1. Direct-Current Nanogenerator Driven by Ultrasonic Waves
Bryan Schubert
EE C235
April 9, 2008
X. Wang, J. Song and Z. L. Wang, Science 316, 102 (2007).

2. Application Energy scavenging Remote powering of implanted devices
Force/pressure sensors
X. Wang, J. Song and Z. L. Wang, Science 316, 102 (2007).

3. Principle of operation
Piezoelectric effect:
d is piezoelectric coefficient
Z. L. Wang and J. Song, Science 312, 242 (2006).

4. Principle of operation
Pt-ZnO Schottky barrier
AFM scan of nanowire array
Z. L. Wang and J. Song, Science 312, 242 (2006).

5. Principle of operation
Nanowire contact scenarios:
I. & II. Nanowire is bent until compressed side contacts electrode.
III. Resonating nanowire.
IV. Compressed nanowire.
X. Wang, J. Song and Z. L. Wang, Science 316, 102 (2007).

6. Fabrication ZnO Nanowires Pt-coated Si zigzag electrode Total device
Grown on Al2O3, using Au particles as catalyst for Vapor-Liquid-Solid process.
10/μm2 density
1 μm long
40 nm diameter
Pt-coated Si zigzag electrode
Wet-etching*
1 μm peak-to-peak
200 nm Pt layer
Total device
2 x 106 μm2 area
X. Wang, J. Song and Z. L. Wang, Science 316, 102 (2007).
*J. Frühauf and S. Krönert, Microsyst. Technol. 11, 1287 (2005).

7. Performance Equivalent circuit Vs, nanowire source
Ri, active NW contact resistance w/ electrode
Rw, inactive NW resistance – 30 kΩ
Rc, measurement device contact resistance w/ electrode – 30 Ω
IA ≈ Vs/(Rc+Ri)
V ≈ -VsRw/(Ri+Rw)
Output for 41 kHz wave
0.15 nA increase in IA
V = -0.7 mV output
R = 3.56 kΩ
Estimated 250 to 1000 NW engaged
X. Wang, J. Song and Z. L. Wang, Science 316, 102 (2007).

8. Performance Alternative designs CNTs are not piezoelectric
Flat electrode does not allow contact of compressed edge.
X. Wang, J. Song and Z. L. Wang, Science 316, 102 (2007).

9. Performance Durability Power Efficiency*
Can produce dc output for over 1 hour
Power
1 to 4 fW per fiber
1 pW total output
to 0.005% of fibers contribute
Efficiency*
Mechanical-to-electrical, 17 to 30%
X. Wang, J. Song and Z. L. Wang, Science 316, 102 (2007).
* Z. L. Wang and J. Song, Science 312, 242 (2006)

10. Improvements
Control nanowire dimensions to optimize power per nanowire (1 fW to 10 fW per fiber).
Control spacing and patterning to optimize nanowire co-operation (10 μW/cm2 => 0.2 μW for this device).