NIR-enhanced image sensor using multiple epitaxial layers

We present the performance characteristics of a CMOS image sensor, manufactured on wafers with a specially designed multiple epitaxial layer. At the homo-junction between two consecutive epitaxial layers a small potential drop or electric field represents a barrier for electrons diffusing towards the back of the wafer. The multiple epitaxial layer stack results thus in a net drive or confinement of photo-charges towards the surface. As a result there is anisotropical diffusion of charge that are generated deep in the Silicon, e.g. by near infrared (NIR) or X-ray radiation. The spectral response is an order of magnitude higher for than for the same image sensor on "regular" wafers. The anisotropical diffusion results in a limited MTF degradation compared to wafers with a single thick epitaxial layer.