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Femtosecond Laser

Micromachining of BioMEMS

BioMEMS Lab

Mechanical and AerospaceEngineering

University of Texas Arlington

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Comparison of Micromachining Processes

Process Resolutionm

SurfaceRoughness m Side Effects

Mechanical 100 6.3-1.6 Burring, requires polishing

EDM 100 4.75-1.6 Electrode wear, roughfinish, slow and unclean

process

Chemical Etch 250 6.3-1.6 Undercutting

LIGA 5 1-2 Synchrotron source: veryexpensive

Nd: YAG Laser 50 1 Redeposition

Excimer Laser 5 > 1 m (nm range) Recast Layer, aspect ratios

Ti:sapphireUltrafast Laser

< 1 nm range Higher power ranges mayrequire vacuum

environment

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Laser Micromachining Process

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Advantages of Laser Micromachining

Non-contact machining

Very high resolution, repeatability and aspect ratios

Localized heating, minimal redeposition

No pre/post processing of material

Wide range of materials: fragile, ultra-thin and

highly reflective surfaces

Process can be fully automated

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Effect of Laser Micromachining Process

Parameters

Process Parameters Effect

Wavelength,

Focal length of lens

Feature size

Beam shape

(Gaussian/square wave)

Feature shape

Beam energy,

Pulse width

Size of heat affected

zone

Depth of focus Aspect ratio

Vacuum or inert gas

environment

Amount of redeposition,

size of recast layer

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Characteristics of Femtosecond Laser

Micromachining

Very high peak powers in the range 1013W/cm2

provide for minimal thermal damage to surroundings

Very clean cuts with high aspect ratios

Sub-micron feature resolution

Minimal redeposition Possible to machine transparent materials like glass,

sapphire etc

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Ultrashort Pulses vs. Long Pulse

Micromachining

Ti: sapphire,120fs a) air b) vacuum c) Nd:YAG, 100nsCourtesy: Sandia National Labs

Extremely short pulses provide for minimal thermaldamage to surroundings

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Femtosecond Laser System at BioMEMS Lab

Spectra PhysicsHurricaneFemtosecond Ti: sapphireLaser

Pulse width: 106fs

Wavelength range: 750nm-850nm

Average energy: 1mJ/pulse

Beam profile: Gaussian

Polarization: linear, horizontal

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Femtosecond Laser Micromachining(Preliminary Experimental Testbed)

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Additional Equipment for Femtosecond Laser

Micromachining Ultra-high precision 3-axis linear stage assembly byAerotech

Inc.

Ultrafast High Energy Beam Attenuator by Newport Corporation.

Power Meter by Scientech Inc.

2GHz Oscilloscope by Hewlett Packard

Under development

10-3 Torr, 1m3 Vacuum Chamber with inert gas and electrical

and power ports

Fully automated multiple lens changer

LabView based control environment

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Preliminary Experimental Results

(a)Array of shots (b) Thru-hole drilled after 33 shots at apulse energy of 14J

Micromachining in 18m Thick Aluminum Foil

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Single Shots in 18m Thick Aluminum Foil

Focal position Off-focal position

Preliminary Experimental Results

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Thru-holes Drilled in 25m Thick Brass Foil

56J/pulse 27J/pulse

Preliminary Experimental Results

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Ablation Rate vs. Energy Density in 18m

Thick Aluminum Foil

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 10 20 30 40 50

Energy Density (J/cm2)

AblationRate(m/puls

e)

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Optimization of Pulse Energy Required to

Drill Thru-Holes

0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40 50

Energy Density (J/cm2)

TotalPulseEnergy(

J)

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Femtosecond Laser Bonding of Optically

Transparent Materials

Explore femtosecond laser bonding of optically

transparent PMMA or glass to a substrate

Automatic lens changer will be used to study the

effect of variable focal length on the bond strength

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Laser Intensity Distribution in PMMA

Focal length of 9mm Focal length of 40mm

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Through the Thickness Intensity

Distribution of Transmitted Laser Beam inPMMA

Focal length of 9mm Focal length of 40mm

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Automation of Laser Micromachining

Process

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Conceptual Solid Model of LaserMicromachining Setup