1. Miniature Tunable Antennas for Power Efficient Wireless Communications Darrin J. Young Electrical Engineering and Computer Science Case Western Reserve University Cleveland, Ohio 44106 CWRU

2. Acknowledgement CWRU NASA under Grant #: NAG3_2578 Collaborator: Professor Wen Ko Graduate Student: Brian Quach

3. Outline CWRU Motivation Proposed Power Efficient System MEMS Tunable Capacitors MEMS Fabrication Technology Conclusion

4. Motivation CWRU 3 dB Loss 2 W PA output 1 W @ antenna Shortened battery life Degraded receiver sensitivity Conventional Radio Front-End Architecture Receive LNA Image Reject Receive BPF Receive Mixer Transmit PA Image Reject Transmit BPF Transmit Mixer Main LO Offset LO Antenna Duplexer Low Power Transceiver: Critical for Wireless Communication

5. Proposed Power Efficient Architecture CWRU Receive Patch Antenna Receive LNA Image Reject Receive BPF Receive Mixer Transmit Patch Antenna Transmit PA Image Reject Transmit BPF Transmit Mixer Main LO Offset LO Tuning Capacitor Eliminating Duplexer Power Saving! Narrow-Band Antennas Frequency Tuning

6. Patch Antenna CWRU 1.6 GHz Patch Antenna S11 Measurement Tuning Capacitor Patch Antenna Tuning Antenna Model C ~ 26 pF L ~ 0.4 nH R ~ 50 Ω

7. Tuning Capacitor CWRU 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 MEMS Tunable Capacitor Only Solution

8. MEMS Tunable Capacitor CWRU Top View Si Cross-Section View Tuning Voltage Top Electrode Isolation layer Substrate Bottom Electrode Vacuum MEMS Capacitor Finite-Element Model

9. MEMS Capacitor Design CWRU Diaphragm Radius Insulator Thickness Electrode Radius Gap Diaphragm Thickness 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) (6) Bottom Electrode Radius: 80 mm

10. MEMS Capacitor Simulation CWRU MEMS Capacitor Under 0VMEMS Capacitor Under 10V Nominal Capacitance: 2 pF Tuning Ratio: 55% @ 5V and 120% @ 10V Estimated Q @ 1GHz: 340 MEMS Large Voltage Swing RF Insensitive

11. CWRU Fabrication Technology Silicon Substrate Cavity and bottom electrode formation Top electrode formation (P + Si to oxide bonding & etching) Vacuum seal & metalization

12. CWRU Current Status & Future Plan Current Status Devices in fabrication Future Plan Device characterization Tunable antenna perform evaluation

13. CWRU Conclusions 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