deposited on them.
-
Integrated
circuits are composed of many overlapping layers, each defined by
photolithography, and normally shown in different colors. Some
layers mark where various dopants are diffused into the substrate
(called diffusion layers), some define where additional ions are
implanted (implant layers), some define the conductors (polysilicon
or metal layers), and some define the connections between the
conducting layers (via or contact layers). All components are
constructed from a specific combination of these layers.
A random
access memory is the most
regular type of integrated circuit; the highest density devices are
thus memories; but even a microprocessor will have memory on the chip. (See the regular array structure at the
bottom of the first image.) Although the structures are intricate –
with widths which have been shrinking for decades – the layers
remain much thinner than the device widths. The layers of material
are fabricated much like a photographic process, although light waves in the visible
spectrum cannot be used to
"expose" a layer of material, as they would be too large
for the features. Thus photons of higher frequencies (typically ultraviolet)
are used to create the patterns for each layer. Because each feature
is so small, electron
microscopes are essential tools
for a process engineer who might be debugging a fabrication process.
Back to Top
A sensor is a type of transducer.
Direct-indicating sensors, for example, a mercury
thermometer, are
human-readable. Other sensors must be paired with an indicator or
display, for instance a thermocouple.
Most sensors are electrical or electronic,
although other types exist.
Sensors are used in everyday life. Applications include automobiles,
machines, aerospace, medicine, industry and robotics.
Technological progress allows more and more sensors
to be manufactured on the microscopic scale as microsensors using MEMS technology. In most cases a microsensor reaches a
significantly higher speed and sensitivity compared with macroscopic approaches. See also MEMS
sensor generations.
Types
Since a significant change involves an exchange of energy,
sensors can be classified according to the type of energy transfer
that they detect: Thermal, Electromagnetic,
Mechanical, Chemical, Optical radiation, Ionising radiation,
Acoustic, Other.
Back to Top
