A semiconductor device may include a plurality of single-photon avalanche diode (SPAD) pixels. The semiconductor device may be a backside device having a substrate at the backside, dielectric layers on the substrate, metal layers interleaved with the dielectric layers, and a through silicon via (TSV) formed in the backside through the substrate and the dielectric layers. TSV seal rings may be formed around the TSV to protect the semiconductor device from moisture and/or water ingress. The TSV seal rings may be coupled to a high-voltage cathode bond pad and be coupled to offset portions of one of the metal layers to reduce leakage and/or parasitic effects due to the voltage difference between the cathode and the substrate. The TSV seal rings may also be merged with die seal rings at the edge of the substrate.