summary of introduction mems (u.s.) sometimes microsystems in europe. mems=microelectromechanical...

Summary of Introduction• MEMS (U.S.) Sometimes Microsystems in Europe.

• MEMS=MicroElectroMechanical Systems

• Very broad definition in practice: Mechanical, Electrical, Optical, Thermal, Fluidic, Chemical, Magnetic.

• Generally systems created using microfabrication that are not integrated circuits. Many (but not all) of the microfabrication techniques were borrowed from the IC industry.

• Market is smaller than IC market, but more diverse and growing faster.

Some Examples• Accelerometer

– Electrical/Mechanical

• TAS or Micro Total Analysis System– Purifies, amplifies, and detects DNA, for example.

– Fluids/Biochemistry/Optical/Electrical

• TI DLP– Optical/Mechanical/Electrical/Surface Science

• Microrelay– Mechanical/Electrical/Surface Science

• Microplasma Source– Electrical/Electromagnetic/Plasma

• What do you need to know for MEMS?

• Everything???!!!

• Truly an interdisciplinary field.

What are we going to do?• Learn a useful subset of techniques needed for designing MEMS

devices. Not all!!

• We will design MEMS devices.– Project teaming survey is due Friday – see web site.

– Project assignment is on the web site.

• We will discuss examples of MEMS devics and use the techniques we have developed.

• First we will look at microfabrication and process integration.

• Other notes:– First homework is due today. (Some flexibility here – students joining class, thurn-

in mechanism …)

– Second homework is due on Tuesday.

Microfabrication: Types of Micromachining for MEMS

• Bulk Micromachining– Etch away large parts of the silicon wafer.

– Traditionally, KOH or other chemical etch.

– Recently DRIE (Deep Reactive Ion Etch), an anisotropic plasma etch.

• Surface micromachining– On surface of wafer/substrate

– Sometimes can be a post-process on top of CMOS wafer for process integration with electronics.

– Typically much thinner structures than bulk micromachining, but metal structures can be fairly thick.

• LIGA– X-ray lithographie, galvanoformung, abformtechnik (or lithography,

electrodeposition, and molding).

– A special type of surface micromachining, not much used in its original form.

– Now sometimes refers to using very thick photoresist to make thick electroplated structures.

Packaging• Ideally, part of fabrication process, then just use a cheap plastic

package.

• Often, a surface micromachined device is bonded to a bulk micromachined package (the cavity to contain the device is etched from the wafer using bulk micromachining).

• Sometimes the package is the most expensive part of the device (pressure sensors, microfluidics). Especially true when the device interacts with the outside environment.

References: Text (brief), Campbell or other IC fabrication text (generally good, but incomplete for MEMS), Madou (specific to MEMS).

Silicon wafer fabrication• Taken from www.egg.or.jp/MSIL/english/index-e.html

Silicon wafer fabrication – slicing and polishing

• Taken from www.egg.or.jp/MSIL/english/index-e.html

Wee

k 1

Wee

k 2

N -type Si wafer <100>

Pre-diffusion cleanPad oxidation

Deposit LPCVD nitride

Spin photoresist

PR

Si N3 4

SiO 2

O 2

SiH ClNH

2 2

3

ECE 1233 PMOS Fabrication Sequence

We

ek 2

Wee

k 3

Expose PR with active area maskand develop

Reactive ion etch nitride layerStrip PR

Pre-diffusion cleanField oxidation

Strip nitride and pad oxideSacrific ial oxidation

OH O

2

2

O 2

CHFO

3

2

Wee

k 3

Wee

k 4

Strip sac ox

Gate oxidation

Deposit LPCVD polysilicon

Poly

PR/etch gate m askStrip PR

O 2

SiH 4

SFO

6

2

LPCVD SystemsTaken from http://www-bsac.EECS.Berkeley.EDU/~pister/245/

Wee

k 5

Wee

k 6

Ion im plant BF 2

+

Pre-diffusion cleanDrive-in/oxidation

PR/etch contact m askStrip PR

CleanSputter deposit A l/1% Si

Al/Si

P doped areas

OH O

2

2

Ar

Wee

k 6

PR /etch metal m askStrip PRAnneal

Source

DrainGate (contact not shown)

Wee

k 1

Wee

k 2

N -type Si wafer <100>

Pre-diffusion cleanPad oxidation

Deposit LPCVD nitride

Spin photoresist

PR

Si N3 4

SiO 2

O 2

SiH ClNH

2 2

3

ECE 1233 PMOS Fabrication Sequence

Wee

k 1

Wee

k 2

N -type Si wafer <100>

Pre-diffusion cleanPad oxidation

Deposit LPCVD nitride

Spin photoresist

PR

Si N3 4

SiO 2

O 2

SiH ClNH

2 2

3

ECE 1233 PMOS Fabrication Sequence

We

ek 2

Wee

k 3

Expose PR with active area maskand develop

Reactive ion etch nitride layerStrip PR

Pre-diffusion cleanField oxidation

Strip nitride and pad oxideSacrific ial oxidation

OH O

2

2

O 2

CHFO

3

2

Wee

k 3

Wee

k 4

Strip sac ox

Gate oxidation

Deposit LPCVD polysilicon

Poly

PR/etch gate m askStrip PR

O 2

SiH 4

SFO

6

2

Wee

k 5

Wee

k 6

Ion im plant BF 2

+

Pre-diffusion cleanDrive-in/oxidation

PR/etch contact m askStrip PR

CleanSputter deposit A l/1% Si

Al/Si

P doped areas

OH O

2

2

Ar

Wee

k 5

Wee

k 6

Ion im plant BF 2

+

Pre-diffusion cleanDrive-in/oxidation

PR/etch contact m askStrip PR

CleanSputter deposit A l/1% Si

Al/Si

P doped areas

OH O

2

2

Ar

Wee

k 6

PR /etch metal m askStrip PRAnneal

Source

DrainGate (contact not shown)

Electrodeposition/Electroplating

SEM of NEU microswitch

Drain Source

Gate

Beam

Drain Gate Source

Beam

Drain

Gate

Source

Surface MicromachinedPost-Process Integration with CMOS20-100 V Electrostatic Actuation~100 Micron Size

IBM 7-Level Cu Metallization (Electroplated)

Packaging• Ideally, part of fabrication process, then just use a cheap plastic

package.

• Often, a surface micromachined device is bonded to a bulk micromachined package (the cavity to contain the device is etched from the wafer using bulk micromachining).

• Sometimes the package is the most expensive part of the device (pressure sensors, microfluidics). Especially true when the device interacts with the outside environment.

Micromachining Ink Jet Nozzles

Microtechnology group, TU Berlin

Bulk micromachined cavities

• Anisotropic KOH etch (Upperleft)

• Isotropic plasma etch (upper right)

• Isotropic BrF3 etch with compressive oxide still showing (lower right)

Taken from http://www-bsac.EECS.Berkeley.EDU/~pister/245/

Surface Micromachining

Deposit sacrificial layer Pattern contacts

Deposit/pattern structural layer Etch sacrificial layer

Taken from http://www-bsac.EECS.Berkeley.EDU/~pister/245/

so urc e

so urc e

so urc e

g a te

g a te

g a te

d ra in

d ra in

d ra in

NUMEM Microrelay Process

so urc e

so urc e

g a te

g a te

d ra in

d ra in

NUMEM Microrelay Process

Residual stress gradients

More tensile on top

More compressive on top

Just right! The bottom line: anneal poly between oxides with similar phosphorous content. ~1000C for ~60 seconds is enough.

Taken from http://www-bsac.EECS.Berkeley.EDU/~pister/245/

Residual stress gradients

A bad day at MCNC (1996).

Taken from http://www-bsac.EECS.Berkeley.EDU/~pister/245/

DRIE structures

• Increased capacitance for actuation and sensing

• Low-stress structures– single-crystal Si only

structural material

• Highly stiff in vertical direction– isolation of motion to

wafer plane– flat, robust structures

2DoF Electrostatic actuator

Thermal Actuator

Comb-drive Actuator

Taken from http://www-bsac.EECS.Berkeley.EDU/~pister/245/

1 µm

Scalloping and Footing issues of DRIE

Scalloped sid

ewall

Top wafer surface

cathode Top wafer surface

anode

Tip precursors

Scalloped sid

ewall

Top wafer surface

cathode Top wafer surface

anode

Tip precursors

<100 nm silicon nanowire over >10 micron gap

microgridFooting at the bottom of

device layerMilanovic et al, IEEE TED, Jan. 2001.

Sub-Micron Stereo Lithography

Micro Electro Mechanical SystemsJan., 1998 Heidelberg, Germany

New Micro Stereo Lithography for Freely Movable 3D Micro Structure-Super IH Process with Submicron Resolution-

Koji Ikuta, Shoji Maruo, and Syunsuke KojimaDepartment of Micro System Engineering, school of Engineering, Nagoya University

Furocho, Chikusa-ku, Nagonya 464-01, JapanTel: +81 52 789 5024, Fax: +81 52 789 5027 E-mail: ikuta@mech.nagoya-u.ac.jp

Fig. 1 Schematic diagram of IH Process

Fig. 5 Process to make movable gear and shaft (a) conventional micro stereo lithography needs base layer (b) new super IH process needs no base

Fig. 6 Schematic diagram of the super IH process

Sub-Micron Stereo Lithography

Micro Electro Mechanical SystemsJan., 1998 Heidelberg, Germany

New Micro Stereo Lithography for Freely Movable 3D Micro Structure-Super IH Process with Submicron Resolution-

Koji Ikuta, Shoji Maruo, and Syunsuke KojimaDepartment of Micro System Engineering, school of Engineering, Nagoya University

Furocho, Chikusa-ku, Nagonya 464-01, JapanTel: +81 52 789 5024, Fax: +81 52 789 5027 E-mail: ikuta@mech.nagoya-u.ac.jp

Fig. 10 Micro gear and shaft make of solidified polymer(b) side view of the gear of four teeth(d) side view of the gear of eight teeth

Taken from: http://www.imm-mainz.de/english/sk_a_tec/basic_te/liga.html

Simple Carbon Nanotube Switch

Diameter: 1.2 nmElastic Modulus: 1 TPaElectrostatic Gap: 2 nmBinding Energy to Substrate: 8.7x10-20 J/nm

Length at which adhesion = restoring force: 16 nmActuation Voltage at 16 nm = 2 VResonant frequency at 16 nm = 25 GHzElectric Field = 109 V/m or 107 V/cm + Geom.

(F-N tunneling at > 107 V/cm)

Stored Mechanical Energy (1/2 k x2 ) = 4 x 10-19 J = 2.5 eV