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Fundamentals of Microfabrication
Fall 2013
Prof. Marc MadouMSTB 120
http://www.almaden.ibm.com:
80/vis/stm/gallery.htmlNovaSensor (Now GE Sensing)
Accelerometer
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Fundamentals of Microfabrication
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Content
Definitions of ICs
MEMS
Why miniaturization ?
Taxonomy of Microfabrication Processes
Accuracy/precision
Accuracy/precision and standard deviation
Relative vs. absolute tolerance in manufacturing
Merging of two approaches: Top-down and bottom-up machiningmethodologies
Biomimetics
A few concluding words about manufacturing methods
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From ICs to MEMS and NEMS
http://www.almaden.ibm.com:
80/vis/stm/gallery.htmlNovaSensor (Now GE Sensing)
Accelerometer
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From ICs to MEMS and NEMS
Todays car differs from those of the immediate post-war years on
a number of counts. But suppose for a moment that the automobile
industry had developed at the same rate as computers and over the
same period: how much cheaper and more efficient would current
models be? Today you would be able to buy a Rolce-Royce for $
2.15, it would do three million miles to the gallon, and it would
deliver enough power to drive the Queen Elizabeth II. And if you
were interested in miniaturization, you could place half a dozen of
them on a pinhead.
Christopher Evans, 1979
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The transistor was invented 1948by three Bell Laboratory engineersand physicists. John Bardeen wasthe physicist, Walter Brattain the
experimentalist, and WilliamShockley, who became involvedlater in the development, was theinstigator and idea man. The teamwon the 1956 Nobel Prize in
physics for their efforts. Thetransistor demonstrated for thefirst time that amplification insolids was possible.
Definitions of ICs
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Definitions of ICs
Diodes
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There are many different typesof transistors, but the basictheory of their operation is allthe same. The three elements of
the two-junction transistor are(1) the EMITTER, which givesoff, or emits," current carriers(electrons or holes); (2) theBASE, which controls the flow
of current carriers; and (3) theCOLLECTOR, which collectsthe current carriers.
Definitions of ICs
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The arrow always points in the
direction of hole flow, or from
the P to N sections, no matter
whether the P section is theemitter or base. On the other
hand, electron flow is always
toward or against the arrow,
just like in the junction diode.
Definitions of ICs
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A forward biased PN junction is comparable to a low-resistancecircuit element because it passes a high current for a given voltage.
In turn, a reverse-biased PN junction is comparable to a high-
resistance circuit element. By using the Ohm's law formula for
power (P = I2
R) and assuming current is held constant, you canconclude that the power developed across a high resistance is greater
than that developed across a low resistance. Thus, if a crystal were to
contain two PN junctions (one forward-biased and the other reverse-
biased), a low-power signal could be injected into the forward-biased
junction and produce a high-power signal at the reverse-biased
junction. In this manner, a power gain would be obtained across the
crystal. This concept is the basic theory behind how the transistor
amplifies.
Definitions of ICs
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Definitions of ICs
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The term transistor is derived from the words TRANSfer andresISTOR. This term was adopted because it best describes the
operation of the transistor - the transfer of an input signal current
from a low-resistance circuit to a high-resistance circuit.
Basically, the transistor is a solid-state device that amplifies bycontrolling the flow of current carriers through its semiconductor
materials.
Definitions of ICs
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Types of transistors:
Bipolar Junction
Transistor (BJT)
MOS transistor [seeMetal Oxide
Semiconductor (MOS)
Capacitor]
Definitions of ICs
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A chipor an integrated circuit (IC) is a small electronic device
made out of a semiconductor material. The integrated circuit
consists of elements inseparably associated and formed on or
within a single SUBSTRATE (mounting surface). In other words,
the circuit components and all interconnections are formed as aunit.The first integrated circuit was developed in the 1950s by
Jack Kilby of Texas Instrumentsand Robert Noyce of Fairchild
Semiconductor.
Definitions of ICs
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Integrated circuits used to be classified by the number of transistorsand other electronic components they contain:
SSI (small-scale integration):Up to 100 electronic components per chip
MSI (medium-scale integration):From 100 to 3,000 electronic components per chip
LSI(large-scale integration):From 3,000 to 100,000 electronic components per chip
VLSI(very large-scale integration):From 100,000 to 1,000,000 electroniccomponents per chip
ULSI(ultra large-scale integration):More than 1 million electronic components perchip
------------------------------------------------------------------------------------------------------------
WSI (Wafer-scale integration): Is a system of building very-large integrated circuitsthat uses an entire silicon wafer to produce a single "super-chip".
SoC or SOC( A system-on-a-chip): This is an integrated circuit in which all thecomponents needed for a computer or other system are included on a single chip.
3D-IC (A three-dimensional integrated circuit): this has two or more layers ofactive electronic components that are integrated both vertically and horizontally into a
single circuit.
Definitions of ICs
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Definition of MEMS
Micro electromechanical systems (MEMS), or micromachining (also micro-
manufacturing and microfabrication), in the narrow sense, comprises the use of
a set of manufacturing tools based on batch thin and thick film fabrication
techniques commonly used in the integrated circuit industry or IC industry.
This involved originally mainly Si based mechanical devices.
DARPA: Hybrid Insect Micro
Electromechanical Systems (HI-MEMS)
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Definition of MEMS
MEMS: Micro electro mechanical systems. In recent years, it has become obvious that Si
is not always the right substrate, that batch is often not good enough and that a
modular approach is sometimes better than an integrated one. This has especially
become clear in the case of biomedical applications (see BIOMEMS course). The
science of miniaturization has become a much more appropriate name than MEMS
and it involves a good understanding of the intended application, scaling laws,
different manufacturing methods and materials .
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Why miniaturization?
Minimizing energy and materials use in manufacturing Redundancy and arrays
Integration with electronics, simplifying systems (e.g., single point vs. multipoint
measurement)
Reduction of power budget
Faster devices
Increased selectivity and sensitivity
Wider dynamic range
Exploitation of new effects through the breakdown of continuum theory in the
microdomain
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Why miniaturization?
Cost/performance advantages
Improved reproducibility (batchconcept)
Improved accuracy and
reliability Minimal invasive ( e.g.
mosquito project)
Do we have a choice? (see nextviewgraph- - the Law ofAccelerating Returns)
probiscus is about 75 m
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Evolution (sophistication) of life-forms or technology speeds up becausethey are build on their own recorded degree of order. Ray Kurzweil callsthis The Law of Accelerating Returns*
This Law of Accelerating Returns gave us ever greater order in technologywhich led to computation -- the essence of order.
For life-forms DNA provides the record. In the case of technology it is theever improving methods to record information.
*Ray Kurzweil in The Age of Spiritual
Machines
Why miniaturization?
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Why miniaturization?
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Why miniaturization?
Moores law (based on a temporary methodology i.e.,
lithography) is only an example of the Law of Accelerating
Returns. Beyond lithography we may expect further
progress in miniaturization based on DNA, quantum
devices, AFM lithography, nanotubes, etc.
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Why miniaturization?
Moores Law: The amounts of information storable on a given amount ofsilicon roughly doubled every year since the technology was invented. Thisrelation, first mentioned in 1964 by semiconductor engineer Gordon Moore(who co-founded Intel four years later) held until the late 1970s, at whichpoint the doubling period slowed to 18 months. The doubling period remained
at that value up to late 1999. Moore's Law is apparently self-fulfilling.
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Taxonomy of Microfabrication Processes
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Accuracy /precision
Accuracy is the degree of
correctness with which a
measuring system yields the
true value of a measured
quantity (e.g. bulls eye).
Accuracy is typically described
in terms of a maximum
percentage of deviation expected
based on a full-scale reading.
http://ull.chemistry.uakron.
edu/analytical/animations/
http://ull.chemistry.uakron.edu/analytical/animationshttp://ull.chemistry.uakron.edu/analytical/animationshttp://ull.chemistry.uakron.edu/analytical/animationshttp://ull.chemistry.uakron.edu/analytical/animations7/24/2019 Class1. 2013
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Accuracy/precision
Precision is the difference
between the instruments
reported values during
repeated measurements of
the same quantity Precision is typically
determined by statistical
analysis of repeated
measurements
http://ull.chemistry.uakron.
edu/analytical/animations/
http://ull.chemistry.uakron.edu/analytical/animations/http://ull.chemistry.uakron.edu/analytical/animations/http://ull.chemistry.uakron.edu/analytical/animations/http://ull.chemistry.uakron.edu/analytical/animations/7/24/2019 Class1. 2013
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Accuracy/precision
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Accuracy, precision and standard deviation
A measurement can be precise, but
may not not be accurate.
The standard deviation (s) is a
statistical measure of the precisionin a series of repetitive
measurements (also often given as
)with N the number of data, xi is
each individual measurement, and xthe mean of all measurements.
The value xi- is called the residual
for each measurement.
X
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Relative vs. absolute tolerance in manufacturing
Lithography is excellent for achieving small absolute tolerances - -we can make much smaller devices with lithography than withmechanical machining. The relative tolerance on those dimensionsthough is not so good; on a 100 m line we might perhaps achieve 1%. In mechanical machining terms this does not even qualify as
precision machining ! For a small relative tolerance, ultra-fine diamond milling is better.
Can be better than 0.01 %. Of course we cannot make things as smallas we can with lithography.
The above argument might decide your choice of machiningapproach or decide the size of the device you want to make.
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Relative vs. absolute tolerance in
manufacturing Lithography (e.g. Si-
micromachining) isexcellent for smallabsolute tolerances
For relative tolerances,
ultra-fine diamond millingis better
In some cases we mightwant to keep ourmicromachine somewhat
larger to optimize relativetolerances (see MassSpectrometer example)
10 km1 km100 m10 m1 m10 cm1 cm1 mm100 m10 m1 m0.1 m0.01 m1 nm1Absolute sizeAbsolute tolerancePrecision Machining Application DomainLinear dimensionLinear dimension0.01Relative ToleranceCityHouseArmOptic
alfer
!irusAtomRelative tolerances for building
a house and a lithography basedmicromachine
"acteria1001 m1 c100 #1 #0.01#mPrecision Machining1%100 %10 %0.1 %0.0001 %0.01
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Relative vs. absolute tolerance in manufacturing
Lawrence LivermoreNational Laboratories(LLNL), at one point usedLIGA to make the nextgeneration massspectrometer
The picture below shows anarray of holes in PMMA toelectroplate Ni posts (poles)
The diameter of each hole is40 m !!
A larger mass spectrometeris machined with
traditional ultra fine
diamond milling at JPL
Relative tolerance is betterthan with the LIGA
machined one, so its
performance is better
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Relative vs. absolute tolerance in
manufacturing
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Merging of two approaches: Top-down and bottom-
up machining methodologies
Most human manufacturing methods of smalldevices involve top-down approaches. Startingfrom larger blocks of material we make smaller andsmaller things. Nature works the other way, i.e.,from the bottom-up. All living things are madeatom by atom , molecule by molecule; from the
small to the large. As manufacturing of very smallthings with top-down techniques (NEMS or nanomechanical devices) become too expensive or hitother barriers we are looking at nature for guidance(biomimetics).
Nature and mankind have developed competitive
manufacturing methods on the macro level (e.g.,steel versus bone). Biomimetics mostly failed in thelarger world (see Icarus). Background reading:Cats Paws and Catapults by Steven Vogel(Efficiency of mechanical systems in biology andhuman engineering in the macro-world).
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Merging of two approaches: Top-down and
bottom-up machining methodologies
On the nanoscale nature isoutperforming us by far (perhapsbecause nature has had more timeworking towards biologicalmolecules/ cells than towards
making larger organisms such astrees and us).
Further miniaturization might beinspired by biology but will mostlikely be different again fromnature -- the drivers for human
and natural manufacturingtechniques are very different.
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Merging of two approaches: Top-down and
bottom-up machining methodologies
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Seeman
Eigler
Montemagno
Merging of two approaches: Top-down and
bottom-up machining methodologies --NEMS
MEMS little brother is NEMS, the top-down approach to nano devices. Thisbiomimetic approach to nano devices Ilike to call nanochemistry. To succeed inthe latter we will need :
self-assembly and directed assembly(e.,g, using electrical fields -see nextviewgraph)
massive parallelism
understanding of molecularmechanisms -- chemomechanics
engineers/scientists who understandwet and dry disciplines
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Merging of two approaches: Top-down and
bottom-up machining methodologies --NEMS
Example nano chemistry approaches:
Natural polymers: e.g., NAs and proteins notonly as sensors but also as actuators and
building blocks (Genetic engineer NAs andproteins-rely on extremophiles for guidance)
Mechanosynthesis
NEMS/biology hybrids --to learn only
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Biomimetics
Bimimetics:
Many examples in nature provide hints
for future manufacturing methods but as
stated earlier the purpose for their
development is different from the
reasons for human manufacturing
methods (e.g., teeth and sea shells might
be excellent strong building materials
but their growth is typically way too
slow to be attractive for human
manufacturing)
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A few concluding words about manufacturing
methods
Serial versus batch versus
continuous manufacturing
methods
Projected versus truly 3D
Additive process versus
subtractive process
Top-down versus bottom-
up
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Something to think about
Looking back at the worst times, it always seems that they were times in
which there were people who believed with absolute faith and absolute
dogmatism in something. And they were so serious in this matter that
they insisted that the rest of the world agree with them. And then they
would do things that were directly inconsistent with their own beliefs
in order to maintain that what they said was true.
From Richard P. Feynman in The Meaning of it All.
If in the course of these lectures I can make you doubt most of the things
you have come to believe then I probably put you on the path ofbecoming a true scientist/engineer.
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Something to think about
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Homework
Describe to a 12 year old, in the shortest and clearestfashion how a transistor works and why it is soimportant in applications all around us (figure is okbut words are required).
Characterize using the following criteria:
projected versus 3D, serial, batch or continuous
top-down versus bottom-up
Laser machining
Mechanical machining
E-beam machining and plastic molding.
Calculate the number atoms in a 100 m long Agline (1 m wide and 1 m heigh). If we put oneatom down per second (e.g., using an STM) howlong will it take to finish this Ag line ?