Towards zero power ICT
Nanoscale energy harvesting, towards
autonomous devices
Natalio Mingo, CEA-Grenoble
Towards zero power ICT, Lyon, November 27, 2008
N. Mingo – LITEN, CEA-Grenoble
Goals:
Energy harvesting at the nm scale
Integration with low power ICT into autonomous
microsensors and actuators
IC power
consumption
Power supply
time
Towards zero power ICT, Lyon, November 27, 2008
N. Mingo – LITEN, CEA-Grenoble
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Self-powered nanoscale electronic devices
Smart dust (Berkeley, 1997- )
Wireless sensor networks
Chem. Commun., 2005, 1375–1383.
power
structural
Power
storage
Physical
input
signal
Sensor
biomedical
emitter
processor
actuator
Goal: 1 mm3
How far are we from “nano”
wireless sensor?
Problem 1: battery size
Problem 2: battery lifetime
220 mm3 for a
10 year
operation
Battery: 63
mm3
Sensor and
communicator:
0.078 mm3
1-10μW
per node
Urgent goal: harvest energy from the environment
Towards zero power ICT, Lyon, November 27, 2008
N. Mingo – LITEN, CEA-Grenoble
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How do we harvest energy? What energy?
Solar power:
1 mW / mm2 outdoor
0.1-10 μW / mm2 indoor
30% efficiency
Good, but it cannot be the only source.
What if there is no light?
Emerging types of energy harvesting:
Thermal
ΔT
Vibrational
Radio frequency
How do we “measure” their suitability for beyond-smart-dust devices?
Metrics:
voltage > 1V,
power density > 1 μW/mm3
Fabrication ease: compatible with IC technology?
Power conditioning challenges
(ac-dc conversion, amplification, impedance matching …)
Towards zero power ICT, Lyon, November 27, 2008
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Direct Conversion of Heat into Electricity
JAP 103, 101301 (2008)
(www.tellurex.com)
Cross plane device
In plane device
Advantages:
compatible with IC fabrication technology
Produces dc current simplifies conditioning for battery charging.
Towards zero power ICT, Lyon, November 27, 2008
N. Mingo – LITEN, CEA-Grenoble
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State of the art in microscale thermoelectric conversion
historical
Cross plane,
IC fabrication
In plane, high
aspect ratios
Nanomaterials
Towards zero power ICT, Lyon, November 27, 2008
N. Mingo – LITEN, CEA-Grenoble
From Hudak and Amatucci, JAP 103, 101301 (2008)
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How to go further?
•
•
•
•
Higher junction densities
Seamless or monolithic contacts
Longer legs
Radically new nano materials
evolutionary
revolutionary
Integration into devices:
“ambient” is different when one is small:
small ΔT⇒ mV;
Fluctuations lead to unsteady flow
(need smart electronics/MEMS)
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Vibrational energy harvesting at small scales
Problems for miniaturization:
-ac current, needs ac-dc convertor
-frequency matching is challenged
by size reduction
From Roundy et al, Comp. Commun. 26 (2003) 1131–1144
Transduction mechanisms:
Inductive
Piezoelectric
Capacitive
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State of the art comparisons
Induction: Sheffield U. (1997),
4 mm3, 0.3 μW at 4400 Hz
and 380 m/s2, 0.003 V
Piezoelectric: Shanghai U. (2006),
1.2 mm3, 2.2 μW at 608 Hz and
9.8 m/s2, 0.6 V
Advantages: more power per volume
than the others, no need for separate
voltage source.
Capacitive: CEA-Grenoble (2005),
18000 mm3, 1050 μW at 50 Hz
and 8.9 m/s2.
Advantages: easily
integrable with MEMS.
General challenges for
scale down:
-frequency matching
-rectification, signal
conditioning.
Towards zero power ICT, Lyon, November 27, 2008
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Some other potentially interesting ambient power
sources and storage systems
• Radio Frequency energy harvesting
• Molecular based thermoelectric junctions
• Bio fuel cells
• …
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Some recent nanoscale breakthroughs
Wang, 2006:
Piezoelectric ZnO vibration power
generator.
Science 316, 102 (2007);
At 41 KHz, 1 mV, predicted 10 mW/cm2.
Self-rectification by wires (dc output)
Shakouri, 2006:
Thermoelectric ZT enhancement by nanoparticles.
Phys. Rev. Lett. 96, 045901 (2006)
ErAs (semimetal)
nanoparticles in
InGaAs
Towards zero power ICT, Lyon, November 27, 2008
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Carrying the idea further
Silicides in SiGe: defect free nanoparticle composites
Do nanoparticles reduce the thermal conductivity
below that of SiGe alloys? Yes, 5 times at 300K.
silicide
Will they affect the electrical properties? Not for a
volume fraction ~ 0.8 %
SiGe
Predicted ZT:
0.5 at 300K, 1.7 at 900K.
Fully Si compatible material !
Mingo et al. Nano Lett (2008, to be published)
Towards zero power ICT, Lyon, November 27, 2008
N. Mingo – LITEN, CEA-Grenoble
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A proposal for monolithically integrated, Si compatible thermoelectric
energy conversion on a chip
Target breakthroughs of proposed new
thermoelectric harvesting:
A multidisciplinary effort
•ZT > 0.5 at 300 K, ZT > 1.5 at high
temperature.
• Theoretical material’s development
• Material’s growth (MOCVD, MBE)
• Nanocomposite thin film thermal conductivity
measurements (time domain thermoreflectance)
• Electrothermal characterization (s, S, ZT)
• Thermoelement fabrication
• Module fabrication
• Packaging
•Sub 1 mm3, 1μW, 1V, under ΔT~K.
•compatibility with silicon technology.
Monolithic integration.
•non-toxicity.
200nm
200nm
60s
Ø=20-50 / e=3-20
30s
200nm
10s
Ø=15-40 / e=3-10
Ø=20 / e=2
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Conclusions
• Smart-dust type concepts are challenged by the size and lifetime of
the battery. It is urgent to provide self-powering, via ambient energy
harvesting at the microscale, beyond 1μW/mm3 at 1V.
• Thermoelectric and vibration energy harvesting are just two examples
of emerging technologies to get energy from a microscopic
environment. Despite important progress, the state of the art is not
quite yet at the sub mm3 level.
• Harvesting device proposals should address integration and signal
conditioning issues as well: ac-dc conversion or additional electronic
needs, IC compatibility, etc.
• Important breakthroughs in nanoscience and nanotechnology will
allow us to overcome miniaturization challenges.
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N. Mingo – LITEN, CEA-Grenoble
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