RF MEMS have potential for energy harvesting by converting electromagnetic energy into electrical charge. The proposed RF MEMS design aims to be scalable and easily integrated in microsystems, unlike existing MEMS energy harvesters that have low efficiency, scaling issues, and high costs. RF MEMS can be fabricated using processes like co-planar waveguide deposition, lithography, aluminum deposition and patterning, and sacrificial layer removal. When activated, the RF MEMS structure can store up to 35 pC of charge per cycle that is generated from the membrane's overlap with the signal isolation layer. However, reliability issues from electrostatic discharge still need to be addressed for practical applications in wireless sensors.

1. ENERGY HARVESTING USING
RF MEMS
RICHU JOSE CYRIAC
M120128EC
MICROELECTRONICS & VLSI DESIGN
NIT CALICUT
WINTER 2012

2. OUTLINE
 Introduction
 Limitation of existing
 RF MEMS
 Design
 Fabrication
 Energy stored by RF MEMS
 Reliability issues
 Conclusion

3. INTRODUCTION
 MEMS energy harvesting – a new alternative
 Electro-magnetic MEMS, Electrostatic MEMS,
Piezoelectric MEMS – low efficiency, scaling
issues, high cost.
 Proposed design – scalable and easily integrated
in microsystems.
 RF MEMS convert solar energy into charge, can
achieve a better benefits than photovoltaic cell.

4. LIMITATIONS OF EXISTING
 Photovoltaic cells and wind power harvesting
have several technical barriers.
 In solar cells, the inherent physical limits, the
black body energy conversion loss, optical loss,
and internal resistance prevent their efficiency
from reaching >20%

5. By applying a photosensitive coating and transparent electrode, the
electric charge can be generated and stored in the RF MEMS structure.

6. RF MEMS-DESIGN
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7. RF MEMS-FABRICATION
1. Co-planar waveguide deposition and lithography
2. Silicon dioxide and wet etching
3. Pattern Sacrificial Photoresist

8. RF MEMS-FABRICATION
4. Aluminum deposition and patterning of Aluminum
Bridges
5. Removal of Sacrificial polymer

9. Microscopic view of RF MEMS

10. ENERGY STORED BY RF
MEMS

11. ENERGY STORED BY RF
MEMS
 Membrane overlap over the signal isolation
layer - determines the maximum energy that
can be stored per area of the RF MEMS.
 C=0.3 pF (switch off), C= 1 pF (switch on)
 A maximum charge of 35 pC was found to be
stored and discharged per cycle per switch.
VCQ

12. RELIABILITY ISSUES
 Mechanical failures such as creep and fatigue
are not a big problem.
 Electrostatic discharge-induced(ESD) failure.
 ESD results in charge injection and charge
trapping in the interface.

13. CONCLUSION
 RF MEMS has potential applications for energy
harvesting.
 Potential application in wireless sensors
application.
 Free energy source is available maintenance-
free throughout the lifetime of the application.
 The pull down voltage of the RF MEMS was
found to be 35V with a resonant-frequency of
25 MHz.
 Reliability issues like ESD still remains.

14. REFERENCE
 Energy Harvesting Using RF MEMS, Yunhan
Huang, Ravi Doraiswami, Michael Osterman, and Michael Pecht,
Electronic Components and Technology Conference 2010

15. THANK YOU