Microengineering & Microtechnology Lecture 2: The Big Picture – Miniaturised Prof. Mark Tracey 6ENT1022 [MTECH] Semester B

Introduction 2 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

Approach of Lecture 3 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

What is Microtechnology ? 4 The enhancement of, or unlocking of, physical effects that do not manifest strongly or cannot be directly exploited, at the macro scale

What is Microtechnology? 5 Facilitation of complexity and the prospect of ‘intelligence’ in compact form Integrated Circuits: Intel’s Pentium P6 compared to Tommy Flower’s Colossus

What is Microtechnology? 6 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.

Is it Just Academic Research? 7 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

Is it Just Academic Research? 8 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

Production MEMS Chip 9

Patterning Planar Surfaces: Structuring 10 lithography – printing whole images (text, graphics, microchannels, microchip metallisation), or steps in a sequence leading to them, in one go

Resist Layers and Etching 11 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

Photolithography: Hands off! 12 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, These are photomasks! Photomasks allow replication: one mask, multiple patterned substrates

Not all MEMS is small.. 13 Plasma screen photomask

Tools: Mask Generation 14 circa 1970: ‘ruby-lith’ mask design Photo-reduction onto mask plate LASI layout editor 2011e-beam mask generator

Tools: Patterning 15 Suss MJB4 4 inch diameter wafer photomask exposure and alignment

Printed Circuits: Structured Layers Commence 16 Printed Circuit Board: Paul Eisler: 1943

Additive, Subtractive and Other Processes 17 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

Additive Processes 18 ‘screen printing’ is used to apply solder paste in surface mount PCB assembly

Additive Processes 19 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

Subtractive Processes for Silicon 20

How does this relate to Microelectronics? 21 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

Intel 4004 The First Microprocessor: Grove, Noyce, Moore: IntelIntel 4004, 4 bit microprocessor

What has all this got to do with MEMS? 23 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

Isn’t Nanotechnology the New, Cool Thing? 24 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...

Scaling: Large Effects of Small Things (or, conversely, Small Effects of Large Things) 25 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: 10 2 ratio of flow rates: 10 8 !

Scaling-up Scaled-down: Economy of Scale 26 Intel’s 4004 in 1970 employed 10µm ‘design rules’ (all features are multiples of this dimension) with 2.4x10 3 transistors on a 144mm 2 die; Intel’s just released ‘Ivy Bridge’ processor employs 22nm design rules and has 1.4x10 9 transistors on a 172mm 2 die Interestingly, Colossus had 1500 valves (do you know what a valve is?) Minimum definable area has scaled-down by 206x10 3 times Transistor count has scaled-up by a very comparable 583x10 3 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’

Scaling-up the Scaled-down: Moore’s Law 27

Complexity 28 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 4x10 3 during the same period Calculations / unit area / unit time has increased by (583x10 3 ) x (4x10 3 ) = 2.3x10 7 times However, in reality, calculation capacity scales in a more complex way with transistor count depending upon processor architecture.

‘Cheap-fast’ Microengineering 29 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.

‘Cheap-fast’ Microengineering 30

Structural Photoresist ’SU8’ 31

PDMS Elastomeric Micropump chips 32

PDMS Elastomeric Chips: Micro-pneumatics 33

Combining Microstructuring with CNC 34

Dean-flow Particle Separator 35

Conclusions 36 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