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A Thermoelectric Cat Warmer from Microprocessor Waste Heat

A Thermoelectric Cat Warmer from Microprocessor Waste Heat. Simha Sethumadhavan Doug Burger Department of Computer Sciences The University of Texas at Austin. Motivation. Hot laptops Cold cats Frozen whiskers Reduced pest control. Solution. Purr. On chip Thermoelectric Generator.

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A Thermoelectric Cat Warmer from Microprocessor Waste Heat

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  1. A Thermoelectric Cat Warmer from Microprocessor Waste Heat Simha Sethumadhavan Doug Burger Department of Computer Sciences The University of Texas at Austin

  2. Motivation • Hot laptops • Cold cats • Frozen whiskers • Reduced pest control

  3. Solution Purr On chip Thermoelectric Generator Heat Current This talk

  4. Hot End Cold End TH Tc i Thermoelectricity • Thermoelectricity: Electricity produced from heat • First observed by Seebeck in 1822 Wire Replica of the apparatus V = S.T Thomas Seebeck

  5. Traditional Uses Seiko “Thermic” watches 5°C body heat, 60W Doped Poly Si, .3% efficiency Cassini space probe 32.8Kg radioactive plutonium fuel, InGaAs thermocouple, 628 Watts, 3-4% efficiency

  6. Cat Mutator Docile Cat Radioactive Plutonium Pellet

  7. e Electrons: current flow Phonons: heat flow p The Physics When a wire is heated electrons and phonons diffuse • Electrons • Higher electron diffusion  more current (good) • Phonons • Collide with other phonons and increase heat flow (bad) or • Either transfer their momentum to electrons (good) or • Lose their momentum due to boundary collisions (good) e e e e e p p p p p p e e e e Hot end Cold end

  8. Traditional Materials Ideally for large thermoelectric current • Low phonon flow • Const temperature difference  Low thermalconductivity • Many high energy electrons • Small resistance  High electrical conductivity • Many phonon electron collisions • Large voltage per unit temperature difference  High Seebeck constant Nanotech allows constants be controlled independently & precisely

  9. New Thin-film Wires • Thin film and metal boundary do not align • More phonon boundary collisions • More electron phonon collisions • Figure of Merit (M = seebeck2. elec/therm) • Traditional Poly Si is 0.4 • Thin-film Bismuth Tellurideis 2.38 • [Venkatasubramanium et al. Nature 2001] e e e e e p p p p p p e e e e Cold end Hot end Thin film (few nanometers)

  10. Generator Efficiency Maximum theoretical efficiency of any generator Chip temperatures • Cold end (Tc) • 27°C • Hot end (TH) • 77° C, 52 ° C • M for Bismuth Telluride • 6x better

  11. Horizontal Generator Horizontal Generator (nanowire bundles) Hot end Cold end Wiring Layers Die • Run a bundle of Bismuth Telluride nanowires from processor hot spot to cold spot • Temperature difference: ~50 degrees

  12. Vertical Generator Wiring Layers Hot surface Die Cold surface Vertical Generator • Run a bundle of Bismuth Telluride nanowires from logic level to the heat spreader • Temperature difference: ~20 degrees

  13. Multiple Generators Vertical Generator Purr Cold surface Die Hot surface

  14. Rough Estimates For Bismuth Telluride: • Seebeck coefficienct 243V/K • Resistivity: 1.2 x 10-5 ohm/meter

  15. Conclusions • Limitations • Manufacturing • Engineering: Hinders cooling, peripheral circuitry overheads • Only cats are supported • Final thoughts • Thermoelectric heat extraction looks interesting • Newer materials can improve power output further • How far can this be pushed? • When does this become interesting to architects? Thank You!

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