1. ME342 Jennifer Blundo Gretchen Chua Yong-Lae Park Ali Rastegar
SNF Grand Rounds July 13, 2006
ME342
Jennifer Blundo
Gretchen Chua
Yong-Lae Park
Ali Rastegar

2. 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

3. 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.

4. BioMEMS: Engineering Specs
Device Requirement
Target Value
1. Apply mechanical strain
Up to 10%
2. Apply electric field
~O(1) V/cm
3. Measure electric potential (ECG)
100μV—1mV
4. Area of mechanical deformation
A < 1cm2
5. Size of electrodes
diameter = 20μm
6. Inter-electrode spacing
spacing = 250μm
7. Area of cell culture
A > 1cm2
8. Thickness of substrate
t < 1mm

5. BioMEMS: Device Design
A. Unstrained state
B. Strained 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

6. Mechanical Strain—In Vitro Model
Goal: To apply cyclic mechanical strain to hESC precursor cells and observe differentiation

7. BioMEMS: Stretchable Electrodes
C. S. Park, M. Maghribi
Characterizing the Material Properties of Polymer-Based Microelectrode Arrays for Retinal Prosthesis

8. Biaxial Loading—10% Strain
Geometry
PDMS: t = 100μm
Gold: t = 100nm, w = 30μm, L = 240μm, pitch (p) = 120μm
Material Properties
PDMS: E = 500kPa, v = 0.5
Gold: E = 78GPa, v = 0.44
Stress Contour Plot
Strain Contour Plot

9. PDMS & Gold Electrode Strain

10. BioMEMS: Loading Curves
Operating pressure < 15psi
Young’s Modulus PDMS E = 500kPa
Thickness = 100um
Membrane diameter = 1cm
Loading post diameter = 0.7cm

11. Fabrication: Baseplate
Step 1: Clean Pyrex ” glass wafer (300μm thick), dehydrate 200°C
Equipment: Acetone/Methanol/IPA/DI rinse Location: MERL
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Glass

12. Fabrication: SU-8 Processing
Step 2: Spin 1st layer SU (100μm thick), prebake 65°C, softbake 95°C, expose, postbake 65°C, 10 95°C
Equipment: Spin coater, hot plate, exposer Location: MERL
SU-8 is a negative resist, exposed areas stay (see Signs)
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Channels to apply vacuum pressure to PDMS membrane
Glass
Glass
Exposed SU-8
Unexposed SU-8

13. Fabrication: SU-8 Processing
Step 3: Spin 2nd layer SU-8 (100μm thick), prebake, expose, postbake
Equipment: Spin coater, hot plate, exposer Location: MERL
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Glass
Exposed SU-8
Unexposed SU-8
Loading post to support PDMS membrane

14. Fabrication: SU-8 Processing
Step 4: Spin 3rd layer SU-8 (100μm thick), prebake, expose, postbake
Equipment: Spin coater, hot plate, exposer Location: MERL
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Glass
Exposed SU-8
Unexposed SU-8

15. Fabrication: SU-8 Processing
Step 5: Spin 4th layer SU-8 (80μm thick), prebake, expose, postbake
Equipment: Spin coater, hot plate, exposer Location: MERL
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Glass
Exposed SU-8
Unexposed SU-8

16. Fabrication: SU-8 Processing
Step 6: Develop SU-8, IPA/DI rinse
Equipment: Location: MERL
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Glass
Exposed SU-8

17. Fabrication: SU-8 Processing
Step 7: Pipette tetrafluoropolymer (PS200 or T2494) to prevent PDMS membrane stiction
Equipment: Location: MERL
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Glass
Exposed SU-8
Tetrafluoropolymer

18. Fabrication: Baseplate Assembly
Step 8: Laser cut Pyrex ” quartz wafer (300μm thick) and bond quartz over SU-8
Equipment: Laser cutter Location: MERL
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
20μm clearance between loading post and PDMS membrane
Glass/Quartz
Exposed SU-8

19. Fabrication: PDMS Membrane
Step 1: Clean 4” silicon wafers
Equipment: wbnonmetal Location: SNF
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Silicon

20. 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 plate Location: MERL
PAA (50 kDa) purchased from Polysciences (Warrington, PA).
Sacrificial layer preparation: The PAA purchased as a 25% (w/v) solution in water was neutralized with a saturated solution of
NaOH until reaching a pH of 7.5 with a pH indicator band test, and then diluted to the appropriate concentration.
The silicon wafers were immersed in a 5% aqueous solution of HCl for 5 min, rinsed with deionized water, and dried with a
stream of nitrogen gas. The surface of the polymeric substrates (e.g., PET) was rendered hydrophilic by a brief exposure to
oxygen plasma (30 s, 18 W). Both of these treatments improved the wettability of the aqueous solutions of PAA and dextran on
the substrates. The solutions of water-soluble polymer were filtered (0.45 mm or 5 mm pore size for solutions of polymer with
less or more than 5% (w/v), respectively) and dispensed onto the substrate until about 90% of the surface was covered with
the solution. The sacrificial layer was then prepared by spin-coating the substrate at 1000–4000 rpm for 15 s, and baking the
film on a hot plate (at 150C for silicon, or 95C for polymeric substrates) for 2 min.
Film-thickness measurements: We dissolved the sacrificial layer from over about half of the surface of the substrate with a
stream of water (from a water bottle), and dried the substratewith a stream of nitrogen gas. The thickness of the film was then
determined by averaging profilometry measurements at three different locations on each substrate.
Microfabrication: We prepared the photoresist structures according to the manufacturer’s instructions. For the characterization of
the etching speed of PAA and dextran, for the experiments with Ni electrodeposition, and for the shadow-mask evaporation of
metals, we used sacrificial layers prepared from solutions of polymer of 5% (w/v) and spin-coated at 3000 rpm. The sacrificial
layers for the free-standing structures were prepared from solutions of 19% PAA and 20% dextran (w/v) and spin-coated
at 1000 rpm. The characterization of the etching of the sacrificial layer was carried out with deionized water. For all other experiments we added Tween 20, at a concentration of 0.05%, to improve the wettability of the water (or NaCl solution) on the SU-8 features. The nickel was electrodeposited at constant current, between 1 and 20 mAcm2. The free-standing features were released by immersion in water for 40 s.
Silicon
PAA

21. 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
Water-Soluble Sacrificial Layers for Surface Micromachining
Vincent Linder, Byron D. Gates, Declan Ryan, Babak A. Parviz, and
George M. Whitesides*
SMALL 2005

22. Sacrificial Layers—PAA & Dextran

23. Fabrication: PDMS Membrane
Step 3: Spin 20:1 Sylgard 184 poly(dimethylsiloxane) (PDMS) (40μm thick), bake (60C, 1 hr), O2 plasma
Equipment: Location: MERL
2mm gap at edge of wafer to prevent lift-off of PDMS during processing
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Silicon
PAA
PDMS

24. Fabrication: Electrode Array
Step 4: Align beryllium copper shadow mask and temporarily bond.
Equipment: EV aligner Location: SNF
30μm width tracks for electrode connections
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Silicon
PAA
PDMS
Shadow Mask Ti Au
20μm diameter electrodes

25. 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
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Silicon
PAA
PDMS
Shadow Mask Ti Au
20μm diameter electrodes

26. Fabrication: Electrode Array
Step 6: Remove shadow mask, O2 plasma
Equipment: Drytek Location: SNF
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Silicon
PAA
PDMS
Shadow Mask Ti Au

27. Fabrication: Electrode Array
Step 7: Prebake 110°C, spin photo-patternable silicone (PPS) WL rpm (6μm thick), expose*, 150°C**, develop
Equipment: Hot plate, Spin coater, Karl Suss*, BlueM oven**, wbgeneral
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Silicon
PAA
PDMS
Shadow Mask Ti Au
PPS
*Proximity exposure
**Need to characterize in BlueM Oven

28. Fabrication: Electrode Array
Step 8: Dissolve sacrificial layer PAA in water
Equipment: wbgeneral Location: SNF
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Silicon
PAA
PDMS
Shadow Mask Ti Au
PPS

29. Fabrication: Electrode Array
Step 9: Air dry device
Equipment: N2 gun
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Silicon
PAA
PDMS
Shadow Mask Ti Au
PPS

30. Fabrication: Assembly
Step 1: O2 plasma PDMS and quartz surfaces
Equipment: Drytek
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate
Silicon
PDMS
PPS Ti Au
Glass/Quartz
SU-8

31. Fabrication: Assembly
Step 2: Bond PDMS membrane to glass
Handle wafer is Au-coated Si wafer
1. Si wafer
Sacrifical layer—ie, thin film of Ti or Au. The metal firm serves as a seed layer for electroplating and facilitates removal of the pdms membrane from the wafer
2. *note need a 2 mm gap at edge of wafer to prevent lift-off of pdms layer during processing
3. Spin thick photoresist (30um)
4. Expose so that elecrodes are raised features
5. Spin PDMS at spin rate to keep membrane thickness below pattern height
6. cure pdms
Clean off any pdms adhered to electrodes
7. Electoplate metal electrodes, strain gauges, and contact pads-Pt or Au
8. O2 plasma-oxidize PDMS surface, allows PR to wet the PDMS surface, eliminating beading and ensuring a smooth, uniform coat of resist.
9. Spin resist
10. Expose area for traces.
11. Re-plasma
12. ITO adhesion layer (20nm)
13. E-beam evaporate gold film (150nm)
14. PR removal-acetone lift-off
15. Ethanol rinse and dry to prepare for passivation
16. O2 plasma
17. Spin PDMS membrane
18. Cure PDMS on top of glass substrate Ti Au
SU-8
Glass/Quartz
PDMS
PPS

32. Next Steps Transparency masks SU-8 molding Laser cutting quartz
Plate electrodes on PDMS
Finish SNF training

33. Acknowledgements

34. Sacrificial Layers—PDMS Micromachining
Challenge: etchants may diffuse through PDMS membrane—these traces may ultimately by harmful to cell culture

35. Sacrificial Layers—PDMS Micromachining
Photoresist—acetone removal through selectively etched holes
Backside etch stop of 4000A thick SiO2—1 mm thick PDMS membrane coated with 540A thick sputtered Cr covers PDMS membrane and a PDMS mold is created to protect the whole PDMS structure.
Water soluble sacrificial layers—dextran and PAA—insoluble in most organic solvents!

36. Sacrificial Layers—PAA & Dextran
Films were prepared by spin-coating (3000 rpm, 15 s) from a 5% (w/v) polymer solution in water.
Films were then dried by placing the substrates on a hot plate at 150C for 2 min.
PAA (50 kDa) purchased from Polysciences (Warrington, PA).
Sacrificial layer preparation: The PAA purchased as a 25% (w/v) solution in water was neutralized with a saturated solution of
NaOH until reaching a pH of 7.5 with a pH indicator band test, and then diluted to the appropriate concentration.
The silicon wafers were immersed in a 5% aqueous solution of HCl for 5 min, rinsed with deionized water, and dried with a
stream of nitrogen gas. The surface of the polymeric substrates (e.g., PET) was rendered hydrophilic by a brief exposure to
oxygen plasma (30 s, 18 W). Both of these treatments improved the wettability of the aqueous solutions of PAA and dextran on
the substrates. The solutions of water-soluble polymer were filtered (0.45 mm or 5 mm pore size for solutions of polymer with
less or more than 5% (w/v), respectively) and dispensed onto the substrate until about 90% of the surface was covered with
the solution. The sacrificial layer was then prepared by spin-coating the substrate at 1000–4000 rpm for 15 s, and baking the
film on a hot plate (at 150C for silicon, or 95C for polymeric substrates) for 2 min.
Film-thickness measurements: We dissolved the sacrificial layer from over about half of the surface of the substrate with a
stream of water (from a water bottle), and dried the substratewith a stream of nitrogen gas. The thickness of the film was then
determined by averaging profilometry measurements at three different locations on each substrate.
Microfabrication: We prepared the photoresist structures according to the manufacturer’s instructions. For the characterization of
the etching speed of PAA and dextran, for the experiments with Ni electrodeposition, and for the shadow-mask evaporation of
metals, we used sacrificial layers prepared from solutions of polymer of 5% (w/v) and spin-coated at 3000 rpm. The sacrificial
layers for the free-standing structures were prepared from solutions of 19% PAA and 20% dextran (w/v) and spin-coated
at 1000 rpm. The characterization of the etching of the sacrificial layer was carried out with deionized water. For all other experiments we added Tween 20, at a concentration of 0.05%, to improve the wettability of the water (or NaCl solution) on the SU-8 features. The nickel was electrodeposited at constant current, between 1 and 20 mAcm2. The free-standing features were released by immersion in water for 40 s.

37. Stimulation Electrodes
Goal: To pattern gold electrodes within a flow chamber for selectively stimulating hESCs
Electrodes 100μm x 5000μm (10 per well)
Interelectrode distance 1000μm
Contacts pads 2mm x 2mm (10 per well)
Polished glass wafers 1 mm thick

38. BioMEMS: Strain gauge
Need a strain gauge and a reference strain gauge for every deformable area.

39. Strain gauge design Length (L) Trace width (w) Number of turns (t)
Distance between turns (p)