MEMS WLP Processes &Examples

1. MEMS WLP Processes &Examples Michael Shillinger Innovative Micro Technology Santa Barbara, California, USA mjs@imtmems.com

2. Introduction • Applications • Optical devices • RF switches • IR devices • Accelerometers • Resonators • Various Bonding Technologies • Si fusion • Anodic • Glass frit • Au-Au thermocompression • Low temperature eutectic • Polymer

3. Bonding Overview • Si Fusion Bonding • Si wafers at 1050°C • No metals • Engineered substrates • Hermetic • Highest strength • Topography intolerant • Anodic • Glass (high sodium) and Si at 300°C-400°C • 300V DC applied • Topography intolerant • Strong and hermetic

4. Bonding Overview • Glass Frit • Any type of substrates at 400°C • 400µm bondline width • Controlled thickness of 100µm • Strong and Hermetic • Up to 12,000 Gs acceleration • Topography tolerant • Au-Au Themocompression • Any type of substrates at 200°C-300°C • Topography intolerant • Strong and Hermetic

5. Bonding Overview • Low temperature eutectic • Any type of substrates 190°C • Reflows at 500°C • Topography tolerant • 50µm bondline width • Hermetic • Polymer • Room temperature • Topography tolerant • Not hermetic • Photodefinable bondline

6. Bonding Overview TSV • Electroplated Cu in etched Si • Oxidation for isolation • Allows for low resistivity electrical connection with die shrink • Good RF performance

7. Bonding Overview TSV

8. Optical Devices • High temperature damages internal components • Mirrors, faraday rotators, circuits, lasers • Hermeciticy required for laser reliability and mirror reflectivity Lid Wafer (hermetically sealed before wafer is sliced) Mirror Bond Pad Ball Lens Laser Rotator

9. Planar Waveguides Optical Devices • Most common bond chosen • Low temperature eutectic • Hermetic • Topography tolerant • 190°C

10. RF Switches • Hermeticiy required • Alignment is critical • +/- 3µm between 3 wafers • Bond line thickness needs to be tightly controlled • Optimizes contact force • TSV incorporated • Reduced die size • More efficient RF performance

11. RF Switches • Most common bond technology • Au-Au thermocompression • Low temperature eutectic • Temperature constraints • Bondline thickness control

12. IR Devices Detectors & Emitters • Single digit mTorr vacuum • Getter required • Most efficient energy consumption • Temperature sensitive • 300°C

13. IR Devices • Most common bond technology • Au-Au thermocompression • Bond temperature activates getter • Hermetic • Narrow bondline widths • WLP is significantly less expensive than traditional packaging

14. Resonators/Accelormeters • Capacitive or resistive sensing • Vacuum requirements are design dependant • Temperature constraints • Due to circuit metallurgy • 300°C • Sensitive to squeeze film damping

15. Resonators/Accelerometers • Most common bond technology • Au-Au thermocompression • Low temperature eutectic • Low temperature • Hermeticity • Narrow bondline widths

16. Conclusion • WLP is used in many different MEMS applications • Certain technologies are better suited than others for particular applications • Vacuum requirements, temperature budget etc.

17. Questions?