Design and implementation of monolithically integrated sealed and unsealed chambers by using the wafer level packaging

This study presents the approaches to simultaneously realize various MEMS devices respectively encapsulated inside sealed and unsealed chambers by using the existing microfabrication and wafer level capping processes. In general, the wafer level capping process could encapsulate MEMS devices inside sealed chambers. In this study, the air leakage paths from the encapsulated chamber to the ambient have been selectively patterned and fabricated using the existing processes, so that the unsealed chambers are also achieved. The unsealed chamber is connected to the ambient and can be employed to encapsulate environmental monitoring devices such as humidity or pressure sensors. However, the sealed chamber is isolated with the ambient. The pressure in the sealed chamber is determined by the vacuum condition during the wafer level capping process. The sealed chamber could encapsulate devices such as motion sensors and resonators in the required vacuum condition. Thus, the presented approaches could enable existing process platforms to monolithically fabricate and encapsulate more devices for various applications. Devices such as micromachined Pirani gauge, resonator, and pressure sensor are fabricated and characterized to verify the present approaches. Measurement results indicate that sensors in different pressure conditions are respectively achieved by unsealed chambers and sealed chambers. (paper)