Developments in Thermoelectric Power Generation Technology

1. Marlow Industries, Inc. Developments in Thermoelectric Power Generation Technology Jim Bierschenk Advanced Concepts in Semiconductor Materials and Devices for Energy Conversion December 7th and 8thSheraton Washington North Beltsville, Maryland

2. Marlow Industries, Inc.a subsidiary of II-VI Incorporated About Marlow Industries, Inc. Headquarters: Dallas, TX (USA) Thermoelectric quality and performance at industry competitive prices. Industry: Thermoelectric Solutions Structure: Operating Subsidiary Founded: 1973 Employees 500+ Manufacturing: Dallas, Vietnam About II-VI Incorporated Headquarters: Saxonburg, PA (USA) Materials Industry: Public/(NASDAQ) IIVI Structure: Marlow Industries- Dallas, TX Center of Technical Excellence 1971 Founded: >6000 Employees II-VI named for their material origin in the compounds listed under II and VI columns on the periodic table: Zn, Cd, S, Se, and Te. $345M FY10 Revenue

3. Marlow Vertical Integration TEC Assembly Sub-System Assembly

4. TE Cooling Markets and Applications Defense, Space & Photonics • Thermal Night Sights • Range Finders and Target Designators • FLIR Calibration Systems Telecommunications • Long Haul Laser Transmitters and Pump Lasers • Short and Mid Range Laser Transmitters/Receivers • Medical • Thermal Cyclers for Polymerase Chain Reactions • Liquid and air refrigerated compartments for blood analyzers • Industrial • Heated & Cooled automotive car seats • Point-of-sale boxes/small refrigerators • Semiconductor processing equipment • Consumer • Water chillers, wine chillers, refrigerators • Personal cooling – bedding, chairs, etc. • Gaming Applications

5. TE Cooling vs. Power Generation Material research driven by waste heat recovery applications Many diverse markets/applications Extensive product customization Flexible manufacturing capability Thermal & mechanical design capability High performance generator materials Many diverse markets/applications Extensive product customization Flexible manufacturing capability Thermal & mechanical design capability Highest performing suite of TE materials

6. TE Power Generation Application Areas Energy Harvesting • Microwatt to low milliwatt power to perpetually power wireless sensors • Battlefield sensors • Engine health monitoring • (temperature, vibration, etc) • Structural health monitoring • (aircraft, building, bridges, etc) • HVAC controls Waste Heat Recovery • Convert heated waste exhaust streams to electric power for improve efficiency • Automotive WHR • Improve fuel economy • & reduce CO2 emissions • Minimize Fuel Consumption • on stationary generators • Convert Industrial Waste Heat to Electricity Co-Generation • Heat produced from burning high energy density fuel. • Self-powered military equipment • Tent heaters • Cooking equipment (ration • tray heaters, griddles) • Cleaner burning 3rd world • cook stoves • Self powered fans for wood stoves and mosquito catchers Direct Power Generation • Burn a hydrocarbon fuel to produce heat – convert heat to electrical using TE Generator • Battery Replace Technology • Unattended Ground Sensors • Soldier power • Robot/UAV power sources • Battery Chargers • Auxiliary Power Units 6

7. Marlow Power Generation • Marlow’s power generation focus is to develop: • Volume production processes for new high temperature materials • Volume production device assembly processes • Single and multistage (cascade capability) • Device and system level thermal and mechanical modeling • Material, device and subsystem test capability • Understand long term reliability • Focus on both low temperature (Bi2Te3) and high temperature applications

8. Energy Harvesting – Why Now? • Evolution of low power sensors, transmitters and power management electronics have made TE energy harvesting practical • Energy harvesting (also known as power harvesting or energy scavenging)

9. Thermoelectric Energy Harvesting RLoad

10. Optimal TEG Design The optimal TEG design for an energy harvesting application: • Thermally matches the combined hot and cold side thermal resistances • Electrically matches the electrical load • Has sufficient couples to provide the minimum threshold voltage for the step-up electronics at the desired source-to-ambient ΔT

11. Interdependence of Thermal and Electrical The electrical load resistance impacts the thermal characteristics of the TEG

12. Energy Harvester TEG Transition Traditional small TE Cooler Can Be used As Energy Harvesting TEG Examples Marlow Energy Harvesting Devices, many of which were co-developed with Sandia National Lab • Prior to low threshold voltage electronics, low ΔT energy harvesting required: • TEGs with hundreds of couples (V is proportional to # couples and ΔT) • High thermal resistance (i.e. large TE element aspect ratios) • Today, with threshold voltages as low as 20 mV, low cost, traditional small TE devices can be used

13. Marlow High Temperature TEG Strategy • Enable a diverse array of thermoelectric power generation applications and markets by developing: • Volume production capability of TE generator devices that can operate to 500 C • Volume production capability for a suite of mid range TE materials • Accurate thermal and mechanical modeling of TEG modules and systems • Test capabilities for materials, devices and subsystems • Quantified reliability

14. N Type Materials P Type Materials Bi2Te3 Power Generation Materials • What power generation materials does Marlow use? • “High Temp” Bi2Te3 (both crystalline and MAM formats) • “PbTe” P and N, TAGS • P and N Skutterudites • Internal and University funded research on other new materials

15. Managing the ZT Envelope • Functionally Graded Materials • Elements made of single alloy with graded composition and/or doping • Segmentation • Elements made of 2+ alloys joined with metal layers that prevent interaction • Cascading • Multistage module with single P and N materials in each stage capability preferred

16. “Traditional” high volume TE module assembly processes used for TE Generator assembly • Single & cascade TE devices • Brazes used instead of solder • Screen print braze paste w/ flux • Wet paste 1-time reflow in CAB Furnace • “Segmented” top ceramic to reduce thermal stresses (i.e. diced into smaller ceramic pieces after assembly) • Simple tools, minimal capital equipment Prototype 50 mm square PbTe Module Marlow CAB Furnace for Braze Assembly • Common device assembly process for both PbTe and Skutterudite materials (different barrier)

17. Prototype TE Generators 2 stage Skutterudite/Bi2Te3 modules 50 mm square Skutterudite modules 2 stage PbTe/Bi2Te3 modules 25 mm square PbTe modules

18. TE Device Test Development • In-house TEG efficiency tester • Vacuum or inert atmosphere • 500 C capability • Up to 40 mm cross sections • Unique device calibration to quantify heat losses • Material Seebeck and resistivity tests to 500 C • Production test capabilities using Harman technique module tester at elevated temperatures • Cycling and constant temperature aging test stand in development

19. Device Level Modeling • Equations governing thermoelectric device behavior (Ioffe, Goldsmid, etc) were derived assuming constant TE material properties • For improved accuracy, these equations are typically used with temperature dependent properties • For cooling, the equations lose accuracy at large ΔT • These fundamental equations were re-derived without the underlying assumption of constant material properties • Provides more accurate modeling of TE coolers and power generators with large ΔTs • Validated with experiment and with full 3D thermoelectric simulations in ANSYS

20. Thermoelectric System Modeling • Model Validation • System test on engine dyno for automotive waste heat recovery system • Output matches Marlow system model prediction

21. DOE CRADAOak Ridge National Lab/Marlow • Objective: “To evaluate materials and devices for waste-heat recovery applications in automotive and heavy vehicle applications up to 500°C.“ • Project Goals: • Thermoelectric and mechanical material properties for TE material • Thermal and mechanical material properties for any supporting material • Develop ANSYS models to evaluate TE devices in automotive applications • Develop life prediction models • Experimental verification of models

22. Power Generation Benefits from Improved in Bi2Te3 • High ZT Inorganic Colloidal Nanocrystal thermoelectric material • Bulk material format addresses a wide range of heat flux applications • Phonon blocking to reduce lattice thermal conductivity • Quantum confinement enhancement of the Seebeck coefficient • Scalable, low cost material fabrication process • Device format and design that minimizes all thermal and electrical losses • High voltage, low current operation enabled by Build-in-Place TEC assembly process • Low electrical contact resistance on a bulk TE material High ZT material  High ZT devices Program: Active Cooling Module (ACM) Program Mgr: Avi Bar-Cohen

23. Thank You! Marlow Industries, Inc. 10451 Vista Park Road Dallas, TX 75283 Jim Bierschenk 214-342-4281 jbierschenk@marlow.com