Asia Symposium & Research Review 2012
Integrated MEMS by Adhesive Bonding
MEMS (Micro Electro Mechanical Systems) have been developed by extending the technology for integrated circuits to 2.5 dimensional and heterogeneous directions. The MEMS are integrated with circuits as SoC (System on Chip) or SiP (System in Package) and used for the user interface of systems and so on. Capacitive sensors as accelerometers, gyroscope and microphone can take advantage of reduced stray capacitance owing to the integration of capacitance detection circuits with sensors. The capacitive sensors are SoC or SiP and mass-produced as sensors for the user interface. On the other hand, arrayed MEMS as ink jet printer head, mirror array for projector and infrared imager are mostly SoC. MEMS for RF components and other devices require advanced heterogeneous integration and for this purpose technologies as adhesive bonding of MEMS wafer to circuit wafer have been developed. Switches and filters fabricated on LSI for multi-band wireless systems require good mechanical properties for the MEMS and small feature size for the LSI. The adhesive bonding methods were applied for the fabrication of integrated MEMS as piezoelectric PZT MEMS switch, micromechanical filter, SAW (Surface Acoustic Wave) filter, tactile sensor and active matrix electron emitter. MEMS wafer is bonded to a LSI wafer and the adhesives are removed if necessary. The MEMS should be encapsulated on a wafer because the moving MEMS are damaged by direct plastic molding. Wafer level packaging with LTCC (Low Temperature Co-fired Ceramics) which has electrical feedthrough for interconnections has been developed for this purpose. Open collaborations such as shared LSI wafer and shared facility have been needed to develop such heterogeneous technologies and produce small volume cost effectively.