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Fabrication Process PDMS Electrode Array. ME342 MEMS Laboratory Jennifer Blundo Gretchen Chua Yong-Lae Park Ali Rastegar. Project Goal.

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fabrication process pdms electrode array

Fabrication Process PDMS Electrode Array

ME342 MEMS Laboratory

Jennifer Blundo

Gretchen Chua

Yong-Lae Park

Ali Rastegar

project goal
Project Goal
  • Design a bioMEMs substrate to apply and measure electromechanical forces in the differentiation of human embryonic stem cell-derived (hESC)-cardiac myocytes (CM)

hESC-CMs organized in embryoid body

Contractility

Electrophysiology

Mechanical force

Undifferentiated hESCs-Fluc-eGFP (DAPI nuclear stain)

bioMEMS device

current microscale devices
Current Microscale Devices

Thin-film gold strain gauges (200nm) encapsulated in PDMS (50μm). Wen et al, 2005.

Thin-film stretchable (0—15%) gold electrodes (25nm) on PDMS. Lacour et al, 2005.

64 Electrode array for extracellular recording, Multi Channel Systems

Pressure actuated PDMS membrane (120μm) with S-shaped SiO2 traces. Lee et al, 2004.

biomems device design
BioMEMS: Device Design

B. Strained state

A. Unstrained state

Glass/Quartz: Optically transparent baseplate

PDMS: A biocompatible elastomeric polymer

PPS: A biocompatible elastomeric polymer

Ti: Adhesion layer for electrodes

Gold: Biocompatible thin film electrodes

SU-8: Transparent polymer

fabrication baseplate
Fabrication: Baseplate

Step 1:Clean Pyrex 7740 4” glass wafer (300μm thick), dehydrate 5min @ 200°C

Equipment: Acetone/Methanol/IPA/DI rinse Location: MERL

Glass

fabrication su 8 processing
Fabrication: SU-8 Processing

Step 2: Spin 1st layer SU-8-100(100μm thick), prebake 10min @ 65°C, softbake 30min @ 95°C, expose, postbake 1min @ 65°C, 10 min @ 95°C

Equipment: Spin coater, hot plate, UV Location: MERL

Channels to apply vacuum pressure to PDMS membrane

Glass

Glass

Exposed SU-8

Unexposed SU-8

fabrication su 8 processing1
Fabrication: SU-8 Processing

Step 3: Spin 2nd layer SU-8(100μm thick), prebake, expose, postbake

Equipment: Spin coater, hot plate, UV Location: MERL

Loading post to support PDMS membrane

Glass

Exposed SU-8

Unexposed SU-8

fabrication su 8 processing2
Fabrication: SU-8 Processing

Step 4: Spin 3rd layer SU-8(100μm thick), prebake, expose, postbake

Equipment: Spin coater, hot plate, UV Location: MERL

Glass

Exposed SU-8

Unexposed SU-8

fabrication su 8 processing3
Fabrication: SU-8 Processing

Step 5: Spin 4th layer SU-8(80μm thick), prebake, expose, postbake

Equipment: Spin coater, hot plate, UV Location: MERL

Glass

Exposed SU-8

Unexposed SU-8

fabrication su 8 processing4
Fabrication: SU-8 Processing

Step 6: Develop SU-8, IPA/DI rinse

Equipment:Location: MERL

Glass

Exposed SU-8

fabrication su 8 processing5
Fabrication: SU-8 Processing

Step 7:Pipette tetrafluoropolymer (PS200 or T2494) to prevent PDMS membrane stiction

Equipment:Location: MERL

Glass

Exposed SU-8

Tetrafluoropolymer

fabrication baseplate assembly
Fabrication: Baseplate Assembly

Step 8: Laser cut quartz 4” wafer (300μm thick) and bond quartz over SU-8

Equipment: Laser cutter Location: MERL

20μm clearance between loading post and PDMS membrane

Glass/Quartz

Exposed SU-8

fabrication pdms membrane
Fabrication: PDMS Membrane

Step 1: Clean 4” silicon wafers

Equipment:wbdiffLocation: SNF

Silicon

fabrication pdms membrane1
Fabrication: PDMS Membrane

Step 2: Spin sacrificial layer 5% (w/v) poly(acrylic acid) (PAA) (3000 rpm, 15 s) and bake (150C, 2 min)

Equipment:Spin coater, Hot plateLocation: MERL

¼” Kapton tape at edge, removed after bake to prevent lift-off of PDMS during processing

Silicon

PAA

sacrificial layers pdms micromachining
Sacrificial Layers—PDMS Micromachining
  • Advantages of water-soluble films
    • Deposited by spin-coating
    • The solvent removed at a low temperature (95–150C)
    • The resulting layer can be dissolved in water
    • No corrosive reagents or organic solvents
    • Faster release of features by lift-off
  • Compatible with a number of fragile materials, such as organic polymers, metal oxides and metals—materials that might be damaged during typical surface micromachining processes
biomems fabrication
BioMEMS: Fabrication

Step 3:Spin thick photo resist ~ 10μm

Equipment:SVGcoatLocation: SNF

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

biomems fabrication1
BioMEMS: Fabrication

Step 4:Expose, develop, postbake

Equipment:KarlSuss, SVGdevLocation: SNF

200μm interelectrode distance

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

20μm diameter electrodes

biomems fabrication2
BioMEMS: Fabrication

Step 5: Gold deposition (2μm thick)

Equipment:MetallicaLocation: SNF

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

biomems fabrication3
BioMEMS: Fabrication

Step 6: Resist strip

Equipment:Wbgeneral2Location: SNF

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

biomems fabrication4
BioMEMS: Fabrication

Step 7: Spin photo-patternable silicone (PPS) WL5153 30sec @ 2500rpm (6μm thick), prebake 110°C

Equipment:HeadwayLocation: SNF

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

biomems fabrication5
BioMEMS: Fabrication

Step 8: Expose*, postbake @ 150°C**, develop, hardbake 150°C

Equipment:MetallicaLocation: SNF

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

fabrication electrode array
Fabrication: Electrode Array

Step 9: O2 plasma (several min)* to etch and round PPS as well as promote adhesion of metal deposition

Equipment: Gasonics

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

PPS

*Requires characterization

fabrication electrode array1
Fabrication: Electrode Array

Step 10:Align beryllium copper shadow mask and temporarily bond.

Equipment: EV aligner Location: SNF

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

fabrication electrode array2
Fabrication: Electrode Array

Step 11: Evaporate Ti adhesion layer (10nm thick), Au layer (100nm thick), Ti adhesion layer (10nm thick)

Equipment: Innotec Location: SNF

Maintain 200μm interelectrode distance

30μm width horseshoe tracks for electrode connections

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

30μm diameter to allow 20μm diameter electrodes

fabrication electrode array3
Fabrication: Electrode Array

Step 12: Remove shadow mask, O2 plasma to clean and promote adhesion

Equipment:Location: SNF

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

fabrication electrode array4
Fabrication: Electrode Array

Step 13: Spin 20:1 Sylgard 184 poly(dimethylsiloxane) (PDMS) 90sec @ 1200 rpm (50μm thick), bake (60°C, 1 hr)

Equipment:Location: MERL

Silicon

PAA

PPS

Ti

Au

PDMS

fabrication electrode array5
Fabrication: Electrode Array

Step 14:Dissolve sacrificial layer PAA in water

Equipment: wbgeneral Location: SNF

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

PPS

fabrication electrode array6
Fabrication: Electrode Array

Step 15: Air dry device and transfer with handle wafer (glass)

Equipment: N2 gun Location: SNF

PPS

PDMS

Ti

Au

Glass

fabrication assembly
Fabrication: Assembly

Step 16: O2 plasmaPDMS and quartz surfaces

Equipment: Drytek

PDMS

PPS

Ti

Au

Glass/Quartz

SU-8

fabrication assembly1
Fabrication: Assembly

Step 2: Bond PDMS membrane to glass

Ti

Au

SU-8

Glass/Quartz

PDMS

PPS

process option 2 top to bottom

PDMS Electrode Array

Process Option 2—Top to Bottom

Skip Photoresist—Pattern PPS right on PAA, expose, deposit metal

fabrication electrode array7
Fabrication: Electrode Array

Step 4: Spin photo-patternable silicone (PPS) WL5153 30sec @ 2500rpm (6μm thick), prebake 110°C, expose*, postbake @ 150°C**, develop, hardbake 150°C

Equipment: Hot plate, Spin coater, Karl Suss*, BlueM oven**, wbgeneral

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

PPS

*Proximity exposure

**Need to characterize in BlueM Oven

fabrication electrode array8
Fabrication: Electrode Array

Step 5: O2 plasma (5 min)* to etch and round PPS

Equipment: Gasonics

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

PPS

*Requires characterization

process option 3 bottom to top

PDMS Electrode Array

Process Option 3—Bottom to Top

Pattern PDMS right on PAA, deposit metal, spin PPS, expose, O2 plasma etch down OR HCl dip if use Ti layer

fabrication pdms membrane2
Fabrication: PDMS Membrane

Step 1: Clean 4” silicon wafers

Equipment:wbdiffLocation: SNF

Silicon

fabrication pdms membrane3
Fabrication: PDMS Membrane

Step 2: Spin sacrificial layer 5% (w/v) poly(acrylic acid) (PAA) (3000 rpm, 15 s) and bake (150C, 2 min)

Equipment:Spin coater, Hot plateLocation: MERL

¼” Kapton tape at edge, removed after bake to prevent lift-off of PDMS during processing

Silicon

PAA

fabrication pdms membrane4
Fabrication: PDMS Membrane

Step 3: Spin 20:1 Sylgard 184 poly(dimethylsiloxane) (PDMS) (50μm thick), bake (60C, 1 hr), O2 plasma (1 min)

Equipment:Location: MERL

2mm gap at edge of wafer to prevent lift-off of PDMS during processing

Silicon

PAA

PDMS

fabrication electrode array9
Fabrication: Electrode Array

Step 4:Align beryllium copper shadow mask and temporarily bond.

Equipment: EV aligner Location: SNF

200μm interelectrode distance

30μm width tracks for electrode connections

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

30μm diameter to allow 20μm diameter electrodes

fabrication electrode array10
Fabrication: Electrode Array

Step 5: Evaporate Ti adhesion layer (10nm thick) and Au layer (100nm thick)*

Equipment: Innotec Location: SNF

30μm width tracks for electrode connections

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

30μm diameter to allow 20μm diameter electrodes

*May want second layer of Ti to promote adhesion to PPS on top layer! Use an HCl dip to dissolve this

fabrication electrode array11
Fabrication: Electrode Array

Step 6: Remove shadow mask, O2 plasma

Equipment: Drytek Location: SNF

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

fabrication electrode array12
Fabrication: Electrode Array

Step 7: Spin photo-patternable silicone (PPS) WL5153 30sec @ 2500rpm (6μm thick), prebake 110°C, expose*, postbake @ 150°C**, develop, hardbake 150°C

Equipment: Hot plate, Spin coater, Karl Suss*, BlueM oven**, wbgeneral

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

PPS

*Proximity exposure

**Need to characterize in BlueM Oven

fabrication electrode array13
Fabrication: Electrode Array

Step 8: O2 plasma (5 min)* to etch and round PPS as well as promote adhesio

Equipment: Gasonics

PPS

Silicon

PAA

PDMS

Ti

Au

PPS

*Requires characterization

fabrication electrode array14
Fabrication: Electrode Array

Step 9:Dissolve sacrificial layer PAA in water

Equipment: wbgeneral Location: SNF

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

PPS

fabrication electrode array15
Fabrication: Electrode Array

Step 10: Air dry device and transfer with handle wafer (glass)

Equipment: N2 gun

Silicon

PAA

PDMS

Shadow Mask

Ti

Au

PPS

fabrication assembly2
Fabrication: Assembly

Step 1: O2 plasmaPDMS and quartz surfaces

Equipment: Drytek

Silicon

PDMS

PPS

Ti

Au

Glass/Quartz

SU-8

fabrication assembly3
Fabrication: Assembly

Step 2: Bond PDMS membrane to glass

Ti

Au

SU-8

Glass/Quartz

PDMS

PPS

process option 4 entire device

PDMS Electrode Array

Process Option 4—Entire Device

Pattern PDMS right on top of baseplate with PAA sacrifical layer, follow process option 3

fabrication pdms membrane5
Fabrication: PDMS Membrane

Step 1:Fill baseplate with sacrificial layer—5% (w/v) poly(acrylic acid) (PAA). Spin, squeegy off, bake (150C, 2 min). O2 plasma (1 min)

Equipment: Spinner Location: MERL

20μm clearance between loading post and PDMS membrane

Glass/Quartz

Exposed SU-8

fabrication pdms membrane6
Fabrication: PDMS Membrane

Step 2: Spin 20:1 Sylgard 184 poly(dimethylsiloxane) (PDMS) (50μm thick), bake (60C, 1 hr), O2 plasma (1 min)

Equipment: Spinner, oven Location: MERL

20μm clearance between loading post and PDMS membrane

Glass/Quartz

Exposed SU-8

fabrication pdms membrane7
Fabrication: PDMS Membrane

Final Device: Deposit metal, spin PPS, expose, O2 etch

Glass/Quartz

Exposed SU-8

fabrication pdms membrane8
Fabrication: PDMS Membrane

Final Device: Dissolve PAA

Glass/Quartz

Exposed SU-8

the meander evolution

The Meander Evolution…

Challenge: To maintain electrical connections under strain

material properties geometry
Material Properties & Geometry
  • Material Properties
    • PDMS: E = 500kPa, υ = 0.5
    • Gold: E = 78GPa, υ = 0.44
  • Geometry
    • PDMS: t = 100μm
    • Gold: t =100nm, w = 30μm,

L = 240μm, pitch (p) = 120μm

  • Loading Condition
    • Plane Strain
    • Biaxial Loading—10% Strain

G. Yang, et al. Design of Microfabricated Strain Gauge Array to Monitor Bone Deformation In Vitro and In Vivo. Proc. 4th IEEE Symposium on Bioinformatics and Bioengineering. 2004

1 st generation the sepertine
1st Generation: The Sepertine

Strain Contour Plot

Stress Contour Plot

2 nd generation the horseshoe
2nd Generation: The Horseshoe
  • Geometry
    • PDMS: t = 100μm
    • Gold: t =100nm, w = 30μm,

R = 60μm , H = 45°

D. Brosteaux, et al.. Elastic Interconnects for Stretchable Electronic Circuits using MID (Moulded Interconnect Device) Technology.Mater. Res. Soc. Symp. Proc. Vol. 926. 2006

2 nd generation the horseshoe1
2nd Generation: The Horseshoe

Strain Contour Plot

Stress Contour Plot

Results: Stresses are distributed in a wider region, instead of being concentrated in a small zone at the crests and troughs.

Strains are lower at the boundaries, decreasing potential of delamination

the meander evolution1

The Meander Evolution…

Challenge: What if an electrode breaks?

How do we know if a connection is compromised?

3 rd generation horseshoe hairpin
3rd Generation: Horseshoe Hairpin

Strain Contour Plot

Stress Contour Plot

Results: Stresses are distributed in across the area of the electrode, however, stresses are higher in the immediate turn.

Strains are lower at the electrode.

4 th generation angled horseshoe hairpin
4th Generation: Angled Horseshoe Hairpin

Strain Contour Plot

Stress Contour Plot

updates
Updates
  • Training done:
    • Wbgeneral
    • Innotec
    • Amtetcher
    • Laser Ablator
  • Training still needed:
    • Litho Solvent Bench (if PPS is allowed)
    • EV Aligner
updates1
Updates
  • Fabrication:
    • Spinning of PDMS on Si Wafer
      • 10:1, 50 ums, 1000 RPM, 90 secs (G. Yang, et al.)
      • O2 Plasma in Gasonics for 25 secs (program A, no lamp)
      • Problems – PDMS is a challenge to peel off
      • Possible Solution – PAA sacrificial layer
    • Spinning PR on PDMS (Backup method)
      • SPR 3612 1.6 um, baked in the 90ºC for 30 mins
      • Problems – cracking of PR
      • Possible solution – ramping of temperature instead of baking (suggested by Vikram). Similar to SU-8 stacking
updates2
Updates
  • Fabrication:
    • Exposure of PR on PDMS
      • Karlsuss 2 (down during the weekend ruined 3 wafers)
      • Tried exposure times of 1.6-2 seconds. Contact pads were overexposed, but tracks were not defined
    • Cr/Au deposition in Innotec
      • 100 A Cr/ 1000 A Au
      • Purpose – check adhesion
      • Still need to strip the PR to lift the unwanted metal
updates3
Updates
  • Fabrication:
    • Spinning of PAA
    • Spinning of SU-8
updates4
Updates
  • Masks:
    • SU-8 Masks are already here
    • Shadow Masks Vendors
updates5
Updates
  • Transparency Mask Design:
updates6
Updates
  • Shadow Mask Design:
action items
Action Items
  • Get training on more machines
  • Check actual thickness of PDMS on Dektak
  • Send in shadow masks once finalized
  • Characterize photo-patternable silicone (MERL)
    • Still waiting for SPECMAT, looks like yes from MT but might need an official yes from Ed Meyers and Mahnaz, too
  • Laser cut quartz wafers
  • Trial of Ti and Au adhesion on PDMS