Tunable Spectral Responses in a Color-Sensitive CMOS Pixel for Imaging Applications

The transverse field detector (TFD), a recently proposed type of CMOS color-sensitive pixel for imaging applications, has an intrinsic and peculiar characteristic of tunable spectral response. The TFD color-detection principle relies on the generation of a suitable electric field configuration in a depleted region of a CMOS low-doped silicon active layer. Depending on the applied voltage at the biasing/collecting electrodes, different electric field configurations can be obtained. In the depleted region, carriers' paths are determined by the electric field streamlines. Simulations show how different biasing values lead to different collection by the electrodes of carriers generated at various depth and, thus, to different sets of spectral photoresponses. Experimental results obtained on structures designed in a 90-nm CMOS technology prove the principle and show the amplitude of the allowable tuning range.