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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

http://www.almaden.ibm.com/http://www.almaden.ibm.com/

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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/animations

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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/

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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 ?