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EE C245 – ME C218Introduction to MEMS Design
Fall 2008Fall 2008
Prof Clark T C NguyenProf. Clark T.-C. Nguyen
Dept of Electrical Engineering & Computer SciencesDept. of Electrical Engineering & Computer SciencesUniversity of California at Berkeley
Berkeley, CA 94720y
L t 3 B fit f S li II
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 1
Lecture 3: Benefits of Scaling II
Lecture Outline
• Reading: Senturia, Chapter 1g p• Lecture Topics:
Benefits of MiniaturizationExamplesExamples
GHz micromechanical resonatorsChip-scale atomic clockpMicro gas chromatograph
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 2
NIST F1 Fountain Atomic Clock
Vol: ~3.7 mVol: ~3.7 m33
Power: ~500 WPower: ~500 WAcc: Acc: 11××1010––1515
Stab: 3.3x10Stab: 3.3x10--1515/hr/hr
After 1 sec Error: 10-15 sec
Loses 1 sec every y30 million years!
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 3
Physics Package
1st Chip-Scale Atomic Physics PackageNIST’s Chip-Scale Atomic
Physics Package
1.5 mmPhotodiode
Package
Cell
4.2 mm
Optics
Q tND
1.5 mm Laser 1 mm
GlassND
SiQuartz
Lens
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 4
Total Volume: 9.5 mm3 Stability: 2.4 x 10-10 @ 1sCell Interior Vol: 0.6 mm3 Power Cons: 75 mW
Glass
Alumina
VCSEL
Tiny Physics Package Performance• Experimental Conditions:
Cs D2 ExcitationExternal (large) Magnetic Shielding
Dime
NIST’s Chip-Scale
External (large) Magnetic ShieldingExternal Electronics & LO Cell Temperature: ~80 ºCCell Heater Power: 69 mWC p Sca e
Atomic Physics Package
Cell Heater Power: 69 mWLaser Current/Voltage: 2mA / 2VRF Laser Mod Power: 70μW
Open Loop Resonance: Drift to Be Removed
10-9σ y
Stability Measurement:Drift IssueCs (D2)
5.67
[V]
7.1 kHz
Removed in Phase 3
Sufficient to meet
10-10
Dev
iatio
n,
Q =1.3x106
5.66
PD S
igna
l
Contrast: 0.91% 2.4e-10 Allandeviation @ 1 s
to meet CSAC
program goals
10-11
Alla
n D
Rb (D1) 1 day1 day1 hour1 hour
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 5
40 50 60 70 80 905.65
Frequency Detuning, Δ [kHz] from 9,192,631,770 Hz
100 101 102 103 104 10510-12
Integration Time, τ [s]
1 day1 day1 hour1 hour
Atomic Clock Fundamentals
• Frequency determined by an atomic transition Energy Band Diagram
energy
E it t
ΔE = 1.46 eV
ΔE/hExcite e- to the next orbital
ν = ΔE/h= 352 THz852.11 nm
m = 1 ΔE = 0.000038 eV
ν = ΔE/ħ 133Cs
ν = ΔE/ħ = 9 192 631 770 Hz
m = 0 m = 0
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 6
m = 0f = 4
m = 0f = 3Opposite
e- spins
Miniature Atomic Clock Design
Atoms become transparent to
Carrier(852 nm)
ν = ΔE/ħ
Sidebands
4.6GHz
transparent to light at 852 nm
/= 9 192 631 770 Hz
HyperfineS
9.2GHzλ
Splitting Freq.
ModulatedLaser
PhotoDetector
133Cs vapor at 10–7 torrLaser Cs vapor at 10 torr
Mod fVCXOv
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 7μwave osc
VCXO4.6 GHz Close feedback
loop to lockvo
Chip-Scale Atomic ClockLaser 133Cs vapor at 10–7 torr
GHzGHzResonatorResonator
Mod fVCXOv Photo
Atomic Clock Concept Cs or RbCs or RbVCSELVCSEL
ResonatorResonatorin Vacuumin Vacuumμwave osc
4.6 GHzvo PhotoDetector
p Cs or RbCs or RbGlassGlassDetectorDetectorSubstrateSubstrateMEMS andMEMS and SubstrateSubstrate
Photonic Photonic TechnologiesTechnologies
• Key Challenges:thermal isolation for low power
ll d i f i Q Vol: 1 cmVol: 1 cm33
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 8
cell design for maximum Qlow power μwave oscillator
Vol: 1 cmVol: 1 cm33
Power: 30 mWPower: 30 mWStab: Stab: 11××1010––1111
Chip-ScaleAtomic Clock
Challenge: Miniature Atomic CellLarge Vapor Cell Tiny Vapor Cell
1,000XVolumeVolumeScaling
SurfaceVolume
More wall collisions stability gets worse
tylowest Q
Atomic Resonance
Inte
nsit
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 9
Wall collision dephases atoms lose coherent state
I
Mod f9.2 GHzlower Q
Challenge: Miniature Atomic CellLarge Vapor Cell Tiny Vapor Cell
1,000XVolumeVolumeScaling
Buffer Gas
Soln: Add a buffer gas
Lower the mean free path of the atomic vapor
tyAtomic Resonance Return to
higher QIn
tens
it
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 10
I
Mod f9.2 GHz
Chip-Scale Atomic ClockLaser 133Cs vapor at 10–7 torr
GHzGHzResonatorResonator
Mod fVCXOv Photo
Atomic Clock Concept Cs or RbCs or RbVCSELVCSEL
ResonatorResonatorin Vacuumin Vacuumμwave osc
4.6 GHzvo PhotoDetector
p Cs or RbCs or RbGlassGlassDetectorDetectorSubstrateSubstrateMEMS andMEMS and SubstrateSubstrate
Photonic Photonic TechnologiesTechnologies
• Key Challenges:thermal isolation for low power
ll d i f i Q Vol: 1 cmVol: 1 cm33
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 11
cell design for maximum Qlow power μwave oscillator
Vol: 1 cmVol: 1 cm33
Power: 30 mWPower: 30 mWStab: Stab: 11××1010––1111
Chip-ScaleAtomic Clock
Micro-Scale Oven-Control AdvantagesMacro-Scale Micro-Scale300x300x300 μm3
Atomic Cell @ 80oCHeater
Macro-Oven(containing heater
and T sensor)
LaserInsulationAtomic Cell @ 80oC
Laser
T = P x Rth
Laser25oC
P Rth
T P x Rth
Long, Thin Polysilicon
T Sensor(underneath)
Thermally Isolating Feet
Rth= 38 K/WC = 22 J/K Rth= 83,000 K/W
Cth
R ~ support length
Tethers( )
Cth= 22 J/K thCth= 6.3x10-6 J/K
Cth ~ volume
Rth ~ X-section area
P (@ 80oC) = 2 6 mWP (@ 80oC) = 1 5 W 550x lower power550x lower power
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 12
P (@ 80oC) = 2.6 mW
Warm Up, τ = 0.1 s
P (@ 80oC) = 1.5 W
Warm Up, τ = 16 min.
550x lower power550x lower power
7,300x faster warm up7,300x faster warm up
Physics Package Power Diss. < 10 mW
Heater/Sensor SuspensionC i ll
• Achieved via MEMS-based thermal isolation
SuspensionCesium cell
VCSEL / 20 i LCC
7 mm
Frame Spacer
VCSEL
VCSEL / Photodiode 20 pin LCC
Only ~5 mW heating power VCSEL
Suspension
10
12
g pneeded to
achieve 80oC cell temperatureSymmetricom /
D Ph i
6
8
10
wer
[mW
] MeasuredModel
Draper Physics Package Assembly
0
2
4Pow
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 13
00 20 40 60 80 100 120 140
Temperature [oC]
Thermal Circuit Modeling
Macro-Scale Macro-Oven(containing heater
and T sensor)
Insulation
Laser
Atomic Cell @ 80oC
Laser25oC
Thermally Isolating Feet
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 14
Thermal Circuit Modeling
Insulation
Laser
Atomic Cell @ 80oC
Laser25oC
Thermally Isolating Feet
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 15
Thermal Circuit Modeling
EE C245: Introduction to MEMS Design Lecture 3 C. Nguyen 9/4/08 16