The dataset is small and research-institute weighted rather than dominated by a single corporate leader. The strongest documented relationship links the Interuniversity Microelectronics Centre (IMEC) with KU Leuven's R&D office, which co-filed three families together, plus a related pairing with the Catholic University of Leuven on two more. Beyond that cluster, filings are spread thinly across a handful of universities and companies, and every tracked assignee shows zero filings in the most recent year, so no single organisation currently holds clear leadership by filing volume alone.

Based on the published record, activity is flat to declining rather than growing. Filings rose to a peak of five in 2020, then the 2022 midpoint shows zero, and no family has yet published in 2026. Publication lag of roughly eighteen months means the very latest years are always undercounted, but the multi-year gap in the middle of the trend is a genuine signal, not just a lag artefact.

US20210119069A1, assigned to IMEC VZW, claims a single-photon avalanche diode built around a rotationally symmetric inner doped region surrounded by an outer doped region of different dopant type and a lowly doped depletion volume of a defined depth. It is a device-structure claim focused on the junction geometry, not on array-level readout or system integration. A new design that uses a materially different doping geometry or depletion-region structure would sit outside its specific claim scope, but any design mirroring that rotationally symmetric doped-region arrangement should be checked against it directly.

IPC composition shows the imbalance clearly: eleven of twelve records fall under H01L (semiconductor device structures), while H04N (imaging/pictorial systems) and H10F (photovoltaic-adjacent devices) each carry only a single record. That suggests on-chip TDC array calibration, SPAD array readout multiplexing, and system-level imaging packaging around SPAD arrays are comparatively under-claimed relative to the core diode architecture, though this should be cross-checked against the broader CMOS image sensor patent body before treating it as fully open.

Among the twelve published records, China accounts for the largest share of receiving-office filings at four, followed by the European Patent Office at three and the United States at two. Single filings also appear via Austria, Taiwan, and the PCT international route. The spread across several offices without one dominant jurisdiction is consistent with a field still driven by research institutions rather than a small set of commercial filers concentrating on one home market.