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 i ntegration of free-hanging transducers. The transducer structures are proce ssed on the original substrate wafer (sacrificial device wafer) and then tr ansferred to a new substrate wafer (target wafer). The technology consists only of low-temperature processes, thus it is compatible with integrated ci rcuits. We have applied the new membrane transfer bonding technology to the fabrication of infrared bolometers for use in uncooled infrared focal plan e arrays (IRFPAs). In the future this may allow bolometers to be integrated with high-temperature-annealed, high-performance thermistor materials on C MOS-based uncooled IRFPAs. Membrane transfer bonding is based on low-temper ature adhesive bonding of the sacrificial device wafer to the target wafer. The device wafer is sacrificially removed by etching or by a combination o f grinding and etching, while the transducer structures remain on the targe t wafer. The transducer structures are mechanically and electrically contac ted to the target wafer and the adhesive bonding material is sacrificially removed. The free-hanging transducers remain on the target wafer. One of th e unique advantages of this technology is the ability to fabricate and inte grate free-hanging transducers with very small feature sizes. In principle, membrane transfer bonding can be applied to any type of free-hanging trans ducer including ferroelectric infrared detectors, movable micro-mirrors and RIF MEMS devices.