AR-concepts for hermetic wafer level packaging of uncooled FIR bolometer arrays

Uncooled FIR-bolometer image sensors are established in many applications like building inspections, cold bridge analyses and predictive maintenance. New fields of application are discovered, like automotive night vision, advanced presence detection, gesture recognition etc. but these require a lower cost, small form factor packaging of the μ-bolometer sensors. Wafer level packaging (WLP) is seen as the enabling housing technology compared to ceramic packages for high volume production. Monolithic integrated μ-bolometer image sensors require a vacuum packaging with vacuum level in the range of 10^-3 mbar or less. The growing demand for reliability especially in automotive applications has also a large impact on the package construction. The overall challenge for high sensitive μ-bolometer sensors is to create a small package that allows for a maximum IR transmission at minimum cost. The work describes a wafer level technology on 200mm wafers with a hermetic sealing for large evacuated cavity dimensions with the process integration of different anti-reflective surface treatments. Cavities are created with 90μm thick poly-silicon frames in an additive deposition technology. The IR window region in the caps features different customer specific anti-reflective concepts. One approach is a double side moth eye pattern that can be designed to suppress short wavelength by destructive interference. It is possible to use different geometries of moth eyes in- and outside of the cavities to create a low cost filter. To reduce sunlight transmission a combination of moth eyes inside the cavities and a multi-layer filter coating outside can be achieved. The moth eyes patterns are realized in silicon wafers by reactive ion etching. To generate a high vacuum up to 10^-4 mbar a getter with large exposed surface is required. A 3D structured getter solution is presented that generates a maximum getter surface in a small area in the c- p. First wafers with a good optical resolution and thermoelectric sensitivity have been achieved by a eutectic wafer bonding process.