Air-gap guard ring for pixel sensitivity and crosstalk improvement in deep sub-micron CMOS image sensor

An air-gap guard ring around the pixel sensor, to improve pixel sensitivity and crosstalk, in 0.18 /spl mu/m CMOS image sensor technology has been successfully developed. By using the RI (refractive index) difference between the air gap (RI/spl sim/1) and dielectric films (RI=1.4/spl sim/1.6), the major incident light is collected in the targeted pixel due to the total internal reflection occurred in the air-gap/dielectric-film interface. The small pixel pitch of 2.8 /spl mu/m/spl sim/4.0 /spl mu/m has been characterized and demonstrates excellent optical performance. For a 3.0 /spl mu/m pixel, the pixel sensitivity shows 45% enhancement and optical spatial crosstalk achieves 90% reduction at 20/spl deg/ incident angle.