title: Sputtered Encapsulation as Wafer Level Packaging for Isolatable MEMS Devices: A Technique Demonstrated on a Capacitive Accelerometer.
abstract: This paper discusses sputtered silicon encapsulation as a wafer level packaging approach for isolatable MEMS devices. Devices such as accelerometers, RF switches, inductors, and filters that do not require interaction with the surroundings to function, could thus be fully encapsulated at the wafer level after fabrication. A MEMSTech 50g capacitive accelerometer was used to demonstrate a sputtered encapsulation technique. Encapsulation with a very uniform surface profile was achieved using spin-on glass (SOG) as a sacrificial layer, SU-8 as base layer, RF sputtered silicon as main structural layer, eutectic gold-silicon as seal layer, and liquid crystal polymer (LCP) as outer encapsulant layer. SEM inspection and capacitance test indicated that the movable elements were released after encapsulation. Nanoindentation test confirmed that the encapsulated device is sufficiently robust to withstand a transfer molding process. Thus, an encapsulation technique that is robust, CMOS compatible, and economical has been successfully developed for packaging isolatable MEMS devices at the wafer level.
authors.affiliation: Institute of Microengineering and Nanoelectronics (IMEN), Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia. azlanhamzah@ukm.my.
authors.forename: Azrul Azlan
authors.initials: AA
authors.lastname: Hamzah
authors.affiliation: Institute of Microengineering and Nanoelectronics (IMEN), Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia.
authors.forename: Jumril
authors.initials: J
authors.lastname: Yunas
authors.affiliation: Institute of Microengineering and Nanoelectronics (IMEN), Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia. burhan@vlsi.eng.ukm.my.
authors.forename: Burhanuddin Yeop
authors.initials: BY
authors.lastname: Majlis
authors.affiliation: Department of Electrical, Electronics, and Systems Engineering, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia. ibrahim@vlsi.eng.ukm.my.
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Ahmad
keywords: Silicon encapsulation; capacitive accelerometer; liquid crystal polymer; sputtering; wafer level packaging