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Si wafer bonding for use in fuel cells
- 1. Silicon Wafer Bonding for Use in Fuel Cells Slobodan Petrovic, Bryan McGinnes, and Chetan Chaudhari Arizona State University
- 2. MOTIVATION Support creation of manufacturing process for silicon-based fuel cell Develop comprehensive methodology for polymer bond evaluation Enable fast and reliable screening of candidate bonding materials Designed bonding Develop practical products and processes Goal for this presentation: connect wafer bonding with important field of energy
- 3. HYDROGEN ECONOMY: SOLAR- HYDROGEN CYCLE H2O H2 Fuel Cell Electricity Generation Transportation Stationary Residential Commercial Industry H2O Storage Electrolyser
- 4. FUEL CELLS Fuel cells are devices that convert chemical energy of fuel into electricity H+ H+ H2 2H+ + 2e- 2H+ + ½ O2 + 2e- H2O LOAD e- H2 O2 CHEMICAL ENERGY OF FUEL ELECTRICAL ENERGY THERMAL ENERGY MECHANICAL ENERGY Cell Reaction: 2H2 + O2 = 2H2O + Electricity + Heat
- 5. FUEL CELL CLASSIFICATION FUEL CELL SYSTEM TEMPERATURE RANGE EFFICIENCY ELECTROLYTE APPLICATION AREAS Alkaline (AFC) 60-900 C 50-60% 35-50% KOH Space Traction Polymer Electrolyte (PAFC) 50-800 C 50-60% Polymer membrane (Nafion, Dow) Space Phosphoric Acid (PAFC) 160-2200 C 55% H3PO4 (conc.) Dispersed power Molten Carbonate (MCFC) 620-6600 C 60-65% LiCO3/Na2CO3 Power generation Solid Oxide (SOFC) 800-10000 C 55-65% ZrO2/Y2O3 Power generation
- 6. PEM FUEL CELLS (CF2CF2)X - (CFCF2) - O (CF2CF)n- (CF2)m - SO- 3H+ CF3 Membrane material Carbon support Pt catalyst H2 O2 Water ANODE Polymer Electrolyte Membrane H+ CATHODE Proton exchange membrane: Nafion type Catalyst layer: Pt Electrode substrate- backing layer: carbon Flow field plate - carbon Gas channels Gas channels MEMBRANE CARBONPAPERORCLOTH CARBONPAPERORCLOTH
- 7. FUEL CELL MARKET TIMING Fuel cell technology is not market ready. Fuel cell cost must be drastically reduced while performance improves. 100,000 10,000 1,000 100 10 Systemprice,$/kW 2000 2010 2020 2030 Remote Stationary Residential CHP Automotive Mass markets Portable Backup UPS
- 8. SILICON-BASED FUEL CELLS Silicon substrate High thermal conductivity Low density High corrosion resistance High thermal stability High pattern stability Very low gas permeability Adjustable electronic conductivity High-volume manufacturing Proton exchange membrane: PBI Catalyst layer: Pt Flow field plate - Silicon Gas channels H2 H+ e- BULK MEMBRANE H+ e- e-
- 9. 9 SCALABILITY OF SILICON BASED FUEL CELLS kW range W range
- 11. WAFER BONDING SIGNIFICANCE Air in H2 inH2 out Air out ANODE CATHODE BondingBond Catalyst Catalyst MEMBRANE Au Au Si Si Next cell Bond
- 12. EXPERIMENTAL STRATEGY Bonding material requirements: Low-temperature curing Excellent dielectric properties Low permeability for gases Good mechanical properties No change in properties: • Bias • Elevated temperature • Moisture • Acidic environment Bond evaluation using Electrochemical Impedance Spectroscopy “No-bias voltage” evaluation for basic bond integrity Evaluation under bias voltage Evaluation after exposure to acidic medium Elevated temperature CATHODE 3H2O2 + 6e- + 6H+ 6H2O ANODE CH3OH + H2O 6H+ + 6e- + CO2 H+ through electrolyte LOAD Electrons flow round the external circuit
- 13. POLYMER BONDING MATERIALS Compound Supplier Chemical type Curing conditions Dielectric Constant Dielectric Strength Dissipation factor Volume resistivity Elastosil LR3003/50 Wacker Silicones Division Polydimethyl siloxane 115°C for 1 hour 3.1 @ 50Hz 23 kV / 1mm 0.003 @50Hz 5x10^15 ohm-cm Sylgard 184 Dow Corning Corp Silicone Elastomer at 80°C for 1.5 hours 2.65 @100Hz, 540V / mil 0.0005@100 Hz 1.2x10^14 ohm-cm EPO-TEK 301-2 Dow Corning Corp epoxy resin 80°C for 1.5 hour 3.1-3.67 @100kHz 500 V/mil, 0.012 @1kHz 2x10^12 ohm-cm EPO-TEK 353 Dow Corning Corp thixotropic epoxy 80°C for 30 minutes 3.1 @ 1kHz 18kV/mm 0.003 @1kHz 4x10^12 ohm-cm EPO-TEK 377 Dow Corning Corp high Tg, epoxy adhesive 150°C for 1 hour 3.36 @ 1kHz / 0.005 @1khz 1x10^13 ohm-cm
- 15. EXPERIMENTAL Compound Res. = Measured Sample Res. – Copper Res. – Silicon Res.
- 17. EIS WITH “NO-BIAS” Blue LR3003 Light Blue Sylgard Green EPO-TEK301 Light Green EPO-TEK353 Red EPO-TEK377
- 18. EIS WITH BIAS VOLTAGE - EXAMPLE LR3003/50 Blue 0.7V Light Blue 0.8V Green 0.9V Light Green 1.0V Red 1.1V Light Red 1.2V
- 19. SAMPLES UNDER BIAS 0.7 V Light Blue LR3003 Blue Sylgard Green EPOTEK301 Light Green EPOTEK353 Red EPOTEK377
- 20. EIS UNDER BIAS AND HUMIDITY - EXAMPLE EPO-TEK353 Blue No bias, no humidity Green 0.7V bias Light Green 1.2V bias Red 0.7V with humidity Light Red 1.2V with humidity
- 21. SAMPLES UNDER BIAS AND HUMIDITY CONDITIONS 0.7 V Blue Sylgard Light Blue LR3003 Green EPO-TEK301 Light Green EPO-TEK353 Red EPO-TEK377
- 22. CONCLUSIONS First part of a comprehensive protocol was developed Using EIS, differences in polymer material behavior under bias and humidity conditions were detected One polymer exhibited very good performance Two polymers showed poor performance PDMS materials show better performance than epoxy materials EIS is a very suitable technique to study complete properties of bond polymers for use in fuel cells Using this technique and expanded protocol, suitable candidate materials can be found that will have predictable performance when used in fuel cells
- 23. FUTURE WORK Continue work under bias and humidity Elevated temperature pressure Other fuels: e.g. methanol Mechanical testing: “pull-test”, hardness Permeability testing Polymer decomposition Equivalent circuit model for wafer bond Designed bonding