Fabrication of polymeric vacuum-sealed cavities on a silicon wafer

A method to fabricate low temperature adhesively bonded vacuum-sealed insulated polymeric cavities on a silicon substrate is presented. Multi-purpose use of the same polymer (Benzocyclobutene (BCB)) as the cavity structural material and also as an adhesive bonding agent minimizes process complexity, cost, and dielectric charging. Scanning electron microscopy (SEM) based characterization results show excellent planarity of BCB surfaces and high quality bonding which is indicative of better reliability. The method paves the way to fabricate the package and the sensor in the same process run to enable higher level of integration and minimize the cost further. The technique can be used to realize capacitive micromachined ultrasonic transducers (CMUTs), MEMS pressure sensors, and 3D embedded packaging and integration of heterogeneous dies.