Integrated vacuum packaging for low-cost light-weight uncooled microbolometer arrays

Uncooled thermal infrared sensors (1) require to be operated in an ambient gas pressure of about 50mTorr or less to avoid sensitivity being reduced by thermal conduction through the gas. Although sealed packages have been developed which can retain a sufficiently low internal pressure for many years, the packaging process (cleaning, assembly, pumping, baking, getter firing, sealing) and materials add significant cost and weight. Lower cost is the major reason for the development of uncooled arrays, and low weight is essential for many applications (eg unmanned aerial vehicles, helmet mounted applications). In response to these needs, Honeywell has developed a silicon "Integrated Vacuum Package" (IVP) process which produces a low-cost lightweight (0.2 gram) compact vacuum package by a wafer-scale process (2). The IVP process basically consists of bonding a silicon "topeap" wafer to the array wafer, to produce a bonded double-wafer with multiple arrays protected in individual vacuum packages. The double-wafer may be easily handled without damage to the protected arrays, and diced into individual dies using normal silicon dicing techniques. It has been found helpful to use an etched evacuation via, which allows wafer bonding, pumping, baking and sealing to be performed in separate stages, at their, different optimum times and temperatures. The IVP process will be described, and packages suitable for linear and two-dimensional uncooled arrays will be reported, with performance and lifetime measurements.