1. MEMS Tuning-Fork Gyroscope Group 8: Amanda Bristow Travis Barton Stephen Nary

2. Outline 1.Introduction: What is a MEMS Gyroscope? 2.Purpose 3.Mechanical Structure: Design and Optimization 4.Electrical Structure: Theoretical Calculations 5.Design Results 6.Manufacturing Process 7.Testing Equipment: PCB 8.Conclusion

3. What is a MEMS Gyroscope? ● A small, silicon device that senses rotation ● Benefits: ● Small size ● Low power ● Cheap to mass produce Common Applications: iPhone 4 Wii Motion Plus MEMS Gyroscope viewed under a microscope

4. Purpose ● To assist Dr. Hao’s research by refining an existing MEMS Gyroscope design to improve accuracy ● To examine the method of fabrication for MEMS devices ● To gain practical experience with the testing of MEMS devices using the existing design

5. Structure of a MEMS Gyroscope Drive electrode Sense electrodes Anchors Proof mass Drive electrode ● Symmetric mechanical structure ● Gyroscope structure free to move, except at anchors ● Comb Drive Transducers used to drive proof masses ● Sense electrodes used to detect rotation Gyroscope Structure

6. Drive Mode ● Structure made to vibrate at natural frequency ● Vibration of proof mass provides necessary velocity for Coriolis Acceleration Drive Mode Vibration

7. Sense Mode ● When rotation is applied, Coriolis force causes proof mass direction to change Coriolis Acceleration Sense Mode Vibration

8. Optimization of Mechanical Structure ● Ideal frequency range: 15 kHZ – 30 kHz ● Ideal difference between drive mode and sense mode: 50 Hz – 100 Hz ● Key Dimensions for adjusting frequency: ● L2 → Sense Mode ● L1 → Drive Mode L2 L1 Key Dimensions

9. Optimization of Mechanical Structure TrialL1, μmDriveL2, μmSenseDifference 552014924.58762015904.967980.381 1349415872.90662015951.40178.495

10. Comb Drive Transducers Drive electrode Anchors Proof mass Drive electrode ● Form capacitors with proof masses ● Use “fingers” to increase surface area ● AC voltage applied to one transducer to excite proof masses to vibrate ● Other transducer used to monitor drive mode vibration Comb Drive Transducers

11. Designing the Comb Drive Transducers V DC ~ v AC Voltage Sources Proof Mass Vibration Amplitude Magnified View: Proof Mass and Comb Drive Fingers

12. Designing the Sense Electrodes Sense Electrodes form parallel plate capacitor with proof mass Sensitivity of Gyroscope (ratio of current to input signal):

13. Design Results Drive Mode Frequency15872.9 Hz Sense Mode Frequency15951.4 Hz Vibration Amplitude3.636x10 -6 m AC Voltage Amplitude0.4810 V Drive Mode Current6.4214x10 -8 A Sensitivity1.1554x10 -6

14. CAD Model for Mask - Calculations determine structure dimensions - Total of 25 fingers on proof mass - 2 micron interference for comb transducers - 3 micron sense gap

15. Manufacturing of MEMS Gyroscope 1. Design is laser etched onto a chrome plated mask. 2. Align mask above silicon wafer. 3. Expose wafer and mask to UV light. Mask Photo resist Silicon Substrate Mask Photo resist Silicon Substrate

16. Manufacturing of MEMS Gyroscope 5. Developing

17. Mechanical structure needs to move freely. Therefore special wafer is used. 6. Etch SiO2 Note: HF does not etch away all SiO2 Manufacturing of MEMS Gyroscope

18. Gyroscope Testing - PCB Weak sense current from gyroscope requires amplification to aid detection Operational Amplifiers and large resistors used to increase current PCB with major components highlighted

19. Conclusion Successes: Gyroscope frequencies within design parameters Theoretical calculations for electrical components within acceptable ranges Desirable Further Work: Fabrication Testing Comparison with existing design

20. Questions?