Semiconductor capacitor for stacked pixel

An image sensor comprising:

• a plurality of photodetectors and a floating diffusion node disposed within a first substrate, wherein the floating diffusion node is disposed between the photodetectors;
• a plurality of pixel transistors disposed on a second substrate under the first substrate, wherein the plurality of pixel transistors comprises a first pixel transistor having a first source/drain region directly electrically coupled to the floating diffusion node;
• and
• a semiconductor capacitor disposed on the second substrate, wherein the semiconductor capacitor comprises a doped capacitor region on the second substrate, a first capacitor electrode over the doped capacitor region, and a capacitor dielectric layer directly between the doped capacitor region and the first capacitor electrode, wherein the first capacitor electrode comprises a plurality of protrusions disposed in the second substrate, wherein the doped capacitor region continuously laterally wraps around the protrusions, and wherein the semiconductor capacitor is directly electrically coupled to a second source/drain region of the first pixel transistor.

An image sensor, comprising:

• a photodetector in a first substrate;
• a floating diffusion node in the first substrate and adjacent to the photodetector;
• a second substrate under the first substrate and comprising opposing sidewalls demarcating a trench extending into a first surface of the second substrate;
• a capacitor on the second substrate, wherein the capacitor comprises a capacitor electrode, a capacitor dielectric layer, and a doped region, wherein the capacitor electrode comprises a vertical segment in the trench, wherein the doped region extends along the opposing sidewalls of the second substrate, wherein the capacitor dielectric layer is arranged between the capacitor electrode and the doped region;
• and
• a transistor on the first surface of the second substrate and coupled between the capacitor and the floating diffusion node.