A Sealing Technique for Stacking MEMS on LSI Using Spin-Coating Film Transfer and Hot Pressing

This paper describes a novel sealing technique that uses spin-coating film transfer and hot pressing (STP). STP is a key technique in integrating microelectromechanical systems (MEMS) on large-scale integrated circuits (LSIs). It enables us to form a film over cavities and concavities easily by hot-pressing a dielectric in vacuum. Based on an analytical model, the effect of critical parameters for sealing was clarified. in the experiments, concave line-patterns 100 mum wide were scaled with a 20-mum-thick dielectric. The sealing characteristics were also examined experimentally with regard to film thickness and width of cavities, which quantitatively shows that the technique has the possibility of sealing patterns of various sizes. We applied this technique to the fabrication of a MEMS fingerprint sensor, whose MEMS structures with cavities must be stacked on an LSI. Using the fabricated sensor, we succeeded in capturing a fingerprint image, which indicates that the sealing technique does not cause damage and is compatible with the underlying LSI. This sealing technique will be a driving force in extending seamless integration technology to produce high-functionality MEMS devices on LSIs.