Study of an infrared hybrid chalcogenide silicon lenses compatible with wafer-level manufacturing process for automotive applications – in SPIE Optical Systems Design 2021

Infrared cameras could serve automotive applications by delivering breakthrough perception systems for both in-cabin passengers monitoring and car surrounding. However, low-cost and high-throughput manufacturing methods are essential to sustain the growth in thermal imaging markets for automotive applications, and for other close-to-consumer applications which have a fast growth potential. Fast low cost infrared lenses suitable for microbolometers are currently already sold by companies like Umicore, Lightpath, FLIR… They are either made of a single inverse meniscus Chalcogenide glass or of two Silicon optics. In this paper, we explore hybrid systems with a large field of view around 40° combining Chalcogenide and Silicon in order to take advantage of both materials. Both are compatible with wafer-level process. Silicon optics can be manufactured by photolithography process and are expected to be more cost-effective than Chalcogenide ones. However they are constrained in shape and sag height. On the other hand, Chalcogenide optics can be collectively molded and could have more free shapes. They are thus more suitable to reach high-demanding performance. So hybrid designs could be seen as a compromise between cost and performance. In this paper, we show that fast lenses with diameter constraints to few millimeters to make affordable wafer-level process lead to small size detectors. As a consequence, the pixel pitch reduction of microbolometers is a key point to maintain a good resolution. Finally, strategies to improve the production yield of hybrid lenses are explored.