Filing activity in this dataset is concentrated among a small group of large sensor and semiconductor manufacturers, with a long tail of single-filing entrants beneath them. Several of the most active assignees in the historical record show zero filings in the most recent year, which suggests the core architectural claim space has matured rather than that these companies have exited the field. Anyone assessing competitive position should look at the assignee ranking table alongside the filing-year trend rather than at either alone, since recent-year momentum and total historical volume tell different parts of the story.

Stacked back-side-illuminated integration refers to a sensor architecture where the pixel array and the supporting logic or memory circuitry are fabricated on separate wafers and bonded together, rather than built side-by-side on a single die. In patent claims this typically appears as language specifying a photodiode layer stacked over or bonded to a separate control or logic substrate, often with defined interconnect or via structures between them. The most-cited record in this dataset, US20120293698A1, centres on exactly this kind of solid-state image sensor and camera-system integration, which is why it carries the heaviest citation weight in the set.

The filing trend in this dataset peaked at 23 families in 2018 and fell to a midpoint of 8 by 2022, which typically indicates that the foundational packaging and stacking architectures had already been claimed and filers shifted effort toward refinement, licensing or adjacent functional claims rather than new foundational filing. It does not necessarily mean commercial development slowed, since patent filing and product development cycles are not the same thing. Readers should also account for publication lag: the most recent one to two years in any filing trend are understated because publications typically appear roughly 18 months after the underlying filing date.

The classification spread in this dataset shows optical elements (G02B, 14 records) and photographic apparatus (G03B, 9 records) are far thinner than semiconductor device packaging (H01L, 183 records), which points to optical-path and lens-integration claims tied to a specific stacking geometry as comparatively under-claimed. The intersection between global-shutter or computer-vision-oriented pixel circuits and positioning/ranging classifications (G01S, 17 records) is another area with limited density relative to its recency. A first claim there would need to tie a specific packaging or stacking geometry to a functional element — optical path or ranging output — rather than claiming either in isolation.

US20090045441A1 claims a specific architecture: a substrate with a cavity that holds a control chip separately from a pixel array sensor stacked on the substrate surface. It constrains designs that use a cavity-recessed control chip specifically to reduce package footprint, but it does not block architectures that avoid a substrate cavity or that route control logic off-package. Because it was published in 2009 and predates several more heavily cited packaging families in this dataset, it functions more as background prior art that later filings distinguish from than as an active universal blocker, though its specific cavity-and-substrate claim scope still needs to be checked against any new design that uses a similar recessed-chip construction.