CS252 S05 1

Lecture 1

MEMSMEMS

(Micro Electro Mechanical Systems)

By

Dr. Ahmad Sinjari

• The objective of this course is to review the advanced topics related to the

theory and modeling of MEMS design and fabrication processes.

• Topics to be covered include:

Course Objective

Topics to be covered include:

1. Micromachining techniques

2. Microelectromechanical sensing and actuation

3. MEMS materials

4 MEMS d i h d l d di

2

4. MEMS design methodology and case studies

• Emphasis is on theory, lumped element modeling, 3-D finite element modeling

and simulation of device behavior, simulation of fabrication processes using

actual fabrication process parameters, and design verification.

CS252 S05 2

Reference Books:

• Stephen D. Senturia , Microsystem Design

• Muller, Howe, Senturia, Smith, White, Microsensors, IEEE Press

M d F d l f Mi f b i i CRC• Madou, Fundamentals of Microfabrication, CRC

• Elwenspoek and Jansen, Silicon Micromachining, Cambridge

• Keller, Microfabricated High Aspect Ratio Silicon Flexures, MEMS Precision

Instruments

K Mi hi d T d S b k M G Hill

3

• Kovacs, Micromachined Transducers Sourcebook, McGraw-Hill

• Maluf, An Introduction to MEMS Systems Engineering, Artech House

• Ristic, Sensor Technology and Devices, Artec House

• Sze, Semiconductor Sensors, Wiley

• Imagine a machine so small that it is imperceptible to the human eye

• Imagine working machines with gears no bigger than a grain of pollen

• Imagine smart dusts floating in the atmosphere and sending real time climate

data

• Imagine a realm where the world of design is turned upside down, and the

seemingly impossible suddenly becomes so easy

• Imagine artificial muscles and neurons inside your body

4

• Imagine a place where gravity and inertia are no longer important, but the

effects of atomic forces and surface science dominate

CS252 S05 3

1948

5

John Bardeen, Walter Brattain and William

Shockley Inventors of transistor

First transistor

1958

6

Jack Kilby Inventor of IC First Integrated Circuit

CS252 S05 4

2003

7Pentium 4 3.2 GHz 55 million transistors

8

CS252 S05 5

9

• MEMS is a logical evolution of the VLSI technology

• Adds new functional dimensions to a microchip

• Sometimes is referred as the Second Silicon Revolution

• Generally refers to three dimensional microstructures fabricated in a

From IC to MEMS

Generally refers to three dimensional microstructures fabricated in a

microchip using processes similar to conventional VLSI technology

• The resulting micro devices are able to

Sense

Act

Process, and

10

Process, and

Communicate

when combined with microelectronics circuitry

• Co-location of sense, act, process and memory functions in a single

chip provides enhanced levels of perception, control, and performance

CS252 S05 6

An Ant Holding a MEMS Gear

11

Forschungszentrum Karlsruhe Microsystem Technologies

1. Minimizing energy and materials use in manufacturing

2. Integration with microelectronics, simplifying systems

3. Reduction of power budget

Why Microsystems are Attractive

p g

4. Faster devices

5. Increased selectivity and sensitivity

6. Wider dynamic range

7 C t/ f d t

12

7. Cost/performance advantages

8. Improved reproducibility (batch processing)

9. Improved accuracy and reliability

10. Excellent scaling properties

MEMS steam engine

smaller than a spider!

CS252 S05 7

A Typical MEMS Sensor/Actuator System

13

Historical Perspective

• 1750s First electrostatic motors (Benjamin Franklin, Andrew Gordon)

• 1824 Silicon discovered (Berzelius)

• 1948 First transistor (Bardeen, Brattain, Shockley, Bell Lab)

• 1954 Piezoresistive effect in Germanium and Silicon discovered

• 1958 First integrated circuit (Kilby, TI)

• 1961 First silicon pressure sensor (Kulite)

• 1967 Surface micromachining invented (Nathanson)

• 1970 First silicon accelerometer (Kulite)

• 1977 First capacitive pressure sensor (Stanford)

14

• 1984 First polysilicon MEMS device (Howe, Muller )

• 1989 Lateral comb drive (UC Berkeley)

• 1992 Diffraction grating light modulator (Stanford)

• 2000 Micro gas turbine engine (MIT)

• ……………

Microgripper

CS252 S05 8

Typical Applications of MEMS

15

Microsensing and Microactuation techniques

Microactuation

• Electrostatic

• Magnetic

• Piezoelectric

Microsensing

• Piezoresistive

• Piezoelectric

• Capacitive

• Thermal

• Magnetostrictive

• Optical

• Other

• Resonant

• Magnetostrictive

• Thermal

• Other

16

Atomic force microscope tip

CS252 S05 9

Electrostatic Actuation

V

Q

d

AC 0

20 AV

F

17

20

0

2 Xd

AVF ticelectrosta

A= Plate area, V= Drive voltage, ε= Permitivity

Note that the force is dependent of displacement and is nonlinear

Lateral Electrostatic Actuation

• Y-direction forces cancel out

• Forces due to the fringe field flux lines

causes the X directional ( lateral) motion

• Capacitance change is due to an increase

in the area of the exposed faces due to a

change in overlap lengths

• The gap (d) remains constant

Th i h i li

18

• The capacitance change is linear

The force is independent

of displacement

CS252 S05 10

Electrostatic Comb Drive Actuator

Inventor:

19

• Capacitive sensing and actuation

• Linear force-displacement characteristics

• High Q

• Accelerometer, Microelectromechanical filter

Tang, Nguyen, Howe

UC Berkley

Vertical and Lateral Accelerometer

Acceleration is linearly proportional to

20

Schematics of Vertical and lateral Accelerometer

y p pthe position of the proof mass

CS252 S05 11

ADXL 50, First Surface Micromachined Accelerometer

21

The chip includes signal conditioning circuitry. Most North American cars now use ADXL series accelerometers in their air bag units

MEMS Accelerometer Close-up View

22

The output voltage is a linear function of displacement

CS252 S05 12

MEMS 3 Axes Gyroscope

23

MEMS Design Examples

24

CS252 S05 13

Gears from Sandia

Gear speed reduction unitA mirror is elevated by a

three-gear torque-multiplying

system. The mirror is shown

in the upright position

25

Chained gear Gear close-up

in the upright position

Power MEMS

Microengine

Microturbine

• 4.2 mm diameter

• 150 μm tall stator and rotor blades

G l b i i

26

• Gas lubrication

• 1 million rpm

• Generated power: 5 Watts

• 15 N thrust, bipropellant, cooled rocket engine

CS252 S05 14

BioDisk: A MEMS Bio-Specimen Analyzer

27

The BioDisk, manufactured by MikroWebFab, Germany can execute up

to 32 analyses of a blood drop simultaneously

Micromirrors: Digital Light Processing

28

• Hinged mirrors are excited electrostatically

• 442,000 mirrors in 16 x 16 mm2 area

• The mirrors are individually addressable by pulses from SRAM

• 100,000 flips per second

CS252 S05 15

Micromirrors: Digital Light Processing

• The Deformable Mirror Device (DMD) technology can achieve higher performance in terms of resolution, brightness, contrast ratio, and convergence than the conventional cathode ray tube and is critical for digital high definition television applications.

• A DMD consists of a large array of small mirrors with a typical area of 16 μm ~16 g y yp μμm.

• Each mirror is capable of rotating by ±10 degrees, corresponding to either the “on” or “off” position, due to an electrostatic actuation force.

• Light reflected from any on-mirrors passes through a projection lens and creates images on a large screen.

• Light from the remaining off-mirrors is reflected away from the projection lens to

29

g g y p jan absorber.

• The amount of time during each video frame that a mirror remains in the on-state determines shades of gray, from black for zero on-time to white for a hundred percent on-time.

Detailed Layout of a DMD Pixel

• On-state duration determines shades of gray

• Color can be added by a color wheel or a three-DMD chip setup

• The three-DMD chips are used for projecting red, green, and blue colors.

30

CS252 S05 16

DMD Fabrication

• The yoke is tilted over the second gap by an electrostatic actuation force, thereby rotating the mirror plate.

• The SRAM determines which angle the mirror needs to be tilted by applying proper actuation voltages to the mirror and address electrodes.

• The DMD is fabricated using an aluminum-based surface micromachining technology.

• The micromachining process is compatible with standard CMOS SEM micrograph of a close view

31

compatible with standard CMOS fabrication, allowing the DMD to be monolithically integrated with a standard CMOS address circuit technology, thus achieving high yield and low cost

g pof a DMD yoke and hinges

Diffraction Grating Light Valve (GLV)

Typical GLV pixel

• Electrostatically actuated alternate ribbons create a square-well diffraction grating. This grating introduces phase offsets between the wavefronts of light reflected off stationary and deflected ribbons.

32

stationary and deflected ribbons.

• Can be used to realize highly efficient display, e.g. high-definition TV, optical communications

• A million times faster than conventional LCD display devices

CS252 S05 17

Color Generation in GLV Display

White light

33

• Video input is format converted and then input to a digital driver

• The driver interfaces directly with the GLV device

• Light is diffracted by the GLV device into an eyepiece for virtual display,orinto an optical system for image projection onto a screen

MEMS All Optical System

• A precision alignment and the ability to actuate optical components, such as mirrors, gratings, and lenses, with sufficient accuracy are critical for high performance optical applications.

• Micromachining provides a critical enabling technology, allowing movable optical components to be fabricated on a silicon substrate.

• High-precision component movement can be achieved through electrostatic actuation.

• By combining micromachined movable optical components with lasers, lenses, and fibers on the same substrate, an on-chip, complex, self-aligning optical system can be realized.

34

CS252 S05 18

Electrostatically Actuated Microreflector

• The device consists of a polysiliconmirror plate hinged to a support beam.

• The mirror and the support, in turn, are hinged to a vibromotor-actuator slider.

• The micro-hinge technology allows theThe micro hinge technology allows the joints to rotate out of the substrate plane to achieve large aspect ratios.

• Common-mode actuation of the sliders results in a translational motion.

• Differential slider motion produces an out-of-plane mirror rotation.

35

SEM micrograph of a surface micromachined, electrostaticallyactuated microreflector for laser-to-fiber coupling and external cavity laser applications

• These motions permit the microreflector(mirror) to redirect an optical beam in a desirable location.

• Sliders are actuated by an integrated microvibromotor.

MEMS Vibromotor for Optical Communication

• The vibromotor consists of four electrostatic comb resonators and drives a slider

• The two opposing impacters are• The two opposing impacters are used for each travel direction to balance the forces.

36

CS252 S05 19

2-D Optical Data Switching

• MEMS technology can be used to fabricate arrays of tiny movable mirrors that can redirect incoming beams from input optical fibers to corresponding output fibers.

• All optical system eliminates the delay and extra processing associated with optical-electronic-optical systems

37

3-D Optical Switching

• 3-D optical switching can also be realized using the ame method

• The network consists of arrays of two-axis mirrors to steer optical beams from input fibers to output fibersfrom input fibers to output fibers

• A precision analog closed loop mirror position control is required to accurately direct a beam along two angles, so that one input fiber can be optically connected to any output fiber

38

CS252 S05 20

RF MEMS

• At present, most radio transceivers rely on a large number of discrete

frequency-selection components, such as radio frequency (RF) and

intermediate frequency (IF) bandpass filters, RF voltage-controlled oscillators

(VCOs), quartz crystal, oscillators, solid-state switches, etc.( ), q y , , ,

• These off-chip devices occupy the majority of the system area, thus severely

hindering transceiver miniaturization.

• MEMS technology, however, offers a potential solution to integrate these

discrete components onto silicon substrates with microelectronics, achieving a

39

size reduction of a few orders of magnitude.

• It is therefore expected to become a technology that will ultimately enable the

miniaturization of radio transceivers for future wireless communications.

MEMS Variable Capacitors

SEM micrograph of four MEMS

aluminum variable capacitors

connected in parallel

SEM micrograph of a silicon

40

SEM micrograph of a silicon tunable capacitor using a comb drive actuator

CS252 S05 21

MEMS Inductors

SEM micrograph of a 3-D coil inductor fabricated on a silicon substrate

SEM micrograph of a g pself assembled out-of plane coil inductor

SEM micrograph of a levitated spiral inductor fabricated on a glass

b t t

41

substrate

SEM micrograph of an interlocking trace from a self-assembled out-of-plane coil inductor

MEMS Switches

Top view photo of a fabricated RF MEMS capacitive switch

Cross-sectional schematics of an RF MEMS capacitive switch

42

SEM micrograph of a polysilicon surface micromachined two-resonator springcoupledbandpass micromechanical filter

Cross-sectional schematic of a

metal-to-metal contact switch

CS252 S05 22

MEMS Radar

• Planar

• Phased antenna arrays

• Beam steering and switching capability

• RF MEMS switches for phase shifting and low-insertion loss switching

• Flip chip mountingp p g

43

Common Materials for MEMS Fabrication

• Metals (Al, Au, Cu, Cr, Ni, Ti)

• Insulators (SiO2, Si3N4)

• Polymers

• Single crystal or polycrystalline silicon

• Polysilicon-Germanium (Poly-SiGe)

• Diamond

• SiC

44

CS252 S05 23

Physical Properties of Selected materials

45

MEMS Fabrication Process

• Bulk micromachining

46

• Surface micromachining

• LIGA

• Combined bulk and surface micromachining

CS252 S05 24

Fabrication: Deposition (Additive Processes)

• Thin film deposition

– Structural layers

– Sacrificial layers

• Thermal oxidation of silicon

• Chemical vapor deposition

– Low pressure chemical vapor deposition (LPCVD)

– Plasma enhanced chemical vapor deposition (PECVD)

– Atmospheric pressure chemical vapor deposition (APCVD)

• Physical vapor deposition

47

– Evaporation

– Sputtering

• Electrodeposition

• Lift off

• Spin

Fabrication: Etching (Subtractive Processes)

• Wet

– Isotropic (HNA, PAN, RCA, Piranha)

– Anisotropic (KOH, EDP, TMAH)

D• Dry

– Isotropic

• XeF2

– Anisotropic (Plasma/Reactive ion)

• SF6+O2

Cl2

48

• Cl2

• CHF3

• O2

• CF4

• CCl4

CS252 S05 25

Fabrication: Photolithography (UV)

49

Bulk Micromachining: Isotropic Etch

50

CS252 S05 26

Bulk Micromachining: Anisotropic Etch

51

• Anisotropic etches have direction dependent etch rates in crystals

• Typically the etch rates are slower perpendicularly to the crystalline planes with the highest density

Deep Reactive Ion Etching (DRIE)

52

CS252 S05 27

Oxford Plasma Lab 80: DRIE Equipment

Front side Chamber open Argon plasma

53

Oxygen plasma

Surface Micromachining

54

CS252 S05 28

LIGA Process

55PMMA – Polymethyl methacrylate

Critical point CO2 Drier

56

CS252 S05 29

IntelVac E-beam Evaporation

57

Mask Aligner

58

CS252 S05 30

Single-Pole-Triple Throw (SP3T) RF Switch

59

MEMS Rotman Lens

60

CS252 S05 31

Rotman Lens Simulation Using HFSS

61

Rotman Lens Simulation Using HFSS

62

CS252 S05 32

Rotman Lens Fabrication

63

Design Approach: Four Broad Modeling Approach

64

CS252 S05 33

System Level

• Block diagram description of the system

• Lumped element circuit model

• Result:

1. A coupled set of ordinary differential equations p y qdescribing the dynamic behavior of the system

2. First or second order ordinary differential equations

3. State variables

4. State equations

65

Equation of motion:

State equations:

Physical Level

• Behavior or real device in 3-D continuum

• Governing equations are partial differential equations

• Accurate solution needs numerical methods. Such as:

1. Finite element

2. Boundary element

3. Finite difference

66

CS252 S05 34

Device Level

• Simplified macro models or reduced order models that captures the essential physical behavior of a component in the system

• Directly compatible with system level design

Process LevelProcess Level

• Process sequence

• Photo mask design

• Process modeling by numerical technique

• Predicts device geometry from masks and process sequence

67

• Material properties are needed to know to choose an appropriate process

MEMS Design Flow

68

CS252 S05 35

MEMS DESIGN TOOLS

• Analytical modeling

1. Matlab

• 3-D FEA modeling

1. HFSS

2. INTELLISUITE

3. COVENTORWARE

4. MEMSCAP

69

5. FEMLAB

6. ANSYS

7. ALGOR

MEMS FEA Simulation Example

70

Foot print area: 100 x 100 μm2

CS252 S05 36

Meshing and potential distribution

71

2002 MEMS Market Share Estimate

72

CS252 S05 37

2007 MEMS Market Share Projection

73

Total MEMS Revenue 2002-2007

74

CS252 S05 38

Cost Distribution of a Typical MEMS Device

75