Optimization of CMOS image sensors with single photon-trapping hole per pixel for enhanced sensitivity in near-infrared

Single microhole per pixel for thin Ge-on-Si complementary metal-oxide semiconductor image sensor with enhanced sensitivity up to 1700 nm

“…Microhole arrays were shown to enhance the optical absorption of Si for the 800-1000 nm wavelength range 16 and the Ge for the 1400 to 1800 nm wavelength. 17 The study 6,7 shows that a single microhole per pixel provides a better increase in QE. The optimal microhole size is comparable to the small-sized pixels.…”

“…This study considers Ge-on-Si backside-illuminated sensors layered over a signal processing circuit chip with a low-noise structure. 6,7,9 The simulations do not include the metal contacts. The contacts will add small optical losses that can reduce the results by a few percent.…”

“…7 We have presented the crosstalk index between each pair of colors, e.g., the red-green crosstalk, i.e., the response of the green pixel at the red wavelength, in our previous work. 7 This definition implies that a higher value of the index of crosstalk corresponds to higher contrast and lower crosstalk. The trenches could be optimized to reduce the crosstalk by varying depths and thicknesses.…”

“…Establishing a trade-off between the optical sensitivity in the pixel and the bandwidth of the imager is challenging. Absorption enhancement in a thin absorber layer by the pixel surface nanostructures or single microholes per pixel 6,7 helps attain high sensitivity without compromising the bandwidth. The reduction of pixel sizes also can have a parasitic charge exchange between neighboring pixels (crosstalk) that can be successfully reduced using deep trench isolation (DTI).…”