1. Chapter 9b: Example of a Micromachined Device: The SA30 Crash Sensor from SensoNor Picture shows the interior chip assembly of SensoNor’s SA30 Crash Sensor The course material was developed in INSIGTH II, a project sponsored by the Leonardo da Vinci program of the European Union

2. Slide 2 Presentation at Transducers ’97, Chicago, USA, June 1997: An Integrated Resonant Accelerometer Microsystem for Automotive Applications Authors: Per Ohlckers*, Reidar Holm*, Henrik Jakobsen*, Terje Kvisteroy*, Gjermund Kittilsland*, Martin Nese*, Svein M. Nilsen* and Alain Ferber** * SensoNor asa, ** SINTEF Electronics and Cybernetics,

3. Slide 3 Outline of presentation: “An Integrated Resonant Accelerometer Microsystem for Automotive Applications” Background and motivation Design and technology evaluations Design Fabrication process ASIC, integration and packaging Results and discussions Future work Conclusions

4. Slide 4 Background and motivation SensoNor has a strong market position: ~ 23 million units (medio 1997) accumulated production of our SA20 Crash Sensor Growing Market for Automotive Crash Sensors: World Market Estimate of more than 60 million units per year in year 2000 Silicon Microsystem Technology can be used to get improved performance at reduced cost

5. Slide 5 Design and Technology Evaluation In a feasibility study we considered: –Piezoresistive element, bulk micromachined –Capacitive element, bulk or surface micromachined –Resonating element, bulk or surface micromachined  Thermal vibration excitation  Piezoresitive vibration detection The resonating principle was chosen: –Excellent performance –Inherent continuous self test function –Excellent mechanical shock survival versus measurement range –Low production cost

6. Slide 6 SA30: Modes of Vibration- Model 4 -7

7. Slide 7 SA30: Modes of Vibration- Model 8 -11

8. Slide 8 SA30 Sensor Die: Beam Deflections and Stresses in Mode 9 Mode 9. Resonance around 650kHz Sensitivity: Around 6-7Hz/g

9. Slide 9 Fabrication Process Important process steps: –Deep n-diffusion to define thickness of mass structure –Epitaxial layer to define thickness of beams –Buried conductors –Anisotropic wet etching from back side –RIE etch from front side to release mass and beam structures –Triple stack anodic bonding of glass and silicon wafers

10. Slide 10 The micromachining process steps Cross sectioned view showing the micromachining process steps in four different stages.

11. Slide 11 The Microsystem ASIC ASIC for vibration control and signal output

12. Slide 12 Integration and Packaging Hybrid integration in surface mount transfer molded epoxy package

13. Slide 13 Results and Discussions: Thickness Measurements of Beams Thickness control with Fourier Transform Infrared Spectroscopy for 56 samples from 5 different batches: Mean: 3.08 micrometer Standard dev: 0.06 micrometer

14. Slide 14 Results and Discussions: Thickness Measurements of Mass Thickness control with Fourier Transform Infrared Spectroscopy for 21 samples: Mean: 23.2 micrometer Standard dev: 0.1 micrometer

15. Slide 15 SA30 Sensor Die: Measurements of Sensitivity and Linearity Modeling: Non-linearity less than 0,1% Measurements: Less than 0.2-0.3 % (Measurement set up limited)

16. Slide 16 SA30 Sensor Die: Measurements of Mode Sensitivity and Separation

17. Slide 17 SA30 Sensor Die: Measurements of Mode Phase Shift Mode 9

18. Slide 18 SA30 Sensor Die: Measurements of Mode Sensitivity and Separation

19. Slide 19 SA30 Sensor Die: Measurements of Mode Phase Shift

20. Slide 20 SA30 Sensor Die: Measurements of Mode Sensitivity and Separation

21. Slide 21 SA30 Sensor Die: Measurements of Mode Phase Shift

22. Slide 22 Future Work and Manufacturing New version of the ASIC to be verified Demonstrate fully operational microsystem Pilot production Full scale production: Millions per year

23. Slide 23 Conclusions Feasibility of chosen design and process technology demonstrated, using: –An acceleration sensitive resonant structure in silicon –An ASIC for resonance control and signal conditioning –Hybrid integration with surface mount transfer molded plastic package Future work: –Demonstrating the fully operational microsystem and ramp up of high volume production

24. Slide 24 Update Primo Year 2000 Fully functional devices produced in sample quantities However: –ASIC too complex and thereby too expensive, thereby target cost was not met –Development was too much delayed to make it for the next generation of air bag systems Therefore, SensoNor has at present decided to put ramp up of production on hold