Wafer-level Packaging, Equipment Made in House, and Heterogeneous Integration

Micro-electromechanical systems (MEMS) have been developed for sensors and other systems since 1971 at Tohoku University. Ion-sensitive FET (ISFET) probes made by micromachining were commercialized for pH and PCO2 catheters. Special attention was paid to packaging and wafer-level packaging based on glass-to-Si anodic bonding was applied for integrated capacitive pressure sensors, capacitive diaphragm vacuum gauges, MEMS switches, and other devices. Process equipment for not only MEMS but also integrated circuits (ICs) has been made in house because it is important for flexible prototyping and fabrication of novel devices. Equipment for deep reactive ion etching (RIE) of Si was developed and applied for an electrostatically levitated rotational gyroscope and other devices. Heterogeneous integration as MEMS on LSI has been made possible by the transfer of MEMS on a carrier wafer to an LSI wafer or by stacking a MEMS wafer on an LSI wafer using electrical interconnection with a through Si via (TSV). A piezoelectric MEMS switch on an LSI chip, surface acoustic wave (SAW) filters on an LSI chip, a tactile sensor network, and an active matrix electron emitter array are shown as examples of these technologies.