Wireless Sensor Networks. Picocube

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1 Wireless Sensor Networks Low Power Radio Power Storage Sensor Renewable Power Picocube Supply

2 Vibrational Energy Scavenging Nathan Emley DRETD TAC Meeting February 19, 2008 Vibrational Scavenger Team: Lindsay Miller Padraic Shafer

3 Vibrational Energy Scavenging Viable renewable energy generation technique (~10 2 µw/cm 3 ). Sol-gel-derived lead zirconate titanate (PZT) moves us to volume manufacturing. Allows for practical integration with standard silicon processing.

4 Why Vibrational Scavenging? Piezoelectrics provide high electromechanical conversion without external power source Piezobenders amplify strain power Roundy et al., Pervasive Computing, 28-35, Jan.-Mar. 2005

5 Piezoelectric PZT More charge (Q) can be generated with larger piezoelectric coefficients (d ij ). Piezo coefficient Stress P d 33 mode + - V

6 Piezoelectric PZT More charge (Q) can be generated with larger piezoelectric coefficients (d ij ). Piezo coefficient Stress P d 33 mode + - V S. Trolier-McKinstry & P. Muralt, J. Electroceramics, 12 pp.7-17 (2004)

7 Previous Scavenger Devices Pulsed-Laser Deposited (PLD) PZT Estimated power density: E. K. Reilly, Ph.D. Thesis, Univ. Cal, Berkeley (2007). Single beam: 1-5 nw Volume: ~10 2 µw/cm 3 Gold mass 400 nm Metals 300 nm PZT 1000 nm SRO 50 nm STO 20 nm Si 500 µm

8 Limitations of PLD PZT Ultra-high vacuum deposition technique Lengthy deposition (2-3 samples/day) Limited device area (~ 1 cm 2 )

9 Limitations of PLD PZT Ultra-high vacuum deposition technique Lengthy deposition (2-3 samples/day) Limited device area (~ 1 cm 2 ) Spin-on piezoelectric: moves us to volume manufacturing (arbitrary wafer size coverage). faster turnaround time for device testing. Sol-gel PZT

10 Sol-gel PZT Chemical Precursors Lead Acetate Trihydrate: Zirconium n-propoxide: Titanium iso-propoxide: Solvents, Diluents, Catalysts acetylacetone, 2-methoxymethanol, propyl alcohol, acetic acid, distilled water, etc.

11 Sol-gel PZT Deposition Pb:Zr:Ti = 125:52:48 Spin coat

12 Sol-gel PZT Deposition Pb:Zr:Ti = 125:52:48 Solvent bake 75ºC Spin coat

13 Sol-gel PZT Deposition Pb:Zr:Ti = 125:52:48 Solvent bake 75ºC C H C H Amorphous film Spin coat Pyrolysis 400ºC

14 Sol-gel PZT Deposition Pb:Zr:Ti = 125:52:48 Solvent bake 75ºC C H C H Amorphous film Spin coat Pyrolysis 400ºC Pb O 2 O 2 Polycrystalline film Crystallization Anneal 700ºC

15 Sol-gel PZT Deposition Pb:Zr:Ti = 125:52:48 Solvent bake 75ºC C H C H Amorphous film Spin coat Pyrolysis 400ºC Pb O 2 O 2 Polycrystalline film Crystallization Anneal 700ºC Subsequent spin coating

16 Sol-gel PZT Is Piezoelectric Pt electrode PZT QuickTime and a H.264 decompressor are needed to see this picture. Release etch 10 Vpp; 5 V offset; 5 Hz QuickTime and a Video decompressor are needed to see this picture.

17 Scavenger Behavior Estimated output power for PLD PZT cantilevers E. K. Reilly et al., Proc. Body Sensor Networks, MIT, Boston (2006).

18 Scavenger Behavior Estimated output power for PLD PZT cantilevers HVAC Clothes dryer Refrigerator 60 Hz S. Roundy, Computer Communications, 26 pp (2003). E. K. Reilly et al., Proc. Body Sensor Networks, MIT, Boston (2006).

19 Goals for Vibrational Scavengers Reduce resonant frequency to practical ambient levels. Young s modulus Mass density

20 Goals for Vibrational Scavengers Reduce resonant frequency to practical ambient levels. Young s modulus Mass density polymers dielectrics

21 Goals for Vibrational Scavengers Engineer a more broadband response. Illustrative data 60 Hz 120 Hz

22 Goals for Vibrational Scavengers Engineer a more broadband response. Non-orthogonal modes 60 Hz 120 Hz 60 Hz 120 Hz

23 Goals for Vibrational Scavengers Engineer a more broadband response. Simulated data (10 µm thick Poly-Si structure): E = 160 GPa ρ = 2320 kg/m3 400µm 10µm 300µm

24 Goals for Vibrational Scavengers Engineer a more broadband response. Simulation

25 Vibrational Energy Scavenging Viable renewable energy generation technique (~10 2 µw/cm 3 ). Sol-gel-derived piezoelectric PZT moves us to volume manufacturing. Allows for practical integration with standard silicon processing. QuickTime and a Video decompressor are needed to see this picture.