I MSC ECS
SUBJECT NAME : MEMS AND POWER ELECTRONICS
Mems and micro systems – typical mems and micro system products – micro systems
and micro electronics – the multidisciplinary nature of micro system design and manufacture
– application examples of micro systems – micro sensors – micro actuation – mems with
micro actuators – micro accelerometers – micro fluidics.
UNIT II FABRICATION PROCESS OF MEMS
Materials for mems and micro systems – silicon as a substrate material –
silicon compounds – silicon piezo resistors – photolithography – ion implantation – diffusion
– oxidation – chemical vapour deposition – sputtering – deposition by epitaxy – etching –
bulk micro manufacturing – surface micro machining – the liga process – micro system
design considerations – process design – design of silicon die for a micro pressure sensor –
computer aided design – micro system packaging – introduction to intelligence cad tool for
mems.
UNIT III REVIEW OF OPERATION OF SCR, TRIAC AND UJT.
Thyristor commutation techniques: introduction – natural commutation –
forced commutation – self commutation – impulse commutation – response pulse
commutation – external pulse commutation – load side commutation – line side commutation
– complementary commutation.
Controlled rectifiers – principle of phase controlled converter – single phase semi
converter – single phase series converter – three phase controlled rectifiers .
UNIT IV STATIC SWITCHES
Introduction – single phase ac switches – three phase ac switches – three phase
reversing switches – ac switches for bus transfer – dc switches – solid state relays.
AC VOLTAGE CONTROLLER
Introduction – principle of on/off control – principle of phase control – single phase
bi-directional controllers with resistive loads & inductive loads - cyclo converters – single
phase cyclo converters.
DC CHOPPERS :
Introduction – principles of step down operation – step down with rl load – principle
of step up operation.
SWITCH MODE REGULATORS
Buck regulator – boost regulator – buck boost regulator – cuk regulator.
UNIT V : INVERTERS :
Introduction – principle of operation – single phase bridge inverter –
three phase inverter. – Voltage control of single phase invertors .
POWER SUPPLIES :
Introduction – Dc Power Supplies – Switched Mode Dc Power Supplies
–Resonant Dc Power Supplies – Bi Directional Power Supplies - Ac Power Supplies – Ups
REFERENCE BOOKS :
1. MUHAMMED RASHID “POWER ELECTRONICS, CIRCUITS, DEVICES AND
APPLICATIONS”, PRENTICE HALL EDITION, II EDITION, 1999.
UNIT I OVERVIEW AND WORKING PRINCIPLES OF MEMS
Mems and micro systems – typical mems and micro system products – micro systems
and micro electronics – the multidisciplinary nature of micro system design and manufacture
– application examples of micro systems – micro sensors – micro actuation – mems with
micro actuators – micro accelerometers – micro fluidics.
Microsystems engineers apply the principles of electronic and mechanical systems to develop
new microelectromechanical systems (MEMS), devices, and novel applications of MEMS
devices. Some applications of MEMS devices include crash sensors, vehicle exhaust sensors,
pressure sensors for vehicle fuel-injection systems, micro-mirrors in video projection systems,
inkjet printer cartridges, and biosensors that can fit into a blood vessel and measure the levels of
oxygen, carbon dioxide, and blood pH. Microelectromechanical systems are used in the
automotive, aerospace, and health-care industries, and in industrial, consumer, and
telecommunications products.
The typical microsystem consists of microelectronics, the brains of the system, and
microelectromechanical systems that act as the eyes and arms of the system.
Microelectromechanical systems are built using thermal, magnetic, electromechanical, fluidic,
and optical devices like sensors and actuators. Sensors are devices that perceive useful
information and actuators are devices that act upon the perceived information by manipulating
themselves or other mechanical devices. These devices can range in size from less than the width
of a human hair to about 1 mm. Microsystems or MEMS can sense and control the environment
in which they are placed.
MEMS technology is an extension of integrated-circuit technology, and microsystems engineers
must be knowledgeable in fabrication techniques such as microlithography, chemical and plasma
etching, vapor deposition, and electroplating. Because MEMS devices are moving devices, the
microsystems engineer must have a working knowledge of materials science and how materials
act under fabrication and test conditions. Microsystems engineers design MEMS and MEMS
devices using computer-aided design and modeling software. They develop and are responsible
for every aspect of MEMS manufacturing processes and recommend equipment upgrades. In
addition, they troubleshoot equipment and make decisions about non-conforming product. Since
microsystems engineers work in integrated circuits fabrication laboratories, they write the
training and operating documents that laboratory personnel use. They also develop methods for
testing MEMS and MEMS devices and perform failure analysis.
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Work Environment
Most microsystems engineers work in
office buildings and laboratories where
devices and wafers are fabricated.
Many microsystems engineers work a
standard 40-hour week. At times,
deadlines or design standards may
bring extra pressure to a job, requiring
microsystems engineers to work longer
hours.
Training, Other
Qualifications
Watch this detailed video to learn about the various
applications for microsystems and MEMS devices
and how they are fabricated.
Microsystems engineers enter the occupation with a master's degree in electrical or mechanical
engineering, but some research positions require a PhD. Attending courses and professional
conferences enable the microsystems engineer to keep current with rapidly changing technology.
Education and Training
The minimum degree required for an entry-level position as a microsystems engineer is a
master's degree in electrical engineering, mechanical engineering, or physics. However, many
employers accept candidates with a bachelor's degree and three to five years of work experience
in microsystems engineering. A PhD is essential for engineering faculty positions and some
research and development programs, but it is not required for the majority of entry-level
engineering jobs. Many experienced engineers obtain graduate degrees in engineering or
business administration to learn new technology and broaden their education. Return to top of
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Other Qualifications
Microsystems engineers should be creative, inquisitive, analytical, and detail oriented. They
should be able to work as part of a team and to communicate well, both orally and in writing.
Communication abilities are becoming increasingly important as engineers interact more
frequently with specialists in a wide range of fields outside engineering.
Microsystems engineers who work for the federal government usually must be U.S. citizens.
Some engineers working for defense contractors need to hold a security clearance.
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On the Job
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Conduct harsh environmental testing, accelerated aging, device characterization, or field
trials to validate devices, using inspection tools, testing protocols, peripheral
instrumentation, or modeling and simulation software.
Validate fabrication processes for microelectromechanical systems (MEMS), using
statistical process control implementation, virtual process simulations, data mining, or
life testing.
Conduct analyses addressing issues such as failure, reliability, or yield improvement.
Conduct experimental or virtual studies to investigate characteristics and processing
principles of potential MEMS technology.
Conduct or oversee the conduct of prototype development or microfabrication activities
to ensure compliance to specifications and promote effective production processes.
Create schematics and physical layouts of integrated MEMS components and packaged
assemblies consistent with process, functional, and package constraints.
Develop formal documentation for MEMS devices, including quality assurance guidance,
quality control protocols, process control checklists, data collection, and reporting.
Develop or validate product-specific test protocols, acceptance thresholds, or inspection
tools for quality-control testing and performance measurement.
Develop or validate specialized materials characterization procedures, such as thermal
withstand, fatigue, notch sensitivity, abrasion, and hardness tests.
Devise MEMS production methods, such as integrated circuit fabrication, lithographic
electroform modeling, and micromachining.
Evaluate and select materials, fabrication methods, joining methods, surface treatments,
or packaging to ensure acceptable processing, performance, cost, and availability.
Investigate characteristics, such as cost, performance, and process capability, of potential
MEMS device designs, using simulation and modeling software.
Operate or maintain MEMS fabrication and assembly equipment, such as handling,
singulation, assembly, wire-bonding, soldering, and package sealing.
Propose product designs involving MEMS technology, considering market data or
customer requirements.
Refine final MEMS design to optimize design for target dimensions, physical tolerances,
and processing constraints.
Conduct acceptance tests, vendor-qualification protocols, surveys, audits, correctiveaction reviews, or performance monitoring of incoming materials and components to
ensure conformance to specifications.
Create or maintain formal engineering documents, such as schematics, bill of materials,
components and materials specifications, and packaging requirements.
Demonstrate miniaturized systems that contain components such as microsensors,
microactuators, or integrated electronic circuits fabricated on silicon or silicon carbide
wafers.
Develop and communicate operating characteristics or performance experience to other
engineers and designers for training or new product development purposes.
Develop and file intellectual property and patent disclosure or application documents
related to MEMS devices, products, and systems.
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Develop and verify customer documentation, such as performance specifications, training
manuals, and operating instructions.
Develop or implement MEMS processing tools, fixtures, gauges, dies, molds, and trays.
Identify, procure, or develop test equipment, instrumentation, and facilities for
characterization of MEMS applications.
Manage new product introduction projects to ensure effective deployment of MEMS
devices and applications.
Plan or schedule engineering research or development projects involving MEMS
technology.
Micro-Electro-Mechanical Systems, or MEMS, is a technology that in its most general form can
be defined as miniaturized mechanical and electro-mechanical elements (i.e., devices and
structures) that are made using the techniques of microfabrication. The critical physical
dimensions of MEMS devices can vary from well below one micron on the lower end of the
dimensional spectrum, all the way to several millimeters. Likewise, the types of MEMS devices
can vary from relatively simple structures having no moving elements, to extremely complex
electromechanical systems with multiple moving elements under the control of integrated
microelectronics. The one main criterion of MEMS is that there are at least some elements
having some sort of mechanical functionality whether or not these elements can move. The term
used to define MEMS varies in different parts of the world. In the United States they are
predominantly called MEMS, while in some other parts of the world they are called
“Microsystems Technology” or “micromachined devices”.
While the functional elements of MEMS are miniaturized structures, sensors, actuators, and
microelectronics, the most notable (and perhaps most interesting) elements are the microsensors
and microactuators. Microsensors and microactuators are appropriately categorized as
“transducers”, which are defined as devices that convert energy from one form to another. In the
case of microsensors, the device typically converts a measured mechanical signal into an
electrical signal.
Over the past several decades MEMS researchers and developers have demonstrated an
extremely large number of microsensors for almost every possible sensing modality including
temperature, pressure, inertial forces, chemical species, magnetic fields, radiation, etc.
Remarkably, many of these micromachined sensors have demonstrated performances exceeding
those of their macroscale counterparts. That is, the micromachined version of, for example, a
pressure transducer, usually outperforms a pressure sensor made using the most precise
macroscale level machining techniques. Not only is the performance of MEMS devices
exceptional, but their method of production leverages the same batch fabrication techniques used
in the integrated circuit industry – which can translate into low per-device production costs, as
well as many other benefits. Consequently, it is possible to not only achieve stellar device
performance, but to do so at a relatively low cost level. Not surprisingly, silicon based discrete
microsensors were quickly commercially exploited and the markets for these devices continue to
grow at a rapid rate.
More recently, the MEMS research and development community has demonstrated a number of
microactuators including: microvalves for control of gas and liquid flows; optical switches and
mirrors to redirect or modulate light beams; independently controlled micromirror arrays for
displays, microresonators for a number of different applications, micropumps to develop positive
fluid pressures, microflaps to modulate airstreams on airfoils, as well as many others.
Surprisingly, even though these microactuators are extremely small, they frequently can cause
effects at the macroscale level; that is, these tiny actuators can perform mechanical feats far
larger than their size would imply. For example, researchers have placed small microactuators on
the leading edge of airfoils of an aircraft and have been able to steer the aircraft using only these
microminiaturized devices.
A surface micromachined electro-statically-actuated micromotor fabricated by the MNX. This device is an
example of a MEMS-based microactuator.
The real potential of MEMS starts to become fulfilled when these miniaturized sensors,
actuators, and structures can all be merged onto a common silicon substrate along with integrated
circuits (i.e., microelectronics). While the electronics are fabricated using integrated circuit (IC)
process sequences (e.g., CMOS, Bipolar, or BICMOS processes), the micromechanical
components are fabricated using compatible "micromachining" processes that selectively etch
away parts of the silicon wafer or add new structural layers to form the mechanical and
electromechanical devices. It is even more interesting if MEMS can be merged not only with
microelectronics, but with other technologies such as photonics, nanotechnology, etc. This is
sometimes called “heterogeneous integration.” Clearly, these technologies are filled with
numerous commercial market opportunities.
While more complex levels of integration are the future trend of MEMS technology, the present
state-of-the-art is more modest and usually involves a single discrete microsensor, a single
discrete microactuator, a single microsensor integrated with electronics, a multiplicity of
essentially identical microsensors integrated with electronics, a single microactuator integrated
with electronics, or a multiplicity of essentially identical microactuators integrated with
electronics. Nevertheless, as MEMS fabrication methods advance, the promise is an enormous
design freedom wherein any type of microsensor and any type of microactuator can be merged
with microelectronics as well as photonics, nanotechnology, etc., onto a single substrate.
A surface micromachined resonator fabricated by the MNX. This device can be used as both a microsensor as
well as a microactuator.
This vision of MEMS whereby microsensors, microactuators and microelectronics and other
technologies, can be integrated onto a single microchip is expected to be one of the most
important technological breakthroughs of the future. This will enable the development of smart
products by augmenting the computational ability of microelectronics with the perception and
control capabilities of microsensors and microactuators. Microelectronic integrated circuits can
be thought of as the "brains" of a system and MEMS augments this decision-making capability
with "eyes" and "arms", to allow microsystems to sense and control the environment. Sensors
gather information from the environment through measuring mechanical, thermal, biological,
chemical, optical, and magnetic phenomena. The electronics then process the information
derived from the sensors and through some decision making capability direct the actuators to
respond by moving, positioning, regulating, pumping, and filtering, thereby controlling the
environment for some desired outcome or purpose. Furthermore, because MEMS devices are
manufactured using batch fabrication techniques, similar to ICs, unprecedented levels of
functionality, reliability, and sophistication can be placed on a small silicon chip at a relatively
low cost. MEMS technology is extremely diverse and fertile, both in its expected application
areas, as well as in how the devices are designed and manufactured. Already, MEMS is
revolutionizing many product categories by enabling complete systems-on-a-chip to be realized.
Nanotechnology is the ability to manipulate matter at the atomic or molecular level to make
something useful at the nano-dimensional scale. Basically, there are two approaches in
implementation: the top-down and the bottom-up. In the top-down approach, devices and
structures are made using many of the same techniques as used in MEMS except they are made
smaller in size, usually by employing more advanced photolithography and etching methods. The
bottom-up approach typically involves deposition, growing, or self-assembly technologies. The
advantages of nano-dimensional devices over MEMS involve benefits mostly derived from the
scaling laws, which can also present some challenges as well.
An array of sub-micron posts made using top-down nanotechnology fabrication methods.
Some experts believe that nanotechnology promises to: a). allow us to put essentially every atom
or molecule in the place and position desired – that is, exact positional control for assembly, b).
allow us to make almost any structure or material consistent with the laws of physics that can be
specified at the atomic or molecular level; and c). allow us to have manufacturing costs not
greatly exceeding the cost of the required raw materials and energy used in fabrication (i.e.,
massive parallelism).
A colorized image of a scanning-tunneling microscope image of a surface, which is a common imaging
technique used in nanotechnology.
Although MEMS and Nanotechnology are sometimes cited as separate and distinct technologies,
in reality the distinction between the two is not so clear-cut. In fact, these two technologies are
highly dependent on one another. The well-known scanning tunneling-tip microscope (STM)
which is used to detect individual atoms and molecules on the nanometer scale is a MEMS
device. Similarly the atomic force microscope (AFM) which is used to manipulate the placement
and position of individual atoms and molecules on the surface of a substrate is a MEMS device
as well. In fact, a variety of MEMS technologies are required in order to interface with the nanoscale domain.
Likewise, many MEMS technologies are becoming dependent on nanotechnologies for
successful new products. For example, the crash airbag accelerometers that are manufactured
using MEMS technology can have their long-term reliability degraded due to dynamic in-use
stiction effects between the proof mass and the substrate. A nanotechnology called SelfAssembled Monolayers (SAM) coatings are now routinely used to treat the surfaces of the
moving MEMS elements so as to prevent stiction effects from occurring over the product’s life.
Many experts have concluded that MEMS and nanotechnology are two different labels for what
is essentially a technology encompassing highly miniaturized things that cannot be seen with the
human eye. Note that a similar broad definition exists in the integrated circuits domain which is
frequently referred to as microelectronics technology even though state-of-the-art IC
technologies typically have devices with dimensions of tens of nanometers. Whether or not
MEMS and nanotechnology are one in the same, it is unquestioned that there are overwhelming
mutual dependencies between these two technologies that will only increase in time. Perhaps
what is most important are the common benefits afforded by these technologies, including:
increased information capabilities; miniaturization of systems; new materials resulting from new
science at miniature dimensional scales; and increased functionality and autonomy for systems.
Whether you are interested in developing MEMS or nano-devices, the MNX is the world’s
leading fabricator for these technologies and can help you with your development or research
project. Please contact us at engineering@mems-exchange.org or 703-262-5368 for more
information
The invention of the transistor and the integrated circuit marked the genesis of microelectronics
and set the stage for the unprecedented technological advances of the 20th century, which
impacted virtually every aspect of modern life. Indeed, it is said that no invention in the history
of humanity has so quickly spread throughout the world, or so profoundly pervaded so many
aspects of human existence as the microprocessor. The field of microelectronics has enabled
such life-altering breakthroughs as implantable cardiac pacemakers, personal computers,
wireless cellular telephones, optoelectronic-fiber networks, communication satellites and the
Internet.
ECE offers its graduate students many opportunities to work as Graduate Research Assistants or
Graduate Teaching Assists. Virtually all Ph.D. students receive funding support through teaching
or research.
Moving devices are ubiquitous. There could be even more if small
and powerful electric motors were available.
Encrea, jointly with the CRIM Lab, developed the micromotor with the highest torque to volume ratio.
(On the right, a 1.8 mm OD stepper motor over a coin).
UNIT II FABRICATION PROCESS OF MEMS
Materials for mems and micro systems – silicon as a substrate material –
silicon compounds – silicon piezo resistors – photolithography – ion implantation – diffusion
– oxidation – chemical vapour deposition – sputtering – deposition by epitaxy – etching –
bulk micro manufacturing – surface micro machining – the liga process – micro system
design considerations – process design – design of silicon die for a micro pressure sensor –
computer aided design – micro system packaging – introduction to intelligence cad tool for
mems.
Microelectromechanical systems (MEMS) (also written as micro-electro-mechanical,
MicroElectroMechanical or microelectronic and microelectromechanical systems) is the
technology of very small devices; it merges at the nano-scale into nanoelectromechanical
systems (NEMS) and nanotechnology. MEMS are also referred to as micromachines (in Japan),
or micro systems technology – MST (in Europe).
MEMS are separate and distinct from the hypothetical vision of molecular nanotechnology or
molecular electronics. MEMS are made up of components between 1 to 100 micrometres in size
(i.e. 0.001 to 0.1 mm), and MEMS devices generally range in size from 20 micrometres (20
millionths of a metre) to a millimetre (i.e. 0.02 to 1.0 mm). They usually consist of a central unit
that processes data (the microprocessor) and several components that interact with the outside
such as microsensors.[1] At these size scales, the standard constructs of classical physics are not
always useful. Because of the large surface area to volume ratio of MEMS, surface effects such
as electrostatics and wetting dominate volume effects such as inertia or thermal mass.
The potential of very small machines was appreciated before the technology existed that could
make them—see, for example, Richard Feynman's famous 1959 lecture There's Plenty of Room
at the Bottom. MEMS became practical once they could be fabricated using modified
semiconductor device fabrication technologies, normally used to make electronics. These include
molding and plating, wet etching (KOH, TMAH) and dry etching (RIE and DRIE), electro
discharge machining (EDM), and other technologies capable of manufacturing small devices. An
early example of a MEMS device is the resonistor – an electromechanical monolithic
resonator.[2][
In electronics, a wafer (also called a slice or substrate[1]) is a thin slice of semiconductor
material, such as a silicon crystal, used in the fabrication of integrated circuits and other
microdevices. The wafer serves as the substrate for microelectronic devices built in and over the
wafer and undergoes many microfabrication process steps such as doping or ion implantation,
etching, deposition of various materials, and photolithographic patterning. Finally the individual
microcircuits are separated (dicing) and packaged.
Several types of solar cell are also made from such wafers. On a solar wafer a solar cell (usually
square) is made from the entire wafer.
The piezoresistive effect describes change in the electrical resistivity of a semiconductor when
mechanical stress is applied. In contrast to the piezoelectric effect, the piezoresistive effect only causes
a change in electrical resistance, not in electric potential.
Photolithography (or "optical lithography")(or "UV lithography") is a process used in
microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light
to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or
simply "resist," on the substrate. A series of chemical treatments then either engraves the
exposure pattern into, or enables deposition of a new material in the desired pattern upon, the
material underneath the photo resist. For example, in complex integrated circuits, a modern
CMOS wafer will go through the photolithographic cycle up to 50 times.
Photolithography shares some fundamental principles with photography in that the pattern in the
etching resist is created by exposing it to light, either directly (without using a mask) or with a
projected image using an optical mask. This procedure is comparable to a high precision version
of the method used to make printed circuit boards. Subsequent stages in the process have more in
common with etching than with lithographic printing. It is used because it can create extremely
small patterns (down to a few tens of nanometers in size), it affords exact control over the shape
and size of the objects it creates, and because it can create patterns over an entire surface costeffectively. Its main disadvantages are that it requires a flat substrate to start with, it is not very
effective at creating shapes that are not flat, and it can require extremely clean operating
conditions.
Ion implantation is a materials engineering process by which ions of a material are accelerated in an
electrical field and impacted into a solid. This process is used to change the physical, chemical, or
electrical properties of the solid. Ion implantation is used in semiconductor device fabrication and in
metal finishing, as well as various applications in materials science research. The ions alter the elemental
composition of the target, if the ions differ in composition from the target, stop in the target and stay
there. They also cause much chemical and physical change in the target by transferring their energy and
momentum to the electrons and atomic nuclei of the target material. This causes a structural change, in
that the crystal structure of the target can be damaged or even destroyed by the energetic collision
cascades. Because the ions have masses comparable to those of the target atoms, they knock the target
atoms out of place more than electron beams do. If the ion energy is sufficiently high (usually tens of
MeV) to overcome the coulomb barrier, there can even be a small amount of nuclear transmutation.
Diffusion describes the spread of particles through random motion from regions of higher concentration
to regions of lower concentration. The time dependence of the statistical distribution in space is given
by the diffusion equation. The concept of diffusion is tied to that of mass transfer driven by a
concentration gradient. Diffusion is invoked in the social sciences to describe the spread of ideas.
Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate, where the
overlayer is in registry with the substrate. In other words, there must be one or more preferred
orientations of the overlayer with respect to the substrate for this to be termed epitaxial growth.
The overlayer is called an epitaxial film or epitaxial layer. The term epitaxy comes from the
Greek roots epi, meaning "above", and taxis, meaning "in ordered manner". It can be translated
"to arrange upon". For most technological applications, it is desired that the deposited material
form a crystalline overlayer that has one well-defined orientation with respect to the substrate
crystal structure (single-domain epitaxy).
Epitaxial films may be grown from gaseous or liquid precursors. Because the substrate acts as a
seed crystal, the deposited film may lock into one or more crystallographic orientations with
respect to the substrate crystal. If the overlayer either forms a random orientation with respect to
the substrate or does not form an ordered overlayer, this is termed non-epitaxial growth. If an
epitaxial film is deposited on a substrate of the same composition, the process is called
homoepitaxy; otherwise it is called heteroepitaxy.
Homoepitaxy is a kind of epitaxy performed with only one material. In homoepitaxy, a
crystalline film is grown on a substrate or film of the same material. This technology is used to
grow a film which is more pure than the substrate and to fabricate layers having different doping
levels. In academic literature, homoepitaxy is often abbreviated to "homoepi".
Heteroepitaxy is a kind of epitaxy performed with materials that are different from each other.
In heteroepitaxy, a crystalline film grows on a crystalline substrate or film of a different material.
This technology is often used to grow crystalline films of materials for which crystals cannot
otherwise be obtained and to fabricate integrated crystalline layers of different materials.
Examples include gallium nitride (GaN) on sapphire, aluminium gallium indium phosphide
(AlGaInP) on gallium arsenide (GaAs) or diamond or iridium[1].
Heterotopotaxy is a process similar to heteroepitaxy except for the fact that thin film growth is
not limited to two dimensional growth. Here the substrate is similar only in structure to the thin
film material.
Epitaxy is used in silicon-based manufacturing processes for BJTs and modern CMOS, but it is
particularly important for compound semiconductors such as gallium arsenide. Manufacturing
issues include control of the amount and uniformity of the deposition's resistivity and thickness,
the cleanliness and purity of the surface and the chamber atmosphere, the prevention of the
typically much more highly doped substrate wafer's diffusion of dopant to the new layers,
imperfections of the growth process, and protecting the surfaces during the manufacture and
handling.
PROPERTIES OF PRESSURE SEN
Pressure sensors and systems by Tekscan provide an array of
force sensitive cells that measure the pressure distribution
between virtually any two mating or contacting surfaces.
Tekscan's pressure sensors and systems can fill your tactile
pressure and force measurement needs by providing insight
into static and dynamic pressure events, helping you to
improve product design, reduce testing time, and perform
quality control inspections.
Accuracy
Better than ± 10%
Linearity
< ±3%
Repeatability
< ±3.5%
Hysteresis
< 4.5%
Drift per log time
< 5%
Lag Time
5 µsec
Spatial Resolution
Thinness
As fine as 0.025" x 0.025" (0.
0.004" (0.1 mm)
Tekscan pressure sensors and systems are simple to use and
include pressure sensors, sensor scanning electronics, and
software. The pressure sensors and systems enable you to
optimize design choices by providing high-resolution
displays of tactile pressure data in real-time or 2-D and 3-D
images.
Applications that use Pressure Sensors
Automotive Applications
Use pressure sensors to capture tire footprints for various
passenger and truck tires
Ergonomic Grip Pressure Measurement
Measure pressure distribution on different parts of the hand and
fingers to improve product design
Mattress & Seating Design
Pressure sensors provide valuable feedback when evaluating
the comfort of support surfaces
Pinch Pressure Measurement
Achieve evenly distributed pressure across a roller surface
Developed with the R&D market in mind, the PlasmaPro Estrelas100 offers the ultimate in
process flexibility. Nano
and micro structures can be realised as the hardware has been designed with the ability to run
Bosch™ and cryo etch technologies in the same chamber.
From smooth sidewall processes to high etch rate cavity etches, the PlasmaPro Estrelas100 has
been designed to ensure that the wide range of MEMS applications can be realised without the
need to change the chamber hardware.
UNIT III REVIEW OF OPERATION OF SCR, TRIAC AND UJT.
Thyristor commutation techniques: introduction – natural commutation –
forced commutation – self commutation – impulse commutation – response pulse
commutation – external pulse commutation – load side commutation – line side commutation
– complementary commutation.
Controlled rectifiers – principle of phase controlled converter – single phase semi
converter – single phase series converter – three phase controlled rectifiers .
A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type
material. They act as bistable switches, conducting when their gate receives a current trigger, and
continue to conduct while they are forward biased (that is, while the voltage across the device is
not reversed).
Some sources define silicon controlled rectifiers and thyristors as synonymous.[1]
Other sources define thyristors as a larger set of devices with at least four layers of alternating N
and P-type material, including
The commutation cell is the basic structure in power electronics. It is composed of an electronic
switch (today a high-power semiconductor, not a mechanical switch) and a diode. It was
traditionally referred to as a chopper, but since switching power supplies became a major form of
power conversion, this new term has become more popular.
The purpose of the commutation cell is to "chop" DC power into square wave alternating current.
This is done so that an inductor and a capacitor can be used in an LC circuit to change the
voltage. This is in theory a lossless process, and in practice efficiencies above 80-90% are
routinely achieved. The output is then usually run through a filter to produce clean DC power.
By controlling the on and off times (the duty cycle) of the switch in the commutation cell, the
output voltage can be regulated.
This basic principle is the core of most modern power supplies, from tiny DC-DC converters in
portable devices to huge switching stations for high voltage DC power transmission
To maintain voltage stability in electric power systems, self-commutated static VAr compensators (selfcommutated SVCs) employing high power gate turn-off thyristors (GTOs) have been developed. This
paper presents a lower harmonic two-pulse PWM control technique which can decrease the harmonics
in output voltage by selecting switching angles. Because of the lower GTO switching frequency, high
efficiency power converters can be obtained. The decreased harmonics by the proposed PWM control
were confirmed by numerical analysis and experiments using small-scale equipment. The technique has
been applied to a 50 MVA self-commutated SVC which has been installed in the Shinshinano substation
of Tokyo Electric Power Company, and field testing of this equipment is now in progress.