Wafer-level membrane transfer bonding of polycrystalline silicon bolometers for use in infrared focal plane arrays

In this paper we present a new, innovative technology for fabrication and integration of free-hanging transducers. The transducer structures are processed on the original substrate wafer (sacrificial device wafer) and then transferred to a new substrate wafer (target wafer). The technology consists only of low-temperature processes, thus it is compatible with integrated circuits. We have applied the new membrane transfer bonding technology to the fabrication of infrared bolometers for use in uncooled infrared focal plane arrays (IRFPAs). In the future this may allow bolometers to be integrated with high-temperature-annealed, high-performance thermistor materials on CMOS-based uncooled IRFPAs. Membrane transfer bonding is based on low-temperature adhesive bonding of the sacrificial device wafer to the target wafer. The device wafer is sacrificially removed by etching or by a combination of grinding and etching, while the transducer structures remain on the target wafer. The transducer structures are mechanically and electrically contacted to the target wafer and the adhesive bonding material is sacrificially removed. The free-hanging transducers remain on the target wafer. One of the unique advantages of this technology is the ability to fabricate and integrate free-hanging transducers with very small feature sizes. In principle, membrane transfer bonding can be applied to any type of free-hanging transducer including ferroelectric infrared detectors, movable micro-mirrors and RIF MEMS devices.