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Microengineering & MicrotechnologyLecture 2:

The Big Picture – MiniaturisedProf. Mark Tracey

6ENT1022 [MTECH]Semester B 2012

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Introduction

• Microtechnology is broad and omnipresent

• You may not realise that you have already studied aspects of it

• It draws upon almost all aspects of technology and science

• This lecture is intentionally broader than the more detailed lectures to follow

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Approach of Lecture

• To introduce Microengineering by referring particularly to the quite recent history of Microelectronics: the first, and most successful, Microtechnology

• Review the engineering approaches adopted to overcome problems and hence better understand techniques we know today

• Many of the ‘tricks’ adopted by earlier technologists may still be applicable or may inspire us to develop further ‘tricks’ derived from them

• The Microelectronics industry has exemplified the effects of scaling as enshrined in Moore’s Law

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What is Microtechnology ?

• The enhancement of, or unlocking of, physical effects that do not manifest strongly or cannot be directly exploited, at the macro scale

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What is Microtechnology?

• Facilitation of complexity and the prospect of ‘intelligence’ in compact form

• Integrated Circuits: Intel’s Pentium P6 compared to Tommy Flower’s Colossus

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What is Microtechnology?

•Economy of Manufacture via ‘standard process’

• Standard process is analogous to a high-level programming language

• Moore’s Law

Gordon Moore, co-founder Intel Inc.

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Is it Just Academic Research?

• Global IC industry physical ‘chip’ market is $300 Billion per annum (world GDP $63,000 Billion) => 0.5% world GDP

• PV panels are ‘large format’ microengineering and have a $50Billion

• Inkjet printer cartridges are microfluidics with a $21 Billion per annum global market

• Global MEMS market is $9 Billion (2010) with 14% compound projected growth

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Is it Just Academic Research?

• Flat panel displays are ‘large format’ microengineering

• Consumer electronic orientation and displacement sensors are MEMS: Nintendo Wii Remote and Apple iPhone (accelerometer) and Playstation 3 Dualshock controller (three axis gyroscope)

• Automotive engine management uses MEMS pressure sensors, Electronic Stability Systems use MEMS gyros

• Consumer sphygmomanometers (blood pressure monitors) use pressure sensors

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Production MEMS Chip

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Patterning Planar Surfaces: Structuring

• lithography – printing whole images (text, graphics, microchannels, microchip metallisation), or steps in a sequence leading to them, in one go

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Resist Layers and Etching

• Daniel Hopfer’s technique, circa 1500, deposited a protective, wax-like layer (to us ‘resist’) over a metal plate, manually scrapped-away the layer where metal was to be removed, and immersed the metal in acid

• Hobbyist printed circuit boards can be made in a closely related manner

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Photolithography: Hands off!

• Hopfer’s techniques required manual removal of resist: laborious, error prone and macro-scale

• Photography provided the next steps: photomasks

• Early photolithography: Nicéphore Niépce, Chalon-sur-Saône, 1826

• Collodion Process (negative glass plates) : Frederick Scott Archer, likely of Hertford, 1848. These are photomasks!

• Photomasks allow replication: one mask, multiple patterned substrates

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Not all MEMS is small..

Plasma screen photomask

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Tools: Mask Generation

circa 1970: ‘ruby-lith’ mask design Photo-reduction onto mask plate

LASI layout editor 2011 e-beam mask generator

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Tools: Patterning

Suss MJB4 4 inch diameter wafer photomask exposure and alignment

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Printed Circuits: Structured Layers Commence

• Printed Circuit Board: Paul Eisler: 1943

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Additive, Subtractive and Other Processes

• PCB manufacture is ‘subtractive’: material is removed from a substrate by, in this case, ‘wet etching’

• In MEMS this is also known as ‘bulk micromachining’

• Microelectronics is generally additive (ignoring doping): for instance deposition and patterning of metal interconnects (a miniature PCB)

• In MEMS chip and wafer bonding (adhesive free) processes are sometimes employed to structure vertically

• MEMS also employs replication techniques such as micromolding

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Additive Processes

• ‘screen printing’ is used to apply solder paste in surface mount PCB assembly

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Additive Processes

• A number of techniques allow deposition of thin material layers such as metals from liquid, or more typically, vapour phase

• Metal deposition used to be normal in filament light bulbs: the darkening of the bulb-glass is metal deposition

• Layers normally need to be ‘patterned’. This can be by etching as we have seen, or by other techniques: such as ‘lift off’, as shown here

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Subtractive Processes for Silicon

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How does this relate to Microelectronics?

• Shockley, Bardeen, Brittain produced first transistor at Bell Labs in 1947• Joint Nobel Prize for Physics in 1956• Shockley Semiconductor formed , but eight key staff left to form Fairchild• Fairchild founders included Gordon Moore, Robert Noyce and Andy Grove• Fairchild produce first silicon IC in 1960 (TI produced a germanium IC in ‘58)• Noyce, Moore and Grove founded Intel in 1968• Intel 4004, the first microprocessor in 1970• Intel now produce 82% of the world’s microprocessors

The first Fairchild silicon IC: a 4 transistor flip-flop

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Intel 4004 The First Microprocessor: 1970

Grove, Noyce, Moore: Intel Intel 4004, 4 bit microprocessor

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What has all this got to do with MEMS?

•Two things:

1. Technological infrastructure

• MEMS originated as ‘silicon micromachining’, leveraged by existing silicon processing techniques, tools and infrastructure

• Much commonality still exists especially for photolithography

• If the microelectronics industry had not existed, MEMS would probably never have started

2. Innovative Culture

• microelectronics was, and is, the core of ‘Silicon Valley’

• The ‘university spin-out’ venture-capital model of Silicon Valley is the model for MEMS start-ups

• microelectronics required multidisciplinarity and lateral thinking: so does MEMS

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Isn’t Nanotechnology the New, Cool Thing?

• For politicians and journalists, yes. For engineers, not quite yet.

• Nanotechnology primarily concerns ‘bottom-up’ techniques treating atoms and molecules as building-blocks, whereas Microtechnology is predominantly top-down

• Behaviour of Nanotechnology is governed by nanoscale effects such as molecular bonding forces and indeed quantum mechanical behaviour

• Deposition of layers upon, and chemical modification of, component surfaces is arguably ‘nano’ but widely used in ‘micro’.

• Nanobiology is likely to be ‘the big thing’ of C21

• However, microelectronics breaks several of these assertions: it’s ‘nano-now’ and top-down: enough money can push technology a long way, fast...

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Scaling: Large Effects of Small Things(or, conversely, Small Effects of Large Things)

• Example from microfluidics, consider the Hagen-Poiseuille equation governing laminar liquid flow in pipes:

Where:

Q is volumetric flow rate of liquid; ∆P is pressure drop L is tube length r is tube radius µ is dynamic viscosity

• Small conventional tubing: radius circa 0.5mm• UH microfabrication of a 5um hydraulic radius channel is relatively easy• ratio of radii: 102

• ratio of flow rates: 108 !

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Scaling-up Scaled-down: Economy of Scale

• Intel’s 4004 in 1970 employed 10µm ‘design rules’ (all features are multiples of this dimension) with 2.4x103 transistors on a 144mm2 die;

• Intel’s just released ‘Ivy Bridge’ processor employs 22nm design rules and has 1.4x109 transistors on a 172mm2 die

Interestingly, Colossus had 1500 valves (do you know what a valve is?)

• Minimum definable area has scaled-down by 206x103 times

• Transistor count has scaled-up by a very comparable 583x103 times

• Increase in transistor count is overwhelmingly due to feature size reduction

• This process is the basis of Moore’s Law:

‘transistor count doubles every two years’

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Scaling-up the Scaled-down: Moore’s Law

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Complexity

• Complexity, in terms of transistors per unit area, has scaled similarly

• Calculations per unit area scale by ∆(transistors/unit area) x ∆ clock speed

• Intel 4004 Fck ≈ 0.75MHz

• Current Intel clock speed ≈ 3000MHz

• Fck has scaled by 4x103 during the same period

• Calculations / unit area / unit time has increased by

(583x103) x (4x103) = 2.3x107 times

• However, in reality, calculation capacity scales in a more complex way with transistor count depending upon processor architecture.

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‘Cheap-fast’ Microengineering

• Whilst silicon provided the initial impetus, it is expensive to access.

• Often silicon’s properties (semiconducting in particular) aren’t required.

• Microcasting of silicone elastomers has become very popular in microfluidics and is used extensively at UH

• Chrome photomasks cost, at a minimum, £300.

• High resolution, laser-written, plastic film printing can be (and is at UH) used for features above circa 20µm for a few pounds per mask.

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‘Cheap-fast’ Microengineering

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Structural Photoresist ’SU8’

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PDMS Elastomeric Micropump chips

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PDMS Elastomeric Chips: Micro-pneumatics

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Combining Microstructuring with CNC

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Dean-flow Particle Separator

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Conclusions

• Microtechnology is a very diverse group of applications and techniques

• In fact there are arguably as many as in all of macro technology

• Certain areas have advanced amazingly, in particular Microelectronics

• Despite the apparent gap in sophistication between advanced ICs and ‘cheap-fast’ prototype microfluidics, both are ‘leading edge’

• Universal ‘design rules’ don’t, in general, exist: good engineering principles, scientific fundamentals and ingenuity are key.

• Multidisciplinary is the norm