Class 4. Fundamentals of Microfabrication-Some History

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Class 4. Fundamentals of Microfabrication-Some
History

• Dr. Marc Madou,
• 2012 , UCI

http//www.almaden.ibm.com 80/vis/stm/gallery.htm
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From ICs to MEMS and NEMS
http//www.almaden.ibm.com 80/vis/stm/gallery.htm
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NovaSensor Accelerometer
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From ICs to MEMS and NEMS
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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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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
  machining methodologies
• Biomimetics
• A few concluding words about manufacturing methods

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Definitions of ICs

• The transistor was invented 1948 by three Bell
  Laboratory engineers and physicists. John Bardeen
  was the physicist, Walter Brattain the
  experimentalist, and William Shockley, who became
  involved later in the development, was the
  instigator and idea man. The team won the 1956
  Nobel Prize in physics for their efforts.  The
  transistor demonstrated for the first time that
  amplification in solids was possible.

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Definitions of ICs
Diodes
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Definitions of ICs

• There are many different types of transistors,
  but the basic theory of their operation is all
  the same. The three elements of the two-junction
  transistor are (1) the EMITTER, which gives off,
  or emits," current carriers (electrons or holes)
  (2) the BASE, which controls the flow of current
  carriers and (3) the COLLECTOR, which collects
  the current carriers.

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Definitions of ICs

• The arrow always points in the direction of hole
  flow, or from the P to N sections, no matter
  whether the P section is the emitter or base. On
  the other hand, electron flow is always toward or
  against the arrow, just like in the junction
  diode.

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Definitions of ICs

• A forward biased PN junction is comparable to a
  low-resistance circuit 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 I2R) and
  assuming current is held constant, you can
  conclude 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.

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Definitions of ICs
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Definitions of ICs

• The term transistor is derived from the words
  TRANSfer and resISTOR. 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
  by controlling the flow of current carriers
  through its semiconductor materials.

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Definitions of ICs

• Types of transistors
• Bipolar Junction Transistor (BJT)
• MOS transistor see Metal Oxide Semiconductor
  (MOS) Capacitor

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Definitions of ICs

• A chip or 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 a unit. The first
  integrated circuit was developed in the 1950s by
  Jack Kilby of Texas Instruments and Robert Noyce
  of Fairchild Semiconductor.

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Definitions of ICs

• Integrated circuits are often classified by the
  number of transistors and 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 electronic components per chip
• ULSI (ultra large-scale integration) More than 1
  million electronic components per chip

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Definition of MEMS
Sandia, Poly-Si steam engine

• 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.

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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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Definition of MEMS
Isometric Scaling
LIGA
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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 (batch concept)
• Improved accuracy and reliability
• Minimal invasive ( e.g. mosquito project)
• Do we have a choice? (see next viewgraph- - the
  Law of Accelerating Returns)

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Why miniaturization?

• Evolution (sophistication) of life-forms or
  technology speeds up because they are build on
  their own recorded degree of order. Ray Kurzweil
  calls this The Law of Accelerating Returns
• This Law of Accelerating Returns gave us ever
  greater order in technology which led to
  computation -- the essence of order.
• For life-forms DNA provides the record. In the
  case of technology it is the ever improving
  methods to record information.
• Ray Kurzweil in The Age of Spiritual
• Machines

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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 of silicon roughly
  doubled every year since the technology was
  invented. This relation, first mentioned in 1964
  by semiconductor engineer Gordon Moore (who
  co-founded Intel four years later) held until the
  late 1970s, at which point 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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Why miniaturization?
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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.

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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

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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 precision in a series of
  repetitive measurements (also often given as ??
  with N the number of data, xi is each individual
  measurement, and x the mean of all
  measurements.
• The value xi - is called the residual for each
  measurement.

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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 with mechanical
  machining. The relative tolerance on those
  dimensions though is not so good on a 100 µm
  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 small
  as we can with lithography.
• The above argument might decide your choice of
  machining approach 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) is excellent
  for small absolute tolerances
• For relative tolerances, ultra-fine diamond
  milling is better
• In some cases we might want to keep our
  micromachine somewhat larger to optimize relative
  tolerances (see Mass Spectrometer example)

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Relative vs. absolute tolerance in manufacturing

• Lawrence Livermore National Laboratories (LLNL),
  at one point used LIGA to make the next
  generation mass spectrometer
• The picture below shows an array of holes in
  PMMA to electroplate Ni posts (poles)
• The diameter of each hole is 40 µm !!

• A larger mass spectrometer is machined with
  traditional ultra fine diamond milling at JPL
• Relative tolerance is better than 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 small devices
  involve top-down approaches. Starting from larger
  blocks of material we make smaller and smaller
  things. Nature works the other way, i.e., from
  the bottom-up. All living things are made atom by
  atom , molecule by molecule from the small to
  the large. As manufacturing of very small things
  with top-down techniques (NEMS or nano
  mechanical devices) become too expensive or hit
  other 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
  the larger world (see Icarus). Background
  reading Cats Paws and Catapults by Steven Vogel
  (Efficiency of mechanical systems in biology and
  human engineering in the macro-world).

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Merging of two approaches Top-down and
bottom-up machining methodologies

• On the nanoscale nature is outperforming us by
  far (perhaps because nature has had more time
  working towards biological molecules/ cells than
  towards making larger organisms such as trees and
  us).
• Further miniaturization might be inspired by
  biology but will most likely be different again
  from nature -- the drivers for human and
  natural manufacturing techniques are very
  different.

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Merging of two approaches Top-down and
bottom-up machining methodologies
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Merging of two approaches Top-down and
bottom-up machining methodologies --NEMS

• MEMS little brother is NEMS, the top-down
  approach to nano devices. This biomimetic
  approach to nano devices I like to call
  nanochemistry. To succeed in the latter we will
  need
• self-assembly and directed assembly (e.,g, using
  electrical fields -see next viewgraph)
• massive parallelism
• understanding of molecular mechanisms --
  chemomechanics
• engineers/scientists who understand wet and
  dry disciplines

Seeman
Montemagno
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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 not only
  as sensors but also as actuators and building
  blocks (Genetic engineer NAs and proteins-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 of
  becoming 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
  clearest fashion how a transistor works and why
  it is so important in applications all around us
  (figure is ok but 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 µm long Ag
  line (1 µm wide and 1 µm heigh). If we put one
  atom down per second (e.g., using an STM) how
  long will it take to finish this Ag line ?