JASS 2006St. Petersburg Cornelia Hartmann slide 1
JASS 2006
MEMS and
Nanotechnology
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table of contents
1. introduction2. definition of MEMS & NEMS3. active principles4. types of MEMS5. fabrication6. problems with the fabrication
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progress
1. introduction2. definition of MEMS & NEMS3. active principles4. types of MEMS5. fabrication6. problems with the fabrication
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introduction
The Beginning
In Dec. 1959 Richard Feynman offered a prize of $1,000.
Challenge: build an electrical motor, each side smaller than
164
in≈0.397mm
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introduction
diameter: 381μm
tools used for assembly:
● microscope● sharpened tooth pick● hairs of a fine artist's brush
McLellan's micromotor photographed under a microscope (Caltech Institute Archives)
electrical motor by WilliamMcLellan
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progress1. introduction2. definition of MEMS & NEMS
2.1. What is MEMS?2.2. What is NEMS?2.3. problems with NEMS
3. active principles4. types of MEMS5. fabrication6. problems with the fabrication
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What is MEMS?
MEMS - microelectromechanical systems
transformation of energy:
MEMS mainly move by elastic deformation of their flexible components.
electricitylight
thermal energy...
mechanical motion
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What is MEMS?
Courtesy of Sandia National Laboratories, SUMMiTTM Technologies, www.mems.sandia.gov
spider mite (length: approx. 0.5mm)
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What is NEMS?
NEMS - nanoelectromechanical systems
● similar to MEMS but smaller (nanoscale)● future prospects: ability to measure small displacements and forces at a molecular scale
The border between MEMS and NEMS can hardly be defined: 500nm or 0.5μm ?
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problems with NEMS-technology
It is possible to create structures with only severalnanometers in size, BUT:● nanoscale cantilevers/beams: a considerable big number
of atoms are surface atoms● interference with surrounding molecules● additional physical effects have to be considered
(e. g. increased influence of adhesion)
⇒ just scaling down MEMS layouts does not work!
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problems with NEMS-technology
some examples:
● NEMS can respond to masses of single atoms: sensors could respond to impacts of molecules
● measurment of small deflection/forces also means small signals: difficulty to tell the signals apart from the noise
● adhesion of pieces that operate as capacitive electrodes could induce short circuits
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problems with NEMS-technology
● effects, that are irrelevant to micro devices, have to be considered for nano devices
● new design approaches have to be found ● production and packaging have to take place in an
extremely clean environment
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progress1. introduction2. definition of MEMS & NEMS3. active principles
3.1. thermal transduction3.2. electrostatic transduction 3.3. piezo-resistive effect
4. types of MEMS5. fabrication6. problems with the fabrication
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active principles
thermal transduction
ntdisplaceme no FF b
⇒=
A: cross-sectional areaE: Young's modulusα: thermal coefficient change in length:
Δ l=α⋅l⋅Δ Tblock force :Fb=E⋅A⋅α⋅Δ T
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active principles
thermal transduction
fixed
moveable
vertical motion
bent beam actuator bi-metal actuator
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active principles
advantages & disadvantages of thermal transduction
+ large forces/displacements – large input energies – low frequencies
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active principles
electrostatic transduction
Δ U=−Q xε Δ A
parallel plate movement: Δ xcomb finger movement: Δ A
–ΔA
d
d +Δ x
parallel plate
comb fingers
Δ U=Q Δ xε A
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active principles
electrostatic transduction
comb drives
10μm
75μmparallel
electrodesd
spring elements
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active principles
advantages & disadvantages of electrostatic transduction
+ fast response+ easy integration with CMOS– small actuation force
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active principles
piezo-resistive effect
⇒ change in length
connect piezo actuator to voltage source
VlΔ l
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active principles
⇒ potential difference
piezo-resistive effect
compress or expand piezo sensor
F
F
V l−Δ l
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active principles
piezo-resistive effect in polysilicon
gauge factor
thin film of polysilicon (p- or n-doped)isolator (e. g. SiO2, Si3N4)
cantilever/beam/membrane
K=
Δ RRΔ ll
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active principles
piezo-resistive effect in polysilicon
maximum gauge factorp-doped: – 40 n-doped: 20
NA/D≈1019cm-3
TCVD=560°C annealing: 1000...1100°C
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progress
1. introduction2. definition of MEMS & NEMS3. active principles4. types of MEMS
4.1. sensors4.2. actuators
5. fabrication6. problems with the fabrication
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types of MEMS
• sensors - accelerometers - gyroscopes
• actuators - micromirrors - droplet generator - microengines - micropumps
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sensors: accelerometersaccelerometers
● in automotive applications to activate safety systems and to implement vehicle stability systems
● hard disc protection systems● ...
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sensors: accelerometersaccelerometers
a simple MEMS accelerometer is designed as followed:● the proof mass is suspended by one to four silicon beams● basic design and mechanical equivalent:
suspension beams
proof mass
a
x
m
D
K
proof mass
reference frame
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sensors: accelerometersaccelerometers
● acceleration causes displacement of the proof mass● displacement of the proof mass can be measured by
strain gauges in the beams
proof mass with capacitive electrodes
or change in capacitancesuspension beams with strain gauges
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sensors: accelerometersaccelerometers
depending on the change in each capacitance, the three-dimensional acceleration vector can be derived
horizontal accelerationvertical acceleration
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sensors: gyroscopes
gyroscopes
vibratory gyroscopes: transfer of energy between two vibration modes
vibrating mechanical element: proof mass
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sensors: gyroscopes
gyroscopes
Coriolis accelaration ω
a
v
ac=2 ω×v
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sensors: gyroscopes
tuning fork gyroscope
Draper Lab comb drive tuning fork gyroscope
rotation detection by capacitive electrodes under the proof mass
ωa
v
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actuators: micromirrors
micromirrors for phase modulation
16 μm
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actuators: droplet generator
heating element
nozzle
ink reservoir
cooling hole
membrane
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actuators: microengines
microengine with electrostaticly driven combdrives
Courtesy of Sandia National Laboratories, SUMMiTTM Technologies, www.mems.sandia.gov
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actuators: microengines
Courtesy of Sandia National Laboratories, SUMMiTTM Technologies, www.mems.sandia.gov
close-up view on different linkage designes
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actuators: microengines
torque : Mi=Fi⋅r⋅∣sinφi∣
r
φ1
φ2
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actuators: micropumps
micropump with piezo actuators
frequency controlledflow rate
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progress
1. introduction2. definition of MEMS & NEMS3. active principles4. types of MEMS5. fabrication6. problems with the fabrication
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fabrication
epitaxial growth
• thermal oxidation (SiO2-layers)
• chemical vapour deposition• thermal evaporation (metalic layers)• electrolytic deposition
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fabrication
chemical vapour deposition (CVD)
e. g. layer of phosphorus-doped silicon
⇒ n-doped silicon layerSiH4
+ PH3
heated chamber
wafers
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fabrication
minimum structure width: ultraviolet light: 1μme-beam, x-ray: <1μm
plasma etching,KOH-etching (Si),HF-etching (SiO2),...
mask
photo resist
Si, SiO2
ultraviolet light
etching
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fabrication
etching
isotropic
anisotropic
e. g. SiO2 etched by HF
e. g. <100> - Si etched by KOH
e. g. plasma etched Si
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fabrication
silicon wet etching (e. g. with KOH)
selective etching rate:1
30plane}- crystal 111{ Rplane}- crystal 100{ R =
><><
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fabrication
silicon wet etching (e. g. with KOH)
Si + 2 OH– + 2 H2O → SiO2(OH)2 –
– + H2
silicon surface
surface structure of <111> - silicon surface structure of <100> - silicon
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fabrication
reactive ion etching
reactive ion etching: combines chemical and physikal etchinge. g. flour ions react with silicon AND heavy ions impact on the surfaceattention: physical etching
also attacks the pattern
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fabrication
reactive ion etching
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fabrication
reactive ion etching
Si: SiCl4, CCl4, BCl3, SF6
SiO2: C2F6, CHF3
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progress
1. introduction2. definition of MEMS & NEMS3. active principles4. types of MEMS5. fabrication6. problems with the fabrication
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problems with the fabrication
● microscopic contaminations (dust)
● molecular dirt:e. g. oil fog from vacuum pumps
→ adhesion degradation of epitaxial layers
contamination
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problems with the fabrication
KOH-etching: dust particles may result in hillockshillocks
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list of references & picture credits
N. Lobontiu, E. Garcia: Mechanics of Microelectromechanical Systems, Kluwer Academic Publishers, 2005M. Glück: MEMS in der Mikrosystemtechnik, B.G. Teubner Verlag, Wiesbaden 2005M. Elwenspoek, R. Wiegerink: Mechanical Microsensors, Springer-Verlag, Berlin 2001M. Gad-el-Hak (editor): The MEMS Handbook, CRC Press, Boca Raton 2006W. Lachermeier: Das Labor in der Westentasche, Mechatronik F&M, 3/2006http://mems.sandia.govhttp://www.wikipedia.comhttp://physicsweb.orghttp://news.bbc.co.ukhttp://archives.caltech.eduhttp://www.invensense.comhttp://mems.cwru.edu