Curved Full-Frame CMOS Sensor: Impact on Electro-Optical Performances

Optical designs generate curved focal planes for which field flatteners must be implemented. A field flattener consists of an additional lenses block with a consequent loss of throughput and performances. With the recent packaging development for curved sensors, this can be omitted and the optical system simplified. In this paper, we first describe advantages of curved sensors and associated packaging process fabrication, applied on a full-frame format 20Mpx global shutter CMOS image sensor (AMS CMV20000 product). Mechanical limits for curving such full-frame sensor type are discussed, using Finite Element Modelling to manage die breaks. We have curved sensors with a spherical shape from concave Rc=150mm to convex Rc=280mm. We packaged them into their ceramic package and we carried out electro-optical characterization, in collaboration with the AMS CIS characterization team. The electro-optical performances of the curved sensors are investigated and the results compared to the datasheet. We mainly focus on response uniformity, dark noise and dark current results. We present those characteristics in the form of mappings in order to investigate any impact of curvature process on image sensor performances. All these experiments and their electro-optical results demonstrate the feasibility of curving full-frame image sensor with only small electro-optical parameter shift compared to a typical flat reference.