Transcript Micro Power Telemetry Link for MEMS Sensing

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Miniature Tunable Antennas for Power
Efficient Wireless Communications
Darrin J. Young
Electrical Engineering and Computer Science
Case Western Reserve University
Cleveland, Ohio 44106
Acknowledgement
NASA under Grant #: NAG3_2578
Collaborator: Professor Wen Ko
Graduate Student: Brian Quach
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Outline
• Motivation
• Proposed Power Efficient System
• MEMS Tunable Capacitors
• MEMS Fabrication Technology
• Conclusion
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Motivation
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Low Power Transceiver: Critical for Wireless Communication
Conventional Radio Front-End Architecture
Receive LNA
Antenna
Image Reject
Receive BPF
Receive Mixer
Main LO
Duplexer
3 dB Loss
Transmit PA
Image Reject
Transmit BPF
Offset LO
Transmit Mixer
2 W PA output  1 W @ antenna
Shortened battery life
Degraded receiver sensitivity
Proposed Power Efficient Architecture CWRU
Receive Patch Antenna
Receive LNA
Image Reject
Receive BPF
Receive Mixer
Tuning Capacitor
Main LO
Transmit Patch Antenna
Transmit PA
Image Reject
Transmit BPF
Offset LO
Tuning Capacitor
Transmit Mixer
Eliminating Duplexer  Power Saving!
Narrow-Band Antennas  Frequency Tuning
Patch Antenna
1.6 GHz Patch Antenna
S11 Measurement
Patch Antenna Tuning
C ~ 26 pF
L ~ 0.4 nH
R ~ 50 Ω
Antenna
Model
Tuning
Capacitor
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Tuning Capacitor
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• Nominal Capacitance: 1 ~ 2 pF
• Tuning Ratio: 100 % with 5 to 10 V  (~100MHz)
• High Quality Factor (Q): ~ 100 at RF (GHz)
• High Voltage Handling: 1 W  20 V peak to peak
• Insensitive to RF Signals
Only Solution
MEMS Tunable Capacitor
MEMS Tunable Capacitor
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Si
Top View
Vacuum
Top Electrode
MEMS Capacitor Finite-Element Model
Isolation
Substrate
layer
Bottom Electrode
Cross-Section View
Tuning
Voltage
MEMS Capacitor Design
Diaphragm
Thickness
Insulator
Thickness
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Diaphragm Radius
Gap
Electrode Radius
Critical Design Parameters:
(1) Touch point pressure (TPP): 12 psi
Large TPP  small initial touched area  large tuning ratio
(2) Diaphragm thickness: 2 mm (small initial capacitance & accurate process
control)
(3) Gap: 1 mm (accurate process control)
(4) Diaphragm Radius: 120 mm (for TPP of 12 psi)
(5) Insulator (Oxide) Thickness: 300 Å (Thin Layer  Large tuning, limited by BD)
MEMS Capacitor Simulation
MEMS Capacitor Under 0V
• Nominal Capacitance: 2 pF
• Tuning Ratio: 55% @ 5V and 120% @ 10V
• Estimated Q @ 1GHz: 340
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MEMS Capacitor Under 10V
• MEMS  Large Voltage Swing
 RF Insensitive
Fabrication Technology
Silicon Substrate
Silicon Substrate
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Cavity and bottom
electrode formation
Top electrode formation
(P+ Si to oxide bonding &
etching)
Vacuum seal & metalization
Silicon Substrate
Current Status & Future Plan
• Current Status
Devices in fabrication
• Future Plan
Device characterization
Tunable antenna perform evaluation
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Conclusions
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• Tunable patch antennas for low power wireless applications
• MEMS tunable capacitor provides:
High-Q
Large tunable range
Large voltage handling
Insensitive to RF signals
• MEMS capacitors for tuning patch antennas
transmitter output matching networks
high spectral purity RF oscillators